NOSING DIES 4g handbook vukotaboljanovicsheetmetalformingprocesses

182 Tool and Die Materials Table 13.9 continued D2 D3 D5 0 1 0 2 0 6 50 35 50 90 fairly 125 57 to 62 57 to 64 59 to 63 59 to 61 57 to 61 45 to 63 Very high wear resistance. Excellent size stability, deep hardening in air. Typical applications include dies, drawing dies, shear blades, forming rolls, and trim dies. Excellent abrasion resistance, very high compressive strength, high hardening response. Typical applications include blanking dies, drawing dies, shear blades, forming rolls, punches, and cold trimming dies Very high wear resistance, optimum size stability, and superior resistance to tempering. Applications include blanking dies, shear blades, forming rolls, hot and cold punches, swaging dies, and cold trimming dies. Moderate wear resistance, relatively safe to harden, easy to machine. Common applications include blanking and forming dies, bending and drawing dies, plastics molds, and shear blades. Fairly good wear resistance, relatively safe to harden, fairly easy to machine. General-purpose tooling with a combination of wear resistance and moderate toughness. Excellent machinability, outstanding resistance to wear and galling, easy hardening. Typical applications are gages, punches, cold forming, blanking, and trimming dies, bushings, and other machine tool parts. 13.4 NONFERROUS METALS Many nonferrous metals are used in tool and die, jig, and fixture design. Such materials include alloys of aluminum, magnesium, brass, bronze, zinc-base alloys, and beryllium. Although more expensive than fer- rous metals, nonferrous metals and alloys have important applications because of their numerous positive characteristics, such as low density, corrosion resistance, ease of fabrication, and color choices. Aluminum alloys. The most important factors in selecting aluminum alloys for use in tool and die design are their high strength-to-weight ratio, ease of machinability, resistance to corrosion by many chem- icals, and nonmagnetic properties. Aluminum alloys of series 2024 and 7075 are two of the more widely used alloys for temporary dies, limited production runs, fixture bodies, or other special purposes. Copper alloys. Copper alloys are often attractive for applications where a combination of desirable properties, such as strength, corrosion resistance, thermal conductivity, wear resistance, and lack of Tool and Die Materials 183 netic polarization are required. The most common copper alloys used in tool and die design are bronzes. Bronze is an alloy of copper and tin. There are also other bronzes, such as aluminum bronze, which is an alloy of copper and aluminum; beryllium bronze; and phosphor bronze. Aluminum bronze is most widely used in die design for guide bushings. Zinc-based alloys. These alloys are used extensively in die-casting. They may be cast into shapes quickly for the purposes of being used as short-run punches and dies for either short-run production or for experimental short runs. One of the better-known zinc-based die materials is Kirksite. Kirksite is a nonferrous alloy for the production of press tooling, sheet metal forming, and plastics molds. . Kirksite is a zinc-based alloy of 99.99 pure zinc and contains precise amounts of alloying elements that give it very high impact strength. It is also very free flowing when molten. Kirksite has good machinability and abrasion resistance with rel- ative freedom from loading and galling wearing away by friction, and it can quickly be polished to a high surface finish. It is very useful for blanking dies using no reinforcement at all, the Kirksite being simply cast around a steel punch that may have a very complex profile. Another advantage of this material is that it may be remelted and used over again. Bismuth alloys. These low-melting alloys expand upon solidification, especially those with high bismuth content. This characteristic of bismuth makes it possible to use these alloys for duplicating mold configurations that would otherwise require many operations to reproduce. The material is suit- able for making forms used in stretch forming and has also been used for other components in punch- es and dies.

13.5 NON-METALLIC MATERIALS

In addition to the ferrous and nonferrous metals, there is a wide variety of non-metallic materials that are important to the tool designer. Several of these are discussed in this text. Plastics. Plastics are composed of polymer molecules and various additives. Polymers are long-chain molecules formed by polymerization, that is, by linking and cross-linking of different monomers. Thermosetting plastics such as epoxy, polyester, and urethane are used widely as tooling material. These thermosets cure harden at room temperature. Although curing takes place at ambient temperatures, the heat of the reaction cures the plastics. To impart certain specific properties for tooling material, polymers are usually compounded with additives. These additives modify and improve certain characteristic of plas- tics, such as their stiffness, strength, hardness, abrasion resistance, dimensional stability, color, etc. In some instances, steel wear plates are inserted in the plastics. Plastics tooling is used in many operations, such as drawing and forming dies, drill jigs, and in assembly and inspection fixtures. These materials have advantages over many other materials. They are resistant to chemicals, moisture, and temperature. Generally they are easy to machine, rework, and modify. Elastomers comprise a large family of amorphous polymers having a low glass-transition tempera- ture. They have a characteristic ability to undergo large elastic deformations without rupture; they are also soft and have a low elastic modulus. The terms “rubber’ and “elastomer” are often used interchangeably. Generally, an elastomer is defined as being capable of recovering substantially in shape and size after a distorting load has been removed. Rubber is defined as being capable of recovering from large deformations quickly. A rubber pad 184 Tool and Die Materials confined in a container is used as the forming die. Operations such as forming, blanking, bulging, and drawing may be done with a rubber or polyurethane member as one of the components of the die set. Polyurethane has very good overall properties of high strength, stiffness, hardness, and exceptional resistance to abrasion, cutting, and tearing. Typical applications as a tool material include cushioning and diaphragms for rubber forming of sheet metals. BLANK DIAMETER OF SHELLS In the accompanying diagrams it should be noted that the solid line is the mean line of the drawn part. This line and its associated dimension should be used when calculating the diameter for drawn shells. In Table . given some equations for blank-diameter calculation of symmetrical shells. Table A l . l Equations for calculating blank-diameters of drawn shells I D = + 4dh 3. 2. R D = +4d H 185