The stockless challenge: a Lego lean game

Using kanbans to control workflows in repetitive manufacturing

For organisations wanting to improve efficiency, reduce work in progress and improve customer satisfaction, kanbans and lean methodologies can help. 

In a manufacturing context, the kanban system uses visual triggers to determine whether or not a task needs doing. At its simplest, an empty kanban requires a task to be completed, and when completion of the task fills the Kanban, work stops.

You can learn more about the kanban lean method here and in the sections below, but the main purpose of this blog post is to introduce a Lego lean game you can use to teach kanban concepts in your organisation.

Download your FREE Lean Game resources 👇

Click here to jump straight to the activity, or read on as we explore the following:

What are the basic kanban principles?

In manufacturing, a kanban is a space in a work area on which to place assemblies, often taking the form of squares that are large enough to contain just one assembly. The technique is a useful way to control the flow of work in an assembly area.

To use kanbans, each worker needs at least one output Kanban. The first worker gets raw materials from a supply bin or other stock output; other workers have input kanbans. Components – either raw materials or sub-assemblies – are taken from an input area and completed work – either sub-assemblies or full assemblies – is put into an output area. An output kanban for one person becomes an input kanban for the following worker or for dispatch to the customer.

Kanbans should be full at all times and there are two key rules:

  • work starts when an output kanban becomes empty
  • work stops when all output kanbans are full

Using kanbans for stockless manufacture

This section illustrates the basic kanban principles for use with Lean games or ‘stockless production’ simulations.

New assembly areas: things to consider

Before designing a new assembly area, there are three important factors to consider:

  • What is your target production rate? This can be given as a rate per hour or a timed delivery rate, e.g. every 30 seconds.
  • How much time is needed to build the whole assembly? This is the expected time for a worker to complete the task, e.g. 2 minutes.
  • How quickly does the customer need the product? This is given with reference to the time of them placing an order, e.g. within one minute.

Using the example figures above – delivery time every 30 seconds and total assembly time 120 seconds – at least 4 people would be needed with the work shared out between them to balance the flow and make the process effective.

Next: do you need to hold stock?

Next you need to consider whether or not stock needs to be held. 

Again, in the example above, each person may need to complete their assembly task in 30 seconds, but if the customer needs the product in less than 30 seconds, this would dictate a need to hold stock to ensure 100% customer service – at least one of every product variant. 

This raises a new set of considerations:

  • Holding finished stock requires space and money. 
  • Stock may become obsolete or have a limited shelf life.

What about delivery times?

By contrast, if customers are willing to wait a little longer for delivery, a work area designed as a ‘production line’ could be effective. 

Here, the assemblies move from person to person with each person adding a predefined set of components. The specification of the assembly is known as soon as it starts moving down the production line and each person will know which components to add. 

If the target assembly time for each person is 30 seconds, customer collection could be promised within, say, 3 minutes of placing an order.

Controlling Kanban components

Visual triggers may also be used to control the supply of components into a work area, either from a central or local warehouse or directly from suppliers. 

Two kanbans – in this case, containers or bins – are needed in this context because re-supply cannot be immediate. Containers each have their assigned components, with a planned quantity in each.

This leads to two additional rules:

  • only use components from one of the two containers at a time
  • the container quantity must be at least ‘refill time’ multiplied by the ‘usage’.

If a container is able to be refilled within, say, 2 minutes, with each product needing 2 of the assigned components and the delivery every 30 seconds, the minimum container quantity should be 8. 

2 components /  0.5 minutes  = 4 components used per minute

4 components used per minute x 2 minute refill time = 8 components per container

The quantity may be larger, but this takes more money and requires more space. To achieve rapid component delivery, suppliers need a good forecast of component demand.

Lego lean game: The Stockless Challenge

Conceptualising or teaching kanban can be tricky, so we’ve put together a quick, easy-to-run lean game to demonstrate the core concepts in an engaging format.

Or if you don’t have any Lego laying around, check out MTa KanDo Lean: our tailored kit that covers all 5 phases of lean.

What is the Stockless Challenge?

The Stockless Challenge is a tabletop activity for teams of 3-5 participants. The activity simulates a manufacturing process and illustrates how kanban principles can be applied. 

The goal is to design a work area for a Lego product: a Small Trolley with 6 variants, requiring the assembly of a total of 4 sub-assemblies. Variation is based around colour of components, reflected in the name of each variant:

  • BWB: black block at the back, white plate next to handle, black plate at the front
  • RWB: red block, white plate, black plate
  • GWB: grey, white, black
  • BBW: black, black, white
  • RBW: red, black, white
  • GBW: grey, black white

The image below illustrates an example kanban layout to be used in the activity:

  • There are 4 workstations
  • Raw materials are in circles
  • Kanbans are squares, with the required sub-assembly shown
  • The process moves from top to bottom
  • The final worker assembles the required variant according to demand: all variants are shown at the bottom

How does the Stockless Challenge work as a lean game?

This activity simulates a manufacturing scenario to illustrate the contrast between traditional manufacturing and one-piece flow using kanbans. Participants use both methods, and the activity is designed such that kanbans become the key to success.

This is a lean game built on experiential learning principles: after completing the manufacturing steps, participants review the relative performance of the two manufacturing methods during the structured review sections of the activity.

The accompanying downloads enable you to create your own experiential learning workshop suitable for traditional facilitation, remote facilitation or team self-facilitation. 

You can find instructions below or download the resources to it here:

Download your FREE Lean Game resources 👇

The Stockless Challenge instructions

Here are the steps for the Stockless Challenge:


  1. Download your resources
  2. Gather up some Lego
  3. Brief the participants 

Phase 1: Getting to know the product

  1. Individuals build product variants
  2. Review Phase 1

Phase 2: Testing the maximum output

  1. Test the maximum output
  2. Review Phase 2

Phase 3: Incorporating kanbans

  1. Agree a target rate for a controlled flow
  2. Design a layout using kanbans
  3. Complete a production run of 6 deliveries
  4. Review Phase 3

Full instructions below.


1. Download your resources

It’s possible to run the activity without the resources, but you’ll likely achieve more insightful outcomes if you use them. Download them right here.

2. Gather up some Lego

If you’re using our Lego model, make sure you have enough parts for all groups to build all variations of the required models:

We recommend getting about twice as many of each Lego piece as you’ll need, so that it’s not made obvious by what’s available which pieces participants should use.

3. Brief the participants

Run participants through the briefing slides. For best results, use teams of 3-5 for this activity. Split participants out into as many groups as required to achieve this.

Phase 1: Getting to know the product

4. Individuals build product variants

In this phase, each individual participant builds one product variant to assess how the sub-assemblies and final assembly are built, how long it takes, and to understand the key product quality features.

Allow 10 minutes for this stage.

5. Review phase 1

Run through the phase 1 review questions, designed to refine participants’ understanding of the process and highlight potential shortfalls.

Phase 2: Testing the maximum output

6. Test the maximum output

In this phase, participants gather into their teams. Each team has 5 minutes to build as many full product assemblies as possible, including at least one of each type. It is up to them how to approach construction.

7. Review phase 2

Run through the phase 2 review questions, designed to refine participants’ understanding of the process and highlight potential shortfalls.

Phase 3: Incorporating kanbans

8. Agree a target rate for a controlled flow

In this phase we begin to explore the introduction of kanbans into the process.

The customer is going to order 6 trolleys, one of each, but participants are unsure in what order. They will be ordered at regular intervals, and participants need to decide how long they want that interval to be – this is referred to as the ‘takt time’. 

Allow 10 minutes for this phase.

9. Design a layout using kanbans

In this phase, participants combine their refined knowledge of the product with their agreed rate to design and layout an appropriate work area. 

Allow 15 minutes for this phase.

10. Complete a production run of 6 deliveries

The final phase involves testing the Kanban layout to deliver 6 assemblies at the target rate agreed in step 9, in the order indicated by the 6 product cards. 

Allow 10 minutes of preparation time for teams to refine layouts and fill each Kanban with the assigned assembly.

Because groups arrive at their own takt time, the time for the production run will vary.

11. Review Phase 3

The review questions in this phase are designed to help participants reflect on the differences between phases 2 and 3. 

You can get full details about the activity and instructions it right here:

Download your FREE Lean Game resources 👇

If you’re looking for more in-depth lean game capabilities, check out our KanDo Lean Kit. This kit has been a flagship part of our range for over 20 years, and continues to be used by organisations all over the world!