Introduction to Mfg Process 1. Suppose we want to manufacture a product, what are product features that we must consider when selecting manufacturing process(es) to make them? Name at least four. 2. What are the effects of these considerations on manufacturing cost? Circle appropriate answer. Manufacturing time increase leads to manufacturing cost increase / decrease Part tolerance increase leads to manufacturing cost increase / decrease Material scrap increase leads to manufacturing cost increase / decrease 3. What are the main considerations to select material for the product? Name at least three. 4. How do companies that manufacture products compete with each other? Name at least four categories. 5. Suppose we are comparing two manufacturing processes to make a product. We look at three cost components-namely material cost, labor cost and tooling cost, all in baht per piece as described below. • Process A requires raw material bar 6.4 m long, cut into 12 pieces. Each piece is then converted by process A into a product. The 6.4 m bar cost 340 baht each. Process A requires 2 workers to operate, resulting in 60 pieces per hour. We need to pay each operator 60 baht an hour. The tooling used by process A costs 80,000 baht. We expect to use the tooling to produce 5,000 pieces of product over its lifetime. • Process B raw material bar 7.0 m long, also cut into 12 pieces. Each piece is then converted by process B into a product. The 7.0 m bar cost 410 baht each. Process B requires only one worker to operate, resulting in 45 pieces per hour. We need to pay each operator 60 baht an hour. The tooling used by process B costs 130,000 baht. We expect to use the tooling to produce 10,000 pieces of product over its lifetime. (a) Which process has the highest total cost per piece, considering these three cost components? (b) Based on past experience we know that process A has a defect rate of 3% while process B has a defect rate of 1.5%. Assuming that defect cannot be reworked. All defects have to be thrown away. If we plan to produce 100 pieces of product, which process will have the least total cost? 6. Suppose we are comparing two manufacturing processes to make a product. In order to make 1 piece of product, process A requires raw material as a rod with ¾ inch diameter and 10 inch length. The process has a scrap rate of 15%. Process B requires same material, a rod with 1 inch diameter and 9 inch length. Process B has a scrap rate of 8%. Let us assume raw material is sold strictly in weight, say x baht per kilogram. (Always explain how you come up with the solution.) (a) Which process requires more money to buy raw material? A or B? (b) Which process throws away more material, in kilogram unit? A or B? (c) If we can sell all material scrap, also sell in kilograms, say y baht per kg. Usually scrap material is sold cheaply, let us assume that y = 2x. Which process will have the lowest net material cost? 7. You are working for a company that manufactures plastics product. You are asked by your boss to find a way to reduce the cost of a product without reducing its quality or changing its appearance. What would be your strategies to do that? Give at least 3 specific actions you might take. 8. Let’s say your company wants to make a new product, fluorescent cover such as shown in the picture below. You are responsible to provide initial material property requirements for the product. What would be your material property specifications? Name at least three. 9. We make a hook such as that shown below with a bar of steel diameter 2 inches and 5 inches long. Its original weight, before forming, is 800 gram. After a series of forging operations, the final product, the hook, comes out at 514.7 gram. What would be your scrap percentage of this product? 10. There are people who love to buy IPHONE6 and there are people who prefer SAMSUNG Galaxy Note. Can you see the product strategy differences between the two? What are they? Explain. Material Properties 1. A paper clip is made of wire 1.5 mm in diameter. If the original material from which the wire is made of a rod 20 mm in diameter, calculate the longitudinal engineering and true strains that the wire has undergone during the process. 2. A piece of steel has a hardness of 400 HB, calculate the tensile strength in MPa. 3. A cable is made of materials with strength coefficient K = 800 MPa and strain hardening exponent n = 0.5 with cross sectional area = 4.76 mm2. What would be the maximum tensile force that this cable can withstand prior to necking? 4. Which alloy is used to improve corrosion resistance in steel? 5. An aircraft component, made of 7075-T6 Aluminum alloy, can be represented as a bar of diameter 22 mm and length 400 mm, loaded in pure tension. Properties of Aluminum alloy is as follows: elasticity E= 70 GPa, yield strength YS = 496 MPa, ultimate tensile strength TS = 558 MPa. Please calculate strain of the bar under an imposed load of 80 kN 6. A cable is made of materials with strength coefficient K = 800 MPa and strain hardening exponent n = 0.5 with cross sectional area = 4.76 mm2. What would be the maximum tensile force that this cable can withstand prior to necking? 7. Steel wire has yield strength = 2100 MPa. How much elastic extension (in %) is possible before permanent deformation sets in? Steel has elasticity 190-200 GPa. 8. A material has the following properties: Engineering ultimate tensile strength = 60,000 psi and strain-hardening exponent n = 0.4. Please calculate strength coefficient K. (Hint: we need to calculate true force and true area in order to find true ultimate strength first) Casting 1. Please circle the effect of casting parameters If we increase cooling rate of the casted mold, voids in the casting will increase / decrease If we increase fluidity of the molten metal, porosity will increase / decrease If we increase carbon content, porosity will increase / decrease 2. Please match each casting process with appropriate description. (draw lines between process and description) Sand casting has the lowest cycle time. Die casting requires multiple coating of pattern. Investment casting has the cheapest molding cost. 3. Suppose we want to cast a piece of 1% carbon steel with a final shape that weighs 1.25 kg. What would be the minimum weight of motel steel to be poured into the mold. 4. If we are casting two workpieces, one is cylindrical shape (10 mm diameter and 10 mm long) and the other is sphere of 10 mm diameter, using the same metal and same mold material. Which one would solidify faster? Why? 5. If we are casting two workpieces, one is cylindrical shape (10 mm diameter and 53.33 mm long) and the other is sphere of 10 mm diameter, using the same metal and same mold material. Which one would solidify faster? Why? 6. If we are casting two workpieces, one is cylindrical shape (10 mm diameter and 50 mm long) and the other is a square tube of 10x10 mm2 and 45 mm long, using the same metal and same mold material. Which one would solidify faster? Why? 7. Suppose you are asked to help a company fix its casting defects. It is found that in one particular product, the casting (workpiece) often has porosities inside. What would you recommend the company to do to solve this defect? (Specific actions please) 8. In casting, what parts of the mold that are usually cut off after the material is cooled off? 9. What should be the minimum cooling rate if we want to improve grain structure in casting? Why? 10. Suppose you are asked to help a company fix their casting defects. It is found that in one particular product, the casting (workpiece) often has hot tears such as shown in the figure below. What would you recommend the company to do to solve this defect? 11. Suppose we would like to cast steel components, what would be the minimum temperature required for the furnace to prepare the material? 12. Our casting product has a critical defect (hot tears) as shown in the picture below. What would be your recommendations to solve this problem? Explain your reasoning in details. Rolling 1. Suppose we want to use rolling process to manufacture a part. This part requires good surface finish and tight tolerance. Which rolling process should we use? Cold rolling or hot rolling? Why? 2. When rolls are used for a long time, they tend to flatten. What would be the action to minimize/slow down the flattening. Give at least 3 methods. 3. We have a rolling machine with roll radius R = 300 mm. If we estimate that friction coefficient between rolls and workpiece should not exceed 0.2, what would be the maximum thickness reduction achievable from this machine? 4. We are asked to help a company solve their problem. They are using rolling a rectangular slab into thinner cross section. It is found that workpieces that come out of the rolls are not flat. They are wavy. What would you do to solve this problem? 5. Which process … (circle appropriate answer). has more than one set of dies shape rolling / thread rolling creates uniform cross section thread rolling / ring rolling requires the die to rotate and move at the same time shape rolling / tube rolling 6. A piece of AISI 1020 carbon steel strip, 400 mm wide and 10 mm thick is rolled to a thickness of 7 mm. What would be the true strain for the material? 7. Calculate the roll force for AISI 1020 carbon steel strip, 400 mm wide and 10 mm thick, rolled to a thickness of 7 mm. The roll radius is 200 mm, and it rotates at 200 rpm. Assuming AISI 1020 carbon steel has strength coefficient K = 530 MPa and strain hardening exponent n = 0.26. (Hint: we need to estimate average yield stress Yavg by true stress) 8. Please explain why wire speed increases from payoff reel to take-up reel in the tandem rolling below. Forging 1. What are the differences between shape rolling and roll forging? 2. What is the purpose of “gutter” in the forging die? 3. Why do we need draft angle in forging dies? 4. How do we reduce forging force required to form a part? Name at least 3 strategies. 5. Which forging process is used to manufacture parts below? 6. Forging process is a forming process, yet it can remove material in some cases. Which forging process can be used to remove material? You can select (✓) more than one. Open die forging Impression die forging Coining operation Heading operation Piercing operation Skew operation Orbital forging Rotary swaging 7. Please circle the answer Which process requires higher force Which heading process requires higher force Which process requires higher force open-die forging / closed-die forging head formed in punch / head formed in die roll forging / skew rolling 8. We can make a beam of solid square cross section with either rolling or forging operations. You visit a plant that makes such beams. They are using forging. What would be the reasons (or benefits) they select forging over rolling operation? Name at least 3 reasons. Extrusion 1. What are the main differences between extrusion and shape rolling operations? 2. A company has asked you to solve their defect problem (again?!). They are extruding aluminum 6061 and has found cracks on the surface of workpiece. What would you recommend them to check and do? 3. What are the main differences between wire drawing and tube rolling? 4. An aluminum profile part is extruded from billet with diameter 178 mm to final shape that has cross sectional area = 980 mm2 What would be the extrusion ratio? 5. Calculate the force required in extruding copper at 700oC if the billet diameter is 100 mm and the extrusion ratio is 20. You can make an estimate of an extrusion constant by the following graph. Sheet Metal Forming 1. Suppose we want to punch a 10-mm hole diameter through a 0.5 mm thick AISI 1020 Steel (with ultimate tensile strength = 440 MPa). What would be a maximum punch force? 2. What are the strategies to reduce/minimize springback in bending operations? Give at least three strategies 3. What are the strategies to reduce/minimize burrs in shearing operations without changing workpiece material? Give at least two strategies. 4. What are the strategies to reduce/minimize burrs in shearing operations without changing workpiece material? Give at least two strategies. 5. A sheet of 1-mm thick is bent around radii of 2, 10 and 50 mm, which bent radius will have highest springback and why? 6. How can we prove that shearing a sheet metal requires higher force than bending it? Assume that we shear or bend that same material with same thickness T, width of cut L and die opening W. 7. We would like to compare the forces required to punch a hole and draw a cup of diameter Dp=75 mm through circular blank of original diameter D0=200 mm with thickness T=1.2 mm. Assume the material is annealed aluminum alloy 5052, which has ultimate tensile strength of 190 MPa and yield strength (Y) of 90 MPa. Drawing force Pd can be calculated from , where Y = yield strength (a) Please calculate the maximum punch force required (for punching a hole) (b) Please calculate the force required for drawing a cup (c) If the hole obtained from punching operation has burrs on the bottom edges. We would like to minimize burrs caused by this punching operation, what would be your suggestions? Name at least three. 8. Circular blanks (slugs) of Al 1100, diameter d = 25 mm and thickness h = 3 mm, are to be massproduced as the starting material for toothpaste-tube extrusion. The press is of 500-kN capacity. Assume Al 1100 has ultimate tensile strength of 90 MPa. (a) Please calculate the force required for blanking a single slug (b) What would be the maximum number of slugs that can be blanked simultaneously with the available press. (c) Please explain what manufacturing process should be used to create cylindrical tube with 0.5 mm uniform thickness and one end closed. Use drawing to explain how the process works. Plastics Forming 1. What are the main difference between plastic extrusion and injection molding processes? 2. Identify what are the manufacturing process used for these products? Plastic sandwich container Rubber grommet Rubber sheet 3. How do we know what type of plastic we are using? 4. What kind(s) of plastic is used for bottled water? 5. Supposed you are assigned to control the process of film extrusion as shown in the figure below in order to make plastic film with uniform thickness. (a) What would be critical parameters you need to control? Name at least three. (b) The plastic bag to be made is 300 mm wide and 0.3 mm thick. Suppose we adjust air pressure so that plastic blown film expands about 2 times after the extrusion die. What would be extrusion die diameter used? And what would be film thickness after the extrusion process? 6. In thermoforming process, what could be the defects involved? Please describe at least three defects that could happen. You can also draw pictures to help explain your answers. 7. If we can form an elastomer part with either simple compression molding or transfer molding, which one would require higher force exerted from the machine? Why? 8. Circle which process (only one please) may not have material loss? Sheet and film extrusion Injection molding process Blow molding process Thermo-forming Compression molding Calendering 9. Identify where do we lose material in injection molding process? Give at least two examples. 10. Why do we need transfer mold in some of compression molding processes? Machining 1. Suppose we have done some experiments for specific cutting tool X and workpiece material and found that tool life (for this cutting tool X) can be estimated by the following Taylor Tool Life equation: VT0.15d0.15f 0.6 = constant, (a) If someone gives a new cutting tool Y to be used with same work material. We also use the same cutting speed, feed and depth of cut as the previous cutting tool X. It turned out that cutting tool Y has tool life 3 times larger than that of cutting tool X. Can we estimate Taylor Tool Life equation of this cutting Y? Explain your reasons. (b) We would like to double tool life from the current process parameter. What would be your strategies? Give at least three. Please be specific what would be increased/decreased and by how much. (c) What would happen to the tool life if the feed rate is decreased by 30%? (d) What would happen to the tool life if the cutting speed is increased by 50%? 2. Suppose we have done some experiments for specific tool and workpiece material and found that tool life can be estimated by the following Taylor Tool Life equation: VT0.15d0.15f0.6 = constant, where velocity V ranges from 0-300 m/min, depth of cut d ranges from 0-2 mm and feed rate f ranges from 0-2 mm/rev. (a) Without lowering material removal rate (MRR) or changing workpiece material, how can we increase tool life? Give at least two strategies. (b) Suppose we try to increase tool life as proposed in (a) but could not increase tool life significantly. We now need to increase tool life by lowering MRR. Since MRR affects machining cycle time, we would like to lower MRR as little as possible. Which one among V, d, and f would you lower first? Why? (c) What would be your strategies to improve surface finish in turning operations? Give at least 3 strategies. 3. Suppose we machine Aluminum alloy and Steel with the same cutting tool, cutting speed, feed rate and depth of cut. Aluminum alloy has specific energy = 0.8 W-s/mm3 while steel has specific energy = 8 W-s/mm3. Which one would require more cutting force, and why? 4. Which type of cutting chip is the most favorable and why? 5. We are asked to help a technician solve a manufacturing process problem. The cutting tool used has very short life. Technicians found built-up edge formed around the tool tip quickly after machining a few workpieces. What would be your recommendation to solve this problem? Specify at least three strategies. Please be specific as much as you can. (For example, you cannot just say change the cutting tool. You have to specify what geometrical or physical aspects should be changed.) 6. We want to turn a 4340 steel bar (specific cutting energy 1.6 W-s/mm3). Depth of cut is 0.5 mm. The average cutting speed is 220 m/min. The feed rate is 0.3 mm/rev. (a) What would be the torque required for the tool? (b) What would be the power required for the tool? 7. We want to perform rough turning on annealed aluminum–alloy round bar, from diameter 100 mm down to 96 mm using high speed steel tool. The machining length is 300 mm on the bar. According to the tool handbook, recommended depth of cut is 0.25-8.8 mm, feed rate is 0.080.62 mm/rev and cutting speed is 200-670 m/min. Specific cutting energy for aluminum alloy is 0.9 W-s/mm3. What would be the time required for the machining? Explain your calculation. 8. A 5-mm diameter drill is used on a drill press operating at 150 rpm. If the feed is 0.1 mm/rev. (a) What is material removal rate for this? (b) If the specific energy of this workpiece is 8 W-s/mm3, what would be the torque required for the drilling? (c) If the drill diameter is doubled, what would MRR be? 9. Suppose we want to drill stepped holes as shown in the picture. We want to make the shape as precise to this picture as much as possible. Please explain the machining steps you would take to make such a workpiece. 10. Does the force or torque in drilling change as the hole depth increases? Why? 11. Between cold forming and machining processes, ie. punching a hole and drilling a hole, which one requires more power? Why? 12. What are the major considerations in choosing tools and machining parameters? For example, in drilling operations. 13. What kinds of drill do we need, if we want to • have smooth surface within a hole? • create internal thread? • mark a location of a hole before drilling? • drill a very deep hole? • drill a blind hole? 14. You have been working for a company. They have used an end mill to machine a large surface. Usually there is visible feedmarks left on the surface. The company would like to improve the surface finish of this large surface so that it becomes shiny, mirror-like surface. Please give at least two strategies for the company to improve their milling operations to achieve this. 15. If we use an end mill with diameter D=30 mm to machine stainless steel workpiece with depth of cut d =3 mm, feed rate v=0.3 mm/min and tool rotation N=300 rpm. Stainless steel has specific cutting energy 1.4 W.s/mm3. Please calculate torque required for the machining. 16. You are called upon as an expert in machining process. It is found that workpiece has significant burrs on the edges remaining after the machining. What would you recommend to the company to solve the problem? 17. For milling operation below, cutter diameter D=150 mm, workpiece width w = 60 mm, workpiece length l=500 mm, depth of cut d =3 mm, feed rate v=0.6 m/min and tool rotation N=100 rpm. The cutter has 10 inserts. Workpiece is high-strength aluminum alloy with specific cutting energy 1.1 W.s/mm3. Please show all calculations to support your answer. (a) (b) (c) (d) What is material removal rate? What is the feed per tooth? What would be the cutting force required? If we double feed per tooth while maintaining material removal rate to be the same, the cutting force required for the cutting. 18. The picture below compares maximum cross section areas of undeformed chip thickness between two face milling tools. The first one has lead angle of 45o while the other has 0o. Please compare the cross section area between the two tools assuming that feed rate per tooth, f and depth of cut, d are the same for both tools. Which one requires higher maximum cutting force? 19. On another occasion, the company has called you again. This time, the workpiece has poor surface finish. The company has used the same cutting tool (an end mill) and same machining parameters (cutting speed, feed and depth of cut) on the same workpiece before without any problem. But this time the operators heard a loud noise then the tool breaks. What do you think is the cause of this? What would you recommend the company to do to solve this problem? Grinding 1. What are the factors involved in selecting appropriate grinding process for a particular application? Give at least 3 factors. 2. What are the factors involved in selecting appropriate grinding wheel for a particular application? Give at least 3 factors. 3.What are the differences between centerless grinding and cylindrical grinding? 3. What factors determine whether a welding process can be used for workpieces in horizontal, vertical or upside down positions? 4. We are using surface grinder to finish an entire surface of rectangular workpiece size 50 x 75 mm. The grinding wheel is 70 mm in length and has diameter of 150 mm rotating at 2000 rpm. The depth of cut is 0.8 mm. The feed rate is 1.2 mm/min. What would be your estimate on grinding time? Welding 1. If we have to weld two components together, and they are made with the same material. We want to make sure that each component, after being welded, does not change its original shape, or distort as little as possible. Please specify which welding process you will use. Also describe how you will make sure that the distortion is as little as possible. You may sketch the process setting to help explain your idea. 2. If we would like to make a lot of similar parts using welding. (mass production) Which welding process, in your opinion, is the most suitable? Why? 3. What do we need to consider when selecting electrode for arc-welding?
