Die Casting: Dies—Machines—Methods

by Chester L. Lucas

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.

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.