hw03

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183A

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Aerospace Engineering

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Dec 6, 2023

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MAE 183A: Spring Quarter 2023 Last Name First Name Page 1 of 2 Homework Assignment #03: Due Tuesday, April 25, 2023 Multiple Choice: MC17.1: Which of the following are desirable properties of work material in metal forming? (a) high ductility, (b) high tensile strength, (c) high yield strength, (d) low ductility, (e) low tensile strength, (f) low yield strength MC17.2: Which of the following describes the typical starting work geometry in sheet metal processes? (a) high volume to area ratio or (b) low volume to area ratio MC17.3: The flow curve expresses behavior of a metal in which region of the stress strain curve? (a) elastic region or (b) plastic region MC17.4: Which of the following are advantages and characteristics of hot working relative to cold working? (a) fracture of work part is less likely, (b) friction is reduced, (c) increased strength properties, (d) isotropic mechanical properties, (e) less total energy is required, (f) lower deformation forces are required, (g) more significant shape changes are possible, (h) strain-rate sensitivity is reduced MC18.1: Which of the following are basic bulk deformation processes in metal forming? (a) bar drawing, (b) blanking, (c) deep drawing, (d) extrusion, (e) forging, (f) stamping MC18.2: In flat rolling, the draft is: (a) reduction in thickness divided by the starting thickness, (b) reduction in thickness during one pass, (c) thickness after rolling divided by thickness before rolling, (d) thickness before rolling divided by thickness after rolling? MC18.3: Flash in impression die forging serves no useful purpose and is undesirable because it must be trimmed from the part after forming? (a) true (b) false MC18.4: Which of the following stress/strength parameters are used in computation of extrusion force? (a) average flow stress, (b) compression strength, (c) final flow stress, (d) tensile strength, (e) yield strength MC19.1: Typical sheet-metal thicknesses are between 0.4 mm (1/64 in) and 6 mm (1/4 in). When thickness exceeds the upper limit of this range, the stock is usually referred to as? (a) bulk stock, (b) oversized, (c) plate, (d) thick sheet MC19.2: Cutting force in sheet-metal blanking depends on which mechanical properties? (a) compressive strength, (b) modulus of elasticity, (c) shear strength, (d) strain rate, (e) tensile strength, (f) yield strength MC19.3: Which of the following is the best definition of bend allowance? (a) amount by which the die is larger than the punch, (b) amount of elastic recovery experienced by the metal after bending, (c) safety factor used in calculating bending force, (d) length before bending of the straight sheet-metal section to be bent MC19.4: Springback in sheet-metal bending is the result of which of the following? (a) elastic modulus of the metal, (b) elastic recovery of the metal, (c) overbending, (d) overstraining, (e) yield strength of the metal MC20.1: Which of the following are features of the orthogonal cutting model? (a) a circular cutting edge is used, (b) a multiple-cutting-edge tool is used, (c) a single-point tool is used, (d) only two dimensions play an active role in the analysis, (e) the cutting edge is parallel to the direction of cutting speed, (f) the cutting edge is perpendicular to the direction of cutting speed, (g) the two elements of tool geometry are rake angle and relief angle MC20.2: According to the Merchant equation, an increase in rake angle has which of the following effects if all other factors are the same? (a) decrease in friction angle, (b) decrease in power requirements, (c) decrease in shear plane angle, (d) increase in cutting temperature, (e) increase in shear plane angle MC20.3: Of the total energy consumed in a machining operation, what is the proportion of energy converted to heat? (a) 50%, (b) 75%, (c) 90%, (d) 98%, (e) 100% MC20.4 Which of the following cutting conditions has the strongest effect on cutting temperature? (a) cutting speed, (b) depth of cut, (c) feed
MAE 183A: Spring Quarter 2023 Last Name First Name Page 2 of 2 Review Questions: Chapter 17: 17.4, 17.13, 17.18 Chapter 18: 18.7, 18.32, 18.38 Chapter 19: 19.5, 19.6 Chapter 20: 20.7, 20.15, 20.19 Chapter 21: 21.21, 21.28 Problems: Chapter 17: 17.3, 17.6, 17.9 Chapter 18: 18.2, 18.14, 18.24, 18.32 Chapter 19: 19.2, 19.8 Chapter 20: 20.3, 20.8, 20.18, 20.23 Chapter 21: 21.6, 21.13
HW 3 Review Questions 17.4 What is the difference between bulk deformation and sheet metalworking? The difference between bulk deformation and sheet metalworking lies in the surface area-to- volume ratio. In bulk deformation processes the surface area-to-volume ratio is relatively small, whereas in sheet metalworking the ratio is high. 17.13 What are some of the advantages of warm working relative to cold working? Some of the advantages of warm working relative to cold working are lower forces and power are required, more intricate work geometries are possible, and the need for annealing may be removed. 17.18 Why is friction in metal forming different from friction encountered in most mechanical systems such as gear trains, shafts in bearings, and other components involving relative motions between surfaces? The other cases are usually have low contact pressures, low to moderate temperatures, and plenty of lubrication in order to minimize the metal-to-metal contact. However, in a metal forming environment, there is high pressure between the surface of a hardened tool and a soft work part, plastic deformation of the softer material, and high temperature in hot working. These conditions can lead to relatively high coefficients of friction in metal working, even with lubricants present. 18.7 Identify some ways in which force in flat rolling can be reduced. One way to reduce force in flat rolling is to use hot rolling rather than cold rolling in order to reduce the strength and the strain hardening of the work material. Another way is to reduce the draft in each pass. A third way is to use a smaller roll radius, which directly reduces the force. A final way is to use a lower rolling speed to reduce power. 18.32 Why is friction a factor in determining the ram force in direct extrusion but not a factor in indirect extrusion? Friction is a factor in determining the ram force in direct extrusion but not in indirect extrusion because in indirect extrusion the billet is not forced to move relative to the container, thus resulting in no friction at the container walls. The ram force is lower than in direct extrusion because of the lack of friction. 18.38 In a wire drawing operation, why must the drawing stress never exceed the yield strength of the work metal? When draw stress exceeds the yield strength of the work material, the drawn wire will merely lengthen instead of new material squeezing through the die opening.
19.5 In blanking of a circular sheet-metal part, is the clearance applied to the punch diameter or the die diameter? The clearance is applied to the die diameter. 19.6 What is the difference between a cutoff operation and a parting operation? Cutoff is a type of shearing operation where blanks are separated from a sheet metal strip by cutting the opposite sides of the part in sequence. This creates a new part with every cut. The cut edges are not necessarily straight, and the blanks can be perfectly nested on the strip to prevent scraps. However, parting cuts a sheet metal strip with two cutting edges that match the opposite sides of the blank by a punch. This can be a result of the part outline having a nonuniform shape that prevents the blanks from nesting on the strip. Parting is less efficient than cutoff because it results in wasted material. 20.7 Explain the difference between roughing and finishing operations in machining. A roughing cut is meant to remove as much work material as possible from the starting work part to get a general shape, whereas a finishing cut are meant to complete the part and obtain the final dimensions, tolerances and surface finish. 20.15 Identify the two forces that can be measured in orthogonal cutting. The cutting force and the thrust force. 20.19 How is the power required in a cutting operation related to the cutting force? The power required in a cutting operation can be calculate by the product of cutting force and speed. 21.21 What is the difference between counterboring and countersinking? Countersinking and counterboring are similar, but in countersinking the step in the hole is cone- shaped for flat head screws and bolts. 21.28 What is the chip load in a milling operation? In milling, the feed, also known as the chip load, is usually given as the feed per cutter tooth. It is a representation of the size of the chip formed by each cutting edge.
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