Organization of Workstations

1. Organization of Workstations • Applications in traditional and lean systems • Tradeoffs among guidelines depend on type of production, number and types of items being produced, etc. • Nine guidelines: • Use Specialization Even Though It Sacrifices Versatility • Consider Group Technology • Consider Both Non-progressive and Progressive Assembly • Balance Flow Lines • Minimize Material Handling Cost • Decouple Tasks • Make Several Identical Items at the Same Time • Combine Operations and Functions • Vary Environmental Stimulation Inversely with Task Stimulation

2. G1: Use Specialization Even Though It Sacrifices Versatility • Special-purpose equipment • Specialized materials • Specialized labor • Group technology

3. G2: Consider Group Technology • Form families of items that are almost identical. • May be based on part geometry or process similarities. • Classification process depends on solving coding problem. • May be the basis of factory specialization. • Imitate a flow line and shift fixed costs of the flow line to the process. • Find common solutions to common problems.

4. Cell Layout Cell: machines and skills for producing related items placed close together. • Advantages: • Specialization • Minimum material handling • Simpler production control • Shorter throughput times • Lower work-in-process (WIP) inventory • Disadvantages: • Lower equipment utilization • Loss of flexibility • Cost of setting up and maintaining concept

5. G3: 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 should we choose?

6. Non-Progressive Assembly

7. Reasons for Flow Lines • Some of their advantages are emphasized by decision makers. • Cost advantages that favor flow lines are visible, whereas the costs that do not favor them are lost in overhead figures. • Many of their disadvantages can be overcome by good system design. • Work cells in lean production can be combined into flow lines and balanced.

8. G4: Balance Flow Lines • Balance the tradeoffs between number of stations or cells and the amount produced by each station to meet production times as smoothly and efficiently as possible. • 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 (Takt time) • Determine: • Number of stations/cells • Number of workers at each station/cell • Elements to be done at each station/cell

9. Standard Balancing Technique Example: Final assembly of an electronic organ (from Weiss and Gershon, Production and Operations Management (2nd ed.), 1993, Allyn & Bacon.)

10. Line balancing • Step 1: draw the precedence diagram

11. Line balancing • Step 2: Determine quantity to be made and takt time. • Example: Production goal = 200 organs/day (set by customer demand) Cycle time = (1 day/200 organs) * (8hrs/day) * (3600 sec/hr) = 144 sec/organ • Estimate an approximate number of stations. • Example: Number of stations = total time required / takt time = 510 sec / 144 sec = 3.54 = _______

12. Line balancing • Step 3: Make a trial solution. • Longest task time rule: from among the available tasks, choose the one that takes the longest. In case of a tie, choose the one with the most followers.

14. Line balancing • Step 4: Determining the efficiency idle time = (# of stations * cycle time) - (time to produce 1 unit) efficiency = (time to produce 1 unit) / (# of stations * longest station time) or efficiency = (theoretical minimum cycle time) / (achieved cycle time)

15. Line Balancing • Problems: • Mean times for stations are not equal, so there is balance-delay time. • The speed at a station in a balanced line must be set at the speed of a slow operator on a slow station. • Cycle times vary. • Options • Consider element 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. • kanban - inventory control pull system • parts placed in containers for next cell • when parts are pulled, they must be replaced

16. G5: Minimize Material Handling Cost • Elements of material handling cost: • Material handling cost/year = Capital cost + Operating cost • Operating cost = Number of trips/year × Cost/trip • Cost/trip = Fixed cost/trip + (Variable cost/distance × distance/trip) • Reduce material handling cost by … • 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.

17. Strategies to Reduce 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.

18. G6: Decouple Tasks • Types of flow lines: • Operation-only line • Order-picking line • Assembly line • Decisions to consider: • Single product or multiple products? • Assemble in sub-assemblies or on the line? • How to divide tasks among stations? • Balanced or unbalanced? • Characteristics of well-designed lines: • Minimum idle time at the stations • High quality (enough time at each station) • Minimum capital cost

19. Lean Manufacturing (Just-in-Time) Reduction of work-in-process inventories to minimal amounts, to force management to solve problems by revealing them. • Little product variety • Producing only what the customer wants, when it is wanted • High quality • High equipment availability • Short setup times • Cross-trained skilled workers

20. Shocks and Disturbances • Cause cycle times to vary. • May result from operator variability, station starvation, or station blockage. • Buffers provide flexibility/tolerance. • In lean systems, the presence of inventory buffers indicate waste • opportunities to improve process • goal is to eliminate the need for buffers

21. Buffering Techniques • Decouple by changing product flow • Buffers at or between stations • Buffers due to carrier design • Buffers off-line • Decouple by moving operators • Utility operator • Help your neighbor • n operators, n workstations • n operators, >n workstations

22. G7: 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.

23. G8: Combine Operations and Functions • Use multi-function materials. • Use multi-function tools.

24. G9: Vary Environmental Stimulation Inversely with Task Stimulation • Low-stimulation tasks: • Add physical movement to the task • Add stimulation to the environment • High-stimulation tasks: • Make privacy possible • Discourage excess conversation