Mechanical Assembly - Oxford University Press
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Team Members:
Agus Sudjianto
Jared Clark
Milind Oak
Eiichi Tanabe
Gaurav Shukla
Problem Statement 4
3.6-Volt Sears/Craftsman( Cordless Screwdriver 4
1. Report #1: Product Description 5
1.1 Product Assembly Drawing 6
1.2 Transmission Assembly 7
1.3 Exploded View of Transmission Assembly 8
1.4 Clearance Specification 9
1.5 Screwdriver Component Breakdown 11
1.6 Bill Of Materials 12
1.7 Assembly Tree 14
1.8 Functional Flow Model 15
1.9 System Hierarchy Breakdown 16
1.9.1 Battery Module System Breakdown 16
1.9.2 Driver Mechanism System Breakdown 17
1.10 Liaison Diagrams of Part Mating 18
1.10.1 Product Main Assembly 18
1.10.2 Battery and Housing Assembly 18
1.10.3 Torque Limiter 18
1.10.4 Transmission 19
1.10.5 Motor Assembly 19
2. Report #2: DATUM FLOW CHAIN 20
2.1 Overall Transmission Key Characteristics 20
2.2 Feature, Mate, and Contact Table 24
2.3 Complete Bill Of Materials 25
2.4. Exploded View 27
3. Report #3: Assembly Sequence 28
3.1 Revised Liaison Diagram 28
3.2 Revised Datum Flow Chain 28
3.3 All Possible Assembly Sequence 29
3.4 The Most Conveniencee Assembly Sequence 30
3.5 Required Gross and Fine Motions 31
3.6 Futures, Chamfers and Lead ins 31
3.7 Difficulties & Ideas in Assembly 33
3.8 Feature Parts and Associated Assembly Tool and Fixtures 34
3.9. Fixtures and Tools for Assembly 35
3.10 Gear Set Architecture Redesign 36
3.11 Improvement highlight 37
4. Report #4: Assembly Floor Layout Analysis 38
4.1. Assembly Sequence 38
4.2 Assembly Process time 39
4.3 Assembly Line Design and Assumptions 41
4.3.1 Design Parameters 42
4.3.2 Supplied Material 42
4.4 Assembly operation style 42
4.4.1 Assembly Line Design 42
5. Report #5: Workstation Design 46
5.1 Required cycle time to complete the planned operations 46
5.1.1 Assembly Flow Diagram 46
5.1.2 Final Assembly 47
5.1.3 Testing and Packaging 47
5.1.4 Transmission Assembly 48
5.1.5 Grip Housing/Battery Assembly 48
5.2 Station lay out: in and out flows of assemblies and parts 50
5.3 Required motions of equipment and people 51
5.4 Necessary inspections or tests 52
5.5 Gantt chart of required time of activities and a complete cycle 53
5.6 Cost estimation of workstations 56
5.7 Estimation of the cost of performing one assembly cycle 57
6. Report #6: Economic Analysis and Assembly Line Simulation 59
6.1 Economic analysis of this assembly layout 59
6.1.1 Estimated Manufacturing Cost 60
6.1.2 Inventory Cost and Distribution Cost 60
6.1.3 Development Cost 61
6.1.4 Unit Part Costs 62
6.1.5 Economic Analysis 63
6.2 Discrete event simulation of assembly line 64
6.2.1 Discrete Event Simulation: Configuration Study 64
6.2.2 Selection of Final Assembly Process 72
|Problem Statement |
|3.6-Volt Sears/Craftsman( Cordless Screwdriver |
September 29, 1999
Clients: Dr. Dan Whitney
Project Team:
|Name |E-mail |
|Agus Sudjianto |asudjian@ |
|Jared Clark |jclark15@ |
|Milind Oak |moak@ |
|Gaurav Shukla |Gaurav@mit.edu |
|Eiichi Tanabe |eitanab@ |
|The team decided to analyze Sears/Craftsman( 3.6-Volt Cordless Screwdriver. The product has dual-position handle design: in-grip |
|position to work in confined areas which can be easily converted into pistol-grip for normal screw-driving tasks. |
| |
|[pic] |
| |
|The followings are some notable features of the product: |
|Two-speed, 130 and 400 RPM, with 2-speed gear box to match the need for applications of high speed fast screw-driving and low-speed|
|high-torque heavy duty screw-driving. |
|Planetary spur gears to provide the torque and power needed. |
|Adjustable torque clutch to match driving torque task |
|Trigger switch for reverse-off-forward control. |
|Impact resistant glass-filled nylon housing. |
|¼-in. hex collet with automatic spindle lock. |
|3.6-volt 3-cell rechargeable batteries. |
|Power supply to recharge the batteries. |
|NOTE: |
|The battery charger sub-system is excluded from this study. |
|Sum of the sub-assembly such as motor may be treated as a module. |
| |
|1. Report #1: Product Description |
In this report Sears/Craftsman( 3.6-Volt Cordless Screwdriver is described as follows,
• Product Drawings
• Product Assembly Drawing
• Transmission Assembly
• Exploded View of Transmission Assembly
• Clearance Specification
• Screwdriver Component Breakdown
• Bill Of Material (Including Parts List, Function and Material)
• Assembly Tree
• Functional Flow Model
• Functional System Breakdown
• System Hierarchy Breakdown
• Battery Module System Breakdown
• Driver Mechanism System Breakdown
• Liaison Diagrams of Part Mating
• Product Main Assembly
• Battery and Housing Assembly
• Torque Limiter
• Transmission
• Motor Assembly
|1.1 Product Assembly Drawing |
[pic]
|1.2 Transmission Assembly |
[pic]
|1.3 Exploded View of Transmission Assembly |
[pic]
|1.4 Clearance Specification |
[pic]
[pic]
|1.5 Screwdriver Component Breakdown |
[pic]
|1.6 Bill Of Materials |
|No |Syst #|System Name |Part #|Part Name |Quantity |Function |Note |Material |
|1 |1 |Battery |1.1 |Battery Charger |1 |Charge Battery |6V DC Power supply |N/A |
| | |Charger | | | | | | |
|2 |2 |Battery |2.1 |Charger Contact |2 |Contact Power |Provide contact of battery charger|SUS304 |
| | |Closure | |Plates | | |to battery | |
|3 | | |2.2 |Battery Left Housing |1 |Enclose Battery |Also function as hand grip |Glass-filled |
| | | | | | | | |nylon |
|4 | | |2.3 |Bettery Right Housing|1 |Enclose Battery |Also function as hand grip |Glass-filled |
| | | | | | | | |nylon |
|5 | | |2.4 |Battery Cover |1 |Enclose Battery | |Glass-filled |
| | | | | | | | |nylon |
|6 | | |2.5 |Baterry Housing |2 |Hold battery | |N/A |
| | | | |Fasteners | |housing | | |
|7 |3 |Power |3.1 |Rechargable Batteries|3 |Store power |Total of 3.6V battery |N/A |
| | |Storage | | | | | | |
|8 | | |3.2 |Battery Cables |2 |Transmit power |Provide connection from battery to|N/A |
| | | | | | | |switch (+/-) | |
|9 | | |3.3 |Battery Connectors |2 |Connect cable |Connecting cables to battery |SUS304 |
|10 | | |3.4 |Switch to Motor |2 |Transmit power |Provide connection from switch to | Polypropylene |
| | | | |Cables | | | | |
|11 | | |3.5 |Crim Connectors |2 |Hold cable |Holding cable to motor |SUS304 |
|12 | | |3.6 |Shrink wrap |1 |Hold batteries | |Polypropylene |
|13 | | |3.7 |Tape |1 |Hold cable | |cellophane |
|14 | | |3.8 |Cable connectors |2 |Connect cables to battery |SUS304 |
|15 |4 |Torque |4.1 |Torque Limiter Outer |1 |Accept hand |Accept hand control to push needle| Polypropylene |
| | |Limiter | |Cap | | |bearing for torque limiter | |
|16 | | |4.2 |Torque Limiter Inner |1 |Accept outer cap | |PS (Polystyrene)|
| | | | |Cap | | | | |
|17 | | |4.3 |Torque Limiter Cap |1 |Hold inner and outer caps |SUS304 |
| | | | |Clip | | | |
|18 | | |4.4 |Needle Bearings |4 |Push PG1 internal |To adjust torque limiter |N/A |
| | | | | | |gear | | |
|19 | | |4.5 |Ball Bearings |6 |Allow internal gear PG1 slippage |N/A |
|20 | | |4.6 |Bearing holder plate |1 |Hold ball bearings | |SUS304 |
|21 | | |4.7 |Torque Limiter |4 |Hold bearing holder|4 springs to privide uniform flex |SUS304 |
| | | | |Springs | |plate |suport | |
|22 | | |4.8 |Torque Limiter Base |1 |Support springs | |Nylon |
| | | | |Support | | | | |
|23 | | |4.9 |Torque Limiter |2 |Hold base support to motor |N/A |
| | | | |Fasteners | | | |
|24 |5 |Drive |5.1 |Drive Left Housing |1 |Provide enclosure |Also to isolate noise |Glass-filled |
| | |Closure | | | |to drive | |nylon |
|25 | | |5.2 |Drive Right Housing |1 |Provide enclosure |Also to isolate noise |Glass-filled |
| | | | | | |to drive | |nylon |
|26 | | |5.3 |Grip Locking Switch |1 |Hold grip position | |Polypropylene |
|27 | | |5.4 |Grip Locking Spring |1 |Support grip locking switch |SUS304 |
|28 | | |5.5 |Drive Housing Long |2 |Hold housing | |N/A |
| | | | |Fasteners | | | | |
|29 | | |5.6 |Drive Housing Medium |2 |hold drive | |N/A |
| | | | |Fasteners | | | | |
|30 | | |5.7 |Drive Housing Short |2 |hold housing | |N/A |
| | | | |Fasteners | | | | |
|31 |6 |Power |6.1 |DC Motor |1 |Convert EE to Kinetic Energy |N/A |
| | |generator | | | | | |
|32 | | |6.2 |On/Off Button |1 |Connect electric | |Polypropylene |
| | | | | | |power | | |
|33 | | |6.3 |On/Off Spring |1 |Support On/Off | |SUS304 |
| | | | | | |Button | | |
|No |Syst #|System Name |Part #|Part Name |Quantity |Function |Note |Material |
|34 | | |6.4 |F/R/S Lever |1 |Provide control for rotation direction | Polypropylene |
|35 | | |6.5 |F/R/S Switch Circuit |1 |Control polarity connection to battery |PS (Polystyrene)|
|36 |7 |Bit Holder |7.1 |Collet |1 |Transmit torque |Also to hold bit |SUM |
|37 | | |7.2 |Bit Holder Housing |1 |Provide housing to drive mechanism |PS (Polystyrene)|
|38 | | |7.3 |Direction Stopper |2 |Hold PG3 carrier |To allow counter rotation |SUS304 |
| | | | |Clips | | | | |
|39 | | |7.4 |Direction Stoppper |4 |Hold stopper clips | |PS (Polystyrene)|
| | | | |Supports | | | | |
|40 | | |7.5 |Screwdriver bit |1 |Act on screw | |SUM |
|41 |8 |Transmission|8.1 |Planetary Gear 1 |1 |Enclose pinion | |SUS304 |
| | | | |(PG1) Washer | |gears | | |
|42 | | |8.2 |PG1/PG3 Pinion Gears |6 |Increase torque | |SMF |
|43 | | |8.3 |PG1 Internal Gears |1 |Coordinate pinion |Allows all pinion gears to rotate |SMF |
| | | | | | |gears |along its internal gear | |
|44 | | |8.4 |PG1 Carrier/PG2 Sun |1 |Hold pinion gears |Also transmit torque |SUM |
| | | | |Gear | | | | |
|45 | | |8.5 |PG1 Sun Gear |1 |Transmit torque | |SMF |
|46 | | |8.6 |PG2 Pinion Gears |3 |Reduce speed | |SMF |
|47 | | |8.7 |PG2 Washer |1 |Enclose pinion | |SUS304 |
| | | | | | |gears | | |
|48 | | |8.8 |PG2 Coupling Gear |1 |Hold pinion gears | |PS (Polystyrene)|
|49 | | |8.9 |PG2 Locking Gear |1 |Hold PG2 system | |PS (Polystyrene)|
|50 | | |8.10 |Hi/Lo Lever |1 |Transmit control |By shifting coupling gear |SUS304 |
|51 | | |8.11 |Hi/Lo Button |1 |Accept Hi/Lo | | Polypropylene |
| | | | | | |control | | |
|52 | | |8.12 |Hi/Lo Fasteners |2 |Hold Hi/Lo lever | |N? |
|53 | | |8.13 |PG2 Carrier/PG3 Sun |1 |Hold pinion gears | |SUM |
| | | | |Gear | | | | |
|54 | | |8.14 |PG3 Washer |1 |Enclose pinion | |SUS304 |
| | | | | | |gears | | |
|55 | | |8.15 |PG3 Internal |1 |Coordinate pinion |Allows all pinion gears to rotate |SMF |
| | | | |Gear/Direction | |gears |along its internal gear | |
| | | | |Openner | | | | |
|56 | | |8.16 |PG3 Carrier |1 |Hold pinion gears | |SUM |
|1.7 Assembly Tree |
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|1.8 Functional Flow Model |
[pic]
[pic]
|1.9 System Hierarchy Breakdown |
[pic]
1.9.1 Battery Module System Breakdown
[pic]
1.9.2 Driver Mechanism System Breakdown
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|1.10 Liaison Diagrams of Part Mating |
1.10.1 Product Main Assembly
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1.10.2 Battery and Housing Assembly
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1.10.3 Torque Limiter
[pic]
1.10.4 Transmission
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1.10.5 Motor Assembly
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|2. Report #2: DATUM FLOW CHAIN |
Transmission/Motor sub-assembly is selected for a detailed Datum Flow Chain (DFC) analysis. The exploded view of this module is shown in Figure 7. Figure 1 shows the DFC of overall sub-assembly. Detailed analysis of Hi/Lo speed conversion is presented in Figures 2-6.
[pic]
Figure 1. Datum Flow Chain (DFC) of Transmission/Motor Module
|2.1 Overall Transmission Key Characteristics |
KC#1: In order for screwdriver to function properly, Bit Holder rotation axis must be concentric with Power Generator axis. Thus concentricity is a key characteristic.
KC#2: The distance between PG3 Internal Gear & PG1 Internal Gear is important because this subassembly has to fit within the space provided by Transmission/Bit Holder housing. So Stack-up length is a key characteristic.
KC#3-#5: Hi/Low Speed Configuration and Their Key Characteristics
The gear configurations for the high/low speeds and the transition are shown in the following figure.
| High Speed |Speed Transition |Low Speed |
|[pic] |[pic] |[pic] |
Figure 2. Hi/Lo speed gear configurations.
There are distinct key characteristics for each configuration as follows.
❑ High Speed: The Coupling Gear must successfully engage to lock PG2 Carrier and PG2 Pinion Gears together so that they become an integral unit. Therefore, the engagement of PG2 Carrier and Pinion Gears is the KC (KC#3).
[pic]
Figure 3. DFC for High Speed condition
❑ Transition: The Coupling Gear must not engage with either PG2 Carrier or Locking Gear. Therefore, the KC is the gap between PG2 Carrier and Locking Gear (KC#4).
[pic]
Figure 4. DFC for transition condition
❑ Low Speed: The Coupling Gear and the Locking Gear must be properly engaged to become an integral unit so that the Pinion Gear can rotate around the Coupling/Locking Gear unit. The situation of the KC is shown in the following figure.
[pic]
Figure 5. Low speed condition
If (g1 – g2) < 2h then stress built up is occurring (over-constrained) and the mechanism will fail. On the other hand, if (g1 – g2) > 2h + ε, where ε is the acceptable clearance, then wobbling problem is occurring. The former problem is more severe than the later problem. Therefore, the KC (KC#5) is defined by the Pinion Gears and the Locking Gear. The success of engagement between the Locking and Coupling gear is a key condition to this mechanism. The Datum Flow Chains for the above conditions are shown in the following figures.
[pic]
Figure 6. DFC for low speed condition
|2.2 Feature, Mate, and Contact Table |
|Feature Number |Part No. |Part A |Part No. |Part B |DOF |MATE/ |Comments |
| | | | | | |CONTACT | |
|1 |7.2 |Bit Holder Housing |8.16 & 7.1|Carrier & Bit |Five |Mate |Peg & Hole |
| | | | |Holder | | | |
|2 |7.2 |Bit Holder Housing |8.15 |Internal Gear |Five |Mate |Peg & Hole |
|3 |8.16 & 7.1 |Carrier & Bit Holder |8.2 |Pinion Gears |Five |Mate |3 Peg & Holes for 3 pinions |
|4 |8.2 |Pinion Gears |8.13 |PG2 Carrier/PG3 Sun|Five |Mate |Overconstrained Dofs, Clearance |
| | | | |Gear | | | |
|5 |8.2 |Pinion Gears |8.14 |Washer |Three |Mate |Overlap of 2 plates, OverCons. With #7 |
|6 |8.15 |Internal Gear |8.2 |Pinion Gears |Four |Mate |Overconstrained Dofs, Clearance |
|7 |8.15 |Internal Gear |8.14 |Washer |Three |Mate |Overlap of 2 plates, OverCons. With #5 |
|8 |8.14 |Washer |8.13 |PG2 Carrier/PG3 Sun|Three |Mate |Overlap of two Plates |
| | | | |Gear | | | |
|9 |8.13 |PG2 Carrier/PG3 Sun Gear|8.6 |PG2 Pinion Gears |Five |Mate |3 Peg & Holes for 3 pinions |
|10 |7.2 |Bit Holder Housing |8.9 |PG2 Locking Gear |Five |Mate |Peg & Hole |
|11 |7.2 |Bit Holder Housing |8.1 |Hi/Lo Lever |Five |Mate |Peg & Hole |
|12 |8.6 |PG2 Pinion Gears |8.7 |PG2 Washer |Three |Mate |Overlap of 2 plates, OverCons. With #14 |
|13 |8.6 |PG2 Pinion Gears |8.4 |PG1 Carrier/PG2 Sun|Five |Mate |Overconstrained Dofs, Clearance |
| | | | |Gear | | | |
|14 |8.7 |PG2 Washer |8.4 |PG1 Carrier/PG2 Sun|Three |Mate |Overlap of 2 plates, OverCons. With #12 |
| | | | |Gear | | | |
|15 |8.6 |PG2 Pinion Gears |8.8 |PG2 Coupling Gear |Five |Mate |Overconstrained Dofs, Clearance |
|16 |8.4 |PG1 Carrier/PG2 Sun Gear|8.2 |PG3 Pinion Gears |Five |Mate |3 Peg & Holes for 3 pinions |
|17 |8.2 |PG3 Pinion Gears |8.1 |Pinion Gears 1 |Three |Mate |Overlap of 2 plates |
| | | | |Washer | | | |
|18 |8.2 |PG3 Pinion Gears |4 & 6 |Torque Limiter & |Five |Mate |Gear mate |
| | | | |Power Generator | | | |
|19 |8.1 |Pinion Gears 1 Washer |8.3 |PG1 Internal Gear |Three |Mate |Overlap of 2 plates |
|20 |8.3 |PG1 Internal Gear |4 & 6 |Torque Limiter & |Three |Mate |Overlap of 2 plates |
| | | | |Power Generator | | | |
|21 |8.1 |Hi/Lo Lever |8.8 |PG2 Coupling Gear |One |Mate | |
|22 |8.13 |PG2 Carrier/PG3 Sun Gear|8.8 |PG2 Coupling Gear |Five |Mate |Gear mate |
|23 |8.9 |PG2 Locking Gear |8.8 |PG2 Coupling Gear |Six |Mate |Properly constrained |
|24 |7.2 |Bit Holder Housing |8.8 |PG2 Coupling Gear |Three |Mate |Oversize hole |
|25 |7.2 |Bit Holder Housing |8.3 |PG1 Internal Gear |Three |Mate |Oversize hole |
|26 |7.2 |Bit Holder Housing |4 & 6 |Torque Limiter & |Six |Mate |Properly constrained |
| | | | |Power Generator | | | |
|27 |8.2 |PG3 Pinion Gears |8.3 |PG1 Internal Gear |Five |Mate |Gear mate |
|2.3 Complete Bill Of Materials |
|No |Syst #|System Name |Part #|Part Name |Quantity |Function |Note |Material |
|1 |1 |Battery |1.1 |Battery Charger |1 |Charge Battery |6V DC Power supply |N/A |
| | |Charger | | | | | | |
|2 |2 |Battery |2.1 |Charger Contact |2 |Contact Power |Provide contact of battery charger|SUS304 |
| | |Closure | |Plates | | |to battery | |
|3 | | |2.2 |Battery Left Housing |1 |Enclose Battery |Also function as hand grip |Glass-filled |
| | | | | | | | |nylon |
|4 | | |2.3 |Bettery Right Housing|1 |Enclose Battery |Also function as hand grip |Glass-filled |
| | | | | | | | |nylon |
|5 | | |2.4 |Battery Cover |1 |Enclose Battery | |Glass-filled |
| | | | | | | | |nylon |
|6 | | |2.5 |Baterry Housing |2 |Hold battery | |N/A |
| | | | |Fasteners | |housing | | |
|7 |3 |Power |3.1 |Rechargable Batteries|3 |Store power |Total of 3.6V battery |N/A |
| | |Storage | | | | | | |
|8 | | |3.2 |Battery Cables |2 |Transmit power |Provide connection from battery to|N/A |
| | | | | | | |switch (+/-) | |
|9 | | |3.3 |Battery Connectors |2 |Connect cable |Connecting cables to battery |SUS304 |
|10 | | |3.4 |Switch to Motor |2 |Transmit power |Provide connection from switch to | Polypropylene |
| | | | |Cables | | | | |
|11 | | |3.5 |Crim Connectors |2 |Hold cable |Holding cable to motor |SUS304 |
|12 | | |3.6 |Shrink wrap |1 |Hold batteries | |Polypropylene |
|13 | | |3.7 |Tape |1 |Hold cable | |cellophane |
|14 | | |3.8 |Cable connectors |2 |Connect cables to battery |SUS304 |
|15 |4 |Torque |4.1 |Torque Limiter Outer |1 |Accept hand |Accept hand control to push needle| Polypropylene |
| | |Limiter | |Cap | | |bearing for torque limiter | |
|16 | | |4.2 |Torque Limiter Inner |1 |Accept outer cap | |PS (Polystyrene)|
| | | | |Cap | | | | |
|17 | | |4.3 |Torque Limiter Cap |1 |Hold inner and outer caps |SUS304 |
| | | | |Clip | | | |
|18 | | |4.4 |Needle Bearings |4 |Push PG1 internal |To adjust torque limiter |N/A |
| | | | | | |gear | | |
|19 | | |4.5 |Ball Bearings |6 |Allow internal gear PG1 slippage |N/A |
|20 | | |4.6 |Bearing holder plate |1 |Hold ball bearings | |SUS304 |
|21 | | |4.7 |Torque Limiter |4 |Hold bearing holder|4 springs to privide uniform flex |SUS304 |
| | | | |Springs | |plate |suport | |
|22 | | |4.8 |Torque Limiter Base |1 |Support springs | |Nylon |
| | | | |Support | | | | |
|23 | | |4.9 |Torque Limiter |2 |Hold base support to motor |N/A |
| | | | |Fasteners | | | |
|24 |5 |Drive |5.1 |Drive Left Housing |1 |Provide enclosure |Also to isolate noise |Glass-filled |
| | |Closure | | | |to drive | |nylon |
|25 | | |5.2 |Drive Right Housing |1 |Provide enclosure |Also to isolate noise |Glass-filled |
| | | | | | |to drive | |nylon |
|26 | | |5.3 |Grip Locking Switch |1 |Hold grip position | |Polypropylene |
|27 | | |5.4 |Grip Locking Spring |1 |Support grip locking switch |SUS304 |
|28 | | |5.5 |Drive Housing Long |2 |Hold housing | |N/A |
| | | | |Fasteners | | | | |
|29 | | |5.6 |Drive Housing Medium |2 |hold drive | |N/A |
| | | | |Fasteners | | | | |
|30 | | |5.7 |Drive Housing Short |2 |hold housing | |N/A |
| | | | |Fasteners | | | | |
|31 |6 |Power |6.1 |DC Motor |1 |Convert EE to Kinetic Energy |N/A |
| | |generator | | | | | |
|32 | | |6.2 |On/Off Button |1 |Connect electric | |Polypropylene |
| | | | | | |power | | |
|33 | | |6.3 |On/Off Spring |1 |Support On/Off | |SUS304 |
| | | | | | |Button | | |
|No |Syst #|System Name |Part #|Part Name |Quantity |Function |Note |Material |
|34 | | |6.4 |F/R/S Lever |1 |Provide control for rotation direction | Polypropylene |
|35 | | |6.5 |F/R/S Switch Circuit |1 |Control polarity connection to battery |PS (Polystyrene)|
|36 |7 |Bit Holder |7.1 |Collet |1 |Transmit torque |Also to hold bit |SUM |
|37 | | |7.2 |Bit Holder Housing |1 |Provide housing to drive mechanism |PS (Polystyrene)|
|38 | | |7.3 |Direction Stopper |2 |Hold PG3 carrier |To allow counter rotation |SUS304 |
| | | | |Clips | | | | |
|39 | | |7.4 |Direction Stoppper |4 |Hold stopper clips | |PS (Polystyrene)|
| | | | |Supports | | | | |
|40 | | |7.5 |Screwdriver bit |1 |Act on screw | |SUM |
|41 |8 |Transmission|8.1 |Planetary Gear 1 |1 |Enclose pinion | |SUS304 |
| | | | |(PG1) Washer | |gears | | |
|42 | | |8.2 |PG1/PG3 Pinion Gears |6 |Increase torque | |SMF |
|43 | | |8.3 |PG1 Internal Gears |1 |Coordinate pinion |Allows all pinion gears to rotate |SMF |
| | | | | | |gears |along its internal gear | |
|44 | | |8.4 |PG1 Carrier/PG2 Sun |1 |Hold pinion gears |Also transmit torque |SUM |
| | | | |Gear | | | | |
|46 | | |8.5 |PG2 Pinion Gears |3 |Reduce speed | |SMF |
|47 | | |8.6 |PG2 Washer |1 |Enclose pinion | |SUS304 |
| | | | | | |gears | | |
|48 | | |8.7 |PG2 Coupling Gear |1 |Hold pinion gears | |PS (Polystyrene)|
|49 | | |8.8 |PG2 Locking Gear |1 |Hold PG2 system | |PS (Polystyrene)|
|50 | | |8.9 |Hi/Lo Lever |1 |Transmit control |By shifting coupling gear |SUS304 |
|51 | | |8.10 |Hi/Lo Button |1 |Accept Hi/Lo | | Polypropylene |
| | | | | | |control | | |
|52 | | |8.11 |Hi/Lo Fasteners |2 |Hold Hi/Lo lever | |N? |
|53 | | |8.12 |PG2 Carrier/PG3 Sun |1 |Hold pinion gears | |SUM |
| | | | |Gear | | | | |
|54 | | |8.13 |PG3 Washer |1 |Enclose pinion | |SUS304 |
| | | | | | |gears | | |
|55 | | |8.14 |PG3 Internal |1 |Coordinate pinion |Allows all pinion gears to rotate |SMF |
| | | | |Gear/Direction | |gears |along its internal gear | |
| | | | |Openner | | | | |
|56 | | |8.15 |PG3 Carrier |1 |Hold pinion gears | |SUM |
|2.4. Exploded View |
[pic]
Figure 7. Exploded view of Transmission Sub-assembly.
|3. Report #3: Assembly Sequence |
|3.1 Revised Liaison Diagram |
[pic]
|3.2 Revised Datum Flow Chain |
[pic]
|3.3 All Possible Assembly Sequence |
|[pic] |[pic] |
|3.4 The Most Conveniencee Assembly Sequence |
[pic]
|3.5 Required Gross and Fine Motions |
The Gross and Fine motions are estimated using the Boothroyd & Dewhurst DFA table as follow.
[pic]
The Boothroyd and Dewhurst DFA suggest total assembly time of 226.89 seconds or 3 minutes and 46.89 seconds. The actual manual assembly experiments by us took about 4 minutes and 30 seconds without putting any grease.
|3.6 Futures, Chamfers and Lead ins |
|Feature Number |Part No. |Part A |Part No. |Part B |Chamfers and |MATE/ |Comments |
| | | | | |Lead-ins |CONTACT | |
|1 |7.2 |Bit Holder Housing |8.16 & 7.1|Carrier & Bit |Not Applicable |Mate(5) |Peg & Hole |
| | | | |Holder | | | |
|2 |7.2 |Bit Holder Housing |8.15 |PG3 Ring Gear |N. A. |Mate(5) |Peg & Hole |
|3 |8.16 & 7.1 |Carrier & Bit Holder |8.2 |Pinion Gears |N. A. |Mate(5) |3 Peg & Holes for 3 pinions |
|4 |8.2 |Pinion Gears |8.13 |PG2 Carrier/PG3 Sun|Chamfer and Lead-in |Mate(5) |Over-constrained Dofs, Clearance |
| | | | |Gear |on all 3 Pinion | | |
| | | | | |Gears and on Sun | | |
| | | | | |Gear | | |
|5 |8.2 |Pinion Gears |8.14 |Washer |N. A. |Mate(3) |Overlap of 2 plates, Over-Cons. With |
| | | | | | | |#7 |
|6 |8.15 |PG3 Ring Gear |8.2 |Pinion Gears |Chamfer and Lead-in |Mate(4) |Over-constrained Dofs, Clearance |
| | | | | |on all 3 Pinion | | |
| | | | | |Gears and on | | |
| | | | | |Internal Gear | | |
|7 |8.15 |PG3 Ring Gear |8.14 |Washer |N. A. |Mate(3) |Overlap of 2 plates, Over-Cons. With |
| | | | | | | |#5 |
|8 |8.14 |Washer |8.13 |PG2 Carrier/PG3 Sun|N. A. |Mate(3) |Overlap of two Plates |
| | | | |Gear | | | |
|9 |8.13 |PG2 Carrier/PG3 Sun Gear|8.6 |PG2 Pinion Gears |N. A. |Mate(5) |3 Peg & Holes for 3 pinions |
|10 |7.2 |Bit Holder Housing |8.9 |PG2 Locking Gear |N. A. |Mate(5) |Peg & Hole |
|11 |7.2 |Bit Holder Housing |8.1 |Hi/Lo Lever |N. A. |Mate(5) |Peg & Hole |
|12 |8.6 |PG2 Pinion Gears |8.7 |PG2 Washer |N. A. |Mate(3) |Overlap of 2 plates, Over-Cons. With |
| | | | | | | |#14 |
|13 |8.6 |PG2 Pinion Gears |8.4 |PG1 Carrier/PG2 Sun|Chamfer and Lead-in |Mate(5) |Over-constrained Dofs, Clearance |
| | | | |Gear |on all 3 Pinion | | |
| | | | | |Gears and on Sun | | |
| | | | | |Gear | | |
|14 |8.7 |PG2 Washer |8.4 |PG1 Carrier/PG2 Sun|N. A. |Mate(3) |Overlap of 2 plates, Over-Cons. With |
| | | | |Gear | | |#12 |
|15 |8.6 |PG2 Pinion Gears |8.8 |PG2 Coupling Gear |Chamfer and Lead-in |Mate(5) |Over-constrained Dofs, Clearance |
| | | | | |on all 3 Pinion | | |
| | | | | |Gears and on | | |
| | | | | |Coupling Gear | | |
|16 |8.4 |PG1 Carrier/PG2 Sun Gear|8.2 |PG3 Pinion Gears |N. A. |Mate(5) |3 Peg & Holes for 3 pinions |
|17 |8.2 |PG3 Pinion Gears |8.1 |Pinion Gears 1 |N. A. |Mate(3) |Overlap of 2 plates |
| | | | |Washer | | | |
|18 |8.2 |PG3 Pinion Gears |4 & 6 |Torque Limiter & |Chamfer and Lead-in |Mate(5) |Gear mate |
| | | | |Power Generator |on all 3 Pinion | | |
| | | | | |Gears and on Sun | | |
| | | | | |Gear of Power | | |
| | | | | |Generator | | |
|19 |8.1 |Pinion Gears 1 Washer |8.3 |PG1 Ring Gear |N. A. |Mate(3) |Overlap of 2 plates |
|20 |8.3 |PG1 Ring Gear |4 & 6 |Torque Limiter & |N. A. |Mate(3) |Overlap of 2 plates |
| | | | |Power Generator | | | |
|21 |8.1 |Hi/Lo Lever |8.8 |PG2 Coupling Gear |N. A. |Mate(1) | |
|22 |8.13 |PG2 Carrier/PG3 Sun Gear|8.8 |PG2 Coupling Gear |Chamfer and Lead-in |Mate(5) |Gear mate |
| | | | | |on Sun Gear and on | | |
| | | | | |Coupling Gear | | |
|23 |8.9 |PG2 Locking Gear |8.8 |PG2 Coupling Gear |Chamfer and Lead-in |Mate(6) |Properly constrained |
| | | | | |on Locking Gear and | | |
| | | | | |on Coupling Gear | | |
|24 |7.2 |Bit Holder Housing |8.8 |PG2 Coupling Gear |N. A. |Mate(3) |Oversize hole |
|25 |7.2 |Bit Holder Housing |8.3 |PG1 Ring Gear |N. A. |Mate(3) |Oversize hole |
|26 |7.2 |Bit Holder Housing |4 & 6 |Torque Limiter & |N. A. |Mate(6) |Properly constrained |
| | | | |Power Generator | | | |
|27 |8.2 |PG3 Pinion Gears |8.3 |PG1 Ring Gear |Chamfer and Lead-in |Mate(5) |Gear mate |
| | | | | |on all 3 Pinion | | |
| | | | | |Gears and on | | |
| | | | | |Internal Gear | | |
Description of Chamfers and Lead-ins on Features:
1. Pinion Gears and Sun Gear (Feature #04, #13, #18): Chamfers and Lead-ins are provided on the Pinion Gears and Gun Gear in order to avoid jamming during assembly. Once the assembly operations are over, chamfer plays no role.
2. Pinion Gears and Internal Gear (Feature #06, #27): Chamfers and Lead-ins are provided on the Pinion Gears and Internal Gear to ensure the ease of assembly. Chamfer plays no role during the actual operation of mechanism.
3. Pinion Gears and Coupling Gear (Feature #15): Chamfers and Lead-ins avoid the jamming of these two parts during assembly. They play no role after the product has been assembled.
4. Sun Gear and Coupling Gear (Feature #22): Here, Chamfers and Lead-ins have functional importance. The connection between Sun Gear and Coupling Gear is not permanent. It is established when the Coupling Gear is moved to achieve higher speed. So, the proper chamfer angle and lead-in are very important. They should be chosen in such a way that the connection between Sun Gear and Coupling gear is established irrespective of the angular position of Coupling Gear with respect to Sun Gear.
5. Coupling Gear and Locking Gear (Feature #00): Here again, Chamfers and Lead-ins have functional importance. The connection between Locking Gear and Coupling Gear is established when the Coupling Gear is moved to achieve lower speed. Coupling Gear and Locking Gear together form the Internal Gear and they act as one functional unit in this situation. So, the proper chamfer angle and lead-in are very important. They should be chosen in such a way that the connection between Locking Gear and Coupling gear is established irrespective of the angular position of Coupling Gear with respect to Locking Gear.
|3.7 Difficulties & Ideas in Assembly |
In general, the following alternatives might be considered to eliminate difficult to assemble parts:
❑ Modify assembly sequence or architecture to eliminate difficult to access assembly steps.
❑ Modify assembly sequence or architecture to reduce lengthy assembly time.
❑ Examples of the above approaches may lead to the following changes:
❑ Modify the stacking of planetary gear sets. This step requires architectural changes as discuss in the next section.
❑ Commonize and minimize fasteners.
❑ Eliminate washers.
❑ Avoid the use of fixtures/tools by finding assembly sequence alternatives.
❑ Eliminate reorientation by choosing assembly sequence that requires less number of reorientations.
❑ Eliminate multiple greasing steps.
The following are some of the possible problems and resolutions.
|Liaison # |Part A |Part B |Possible Problems/risks |Possible solutions |
|16 |8.2 |8.16 |Insertion in deep and narrow hole, blind |Separate 7.2 Bit Holder Housing to two cylinders |
| | | |operation |Develop gripper to improve operation (see fig #5) |
|18 |8.6 |8.13 |Insertion in deep and narrow hole, blind |Separate 7.2 Bit Holder Housing to two cylinders |
| | | |operation |Develop gripper to improve operation (see fig #5) |
|27 |6.1 |8.2 |Need to jiggle the motor assembly to get proper|Change the assembly sequence by mating pinion gears to motor assembly|
| | | |gear mating , blind operation |shaft. |
|17 |8.13 |8.2 |Need to jiggle the motor assembly to get proper|Change the assembly sequence by mating pinion gears to motor assembly|
| | | |gear mating |shaft. |
|30 |8.8 |8.10 |Mating 8.10 to 8.8, because 8.8 is so free to |Use fixture to constrain 8.8, Coupling gear. |
| | | |be positioned correctly, and obstructed view | |
|3.8 Feature Parts and Associated Assembly Tool and Fixtures |
The insertion tool, T-2, shown in Figure 5.a is used for loading multiple part into the transmission housing (7.2) during the transmission gear assembly build sequence. The gripper tool design can be used for loading all pinion carrier gears and ring gears.
The parts in the following table will loaded using T-2.
|Subsystem |P/N |Description |Gripping feature |
|Transmission |8.3 |PG1 Ring Gears |Inside diameter |
|Transmission |8.4 |PG1 Carrier |3 pinion shafts |
|Transmission |8.8 |PG2 Coupling Gear |Inside diameter |
|Transmission |8.9 |PG2 Locking Gear |Inside diameter |
|Transmission |8.13 |PG2 Carrier |3 pinion shafts |
|Transmission |8.15 |PG3 Ring Gear |Inside diameter |
The T-2 gripping tool is a spreader design. When tool is in a free (un-gripped) state, the tips of the tool, which contact the part, are in a closed position (see Figure 5.a). This position is maintained at free state by a spring above the tool pivot point.
When gripping pinion gear carriers, the tool is placed between the 3 pinion gear pins and loaded until the tool spreads to make sufficient contact (see Figure 5.a).
When gripping ring gears, the tool is placed anywhere on the inside diameter and loaded until tool spreads to make sufficient contact (see Figure 5.a).
The Pinion Gear Insertion Tool, T-1, shown in Figure 5.b, is used to insert pinion gears into the transmission housing (7.2). This tool is designed with magnetic inserts placed at two different depths to allow for diameters and lengths corresponding to both size pinion gears (8.2 and 8.6). Once the pinion gear has been loaded into the tool and onto a carrier pin, the button on the top of the tool is pressed by the operator to actuate the ejector pin. This motion extracts the pinion gear from the magnet, leaving it in final assembly position.
The transmission housing holding fixture, F-1, shown in Figure 5.c holds and orients the transmission housing (7.2) during transmission assembly buildup. The fixture is hard mounted to the table in a work-cell in front of the operator. The operator mates the housing to the fixture by pushing the collet onto a pin at the base of the fixture. Fixturing the housing prior to gear assembly buildup allows the operator full use of both hands for loading parts into housing.
|3.9. Fixtures and Tools for Assembly |
|[pic] |[pic] |
|Figure 5.a. Tool T-2 |Figure 5.b. Tool T-1 |
| | |
| |[pic] |
| |Figure 5.c. Fixture F-1 |
|3.10 Gear Set Architecture Redesign |
|Original Architecture |Redesigned Architecture |
|[pic] |[pic] |
|3.11 Improvement highlight |
Planetary gear sets are rearranged by moving the Planetary Gear Set #1 next to the Planetary Gear Set #3. This new architecture results in significant part reduction and part integration (function sharing, see item #4 below). The redesign also requires some feature changes as described below.
1. Increasing the length of PG3 ring gear (8.15) to contains both planetary gear #1 and #3. Significant improvement is achieved by:
❑ Eliminating PG3 washer (8.14)
❑ Eliminating locking gear (8.9) by putting its functionality into PG2 Ring Gear (8.3)
2. Feature modification of PG1 carrier (8.4) to fit PG3 planetary gears and PG3 Ring gear.
3. Combining the function of locking gear (8.9) into (8.3)
4. Modification of sun gear at the motor shaft to fit PG2 planetary gears (8.6)
5. Shortening the length of bit holder housing (7.2) results the following benefits:
❑ The assembly of the planetary gear sets #1 and #2 becomes much easier (eliminating deep insertions)
❑ Eliminating multiple greasing steps.
The new architecture also provides significant assembly cost benefit by
❑ Eliminating special tools required in the current design.
❑ Reduction in the time required assembling the modified product.
|4. Report #4: Assembly Floor Layout Analysis |
The following report steps through the analysis required to propose a feasible plant layout to effectively perform operations necessary to assembly package and ship the Sears Craftsman Screwdriver. The team broke the analysis into 3 primary tasks in order to provide the necessary information for a viable operations solution. These analysis activities are outlined in the report as follows:
❑ Assembly Sequence
❑ Assembly Process time
❑ Assembly Line Design and Assumptions
|4.1. Assembly Sequence |
The assembly sequence chosen for the Sears Craftsman Screwdriver are shown in Figures 1 and 2. This sequence was chosen because it was conducive to an efficient flow of assembly operations that were consistent with the overall operations strategy. The sequence allowed for easily "chunking" assembly task into workcells that allowed for optimal assembly line balance. This sequence also allowed the workcell subassemblies to be robust against damage or loss of parts during transition to downstream operation.
[pic]
Figure 1 – Assembly Sequence Tree
[pic]
Figure 2 -Transmission Sub-Assembly Sequence Tree
|4.2 Assembly Process time |
Assembly times were determined using Boothroyd & Dewhurst DFA tables (see Figures 3,4,&5). These techniques used associated times correlated to previously determined manual insertion and handling codes. Once these times were determined, decisions were made as to what workstations needed to be developed for an optimal work flow and assembly line balancing. These decisions were also based on product architecture and interfaces between subsystems, which allow easy and robust transfer to the downstream workstation.
[pic]
Figure 3 - Testing and Packaging
[pic]
Figure 4 - Final Assembly Process Time
[pic]
Figure 5 - Transmission Assembly Process Time
It can be seen from the total assembly times found in the above tables that a total process cycle time of approximately 60-70 seconds should be targeted. The grip housing assembly process time, although not shown in this report, was calculated using the same method and found to be approximately 70 seconds. With this information the workstations were determined to be the following :
Grip Housing Assembly (1 workstation)
Transmission Assembly (3 workstations)
Final Assembly (1 workstation)
Testing and Packaging (1 workstation)
|4.3 Assembly Line Design and Assumptions |
Production Volumes were estimated by gathering information about the product distribution network. This information was found from the Sears website. The table below summarizes all retail outlets where the products are sold in the 2 key markets of U.S and Canada. Phone surveys were then conducted to gain a reasonable estimate of the average number of units sold per month at these outlets.
Estimated Sales Amounts 8,358 /month
Estimated Production 379.9 /day (22 working days/month)
4.3.1 Design Parameters
Considering the estimated production size and the product packaging size, factory-out distribution of this product will be less than once a day and the batch size should be defined assembly process.
Parts supply: Parts for one day production are brought to the working area
by full-time worker, who is also responsible to other production
Batch: 95 units (4 batches/ day)
Set-up time 10 min./batch to carry parts from in-house inventory to each
workstation
Working time :7.5 hours/day (actual working time put off recesses)
Assumptive Cycle Time (temporary setting for designing)
Cycle time/ unit (7.5 hours/day) / (379.9 units/day ) = 71.1 sec.
Cycle time/ batch (Process time/ # of workers) * (95 units) + 10 min. < 71.1*95 sec.
(1 hours and 53 min., 4 batches/ day)
4.3.2 Supplied Material
It was estimated that supplied materials are all part level and all handicrafts are performed in house because of following observations:
▪ This product is made in China, in which labor cost is generally low.
▪ Since this product is an integrated product, possible outside sub-assembles are Battery Assembly and Grip Housing Assembly. However, if these are out-sourced, in comparison, Transmission Assembly operation requires too long time, even if separated to two workstation, and other assembly operations become too simple.
|4.4 Assembly operation style |
Given that the annual production volumes were relatively low for a mass production product and that the assembly operations are in China where labor cost is very low, automated assembly operations were ruled out as a cost-effective means of assembly.
4.4.1 Assembly Line Design
Considering Assumptive Cycle Time, there is no need to organize highly sequential line, however, too much individual workstations increase overheads. To balance minimizing equipment cost and overhead cost, General Assembly Flow becomes as follows:
The production workflow starts with an inventory stockpile that supplies approximately 1 shift of production (see Figure 7 - A). Inventory is transferred manually by laborers to supply all workcells during the shift. Enough inventory is transferred to workcells to supply a batch size of 95 units. This is because the space for stocking inventory is limited at the workcell tables. Also, this allows for the recirculation of the transmission housing fixtures, which are limited in number to approx. 100 to minimize investment cost (see line 1 dotted). The details of these fixtures, T-1, are shown in project report #3.
Workcell B assembles the grip housing assembly concurrently with wokcells C,D&E which assemble the transmissions. These 4 workcells are positioned around a common conveyor system that feeds into a "pool" for use by the final assembly workcell (F). This conveyor system consists of an inclined set of rollers or possibly a steel chute. It is approximately 6 meters in length, so an automated transfer system is not necessary. It is important to note that 3 workcells were used to assemble the transmissions to achieve proper assembly line balancing. This strategy was needed because cycle time for transmission assembly was 185 seconds (218 sec. without tool efficiency, see Figure 6). By having 3 workcells the combined cycle time becomes 62 seconds. This is less than the 72 seconds required for final assembly, which will prevent build up of inventory.
Note: Holding fixtures are used to hold the transmission gear assembly vertical. These fixture are placed on the conveyor along with assembled workpiece. After going through final assembly, these fixtures are recirculated to workcells C,D, and E by a manual labor head.
Workcell F is the place for final assembly. The transmission assembly is picked up and motor is assembled with it. The grip housing assembly is picked up next and it is assembled with it. Other part of the housing is snap fitted on to rest of the sub-assembly.
Workcell G stores the fixtures being used in the transmission assembly These fixtures are sent back to the workcells C,D and E.
Workcell H is for packaging and testing. The fully assembled screwdrivers are picked from workcell G and they are tested both in high speed and low speed operating conditions.
[pic]
Figure 6 –Assembly Flow Diagram
[pic]
Figure 7 –Floor Layout
[pic]
Figure 8 –Workstation table Design
|5. Report #5: Workstation Design |
|5.1 Required cycle time to complete the planned operations |
Following Assembly Flow Diagram shows cycle time for all the operations involved in screwdriver sub-assemblies, final assembly and testing/packing. For more details please refer to individual charts.
5.1.1 Assembly Flow Diagram
[pic]
5.1.2 Final Assembly
[pic]
5.1.3 Testing and Packaging
[pic]
5.1.4 Transmission Assembly
[pic]
5.1.5 Grip Housing/Battery Assembly
[pic]
It can be seen from the total assembly times found in the above tables that a total process cycle time of approximately 60-70 seconds should be targeted. With this information the workstations were determined to be the following:
Grip Housing Assembly (1 workstation)
Transmission Assembly (3 workstations)
Final Assembly (1 workstation)
Testing and Packaging (1 workstation)
Tr1: Transmission Assembly Workstation #1:
Tr2: Transmission Assembly Workstation #2: 61.84 sec.
Tr3: Transmission Assembly Workstation #3:
Bat: Grip Housing/Battery Assembly Workstation: 69.69 sec.
Fin: Final Assembly Workstation: 72.34 sec.
T&P: Testing and Packaging Workstation: 68.69 sec.
Inp: Input Component Inventory, Out: Finished Good Inventory
• We have provided a small buffer (storage) between workstations to protect for process uncertainties, therefore the cycle time of assembly line is directly obtained as a longest cycle time among workstations.
• Cycle Time of Assembly Line = 72.34 sec.
• Critical Workstation is Final Assembly, which is located the second sequence
|5.2 Station lay out: in and out flows of assemblies and parts |
In this report we are focusing on "Transmission assembly". The workstation layout and other details are shown in following diagrams.
Workstation table Design
[pic]
[pic]
|5.3 Required motions of equipment and people |
Evaluation of required motions according to various criteria is very important in manual assembly. The criteria can be summarized under following topics:
Right and left hand should be operative for the same amount of time.
Motions of right and left hand should be synchronized. I.e. the motions of right and left hand should be in succession.
The arm movement should be minimized. The maximum movement of arm should be with in the reach of operator.
The movement of the operator in the workstation area should be minimized.
Parts should be placed in bins in such a way that they can be picked by the operator in correct orientation without any difficulty. I.e. parts should not entangle with themselves in the bins.
These are some of the rules of “motion and time study” which have been given attention while designing the “transmission workstation”. The slides show the configuration of the workstation. Following is the brief summary of the hand motions:
The initial step for the operator is to place the transmission holding fixture (F-1) on the table in front of himself. These fixtures are supplied from the other side of the table where they are loaded onto a spring-loaded riser that feeds the fixtures down an angled chute. These fixtures are continuously being circulated from the final assembly workstation where the finished transmission assembly is removed from the fixture.
Pick up the Bit Holder Housing (BH Housing 7.2) from right hand and shift it to the left hand.
Pick up the T-1 Insertion Tool with right hand.
Pick up PG1 Internal Gear (8.3) with the help of T-1 insertion tool with right hand while putting the BH Housing (7.2) in the Fixture with left hand.
Insert the PG1 Internal Gear (8.3) in the BH Housing (7.2) with right hand.
Put the T-1 Insertion Tool down and pick T-2 Insertion Tool in right hand.
Pick up the PG1 Pinion Gears (8.2) with the help of T-2 Insertion tool and insert them one by one with right hand.
Pick up the Grease Gun in the left hand and put grease in the sub-assembly.
Pick up the PG1 Washer (8.1) with left hand and drop it in the BH Housing (7.2).
Pick up the PG1 Carrier (8.4) with the help of T-2 Insertion tool with right hand and insert it.
Pick up PG2 Pinion Gears (8.6) with the help of T-2 Insertion Tool and insert them one by one.
Pick up PG2 Coupling Gear (8.8) with the left hand, grip it with T-2 Insertion Tool and insert it.
Pick up PG2 Locking Gear (8.9) with the right hand, grip it with T-2 Insertion Tool and insert it.
Pick up the Grease Gun in the left hand and put grease in the sub-assembly.
Pick up the PG2 Washer (8.7) with left hand and drop it in the BH Housing (7.2).
Pick up the PG2 Carrier (8.13) with the help of T-2 Insertion Tool with right hand and insert it.
Pick up PG3 Pinion Gears (8.6) with the help of T-2 Insertion tool and insert them one by one.
Pick up the PG3 Washer (8.14) with left hand and drop it in the BH Housing (7.2).
Pick up the PG3 Internal Gear with left hand and drop it in the BH Housing (7.2).
These are the steps required for the assembly process. Both of the hands have been used intermittently. This sequence has been developed by assuming that the operator is left-handed. If this is not the case, one needs to simply shift the bins on the right to the left and vice-versa. The jobs assigned to the right hand will then be done by left hand. The motion has been kept as synchronized as possible. More importantly, the location of feeder bins containing the Pinion Gears has been designed very close to the right hand of the operator because there are nine pinion gears in total in the part.
Finally, the operator needs to put the finished sub-assembly along with the fixture on the conveyor.
|5.4 Necessary inspections or tests |
Screwdriver testing is done as a part of testing and packaging operation. We decided to test fully assembled screwdriver at "Packaging" station in order to balance times on the assembly line. The testing involves following steps:
The fully assembled screwdrivers are picked from workcell
Test high speed and low speed operating conditions
Test Forward and Reverse feature
Test Adjustable Torque feature (Torque Limiter)
Test dual-position handle and pistol-grip lock feature
After passing the test they are placed in cardboard bin (screwdrivers which fail are kept in a "rework" bin.
|5.5 Gantt chart of required time of activities and a complete cycle |
The complete assembly process is shown in the following diagram where the sequence is bottom-up. The assembly sequence was then broken down in to specific assembly activity steps and a "Gantt" charts were created.
[pic]
Assembly sequence
Assembly process design mainly follows 1) required cycle time, which is obtained from planned production size, 2) modularity, the mass of assembly sequence which is difficult to be separated, 3) efficiency in assembly motions and equipment cost.
In this case, we designed the assembly process from following observations:
Required Cycle Time
As shown in the last report, planned production size is 8358 units/month, therefore;
(7.5 hours/day) / (379.9 units/day) = 71.1 sec.
Modularity
Transmission Assembly is toughly integrated and hard to separate to two or more workstations. Estimated assembly time for this module is 218 sec., which is approximately three times of Required Cycle Time.
Efficiency
One thought to solve modularity problem in Transmission Assembly is organizing three parallel lines all of which perform full assemble sequence.
In this case, estimated impact on the equipment cost is small since our assumption of line designing is full handcraft line. However, motional efficiency must be worse since small motions, for example, transmission assembly, and large motions, for example, packaging and carrying the packaged products to the storage, are combined in each workstation.
Finally, we used following logic to design the assembly process:
Organize three transmission assembly workstations to meet Required Cycle Time.
Organize packaging workstation to separate large motions from small assembly motions.
Organize workstations gathering other activities to meet Required Cycle Time.
The designed assembly process logic is shown in the following figure. For cycle time calculations please refer to section 5.1.
[pic]
The timing of the process is shown in the following Gantt chart.
[pic]
Where
T1: Transmission Assembly #1, T2: Transmission Assembly #2, …
B1: Battery Housing Assembly #1, B2: Battery Assembly #2, …
F1: Final Assembly #1, F2: Final Assembly #2, …
P1: Testing and packaging #1, P2: Testing and packaging #2, …
Where the detailed subprocesses is shown in the following Gantt charts. The timing scale is shown in seconds.
Final Assembly Timing
[pic]
Testing and Packaging Timing
[pic]
Transmission Assembly Timing
[pic]
Grip Housing/Battery Assembly Timing
[pic]
The timing represented in the above Gantt chart is acquired from motion and time study using Boothroyd & Dewhurst's DFA database as shown in the tables in section 5.1.
|5.6 Cost estimation of workstations |
The screwdriver assembly line consists of standard equipment except small parts cases. The estimated purchase and installation costs are as follows:
[pic]
|5.7 Estimation of the cost of performing one assembly cycle |
Original assembly cycle time and cost to perform one assembly are obtained using following formula:
(Transmission AT+Grip Housing AT+Final AT+Packaging & Testing AT)*Labor Rate
= (218.26*85% + 69.69 + 72.34 + 68.69)*(1/3600)*@1.3
= (396.24 sec.)*(1/3600)*@1.3
= $0.143
where;
AT: Assembling Time
1/3600: Seconds to hours translation
85%: 15% tool efficiency
@1.3: $1.3/hour Chinese labor rate
However, actual assembling cost follows Cycle Time of Assembly Line, and it’s obtained with following formula:
(Longest Cycle Time)*(# of Workers)*Labor Rate
= (72.34)*6*(1/3600)*@1.3
= (434.04 sec.)*(1/3600)*@1.3
= $0.157
Where, the overhead of designed assembly line to the ideal assembly is 9.5%.
= (434.04 – 396.24) / 396.24
|6. Report #6: Economic Analysis and Assembly Line Simulation |
|6.1 Economic analysis of this assembly layout |
As shown in following table this assembly line consists of standard equipment except small parts cases. The estimated purchase and installation costs are as follows:
[pic]
(Equipment and Installation costs) / (Production amount: units/year)*(5 years)
= $13,054/((6,490 units/month)*(12 months)*(5 years))
= $0.0202 per unit
*1: This 5 years is an assumptive lifecycle of this product, and means that this equipment is used only for this product, even though many of equipment are reusable to other products.
6.1.1 Estimated Manufacturing Cost
Assembling cost follows Cycle Time of Assembly Line and Set-up Time, which is needed for every batch to supply materials. This cost is calculated with following formula:
((Longest Cycle Time)*(# of Workers) + (Set-up Time)/(Batch size))*Labor Rate
= (72.34)*6*(1/3600)*@1.3
= ((434.04 sec.)*(1/3600) +((15 min.)/(95 units))*(1/60))*@$1.3
= $0.1601 per unit
where;
1/3600: Seconds to hours translation
1/60: minutes to hours translation
@$1.3: $1.3/hour Chinese labor rate
Adding on this, we assume success rate of assembly line to 95% including spec out assembly, equipment down time, and operational delay.
Therefore, actual assembly cost is:
$0.1601/0.95
= $0.1685 per unit
Furthermore, managing costs are usually required to design the assembly line and handle the products. If we suppose that 0.1 manpower/day, whose labor rate is $3.5, is required in average for this product, the managing cost becomes as follows:
((Required managing manpower/day)*(Labor Rate)*(Working hours))
/ (Daily production amounts)
= ((0.1 man/day)*@$3.5*6.93)/((6490 units/month)/(22 working days/month)
= $0.0157 per unit
where;
working hours =(72.34sec/unit)*(295units/day)+(15min)*(4batchs) = 6.93
We don’t include other costs such as land space cost or indirect stuff cost to the manufacturing costs.
6.1.2 Inventory Cost and Distribution Cost
As we mentioned in previous report, this manufacturing system includes in house inventories for materials and finished products.
And, of course, distribution cost is also required to supply products to SEARS shops.
However we directly assume these costs as follows since it’s quite difficult to estimate all numbers relating to these factors reasonably.
Material inventory cost: $0.01 per unit
Finished product inventory cost: $0.03 per unit
Distribution cost: $0.60 per unit (primarily shipping cost from China to U.S)
6.1.3 Development Cost
We assume that this product was designed in the U.S. under the following conditions:
Engineers: 2 people
Engineering labor rate: $10,000 /man-month
Duration: 6 month (including from concept designing to drawing)
Prototype modeling cost: $3,000
The development cost per unit is calculated as follows:
((2 engineers)*(6 month)*($10,000 /man-month) + $3,000)
/ ((6,490 units/month)*(12 months)*(5 years))
= $0.3546 per unit
We don’t consider other costs as follows:
Designing equipment cost, including housing, energy, and devices such as CAD
Managing cost
Indirect stuff cost
Designing supply chain cost, such as negotiating with suppliers and establishing delivery route
6.1.4 Unit Part Costs
|[pic] |
6.1.5 Economic Analysis
The engineering economic analysis for the payback period and Internal Rate of Return is shown in the following table. Since the process is a manual operation with minimum initial investment cost, the analysis indicates a very favorable result in terms of payback period (9 months) and IRR (21.5%).
[pic]
|6.2 Discrete event simulation of assembly line |
6.2.1 Discrete Event Simulation: Configuration Study
The simulation layout for the complete screwdriver assembly is shown in the following figure.
[pic]
From previous report, it is estimated that the required assembly cycle is about 70 second per assembly. Bot of the assembly speeds of "Grip Housing Assembly" and the "Final Assembly" are about 70 seconds. To balance the assembly speed, the "Testing" and "Packaging" stations are combined to reach assembly speed of 70 seconds. Because the speed of assembling grip housing is three times the speed of assembling transmission module, three "Transmission Assembly" stations are employed to balance the total assembly speed.
The final assembly testing is done at the end of the assembly considering that the sub-module testing impractical. That is, the transmission assembly and the grip housing assembly cannot be tested separately. If the assembly is failed upon the testing, the product is sent to the repair station. The repair station is going to "retest", "disassemble", and "reassemble" the product. The repair results are sent back to the "Buffer 5" to be packaged. It is assumed that 1 out of 100 final assembly will have to be repaired.
The statistics and capabilities of each station in the assembly process are summarized in the following table. The capacity of the buffers were set according to the required size from some simulation runs (see the histograms below).
|No. |Name |Process (seconds) |Failure (seconds)[1] |Repair (seconds)[2] |Remark |
|1 |In 1 (Inou_1) |Constant rate = 80/s |- |- |Transmission components |
|2 |In 2 (Inou_2) |Constant rate = 80/s |- |- |Grip Housing components |
|5 |Transmission Assembly 1 |Normal (μ = 218, σ = 21.8)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| |(Mach_5) | | |200) | |
|6 |Transmission Assembly 2 |Normal (μ = 218, σ = 21.8)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| |(Mach_6) | | |200) | |
|7 |Transmission Assembly 3 |Normal (μ = 218, σ = 21.8)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| |(Mach_7) | | |200) | |
|8 |Grip Housing Assembly |Normal (μ = 69.7, σ = 7) |Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| |(Mach_8) | | |200) | |
|11 |Final Assembly (Mach_11) |Normal (μ = 72.7, σ = 7.3)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| | | | |200) | |
|13 |Testing & |Normal (μ = 68.7, σ = 6.9)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| |Packaging (Mach_13) | | |200) | |
|15 |Repair (Mach_15) |Normal (μ = 1200, σ = 300)|Normal (μ = 7200, σ = 900)|Log-Normal (μ = 900, σ = | |
| | | | |200) | |
|3 |Buffer 1 (Buff_3) |Capacity = 24 | | |Transmission component |
| | | | | |buffer |
|4 |Buffer 2 (Buff_4) |Capacity = 30 | | |Grip housing component |
| | | | | |buffer |
|9 |Buffer 3 (Buff_9) |Capacity = 24 | | |Finished transmission |
| | | | | |assembly buffer |
|10 |Buffer 4 (Buff_10) |Capacity = 30 | | |Finished grip housing |
| | | | | |assembly buffer |
|12 |Buffer 5 (Buff_12) |Capacity = 30 | | |Finished screwdriver |
| | | | | |assembly buffer |
|14 |Buffer 6 (Buff_14) |Capacity = 5 | | |Repair buffer |
|1 |Out (Inou_1) |- |- |- |Packaged screwdrivers |
Because the limitation of the student version of Taylor II software to allow only up to 15 elements, the "Out" element after the successful "Testing and Packaging" is combined with the "Inp 1." The Taylor II layout model is shown in the following figure.
[pic]
An example of simulation run result is shown below.
screwd4 Taylor II Element report Date: 27-11-1999 Time: 22:30
=============================================================================
Cluster Elnr Elname Produced AvgQueue Util Down
-------- ---- -------- -------- -------- ------ ------
0 1 Inou_1 360 1.00 100.00
0 2 Inou_2 360 1.00 100.00
0 3 Buff_3 349 5.54
0 4 Buff_4 356 4.13
0 5 Mach_5 116 0.99 89.59 9.13
0 6 Mach_6 117 0.97 89.29 8.21
0 7 Mach_7 113 0.97 85.46 11.27
0 8 Mach_8 355 0.96 86.73 9.40
0 9 Buff_9 334 9.41
0 10 Buff_10 12.78
0 11 Mach_11 333 0.94 83.88 10.08
0 12 Buff_12 332 3.31
0 13 Mach_13 331 0.90 79.06 11.31
0 14 Buff_14 6 0.05
0 15 Mach_15 5 0.26 23.42 9.61
The queue utilization in each buffer is shown in the following histograms.
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
At the beginning of operation when there is nobody taking a break, the buffers are almost empty. The condition of high number of items in the buffers happened when the assembly operators start taking breaks. The large size of buffers are the main concern for the efficiency because in addition to taking space, buffers also mean a tight up capital because the work-in-process inventory is sitting idle in the factory. The length of time that a work in process inventory is sitting in a buffer is shown in the following waiting time histograms.
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
Therefore, it is preferable to minimize the amount of inventory and keeping the throughput as high as possible. This can be done by some alternatives as follows:
❑ To use the underutilized "Repair" person to do various tasks to substitute a person that is taking a break. This simulation model of this situation is too complicated for the student version to handle. Another alternative is described next.
❑ Schedule the break at the same time. Therefore, during the break, the whole assembly line is shut down so that nobody is accumulating work in progress inventory for the next station. The duration of breaks are kept the same as the previous simulation setting. That is, they are following Log-Normal distribution with mean of 15 minutes and standard deviation of 200 seconds.
screwd5 Taylor II Element report Date: 28-11-1999 Time: 12:34
=============================================================================
Cluster Elnr Elname Produced AvgQueue Util Down
-------- ---- -------- -------- -------- ------ ------
0 1 Inou_1 360 1.00 100.00
0 2 Inou_2 360 1.00 100.00
0 3 Buff_3 350 5.83
0 4 Buff_4 355 5.45
0 5 Mach_5 115 0.98 87.65 9.86
0 6 Mach_6 118 0.97 88.34 8.30
0 7 Mach_7 114 0.98 87.72 9.87
0 8 Mach_8 354 0.97 86.32 10.43
0 9 Buff_9 346 1.97
0 10 Buff_10 4.31
0 11 Mach_11 345 0.97 88.15 8.90
0 12 Buff_12 347 1.04
0 13 Mach_13 346 0.93 83.03 10.41
0 14 Buff_14 6
0 15 Mach_15 6 0.24 23.61 11.14
The queue size of each buffer is shown in the following histogram.
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
The corresponding waiting time in queue is shown in the following histogram.
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
Notice now that the required size of buffers 3, 4, 5, and 6 become much smaller than before. The size of buffers 1 and 2 are still the same because we assume that a constant stream of components are coming to these two buffers.
A more realistic situation can be simulated by assuming that the stream of components from "In 1" and "In 2" also follow random pattern with "breaks" represented by MTBF and MTTR. Negative exponential distributions are used for both the inputs to represent a constant supply with random fluctuation. The following are the results of the simulation with simulation parameters shown in the following table.
|No. |Name |Process (seconds) |Failure (seconds)[3] |Repair (seconds)[4] |Remark |
|1 |In 1 (Inou_1) |Neg. exponential, μ = 80/s|Constant every 7200 s |Log-Normal (μ = 900, σ = |Transmission components |
| | | | |200) | |
|2 |In 2 (Inou_2) |Neg. exponential, μ = 80/s|Constant every 7200 s |Log-Normal (μ = 900, σ = |Grip Housing components |
| | | | |200) | |
|5 |Transmission Assembly 1 |Normal (μ = 218, σ = 21.8)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| |(Mach_5) | | |200) | |
|6 |Transmission Assembly 2 |Normal (μ = 218, σ = 21.8)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| |(Mach_6) | | |200) | |
|7 |Transmission Assembly 3 |Normal (μ = 218, σ = 21.8)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| |(Mach_7) | | |200) | |
|8 |Grip Housing Assembly |Normal (μ = 69.7, σ = 7) |Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| |(Mach_8) | | |200) | |
|11 |Final Assembly (Mach_11) |Normal (μ = 72.7, σ = 7.3)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| | | | |200) | |
|13 |Testing & |Normal (μ = 68.7, σ = 6.9)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| |Packaging (Mach_13) | | |200) | |
|15 |Repair (Mach_15) |Normal (μ = 1200, σ = 300)|Constant every 7200 s |Log-Normal (μ = 900, σ = | |
| | | | |200) | |
|3 |Buffer 1 (Buff_3) |Capacity = 20 | | |Transmission component |
| | | | | |buffer |
|4 |Buffer 2 (Buff_4) |Capacity = 15 | | |Grip housing component |
| | | | | |buffer |
|9 |Buffer 3 (Buff_9) |Capacity = 25 | | |Finished transmission |
| | | | | |assembly buffer |
|10 |Buffer 4 (Buff_10) |Capacity = 10 | | |Finished grip housing |
| | | | | |assembly buffer |
|12 |Buffer 5 (Buff_12) |Capacity = 15 | | |Finished screwdriver |
| | | | | |assembly buffer |
|14 |Buffer 6 (Buff_14) |Capacity = 3 | | |Repair buffer |
|1 |Out (Inou_1) |- |- |- |Packaged screwdrivers |
screwd6 Taylor II Element report Date: 28-11-1999 Time: 12:55
========================================================================
Cluster Elnr Elname Produced AvgQueue Util Down
-------- ---- -------- -------- -------- ------ ------
0 1 Inou_1 317 1.00 92.64 7.36
0 2 Inou_2 304 1.00 90.34 9.66
0 3 Buff_3 317 2.65
0 4 Buff_4 304 1.95
0 5 Mach_5 110 0.92 84.24 8.09
0 6 Mach_6 105 0.84 78.18 9.14
0 7 Mach_7 99 0.79 74.12 9.14
0 8 Mach_8 304 0.83 73.06 9.81
0 9 Buff_9 304 7.46
0 10 Buff_10 1.05
0 11 Mach_11 304 0.85 76.92 8.03
0 12 Buff_12 309 1.21
0 13 Mach_13 308 0.82 73.25 10.38
0 14 Buff_14 5 0.03
0 15 Mach_15 5 0.27 23.04 11.40
The corresponding Queue size and waiting time histogram are shown in the following figure.
Queue size hitogram
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
Waiting time histogram
|No. 3 - Buffer 1 |No. 4 – Buffer 2 |No. 9 – Buffer 3 |
|[pic] |[pic] |[pic] |
|No. 10 – Buffer 4 |No. 12 – Buffer 5 |No. 14 – Buffer 6 |
|[pic] |[pic] |[pic] |
6.2.2 Selection of Final Assembly Process
To make more realistic condition, the "Input" elements "In 1" and "In 2" are assumed to supply buffers 1 and 2 in batch sizes of 20 according to an exponential distribution with rate of 900 seconds (15 minutes). This is the estimated time to move the components to the buffers of "Transmission Assembly" and "Grip Housing Assembly" stations. Using this assumption, an investigation was conducted to determine the proper size of the rest of the buffers. The important buffers will be the buffers before the bottleneck station: "Final Assembly" with the longest cycle time (72.7 seconds). The results of the investigation are summarized in the following table.
|No. |Station |Buffer size = 1 |Buffer size = 5 |Buffer size = 10 |Buffer size = 20 |
|1 |In 1 (Inou_1) |53.7 |66.25 |53.33 |48.88 |
|2 |In 2 (Inou_2) |29.24 |31.71 |29.57 |32.09 |
|3 |Buffer 1 (Buff_3) | | | | |
|4 |Buffer 2 (Buff_4) | | | | |
|5 |Transmission Assembly 1 (Mach_5) |59.9 |73.98 |76.62 |77.24 |
|6 |Transmission Assembly 2 (Mach_6) |61.72 |70.22 |77.94 |77.16 |
|7 |Transmission Assembly 3 (Mach_7) |62.14 |71.77 |75.54 |77.75 |
|8 |Grip Housing Assembly (Mach_8) |58.25 |69.74 |75.12 |74.83 |
|9 |Buffer 3 (Buff_9) | | | | |
|10 |Buffer 4 (Buff_10) | | | | |
|11 |Final Assembly (Mach_11) |60.7 |71.63 |74.94 |73.67 |
|12 |Buffer 5 (Buff_12) | | | | |
|13 |Testing & Packaging (Mach_13) |57.88 |69.98 |72.85 |70.82 |
|14 |Buffer 6 (Buff_14) | | | | |
|15 |Repair (Mach_15) |21.92 |44.68 |20 |21.55 |
| |Finish Output |244 |295 |304 |294 |
Buffer size = 10 for the bottleneck station is selected because it is not as much different from buffer size = 5 in terms of size requirement, but it provides higher utilization as well as higher throughput. Buffer #5 and #6 are set equal to 1 (no buffer) because these are not bottleneck stations. The queue and waiting time histograms for this selected setting are shown below.
Queue Histograms
|No. 3 – Buffer 1 |No. 4 – Buffer 2 |
|[pic] |[pic] |
|No.9 – Buffer 3 |No. 10 – Buffer 4 |
|[pic] |[pic] |
Waiting Time Histograms
|No. 3 – Buffer 1 |No. 4 – Buffer 2 |
|[pic] |[pic] |
|No.9 – Buffer 3 |No. 10 – Buffer 4 |
|[pic] |[pic] |
The statistics of this assembly operation is as follow.
screwd7 Taylor II Element report Date: 29-11-1999 Time: 19:55
========================================================================
Cluster Elnr Elname Produced AvgQueue Util Down
-------- ---- -------- -------- -------- ------ ------
0 1 Inou_1 320 1.00 53.33 10.02
0 2 Inou_2 320 1.00 29.57 9.82
0 3 Buff_3 307 8.77
0 4 Buff_4 313 10.84
0 5 Mach_5 102 0.86 76.62 9.11
0 6 Mach_6 102 0.84 77.94 6.48
0 7 Mach_7 100 0.85 75.54 9.37
0 8 Mach_8 312 0.98 75.12 9.06
0 9 Buff_9 302 1.55
0 10 Buff_10 9.37
0 11 Mach_11 301 0.85 74.94 9.33
0 12 Buff_12 305 0.21
0 13 Mach_13 304 0.82 72.85 9.01
0 14 Buff_14 5 0.08
0 15 Mach_15 4 0.28 20.00 10.17
In general, the utilization of the stations (around 75%) are considered appropriate for the assembly workers. The Input stations (Inou_1 and Inou_2) and the repair station (Mach_15) total utilization is about 100% (53.33% + 29.57% + 20%). These three tasks are performed by 2 people instead of 3 people. That is, Inou_2 and repair are done by the same person. A low utilization value of 50% is considered appropriate for these tasks as these people need to walk around in between jobs to transfer the raw materials.
-----------------------
[1] For all these manual operations, failure is the scheduled (allowed) break at about every 2 hours.
[2] Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed because people tend to take a longer than a shorter break than allowed.
[3] For all these manual operations, failure is the scheduled (allowed) break at every 2 hours.
[4] Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed because people tend to take a longer than a shorter break than allowed.
-----------------------
[pic]
= (Analyzed assembly time 218.26 sec.)
* (1 - tool efficiency 15%) / (3 workstations)
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