342 Section 4 Nonferrous Metallurgy by the yield strength of the metal being drawn, as discussed in Chapter 9. For very long lengths of tube, a floating plug applies pressure on the inside of the tube, so that the tube wall is thinned and the inside diameter is consistent, Figure 15-25. 15.5.3 PM Part Production from Powdered Nonferrous Metal Parts are made from powdered nonferrous metals by compa cting on the same equipment used for steel PM parts. If the powdered nonferrous metal is less reactive than iron powder, such as with brass alloys, sintering can be done using the same furnaces. Aluminum is often processed—and titanium powder must be processed—in inert gas or vacuum furnaces. Metal Powders It bears repeating that reactive metal powders must be stored safely and handled with great caution. Powdered metals can cause lung damage and allergic reactions, as well as presenting a fire and explosion hazard. SAFETY NOTE SAFETY NOTE 15.5.4 Forming, Shaping, and Cutting Most nonferrous metals are formed, shaped, and cut easily. For ductile metals, a stamping press will need only small changes in the dies to use different alloys. Consistent thickness of the sheet stock is more important to longevity of stamping dies. The minimum size of the press, the minimum die corner radii, and the maximum drawing depth of the part are all determined by the formability of the workpiece metal. 15.5.5 Heat Treatment Processing Most nonferrous metal heat-treating is done by solutionizing, quenching, and aging. Formed parts are heated in ovens, then quenched in water, oil, or air, and finally aged to develop strength through precipitate second-phase particles. Controlled atmospheres minimize oxidation. Some alloys that develop significant segregation during casting may suffer partial melting, or liquation, if processed incorrectly during reheating for heat treatment. During casting, alloy elements concentrate between the freezing dendrites, as discussed in regard to steel in Chapter 7. These interdendritic regions are small pockets that melt at lower temperatures than expected for the given alloy composition. The effect is especially significant in sand castings, due to solidification times of minutes instead of seconds. Reheating the casting slowly allows the concentrated elements to diffuse and spread throughout the part. A more uniform composition of the workpiece means the strength in different microscopic regions of the heat-treated part is more uniform, and the part-to-part strength is more consistent. In many air ovens, the control thermocouple is not located near the hottest or coolest point in the oven during heating. Responsibility for adjusting heating rates Drawn tube Drawing direction Steel die Floating plug Goodheart-Willcox Publisher Figure 15-25. A floating plug inside a tube “floats” inside the workpiece as the tube is drawn through the drawing die. The floating plug helps thin the tube wall and assures a smooth inner surface. Copyright Goodheart-Willcox Co., Inc.