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.
Fig. 20. Castings which illustrate Points of Shrinkage and Draft
Fig. 21. Die-castings showing Impractical Under-cut Sections; also a Large Gear die-cast on Shaft
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.
Fig. 23. Typical Die-castings illustrating Various Points