assignment
TRANSCRIPT
Assignment -01/02
MPE
Release date: 22.03.2011
Last Submission date: 04.04.2011
You are strongly urged not to copy and reproduce. Evaluation will be done based on your own understanding substantiated through oral presentation. No mark will be considered in case , the submitted assignment is deemed to be copied from somebody else’s answer sheet.
The short questions and problem solving questions are from Casting, Welding, Metal Forming. While answering these questions, you must address to the direct questions from reference books.
Section –E students should answer 5 short questions and 5 problem solving questions from Welding and Metal forming and submit the answer sheet as assignment -2 .
Section-F students should answer 5 questions each from short questions and problem solving questions from Casting Section as Assignment-1. In the same assignment answer balance 10 questions (5 each from balance sections) as Assignment-2 mentioning separately.
Use a standard note book ( not stapled loose papers)!
Q-1 : Identify some of the important advantages of shape casting processes.
Q-1 : What are some of the limitations and disadvantages of casting?
Q-2: What is the difference between an open mold and a closed mold?
Q-3: Name the two basic mold types that distinguish casting processes.
Q-4: Which casting process is the most important commercially?
Q-5: What is the difference between a pattern and a core in sand molding?
Q-6: What is meant by the term superheat during metal melting staage?
Q-7: Why should turbulent flow of molten metal into the mold be avoided?
Q-8: What is the continuity law as it applies to the flow of molten metal in casting?
Q-9 : What are some of the factors affecting the fluidity of a molten metal during pouring into a mold cavity?
Q-10: What does heat of fusion mean in casting?
Q-11: Derive an expression for the total heat extracted during the casting process of cast iron from a temperature of 17000C to room temperature of 250C. Take the fusion temperature from any reference book.
Q-12: How does solidification of alloys differ from solidification of pure metals?
Q-13: What is the relationship known as Chvorinov's Rule in casting?
Q-14: Identify the three sources of contraction in a metal casting after pouring.
Q-15: What is a chill in casting? What material is suggested for chill ?
Q-16: What properties determine the quality of a sand mold for sand casting?
Q-17: What is the Antioch process?
Q-18: What is the difference between vacuum permanent-mold casting and vacuum molding?
Q-19: What are the most common metals processed using die casting?
Q-20: Which die casting machines usually have a higher production rate, cold-chamber or hot-chamber, and why?
Q-21: What is flash in die casting? Suggest countermeasures.
Q-22: What is the difference between true centrifugal casting and semi-centrifugal casting?
Q-23:What are some of the general defects encountered in casting processes?
Q-24: What are the advantages and disadvantages of welding compared to other types of assembly operations?
Q-25: State the importance of surface preparation in different welding processes? Which type of welding process require most strict surface preparation.
Q-26: What is meant by the term faying surface?
Q-27: Derive the generic heat balance equation for any welding process.
Q-28: Define the term fusion weld.
Q-29: What is the fundamental difference between a fusion weld and a solid state weld? Give examples in each category.
Q-30: What is an autogenous weld?
Q-31: What is the difference between machine welding and automatic welding? Which welding processes can be automated.
Q-32: Name and sketch the five joint types in welding.
Q-33: Define and sketch a fillet weld?
Q-34: Define and sketch a groove weld?
Q-35: What is the difference between a continuous weld and an intermittent weld as the terms apply to a fillet weld of a lap joint?
Q-36: Explain power density. Why is it desirable to use energy sources for welding that have high power densities?
Q-37: What is the unit melting energy in welding, and what are the factors on which it depends?
Q-38: Define and distinguish the two terms heat transfer efficiency and melting efficiency in welding.
Q-39: What is epitaxial grain growth, and how is this form of solidification different from that which occurs in casting?
Q-40: What is the heat affected zone (HAZ) in a fusion weld?
Q-41: Name the principal groups of processes included in fusion welding.
Q-42: What is the fundamental feature that distinguishes fusion welding from solid state welding?
Q-43: What do the terms arc-on time, arc time, and operating factor have in common? Provide a definition of these terms.
Q-44:Name and define various types of Electrodes in arc welding .
Q-45: What are the various ways of arc shielding in arc welding?
Q-46: Why is the heat transfer efficiency greater in arc welding processes that utilize consumable electrodes?
Q-47: Describe the shielded metal arc welding (SMAW) process.
Q-48: Why is the shielded metal arc welding (SMAW) process difficult to automate?
Q-49: Describe submerged arc welding (SAW).
Q-50: Describe electrogas welding (EGW) process and identify its major application.
Q-51: Why are the temperatures much higher in plasma arc welding than in other Arc Welding processes?
Q-52: Define and outline the philosophy of resistance welding.
Q-53: What are the desirable properties of a metal that would provide good weldability for resistance welding?
Q-54: Describe the sequence of steps in the cycle of a resistance spot welding operation with help of diagram.
Q-55: What is resistance projection welding? State the application of this welding process.
Q-56: Why is the oxyacetylene welding process favored over the other oxyfuel welding processes? Limitations?
Q-57: Define pressure gas welding. How is it different. State it’s application.
Q-58: What is the disadvantage of Electron beam welding in high-production applications.?
Q-59: Compare the advantages and limitations of LBM with EBM ? Which type of metal and applications are they suited?
Q-60: Name various modern-day variations of forge welding, the original welding process.
Q-61: There are two basic types of friction welding. Describe and distinguish the two types.
Q-62: What is a sonotrode in ultrasonic welding?
Q-63: Distortion (warpage) is a serious problem in fusion welding, particularly arc welding. What are some of the measures that can be taken to reduce the incidence and extent of distortion?
Q-64: What are some of the important welding defects? Describe the reasons of occurrence and necessary countermeasures.
Q-65: Mention the basic categories of inspection and testing techniques used for weldments? Name some typical inspections and/or tests in each category.
Q-66: Identify the factors that affect weldability. How will you improve the same ?
Q-67: How do brazing and soldering differ from the fusion welding processes?
Q-68: How do brazing and soldering differ from the solid state welding processes?
Q-69: What is the technical difference between brazing and soldering? State with their process and applications.
Q-70: Under what circumstances would brazing or soldering be preferred over welding? What is the limiting strength in each process with some applicable material ?
Q-71: What are the two joint types most commonly used in brazing? Compare these joints with nomenclature.
Q-72: What are the special preparations in joint configuration to improve the strength of brazed joints.
Q-73: What are the desirable characteristics of a brazing flux?
Q-74: What is dip brazing?
Q-75: Define braze welding. In which case , you will like to prefer braze welding over brazing?
Q-76: What are some of the disadvantages ,limitations and applications of brazing? Can we opt soldering for such applications?
Q-77: What are the common alloying metals used in solders? Show the phase transformation by drawing phase diagrams for soldering material of at least one typical composition.
Q-78: What is wave soldering? Mention advantages and application over hand soldering. What is desoldering?
Q-79: List the advantages and limitations of soldering as an industrial joining process?
Q-80: Explain and compare the heat balance equations between brazing and soldering ? Show what will be the power density in each case and plot the same in a graph taking similar material for both cases.
Q-81: Discuss different characteristics that distinguish bulk deformation processes from sheet metal processes? Explain this drawing the stress and strain diagram for both engineering and true strain.
Q-82: What is the difference between deep drawing and bar drawing? State from the force/pressure diagram.
Q-83: Indicate the mathematical equation for the flow curve. On what factors this curve depends?
Q-84: Discuss the affect of temperature change in the flow curve equation? Draw the curve for cold, warm and hot working.
Q-85: Mention the advantages of cold working relative to warm and hot working. How to decide to opt for each process.
Q-86: What is isothermal forming? Has it any advantage over hot working.
Q-87: Describe the effect of strain rate in metal forming. Also discuss various parameters governing such diagram.
Q-88: Discuss the importance of friction in metal forming. Is friction always desirable in metal forming operations?
Q-89: What is sticking friction in metalworking?
Q-90: What are the reasons why the bulk deformation processes are important commercially and technologically?
Q-91:List some of the products produced on a rolling mill. State your reasons on what you will prefer cold rolling over hot rolling. State the applications for both the cases.
Q-92: Identify some of the ways in which force in flat rolling can be reduced.
Q-93: What is a two-high rolling mill?
Q-94: What is a reversing mill in rolling?
Q-95: Besides flat rolling and shape rolling, identify some additional bulk forming processes that use rolls to effect the deformation.
Q-96: One way to classify forging operations is by the degree to which the work is constrained in the die. By this classification, name the three basic types.
Q-97: Is flash desirable in impression die forging? Why or why not ?
Q-98: What is isothermal forging? Compare with cold and hot forging in terms of force and energy requirement.
Q-99: Distinguish between direct and indirect extrusion. Mention examples of both cases in your day-to-day life.
Q-100: Name some products that are produced by extrusion. Can we make such parts through other metal forming?
Q-101: In a wire drawing operation, why must the drawing stress never exceed the yield strength of the work metal?
Q-102: Identify various types of sheet metalworking operations. Which is predominately seen in automobile factory.
Q-103: In blanking of a round sheet metal part, indicate how the clearance should be applied to the punch and die diameters.
Q-104: What is the difference between a cut-off operation and a parting operation?
Q-105: Describe V-bending and edge bending.
Q-106: What is springback in sheet metal bending? Which type of material is having highest springback in a autobody.
Q-107: What are some of the simple measures used to assess the feasibility of a proposed cup drawing operation?
Q-107: Distinguish between redrawing and reverse drawing.
Q-108: What are some of the possible defects in drawn sheet metal parts?
Q-109: What is stretch forming?
Q-110: What are the relative advantages and disadvantages of mechanical versus hydraulic presses in sheet metalworking?
Q-111: Identify a major technical problem in tube bending?
Q-112: Distinguish between roll bending and roll forming.
Q-113: Discuss the possible reasons of excessive burrs in sheet metal operations. What can be done to correct the condition?
Q-114: Derive an expression for the reduction r in drawing as a function of drawing ratio DR.
Q-115: Discuss various drawing defects , the reasons of such defects with their countermeasures.
Q-116: A tube of diameter D is bent into a shape with a series of simple tube bending operations. The wall thickness on the tube = t mm. In one of the bends where the bend radius is 25 t mm, the walls of the tube are flattening badly. What can be done to correct the condition?
SECTION-B
Q-1: We have to cast a disc of 40 cm in diameter and 5 cm thick ( material : aluminum) in an open mold operation. Given the melting temperature of aluminum (Tm)= 660°C and the pouring temperature 140°C more than the melting temp. To achieve required fluidity for complete mould cavity fill up, aluminum is heated 5% more than needed. Compute the amount of heat that must be added to the metal to heat it to the pouring temperature, starting from a room temperature of 25°C. The heat of fusion of aluminum = 389.3 J/g. Consider r = 2.70 g/cm3 and specific heat C = 0.21 Cal/g-°C and the specific heat has the same value for solid and molten aluminum.
Q-2: While designing the gating system, it has been estimated that the downsprue of a casting process has a length = 0.18 m. The cross-sectional area at the base of the sprue is 400 mm2. Total volume of mould cavity = 0.001 m3. Determine: (a) the velocity of the molten metal flowing through the base of the downsprue, (b) the volume rate of flow, and (c) the time required to fill the mold cavity. Show the gating system schematically.
Q-3: A mold of casting a thin cylinder has a downsprue of length = 15.0 cm. The cross-sectional area at the bottom of the sprue is 3.5 cm2. The mold cavity = 75x6.25x2.54 cm3. Determine: (a) the velocity of the molten metal flowing through the base of the downsprue, (b) the volume rate of flow, and (c) the time required to fill the mold cavity.
Q-4: Liquid metal is flowing into the downsprue of a mold@ 1 liter/sec. The cross-sectional area at the top of the sprue = 0.600 cm2 , length = 0.2 m. Determine area at the base of the sprue to avoid aspiration of the molten metal? What countermeasures in term of dimension variation should be taken to avoid air entrapment.
Q-5: Molten metal is poured into the downsprue at a constant flow rate through a downsprue of 15 cm long. Its cross-sectional area at the top = 5 cm2 and at the base = 4 cm2. The cross-sectional area of the runner leading from the sprue also = 4 cm2, and it is 20 cm long before leading into the mold cavity, whose volume = 1065 cm3. The volume of the riser located along the runner near the mold cavity = 410 cm3. It takes a total of 3.0 sec to fill the entire mold (including cavity, riser, runner, and sprue. This is more than the theoretical time required, indicating a loss of velocity due to friction in the sprue and runner. Find: (a) the theoretical velocity and flow rate at the base of the downsprue; (b) the total volume of the mold; (c) the actual velocity and flow rate at the base of the sprue; and (d) the loss of head in the gating system due to friction.
Q-6: In the casting of steel in sand moulding, the mold constant in Chvorinov's Rule is known to be Cm = 4.0 min/cm2 .The casting is a flat plate whose length = 30 cm, width = 10 cm, and thickness = 20 mm. Determine how long it will take for the casting to solidify.
Q-7: Considering the dimensions and constant value as given in Q-6 above, find out solidification time by using a value of n = 1.9,1.8,1.5,1.0 in Chvorinov's Rule. What adjustment must be made in the units of Cm? Plot the same ( solidification time
Q-8: A disk-shaped part is to be cast out of aluminum. The diameter of the disk = 500 mm and its thickness = 20 mm. If Cm = 2.0 sec/mm2 in Chvorinov's Rule, how long will it take the casting to solidify?
Q-9: In a casting process ( sand mold), it takes 155 sec for a cube-shaped casting to solidify. The cube is 50 mm on each side. (a) Determine the value of the mold constant Cm in Chvorinov's Rule. (b) If the same material and mold type were used, find the total solidification time for a cylindrical casting in which the diameter = 3 cm and length = 5 cm.
Q-10: A cylindrical shaped steel casting has diameter as 10 cm and weighs 9 kg. This casting takes 6.0 min to completely solidify. Another cylindrical-shaped casting with the same diameter-to-length ratio weighs 5.4 kg. This casting is made of the same steel and the same conditions of mold and pouring were used. Determine: (a) the mold constant in Chvorinov's Rule; and (b) the dimensions, and (c) the total solidification time of the lighter casting. Note: The density of steel = 8172 kg/m3.
Q-11: Compare the total solidification times of three casting shapes : (1) a sphere with diameter = 10 cm, (2) a cylinder with diameter and length both = 10 cm, and (3) a cube with each side = 10 cm. The same casting alloy is used in the three cases. (a) Determine the relative solidification times for each geometry. (b) Based on the results of part (a), which geometric element would make the best riser? (c) If Cm = 3.5 min/cm2 in Chvorinov's Rule, compute the total solidification time for each casting.
Q-12: Compare the total solidification times of three casting shapes : (1) a sphere, (2) a cylinder, in which the L/D ratio = 1.0, and (3) a cube. For all three geometries, the volume V = 1000 cm3. The same casting alloy is used in the three cases. (a) Determine the relative solidification times
for each geometry. (b) Based on the results of part (a), which geometric element would make the best riser? (c) If Cm = 3.5 min/cm2 in Chvorinov's Rule, compute the total solidification time for each casting.
Q-13: A cylindrical riser is to be used for a sand casting mold. For a given cylinder volume, determine the diameter-to- length ratio that will maximize the time to solidify. Calculate the same , if the riser is a combination of hemisphere sandwitched with a cylinder of height=diameter.
Q-14: A riser in the shape of a sphere is to be designed for a sand casting mold. The casting is a rectangular plate, with length = 200 mm, width = 100 mm, and thickness = 18 mm. If the total solidification time of the casting itself is known to be 3.5 min, determine the diameter of the riser so that it will take 25% longer for the riser to solidify.
Q-15: A cylindrical riser is to be designed for a sand casting mold. The length of the cylinder is to be 1.25 times its diameter. The casting is a square plate, each side = 25.4 cm and thickness = 1.90 cm. If the metal is cast iron, and Cm = 2.56 min/cm2 in Chvorinov's Rule, determine the dimensions of the riser so that it will take 30% longer for the riser to solidify.
Q-16: An aluminum-copper alloy casting is made in a sand mold using a sand core that weighs 20 kg. Determine the buoyancy force in Newtons tending to lift the core during pouring. What the minimum cross section area of the core.
Q-17: A sand core located inside a mold cavity has a volume of 2573 cm3. It is used in the casting of a cast iron pump housing. Determine the buoyancy force that will tend to lift the core during pouring. What is the maximum buoyancy force it can sustain , if it is in the form of a cylinder.
Q-18: A certain design of chaplets and the manner in which they are placed in the mold cavity surface allows each caplet to sustain a force of 4.53 kgs. Several caplets are located beneath the core to support it before pouring; and several other caplets are placed above the core to resist the buoyancy force during pouring. If the volume of the core = 5325 cm3, and the metal poured is brass, determine the minimum number of caplets that should be placed: (a) beneath the core, and (b) above the core. Consider the density of metal from any reference book.
Q-19: A sand core used to form a thin cylindrical pipe of steel experiences a buoyancy force of 23 kg. The volume of the mold cavity forming the outside surface of the casting = 5000 cm3. What is the weight of the final casting? Ignore considerations of shrinkage.
Q-20: A tube made of copper is to be casted through horizontal true centrifugal casting. The lengths will be 1.5 m with outside diameter = 15.0 cm, and inside diameter = 12.5 cm. If the rotational speed of the pipe = 1000 rev/min, determine the G-factor. Is this operation likely to be successful?
Q-21: A brass bush with dimensions: L = 10 cm, OD = 15 cm, and ID = 12 cm is to be made through horizontal true centrifugal casting process. (a) Determine the required rotational speed in order to obtain a G-factor of 70. (b) When operating at this speed, what is the centrifugal force per square meter (Pa) imposed by the molten metal on the inside wall of the mold?
Q-22: A large diameter copper tube is to be casted through true centrifugal casting process. The dimension of the tube are length(L) = 1.0 m, inside diameter (d) = 0.25 m, and wall thickness = 15 mm. If the rotational speed of the pipe = 900 rev/min, (a) determine the G-factor (b) Is the rotational speed sufficient to avoid "rain?" (c) What volume of molten metal must be poured into the mold to make the casting if solidification shrinkage and contraction after solidification are
considered?
Q-23: If a true centrifugal casting operation were to be performed in moon, how would weightlessness affect the process? Compare the process in earth and the space station.
Q-24: A vertical true centrifugal casting process is used to make tube sections with length (L) = 26 cm and outside diameter (D)= 15 cm. The inside diameter of the tube = 14 cm at the top and 12.7 cm at the bottom. At what speed must the tube be rotated during the operation in order to achieve these specifications?
Q-25: A vertical true centrifugal casting process is used to produce hollow castings that have dimension of length (L)= 200 mm and outside diameter (D) 200 mm. If the rotational speed during solidification is 500 rpm, determine the inside diameter at the top of the casted section if the diameter at the bottom is 150 mm.
Q-26: A vertical true centrifugal casting process is used to cast brass tubing that is 38 cm long and whose outside diameter = 20.5 cm. Given the speed of rotation during solidification is 1000 rpm, determine the inside diameters at the top and bottom of the tubing if the total weight of the final casting = 33.80 kgs.
Q-27: A large steel sand casting shows the characteristic signs of penetration defect - a surface consisting of a mixture of sand and metal. (a) What steps can be taken to correct the defect? (b) What other possible defects might result from taking each of these steps?
Q-28: During welding, a heat source transfer 3000 J/sec to a metal part surface. The heated area is circular, and the heat intensity decreases as the radius increases, as follows: 60% of the heat is concentrated in a circular area that is 3 mm in diameter. Is the resulting power density enough to melt metal?
Q-29:A rectangular low carbon steel plate of size 200 mm x 350 mm is to be welded. The filler metal to be applied is a harder (alloy) grade of steel, whose melting point is assumed to be the same. A thickness of 2.0 mm will be added to the plate, but with penetration into the base metal, the total thickness melted during welding = 6.0 mm, on average. The surface will be applied by making a series of parallel, overlapped welding beads running lengthwise on the plate. The operation will be carried out automatically with the beads laid down in one long continuous operation at a travel speed v = 7.0 mm/s, using welding passes separated by 5 mm. Ignore the minor complications of the turnarounds at the ends of the plate. Assuming the heat transfer efficiency = 0.8 and the melting efficiency = 0.6, determine: (a) the rate of heat that must be generated at the welding source, and (b) how long will it take to complete the surfacing operation.
Q-30:Prepare sketches showing how the part edges would be prepared and aligned with each other and also showing the weld cross-section for the following welds: (a) square groove weld, both sides,for a butt weld; (b) single fillet weld for a lap joint; (c) single fillet weld for tee joint; and (d) double U-groove weld for a butt weld.
Q-31:Make the calculations and plot on linearly scaled axes the relationship for unit melting energy as a function of temperature. Use temperatures as follows to construct the plot: 250°C, 500°C, 750°C, 1000°C, 1500°C, and 2000°C. On the plot, mark the positions of some of the welding metals.
Q-32: A fillet weld has a cross-sectional area Aw = 20.0 mm2 and is 200 mm long. (a) What quantity of heat (in joules) is required to accomplish the weld, if the metal to be welded is austenitic stainless steel? (b) How much heat must be generated at the welding source, if the heat transfer efficiency = 0.8 and the melting efficiency = 0.6?
Q-33: The power generated in a particular arc welding operation = 3000 W. This is transferred to the work surface with a heat transfer efficiency f1 = 0.9. The metal to be welded is copper ( consider the melting point from reference book). Considering melting efficiency f2 = 0.25. A continuous fillet weld is to be made with a cross-sectional area Aw = 15.0 mm2. Determine the travel speed at which the welding operation can be accomplished.
Q-34: In a certain welding operation to make a groove weld, Aw = 22.0 mm2 and v = 5 mm/sec. If f1 = 0.95, f2 = 0.5, and Tm = 1000°C for the metal to be welded, determine the rate of heat generation required at the welding source to accomplish this weld.
Q-35: A spot weld is to be made using an arc welding operation. The total volume of (melted) metal forming the weld = 0.082 cm3, and the operation required the arc to be on for 4 sec. If f1 = 0.85, f2 = 0.5, and the metal to be welded was aluminum, determine the rate of heat generation that was required at the source to accomplish this weld.
Q-36:A shielded metal arc welding operation is performed on steel at V = 30 volts and I = 225 amps. The heat transfer efficiency f1 = 0.85 and melting efficiency f2 = 0.75. The unit melting energy for steel = 10.2 J/mm3. Solve for: (a) the rate of heat generation at the weld and (b) the volume rate of metal welded.
Q-37:A TIG welding is performed on stainless steel, whose unit melting energy Um = 9.3 J/mm3. The conditions are: V = 25 volts, I = 125 amps, f1 = 0.65, and f2 = 0.70. If filler metal wire of 3.0 mm diameter is added to the operation, and the final weld bead is composed of equal volumes of filler and base metal. If the travel speed in the operation v = 5 mm/sec, determine: (a) cross-sectional area of the weld bead, and (b) the feed rate (in mm/sec) at which the filler wire must be supplied.
Q-38: A Resistance Spot Welding operation is used to make a series of spot welds between two pieces of aluminum, each 2.0 mm thick. The unit melting energy for aluminum Um = 2.90 J/mm3. Welding current I = 6,000amps, time duration = 0.15 sec. Assume that the resistance = 75 micro-ohms. The resulting weld nugget measures 5.0 mm in diameter by 2.5 mm thick. How much of the total energy generated isused to form the weld nugget?
Q-39: The unit melting energy for a certain sheet metal to be spot welded is Um = 10.0 J/mm3. The thickness of each of the two sheets to be welded is 3.0 mm. To achieve required strength, it is desired to form a weld nugget that is 6.0 mm in diameter and 4.5 mm thick. The weld duration will be set at 0.2 sec. If it is assumed that the electrical resistance between the surfaces is 125 micro-ohms, and that only one-third of the electrical energy generated will be used to form the weld nugget (the rest being dissipated into the work), determine the minimum current level required in this operation.
Q-40:A resistance seam welding operation is performed on two pieces of 2.5 mm thick austenitic stainless steel to fabricate a container. The weld current in the operation is 10,000 amps, the weld duration t = 0.3 sec, and the resistance at the interface is 75 micro-ohms. Continuous motion welding is used, with 200 mm diameter electrode wheels. The individual weld nuggets formed in this RSEW operation have dimensions: diameter = 6 mm and thickness = 3 mm (assume the weld
nuggets are disc-shaped). These weld nuggets must be contiguous to form a sealed seam. The power unit driving the process requires an off-time between spot welds of 1.0 s. Given these conditions, determine: (a) the unit melting energy of stainless steel using the methods of the previous chapter, (b) the proportion of energy generated that goes into the formation of each weld nugget, and (c) the rotational speed of the electrode wheels.
Q-41:Suppose in the previous problem that a roll spot welding operation is performed instead of seam welding. The interface resistance increases to 100 micro-ohms, and the center-to-center separation between weld nuggets is 25 mm. Given the conditions from the previous problem, with the changes noted here, determine: (a) the proportion of energy generated that goes into the formation of each weld nugget, and (b) the rotational speed of the electrode wheels. (c) At this higher rotational speed, how much does the wheel move during the current on-time, and might this have the effect of elongating the weld nugget (making it elliptical rather than round)?
Q-42:An experimental power source for spot welding is designed to deliver current as a ramp function of time: I = 100,000 t, where I = amp and t = sec. At the end of the power-on time, the current is stopped abruptly. The sheet metal being spot welded is low carbon steel whose unit melting energy = 10 J/mm3. The resistance R = 85 micro-ohms. The desired weld nugget size is: diameter = 4 mm and thickness = 2 mm (assume a disc-shaped nugget). It is assumed that 1/4 of the energy generated from the power source will be used to form the weld nugget. Determine the power-on time the current must be applied in order to perform this spot welding operation.
Q-43: An oxyacetylene torch supplies 164 cm3 of acetylene per hour and an equal volume rate of oxygen for an OAW operation on 3/16 in steel. Heat generated by combustion is transferred to the work surface with an efficiency f1 = 0.25. If 75% of the heat from the flame is concentrated in a circular area on the work surface whose diameter = 0.95 cm, find: (a) rate of heat liberated during combustion, (b) rate of heat transferred to the work surface, and (c) average power density in the circular area.
Q-44: The voltage in an Electron Beam Welding (EBW) operation = 50 kV and the beam current = 65 milliamp. The electron beam is focused on a circular area that is 0.3 mm in diameter. The heat transfer efficiency f1 = 0.85. Calculate the average power density in the area in watt/mm2.
Q-45: An electron beam welding operation is to be accomplished to butt weld two sheet metal parts that are 3.0 mm thick. The unit melting energy = 5.0 J/mm3. The weld joint is to be 0.35 mm wide, so that the cross-section of the fused metal is 0.35 mm by 3.0 mm. If accelerating voltage = 25 kV, beam current = 30 milliamp, heat transfer efficiency f1 = 0.85, and melting efficiency f2 = 0.75, determine the travel speed at which this weld can be made along the seam.
Q-46: In a tensile test on a metal specimen, true strain = 0.08 at a stress = 265 MPa. When the true stress = 325 MPa, the true strain = 0.27. Determine the flow curve parameters n and K.
Q-47:A tensile test for a certain metal provides flow curve parameters: n = 0.3 and K = 600 MPa. Determine: (a) the flow stress at a true strain = 1.0, and (b) true strain at a flow stress = 600 MPa.
Q-48:A metal is deformed in a tension test into its plastic region. The starting specimen had a gage length = 5 cm and an area = 3.25 cm2. At one point in the tensile test, the gage length = 6.35 cm and the corresponding engineering stress = 1675 kg/cm2; and at another point in the test prior to necking, the gage length = 8.1 cm and the corresponding engineering stress = 1954 kg/cm2. Determine the strength coefficient and the strain hardening exponent for this metal.
Q-49:A tensile specimen is elongated to twice its original length. Determine the engineering strain and true strain for this test. If the metal had been strained in compression, determine the final compressed length of the specimen such that: (a) the engineering strain is equal to the same value as in tension (it will be negative value because of compression), and (b) the true strain would be equal to the same value as in tension (again, it will be negative value because of compression). Note that the answer to part (a) is an impossible result. True strain is therefore a better measure of strain during plastic deformation.
Q-50:Derive an expression for true strain as a function of D and Do for a tensile test specimen of round cross-section.
Q-51:Show that true strain = ln(1 + e).
Q-52:Based on results of a tensile test, the flow curve has parameters calculated as n = 0.40 and K = 551.6 MPa. Based on this information, calculate the (engineering) tensile strength for the metal.
Q-53:A copper wire of diameter 0.80 mm fails at an engineering stress = 248.2 MPa. Its ductility is measured as 75% reduction of area. Determine the true stress and true strain at failure.
Q-54: A metal alloy has been tested in a tensile test to determine the following flow curve parameters: K = 620.5 MPa and n = 0.26. The same metal is now tested in a compression test in which the starting height of the specimen = 62.5 mm and its diameter = 25 mm. Assuming that the cross- section increases uniformly, determine the load required to compress the specimen to a height of (a) 50 mm and (b) 37.5 mm.
Q-55: A torsion test specimen has a radius = 25 mm, wall thickness = 3 mm, and gage length = 50 mm. In testing, a torque of 900 N-m results in an angular deflection = 0.3°. Determine: (a) the shear stress, (b) shear strain, and (c) shear modulus, assuming the specimen had not yet yielded.
Q-56: K = 600 MPa and n = 0.20 for a certain metal. During a forming operation, the final true strain that the metal experiences = 0.73. Determine the flow stress at this strain and the average flow stress that the metal experienced during the operation.
Q-57: A metal has a flow curve with parameters: K = 850 MPa and strain hardening exponent n = 0.30. A tensile specimen of the metal with gage length = 100 mm is stretched to a length = 157 mm. Determine the flow stress at the new length and the average flow stress that the metal has been subjected to during the deformation.
Q-58: A particular metal has a flow curve with parameters: strength coefficient K = 2443 kg/cm2 and strain hardening exponent n = 0.26. A tensile specimen of the metal with gage length = 5.1 cm is stretched to a length = 8.4 cm. Determine the flow stress at this new length and the average flow stress that the metal has been subjected to during deformation.
Q-59: A 40 mm thick plate is to be reduced to 30 mm in one pass in a rolling operation. Entrance speed = 16 m/min. Roll radius = 300 mm, and rotational speed = 18.5 rev/min. Determine: (a) the minimum required coefficient of friction that would make this rolling operation possible, (b) exit velocity under the assumption that the plate widens by 2% during the operation, and (c) forward slip.
Q-60: A 5.0 cm thick slab is 25.4 cm wide and 30 cm long. Thickness is to be reduced in three steps in a hot rolling operation. Each step will reduce the slab to 75% of its previous thickness. It
is expected that for this metal and reduction, the slab will widen by 3% in each step. If the entry speed of the slab in the first step is 12 m/min, and roll speed is the same for the three steps, determine: (a) length and (b) exit velocity of the slab after the final reduction.
Q-61: A series of cold rolling operations are to be used to reduce the thickness of a plate from 50 mm down to 25 mm in a reversing two-high mill. Roll diameter = 700 mm and coefficient of friction between rolls and work = 0.15. The specification is that the draft is to be equal on each pass. Determine: (a) minimum number of passes required, and (b) draft for each pass?
Q-62: In the previous problem, suppose that the percent reduction were specified to be equal for each pass, rather than the draft. (a) What is the minimum number of passes required? (b) What is the draft for each pass?
Q-63: A continuous hot rolling mill has two stands. Thickness of the starting plate = 25 mm and width = 300 mm. Final thickness is to be 13 mm. Roll radius at each stand = 250 mm. Rotational speed at the first stand = 20 rev/min. Equal drafts of 6 mm are to be taken at each stand. The plate is wide enough relative to its thickness that no increase in width occurs. Under the assumption that the forward slip is equal at each stand, determine: (a) speed vr at each stand, and (b) forward slip s.(c) Also, determine the exiting speeds at each rolling stand, if the entering speed at the first stand = 26 m/min.
Q-64: A plat that is 250 mm wide and 25 mm thick is to be reduced in a single pass in a two-high rolling mill to a thickness of 20 mm. The roll has a radius = 500 mm, and its speed = 30 m/min. The work material has a strength coefficient = 240 MPa and a strain hardening exponent = 0.2. Determine: (a) roll force, (b) roll torque, and (c) power required to accomplish this operation.
Q-65: A cylindrical part is warm upset forged in an open die. Do = 50 mm and ho = 40 mm. Final height = 20 mm. Coefficient of friction at the die -work interface = 0.20. The work material has a flow curve defined by: K = 600 MPa and n = 0.12. Determine the force in the operation (a) just as the yield point is reached (yield at strain = 0.002), (b) at h = 30 mm, and (c) at h = 20 mm.
Q-66: A cylindrical work-part has a diameter = 5.0 cm and a height = 10.0 cm. It is upset forged to a height = 6.3 cm. Coefficient of friction at the die -work interface = 0.10. The work material
has a flow curve with strength coefficient = 1745 kg/cm2 and strain hardening exponent = 0.22. Determine the plot of force vs. work height.
Q-67: A cold heading operation is performed to produce the head on a steel nail. The strength coefficient for this steel is K = 550 MPa, and the strain hardening exponent n = 0.24. Coefficient of friction at the die-work interface = 0.10. The wire stock out of which the nail is made is 4.75 mm in diameter. The head is to have a diameter = 9.5 mm and a thickness = 1.5 mm. (a) What length of stock must project out of the die in order to provide sufficient volume of material for this upsetting operation? (b) Compute the maximum force that the punch must apply to form the head in this open-die operation.
Q-68: A hot upset forging operation is performed in an open die. The initial size of the workpart is: Do = 25 mm, and ho = 50 mm. The part is upset to a diameter = 50 mm. The work metal at this elevated temperature yields at 85 MPa (n = 0). Coefficient of friction at the die -work interface = 0.40. Determine: (a) final height of the part, and (b) maximum force in the operation.
Q-69: A hydraulic forging press is capable of exerting a maximum force = 1,000,000 N. A cylindrical workpart is to be cold upset forged. The starting part has diameter = 30 mm and height = 30 mm. The flow curve of the metal is defined by K = 400 MPa and n = 0.2. Determine the maximum reduction in height to which the part can be compressed with this forging press, if the coefficient of friction = 0.1.
Q-70: A connecting rod is designed to be hot forged in an impression die. The projected area of the part is 6,500 mm2. The design of the die will cause flash to form during forging, so that the area, including flash, will be 9,000 mm2. The part geometry is considered to be complex. As heated the work material yields at 75 MPa, and has no tendency to strain harden. Determine the maximum force required to perform the operation.
Q-71: A cylindrical billet that is 100 mm long and 40 mm in diameter is reduced by indirect (backward) extrusion to a 15 mm diameter. Die angle = 90°. If the Johnson equation has a = 0.8 and b = 1.5, and the flow curve for the work metal has K = 750 MPa and n = 0.15, determine: (a) extrusion ratio, (b) true strain (homogeneous deformation), (c) extrusion strain, (d) ram pressure, and (e) ram force.
Q-72: A billet that is 75 mm long with diameter = 35 mm is direct extruded to a diameter of 20 mm. The extrusion die has a die angle = 75°. For the work metal, K = 600 MPa and n = 0.25. In the Johnson extrusion strain equation, a = 0.8 and b = 1.4. Determine: (a) extrusion ratio, (b) true strain (homogeneous deformation), (c) extrusion strain, and (d) ram pressure at L = 70, 40, and 10 mm.
Q-73: An indirect extrusion process starts with an aluminum billet with diameter = 5.0 cm and length = 7.6 cm. Final cross-section after extrusion is a square with 2.5 cm on a side. The die angle = 90°. The operation is performed cold and the strength coefficient of the metal K = 1815 kg/cm2 and strain hardening exponent n = 0.20. In the Johnson extrusion strain equation, a = 0.8 and b = 1.2. (a) Compute the extrusion ratio, true strain, and extrusion strain. (b) What is the shape factor of the product? (c) If the butt left in the container at the end of the stroke is 1.27 cm thick, what is the length of the extruded section? (d) Determine the ram pressure in the process.
Q-74: Wire of starting diameter = 3.0 mm is drawn to 2.5 mm in a die with entrance angle = 15° degrees. Coefficient of friction at the work-die interface = 0.07. For the work metal, K = 500 MPa and n = 0.30. Determine: (a) area reduction, (b) draw stress, and (c) draw force required for the operation.
Q-75: Bar stock of initial diameter = 90 mm is drawn with a draft = 15 mm. The draw die has an entrance angle = 18°, and the coefficient of friction at the work-die interface = 0.08. The metal behaves as a perfectly plastic material with yield stress = 105 MPa. Determine: (a) area reduction, (b) draw stress, (c) draw force required for the operation, and (d) power to perform the operation if exit velocity = 1.0 m/min.
Q-76: A sheet metal part 3.0 mm thick and 20.0 mm long is bent to an included angle = 60° and a bend radius = 7.5 mm in a V-die. The metal has a tensile strength = 340 MPa. Compute the required force to bend the part, given that the die opening = 15 mm.
Q-77: A cup is to be drawn in a deep drawing operation. The height of the cup is 75 mm and its inside diameter = 100 mm. The sheetmetal thickness = 2 mm. If the blank diameter = 225 mm, determine: (a) drawing ratio, (b) reduction, and (c) thickness-to-diameter ratio. (d) Does the operation seem feasible?
Q-78: A cup drawing operation is performed in which the inside diameter = 80 mm and the height = 50 mm. The stock thickness = 3.0 mm, and the starting blank diameter = 150 mm. Punch and die radii = 4 mm. Tensile strength = 400 MPa and a yield strength = 180 MPa for this sheet metal. Determine: (a) drawing ratio, (b) reduction, (c) drawing force, and (d) blank holder force.
Q-79: A drawing operation is performed on 3.0 mm stock. The part is a cylindrical cup with height = 50 mm and inside diameter = 70 mm. Assume the corner radius on the punch = zero. (a) Find the required starting blank size Db. (b) Is the drawing operation feasible?