Training Objective After watching the program and reviewing this printed material, the viewer will become familiar with further aspects of tool design by exploring the materials used in toolmaking. Tool material selection is highlighted Physical and mechanical properties are discussed Both ferrous and nonferrous tool design is shown Nonmetallic tooling is explored Tool Material Properties The principal tool materials are ferrous metals, nonferrous metals, and nonmetallic materials. Proper selection is based upon how the material s physical and mechanical properties will affect the tool s performance and capabilities. Physical properties are inherent in the material and cannot be permanently altered without changing the composition of the material itself. They include: Density Color Electrical conductivity Thermal conductivity Thermal expansion Melting point Mechanical properties can be permanently altered by either thermal or mechanical treatment. Those properties include: Hardness resistance to indentation Wear resistance resistance to abrasion, grinding, and rubbing Toughness ability to absorb sudden impact Brittleness tendency to fracture when a sudden load is applied Plasticity ability to deform without fracture (ductility and malleability are associated with plasticity) Surface finish influences tool quality and tool life expectancy Tests for the basic mechanical properties are: Strength various mechanical devices are used to place material specimens under a variety of loads such as tensile, compressive, shear, and fatigue. Hardness the degree of indentation is determined by using a variety of tests, with the most common being the Brinell or Rockwell tests. Toughness determined by either the Charpy notched bar or the Izod notched bar test. Certain mechanical properties can be obtained by the use of thin film coatings. Surface hardness, wear resistance, reduced friction, and thermal conductivity are typical properties obtained with coating or layers of coatings which often total.001 of an inch (.025 of a millimeter) or less. Strength, hardness, and toughness are mechanical properties that can be enhanced by various heat treating processes including throughhardening, surface hardening and softening processes. Fundamentals of Tool Design Study Guide, DV07PUB1-1 -
Ferrous Tool Materials Ferrous tool materials have iron as a base metal and include the carbon steels, alloy steels, tool steels, and cast irons. Ferrous tool materials are used in the cast, hot-rolled, cold-rolled, or ground condition. Carbon steels contain mostly iron and carbon, with small amounts of other alloying elements. They are designated as having low, medium, and high carbon content ranging from.05% to 1.5%. Alloy steels are carbon steels with additional alloying elements added to enhance specific mechanical properties. Such elements include manganese, silicon, nickel, molybdenum and chromium. Tool steels are comprised of high carbon, high strength alloys with additional elements that provide characteristics needed for specific tool purposes. There are seven major families of tool steels: Water-hardening steels Cold-work steels Shock-resisting steels High-speed steels Hot-work steels Plastic mold steels Special-purpose steels Cast iron is essentially an alloy of iron containing from 2% to 4% carbon,.5% to 3% silicon,.4% to 1% manganese, plus phosphorus and sulfur. Other alloying elements may be added depending on the properties desired. Cast iron appears in gray, nodular, malleable, white, and alloy forms. Nonferrous Tool Materials Nonferrous tool materials have a base metal other than iron, with the most commons types being aluminum, carbide, and cermet. Aluminum is used for special tooling. The principal advantages to using aluminum are its high strength-toweight ratio, nonmagnetic properties, corrosion resistance, and relative ease in machining and forming. Carbide is a powder metallurgy product made of hard carbide particles bonded together by a metal binder. Typical carbides are tungsten, titanium, tantalum, and niobium. Most carbide tools have additional coatings, including titanium carbide, titanium nitride, aluminum oxide, titanium carbonitride, titanium-aluminum nitride, and combinations of some of these. Cermet is a very hard material consisting of titanium carbide or titanium nitride along with a nickel or cobalt binder. Cermet tools are used primarily for semi- or final-finish turning and boring. Fundamentals of Tool Design Study Guide, DV07PUB1-2 -
Nonmetallic Tool Materials Nonmetallic tool materials are used mainly for limited parts production and where the cost of using tool steels and other materials are not economically practical. They may incorporate metallic elements to enhance performance and longevity. The principle nonmetallic tool materials include: Wood, which is used in a variety of forms within low-cost, limited-production tools. Some common applications include short-run or prototype thermoforming molds, steel-rule dies in which wood supports the rule, and jig plates with inserted steel bushings. Composites, which consist of a reinforcing material and a matrix. Special composite tooling materials are used as economical alternatives to metal tooling for composites manufacturing. Composite tooling is desirable since it can have the same thermal expansion characteristics as the composite parts being manufactured and cured. Rubber, which is used in special drawing, blanking, and bulging die operations, as well as for protective elements and other special tools. Silicone rubber, specifically RTV or room temperature vulcanizing silicone, is used as a rapid means of producing soft tooling for low-pressure molding. Ceramic, which has high compressive strength, high hot strength, and resistance to abrasion and galling, along with low heat conductivity. It is used primarily in high-speed cutting tools on very hard and abrasive materials. Ceramic cutting tools can be divided into alumina-based ceramics and silicon nitride-based ceramics, with each having specific applications. Diamond, in synthetic or natural form, is the hardest of materials, and finds limited use for turning and milling operations, grinding wheels and grinding wheel dressers. Diamond tools cannot be used on ferrous metals, such as steel, Because of their high affinity to carbon. Cubic boron nitride or CBN is the second hardest tool material after diamond. It has a compressive strength of 700,000 psi (4,830 mega pascals), twice the thermal conductivity of copper, is thermally stable and resistant to oxidation up to 3,500 F (1,925 C). CBN is used to machine both ferrous and nonferrous metals that cannot be readily cut by other materials. Fundamentals of Tool Design Study Guide, DV07PUB1-3 -
Review Questions 1. The physical properties of tool materials are: a. inherent b. variable c. heat treatable d. altered by cold working 2. Malleability is associated with: a. softness b. hardness c. plasticity d. wear resistance 3. The Charpy notched bar test provides a measure of: a. tensile strength b. compressive strength c. toughness d. fatigue strength 4. Thin film coatings on tool surfaces total: a..005 of an inch (.127 of a millimeter) b..003 of an inch (.0762 of a millimeter) c..010 of an inch (.254 of a millimeter) or more d..001 of an inch (.025 of a millimeter) or less 5. The carbon content of carbon steel ranges from: a. 2% to 4% b..05% to 1.5% c. less than.05% d. less than.01% 6. The range of carbon content of cast iron is: a. 5% to 10% b. 4% to 7% c. 2% to 4% d..01% to.15% 7. Cermet tools are used primarily for: a. final finish turning b. interrupted cutting c. deep hole drilling d. rough turning 8. Diamond tools cannot be used on: a. aluminum b. steel c. composites d. ceramics 9. Cubic boron nitride (CBN) is thermally stable to: a. 1,100 o F (593 o C) b. 2,500 o F (1,370 o C) c. 3,500 o F (1,925 o C) d. 3,800 o F (2,093 o C) Fundamentals of Tool Design Study Guide, DV07PUB1-4 -
Answer Key 1. a 2. c 3. c 4. d 5. b 6. c 7. a 8. b 9. c Fundamentals of Tool Design Study Guide, DV07PUB1-5 -