ISyE415_Spr24_exam2_answers

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Name: ___________________________________ ISyE 415, Spring 2024, Exam #2 **** Answers & Grading Guidelines **** April 4, 2024 Prof. Charlene A. Yauch The exam has a total of 135 points and represents 16% of your final grade. The number of points for each question is indicated. Please read carefully and write neatly. Be sure to put your name on all pages submitted. You may use a calculator and a 3x5 notecard (both sides). You may write on the back side if more space is needed. Good Luck! Multiple-Choice (6 questions at 5 pts. each, 30 pts. total) Carefully read all options before selecting the best response. Choose multiple responses only if directed to do so. 1. Which of the following processes is the slowest at material removal? A. Milling B. Electrochemical Machining C. Chemical Machining D. Drilling E. Broaching 2. What is an electrode? A. A conductive tool that is used for material removal in electrochemical and electrical discharge machining B. A workholding device that is used for conventional machining processes on a mill, lathe, or grinding machine C. A variable related to how much amperage should be used for an electrical discharge machining process D. A device used to detect electrical activity during a laser cutting process E. None of the above 3. Which of the following describe the applicability of a thermoforming process? (select all that apply) A. It can only be used for thermoplastic materials B. It can only be used for thermoset and elastomer materials C. It is typically used for very small production quantities D. The raw material is a thermoplastic sheet E. It is used to make thin-walled, hollow containers ISyE415, Spring 2024, C. Yauch -1 for each incorrect 1

Name: ___________________________________ 4. For which of the following processes is a customized tool used (one that is unique to the part being produced)? (select all that apply) A. Blow molding B. Drilling C. Grinding D. Compression molding E. Extrusion 5. Which of the following is a common problem associated with drilling? A. Not enough heat generated to perform the operation effectively B. A twist drill does not do a good job of achieving positional accuracy C. Too much cutting fluid interferes with the operation D. It can only be used for through holes E. It leaves a solid core of metal inside the hole 6. Which of the following is NOT an injection molding defect? A. Flash (or flashing) B. Heat affected zone (HAZ) C. Weld lines D. Sink marks E. None of the above; these are all possible injection molding defects Short-Answer Questions (7 questions, 10 pts. each, 70 pts. total) Answer the questions below in the spaces provided (draw figures if they help to explain your answer). 7. What is a rational work element for line balancing? It is the smallest increment of work that can be assigned to a station on the production line. It cannot be practically subdivided any further. -1 to -3 if partially incorrect or vague -3 if no mention of it being impractical to subdivide the element further -5 to -7 if incorrect but response attempted ISyE415, Spring 2024, C. Yauch -1 for each incorrect 2

Name: ___________________________________ 8. State one similarity and one difference between counterboring and countersinking. Possible similarities:  Both are used to make it possible to allow insertion of a bolt or screw such that the head is flush with the surface and not sticking out.  Both can be done before or after the hole is drilled (depending on the type of cutting tool used for the operation). Possible differences:  A counterbore is a stepped lead-in to the hole, and a countersink is a tapered lead-in.  A counterbore can be created with an end mill, and a countersink cannot. 5 pts. each OK to say both are holemaking processes (although this is quite broad) -1 to -2 if partially unclear -1 to -3 if partially incorrect 9. How does solidification occur for a thermoset polymer? The polymer chains in the material form bonds with neighboring chains (which is referred to as cross-linking). Once cross-linking has occurred, it cannot be reversed. OK if cross-linking term used without describing it -1 to -2 if cooling mentioned as part of the process (along with cross-linking) -1 to -2 if partially unclear or vague -5 if whole response vague or incomplete -8 if incorrect but response attempted 10. What is a Heat Affected Zone (HAZ)? It is an area within the material that has been exposed to high temperatures such that the material properties have been altered. The material in the HAZ is often more brittle, making it susceptible to cracking/fracturing. -2 to -3 if partially incorrect -2 if changes in material properties mentioned but no specifics -3 to -4 if missing description of how material properties are impacted -5 to -6 if mostly incorrect -8 if incorrect but response attempted ISyE415, Spring 2024, C. Yauch 3

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Name: ___________________________________ 11. For the part shown in the image, along with the additional specifications below, what manufacturing process (or processes) do you think would be used to produce the part? Explain and justify your choice. Material = Aluminum Part Size = 0.75 inch (19.05 mm) diameter x 0.0008 inches (0.0203 mm) thick Note: The part on the right side is enlarged to better show the geometry. Annual Production Volume = 850,000 This part can be created with chemical blanking because it is a very thin sheet of metal and has relatively intricate details in the part geometry. The material is too thin for other processes to be practical (like laser cutting, waterjet cutting, conventional milling, or progressive die punching/ blanking). Chemical blanking can handle the large production volume if it is set up to manufacture parts in a continuous fashion from a coil of raw material. -1 for selecting laser cutting, waterjet cutting, wire EDM (all are feasible to create the geometry if the metal was not so thin) -1 for choosing ECM (because it is similar to chemical machining, but ECM is typically used to create pockets and cavities) -4 for selecting progressive die punching and blanking -4 for selecting EDM (-2 for EDM and wire EDM) -8 for selecting broaching, milling, or any other conventional machining processes -5 if the justification is missing ISyE415, Spring 2024, C. Yauch 4

Name: ___________________________________ 12. What are three of the typical reasons for using an advanced machining process? Possible reasons:  The workpiece material is brittle  The workpiece material is thin and/or flexible  The part geometry is complex  The surface finish and accuracy requirements cannot be achieved through conventional processes  The material must be processed without being exposed to heat (avoid creating a HAZ) 3 pts. each OK if thin and flexible called out as separate reasons -1 to -2 if partially unclear or vague -2 for “lower cost” 13. What is a pre-form and what manufacturing process that we covered in class is it associated with? A pre-form is creating a piece of dough-like material in a particular shape and with a particular weight/volume. This is often used with compression molding processes to make sure the material is situated correctly to fill the cavities in the mold. (It may also be used for a transfer molding process). OK if response relates to injection blow molding instead -2 to -3 if close but not described well -4 to -5 if described incorrectly but correct process mentioned (compression or transfer molding or injection blow molding) -4 if wrong process mentioned -5 if definition for parison given instead (extrusion blow molding) -8 if incorrect but response attempted ISyE415, Spring 2024, C. Yauch 5

Name: ___________________________________ Problems/Calculations (3 questions, varying point values, 35 pts. total) Answer the questions below in the spaces provided. Show your calculations. Clearly indicate your final answer. Equations are provided on the last page of the exam. The page may be torn off for easier reference. 14. An end milling operation is performed with a 0.25” diameter end mill (with 4 flutes). The operation needs to remove material for a 0.4” wide slot across a 4” wide part at a depth of 0.090”. The maximum depth of cut per pass is 0.045”. The speed is 2,800 revolutions per minute, and the feed is 0.002” per tooth. What is the material removal rate for the operation? [9 pts.] N = 2800 rev/min f r = Nn t f = (2800 rev/min)(4 teeth)(0.002 in/tooth) = 22.4 in/min Average width being cut = 0.4”/2 = 0.2” (because 2 surface passes are needed) R MR = wdf r = (0.2”)(0.045”)(22.4 in/min) = 0.2016 in 3 /min -1 if 0.4” or 0.25” used for width (-2 if other incorrect value used) -1 if 0.09” used for depth (-2 if 0.25” or other incorrect value used) -1 if units incorrect or missing on final answer -3 if N and v mixed up -1 if number of teeth missing from feed rate calculation -3 if T m found instead of R MR -1 to -2 for other miscellaneous errors -7 maximum deduction if problem attempted ISyE415, Spring 2024, C. Yauch 6

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Name: ___________________________________ 15. You need to drill a blind hole in an aluminum workpiece with a 3/64” drill to a depth of 0.15”. The drill has a 135-degree point angle. The speed and feed for the operation will be 200 feet per minute and 0.001 inches per revolution, respectively. What is the machining time for the operation? [9 pts.] T m = d/f r f r = Nf = (v/(  D))f = (200 ft/min)(12 in/ft)(0.001 in/rev) / (  (3/64”)) = 16.3 in/min T m = (0.15 in) / (16.3 in/min) = 0.0092 min -3 if R MR found instead of T m -2 if 3/64” used for d -3 if N and v missed up or miscalculated -1 if unit conversion missed in the N calculation (12 inches/foot) -1 if final units missing or incorrect -1 to -2 for other miscellaneous errors -7 to -8 if incomplete (depending on amount of work shown) ISyE415, Spring 2024, C. Yauch 7

Name: ___________________________________ 16. For the assembly process described below, determine a line balancing solution using the ranked positional weight technique. Calculate the efficiency of the resulting assembly line. [17 pts.] Takt time = 50 seconds/pc Element Preceded By Time (seconds) RPW A -- 20 135 B -- 25 140 C A, B 15 115 D C 10 100 E -- 20 110 F D, E 30 90 G F 15 60 H G 15 45 I -- 25 55 J H, I 30 30 Ranking based on RPW: B, A, C, E, D, F, G, I, H, J Total work content = 205 seconds Takt time = 50 seconds/pc Station 1: B, A 25, 20 45 seconds Station 2: C, E, D 15, 20, 10 45 seconds Station 3: F, G 30, 15 45 seconds Station 4: I, H 25, 15 40 seconds Station 5: J 30 30 seconds Efficiency = 205 / [(5)(45)] = 91.1% -1 for a calculation error -1 if 50 seconds used in the efficiency calculation (and not the maximum for the solution) -1 if elements appear to be added in the wrong order (but the right elements are shown) -2 if one element not assigned correctly -1 to -2 if RPW values miscalculated (but ranking still correct) -4 if RPW values miscalculated and ranking incorrect -6 if RPW values not shown but elements assigned correctly -8 if RPW values not shown and elements assigned incorrectly -10 if multiple flaws in approach ISyE415, Spring 2024, C. Yauch A D C H G F B J E I 8

Name: ___________________________________ Machining Formulas > From Groover, Introduction to Manufacturing Processes , 2012 Drilling Equations: Cutting time for a through hole- T m = (t + A)/f r Cutting time for a blind hole- T m = d/f r Feed rate- f r = Nf Rotational speed- N = v/  D Approach allowance- 0.5Dtan(90-  /2) Material removal rate- R MR = (  D 2 f r )/4 Turning Equations: Cutting time- T m = L/f r (* Note: You may ignore approach and overtravel distances for turning operations.) Depth of cut- (D o – D f )/2 Feed rate- f r = Nf Rotational speed- N = v/  D o Material removal rate- R MR = vfd Milling Equations: Cutting time- T m = L/f r (* Note: You may ignore approach and overtravel distances for milling operations.) Feed rate- f r = N n t f Rotational speed- N = v/  D Material removal rate- R MR = wdf r Assembly Line Balancing Formula Line efficiency = (Total work content)/[(number of stations)(max cycle time)] ISyE415, Spring 2024, C. Yauch 9

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