Workcells and Cellular Flow

Designing effective workcells

Other commonly applied terms are:

  • Concurrent Flow
  • Lean Flow
  • Continuous Flow
  • Simultaneous Flow
  • Synchronous Flow
  • Hybrid Layout
  • Group Technology 
  • Prerequisite tools to review when creating a workcell:

  • 5S
  • Process mapping
  • Takt time and Loading / Line Balancing
  • 7-wastes elimination
  • Value Stream Mapping (VSM)
  • Visual Management 
  • Types of Cellular Layouts


    Straight (Linear) Layout

    Linear Workcell

    PROS:

  • Multi-capable personnel once trained
  • Separates raw from finished goods if that is a concern of mixing.
  • Point-of-use supplies can be placed on one side.

    CONS:

  • Requires access on two sides
  • Process independent of one another
  • Cross-training required

    These are possible when there is physical access to both sides of the cell. Sometimes the cell may need to be designed against a wall and a U-shaped cell is the better option since raw and finished parts are at the same side.

    Cage (ONE person & ONE type of operation)

    Cage Workcell - one person for one type of operation

    PROS:

  • No cross-training required, lower learning curve
  • Operator can get more efficient

    CONS:

  • Space needed on all sides for maintenance and/or supplies
  • Employees are separated and more difficult to help one another
  • Increased WIP and Inventory - more batches
  • Lead Time increases and ties up more cash
  • Lack of cross-training, only know how to run one type of equipment
  • Line balancing is more challenging in caged layouts

    Cage (ONE person & >1 type of operation)

    Cage cell with one operator and >1 type of equipment

    PROS:

  • Multi-capable personnel once trained
  • Minimal walking for operator
  • Eliminates any chance of operator interference

    CONS:

  • Space needed on all sides for maintenance and/or supplies
  • Employees are separated and more difficult to help one another
  • Cross-training required

    U-Shaped Layout

    U-shaped workcell

    PROS:

  • Multi-capable personnel once trained
  • Minimal walking, linear layout requires walking across line to start over.
  • Only one side of access needed for raw materials and finished parts.

    CONS:

  • May be traffic concerns, raw and finished part delivery all in same area.
  • Process independent of one another
  • Cross-training required






    Assembling a Workcell

    Three elements to be considered, the flow of:

    1) People
    2) Equipment
    3) Materials

    Workcells may be as simple as one of the above, or it may be a combination of them. Multiple U-turn workcells are combinations of straight and U-shaped cells.

    GOAL: Workcells are intended to reduce floor space, improve throughput of smaller batches, provide more predictable production, and improve cross-training. 

    Questions to consider for cellular flow:

  • What equipment should go into the workcell?
  • Is cross-training needed?
  • What risks are being added?
  • Can these risks be avoided, prevented, or reduced?
  • What items or processes should be produced in workcells?
  • How should people operate the workcell?
  • Which design is optimal for the cell?
  • Is there access for maintenance?
  • What type of manning methods should be employed?
  • Do I understand the takt time?
  • What is the capability (loading)?
  • Do I have a suitable product family?
  • How should the product family be determined?
  • Is there space to perform changeovers?
  • Access for direct and indirect materials?
  • What can and can not be placed at the point-of-use?
  • Can the equipment run independently if needed?
  • Which direction should the cell be designed (read below)?


  • Human Factors

    Clockwise or Counter-Clockwise?

    When designing a U-shaped workcell there should be consideration (if using humans) to whether the operators are left or right handed and perhaps try to accommodate both. 

    At some point a direction must be selected and usually counter clockwise is most efficient for people to work within.

    Most people are right-handed, right eye is more accurate and stronger for most people. Also consider that track events are usually ran in a counter-clockwise direction. 

    Movement

    Strive to:

    Avoid sharp turns, jerks, or rapid acceleration 

    Avoid static positions for extended period of time

    Make out of control conditions quickly visual - at eye level 

    Keep activity at shoulder height

    Most frequently used tools closest to operator and point-of-use

    Use gravity or other mechanical advantages

    Avoid vertical movement and strive for horizontal movement

    Design workstations that suit the operator height (possibly flexible height)

    Design a place for everything (...and audit to ensure everything stays in its place)




    Common Obstacles of Workcells

    Cross Training

    This is probably the most influential factor in successful cellular implementation. Not only does this satisfy workcells, but this also curbs the dependence on specialized operators, vacations, and absences.

    Creating the best product families

    Typical characteristics are the geometry, tooling, and process step commonality. Must understand the components that takes longest to set-up or has the least capacity (bottleneck - determine with takt time and balanced loading).

    Lack of consideration to Human Factors

  • Minimize body motion but also avoid same position for too long
  • Unpleasant sounds, whistles, beepers should be avoided
  • Avoid awkward postures and movements
  • Avoid sharp turns in motion
  • Consider fatigue mats, lighting, double hand controls
  • Design movements to follow rhythm
  • Work at shoulder height when possible
  • Utilize mechanical advantages when applicable.
  • Put monitors and controls on swivels
  • Use Visual Aids, lines, shadow boards, labels. 
  • Past Paradigms 

    Virtually all implementations of significant change or transformation will meet resistance due to past paradigms. The team designing the cell must be enthusiastic, open-minded, and capable. This first cell created will be judged and will set the precedence for the workcell principle and Six Sigma program going forward.

    CHALLENGE EVERYTHING!

    Rules, regulations, standards, work instructions, past practices, are all fair game. All of these items are prone to change and the circumstances of their origin may also be different.



    Success Factors

  • Workcells aren't the answer to all processes, choose wisely
  • Top personnel on the design team
  • Cross-functional team
  • Challenge the past, seek the ultimate future state
  • Keep the workcell flexible and adaptable
  • Maintain simplicity
  • Analyze the work load and takt time calculations carefully and review assumptions
  • Ensure staffing is in place with qualified alternates (if necessary)
     





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