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
