1. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 1 Ch 15 Manual Assembly Lines Sections: 1.Fundamentals of Manual Assembly Lines 2.Analysis of Single Model Assembly Lines 3.Line Balancing Algorithms 4.Mixed Model Assembly Lines 5.Workstation Considerations 6.Other Considerations in Assembly Line Design 7.Alternative Assembly Systems

2. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 2 Manual Assembly Line Defined “A production line consisting of a sequence of workstations where assembly tasks are performed by human workers as the product moves along the line”  Organized to produce a single product or a limited range of products  Each product consists of multiple components joined together by various assembly work elements  Total work content - the sum of all work elements required to assemble one product unit on the line

3. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 3 Manual Assembly Line Configuration of a manual assembly line with n manually operated workstations

4. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 4 Manual Assembly Line  Products are assembled as they move along the line  At each station a portion of the total work content (assigned tasks) is performed on each unit  Base parts are launched onto the beginning of the line at regular intervals (cycle time)  Workers add components to progressively build the product

5. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 5 Manual Assembly Lines  Factors favoring the use of manual assembly lines:  High or medium demand for product  Identical or similar products  Total work content can be divided into work elements  It is technologically impossible or economically infeasible to automate the assembly operations  Most consumer products are assembled on manual assembly lines

6. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 6 Why Assembly Lines are so Productive  Specialization of labor  Specialization of labor (division of labor)  Learning curve (a large job is divided into small tasks and each worker becomes a specialist in performing the single task)  Interchangeable parts  Components made to close tolerances  Work flow principle  Products are brought to the workers (traveling the minimum distance between stations)  Line pacing  Workers must complete their tasks within the cycle time of the line (which paces the line to maintain a specified production rate)

7. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 7 Typical Products Made on Assembly Lines AutomobilesPersonal computers Cooking rangesPower tools DishwashersRefrigerators DryersTelephones FurnitureToasters LampsTrucks LuggageVideo DVD players Microwave ovensWashing machines

8. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 8 Assembly Workstation “A designated location along the work flow path at which one or more work elements (tasks) are performed by one or more workers” A workstation also includes the tools required to perform the task assigned to the station. Typical operations performed at manual assembly stations Adhesive application Sealant application Arc welding Spot welding Electrical connections Component insertion Press fitting Riveting Snap fitting Soldering Stitching/stapling Threaded fasteners

9. Assembly Workstation Manning level of a manual assembly line, M: w= number of workers on the line n= number of stations on the line w u = number of utility workers assigned to the system (responsible for helping workers who fall behind, relieving workers for personal break, material handling tasks and maintenance and repair duties.) w i = number of workers assigned specifically to station i ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 9

10. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 10 Work Transport Systems  Two basic categories:  Manual  Mechanized Both methods provide the fixed routing (all work units proceed through the same sequence of operations) that is characteristic of production lines.

11. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 11 Manual Work Transport Systems “Work units are moved between stations by the workers without the aid of a powered conveyor”  Types:  Work units moved in batches (transfer batch)  Work units moved one at a time  Problems:  Starving of stations (waiting for a work unit)  Blocking of stations (cannot pass the work unit to the next station)  No pacing

12. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 12 Manual Work Transport Systems To mitigate the effects of these problems, storage buffers are sometimes used between stations. The trouble with this method of operation is that it can result in significant WIP, which is economically undesirable.

13. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 13 Mechanized Work Transport Systems “Work units are moved by powered conveyor or other mechanized apparatus”  Categories:  Work units attached to conveyor (large and heavy product – worker walks along)  Work units are removable from conveyor (not a fixed cyle time)  Problems  Starving of stations  Incomplete units (if the worker runs out of time)

14. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 14 Types of Mechanized Work Transport  Continuous transport  Conveyor moves at constant speed  Synchronous transport (for automated lines)  Work units are moved simultaneously with stop-and-go (intermittent) motion to next stations  Asynchronous transport  Work units are moved independently between workstations  Queues of work units can form in front of each station

15. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 15 Continuous Transport Conveyor moves at constant velocity v c

16. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 16 Synchronous Transport All work units are moved simultaneously to their respective next workstations with quick, discontinuous motion (intermittent transport). Not common for manual assembly lines, due to the requirement that the task must be completed within a certain time limit.

17. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 17 Asynchronous Transport Work units move independently, not simultaneously. A work unit departs a given station when the worker releases it. Small queues of parts can form at each station.

18. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 18 Material Handling Equipment for Mechanized Work Transport Continuous transportOverhead trolley conveyor (Ch. 10)Belt conveyor Drag chain conveyor Synchronous transportWalking beam (Ch. 16)Rotary indexing machine Asynchronous transportPower-and-free conveyor (Ch. 10)Cart-on-track conveyor Automated guided vehicles

19. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 19 Line Pacing  A manual assembly line operates at a certain cycle time. On average, each worker must complete his/her assigned task within this cycle time or else the required production rate will not be achieved.  Pacing provides a discipline for the assembly line workers that more or less guarantees a certain production rate for the line  Several levels of pacing: 1.Rigid pacing 2.Pacing with margin 3.No pacing

20. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 20 Rigid Pacing  Each worker is allowed only a certain fixed time each cycle to complete the assigned task  Allowed time is set equal to the cycle time less repositioning time  Synchronous work transport system provides rigid pacing  Undesirable aspects of rigid pacing:  Incompatible with inherent human variability  Emotionally and physically stressful to worker  Incomplete work units if task not completed

21. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 21 Pacing with Margin  Worker is allowed to complete the task within a specified time range, the upper limit of which is greater than the cycle time  On average, the worker’s average task time must balance with the cycle time of the line  How to achieve pacing with margin:  Allow queues of work units between stations (asynchronous transport)  Provide for tolerance time to be longer than cycle time (continous transport)  Allow worker to move beyond station boundaries

22. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 22 No Pacing  No time limit within which task must be completed  Each assembly worker works at his/her own pace  No pacing can occur when:  Manual transport of work units is used on the line  Work units can be removed from the conveyor to perform the task  An asynchronous conveyor is used and the worker controls the release of each work unit from the station There is no mechanical means of achieving a pacing discipline on the line.

23. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 23 Coping with Product Variety  Single model assembly line (SMAL)  Every work unit is the same (products with high demand)  Batch model assembly line (BMAL)  Hard product variety  Products must be made in batches  Mixed model assembly line (MMAL)  Soft product variety  Models can be assembled simultaneously without batching on the line

24. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 24 MMAL vs. BMAL  Advantages of mixed model lines over batch model lines:  No lost production time changing over between models.  High inventories typical of batch production are avoided.  Production rates of different models can be adjusted as product demand changes.

25. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 25 MMAL vs. BMAL  Difficulties with mixed model line compared to batch model line  Line balancing problem is more complex due to differences in work elements among models.  Scheduling the sequence of the different models is a problem  Logistics is a problem - getting the right parts to each workstation for the model currently there.  Cannot accommodate as wide model variations as BMAL.

26. Analysis of Single Model Assembly Lines  The relationships developed here apply to batch model lines with a little modification.  The AL must be designed to achieve a production rate, R p, sufficient to satisfy the demand for the product. R p : production rate (units/hr) D a : annual demand S w : number of shifts/week H sh : number of hours/shift ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 26

27. Analysis of Single Model Assembly Lines This production rate must be converted to a cycle time, T c, which is the time interval at which the line will be operated. Time losses due to:  equipment failures  power outages  lack of components  quality problems  labor problems As a consequence of these losses, the line will be up and operating only a certain proportion of time out of the total shift time available. This uptime proportion is referred to as line efficiency.. 27

28. Analysis of Single Model Assembly Lines T c : cycle time (min/cycle) E: line efficiency Then the ideal cycle rate for the line in cycles/hr: ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 28

29. Analysis of Single Model Assembly Lines T p : average production time ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 29

30. Work content An assembled product requires a certain total amount of time to build, called the WORK CONTENT TIME, T wc. This is the total time of all work elements that must be performed on the line to make one unit of the product. A minimum rational work element is a small amount of work that has a specific limited objective. It cannot be subdivided further. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 30

31. Number of Workers We compute a theoretical minimum number of workers that will be required on the AL to produce a product with known T wc and specified production rate R p. w= number of workers on the line WL= workload to be accomplished in a given time period AT= available time in the period (60 min) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 31

32. Number of Workers w * = theoretical minimum number of workers ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 32

33. Number of Workers If M i =1 and w u =0, then w*=theoretical minimum number of workstations. However, due to below factors, number of workers increases above the theoretical minimum.  Repositioning losses (repositioning of the work unit/worker)  AL balancing (impossible to divide the work content time evenly amongst all workstations) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 33

34. Repositioning Losses T r : the time required each cycle to reposition the worker, the work unit, or both T si : the service time at station i (the time required to perform the assigned task at each station) = T c – T r There will be at least one station at which T si is maximum. This is referred to as the bottleneck station because it establishes the cycle time for the entire line. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 34

35. Repositioning Losses At all stations where T si is less than T s workers will be idle for a proportion of the cycle. When T s <T c -T r, then T c is reduced so that T s =T c -T r. E r : repositioning efficiency ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 35

36. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 36 Components of Cycle Time T c Components of cycle time at several workstations on a manual assembly line. At the bottleneck station, there is no idle time.

37. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 37 Line Balancing Problem  Given:  Total work content consists of many distinct work elements  The sequence in which the elements can be performed is restricted (precedence relation)  The line must operate at a specified cycle time  Problem:  To assign the individual work elements to workstations so that all workers have an equal amount of work to perform

38. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 38 Line Balancing Problem Two important concepts in ALB:  The separation of total work content into min rational work elements  The precedence constraints that must be satisfied by these elements

39. Minimum Rational Work Elements A min rational work element is a small amount of work that has a specific limited objective. It cannot be subdivided any further. T ek : time to perform work element k (min) n e : number of work elements into which the work content is divided We assume that  Element times are constant values  T ek values are additive ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 39

40. Minimum Rational Work Elements The task time, i.e. service time, at station i, T si, is composed of the work element times that have been assigned to that station. n: number of workstations ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 40

41. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 41 Precedence Constraints  Technological restrictions on the order in which work elements can be performed Precedence diagram

42. Example 15.1 No (k)T ek (min)PredecessorNo (k)T ek (min)Predecessor 10.2-70.323 20.4-80.63,4 30.7190.276,7,8 40.11,2100.385,8 50.32110.59,10 60.113120.1211 ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 42 D a =100,000 units/yr, 50 wks/yr, S w =5 shifts/wk, H sh =7.5 hrs/shift, M i =1, E=96%, T r =0.08 min. Find a) T wc, b) R p, c) T c, d) w*, e) T s

43. Measures of Line Balance Efficiency Measures indicate how good a given line balancing solution is. (i)Balance Efficiency: the work content time divided by the total available service time on the line. The closer the values of T wc and wT s, the less idle time on the line (perfect when E b =1.00) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 43

44. Measures of Line Balance Efficiency (ii)Balance Delay: the amount of time lost due to imperfect balancing as a ratio to the total time available. Note that E b +d=1.00. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 44

45. Worker Requirements Three factors that reduce the productivity of a manual assembly line. 1.Line efficiency, E 2.Repositioning efficiency, E r 3.Line balancing efficiency, E b Labor efficiency on the line=E  E r  E b ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 45

46. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 46 Line Balancing Algorithms The objective in line balancing is to distribute the total workload on the AL as evenly as possible among the workers.

47. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 47 Line Balancing Algorithms  Largest Candidate Rule  Assignment of work elements to stations based on amount of time each work element requires  Kilbridge and Wester Method  Assignment of work elements to stations based on position in the precedence diagram  Elements at front of diagram are assigned first  Ranked Positional Weights  Combines the two preceding approaches by calculating an RPW for each element

48. Largest Candidate Rule Work elements are arranged in descending order according to their T ek values. Then 1.Assign elements to the worker at the first workstation by starting at the top of the list and selecting the first element that satisfies precedence requirements and does not cause the total sum of T ek at that station to exceed the allowable T s. When an element is selected for assignment to the station, start back at the top of the list for subsequent assignments. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 48

49. Largest Candidate Rule 2.When no more elements can be assigned without exceeding T s, then proceed to the next station. 3.Repeat steps 1 and 2 for as many additional stations as necessary until all elements have been assigned. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 49

50. Kilbridge and Wester Method This is a heuristic procedure that selects work elements for assignment to stations according to their position in the precedence diagram. 1.Work elements in the precedence diagram are arranged into columns; then the elements can be organized into a list according to their columns, with the elements in the first column listed first. 2.Once the list is established, the same three-step procedure is used as before. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 50

51. Ranked Positional Weights Method RPW k is calculated by summing T ek and all other times for elements that follow T ek in the arrow chain of the precedence diagram. Elements are compiled into a list according to their RPW value, and the algorithm proceeds using the same three steps before. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 51

52. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 52 Mixed Model Assembly Lines “A manual production line capable of producing a variety of different product models simultaneously and continuously (not in batches)”  Problems in designing and operating a MMAL:  Determining number of workers on the line  Line balancing - same basic problem as in SMAL except differences in work elements among models must be considered  Model launching - determining the sequence in which different models will be launched onto the line

53. Number of Workers on the Line The workload consists of the work content time of each model multiplied by its respective production rate during the period. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 53

54. Mixed Model Line Balancing The objective is to spread the workload amongst stations as evenly as possible. In mixed model assembly line balancing, total work element times per hour (or per shift) are used. We assume M i =1, so that n=w. TT si : total service time at station i to perform its assigned portion of the workload ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 54

55. Mixed Model Line Balancing ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 55

56. Mixed Model Line Balancing ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 56

57. Example 15.6 Work element kT eAk (min)Preceded byT eBk (min)Preceded by 13-3- 24141 32131 46151 532-- 64323 7--44 855,647 T wc 2725 ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 57 R pA =4/hr R pB =6/hr E=0.96 T r =0.15 min M i =1 a)Construct the precedence diagram b)Solve the line balancing problem using Kilbridge and Wester method c)Determine the balance efficiency

58. Model Launching in Mixed Model Lines Production on a manual assembly line typically involves launching of base parts onto the beginning of the line at regular time intervals. In a single model line, this time interval is constant and set equal to the cycle time, T c. In a MMAL, the time interval between launches and the selection of which model to launch are interdependent. Determining the time interval between successive launches is referred to as the launching discipline. 1.Variable-rate launching 2.Fixed-rate launching ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 58

59. Variable-Rate Launching The time interval between the launching of the current base part and the next is set equal to the cycle time of the current unit. The time interval in variable rate launching is: Then the models can be launched in any sequence desired. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 59

60. Variable-Rate Launching  Advantage  Units can be launched in any order without causing any idle time or congestion at workstations, as long as the specified model mix is achieved by the end of the shift.  Tehnological and logistical issues  Work carriers on a moving conveyor are usually located at constant intervals.  Problem of supplying the correct components and subassemblies to the stations for the models being assembled at any moment. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 60

61. Fixed-Rate Launching Time interval between two consecutive launches is constant. The launching time interval: R p : total production rate af all models in the schedule or simply the sum of R pj values In fixed-rate launching, the models must be launched in a specific sequence; otherwise, station congestion and/or idle time (starving) can occur. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 61

62. Fixed-Rate Launching Congestion and idle time are the difference between the cumulative fixed-rate launching interval and the sum of the launching intervals for the individual models that have been launched onto the line. m: launch sequence during the period of interest h: launch index number for summation purposes T cjh : the cycle time associated with model j in launch position h (min) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 62

63. Fixed-Rate Launching For each launch m, select j so as to ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 63

64. Fixed-Rate Launching for Three or More Models The sequencing procedure can be adapted for the case of three or more models by adding a term to the equation that forces the desired schedule to be met. For each launch m, select j so as to minimize R pj : quantity of model j to be produced during the period, that is, the product rate of model j (units/hr) Q jm : quantity of model j units remaining to be launched during the period as m (number of launches) increases (units/hr) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 64

65. Workstation Considerations A workstation is a position along the assembly line where one or more workers perform assembly tasks. If a workstation i has a length L si, then the total length of the AL is If L si =L s for all i, then L=nL s. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 65

66. Workstation Considerations A transport system used in MAL is a constant speed conveyor. Base parts are launched onto the beginning of the line at constant time intervals equal to the cycle time, T c. This provides a constant feed rate of base parts. f p : feed rate on the line (units/min) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 66

67. Workstation Considerations A constant feed rate on a constant speed conveyor provides a center-to-center distance between base parts s p : center-to-center spacing between base parts (m/part) v c : velocity of the conveyor (m/min) ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 67

68. Workstation Considerations One way to achieve pacing with margin in a continuous transport system is to provide a tolerance time that is greater than the cycle time. Tolerance time is the time a work unit spends inside the boundaries of the workstation. T t : tolerance time (min/part) If L si are different then T ti will differ. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 68

69. Workstation Considerations The total elapsed time a work unit spends on the assembly line ET: elapsed time a work unit spends on the conveyor during its assembly (min) If all tolerance times are equal then ET=nT t. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 69

70. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 70 Other Considerations in Line Design  Line efficiency  Management is responsible to maintain line operation at efficiencies (proportion uptime) close to 100%  Implement preventive maintenance  Well-trained emergency repair crews to quickly fix breakdowns when they occur  Avoid shortages of incoming parts to avoid forced downtime  Insist on highest quality components from suppliers to avoid downtime due to poor quality parts

71. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 71 Other Considerations - continued  Methods analysis  To analyze methods at bottleneck or other troublesome workstations  Subdividing work elements  It may be technically possible to subdivide some work elements to achieve a better line balance  Sharing work elements between two adjacent stations  Alternative cycles between two workers

72. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 72 Other Considerations - continued  Utility workers  To relieve congestion at stations that are temporarily overloaded  Changing workhead speeds at mechanized stations  Increase power feed or speed to achieve a better line balance  Preassembly of components  Prepare certain subassemblies off-line to reduce work content time on the final assembly line

73. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 73 Other Considerations - continued  Storage buffers between stations  To permit continued operation of certain sections of the line when other sections break down  To smooth production between stations with large task time variations  Parallel stations  To reduce time at bottleneck stations that have unusually long task times

74. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 74 Other Considerations - continued  Zoning constraints - limitations on the grouping of work elements and/or their allocation to workstations  Positive zoning constraints  Work elements should be grouped at same station  Example: spray painting elements  Negative zoning constraints  Elements that might interfere with each other  Separate delicate adjustments from loud noises

75. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 75 Other Considerations - continued  Position constraints  Encountered in assembly of large products such as trucks and cars, making it difficult for one worker to perform tasks on both sides of the product  To address, assembly workers are positioned on both sides of the line

76. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 76 Alternative Assembly Systems  Single-station manual assembly cell  Worker teams  Automated assembly systems

77. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 77 Single-Station Manual Cell “A single workstation in which all of the assembly work is accomplished on the product or on some major subassembly”  Common for complex products produced in small quantities, sometimes one-of-a-kind  Custom-engineered products  Prototypes  Industrial equipment (e.g., machine tools)

78. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 78 Assembly by Worker Teams “Multiple workers assigned to a common assembly task”  Workers set their own pace  Examples  Single-station cell with multiple workers  Swedish car assembly (job enlargement) - product is moved through multiple workstations by AGVS, but same worker team follows it from station to station

79. ©2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Automation, Production Systems, and Computer-Integrated Manufacturing, Third Edition, by Mikell P. Groover. 79 Reported Benefits of Team Assembly  Greater worker satisfaction  Better product quality  Increased capability to cope with model variations  Greater ability to cope with problems that require more time rather than stopping the entire production line  Disadvantage:  Team assembly is not capable of the high production rates of a conventional assembly line