Unit 4 Assignment 1: Review Question Solutions ALL 100% CORRECT FALL-2022 LATEST SOLUTION GUARANTEED GRADE A+ - DT 1410 (DT1410) - Stuvia US

Unit 4 Assignment 1: Review Question Solutions ALL 100% CORRECT FALL-2022 LATEST SOLUTION GUARANTEED GRADE A+ Chapter 9 Unit 4 Assignment 1: Review Question Solutions ALL 100% CORRECT FALL-2022 LATEST SOLUTION GUARANTEED GRADE A+ 1. By what means are white-hot ingots formed into slabs, blooms, and billets? The ingot is passed between rolls in a two- or three-high reversing mill that makes it longer and thinner in cross section. 2. What modern method of steel manufacture bypasses the ingot stage and produces slabs or blooms directly? Strand casting or continuous casting 3. Large dendritic crystals that weaken the metal form in cast metals such as ingots and strand casting. How are these removed from the metal? Hot rolling breaks up the large grains and refine them into smaller, more uniform sculptures by the process of nucleation and recrystallization. 4. Why is a cast ingot (one that has had no working) not able to recrystallize even if heated for a long time? Without the energy stored during the cold working operation, a metal will not recrystallize even if heated for a long period of time. 5. What would be the consequences of finishing a series of metal-working operations at too high a temperature? If hot working operations finish at temperatures well above the recrystallization temperature of the metal (whether ferrous or nonferrous), the metal will be at temperatures in the “grain growth” stage of heating, and larger grains will result. A smaller rather than larger grain size is usually desired because the metal will be stronger. 6. What is anisotropy in metals? Anisotropy in metal is a tendency to be stronger in one axis than another because of directionality of "grain" caused by the rolling process. 7. Why are very large forgings heated although smaller forming operations are sometimes carried out cold? Explain. Heating makes metals more plastic, requiring far less force to shape them. Large forgings would require a prohibitively large machine to cold form them. However, small parts are often cold forged because it is a lower cost operation. 8. What kind of forging machine would you choose to use for a very large open-die operation? Which would you choose for making a run of 10,000 high- precision parts? A hydraulic press would be the best choice for large open-die forging. For a run of 10,000 precision forged parts, a mechanical press and closed-die forging would be a good choice. 9. Hot metal tends to stick to forging dies. What design characteristic helps to prevent this from happening? Draft or taper in the die helps to keep the forging from sticking. 10. What is “flash” and how is it removed? Flash is a thin extrusion of metal that is formed where the die halves come together. It is removed as a secondary operation, usually in a small press that shears it off. 11. If you were required to design a machine part, such as an automobile axle that would be subjected to high shock loads would you choose a forging? A casting? Or would you machine it from solid bar stock? Why? Forgings are better able to withstand shock loads than castings or parts machined from solid stock because of their superior grain structure. 12. How are bolt and nut blanks formed? By the process of hot upset forging or the cold upset process. 13. What kinds of shapes can be made by hot extrusion? Almost any shape of uniform cross section, structural shapes, tubing, gears, and special forms. 14. A tank end having a hemispherical shape must be made of M-in.-thick flat steel. Name two methods by which this operation can be accomplished. This can be done in a plate-forming press or by hot metal spinning. 15. Briefly explain how seamless tubing is made and how common steel water pipe is made. Seamless tubing is made by piercing a heated billet and drawing it over a mandrel and through a die. Water pipe is made of heated skelp, which is flat strip that is rolled into a cylinder and butt or edge welded by pressure and heat to form a pipe. 16. Would extrusion or cold rolling be more practical for producing various odd-shaped cross sections from soft metals such as aluminum in short runs? Why? For short runs the extrusion process would be more practical (and less expensive) than cold rolling. The cost of the tooling would be much less than the cost of specially developed rolls, and the cost of the downtime to change dies in an extrusion press would be much less than a roll change in a rolling mill. Chapter 10 1. What is the property of metals that makes possible the cold deformation of metals? Plasticity. 2. When considerable deformation is required in a metal, what can be done to avoid brittleness or rupture? A process anneal (also called bright anneal) will restore a soft plastic condition in the metal, allowing further cold forming to be done. 3. Are closer dimensional tolerances and better finish advantages of hot forming, or of cold forming? Cold forming. 4. In which type, cold forming or hot forming, is more massive machinery required to form a given size part? Cold forming. 5. What is springback? Springback is the elastic recovery in metals causing them to bounce back to some extent toward their former shape when they are cold formed. 6. What must be done to hot-rolled steel in the mill before it can be cold finished? Hot rolled steel must be descaled by pickling in acid with a lime water rinse before it can be cold finished. 7. Cold-rolled steel strip is the material used for many products such as auto bodies and kitchen appliances. How is it made? A coil of hot rolled steel about 1/8 in. thick passes through a series of rolling mill stands where the steel is reduced in thickness and cut in strips or coiled for shipping. 8. Aluminum foil is used every day in our homes. How is it made? Sendizmer mills are useful in producing thin gage foils of many metals. Foil, made from unalloyed aluminum, is able to be reduced to thicknesses under 0.001 inches (0.0254 mm) using 4-high rolling mills. The last pass in the rolling sequence is usually done by “pack rolling,” i.e., rolling two thicknesses together. (Thus what you buy in the supermarket has one bright, reflective side, and one side that has a satin finish.) 9. What is the difference between blanking and punching? The whole material is saved in blanking and it is scrap in punching. 10. How can a sheet metal blank be formed into a cup shape? By a drawing operation in which a punch draws (pushes) the metal into a cavity, stretching the side walls to assume the correct thickness and depth. 11. How is the process of making wire similar to that of cold drawing bars? Both are pulled through a die or series of dies to reduce their size and give them a good finish and harder temper. 12. Cold-forming upsetting machines can make parts from wire stock at a high rate of production, as much as 36,000 parts per hour. What kinds of parts are usually made on these machines? Small screws, rivets, and bolts 13. Larger, more complex products than those of Question 12 are made from bar stock on cold-forming machines that do combined operations in a sequence of operations. Name two products made on these machines. Nut blanks and spark plug shells. 14. How threads, worms, and gears are cold formed? By a rolling process. 15. Threads cannot be rolled on gray cast iron, die cast metals, and 301 stainless steel. Why not? These metals do not have sufficient plasticity for the thread rolling process. Written for

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DT 1410 (DT1410)

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- 1 by what means are white hot ingots formed into slabs - and billets - 2 what modern method of steel manufacture bypasses the ingot stage and produces slabs o