Synchronizing manufacturing operations helps eliminate waste and increase efficiency. High-volume production systems achieve this by linking processes. For situations where a linked production line is impractical, a kanban system can achieve the same or greater benefits, and at less cost.
This blog explains kanban in manufacturing. It covers implementation steps, challenges to be anticipated, implications for maintenance and the benefits that can be expected.
What is a kanban system?
Kanban is one of the most important tools in Lean manufacturing. By controlling production, it imposes a “pull” system that highlights bottlenecks and drives out waste. It’s also very visual, letting supervisors and workers quickly see the current status of manufacturing orders.
“Kanban” is a Japanese word that loosely translates as “signal.” This signal is used to request delivery of parts or materials in a just-in-time manufacturing operation. This connects operations, but means any unplanned stoppages quickly ripple upstream. Consequently, Lean maintenance is important for success with kanban in Lean manufacturing.
History and principles of kanban
Kanban was developed as part of the Toyota Production System (TPS) when raw materials were in short supply throughout the years following World War II. The TPS uses just-in-time (JIT) production to minimize waste by having downstream departments “pull” production from upstream.
“Pull” is achieved by departments requesting parts or materials from their upstream “suppliers” using kanban. In this way nothing is made until it’s needed.
Western manufacturers have been adopting elements of the TPS since the 1970s. Now known as Lean manufacturing, it usually includes pull systems, JIT and kanban.
The main principles governing use of the kanban process in manufacturing are:
- Visual work
- Limiting work in progress
- Managing flow
- Making process policies explicit
- Continuous improvement
Lean recognizes three main types of kanban: production, withdrawal and transportation. The first is a signal to start making something, the second is a request that parts or materials be issued from stores and the third, generally used on large sites or multisite operations, is a request to ship.
Components of a kanban system
A kanban can take many forms. In some situations, cards are the most practical. Other approaches are kanban boards and the “two bins” system. Kanbans used to request materials from off-site suppliers are usually electronic.
Kanban cards
A department has cards for all the parts or materials it needs. Typically, each card displays the SKU or part number and a quantity. When the department needs material, they send a card to the upstream department (a production kanban), or to the stores (a withdrawal kanban). The required quantity is then produced or withdrawn and sent to the downstream department.
Flow can be balanced by creating a “supermarket” between upstream and downstream departments and adopting a kanban inventory system. Here a withdrawal kanban requests material from the supermarket, which then sends a production kanban upstream to replenish the quantity issued.
Kanban board
This shows the status of work or orders within a department. Usually it has three columns: To-do, in progress and complete. Each order is shown by a card, and the card is moved between columns to show its status.
The cards used on a kanban board could be the same as those used to request production. The request first goes into the to-do column, progressing along until both material and card are delivered to the downstream department.
Two bins
In this approach the bin used to store and transport material is the signal. A downstream operation sends an empty bin upstream as a request for parts or materials, while simultaneously working from inventory in the second bin. In a perfectly balanced process, the new bin arrives from the upstream department just as the last item is taken from the old bin.
A variation of the two bin system is to have squares marked out on the floor for pallets or other dunnage.
WIP limits
The kanban is always for a specific amount of material or quantity of parts. Fixing the number of kanbans automatically fixes the amount of work-in-progress (WIP) inventory that can exist between two departments.
When kanban is first implemented there may be substantial inventory between the connected departments. Continuous improvement entails gradually reducing this until there is the minimum needed to avoid the downstream department being starved of work.
Implementing kanban in manufacturing
Here’s a five-step process:
1. Assess current workflows and identify bottlenecks. These are areas where kanban could be especially helpful.
2. Design and set up the kanban board. This means thinking about how parts or material will be requested and tracked.
3. Create and implement kanban cards: Set quantities that allow feeder departments to maintain a takt time.
4. Establish WIP limits. As the system will almost certainly require some tuning, start with relatively high levels of WIP but plan on progressively reducing the number of kanbans, and hence WIP, as experience is gained and bugs ironed out.
5. Train employees and integrate kanban into daily operations. It’s imperative that everyone understands nothing can be moved without a kanban.
Benefits of kanban systems
Kanban can take time to bed in and for the benefits of lower WIP to become clear. Manufacturers with experience of kanban in a manufacturing process report the following gains:
- Improved efficiency: Reducing WIP tightens connections between departments and kanban synchronizes their work. Together these let orders move through faster, which reduces leadtime.
- Reduced waste: Conventional push manufacturing promotes overproduction to ensure downstream departments have enough to work on. Also, when WIP is high there’s more risk of damage, deterioration and obsolescence.
- Enhanced flexibility: Changes in demand appear as higher or lower frequency of kanban circulation. This message quickly passes upstream, driving each department to adjust the quantities being produced.
- Better communication: Kanban is inherently very visual. By making demand and order status clear, everyone working in production is aware of the workload and priorities, which improves collaboration and cooperations.
Challenges and solutions
While kanban and pull manufacturing are in principle very simple, implementation and ongoing operation can pose problems. Common obstacles include:
- Resistance to change
- Unplanned downtime, which brings upstream departments to a halt
- Implementation mistakes, such as poor visibility and inappropriate kanban quantities
- Fluctuating demand, which can lead to backlogs
Solutions must be developed to suit the specific product being made and manufacturing processes. However, they will usually include:
- Training workers in the goals and operation of the system
- Implementing or upgrading preventive maintenance to reduce downtime
- Starting with a pilot implementation and adapting quickly as lessons are learned
Future trends in kanban systems
As manufacturers gain experience, they look to extend kanban beyond the factory floor. Two future trends are digital kanban and integration with other systems.
Digital kanban is a solution for when departments connected in the workflow are not in proximity. Rather than using physical signals, they will increasingly adopt digital methods that provide much faster communication and response.
A concern with kanban has long been its poor connection to the ERP and MES systems. This results in their data not being an accurate reflection of order status on the factory floor. Thus, a second trend is to integrate kanban with these systems using technologies like bar codes and RFID.
The kanban system in manufacturing
Kanban is an important tool in Lean, thanks to its ability to drive pull manufacturing and reduce waste. Effective kanban systems in manufacturing display an elegant simplicity that dramatically improves visibility and communication, but they can be hard to implement.
Equipment reliability and availability is an often-overlooked aspect of successful kanban implementation. As a leader in industrial asset management, ATS has the experience and resources to help manufacturers confront and resolve issues with unplanned downtime.
