Organization of Workstations

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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

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Step 1 Clean the space
vs

• 5 Ss (from Lean )
• _______________
• _______________
• _______________
• _______________
• _______________

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G1Use specialization even though it sacrifices
versatility

• Special-purpose equipment
• Specialized materials
• Specialized labor
• Group technology

4
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.

5
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

6
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?

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Non-progressive assembly
Advantages Neutral Characteristics Disadvantages
Balance delay time is eliminated. Scheduling flexibility is increased. Shocks do not have multiple effects. Musculoskeletal disorders are less of a problem. Satisfaction may increase. 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. 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.
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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.

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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

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Standard balancing technique

• Example Final assembly of an electronic organ
  (from Weiss and Gershon, Production and
  Operations Management (2nd ed.), 1993, Allyn
  Bacon.)

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Line balancing

• Step 1 draw the precedence diagram

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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 _______

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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.

Station Task Task time Total time Station Idle Time Total Idle time

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Station Task Task time Total time Station Idle Time Total Idle time

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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)

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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

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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.

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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.

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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

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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

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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

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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, gtn workstations

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G7Make 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.

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G8 Combine operations and functions

• Use multi-function materials.
• Use multi-function tools.

25
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