Problem 2 (40 pts) Washer - 20 dia. 1.5 long. (must be free to move up...

 
 
 
 

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Problem 2 (40 pts) Washer - 20 dia. 1.5 long. (must be free to move up and down the shaft against the weak spring) Shaft 5 dia. 50 long (Dimensions mm) 0000 Open-ended spring 6 dia. 40 long Snap fastener 6 dia. 1 long (they tangle) Retainer bush 10 dia. Securing screw 1 dia. 2 long Consider the shaft assembly shown above, whose assembly procedure is as follows: 1. The retainer bush is placed in the work fixture like the one shown below. 2. The shaft is inserted in the bush. 3. The securing screw is inserted into the bush and is difficult to align and position. 4. The spring tangles severely and, when separated from others, is dropped onto the shaft. 5. The washer is inserted onto the shaft and then held down while the snap fastener is positioned using a standard grasping tool. (a) Estimate the manual assembly time and design efficiency of the assembly by filling the DFA worksheet as shown below. The descriptions on how the worksheet was filled are not required but would help if the filled numbers were incorrect. (15 pts) Item # 1 2 Name # of Items (b) Suggest a redesign of this assembly to reduce the number of parts and increase the assembly efficiency. Draw the "after" sketch of the parts in an exploded view like the figure above. Use callouts to indicate modified features (including part consolidation) after the redesign, and identify the design guidelines that suggested them. (10 pts) (c) Estimate the manual assembly time and design efficiency of the redesigned assembly by filling the DFA worksheet as shown in (a). The descriptions on how the worksheet was filled are not required but would help if the filled numbers were incorrect. (15 pts) Total Manual handling estimated times (sec) Parts are easy to grasp and manipulate Parts present handling difficulties (1) Thickness >2 mm Thickness 2 mm Thickness >2 mm Thickness 2 mm Key: Size >15 mm One hand 6 mm size >15 mm Size Size <6 mm >6 mm Size 6 mm Size >15 mm 6 mm size Size Size <6 mm >6 mm Size 6 mm 15 mm 0 1 2 3 4 5 6 7 8 9 0 1.13 1.43 1.88 1.69 2.18 1.84 2.17 2.65 2.45 2.98 (+) < 360 1 15 1.5 1.8 2.25 2.06 2.55 2.25 2.57 3.06 3 3.38 360 (+) <540 540 (+) <720 manipulated by one hand but only Parts can be grasped and an be grasped with the use of grasping tools = 360 180 without the aid of grasping tools Parts can be grasped and manipulated by one hand 2 1.8 2.1 2.55 2.36 2.85 2.57 2.9 3.38 3.18 3.7 3 1.95 2.25 2.7 2.51 3 2.73 3.06 3.55 3.34 4 Parts need tweezers for grasping and manipulation (a+)=720 Parts can be manipulated without Parts require optical magnification optical magnification for manipulation One hand with grasping aids Parts are easy to grasp and Parts present Parts are easy to Parts present handling manipulate difficulties (1) difficulties (1) Thickness Thickness Thickness Thickness Thickness Thickness Thickness Thickness >0.25 mm 0.25 mm >0.25 mm 0.25 mm >0.25 mm 0.25 mm >0.25 mm 0.25 mm grasp and manipulate handling Parts need standard tools other than tweezers or grasping Parts need special tools for and manipulation 0 180 0 1 2 3 4 5 6 7 8 9 4 3.6 6.85 4.35 7.6 5.6 8.35 6.35 8.6 7 7 B = 360 5 4 7.25 4.75 8 6 8.75 6.75 9 8 8 6 4.8 8.05 5.55 8.8 6.8 9.55 7.55 9.8 8 9 180 7 5.1 8.35 5.85 9.1 7.1 9.55 7.85 10.1 9 10 10 B = 360 Parts severely nest or Two hands for manipulation tangle or are flexible but can be grasped and lifted by one hand (with the use of grasping tools if necessary) (2) Parts present no additional handling difficulties Parts present additional handling difficulties (e.g. sticky, delicate, slippery, etc.) (1) = 1800 = 360 a180 = 360 6 mm 6 mm Size Size size >15 mm <6 mm Size >6 mm Size 6 mm Size >15 mm Size Size size <6 mm >6 mm Size 6 mm <15 mm 15 mm 0 1 2 3 4 5 6 7 8 9 8 4.1 4.5 5.1 5.6 6.75 5 5.25 5.85 6.35 7 Parts can be handled by one person without mechanical assistance Parts do not severely nest or tangle and are not flexible Two hands or assistance required for large size Two hands, two persons or mechanical assistance required for grasping Parts are easy to grasp and manipulate a180 = 360 Part weight <10 lb Parts are heavy (>10 lb) Parts present other handling difficulties (1) Parts are easy to Parts present grasp and manipulate other handling difficulties (1) a180 = 360 180 = 360 180 = 360 and transporting parts 9 2 3 2 3 3 4 + Parts severely nest or tangle or are flexible (2) Two persons or mechanical assistance required for parts manipulation 0 1 2 3 4 5 6 7 8 4 5 7 9 location (3) Easy to align and Not easy to align or position during position during assembly Manual insertion estimated times (sec) Alter assembly no holding down required to maintain orientation and assembly (4) Holding down required during subsequent processes to maintain orientation at location (3) Easy to align and position during assembly (4) Not easy to align or position during assembly No Resistance Key: resistance No resistance Resistance No resistance Resistance No resistance Resistance Part added but to Ito insertion (5) insertion to insertion to insertion (5) to to to insertion insertion (5) to insertion (5) insertion not secured 0 1 2 3 6 7 8 9 Part and associated 0 1.5 2.5 2.5 3.5 5.5 6.5 6.5 7.5 tool (including hands) can easily 1 4 5 5 6 8 9 9 10 2 5.5 6.5 6.5 7.5 9.5 10.5 10.5 11.5 reach the desired location Addition of any part (1) where neither the part itself not any other part is finally secured immediately Part and associated tool (including hands) c s) cannot easily reach the desired location Due to obstructed access or restricted vision (2) Due to obstructed access and restricted vision (2) No screwing operation or plastic deformation immediately after insertion (snap/press fits,circlips,spire nuts,etc.) Part secured immediately Part and associated tool (including hands) can easily reach the desired location and the tool can be operated easily Due to er parts are being finally secured immediately Part and associated tool Addition of any part (1) where the part itself and/or other pa (including hands) cannot easily reach desired location or tool cannot be operated easily Plastic deformation immediately after insertion Plastic bending or torsion Riveting or similar operation Not easy to align or position during assembly Easy to align and position with no resistance to insertion (4) Not easy to align or position during asse- mbly and/or resis- tance to insertion (5) Easy to align and position during assembly (4) No resistance to insertion 0 3 2 5 1 4 2 obstructed accessor restricted 4 4.5 7.5 6.5 vision (2) 5 6 9 8 74 6 5 Not easy to align or position during assembly Screw tightening immediately after insertion Resistance to insertion (5) Easy to align and position during assembly (4) No resistance | to insertion 9 4 7 8 6 9. 6 6 80 Resistance to insertion (5) Easy to align and co position with no torsional resistance (4) Not easy to align or position and/or torsional resistance (5) 7.5 8.5 9.5 10.5 11.5 8.5 10.5 Due to obstructed access and restricted vision (2) Separate operation Mechanical fastening processes (part(s) already in place but not secured immediately after insertion) None or localized plastic deformation 10 10 11 12 12 13 133 Non-mechanical fastening processes (part(s) already in place but not secured immediately after insertion) Metallurgical processes Additional material required 0 1 2 9 4 7 5 12 12 7 8 3 4 similar processes Riveting or or other processes Screw tightening Bulk plastic deformation. (large proportion of part is plastically deformed during fastening) No additional material required friction welding, etc.) (e.g. resistance, Soldering processes similar process Bending or 10 12 Non-fastening processes Weld/braze processes (e.g. adhesive bonding, Chemical processes etc.) (e.g. orienting, fittings or adjustment of part(s). etc.) Manipulation of parts or sub-assembly (e.g. liquid insertion, etc.) Other processes 6 12 12 8 8 6 12 12 12 Assembly processes where all solid parts are in place Problem 2 (40 pts) Washer - 20 dia. 1.5 long. (must be free to move up and down the shaft against the weak spring) Shaft 5 dia. 50 long (Dimensions mm) 0000 Open-ended spring 6 dia. 40 long Snap fastener 6 dia. 1 long (they tangle) Retainer bush 10 dia. Securing screw 1 dia. 2 long Consider the shaft assembly shown above, whose assembly procedure is as follows: 1. The retainer bush is placed in the work fixture like the one shown below. 2. The shaft is inserted in the bush. 3. The securing screw is inserted into the bush and is difficult to align and position. 4. The spring tangles severely and, when separated from others, is dropped onto the shaft. 5. The washer is inserted onto the shaft and then held down while the snap fastener is positioned using a standard grasping tool. (a) Estimate the manual assembly time and design efficiency of the assembly by filling the DFA worksheet as shown below. The descriptions on how the worksheet was filled are not required but would help if the filled numbers were incorrect. (15 pts) Item # 1 2 Name # of Items (b) Suggest a redesign of this assembly to reduce the number of parts and increase the assembly efficiency. Draw the "after" sketch of the parts in an exploded view like the figure above. Use callouts to indicate modified features (including part consolidation) after the redesign, and identify the design guidelines that suggested them. (10 pts) (c) Estimate the manual assembly time and design efficiency of the redesigned assembly by filling the DFA worksheet as shown in (a). The descriptions on how the worksheet was filled are not required but would help if the filled numbers were incorrect. (15 pts) Total Manual handling estimated times (sec) Parts are easy to grasp and manipulate Parts present handling difficulties (1) Thickness >2 mm Thickness 2 mm Thickness >2 mm Thickness 2 mm Key: Size >15 mm One hand 6 mm size >15 mm Size Size <6 mm >6 mm Size 6 mm Size >15 mm 6 mm size Size Size <6 mm >6 mm Size 6 mm 15 mm 0 1 2 3 4 5 6 7 8 9 0 1.13 1.43 1.88 1.69 2.18 1.84 2.17 2.65 2.45 2.98 (+) < 360 1 15 1.5 1.8 2.25 2.06 2.55 2.25 2.57 3.06 3 3.38 360 (+) <540 540 (+) <720 manipulated by one hand but only Parts can be grasped and an be grasped with the use of grasping tools = 360 180 without the aid of grasping tools Parts can be grasped and manipulated by one hand 2 1.8 2.1 2.55 2.36 2.85 2.57 2.9 3.38 3.18 3.7 3 1.95 2.25 2.7 2.51 3 2.73 3.06 3.55 3.34 4 Parts need tweezers for grasping and manipulation (a+)=720 Parts can be manipulated without Parts require optical magnification optical magnification for manipulation One hand with grasping aids Parts are easy to grasp and Parts present Parts are easy to Parts present handling manipulate difficulties (1) difficulties (1) Thickness Thickness Thickness Thickness Thickness Thickness Thickness Thickness >0.25 mm 0.25 mm >0.25 mm 0.25 mm >0.25 mm 0.25 mm >0.25 mm 0.25 mm grasp and manipulate handling Parts need standard tools other than tweezers or grasping Parts need special tools for and manipulation 0 180 0 1 2 3 4 5 6 7 8 9 4 3.6 6.85 4.35 7.6 5.6 8.35 6.35 8.6 7 7 B = 360 5 4 7.25 4.75 8 6 8.75 6.75 9 8 8 6 4.8 8.05 5.55 8.8 6.8 9.55 7.55 9.8 8 9 180 7 5.1 8.35 5.85 9.1 7.1 9.55 7.85 10.1 9 10 10 B = 360 Parts severely nest or Two hands for manipulation tangle or are flexible but can be grasped and lifted by one hand (with the use of grasping tools if necessary) (2) Parts present no additional handling difficulties Parts present additional handling difficulties (e.g. sticky, delicate, slippery, etc.) (1) = 1800 = 360 a180 = 360 6 mm 6 mm Size Size size >15 mm <6 mm Size >6 mm Size 6 mm Size >15 mm Size Size size <6 mm >6 mm Size 6 mm <15 mm 15 mm 0 1 2 3 4 5 6 7 8 9 8 4.1 4.5 5.1 5.6 6.75 5 5.25 5.85 6.35 7 Parts can be handled by one person without mechanical assistance Parts do not severely nest or tangle and are not flexible Two hands or assistance required for large size Two hands, two persons or mechanical assistance required for grasping Parts are easy to grasp and manipulate a180 = 360 Part weight <10 lb Parts are heavy (>10 lb) Parts present other handling difficulties (1) Parts are easy to Parts present grasp and manipulate other handling difficulties (1) a180 = 360 180 = 360 180 = 360 and transporting parts 9 2 3 2 3 3 4 + Parts severely nest or tangle or are flexible (2) Two persons or mechanical assistance required for parts manipulation 0 1 2 3 4 5 6 7 8 4 5 7 9 location (3) Easy to align and Not easy to align or position during position during assembly Manual insertion estimated times (sec) Alter assembly no holding down required to maintain orientation and assembly (4) Holding down required during subsequent processes to maintain orientation at location (3) Easy to align and position during assembly (4) Not easy to align or position during assembly No Resistance Key: resistance No resistance Resistance No resistance Resistance No resistance Resistance Part added but to Ito insertion (5) insertion to insertion to insertion (5) to to to insertion insertion (5) to insertion (5) insertion not secured 0 1 2 3 6 7 8 9 Part and associated 0 1.5 2.5 2.5 3.5 5.5 6.5 6.5 7.5 tool (including hands) can easily 1 4 5 5 6 8 9 9 10 2 5.5 6.5 6.5 7.5 9.5 10.5 10.5 11.5 reach the desired location Addition of any part (1) where neither the part itself not any other part is finally secured immediately Part and associated tool (including hands) c s) cannot easily reach the desired location Due to obstructed access or restricted vision (2) Due to obstructed access and restricted vision (2) No screwing operation or plastic deformation immediately after insertion (snap/press fits,circlips,spire nuts,etc.) Part secured immediately Part and associated tool (including hands) can easily reach the desired location and the tool can be operated easily Due to er parts are being finally secured immediately Part and associated tool Addition of any part (1) where the part itself and/or other pa (including hands) cannot easily reach desired location or tool cannot be operated easily Plastic deformation immediately after insertion Plastic bending or torsion Riveting or similar operation Not easy to align or position during assembly Easy to align and position with no resistance to insertion (4) Not easy to align or position during asse- mbly and/or resis- tance to insertion (5) Easy to align and position during assembly (4) No resistance to insertion 0 3 2 5 1 4 2 obstructed accessor restricted 4 4.5 7.5 6.5 vision (2) 5 6 9 8 74 6 5 Not easy to align or position during assembly Screw tightening immediately after insertion Resistance to insertion (5) Easy to align and position during assembly (4) No resistance | to insertion 9 4 7 8 6 9. 6 6 80 Resistance to insertion (5) Easy to align and co position with no torsional resistance (4) Not easy to align or position and/or torsional resistance (5) 7.5 8.5 9.5 10.5 11.5 8.5 10.5 Due to obstructed access and restricted vision (2) Separate operation Mechanical fastening processes (part(s) already in place but not secured immediately after insertion) None or localized plastic deformation 10 10 11 12 12 13 133 Non-mechanical fastening processes (part(s) already in place but not secured immediately after insertion) Metallurgical processes Additional material required 0 1 2 9 4 7 5 12 12 7 8 3 4 similar processes Riveting or or other processes Screw tightening Bulk plastic deformation. (large proportion of part is plastically deformed during fastening) No additional material required friction welding, etc.) (e.g. resistance, Soldering processes similar process Bending or 10 12 Non-fastening processes Weld/braze processes (e.g. adhesive bonding, Chemical processes etc.) (e.g. orienting, fittings or adjustment of part(s). etc.) Manipulation of parts or sub-assembly (e.g. liquid insertion, etc.) Other processes 6 12 12 8 8 6 12 12 12 Assembly processes where all solid parts are in place