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TAM302 Engineering Design Principles. Syllabus Topic: Design for Manufacture & Assemble (DFMA) Boothroyd & Dewhurst. Course Instructor: Mike Philpott Director of Concurrent Design & Manufacture Lab Associate Professor of Mechanical Science & Engineering mphilpot@uiuc.edu.

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TAM302 Engineering Design Principles


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    1. TAM302 Engineering Design Principles Syllabus Topic: Design for Manufacture & Assemble (DFMA) Boothroyd & Dewhurst Course Instructor: Mike Philpott Director of Concurrent Design & Manufacture Lab Associate Professor of Mechanical Science & Engineering mphilpot@uiuc.edu

    2. B & D's DFA technique is a systematic way to achieve cost reduction through reducing the number of parts to be assembled and then ensuring that the remaining parts are easy to assemble. Boothroyd and Dewhurst DFA Method Select Assembly Method Analyze for Assembly Improve the design Stage 3 Stage 2 Stage 1

    3. 1. Manual Bench or transfer line assy. using simple tools 2. Robotic (general purpose)  one-arm robot assembly station  two-arm robot assembly station  multi-station robot assembly system 3. Special-purpose  with indexing transfer device (rotary or in-line)  with free transfer device (non-synchronous) B&D's DFA - Stage 1 Selection of Assembly Method

    4. One Arm Robot Assembly Station Bowl feeder Completed assemblies Parts Robot Magazines

    5. Two Arm Robot Assembly Station Bowl feeders Parts Robots Magazines Host Control of both robots simultaneously

    6. Multi-Station Robot Assembly System Free-transfer line Buffers Robots Bowl feeders Magazines

    7. Special Purpose Transfer Machines Free-transfer in-line machine Rotary indexing transfer machine

    8. Plots of 'Annual Volume' against 'Number of Parts' give 'regions' for the likely most economic method. 2 sets of colored charts: for single style products, and for multi-style products. The ratio of total parts to number in one typical assembly(NT/NA) is used.  3 charts in each set represent conditions for different equipment payback periods in 'shift years' (years x shift #) Assembly Method Selection Charts

    9. E.g. One Style, 8 parts in assembly, 6 shift-year payback Single Robot Multi- Robot Special Free Manual Bench Two Robot Special Indexing 1000k 5000k 500k 100k Annual Production Volume

    10. Analyze for Special-purpose assembly transfer machines) B&D's DFA - Stage 2 Analyze for Assembly OR OR Analyze for Manual Assembly Analyze for Robot Assembly

    11. The analysis will primarily give: A decision as to whether the part can be considered a candidate for elimination or combination with other parts in the assembly Estimation of the time taken to grasp, manipulate, and insert each part The 'theoretical minimum number of parts' The total assembly cost The manual assembly 'design efficiency' (%) Analysis For Manual Assembly

    12. Pneumatic Piston Sub-Assembly Original Design

    13. Re-Design using DFA

    14. Obtain the best information about the product / assembly (e.g. existing product, prototype, drawings, etc.) 1. Assemble the product (or imagine doing so) one part at a time and complete one row of a worksheet for each part (and special operation). 2. Total columns to give the manual assembly time (TM), manual assembly cost (CM), and the theoretical minimum number of parts (NM) 3. Calculate: DFA Efficiency = 3 x NM/TM Analysis Procedure DFA Manual Assembly

    15. BDI - DFA Handling Chart (1of2)

    16. BDI - DFA Handling Chart (2of2)

    17. symmetry:rotational symmetry about an axis perpendicular to the axis of insertion DFA Worksheet Part Orientation ? 1800 3600 = =

    18. symmetry: rotational symmetry about its axis of insertion DFA Worksheet Part Orientation  = ?  = 1800  = 00

    19. Thickness:The length of the shortest side of the smallest rectangular prism which encloses the part. Size: The length of the longest side of the smallest rectangular prism that can enclose the part. DFA Worksheet Part Grasping Thickness Size Thickness = radius Exception when cylindrical and Dia. < Length General Rule

    20. Parts Present Handling Difficulties: Parts that are Slippery: easily slip from fingers or tool Fragile or Delicate: require careful handling Nest or tangle: but can be separated one handed Sharp: or present other hazards to operator Stick together: e.g. magnetic force or grease Part Handling Chart Interpretation Notes (1)

    21. Parts that Severely Nest or Tangle: Those that interlock & require two hands to separate Flexible Parts: Those that require two hands to manipulate, i.e. large gaskets, belts, bands etc. Part Handling Chart Interpretation Notes (2)

    22. Holding Down Required: part requires realignment or holding down prior to, or during, the next assembly operation Easy to align and position during assembly: part is aligned and positioned by well designed locating features: e.g. chamfers. Part Insertion Chart Interpretation Notes(1)

    23. Resistance to Insertion: insertion against a large force,small clearances, any tendency wedge. Obstructed Access & Restricted Vision: restricted space or the operator has to rely on 'feel' during the assembly process Part Insertion Chart Interpretation Notes(2)

    24. BDI - DFA Insertion Chart (1of2)

    25. BDI - DFA Insertion Chart (2of2)

    26. **Assembly cost = Assembly time x 0.8¢ where 0.8¢ is the cost/sec for a $30 per hr assembly labor rate *Total assy. time for screwing: 3 secs allowed for picking up power screw driver and put it back down again: Assy. time = # (handling + Insertion - 3) + 3 This example: Assy. time = 4 (1.5+6-3)+3 = 21 secs DFA Worksheet Special Notes

    27.  Does the part move relative to all other parts already assembled? (small motions where elastic hinges are possible can be ignored)  Must the part be a different material than or be isolated from all other parts already assembled? (Only fundamental material property reasons)  Must the part be separate from all other parts already assembled because of impossible assembly/disassembly? Theoretical Minimum No. of Parts Column If the answer to any of the following questions is 'yes' then either a "1" is placed in the column or for multiple parts, the min. number necessary to perform the function; if not put "0" :

    28. Re-Design using DFA

    29. Results forToilet Ballcock Exercise

    30. The Plumb Shop Ballcock s= 18mm t= 4mm Float Lever s= 50mm t= 12mm Rivet Top cap s= 80mm s= 26mm t= 37mm t= 1.5mm Anti-syphon gasket s= 50mm t= 1mm Main O ring Body Valve Metering washer s= 220mm t= 30mm Valve washer Valve sub-assembly s= 30mm t= 10mm Screws Shank Washer Total 15 Parts s= 44mm t= 12mm Locknut s= 37mm t= 10mm

    31.  Examine 'Theoretical minimum number of parts' column. Zero (or less than current quantity of identical parts) indicates that these parts can be eliminated or combined.  Examine handling and insertion times. The greater the time, the greater the potential saving. Use the charts as a guide to reviewing possible design changes. B&D's DFA - Stage 3 Improve the Design

    32. Main Body 1 1.5 1.5 3 2.4 1 Anti-s. gasket 1 1.69 1.5 3.19 2.6 1 Valve sub-assy. 1 1.5 1.5 3 2.4 1 Top cap 1 1.5 5.5 7.0 5.6 1 Screws 4 1.5 6.5 21.0* 16.8 0 DFA Work sheet Ballcock Part ID. No. and/or Description **

    33. **Assembly cost = Assembly time x 0.8¢ where 0.8¢ is the cost/sec for a $30 per hr assembly labor rate *Total assy. time for screwing: 3 secs allowed for picking up power screw driver and put it back down again: Assy. time = # (handling + Insertion - 3) + 3 This example: Assy. time = 4 (1.5+6-3)+3 = 21 secs DFA Worksheet Special Notes

    34. Float Lever 1 1.95 6.5 8.45 6.8 0 Rivet 1 1.5 8 9.5 7.6 0 Re-orientation 1 - 9 9 7.2 0 Shank washer 1 1.5 5.0 6.5 5.2 1 Locknut 1 1.5 6.0 7.5 6.0 0 DFA Work sheet Ballcock Part ID. No. and/or Description **

    35. Total Assembly Time (TM) 91.6 Total Assembly Cost (CM) 73.4 Theoretical min. no. of parts (NM) 5 DFA Work sheet Ballcock Part ID. No. and/or Description ** DFA Efficiency = 3 x NM/TM = 3x5/91.6 = 0.16 or 16%

    36. DFA Analysis Example New Ballcock Living hinge Snap fit cap and main body Old Design = 15 parts Insert molded valve stem New Design = 5 parts Washer not assembled

    37. Main Body 1 1.5 1.5 3 2.4 1 Anti-s. gasket 1 1.69 1.5 3.19 2.6 1 Valve sub-assy. 1 1.5 1.5 3 2.4 1 Top cap 1 1.5 5.06.5 5.2 1 Shank washer* 1 1.5 1.5 3.0 2.4 1 DFA Work sheet New Ballcock Part ID. No. and/or Description **

    38. Total Assembly Time (TM) 18.7 Total Assembly Cost (CM) 15 Theoretical min. no. of parts (NM) 5 DFA Work sheet New Ballcock Part ID. No. and/or Description ** DFA Efficiency = 3 x NM/TM = 3x5/18.7 = 0.80 (was 16%) or 80%