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Title: Die Casting: Dies—Machines—Methods

Author: Chester L. Lucas

Release date: September 17, 2016 [eBook #53064]
                Most recently updated: October 23, 2024

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK DIE CASTING: DIES—MACHINES—METHODS ***

Transcriber’s Note: Subscripts are preceded by an acute accent mark `;
italic text is enclosed in _underscores_.




[Illustration]




  MACHINERY’S REFERENCE SERIES


  EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF MACHINE DESIGN
  AND SHOP PRACTICE REVISED AND REPUBLISHED FROM MACHINERY


  NUMBER 109

  DIE CASTING
  DIES--MACHINES--METHODS

  By CHESTER L. LUCAS




CONTENTS


    Die Casting                                      3

    Making Dies for Die-Casting Machines            15

    Van Wagner Mfg. Co.’s Die-Casting Practice      27


  Copyright, 1913, The Industrial Press, Publishers of MACHINERY,
  49-55 Lafayette Street, New York City




CHAPTER I

DIE CASTING


Die-casting, a comparatively recent method for producing finished
castings, is rapidly proving itself an important factor in the
economical manufacture of interchangeable parts for adding machines,
typewriters, telephones, automobiles and numerous other products where
it is essential that the parts be nicely finished and accurate in
dimensions. The term “die-casting” is self-explanatory, meaning “to
cast by means of dies”; described briefly, the process consists of
forcing molten metal into steel dies, allowing it to cool in them, and
then opening the dies and removing the finished casting. It is the
purpose of this treatise to give a general outline of the die-casting
process, showing its possibilities and limitations, and also to give
a description of the die-casting machinery and its operation, of
the fundamental principles involved, and of the methods used in the
die-making. Illustrative examples of the best types of dies, based on
results obtained from actual experience, will also be given.


Origin of Die Casting

The origin of the die-casting process is somewhat difficult to
ascertain. We may look into the history of type founding and find
that away back in 1838, the first casting machine for type, invented
by Bruce, was a machine that involved the principles of die-casting
as it is practiced to-day. More recently, in 1885, Otto Mergenthaler
brought out the linotype machine. This machine is a good example of
a die-casting machine. However, as we interpret the word to-day,
die-casting is a broader term than type-casting or linotyping, although
its development without doubt is due to the success of the linotype
machine. It is doubtful if die-casting, properly speaking, was
originated until about fifteen years ago, and it is certain that it is
only during the past few years that the activities in this line have
been very noticeable.

One of the first experiments in the direction of die-casting was
undertaken to get out some rubber mold parts cheaply enough to leave a
profit on a job that was beginning to look dubious from the financial
side. The molds were for making rubber plates about three inches
square and one-eighth inch thick, the top side of which was decorated
with fine raised scroll work; it was this latter feature that gave
the trouble. After wasting much time and money trying to stamp the
mold parts, a metal-tight box was made as shown in Figs. 1 and 2 with
a block screwed in it, the purpose of which was to shape the mold
impression and impart to it the scroll design. As shown, the ends of
the box were removable, being screwed on. This box was placed under
a screw press and a straight plunger that just filled the top of the
box was fitted to the head of the press. After the two were lined up,
molten type metal was poured into the box, and as soon as the metal
had cooled to the “mushy” state, the ram of the press was forced down
as shown in Fig. 2. Next, the ends of the box were removed, the screw
holding the block taken out, and the die-casting pushed from the box.
The object in having the inclined side to the box was to produce a
piece shaped with the proper inclination for its position in the final
mold used for casting the rubber plates. The illustrations give an idea
of the compression that took place. The die-casting was found to be
sharp at the corners and free from flaws, and the scroll work came up
in fine shape. Naturally the rest of the mold parts were made in the
same way and the job turned from failure into success.

[Illustration:

  Fig. 1. An Early Experiment in Die Casting--Before Applying Pressure

  Fig. 2. An Early Experiment in Die Casting--After Applying Pressure
]

From such simple experiments as these, the die-casting industry has
developed to its present stage. In view of the advances that have been
made in die-casting, it is singular that there are to-day only about
a dozen concerns in the business in this country, but as the subject
becomes better understood, and the possibilities of the process are
realized, the demand for this class of castings will result in many
other firms going into the work, and it is not improbable that a large
number of factories will install die-casting plants of their own to aid
them in producing better work in a more economical way.


Advantages, Possibilities and Limitations of Die Casting

The greatest advantage of die-casting is the fact that the castings
produced are completely and accurately finished when taken from the
dies. When we say completely, we mean that absolutely no machining is
required after the piece has been cast, as it is ready to slip into its
place in the machine or device of which it is to be a part. When we say
accurately, we mean that each piece will come from the die an exact
counterpart of the last one; and if the dies are carefully made, the
castings will be accurate within 0.001 inch on all dimensions, whether
they are outside measurements, diameters of holes or radii. All holes
are cast and come out smoother than they could be reamed; lugs and gear
teeth are cast in place; threads, external and internal, and of any
desired pitch can be cast. Oil grooves can be cast in bearings, and, in
a word, any piece that can be machined can be die-cast.

The saving in machining works both ways; not only is all machine work
eliminated by the one operation of casting, but the machine tools and
the workmen necessary for their operation and up-keep are dispensed
with, the expense of building jigs and fixtures is stopped; and no
cutters, reamers, taps or drills are required for this branch of the
production. In addition, the labor required for operating the casting
machines may be classed as unskilled. No matter how intricate and
exacting the machine work on a piece has been, and how skillful a
workman was required to produce the work when machine-made, the same
result may be brought about by die-casting, and usually the work is
excelled, and, excluding the die-making, unskilled men can make the
parts.

From a metallurgical standpoint a die-casting is superior to a
sand-casting on account of its density, strength and freedom from
blow-holes. Also, when the hot metal comes in contact with the cool
dies, it forms a “skin” similar to the scale on an iron sand-casting.
As the die-casting requires no machining after leaving the dies, this
skin increases the wearing qualities of the casting.

The possibilities of die-casting are numerous. By this method of
manufacturing it is possible and practical to cast pieces that could
not possibly be machined. It is an every-day occurrence to make
castings with inserted parts of another metal, as, for instance, a
zinc wheel with a steel hub. It is also possible to make babbitt
bearings that are harder and better than can be made in any other way.
Often there are two or more parts of a device that have formerly been
made separately, machined and assembled, that can be die-cast as one
piece. In such cases the saving in production is very great. Figures
and letters may be cast sunken or in relief on wheels for counting
or printing, and of course ornamentation may be cast on pieces that
require exterior finish. As to size, there is no definite limit to the
work that can be cast. One job that is being done at the present time
is a disk 16 inches in diameter with a round flange 1 inch in diameter,
around the rim.

[Illustration: Fig. 3. Examples of Die-castings]

“There is no great gain without some small loss,” is just as true of a
process like die-casting as it is of anything else. The limitations of
this work are few, however, and they are here given so as to state the
situation fairly. Generally speaking, a part should not be considered
for die-casting if there are but few pieces required, because the cost
of the dies would usually be prohibitive. Often, however, it happens
that because of the large amount of accurate machine work being done on
a machine part, it is economical to make a die for the comparatively
small number of parts required and die-cast them. A case illustrating
this phase of the matter recently occurred in actual practice. In
getting out an order of two hundred vending machines, it was decided
to try die-casting on a part that was difficult to machine. The dies
were expensive, costing $200, and as there were only 200 pieces to be
cast, the die cost per piece was one dollar; but even with that initial
handicap, it was found that on account of the difficult machining that
had formerly been required, the die-cast parts effected a large saving,
and of course the results were superior.

A rough part that would require little or no machining should not
be die-cast, because pound for pound, the die-casting metals cost
more than cast iron or steel. The casting machine cannot make parts
as rapidly or of as hard metals as the punch press or the automatic
screw machine. For this latter reason a part that necessarily must be
made of brass, iron or steel, cannot be die-cast, although mixtures
approximately equal in strength to iron and brass are readily die-cast.
To give added strength to a die-cast part it is often advisable to
add webs and ribs or to insert brass or iron pins at points that are
weak or subject to hard wear. Roughly speaking, it is the part that
has required a good deal of accurate machine operations that shows the
greatest difference in cost when die-cast, and sometimes the saving is
as great as 80 per cent.


The Metals used in Die Casting

The metals that produce the best die-castings are alloys of lead, tin,
zinc, antimony, aluminum and copper, and the bulk of the die-castings
made at the present time are mixtures of the first four of these
metals. From them, compositions may be made that will meet the
requirements of nearly any part.

For parts that perform little or no actual work, save to “lend
their weight,” such as balance weights, novelties and ornaments for
show windows, etc., a mixture consisting principally of lead, often
stiffened with a little antimony, is used. There is but little strength
to this metal, but it is used because of its weight and low cost.
For parts that are subject to wear, such as phonograph, telephone,
gas-meter and adding machine parts, an alloy composed of zinc, tin and
a small amount of copper is used. This alloy may be plated or japanned,
and is a good metal to use on general work.

Another metal, used chiefly for casting pieces that have delicate
points in their design but are not subjected to hard wear, consists
principally of tin alloyed with lead and zinc to suit the requirements
of the work. This mixture casts freely, and the finished castings come
out exceptionally clean. Still another metal, used chiefly for casting
pieces that have letters and figures for printing, is similar to the
standard type metal--5 parts lead and 1 part antimony; but if there are
teeth cast on the sides of the printing wheel a harder mixture will be
required to give longer life to the gears.

The following mixtures are typical of die-casting or “white brass”
alloys: copper, 10 parts; zinc, 83 parts; aluminum, 2 parts; tin, 5
parts. Another is copper, 6 parts; zinc, 90 parts; aluminum, 3 parts;
tin, 1 part. Another containing antimony is copper, 5 parts; zinc, 85
parts; tin, 5 parts; antimony, 5 parts. Shonberg’s patented alloy is
copper, 3 parts; zinc, 87 parts; tin, 10 parts. Alloys containing 15 to
40 per cent copper and 60 to 85 per cent zinc are brittle, having low
strength and low ductility. An alloy of 8 per cent copper, 92 per cent
zinc has greater resilience and strength but not the ductility of cast
zinc.

Aluminum may be cast, but it is a difficult metal to run into thin
walls and fine details; it plays, however, an important part in some
good mixtures used for die casting. Experiments are now being conducted
for die-casting manganese bronze, and it is said that some very good
castings have already been made. Its wearing qualities are so valuable
that it is particularly desirable for making die-castings.


The Die-casting Machine

The three important requisites for good die-casting are the machine,
the dies and the metal. The casting machine is fully as essential as
either of the other requisites, and although there are a number of
different styles of casting machines in use, each of which has its
advantages over the others, especially in the eyes of their respective
designers, the fundamental principles upon which they all operate are
the same. In each there is the melting pot and the burner, the cylinder
and the piston for forcing the metal into the dies, and the dies with
the opening and closing device. In some machines pressure is applied to
the metal by hand, in others power is used, and in still another class
the metal is forced into the dies with compressed air. The provisions
for opening and closing the dies vary in the different machines; there
are various means employed for cutting the sprue, and the styles of
heaters are numerous.

One or two of the largest firms in the die-casting industry have
automatic casting machines for turning out duplicate work in large
quantities very rapidly. These machines are complicated and are only
profitable on large quantities of work, and for that reason their
use is not extensive. In general, their operating principles are the
same as in the case of the hand machines, but provision is made for
automatically opening and closing the dies, compressing the metal, and
ejecting the castings.


The Soss Die-casting Machine

The Soss die-casting machine, manufactured and sold by the Soss
Manufacturing Co., Brooklyn, N. Y., was the first die-casting machine
to be placed on the open market. This machine is shown in Figs. 4 and
5, and in section in Fig. 6. The Soss Manufacturing Co. originally
manufactured invisible hinges exclusively. At the advent of the
die-casting era, they commenced to make these hinges from die-castings,
and placed orders with a leading die-casting concern amounting to
thousands of dollars each year. After the die-cast hinges had been on
the market for a short time, complaints commenced to come in, some to
the effect that the hinges were breaking and others that the hinges
were corroding. Either of these faults was serious enough to blast the
reputation of the hinge, but the first trouble, breakage, was the more
important. Examination of the broken hinges showed that the castings
were porous and full of flaws, and as the makers of the castings
could not produce castings sufficiently strong for the hinges, Mr.
Soss started to experiment for himself. This experimenting led to the
production of the Soss die-casting machine.

[Illustration: Fig. 4. General View of the Soss Die-casting Machine]

Referring to the illustrations Figs. 5 and 6, _A_ is the base and frame
of the machine, _B_ is the heating chamber located at one end of the
machine, and within this heating chamber is the tank _C_, shown in Fig.
6. This tank contains the metal from which the die-castings are made,
and the metal is heated by the burners _D_. These burners are fed by
air and gas through piping on the side of and beneath the furnace. To
facilitate lighting the burners and inspecting their condition at any
time, there is an opening (not shown) through the firebrick lining of
the furnace and the outer iron wall, on a level with the top of the
burners. There is also another opening through the furnace wall to
allow the gases due to the combustion to escape. Through the bottom of
the tank, well to the inner side of the furnace, runs the cylinder _E_.
Below the bottom of the tank, the cylinder makes a right-angle turn,
extending through the furnace wall and terminating just outside of the
wall. The orifice of this cylinder is controlled by gate _F_. In that
part of the cylinder that extends upward into the tank, there is an
opening _G_ that allows the molten metal to run into the cylinder from
the tank. Working in this cylinder, is the piston _H_, that is used in
forcing the metal into the dies. The compression lever _I_, hinged over
the inner furnace wall, is kept normally raised by spring pressure, and
is connected to the piston by means of the link _J_.

[Illustration: Fig. 5. Working Parts of the Soss Die-casting Machine]

At the opposite end of the machine from the furnace, is the mechanism
for operating the dies. This mechanism consists of a pair of square
rods _K_, upon which are mounted the sleeves _L_. These sleeves have
a long bearing surface and are attached to the die-plate _M_. Lever
_N_ at the end of the operating mechanism controls the movement of
these sleeves by means of links _O_. Upon these sleeves is mounted a
secondary set of sleeves _P_, attached to the other die-plate _Q_,
and whose movement is controlled by lever _R_, through links _S_.
This second set of sleeves is free to travel with the first set, and
in addition has an independent movement of its own on the primary
sleeves. It is the function of lever _R_ to bring die-plate _Q_ up
to die-plate _M_ by means of links _S_ and sleeves _P_; and it is
the function of lever _N_ to bring both of the die-plates up to the
outlet of the cylinder by means of links _O_ and sleeves _L_. This
system of sleeve-mounting is one of the distinctive patented features
of the Soss machine. The orifice of the cylinder _E_ is conical in
shape and exactly fits the cup-shaped opening in die-plate _M_, so
that when the two are brought together, the joint is metal tight. At
the center of this opening, and extending through the die-plate _M_,
is an opening that leads to the dies mounted on the inner faces of the
two die-plates, and a continuation of this opening extends through
die-plate _Q_ in which the sprue-cutter _U_ works. Attached to the
outer side of this die-plate are two slotted brackets. In the slot of
one of these is pivoted the lever _T_, and in the slot in the opposite
bracket are bolted two stops that limit the motion of the lever. This
lever operates the sprue cutter _U_, that works through the opening in
die-plate _Q_. The sprue-cutting mechanism is best shown in Figs. 5 and
6. At the left of Fig. 5 may be seen a rubber hose connected to the air
piping. This hose is used for cleaning out the dies after each casting
operation.


Operation of the Die-casting Machine

The metal for the die-casting machine is mixed in the proper
proportions for the work in hand by means of a separate furnace, before
being poured into the tank of the machine itself. The burners are
lighted and the dies are set up on the two die-plates. As soon as the
machine has “warmed up,” so that the metal is in a thoroughly melted
condition, the sprue-cutting lever _T_ is thrown back, leaving a clear
passageway to the die cavities. Lever _R_ is pulled backward, thus
bringing die-plate _Q_ up to die-plate _M_, which operation closes
the two halves of the die. Then lever _N_ is thrown forward, thereby
bringing the closed die up to the body of the machine, with the nozzle
in close contact with the outlet of the cylinder. Next, the gate _F_
is opened, and the man at the compression lever _I_ gives the lever a
quick, hard pull, forcing the metal in the cylinder downward and into
the dies. The molten metal literally “squirts” into the dies. Gate _F_
is now closed; lever _N_ is pulled back to remove the dies from the
cylinder outlet; and the sprue-cutting lever _T_ is pushed forward,
cutting off the sprue and pushing it out of the nozzle into the kettle
placed beneath it. The lever _R_ is pushed forward, and a finished
casting is ejected from the dies.

An important advantage that this machine has over other die-casting
machines is the fact that the metal for the castings is taken from the
_bottom_ of the melting pot, whereas most other machines use metal from
the top of the tank. At the bottom of the tank the metal is always the
best, as it is free from impurities and dross; hence, there is little
chance for the formation of blow-holes. A handful of rosin thrown
into the melting tank occasionally helps to keep the metal clean,
but the metal nearest the surface always contains more or less foreign
matter.

[Illustration: Fig. 6. Section of Soss Die-casting Machine]

While this description of the operation of the die-casting machine may
convey the idea that the process is a slow one, as a matter of fact,
the time required is, on the average, not over a minute and a half
for turning out a finished casting. With the ejection of the casting
from the dies, the product is completed, in theory; but in practice
there are always a few small thin fins, caused by the air vents or by
improperly fitted portions of the dies. It is, however, but the work
of a few seconds to break off these fins, and unless there are many of
them, or they are excessively thick, they are detrimental neither to
the quality nor the quantity of finished castings.


Points on the Operation of the Die-casting Machine

We have now taken up the description and general operation of the
die-casting machine, but like every other machine, there are numerous
little kinds and practices in its working the observing of which makes
the difference between good and poor die-casting. Some of these points
are here given.

The casting machine is best operated by three men, one of whom attends
to the compression lever and the metal supply in the tank. The other
two men stand on each side of the die-end of the machine, and it is
their duty to operate the sprue-cutter, open the dies and remove the
finished casting, clean the dies with air and close them, throw back
the die-plates to their casting position over the cylinder outlet, and
do any other work incident to the operation of the machine. While it
requires three men to operate a die-casting machine in the best manner,
the man who attends to the compression lever has a good deal of spare
time between strokes, and if two or even three of the machines are
conveniently placed, one man can easily pull levers for all three.

The metal should be kept just above the melting point and at a
uniform temperature. If the metal is worked too cold, the result will
manifest itself in castings that are full of seams and creases, and it
will be difficult to “fill” the thin places in the dies. If, on the
other hand the metal is allowed to get too hot, the die will throw
excessively long fins, the castings will not cool as quickly in the
die, and consequently they cannot be made as rapidly. On account of
the importance of keeping the metal at a uniform heat, the fresh metal
that is added to that in the tank from time to time, is kept heated in
a separate furnace. Therefore, when the metal in the tank gets low, the
new supply does not reduce the temperature of the metal being worked.
Some casters use a thermometer to indicate the heat of the metal.

Casting-dies require lubrication frequently. Just how often they should
be lubricated depends on the shape of the die, the composition of the
casting metal, and the general performance of the dies. Beeswax is
the common lubricant, and the lubrication consists in merely rubbing
the cake over the surfaces of the dies that come in contact with the
casting metal. In die-casting large parts, the dies must be kept cool
by some artificial means, for hot dies are conducive to slow work and
poor castings. To reach this end, large dies are sometimes drilled and
piped so that water may be circulated through them to keep them cool.

In the Soss machine, the burners are so placed that the metal in the
cylinder is kept at a slightly higher heat than that in the tank
proper. This condition is brought about by having the cylinder directly
over the burners. The value of this feature lies in the fact that
gas is not wasted in heating the entire tank full of metal to this
higher heat, but still the metal under compression is at the required
temperature. The gas consumption of the average die-casting machine is
about 100 cubic feet per hour.

The speed at which die-castings may be produced varies with the size of
the castings being made, the composition of the metal being cast, and
the style of dies that must be employed. In many cases, in die-casting,
separate brass or steel pieces are used, that must be placed in the
dies before each operation so that they will be inserted in and become
a part of the finished casting. The dies may be difficult of operation
on account of draft problems or pins and screws that must be inserted
in the dies and removed from each casting before another can be made.
These different types of dies will be more fully described in the next
chapter. Taken as a whole, from ten to sixty pieces per hour are the
maximum limits for speed in die-casting, and with a well-working die,
of simple construction, a speed of forty pieces per hour is considered
good production. It is possible, however, when the castings to be
produced are small in size and simple in shape, to gate a number of
them together, or rather to construct the dies so that six or more
castings may be made at once. By this means it is often possible to
cast five or six thousand pieces per day of ten hours, on a hand
die-casting machine.




CHAPTER II

MAKING DIES FOR DIE-CASTING MACHINES


The making of casting-dies calls for ingenuity and skill of the highest
order on the part of the die-maker. There is probably no class of
die-making in which the work produced is more faithful to the dies,
both in showing up the little details in the making that reflect credit
on the dies, and in exposing the defects and shortcomings in the
workmanship, if there be any. The castings from casting-dies or molds
as they are sometimes called, may be produced in dimensions down to
ten-thousandths for accuracy if necessary, and once the dies are made
the castings will not vary in the slightest degree, if the working
conditions are kept uniform.

In spite of the close work required in making casting-dies, the work is
very fascinating. Perhaps it is on account of this accuracy; possibly
it is on account of the fact that they are made from machine steel;
but most likely it is because there are no hardening troubles to be
contended with. Another factor that makes the work interesting is the
ingenuity required in the work, for almost every die-maker, if he is
worthy of the name, likes to figure out and plan for the best way of
building a die for a difficult job.


General Principles of Casting-die Making

Casting-dies, or molds, have little in common with sand molds. It
is true that the dies for die-casting are composed of two parts
corresponding to the cope and nowel of the sand mold, but they are
so different in every other way that no benefit would result from a
comparison.

Generally speaking, casting-dies are made of machine steel; the parts
which are exceptions are the heavy bases and frames, which are made of
cast iron, and the dowel pins and small cores, usually made of tool
steel. Except in rare instances, there are no hardened parts about a
casting-die; this is the case because the melting points of some of the
alloys that are die-cast are high enough to draw the temper from any
hardened parts of the dies.

The ideal die is simple in construction, with as few parts as
practicable; the castings should be easily ejected and should come
from the dies as nearly free from fins as possible. To meet these
requirements in the best way is the proposition that confronts the
ingenuity of the die-maker. As the die is primarily in two parts, there
must be a parting line on the casting. This line is always placed at
the point that will permit the casting to be ejected from the dies in
the easiest manner possible, bearing in mind the effect the joint will
have on the appearance of the finished casting; this is a point far
less important than with sand casting, for, if the dies are properly
made this seam will be barely perceptible. When it is practicable to
do so, it is wise to have the parting line come on an edge of the
die-casting. Draft is unnecessary on the straight “up-and-down”
places, but of course it is impossible to draw any parts that are
undercut. Means must be provided for ejecting the casting from the
dies after completion and it is usually done by means of ejector pins,
though frequently it is better to have the bottom of the die or some
other section movable and do the ejecting on the same principle that
is used on drawing dies of the compound type. On close work, shrinkage
plays an important part, and the amount of shrinkage varies from 0.002
to 0.007 of an inch per inch. Aluminum shrinks the greatest amount,
Parsons white brass shrinks considerably, while tin shrinks but little.
Thus, it may be easily seen that to figure the shrinkage allowance for
an alloy that contains three or four metals with different shrinkages,
requires judgment. To prevent the air from “pocketing,” air vents are
necessary at frequent intervals around the die-cavity. These vents are
made by milling a flat shallow cut from the die-cavity across the face
of the die to the outside edges of the block. From ¼ inch to ½ inch
is the usual width and from 0.003 to 0.005 of an inch, the customary
depth, varying with the size and shape of the die in question.

[Illustration: Fig. 7. Disk cast in Simple Casting-die]

The dies or molds for die-casting are of various styles, as are also
punch-press dies, and it would be difficult to lay down specific
rules for their classification. There are the plain dies, without
complications of any kind; slide dies with one or more slides; dies
for bearings, both of the “half-round” and of the “whole-round” types;
dies for gated work; and many other less important classes. Then there
are dies that have features that belong to more than one of these
types, so that it is easily seen that to decide upon the style of die
that would be best for a given piece of work requires a good deal of
experience. Some of the most important of these types can best be shown
by illustrating dies made in the various styles, showing, step by step,
how the dies are made and assembled. To begin with, consider the making
of a casting-die of the very simplest form.

In Fig. 7 is shown a plain flat disk made by die-casting. In actual
practice, a die would not be made for such a simple piece, unless
there were some features about it that would prevent it being made
on a screw machine or with press tools. It might have a cam groove
cut in one of its flat sides, the sides might be covered with scroll
work, there might be gear teeth around its circumference, or a hundred
and one other conditions to make die-casting a desirable method of
manufacturing. All these complications are omitted for the sake of
simplifying this initial description of a casting-die.

[Illustration: Fig. 8. Simple Casting-die for Casting Block shown in
Fig. 7]

Fig. 8 shows the die for this piece in plan and sectional elevation.
_A_ is a square cast-iron frame, made from a single casting. This frame
or box, as it is generally called, is planed on the top and bottom
only. Next, the two die-halves _B_ and _C_ are shaped up from machine
steel. In this casting-die, and in the majority of others, these
die blocks are square. The lower half of the die _B_ is held to the
cast-iron frame by fillister head screws, set in counterbored holes,
thus sinking the screw-heads under the surface of the block. The upper
half of the die _C_ is located upon _B_ by dowel pins driven into _B_
which have a sliding fit in the reamed holes in _C_. This being done,
the die-half _B_ is fixed to the faceplate of the lathe and the recess
bored for the die-cavity. This operation is a simple one in this case,
for it is merely a straight hole one-half inch deep and three inches in
diameter. Of course this recess must be carefully finished with a tool
that has been stoned up to a sharp edge, using lard oil. Emery cloth
should be used as little as possible. It is unnecessary to give this
hole draft, but it must be free from ridges or marks that would prevent
the casting from being pushed out. If the faces of the dies are spotted
with a small piece of box wood or rawhide held in the drill press and
kept charged with flour emery, the die-casting will reproduce this
“bird’s-eye” finish and the appearance will well repay the few minutes
additional time that it will take. The spotting should be done with dry
emery (without oil) to get the brightest finish. The upper die-half _C_
is simply ground on its working face. The outside corners and edges of
the faces of both die-halves should be well rounded off so as to insure
the absence of slight dents or rough places that might prevent the dies
from fitting perfectly.

The ejecting mechanism must next be considered. Lever _D_, pivoted
from bracket _E_, has a steel pin _F_ that engages in the elongated
hole in bracket _G_, so that an upward pull of the lever _D_ raises
bracket _G_, which is attached to ejector-pin plate _H_. This plate is
a loose fit over the guide screws _I_ that are attached to the lower
die-half _B_. The ejector pins _J_, four in number, in this die, are
riveted into the ejector-pin plate, and they work through holes drilled
and reamed through the lower die-half. The ends of these pins must be
finished off so as to lie perfectly flush with the inside of the die
when ready for operation and, of course, they must be a sliding fit in
the holes in the die.

An important feature of a casting-die is the sprue cutter, shown in
this die at _K_. If the disk for which this die was made, had had a
hole or central opening of any kind, the sprue cutter would best be
operated at that point; but, as this disk is plain, the sprue cutter
must be placed at the edge. At the outside of the die-cavity, as shown
in Fig. 8, the opening for the sprue cutter is laid out, drilled
and filed to shape. It is obvious that the side of the sprue cutter
adjacent to the die must fit the outline of the die perfectly, so that
there will be no break in the appearance of the casting. The opening
for it is extended through the upper die-half, and from a point ¼ of an
inch from the inside face of the die this hole is flared out nearly as
large as the opening through the die-plate of the machine. Of course
the apperture in the upper die-half must be no larger than the opening
through the die-plate; otherwise the sprue could not be pushed out. The
sprue cutter itself is a long rod, whose section is of the same shape
and size as the openings just made, and it is connected to the sprue
cutting mechanism of the machine. Of course it is unnecessary to shape
the entire length of the sprue cutter to size; after the working end is
milled to shape for a distance of six or eight inches, the rest of the
rod may be left round. The sprue cutter is finished first, after which
both the openings in the die are fitted to it; and while the fit should
be metal tight, it must be perfectly free to slide.

The dies are mounted on the die-plates of the casting machine by means
of straps, much the same as bolsters are held on punch press beds. The
position of the die on the die-plate must be such that the opening for
the sprue cutter will line up with the nozzle at the outlet of the
cylinder. At the time of casting, the position of the sprue cutter is
as shown in the illustration of this die, Fig. 8. In this position
there is room for the metal to enter the die-cavity, and yet there is
but a small amount of metal to be cut off and pushed back after the die
has been filled with metal.

With slight modifications, the above style of die may be used for
die-casting any piece that will draw or pull out of a two-part die. If
holes must be cast through the piece, it is only necessary to add core
pins to the lower die _B_, a point that will be more fully described
later. It is unnecessary to add that both halves of the die may be
utilized in making the cavity for the die, should they be needed. Also,
it is often easier to machine out the recess larger than is needed, and
set in pieces in which parts of the outline of the die-casting have
been formed. Gear teeth are put in the die in this way; a broach is cut
similar to the gear desired, then hardened and driven through a piece
of steel plate which is afterward fitted to its place in the die.


Slide Dies

The die illustrated in Fig. 9 is one of the most successful of the
various types of casting-dies, and if properly made is an interesting
piece of die work. The principal use of this particular style of die,
called a slide die, is to cast parts like the one shown in Fig. 10,
which is a disk similar to the one which the last die described was
to cast, except that it has raised letters at the edge and a hole in
the center. It is obvious that the die last described, (Fig. 8), would
not do for disks or other pieces having projections or depressions
around their edges, as, for instance, printing or counting wheels with
raised or sunken characters, or grooved pulleys. Briefly, this style
of die is similar to the simple casting-die, except that slides are
provided, to the required number, which form the edge of the casting.
A die for a plain grooved pulley would require but two slides, while
a die for a printing wheel with forty letters around its edge would
necessitate forty slides, one for each of the letters. The die about to
be described, shown in Fig. 9, was made to cast a wheel with six raised
letters.

Referring to Fig. 9, _D_ is the cast-iron box or frame, _E_, the lower
die, and _F_ the upper die. In making the lower die-half, the stock is
first shaped to size and doweled to the blank for the upper die-half,
and the holes for attaching to the frame are drilled. For the sake of
clearness, these holes and screws are omitted from the illustration as
are also the vents, since they have been fully explained. The lower
die is next strapped to a faceplate, trued up, and bored out nearly
to the diameter of the body of the piece to be cast, exclusive of the
raised letters. The depth of this recess is equal to the thickness of
the printing wheel plus 3/16 inch to allow for the cam ring _G_ that is
used to reciprocate the slides of the die. The cam ring is made large
enough to cover the die-cavity as well as the slides that surround
it, with an allowance of an inch or two for the cam slots _H_. The six
slides _I_ are made long enough to have good bearing surfaces. With the
size of the cam ring determined, the die is next bored out to receive
this cam ring and the last inch of the recess is carried down to the
depth of the die cavity so as to make an ending space for the slots
that the slides are to work in. The die is now taken from the faceplate
and the slots for the slides laid out.

[Illustration: Fig. 9. Slide Die for Casting the Printing Wheel shown
in Fig. 10]

These slots may be milled or shaped, but milling is to be preferred.
The next step is the making and fitting of the slides, which are of
machine steel, having a good sliding fit in the slots. The six slides
are fitted in position and left with the ends projecting into the die
proper. The slots _H_ are next profiled in the cam ring _G_, and the
pins _J_ that work in them are made and driven into the holes in the
slides. With the slides and cam ring in place, the cam ring is rotated
to bring all the slides to their inner position where they are held
temporarily by means of the cam ring and temporary screws. The die-half
with the slides thus clamped in the inner or closed position, is set up
on the lathe faceplate and the die-cavity indicated up and bored out to
the finish size, which operation also finishes the ends of the slides
to the proper radius. The die may now be taken down and the slides
removed to engrave the letters upon their concave ends. The engraving
can be done in the best manner on a Gorton engraving machine, but if
such a machine is not available they may be cut in by hand. Stamping
should never be resorted to for putting in the letters, because the
stock displacement would be so great that it would be impossible to
refinish the surface to its original condition. Before fitting the
cam ring, an opening must be milled in the die to allow the handle to
be rotated the short distance necessary. After the cam ring has been
fitted, it is held in by the four small straps _K_, attached by screws
to the lower die-half at the corners.

[Illustration: Fig. 10. Printing Wheel cast in a Slide Die]

The sprue cutter, which is not shown, is operated through the hole
in the center of the piece and is, of course, round in this die.
Its action is the same as was the one previously described, and the
ejecting device is similar, with the exception that the brackets _L_
that are attached to the ejector-pin plate M, are widely separated so
as to make room for the sprue cutter that works through a hole in the
plate _M_.


Die for Casting with Inserted Pieces

For making die-castings that are to have pieces of another metal
inserted, it is necessary to have a die with provisions for receiving
the metal blank and holding it firmly in position while the metal is
being cast around it, and of course the piece must be held in such a
manner that it can be easily withdrawn from the die with the finished
casting.

The die illustrated in Fig. 11 is for a part that is used as a swinging
weight, shown in Fig. 12. The upper part of the piece is made from a
sheet steel punching, so as to lighten this part of the piece as well
as to give increased strength, especially at the hole at the pivoted
end of the work. The cast portion of the piece is slotted lengthwise,
as the illustration shows; and three holes pass through the casting,
piercing the sides of the slot. In addition to showing the method of
making dies for inserted pieces, this die shows the principles of
simple coring.

[Illustration: Fig. 11. Casting-die for Making Castings with Inserted
Pieces like that shown in Fig. 12]

In making this die, two machine-steel blanks are planed up for the
upper and lower halves of the die, _A_ and _B_, the lower die being
made nearly twice as thick as the upper die because it is in this part
that the most of the die-cavity will be made. In this lower half of
the die the stock is milled out to the same shape as the outline of
the plan view of the casting, being carried down to the exact depth
of the thickness of the casting. From the wide end of this recess the
stock is milled or shaped out in a parallel slot to the outside of the
die-block. At the bottom of the side of this wide slot are T-slots
to guide the slide _E_ that is to work in this opening. The side is
milled and fitted to the T-slots and opening in the die, but is left
considerably longer than the finish size. Next, the slide is mounted
on the faceplate of a lathe and turned out on the end with the proper
radius and a tongue to form the slot that is to be in the curved end
of the casting. At the outer end of the slide is left a lug that is
drilled and tapped for the operating lever _F_ that reciprocates the
slide, using the stud in bracket _K_ as a fulcrum.

Two pieces of machine steel are next shaped and finished up to form the
chamfered part of the casting and to locate the inserted steel punching
in the die. The combined thickness of these pieces _C_ and _D_ is equal
to the thickness of the casting, less the thickness of the inserted
piece. It is now an easy matter to seat section _D_ in the bottom of
the milled part of the lower die-half, and to locate section _C_ in its
proper position on the upper half. A pilot pin _M_ is fitted in _D_ to
hold the steel punching in position by means of the hole that is in the
extreme upper end of the punching. The pilot pin extends through this
hole into a corresponding hole in section _C_. At the lower end of the
steel part that is inserted, there are two holes the object of which
is to secure the punching to the die-casting, for the molten metal
runs through these holes, practically riveting the die-casting to the
inserted piece.

[Illustration: Fig. 12. Die-cast Weight with Inserted Sheet-steel
Punching]

Provision has now been made for holding the sheet-metal part that is
to be inserted, and the cavity has been completed for the casting,
including the tongue at the end; it now remains to describe the manner
of forming the holes that pierce the casting through the slotted
portion. In the lower die-half the positions of the three holes _H_ are
laid out, drilled and reamed. Then, with the two die-halves together
and the slide clamped at its inner position, the holes are transferred
through the slide and the upper die. This being done, it is an easy
matter to make core pins and drive them into the upper die at the two
end holes, the center hole being taken care of by the sprue cutter _L_
that will be described later. The core pins should be a nice sliding
fit through the slide and in the holes in the lower die, into which
they should extend from a quarter to half an inch. In addition to
coring the holes, these pins act as a lock to hold the slide _E_ in its
proper position at the time of casting.

The sprue cutter _L_ is most conveniently operated in the center hole,
thus doing away with the core pin that would otherwise be required. The
sprue cutter needs little description in this die, for as in the slide
die, it is merely a plain round rod that fits closely in the holes
through the dies and slide. The ejector mechanism is the same in this
die as in the dies already described; therefore further description is
unnecessary.

[Illustration: Fig. 13. Casting-die for the Half-round Bearing shown in
Fig. 14]

The operation of this die is very simple. The sheet-steel piece is laid
in the recess in the open die, being located by the pin _M_. Slide
_E_ is thrown in by means of lever _F_, and the dies are closed. At
the time of casting, the sprue cutter in is the position shown in
the sketch, being nearly through the die-cavity. As before explained,
this position admits the molten metal to pass into the die-cavity, but
still leaves very little sprue to be cut off after the die-casting is
completed. It should be stated that the steel piece that is inserted
must be perfectly flat and free from burrs that would prevent the
die-halves from coming together properly.


Bearing Dies

Bearing dies are one of the most important of the various classes of
casting-dies. The bearings produced by die-casting are so far superior
to those made by other casting methods and machining that their use is
now very extensive. Dies are made for “half-round” and “whole-round”
bearings. There is little out of the ordinary about a whole-round die,
but the half-round die involves many interesting methods of die-making,
and for that reason is here described.

Fig. 13 shows a casting-die for half-round bearings. Half-round bearing
dies are usually made to cast two bearings at a time, for the reason
that it is just as easy to cast two pieces of such a shape as it is to
cast one, and, in addition, the die is balanced in a better manner. As
with other dies, the first step is to machine up the frame _A_ and the
two die-halves _B_ and _C_. The pieces _D_ and _E_ that are to form
the insides of the bearings are then turned up and one side of each
shaped and keyed to fit the slots that have previously been milled in
die-half _C_. These parts are held in place by dowels and screws. One
of the bearings produced by this die is shown in Fig. 14, and it will
be noticed that there is an oil groove within that covers the length
of the bearing. To produce this groove in the die-castings, a shell
must be turned up and bored out whose inside diameter is that of the
inside of the bearing, and whose thickness equals the depth of the oil
groove. This being done, the oil grooves are laid out upon the shell
and cut out by drilling and filing. After rounding the outside corners,
these little strips are pinned to the cores _D_ and _E_ in their proper
places.

[Illustration: Fig. 14. Die-cast Half-round Bearing, Showing the Cast
Oil Grooves]

Another little kink in this connection is worthy of noting. So many
different styles and sizes of bearings are made by a concern doing much
die-casting that it is essential that the die-cast bearings should
bear some distinguishing number to identify them. As this number is
of no consequence to the user it is well to have the number in an
inconspicuous place, but it must be where it will not be effaced by
scraping, etc. Bearing in mind that it is much easier to produce raised
lettering by die-casting than to produce sunken lettering, it will be
readily seen that the oil groove affords a good place in which to
put the bearing number. This is easily done by stamping the figures
upon the narrow strip that forms the oil groove. In this place on the
bearing it may be easily found if needed, and of course there is no
danger of its being taken out by machining.

The lower die consists of two blocks _F_ and _G_, each of which
contains an impression of a bearing. The best way to make these parts
is to lay out the ends of each of the blocks with the proper radius,
taking care to have the center come a little below the surface of the
face of the block. Then the blocks should be shaped out to get the bulk
of the stock out, before setting up in the lathe. After the lathe work
is done on each piece, which of course is usually done separately, the
faces of the two blocks are faced down just to the exact center of the
impression. It will be noticed that two blocks are used for the lower
part of the die. The reason is to facilitate the locating of the female
parts of the die in proper relation to the male parts. After properly
locating, they may be doweled and screwed to baseplate _B_.

[Illustration: Fig. 15. Interesting Examples of Die-castings]

The sprue cutter _H_, better shown in the plan view, is square in shape
and connects with the die-cavities in a thin narrow opening on either
side of the sprue cutter. The ejector pins, _I_, two to each die, are
at the ends of the bearings. The ejector-pin plate _J_ is necessarily
large, and is operated by lever _K_.

Fig. 15 shows a number of interesting examples of die-castings.




CHAPTER III

VAN WAGNER MFG. CO.’S DIE-CASTING PRACTICE


In 1907, Mr. E. B. Van Wagner, of Syracuse, N. Y., established the
E. B. Van Wagner Mfg. Co. for the production of die-castings. The
factory comprises the office section, the machine shop where the dies
and casting machines are built, the metallurgical laboratory where the
metals are alloyed, the casting department shown in Fig. 17 where the
die-castings are made, and the trimming department.


Possibilities and Limitations of Die Casting

[Illustration: Fig. 16. Die-casting Constructions to be avoided]

At the outset we may say that it is possible to die-cast almost any
piece, but it is not by any means practicable to do so. It must be
remembered that to die-cast on a practical basis the dies must be
constructed in such a manner that the cost of their operation and
up-keep will be light, or there will be no profit in die-casting. It
is impracticable to produce under-cut work, that is, work having no
draft and which is therefore impossible to draw from the die. Such
an instance is that illustrated at _A_, Fig. 16, and by the internal
section of _M_, Fig. 21, and the internal groove in _O_, also shown
in Fig. 21. If absolutely necessary, work of this kind can be done by
the use of collapsible cores; but here, again, we meet resistance in
maintaining the dies in proper condition, and, moreover, this method
is commercially impracticable, owing to the difficulty of operating
these cores rapidly. Hollow work, requiring curved cores, like faucets
and bent piping of the character illustrated at _C_ in Fig. 16, are
difficult to produce. If, in designing the piece, it can be planned to
have the parts of such a shape that the cores can be readily withdrawn,
employing a two-piece core with a slight draft in each direction,
the division coming as indicated by the core line of _C_ in Fig. 16,
the problem becomes simpler. Oftentimes this work can best be done
by casting in a straight piece, afterward bending the die-casting.
It does not pay to cast rough heavy work that can be made just as
efficiently by sand casting. Generally speaking, the greatest saving
can be effected by die-casting small pieces which have previously
required a large amount of machining to produce. On large plain work
the amount of metal required for the casting makes the cost excessive
on account of the difference in cost of the metals. If, however, the
large work must be finely finished by polishing, etc., it is oftentimes
found of advantage to die-cast. Corners, especially those joining thick
and thin sections, as at _B_, Fig. 16, should be heavily filleted
as shown on one side of this piece. Regarding the casting of thin
sections, it is not practicable to try to cast sections under 3/64
inch in thickness, as the metal runs with difficulty into such narrow
places. A casting having walls 1/16 inch, like that shown at _X_, Fig.
24, is easily cast. Threaded sections, if the threads are fine, say,
under twenty-four to the inch, should not be die-cast, because under
moderate pressure they will strip. A good way to treat constructions of
this kind is to enclose brass or steel bushings in the die-castings in
which the threads are required.

[Illustration: Fig. 17. View of the Casting Room]

As to the accuracy with which die-castings may be produced, it is
possible to keep dimensions within 0.0005 inch of standard size, but to
do so requires considerable expense in keeping the dies in condition.
A limit of 0.002 inch, however, is entirely practicable, and can be
maintained easily. In specifying the accuracy with which die-castings
are to be made, only those parts which are absolutely essential should
be held to size, in order to keep the cost of the work nominal. One of
the great advantages of the use of die-castings is that no finishing is
required after the pieces leave the molds. Finish requirements should
be plainly stated in ordering die-castings, as the alloy must be suited
to these requirements.

[Illustration: Fig. 18. Methods of attaching Die-cast Gears, etc., to
Shafts]

Another great saving is effected on lettered work, either raised or
sunken. One of these jobs is illustrated at _Q_, Fig. 22, which shows
an example of die-cast lettering. Sunken lettering is to be preferred
to raised lettering, as the latter is more easily injured. Knurled
work may be produced easily, if straight knurls are used, and threaded
sections over ¼ inch in size are entirely practicable, either internal
or external. External die cast threads are illustrated at _R_ and _S_,
Fig. 22. The casting of gears and segments is a familiar application
of die-casting; this is illustrated by the large gear at _N_, Fig. 21,
and the segment at _W_, Fig. 23, which give an idea of the general
character of this class of work. The casting of pulleys, gears, and
similar parts on shafts may be easily effected as shown by the gear on
the shaft at _N_, in Fig. 21. The views shown in Fig. 18 are intended
to convey an idea of three methods of die-casting around shafts. At
_D_ is shown a die-casting cast around a steel shaft. If the surface
of the shaft coming within the pulley has been previously knurled,
the pulley will grip it much better, but for ordinary purposes the
shrinkage of the die-cast metal around the shaft is sufficient. If any
heavy strain is to be imposed on the work, it is better to provide
anchor holes through the shaft, like those indicated at _E_. It will be
readily seen that the die-cast metal runs through these holes in the
shaft, forming rivets which are integral with the casting. For locating
levers upon the ends of shafts, etc., a good way is to flatten opposite
sides of the shaft and cast around them, as shown at _F_, Fig. 18. The
screw seen projecting beneath the piece at _Q_, Fig. 22, was die-cast
in place. Any of these methods are to be recommended, and a proper
knowledge of possibilities of this kind will increase the scope of
die-casting.

[Illustration: Fig. 19. A Few Possibilities of Die Casting]

Another phase of die-casting which can well be borne in mind is the
possibility of inserting steel or other parts in the die-casting.
Such an instance is shown at _G_ in Fig. 19--a die-casting which was
made by the Van Wagner Co. as a part of an electrical apparatus, the
steel inserts being contact points. Oftentimes it is found advisable
to include brass bearing rings to give additional durability at points
where the die-cast metal would not stand up. The die-casting shown at
_U_, Fig. 23, in which the brass ring at _T_ has been incorporated,
is typical of such cases. To die-cast pieces like those shown at
_H_ in Fig. 19, and similarly at _V_ in Fig. 23, having inverted
conical openings, might at first thought seem difficult, but this is
entirely practicable. Similarly, split bushings like those shown at
_I_, Fig. 19, and at _W_, Fig. 23, may be cast with projecting lugs
for the reception of screws for clamping upon shafts, etc., but this
construction should not be used if frequent tightening or loosening
will be necessary.

[Illustration: Fig. 20. Castings which illustrate Points of Shrinkage
and Draft]

[Illustration: Fig. 21. Die-castings showing Impractical Under-cut
Sections; also a Large Gear die-cast on Shaft]

[Illustration: Fig. 22. Die-castings which show Lettering and Thread
Castings]

The shrinkage problem manifests itself in die-casting in the same
measure that it does in other casting operations. Different metals
shrink in different degrees, as will be explained later on. However,
one important point can be mentioned at this time: that is, the amount
of shrinkage is often dependent upon the shape of the piece. For
instance, pieces like those shown at _K_ in Fig. 20 or at _X_ in Fig.
24, will shrink very little on account of the fact that the steel mold
is of such shape that the central core will prevent the die-casting
from shrinking. However, pieces like those shown at _L_ in Fig. 20,
or at _V_ in Fig. 24, which have nothing to hold them from pulling
together as they cool, will shrink to the greatest extent. All of
these points must be taken into consideration when designing work for
die-casting. Practically no draft is necessary on a die-casting, except
on very deep sections, as indicated at _J_ in Fig. 20, where a draft
of 0.001 inch to the inch is desirable. Perfectly straight sections,
however, can be cast, as the shrinkage of the metal is usually enough
to free it from the die.

[Illustration: Fig. 23. Typical Die-castings illustrating Various
Points]

[Illustration: Fig. 24. Die-castings illustrating the Extremes of
Shrinkage]

It is the opinion of the Van Wagner Co. that die-casting costs can
be materially reduced if designers will bear this point in mind when
bringing out new designs. Even though it is often possible to cast
special pieces, incorporating several parts in one, and thereby
accomplishing what seems to be a great stunt to the designer, it is
sometimes more practicable to make the piece in several sections and
later assemble it. Not only is this simpler for the die caster, but it
is also more economical for the customer. Such points as avoiding thin
sections, including large fillets at corners, as well as taking account
of the under-cut problem, are simply matters of common sense, but they
can profitably be considered by the designer.


The Van Wagner Die-casting Machine

The first essential to good die-casting is a good casting machine.
Perhaps the best known types of casting machines are of the familiar
plunger type, of which there are several varieties, the pneumatic type
and the rotary or automatic type. (For descriptions of various types of
die-casting machines, see “Die Casting Machines,” MACHINERY’S Reference
Book No. 108.) For the economical production of die-castings, however,
the hand-operated machines are rather too slow, and automatic machines
are applicable only to a class of work which may be made in very large
quantities. For these reasons, therefore, the Van Wagner Co. employs
the compressed air type of die-casting machine which was patented by
Mr. E. B. Van Wagner in 1907. In the casting department of the Van
Wagner shop, illustrated in Fig. 17, there are installed about thirty
machines. Fig. 27 shows a die-casting machine in the open position.
Fig. 26 shows a closer view of the die-operating mechanism and Fig. 25
is presented to give a general idea of the construction of the entire
machine.

[Illustration: Fig. 25. Drawing illustrating Principle of Van Wagner
Die-casting Machine]

By referring to the line illustration Fig. 25, which shows the Van
Wagner pneumatic die-casting machine in part, and comparing this
illustration with Fig. 26, which shows the general appearance of the
die-operating and other mechanism of the casting machine, a good idea
may be obtained of its construction and working. At _A_ may be seen
the base of the machine in which is located the melting pot _B_. This
melting pot is heated by means of fuel oil passing through the supply
pipe _C_ to the burners _C_`1. A vent pipe _D_ is provided to take
away the gases incident to combustion. The pressure for “shooting” the
metal into the die cavity is supplied by air through the supply pipe
_E_. A valve controls this air supply. The pressure is regulated to
suit the particular casting or die, the proper amount being determined
by experiment. Similarly, an air exhaust pipe _F_, which may be seen
directly above the supply pipe, sub-divides into two tubes which
extend to the die cavity to exhaust the air before the metal is
admitted. There are two methods of overcoming the presence of air in
the die cavity--the exhaust method and the venting method, and it is
the former that is here described.

[Illustration: Fig. 26. View of Machine showing Die-operating Mechanism]

A “goose-neck” _G_, shown in Fig. 25, serves to temporarily contain
the metal which is forced into the mold. An amount of metal slightly
in excess of that required for one die-casting is placed in this
goose-neck with a hand-ladle, previous to each operation of the
machine. One end of the goose-neck is connected to the air pipe, _E_,
while the other end terminates in the nozzle _G_`1. This nozzle may
best be seen by referring to the illustration of the machine shown in
Fig. 27, in connection with Fig. 25. One of the advantages in using
this goose-neck is that the entire air pressure is expended upon the
metal in the goose-neck, and, by reason of its isolated position, the
goose-neck and its contents are kept slightly hotter than the contents
of the melting pot.


The Die-operating Mechanism

The die-operating mechanism of the machine is contained within a hinged
framework, shown in position for the removal of the die-casting in Fig.
27. Referring to Fig. 26, in connection with the line illustration Fig.
25, it will be seen that the die-holding mechanism is all supported
upon the lower die-holding plate _H_, which is hinged to the edge
of the base of the machine. A lock _J_ serves to hold the dies and
operating mechanism in the upright operating position, and by means
of a counterbalance, suspended from an overhead rope which connects
with the top of the mechanism at _P_, the changing of the position of
this mechanism is easily effected, and when thrown into the horizontal
position, as indicated in Fig. 27, it rests upon a support while the
dies are being opened and the castings ejected.

[Illustration: Fig. 27. Die-casting Machine in Position for Removal of
Casting]

The lower die is shown at _H_`1 and the upper die _K_`1 is mounted
upon the upper die-holding plate _K_. Four rods _L_ act as guiding
members for the upper die-holding plate to slide upon. These rods _L_
are mounted in fixed positions at the corners of the lower die-holding
plate _H_, and at their upper ends the operating shaft supporting plate
_M_ is located in a fixed position, serving to support the upper ends
of these rods. The position of this plate _M_ is adjustable upon the
rods by means of check-nuts, thus providing for the accommodation of
thick as well as thin dies. A shaft _O_ is supported in this top plate,
and by means of the operating lever _N_ working through slotted levers
_O_`1 and links _O_`2, the upper die-holding plate and die can thus
be removed from contact with the lower die at will.

The metal enters the die cavity through the nozzle _G_`1 and after
setting, it is necessary to cut the sprue formed by the surplus metal
that remains outside the die cavity. For this purpose, a sprue-cutter,
operated by means of hand-lever _Q_`1, is employed. This sprue-cutting
lever is hinged in the fulcrumed link _Q_`2, and is held in its
casting position by means of an adjustable stop on bracket _Q_`3.

[Illustration: Fig. 28. General View of Trimming Department]

In many dies, it is necessary that water be circulated through the
die-blocks to keep them cool during the die-casting operation. In
Fig. 26, the water pipe may be seen at _R_, and hose pipes run from
this supply to each side of the die-blocks, thus providing a cooling
circulation. In this illustration, the pipes used for exhausting the
air from the die cavity are apt to be confused with the cooling pipes,
but by following the two pipes leading vertically down to the machine,
the exhaust pipes may be seen and kept distinct from the water pipes.


Making a Die-casting

In order to clearly understand the operation of the die-casting
machine, let us follow the sequence of events that takes place in
producing a casting. Two men are required to operate the machine. In
Fig. 27, the operators may be seen in their working positions. The
first step is taken by the operator at the left who, with a hand-ladle,
dips enough metal for one casting from the melting pot and pours it
through nozzle _G_`1 into the goose-neck. The second operator in the
meantime is replacing the cores in the dies, adjusting the position of
the sprue-cutter and closing the dies preparatory to making a casting.
This being done, he elevates the dies and their operating mechanism,
which are hinged and counterbalanced, as previously described, bringing
them to an upright position. The die operator now mounts the box,
raises the sprue-cutter to its open position to admit the metal; after
which the machine operator turns the air valve with his left hand. The
operation of this air valve admits the air behind the metal, forcing it
into the die, and the same movement opens the exhaust valve slightly in
advance. The exhaust valve is located upon the second length of piping
just above the air valve, and as a link connects the two valves, the
single motion exhausts the air from the die cavity and immediately
afterward the air is admitted behind the metal, thereby “shooting” the
metal into the die. This being done, the air is shut off and the die
operator cuts the sprue by means of lever _Q_`1, withdraws the cores
in the die, throws the dies to the open position (which is indicated
in Fig. 27), and operates the ejecting mechanism, thus removing the
casting from the die. In the meantime, the machine operator is tending
to his metal supply and getting a ladle full of metal ready for the
next die-casting operation. By referring to the machines shown in Fig.
17, it will be noticed that only a few are provided with exhaust piping
for venting the dies. Another venting method will be described later.

[Illustration: Fig. 29. Trimming Die-castings on a Filing Machine]

The number of die-castings which can be made on one machine per day of
ten hours varies with the character of the pieces being die-cast, the
number of pieces made at each operation of the machine and the ease
with which the dies may be worked, which depends, of course, upon the
number of cores and parts to be handled at each die-casting operation.
The dies shown in the machine in Fig. 26, produce four bearings at each
operation.


Trimming Die-castings

At the end of each run the operators of the machines go over their
work, breaking the castings from the sprues and throwing out all that
are defective. No matter how carefully the die-casting molds have been
made, there is always a certain amount of trimming to be done on the
finished die-castings, on account of the crevices left in the die for
air vents, or which exist from improper fitting of the parts of the
dies. These “fins,” as they are called, are trimmed by hand operators
in a special department. A general view of this trimming room is shown
in Fig. 28. Usually it is sufficient to scrape these fins off with a
scraping knife, but if the casting is especially difficult to produce,
so that a large opening is required to admit the metal, it is sometimes
necessary to trim unusually thick sprue sections by filing. Fig. 29
illustrates the method of trimming such die-castings on a filing
machine.

[Illustration: Fig. 30. General View of E. B. Van Wagner Co.’s Die
making Department]

[Illustration: Fig. 31. A Typical Die-casting Mold]


The Dies Used

Next to the casting machine, the dies or molds are the most important
necessary factor. A general view of the Van Wagner Co.’s die-making
department is shown in Fig. 30. In order to gain a proper conception of
the work required in producing a high-grade die-casting mold, we will
follow the different steps which are necessary in making the mold. The
first and most important step is the proper planning of the die. Before
any work at all can be done, it is necessary to plan the die, _i. e._,
to decide just where the parting lines will come; just what method
will be used for ejecting the piece; what alloy will be used; where
the casting will be gated; and a hundred and one minor points, all of
which have a direct bearing upon the performance of the finished dies.
All these decisions have to be made by the diemaker, and in Fig. 37 he
is shown, micrometer in hand, computing the shrinkage allowances that
he will make in the dies. This is a very important factor on accurate
work as the shrinkage varies from 0.001 to 0.004 inch, according to the
alloy and the general shape of the piece.

[Illustration: Fig. 32. Die-casting Mold shown in Fig. 31, disassembled]

Before taking up the actual machining operations of the mold-making
as conducted in this factory, it will be well to take a typical
die-casting mold and note its general construction. Fig. 31 shows a
typical die-casting mold closed, while Fig. 32 shows the same mold
disassembled on the bench to show its construction. The piece for
which the mold has been made is also shown. Fig. 33 shows a similar
die in section. From the three illustrations a good idea of an average
die-casting mold can be obtained. Referring to these illustrations, the
principal parts of this die are the ejector box _A_, and the ejector
plate _B_ which is operated by the racks _C_. For operating the ejector
plate, the pinion shaft _D_ having a handle suitable for turning, is
furnished. This, of course, fits into a bored hole in the ejector box,
bringing the pinion into mesh with the racks for raising the ejector
plate. In the ejector plate are three ejector pins _E_ for removing
the casting from the mold. The ejector pins operate through holes _F_.
Beyond the pinion shaft may be seen the casting for which this mold
has been made. It will be noticed that the top side of the casting has
three projecting lugs through which are small holes. Provision for
forming this side of the die-casting is made in the lower half of the
mold _G_, while the upper half of the die-casting is taken care of
by the top plate _H_. One of the toggles for operating the core pins
through these three lugs is shown at _I_. These parts will be described
more fully later. The sprue cutter is shown in position in the die at
_J_.


Machining the Die Cavities

As will be noticed from Fig. 30, the machinery in the die-making
department is of modern design, for no other class of work demands as
good tool equipment and as much skill in the making as die-casting
molds. The die-blocks are made of machinery steel. Fig. 34 illustrates
the first step in making a die-casting mold after the die-block has
been shaped approximately to size. This operation consists in carefully
facing off the die surfaces on a vertical-spindle grinding machine.
This, of course, is a quick method of surfacing the die-block, and
it insures that the top and bottom surfaces of these plates will be
parallel, permitting the die-faces to come together properly.

[Illustration: Fig. 33. Section through a Die-casting Mold]

The next step consists of laying out the die, as shown in Fig. 36. This
is done in the usual manner, by working on a coppered surface, using
dividers, scales, and a center punch. When laying out the die, the
necessary allowances are made for shrinkage and finish, these points
having been planned before actual work on the die has been started. As
in other phases of die-work, the machining operations are performed,
as far as possible, before any hand-work is done. In Fig. 38 may be
seen a die-maker turning the cavity in a part of the die-casting mold.
The highest type of skilled workmanship is called for on this machine
work, and as may be surmised from Fig. 38, where the die-maker is shown
measuring the die with a vernier caliper, the measurements must be
exact, for no grinding operations follow the machine work.

[Illustration: Fig. 34. First step in making the Mold--Grinding
Surfaces of Blocks]

[Illustration: Fig. 35. A Milling Operation on a Die]

Figs. 35 and 39 show typical milling operations being performed on
die-casting molds. In Fig. 39 the diemaker is shown indicating a pin in
one corner of the mold cavity, preparatory to doing additional milling.
The block is held in the usual manner by being clamped on the bed of
the milling machine, and after it has been properly located under the
cutter head, tools are substituted for the indicator and the milling
of the cavity is completed. Fig. 35 shows one of the sections of the
die-casting mold which is to be used in producing the casting shown at
the right of the work. In this case the diemaker is milling the recess
for the steel arbor which may be seen directly in the foreground. This
will be fitted in place to provide for the forming of the hole in the
side of the piece.

[Illustration: Fig. 36. Laying out One of the Mold Parts]

[Illustration: Fig. 37. Planning the Die-casting Mold]

[Illustration: Fig. 38. Turning out a Die-casting Mold]

[Illustration: Fig. 39. Indicating a Mold on the Milling Machine]

Fig. 40 illustrates several important points in the making of a
die-casting mold. This illustration shows the ejector box with the
lower half of the mold on it, the ejector plate being held against the
under side of the die-plate by means of the pinion shaft. The operation
being done is the drilling of the ejector-pin holes. Referring back to
Fig. 32, which by the way shows the die here illustrated disassembled,
the holes being drilled are those shown at _F_ for the reception of the
pins _E_. The method employed is to drill the holes through the die and
into the ejector plate, afterward reaming all holes to size and driving
the pins into position in the ejector plate, while they are allowed to
slide freely through the die-plate. We will now assume that the ejector
box and plate have been completed and fitted, a pinion shaft for
operating this plate also fitted, the lower and upper dies completed
by the machining operations previously described, and all assembled.
The final operation of the fitting of the pins is shown in Fig. 41 in
which the die-maker may be seen filing off the ends of these pins so
that when dropped to the lower position they will lie flush with the
surface. If of uneven lengths, these pins will cause irregular spots in
the casting. It now remains to describe the toggles used for operating
the cores which form the holes through the three lugs in the casting.
One of these toggles, of which there are three, is shown at _I_, in
Fig. 31, and also in Fig. 32. These toggles consist of brackets which
are attached to the die-plate, and levers which are fulcrumed at the
ends of the brackets so that their operation works the core pins. It is
necessary to remove these core pins after each casting has been made
and position them before another casting can be produced.

[Illustration: Fig. 40. Drilling the Ejector-pin Holes]

The fitting of the parts of a die-casting mold is one of the
most important parts of the work. It demands the highest type of
workmanship, for a poorly fitted die means a die which works hard
in addition to producing poor castings. It is very important that
all movable parts should work freely. Fig. 42 shows the assembling
operation on a die-casting mold, the casting which is to be duplicated
being shown in the immediate foreground. These parts must all be
screwed into their respective places, making the joints as nearly
air-tight as possible. One cause of poor die-castings arises from the
trapping of air in the die, and different methods are employed for
overcoming this trouble.


Venting the Dies

There are two methods of preventing air from being trapped in
die-casting molds; either by constructing the dies so that the air
may be exhausted from the mold cavity before admitting the metal, or
by venting the die so that the air may be forced out by the inrushing
metal. In the first of these methods it is necessary that the joints in
the mold be made as close as possible, otherwise it will be impossible
to produce anything like a vacuum in the mold cavity. If, however, it
has many parts which must be fitted, it is usually considered advisable
to provide the die with vents consisting of milled recesses a few
thousandths inch deep. Several vents are provided, from which the air
can escape when the metal is admitted to the dies. The hot metal, of
course, “shoots” through them in thin ribbons, but not enough escapes
to affect the pressure on the metal which goes into the casting.

[Illustration: Fig. 41. Fitting Ejector-pins]

No matter how carefully a die may have been constructed, or how
carefully it has been assembled, there is always a certain amount of
“babying” to be done before it will work satisfactorily. The casting
may stick a little here, or there may be a rough spot there, and it
is the successful elimination of these troubles which constitutes the
production of a good die-casting.


Die-casting Metals

One of the purposes of this book is to correct several erroneous
impressions which are prevalent in regard to die-casting possibilities.
Many people seem to think that nearly all metals can be die-cast, but
as a matter of fact, those metals which can be successfully die-cast
can be numbered on the fingers of one hand, being alloys of lead, zinc,
tin, copper and antimony. The tin base metals shrink very little, while
the zinc base metals shrink considerably, and those with a large per
cent of aluminum have a very high shrinkage. Without doubt, the most
used die-casting metals are the zinc base metals. A typical metal of
this class contains about 85 per cent zinc; 8 per cent tin; 4 per
cent copper and 3 per cent aluminum. The melting point of this metal
is about 850 degrees F. While this alloy is one of the most common,
it is not by any means the best, as there is too little tin employed,
but it is a comparatively cheap metal, which probably accounts for its
large use. This metal is easily affected by heat and cold, and rapidly
deteriorates with age. The lead base metals may be typified by an alloy
containing 80 per cent lead; 15 per cent antimony; 4 per cent tin; and
1 per cent copper. This composition melts at approximately 550 degrees
F. and is used for castings subjected to little wear and where no
great strength is required. The weight of this metal is its greatest
objection, and it is also quite brittle because of the large percentage
of antimony.

[Illustration: Fig. 42. Assembling a Die-casting Mold]

For the best class of die-castings, the tin base metals are employed.
These range from 60 to 90 per cent tin, and from 2 to 10 per cent
copper, together with a little antimony. The melting point of a
mixture of this composition is about 675 degrees F. The castings have
a good color and they are much better in quality than any of the other
alloys. It is absolutely essential that tin base metals be used for
carbureter parts or other parts coming in contact with gasoline. Also,
the tin base metals must be used for parts which come in contact with
food products, as the lead or zinc alloys have a contaminating effect.

Aluminum alloys have been cast in France and Germany in limited
quantities, but very seldom in this country on account of their high
melting point, as well as their effect upon the die. After aluminum
alloys have been run in the dies for a short time, the surfaces of the
molds become pitted. Through some unexplained cause, the metal seems
to flake out particles of the steel in the molds. When an aluminum
alloy is to be used, a good mixture is 80 per cent aluminum, 3 per cent
copper and 17 per cent zinc. This alloy has a high shrinkage and it has
also the same deteriorating effect upon the dies, but to a much less
degree than pure aluminum.




Transcriber’s Notes


Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in this book; otherwise they were not
changed.

Simple typographical errors were corrected; occasional unbalanced
quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

Text uses “die-cavity” and “die cavity”, “die-maker” and “die maker”;
none changed here.







*** END OF THE PROJECT GUTENBERG EBOOK DIE CASTING: DIES—MACHINES—METHODS ***


    

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