Organization of Workstations Chapter 9 Organization of Workstations Supplementary Material from: Groover, M.P. (2007). Work Systems and the Methods, Measurement, and Management of Work, Upper Saddle River, NJ: Pearson Prentice Hall, pp. 59 – 112.

Overview Work Flow Konz & Johnson Guidelines 1 – 3 Work Cell Layout K & J Guideline 4: Line Balancing K & J Guidelines 5 - 9

Work Flow Physical movement of work units through a sequence of unit operations. Unit operations examples Manual operations Move box Load furniture into van File document into filing cabinet Operations involving tools & equipment File part Paint trim around doorway Measure shaft diameter with micrometer Handwrite entries into ledger Apply adhesive Drill hole Mill slot Work Flow Patterns Pure Sequential Operations Mixed Sequential Operations

Pure Sequential Work Flow 1 2 3 4

Mixed Sequential Work Flow 6 1 2 3 4 5 7 8

Types of Movement In a Sequential Workflow Bypassing In-sequence 1 2 3 4 Backflow Repeat

From-To Charts Daily quantities (Qij) of work units moving between 5 workstations. 15 1 40 2 30 3 20 4 10 5 10 25

Bottlenecks Blocking Starving Reasons Upstream operations limited by rate of downstream operations. Starving Downstream operations limited by rate of upstream operations. Reasons Technological factors Work allocation decisions Human factors (ergonomic limitations) Downstream 1 2 3 4 Upstream

Konz & Johnson Guidelines 1. Use Specialization Even Though It Sacrifices Versatility 2. Consider Group Technology 3. Consider Both Non-progressive and Progressive Assembly Konz & Johnson Guideline 1 Use Specialization Even Though It Sacrifices Versatility Special-purpose equipment Specialized materials and supplies Specialized labor Group technology K & J Guideline 2 Consider Group Technology Product families/classes based on similarities form (geometry) process Work cells workstations organized around families K & J Guideline 3 Consider Both Non-progressive and Progressive Assembly Consider an assembly of N elements that requires m people to work. Non-progressive assembly: Each worker does all N elements. Progressive assembly: The job is split so each worker does N/m elements. Which is better?

Non-Progressive Assembly Advantages Neutral Characteristics Disadvantages Advantages of Non-Progressive Assembly Balance delay time is eliminated. Scheduling flexibility is increased. Shocks do not have multiple effects. Musculoskeletal disorders reduced. Satisfaction may increase. Neutral Characteristics Quality may be higher or lower with each type of assembly. Material handling has advantages and disadvantages in both. Space requirements could favor either. Walking may be required in either. Disadvantages of Non-Progressive Assembly Direct labor cost/hour is higher. Skill requirements and training costs are higher. Equipment capital cost is higher. In-process inventory is higher. Supervision is more difficult.

In-Class Exercise What are the work units in your project’s work system? Is the work progressive “assembly” or non- progressive? If non-progressive, what (if anything) would justify progressive?

U-Shaped Work Cell With Manual Handling Common Work Cell Layouts For Progressive Assembly Manual Handling U-shaped Mechanized Handling In-line (linear) Loop

In-Line Work Cell

Loop Work Cell

U-Shaped Work Cell With Mechanized Handling

K & J Guidelines 4. Balance Flow Lines Before balancing flow lines: Ask whether it is appropriate to balance the line. Gather the givens: Table of work elements and times Precedence diagram Required units/minute from line Determine: Number of stations Number of workers at each station Elements to be done at each station.

Line Balancing Determine quantity to be made and time allowed. 20,000 units in 1,000 hours Cycle time = 1,000 h / 20,000 = 0.05 h / item Sum of element times = 0.1818 h Estimate an approximate number of stations. (0.1818 h/item) / (0.05 h/station) = 3.63 ≈ 4 stations One operator at each station Make a trial solution by inspection (K & J). Or use a line balancing heuristic. Or use a line balancing program.

Line Balancing (K & J) 1 2 5 3 4 6 7 8 9 10

Balanced Line (K & J) S1 1 2 5 S3 3 S4 4 6 7 S2 8 9 10 S1 S2 S3 S4 S4 1,2 S2 8,9 S3 3,4,6 S4 5,7,10 S4 6,7

Line Balancing Determine quantity to be made and time allowed. 20,000 units in 1,000 hours Cycle time = 1,000 h / 20,000 = 0.05 h / item Sum of element times = 0.1818 h Estimate an approximate number of stations. (0.1818 h/item) / (0.05 h/station) = 3.63 ≈ 4 stations One operator at each station Make a trial solution by inspection (K & J). Or use a line balancing heuristic. Or use a line balancing program.

Largest Candidate Rule Heuristic Sort work elements in decreasing order of work times. Assign elements to first workstation by starting at top of list and selecting first element that satisfies precedences and does not cause cycle time to be exceeded. Start back at top for more assignments. When no more elements can be assigned without exceeding cycle time, proceed to next station. Repeat steps 1 & 2 until all elements have been assigned.

Element Times and Precedence Diagram 1 2 5 3 4 6 7 8 9 10

Solution (Setup)

Solution (completed)

Balanced Line 1 2 5 3 4 6 7 8 9 10

Balanced Line S1 1 S2 2 5 3 S4 4 6 7 S3 8 9 10 S1 S2 S3 S4 S4 1,2 Modifications Consider element (human, machine) sharing. Remember that cycle times are not fixed. Remember that elements often can be redefined. Interchange elements from the assembly task and the subassembly tasks. 10 S1 1,2 S2 5,3,8,10 S3 4,9 S4 6,7 S4 6,7

Konz & Johnson Guidelines 5. Minimize Material Handling Cost 6. Decouple Tasks 7. Make Several Identical Items at the Same Time 8. Combine Operations and Functions 9. Vary Environmental Stimulation Inversely with Task Stimulation K & J Guideline 5 Minimize Material Handling Cost Consider how utilization affects capital costs vs. operating costs. Eliminate peak loads through scheduling. Replace transportation with communication. Reduce number of trips through scheduling and combining. Reduce fixed costs by using line production. Move more product/labor hour. Reduce distances by efficient layout and arrangement. Use a “bus” instead of a “taxi” system. Emphasize reducing total MH costs rather than individual elements (system perspective). K & J Guideline 6 Decouple Tasks Line Balancing Buffering Techniques Buffers at or between stations Buffers due to carrier design Buffers off-line Decouple by moving operators Utility operator Help your neighbor K & J Guideline 7 Make Several Identical Items at the Same Time Task stages: Get ready Do Put away Reduce cost/unit by prorating get-ready and put-away over more units.

Checklist To Be Used With Process Charts and Flow Diagrams (1) From Work Systems, by Mikell Groover (2007) Questions Related to Material What alternative materials can be used? Could the part be purchased as a commercially available item? Could the functions of several components be combined into one component? Should this part be made or purchased (make/buy)? Questions Related to Processing Operations What is the purpose of each processing operation? Is the processing operation necessary? Can operations be eliminated, combined, or simplified? Is the operation time too high? Could the processing operation be automated? Where else could this be performed to reduce move distances?

Checklist To Be Used With Process Charts and Flow Diagrams (2) Questions Related to Inspection Operations What is the purpose of the inspection operation? Is the inspection operation necessary? Can the inspection operation be combined with the previous processing operation? Could 100% inspection be replaced with sampling inspection? Could the inspection operation be automated? Questions Relating to Moves How could moves be shortened or eliminated by combining or eliminating operations? Could the items to be moved be batched to reduce trips? Could the moves be mechanized or automated? Could the operations sequence be changed to reduce move distances?

Checklist To Be Used With Process Charts and Flow Diagrams (3) Questions Relating to Delays What is the reason for the delay? Can the reason be eliminated? Is the delay avoidable? Why can’t the next operation be started immediately? Questions Relating to Storage Is the storage necessary? Why can’t the item(s) be moved immediately to the next operation? Can just-in-time delivery be used to eliminate storage?