A lean strategy simulation game

Game play, preparation

The objective of All-World Wheelchairs is to train students in strategic lean thinking.  Rather than teach details on individual Lean tools, this game teaches systems analysis, root cause analysis, bottleneck identification, matching tools to problems, prioritization, and planning.­

This game assumes that players have a working knowledge of manufacturing processes, lean manufacturing concepts, and root cause analysis.  The tutorial provides enough detail to allow the players to make good decisions and successfully play the game.  This manual provides more detail, so the instructor can answer questions that may arise during the game.  It is not necessary to share this manual with players.­

The game can be played by individuals or teams, in a collaborative or competitive environment.­

Instructor's Guide

Introduction

The product being built is a manual wheelchair.  Product diagrams and routings are shown at the bottom of this page.  The demand is 200 chairs per month with no extra production or backorders allowed.  Much but not all of the information given below is available to a game player.­

The factory floor has nine workstations.  The general process of making one chair follows this diagram:

Selecting a station and clicking on the clipboard near the left of the table will open a station report.  The following information is given:

  • Current quantity
  • Setup time per batch
  • Number of parts – using that station
  • Total minutes – to make all parts for one chair
  • Efficiency – percent of available time that is productive
  • Reliability – percent of available time station is working
  • Quality – percent of available time good parts are produced
  • Batch size – parts produced for each time of handling and setup.
  • Handling time – moving batch to next station
  • Inventory – of parts LEAVING the station

Capacity calculations

The station report also shows the number of needed machines.  The number is based on the average information listed in the report.  Any given month may have fewer or more problems than average, so actual production may vary from this number.­

Number of machines is time required divided by time available.  Time required is 200 chairs times total minutes per chair plus setup and handling times per batch.  The number of batches per month is the number of parts times then number of batches per month based on batch size.  Time available is 9000 minutes per month (450 minutes/day x 20 days).­

Overtime is automatically scheduled if the number of needed machines exceeds 95% of the current quantity.  Each machine is scheduled for 20 hours per month if the number of needed machines is between 95% and 100%.  Each machine is scheduled for 40 hours per month if the number of needed machines exceeds 100%.­

The color of each workstation relates to its performance during the previous month.  Green = meeting production without overtime.  Yellow = meeting production with overtime.  Red = not meeting production.

Inventory

Inventory is measured in parts PER CHAIR.  So the initial inventory of 93 at the tube bender is enough of each of the 5 parts processed on the tube bender to make 93 chairs.  Purchased parts are similarly ordered per chair.­

Production will produce a maximum of 3 batches ahead, initially 60 or 120 chairs worth of parts.  Assembly will not produce finished chairs ahead of demand.­

Purchased parts are ordered when inventory runs low.  Initially, the re-order point is when inventory falls below 100 chairs of parts.  Each part has its own re-order quantity.   Clicking on the truck icon will open the Purchasing page, which displays the previous month’s orders.

Costs

Monthly revenue and costs are displayed on the orange tab of the Monthly Report at the start of each month.  Costs change in different scenarios.  Key production costs for scenario 1 are as follows:

  •   Chair selling price:  $390      ($415 in scenario 2)
  •   Total labor and material cost for one chair:  $225
  •   Labor, one person per station:  $14/hour or $2240/month
  •   Overtime as needed:  $21/hour or $420-$840/month
  •   Purchasing cost:  $200/order plus material purchase price
  •   Inventory cost:  7% of all raw materials and work-in-process
  •   Scrap cost:  $100/day of bad quality production     ($500/day in scenario 2)
  •   Overhead baseline:  $19,000/month

In general steel and bike vendor parts are more expensive than vinyl and metal vendor parts.  WIP inventory is more expensive the further into the production system.  (Steel, bike, and WIP inventory are more expensive in scenario 2).

Problem list

Clicking on the purple tab of the Monthly Report will open the monthly Problem List.  Affected Station Reports display the same problems.  Problems are deterministic, so the same ones appear for each participant and each time playing a scenario.  Implementation of appropriate Lean tools will prevent many of the problems from appearing.  Possible problems include:

  •   Late parts from vendor – in days of downtime
  •   Machine breakdown – in days of downtime
  •   Quality problem – in days of downtime­

Additional problems occurring as a result of the previous problems or capacity constraints are also presented.  These are all symptoms of other root causes:

  •   Late parts from previous cell/station – in days of downtime.  Initial inventory at a station is used first before downtime is incurred.
  •   Bad parts from previous station – in days of downtime.  Initially parts are checked at the end of each cell (tube bender, paint, sewing), so bad parts from previous stations cause downtime at some succeeding stations.
  •   Station works overtime to try and meet production – expected capacity exceeds 95%.  Yellow station color.
  •     Station cannot meet production due to capacity constraint – actual production is less than 200 for the month.  It does not consider re-filling starved lines.  Red station color.

Lean tools

Clicking on the phone in the office will open the Lean Tools menu.  Lean tools requiring Cells will not be available until the Cells Lean tool has been selected.  Previously selected Lean tools will no longer be available for selection.  Irrelevant Lean tools are not offered – for example, a player cannot select Preventive Maintenance on the Assembly station, which has 100% reliability.­

There are 57 individual options across 13 Lean tool categories which can be selected.  Each Lean tool has a one-time cost to implement.  Lean tools are implemented immediately.  Each month, players are limited to 2 categories of Lean tools, but they can select as many individual options within those tools within a $1000 per month budget.  Lean tools are only available for the first six months of the year.  After July, players won’t be able to implement more Lean tools.  They just observe the results of their decisions.

The Lean Tool tab displays the money left to spend on Lean tools each month.  Clicking on a checkbox will select the lean tool it corresponds to.  Clicking on the Buy button after making a selection will purchase it permanently.  After the desired Lean tools are purchased, clicking on the Next Month button will run the factory for one month.

Lean tools available are:

  •   Kanban – eliminates work-in-process inventory in front of stations in cells:  Drill, Bender, Grind, Paint.  But any downtime at the previous station is repeated at subsequent stations in the cell.
  •   Supermarket – minimizes work-in-process inventory of metal parts in front of the Welding and welded parts in front of Assembly.  As with Kanban, any downtime at the previous station is repeated at subsequent station.
  •   Small lot sizes – reduces lot sizes by 50% in a cell.  This doubles the number of setups and handling trips, but cuts the maximum inventory at a station.
  •   5-S – improves efficiency from 90% to 96% at a station.
  •   SMED (Single minute exchange of die), or quick changeover – reduces the setup time at a station by 80%.
  •   Quality at the source – reduces the days of quality problems by 80%.  Additionally, quality problems are identified at that station, so they do not lead to downtime at subsequent stations.
  •   Cells – reduce overhead by $300/month, eliminates 2 minute handling time moving batches within the cell.  Cells allow the purchase of additional Lean tools:  Kanban, Small lot sizes, Cross training, and Self-directed teams.  Cell design is predefined as Metal cell (Saw, Drill, Bender), Weld cell (Welding, Grind, Paint), Fabric (Fabric cut, Sewing).
  •   Cross training – can reduce the number of workers in a cell.  Rather than hiring one worker for each station, the fractions of workers at all stations in a cell are added and rounded up to the next integer.
  •   Self-directed teams – overhead is reduced by $500/month, but the efficiency of each station in the cell goes down 3%.
  •   Preventive maintenance – reduces the number of days of machine breakdown by 80%.  The number of breakdowns is reduced by 60% and no breakdown is longer than one day.
  •   Vendor certification – reduces order costs 75% to $50 per order and reduces late deliveries by 80%.  Vendors are pre-defined:  Steel (3 tube sizes), Nylon (fabric), Bike (2 wheels, handle, fender), and Metal (brake lever, footrest).
  •   Small purchase lot size – reduces order size by 75% and reduces re-order point to 0.  So the number of orders increases 4 times and any late orders will delay a workstation.
  •   New equipment – increases overhead by $300/month and adds one full-time worker labor.

Part routings

A few times are changed for scenario 2, to change the bottlenecks.

Level     Quantity              Part and assembly           Operation           Workstation       Minutes

0                              Completed wheelchair                  Pack                 Assembly               5

  1            1              Wheelchair assembly                   Final assly/test  Assembly             44

    2          2              Frame side assembly                   Weld/braze        Welding               30

                                                                                     Grind                  Grinder                  6

                                                                                     Paint                   Painting                 8

      3        1              Outer tube                                    Angle cut            Saw                    0.5

                                                                                     Drill 3 holes        Drilling                   2

                                                                                     Two bends         Bending                 3

      3        1              Back tube                                      Angle cut           Saw                    0.5

                                                                                      Bend                  Bending                 2

      3        1              Lower tube                                    Cut                     Saw                    0.2

                                                                                      Two bends         Bending                 3

      3        1              Hand tube                                     Angle cut            Saw                    0.5

                                                                                     Bend                   Bending                 2

      3        1              Horizontal tube                             Angle cut            Saw                    0.5

      3        1              Caster tube                                   Cut                     Saw                    0.2

    2          2              Folding assembly                          Weld/braze        Welding                 8

                                                                                      Grind                  Grinder                  2

                                                                                      Paint                   Painting                6

      3        1              Cross tube                                    Cut/notch 2 ends  Saw                  1.2

                                                                                      Drill 3 holes         Drilling                  2

      3        1              Seat tube                                       Cut                      Saw                   0.2

      3        1              Connecting tube                            Cut                      Saw                   0.2

    2          2              Front wheel assembly                   Assemble components Assembly    4

      3        1              Caster wheel                               

      3        1              Caster fork assembly                    Weld/braze          Welding                2

                                                                                     Crimp 2 ends, grind  Grinder             4

                                                                                      Paint                    Painting                2

        4      1              Caster tube                                   Cut                       Saw                   0.2

                                                                                      Drill 2 holes         Drilling                   2

                                                                                      Bend                   Bending                 2

    2          2              Rear wheel assembly                   Hand drill 4 holes  Assembly             4

      3        1              Rear bike wheel                                         

      3        1              Hand rim assembly                       Weld/braze         Welding                  3

                                                                                       Grind                 Grinder                    2

        4      1              Hand rim                                         Cut                    Saw                      0.2

                                                                                        Bend into ring   Bending                  2

                                                                                        Drill holes         Drilling                     2

    2          2              Footrest assembly                          Weld/braze       Welding                 10

                                                                                       Crimp and grind  Grinder                  3

                                                                                       Paint                  Painting                  3

      3        1              Footrest plate tube                         Angle cut           Saw                      0.5

                                                                                       Bend                  Bending                   2

      3        1              Footrest plate                             

      3        1              Footrest mount tube                      Cut                      Saw                      0.2

    2          1              Brake lever                                   

    2          1              Lock bar                                         Cut                      Saw                      0.2

                                                                                       Bend                   Bending                   1

  2            1              Seat                                                Cut                     Fabric cut                4

                                                                                       Sew seams         Sewing                  12

  2            1              Back                                               Cut                      Fabric cut                8

                                                                                       Sew seams, pocket  Sewing             30

  2            2              Handle                            

  2            2              Fender                           

Assembly sketches