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 the thickness of the wall of the extruded shell. The extruding punch is retained in punch plate F and, because of the high pressure involved, it is backed up by backing plate G.
Figure 2.14 Bulging die that uses rubber as the bulging medium.
Figure 2.15 Swaging die.
Figure 2.16 Extruding die.
2.2.17 Cold-Coining Dies
Cold-coining dies (Figure 2.17) produce workpieces by applying pressure to blanks, squeezing and displacing the material until it assumes the shape of the punch and die. In the illustration at A, a slug is to be formed into a flanged part in a cold coining die. It is placed on punch B located within spring-loaded V gages C. Descent of the upper die causes the material under the upper die block to be displaced outward to form the flange. As the flange increases in diameter, the gages are pushed back as shown. When the die goes up, the part is carried upward within it and ejected near the top of the stroke by knockout plunger D actuated by knockout rod E.
The cylindrical part is the slug (blank); another illustration is the flanged part. This is only one simple example of cold coining dies. A basic postulate of plastic deformation of material states that “the shape (of course, dimensions, too) of blanks can be changed, but volume is constant.”
Figure 2.17 Cold coining die.
2.2.18 Progressive Dies
All of the operations described previously may be performed in progressive dies. For example, a single die of this type may do piercing at the first station, trimming at the second station, bending at the third, forming at the fourth, etc. A progressive die may thus be considered a series of different dies placed side by side with the strip passing through each successively. This analogy has some merit, although it does not give a true picture of the extremely close interrelationship between the various stations.
In Figure 2.18, at A, a pierced, trimmed, and bent part is to be produced complete in a simple progressive die. At the first station the strip is notched and pierced and at the second station the blank is cut off and bent. You should easily recognize all of the elements in this die—the die block, piercing punch, trimming punch, knockout, and stop block, along with all the others.
2.2.19 Sub-Press Dies
Sub-press dies (Figure 2.19) blank and form very small watch, clock, and instrument parts. An example is the small instrument cam shown at A. The die components are retained in a sub-press which is, as its name implies, actually a small press operated in a larger one. The sub-press is composed of base C, barrel B, and plunger D. A long, tapered babbit bearing E provided with longitudinal key slots guides the plunger and prevents rotation. Tightening spanner nut F against bearing E causes it to close around plunger D to remove all looseness. The top portion of plunger D is engaged by actuator G threaded into a central tapped hole. The slot of the actuator is engaged loosely by a yoke fastened to the press ram. Thus, the press ram does not guide the sub-press in any way. It simply applies the up-and-down motion. Sub-press dies are usually of the compound type because of the considerable accuracy required.
2.2.20 Assembly Dies
Assembly dies assemble two or more parts together by press-fitting, riveting, staking, or other means. Components are assembled very quickly and relationships between parts can be maintained closely. Figure 2.20 shows a link and two studs that are to be riveted together in an assembly die. The studs are positioned in die block A and they sit on plungers B. The link is then positioned over the studs, the turned-down ends of the studs engaging in holes in the link. Descent of the press ram causes riveting punches C to deform the ends of the studs into the shape of rivet heads. A hardened plate D backs up the punches to prevent the heads from sinking into the relatively soft material of the die set. Another hardened plate E backs up the plungers.
Figure 2.18 Progressive die.
Figure 2.19 Sub-press die.
Figure 2.20 Assembly die.
THE MATERIAL STRIPS
3.5 Methods for Producing Strips
Most stampings are made of steel. Carbon content varies from AISI-SAE 1010 to AISI-SAE 1030 and, therefore, most blanks are in the machine or cold-rolled steel range. Stampings are also made from these other materials:
1.Aluminum
2.Brass
3.Bronze
4.Copper
5.Stainless steel
6.Silicon steel
7.Fiber
