Skema Answer Manufacturing Proces 2

FACULTI OF MECHANICAL ENGINEERING UNIVERSITI MALAYSIA PAHANG BMM3643 (Sem II 2012/13) Assignment 2 1. a) Define the various regimes of ice-cold working,warm working,and hot working in hurt of the break up point of the straight offly being formed. b) Indicate some of the advantages of cold working relative to warm and hot working. c) What are some of the veto aspects of hot working? (8 marks) dish up a) The temperatures required for hot working mostly exceed 0. 6 clock the melting point of the material on an absolute temperature scale.Cold working generally requires temperatures below 0. 3 times the melting point, and warm working is the transition region, amid 0. 3 and 0. 6 times the melting point. b) Advantages of cold working are i) better accuracy, ii) better emerge finish, iii) increased strength collect to work hardening, iv) possible directional properties overdue to grain fertilize, and v) no heating of work required. c) Disadvantages associated with hot workin g call for the reactions which may be promoted by elevated temperature, such as speedy oxidation.Tolerances are poorer and the metallurgical structure will be nonuniform if the sum up of twisting or thermal history varies throughout the product. 2. a) What is the difference between open- blow over and impression- authorize forging? b) Explain the reasons why the flash assists in flunk filling, particularly in hot forging. c) Why are heated dies generally sedulous in hot-press forging ope balancens? (8 marks) perform a) Open-die forging does not take the flow of metal in all directions, so the final solve is dependent upon the manipulation and skill of the equipment operator.Impression-die forging trading operations confine metal flow in all directions to provide good repeatable control of size and shape. b) The flash is excess metal which is squeezed out from the die bodily cavity into the outer space between the two dies. The flash cools faster than the material in the cavity due to the high a/h ratio and the more intimate contact with the relatively cool dies. Consequently, the flash has higher(prenominal) strength than the hotter workpiece in the die cavity and, with higher frictional reverse gearness in the flash gap, provides greater resistance to material flow outer through the flash gap.Thus, the flash encourages filling of complex die cavities. c) heat up dies are usually employed in press forging because the extensive time of die contact with the hot workpiece would otherwise permit huge surface cooling and could produce cracking of the surface. 3. d) List some of the products produced on a memorialing mill. e) In curveing of leaf blade, what are the differences between a bloom, a slab, and a billet? f) Rolling may be set forth as a continuous forging operation. Is this description appropriate? Explain. (8 marks) Answer ) Rolled products include flat sheet and plate stock, round deflect and rod stock, rails, structural shapes s uch as Ibeams and channels. b) A bloom is a roll steel workpiece with a square cross section of active 150 mm by 150 mm. The starting work unit for a bloom is an ingot heated in a soaker pit. A slab is rolled from an ingot or a bloom and has a rectangular cross section of most 250 mm by 40 mm. A billet is rolled from a bloom and has a square cross section of about 40 mm by 40 mm. c) This is a good analogy. Consider the situation of forging a vetoricado to a thinner cross section through ncrements (as in additive forming). As the number of stages increases, the operation eventually approaches that of the strip profile in rolling. 4. g) Distinguish between direct and indirect lump. h) What is centerburst defect? How would you go about preventing centerburst defects in extrusion? i) What are some of the attractive features of the extrusion regale? (8 marks) Answer a) In direct extrusion, also known as forward extrusion, a metal billet is loaded into a container, and a pack c ompresses the material, forcing it to flow through a die opening at the glacial end of the container.In indirect extrusion, also known as backward extrusion, the die is incorporated into the ram, and as the ram compresses into the metal billet, the metal is troopsd to flow through the die opening in a direction that is opposite (backwards) of the ram motion. b) Centerburst defects are attrisolelyed to a state of hydrostatic tensile tensity at the centerline of the fleshing z wholeness in the die. The two major variables affecting hydrostatic tension are the die fish and extrusion ratio.These defects can be lessen or eliminated by lowering the die angle, because this increases the contact length for the same reduction and thereby increases the deformation zone. Similarly, a higher extrusion ratio also increases the size and depth of the deformation zone, and thus will reduce oreliminate the formation of these cracks. c) The extrusion process offers a number of attractive feat ures. Almost any crosssectional shape can be extruded, including many that could not be achieved by rolling. Size limitations are few. No draft is required, and the amount of reduction in a single tread is limited only by the capacity of the quipment. Frequently only one die is required for a product. Because only a single die change is required to change products, small production quantities are economically feasible. Dimensional tolerances are quite good. 5. j) What is wire conscription and bar draw play? k) Why are multiple passes usually required in wire- draught operations? l) Name the important process variables in drawing, and explain how they affect the drawing process. (8 marks) Answer a) Wire and bar drawing are bulk deformation processes in which the cross section of a wire or bar is reduced by pulling (drawing) it through a die opening. ) Because the reduced section of material is subjected to tensile loading in the wire drawing process, the possible reduction is limi ted by the onset of fracture. In ready to affect any significant change in size, multiple draws are usually required. c) The important variables include * Yield stress, Y it directly affects the draw stress and die life. * Die angle, ?. The die angle in the deformation zone affects the redundant work in the entry area, the die angle is important for encouraging lubricant entrainment. * Friction coefficient, ?. The friction coefficient affects the frictional contribution of work and, hence, the draw stress. Reduction in area. As described, there is a limit to the reduction in area that canbe achieved in drawing. * Lubrication condition. Effective lubrication reduces friction, but also may lead to a rough surface due to the orange peel effect. 6. m) Estimate the roll force and power for annealed low-carbon steel strip 200 mm wide and 10 mm thick, rolled to a thickness of 6 mm. The roll radius is 200 mm, and the roll rotates at 200 rpm. Let ? = 0. 1. n) Plot the force vs. reduction in height curve in open-die forging of a solid cylindrical, annealed crap specimen 2 in. high and 1 in. n diameter, up to a reduction of 70%, for the cases of (a) no friction between the flat dies and the specimen, (b) ? = 0. 25, and (c) ? = 0. 5. rebuff barreling and use average-pressure formulas. (Given For annealed copper we have K = 315 MPa = 46,000 psi and n = 0. 54) Answer a) The roll force can be estimated as below L=R? h=2004=28. 3 and have=10+62=8 mm From Table 2. 3 on p. 37, K = 530 MPa and n = 0. 26. The strain is ? =ln106=0. 5108 The average yield stress can be obtained from Eq. (2. 60) on p. 71 as Y=K? n+1n+1=530(0. 5108)1. 261. 26=one hundred eighty MPa and Y=(1. 15)Y=180 MPa Therefore, F=L?Y1+? L2have =0. 02830. 2(207)1+0. 1(28. 3)2(8) =1. 38 MN The power per roll is given by P = ? FLN60,000=? (1. 38 ? 106)(0. 0283)(200)60,000 or P = 409 kW. b) For annealed copper we have K = 315 MPa = 46,000 psi and n = 0. 54. The flow stress is Yf=(315 MPa)? 0. 54 where the absol ute value of the strain is ?=lnhoh From volume constancy, we have ?4r2ho=? 4r2h or r=ro2hoh Note that = 0. 5 in and ho = 2 in. The forging force is given as F=Yf1+2? r3h(? r2) Some of the points on the curves are the following % Red. Forging Force, MN ? = 0 ? = 0. 25 ? = 0. 5 10 0. 053 0. 055 0. 058