Organization of Workstations

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Chapter 12

• Organization of Workstations

2
Guideline 1

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

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Guideline 2

• Consider Group Technology
• Form families of items that are almost identical.
• Imitate a flow line and shift fixed costs of the
  flow line to the process.
• Find common solutions to common problems.

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Benefits of Product Families

• Product design
• An existing part can be used in place of a
  proposed new part.
• An existing part, modified, can replace a new
  part.
• The existing part can provide design data for a
  new part.
• Common manufacturing
• Lessons can be learned from similar parts.
• Existing tooling can be used.
• Setup and training costs can be reduced.

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Product Families

• May be based on part geometry or process
  similarities.
• Classification process depends on solving coding
  problem.
• May be the basis of factory specialization.

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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 inventory

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Cell LayoutDisadvantages

• Lower equipment utilization
• Loss of flexibility
• Cost of setting up and maintaining concept

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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 should we choose?

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Advantages of Non-Progressive Assembly

• 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.

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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.

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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.

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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.

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Guideline 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.

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Standard Balancing Technique

• Determine quantity to be made and time allowed.
• Estimate an approximate number of stations.
• Make a trial solution.

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Modifications to Standard Technique

• 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.

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Guideline 5

• 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)

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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.

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Strategies to Reduce Material Handling Cost
(cont.)

• 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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Guideline 6

• Decouple Tasks
• Types of flow lines
• Operation-only line
• Order-picking line
• Assembly line

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Flow Line Design

• 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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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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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.

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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.

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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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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.

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Guideline 8

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

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Guideline 9

• 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