Die Design Fundamentals. Vukota Boljanovic
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Figure 2.9 Shaving die.
Figure 2.10 Broaching die.
2.2.10 Broaching Dies
Broaching may be considered to be a series of shaving operations performed one after the other by the same tool. A broach is provided with a number of teeth, each of which cuts a chip as the broach traverses the surface to be finished. Internal broaches finish holes; surface or slab broaches finish outside surfaces. Two conditions make broaching necessary:
1.Blanks are too thick for shaving: If considerable metal must be removed from the edges of thick blanks, a series of shaving dies would be required to produce a smooth finish. It would then be more economical to use a broaching die.
2.When considerable metal must be removed: This occurs when ridges or other shapes are required in the edges of the blank. It is often impractical to blank such shapes directly because the cutting edges would be weak and subject to breakage.
In Figure 2.10, a blank at A must have small pointed serrations machined in the sides. The die is provided with two broaches B supported during the cutting process by hardened backing blocks C. The blank is located in a nest D composed of two opposed plates machined to fit the contour. Pressure pad E, backed up by heavy springs, clamps the blank securely before cutting begins. The first three or four teeth of the broach are made undersize; ordinarily they do no cutting unless an oversize blank is introduced into the die. The last three or four teeth are sizing teeth. Intermediate teeth are called working teeth and they take the successive chips to machine the serrations.
Figure 2.11 Horn die.
2.2.11 Horn Dies
A horn die (Figure 2.11) is provided with a projecting post called a horn. Bent, formed, or drawn workpieces are applied over the horn for performing secondary operations.
In the illustration at A, a blank has been reverse bent in a previous operation and the ends are to be hooked together and seamed in a horn die. The horn B is retained in a holder C fastened to the die holder. When the ram descends, seaming punch D strikes the work-piece to form the seam.
Many other operations, such as piercing and staking, are also performed in horn dies.
2.2.12 Side Cam Dies
Side cams transform vertical motion from the press ram into horizontal or angular motion and they make possible many ingenious operations. In Figure 2.12, at A, a flanged shell requires two holes pierced in its side. The shell is placed over die block B of the die. Descent of the upper die causes pressure pad C to seat the shell firmly over the block. Further descent causes side cams D to move the punch-carrying slides E for piercing the holes. Spring strippers F strip the shell from around the piercing punches as they are withdrawn.
Figure 2.12 Side cam die.
2.2.13 Curling Dies
A curling die (Figure 2.13) forms the material at the edge of a workpiece into a circular shape or hollow ring. Flat blanks may be curled; a common application is a hinge formed of two plates each of which is curled at one side for engagement of the hinge pin. More often, curling is applied to edges of the open ends of cups and shells to provide stiffness and smooth, rounded edges. Most pans used for cooking and baking foods are curled.
In the illustration, a drawn shell shown at A is to be curled. The shell is placed in the curling die where it rests on knockout pad B. Descent of the upper die causes the knockout pad to be pushed down until it bottoms on the die holder. Further descent causes curling punch C to curl the edge of the shell. Near the bottom of the stroke, the lip of the material contacts an angular surface machined in curling ring D to complete the curl. When the punch goes up, the knockout raises the shell for easy removal.
2.2.14 Bulging Dies
A bulging die (Figure 2.14) expands a portion of a drawn shell causing it to bulge. There are two types: fluid dies and rubber dies. Fluid dies use water or oil as the expanding medium and a ram applies pressure to the fluid. In rubber dies, a pad or block of rubber under pressure moves the walls of the workpiece to the desired position. This is possible because rubber is virtually incompressible. Although it can be made to change its shape, the volume remains the same.
In the illustration at A, a drawn shell is to be bulged at its closed end. The shell is placed over punch B of the bulging die and its lower end is confined in lower die C. The upper end of punch B is a rubber ring within which is applied a spreader rod D. This rod is conical at its upper end and it helps the rubber to flow outward to the desired shape. When the press ram descends, the upper die applies a force to the shell bottom, and since the rubber cannot compress, it is forced outward bulging the walls of the shell. When the ram goes up, the rubber returns to its original shape and the bulged shell can be removed from the die. After bulging, a shell is shorter than it was previously.
Figure 2.13 Curling die.
2.2.15 Swaging Dies
The operation of swaging, sometimes called necking, is exactly the opposite of bulging. When a workpiece is swaged a portion is reduced in size. This process causes the part to become longer than it was before swaging. In Figure 2.15, at A, a shell is to be swaged at its open end. It is inserted in the swaging die where it rests on knockout pad B and its lower end is surrounded by the walls of block C. When the ram descends, swaging die D reduces a portion of the diameter of the shell and this portion becomes longer.
2.2.16 Extruding Dies
The function of all the dies discussed so far is to perform work on sheet material—to cut sheet material into blanks, to perform further operations upon the blanks, or to perform operations on workpieces bent, formed, or drawn from the blanks. We come now to some interesting classes of dies that perform secondary operations on small thick blanks called slugs. In these dies, the slugs are severely deformed to make parts having no resemblance to the slugs from which they were made.
The first class of dies are extruding dies. In this type of die, each slug is partly confined in a cavity. Then extremely high pressure is applied by a punch to cause the material in the slug to extrude or squirt out, much like toothpaste is extruded when the tube is squeezed. In Figure 2.16, the slug A is to be extruded into a thin-walled shell having a conical closed end. The slug is placed in die block B, backed up by a hardened plate C. The bottom of the cavity in the die block is formed by the end of knockout rod D. When the press ram descends, extruding punch E first squeezes the slug until it assumes the shape of the die cavity and of the working end of the extruding punch. Continued descent causes the material to extrude upward between the wall of the punch and the wall of the die cavity. The amount of clearance between the two determines