Just In Time - JIT - Manufacturing

Just in Time Manufacturing (JIT) is one of the main principles of lean manufacturing, it is the idea of producing exactly what the customer wants, in the quantities they want, where they want it, when the customer wants it without it being delayed or held up in inventory.

Just In Time (JIT) has been developed from the principles used firstly within Ford’s initial production lines where they tried to use flow. Toyota have then refined this flow principle as they realized that the biggest wastes in manufacturing are overproduction and inventory, making what the customer wants too late or too early and producing in quantities that the customer does not need. In post war Japan to use any of the scarce resources for anything other than what you needed today was a very risky move! The History of Lean Manufacturing will give you some insight as to how these principles have developed.

Inventory that is created by overproduction is part of the Seven Wastes as defined within Lean manufacturing. One of the major aims of implementing lean manufacturing is to reduce waste, although this should be done with an eye to creating flow within the organization, flow that allows product to be manufactured at the pull of the customer, JIT.

Inventory is probably the biggest waste of Lean Manufacturing, the inventory in your system does more than just tie up your hard earned cash, it hides all the other problems that you have like the level of water in a river hides all of the rocks below.

Traditional manufacturing drives the creation of Inventory through the waste of Overproduction, we run large batches of material on our machines before the customer wants it or in quantities in excess of what the customer wants. Why, because we have always done it this way is one simple answer, typically the main reason is due to the setup time of the machine. To ensure that we get the best efficiency out of the machine we try to run an economical batch size to ensure that we get the most out of this resource.

These large batches also cause problems with planning, different batches of materials have to be coordinated to be produced at around the same times, this causes problems at things get out of synchronization and we end up with delays with large amounts of work in progress sat there waiting for other components to be processed.

We also plan to have large amounts of inventory, we allow delays between processes to allow a “cushion” or “safety” stock to build just in case there are problems between processes. This allows each process to have other work to process should there be problems with quality, delivery, breakdowns or any other problem, the planners feel more secure that the processes will not be stopped.

One of the main aims of lean manufacturing is to remove waste, especially the waste of inventory, this is the main waste that is tackled when implementing Just in Time (JIT) as one of the principles of lean manufacturing.

The most obvious problem with inventory is the need for space, large amounts of inventory requires large amounts of space to store it, either on the shop floor as work in progress, or within the stores as finished goods or raw materials. The physical space and the containers are all a cost to our business. Just in Time (JIT) looks to free up this space by eliminating this excessive inventory.

Inventory requires to be moved around, the added cost of people and equipment to do this moving is incurred as well as the opportunity for damage.

The most direct impact that inventory has on our customers is to do with our lead times, these large batches and planning delays tend to ensure that our lead times are measured in weeks rather than days. Producing a value stream map of your business can demonstrate the effect of inventory on your lead times and show the level of improvement that you could gain through implementing Just in time (JIT).

Inventory hides each and every problem within the company, the safety cushion that the inventory provides is like the level of the sea, it hides all of the problem rocks submerged beneath the surface. Implementing Just in Time (JIT) as part of lean manufacturing helps you to tackle all of these issues.

To implement Just In Time (JIT) the first things we need to do is lower inventory levels, to do this we have to tackle several issues, the first to tackle is almost always the issue of setup times. In most companies the size of the batch is driven by the time taken to setup the machines, often many hours to change from one production item to the next. This time has to be paid for so it is allowed for within the cost and an economical batch quantity is defined, normally a few weeks worth of production or more depending on the industry.

The way to tackle setups is to use a lean manufacturing tool called SMED, Single Minute Exchange of Die. The aim of SMED is exactly what it says, it wants to reduce setups to single minutes or seconds. It achieves this by eliminating all of the obvious waste in the setup and separating the “internal” and “external” factors of the setup, the aim being to have as much work done for the setup whilst the machine is still running so that the down time is minimized.

Once setups can be reduced to this level the size of the batch can be reduced, this gives the opportunity to bring operations closer together and enable materials to flow between them. This reduces the need for transportation and excessive amounts of space. The reduction in batch sizes immediately reduces your lead times as each batch will take less time to be processes before you see finished product.

Beyond this we start to look at developing cells and flow lines, then introducing a pull system through Kanban. We can also look at smaller dedicated machines for these cells and lines instead of some of the larger “super” machines that some companies employ to do every product in the factory.

Lowering the level of inventory is like lowering the sea level, each time it gets lower we run the risk of hitting some rocks, we have to either predict which rocks we are going to hit and tackle them or lower the level of inventory and react quickly to the problem that occurs!

The benefits of Implementing Just In Time, Creating “single piece” flow at the pull of the customer using a flow line approach;

Reduced cash tied up in inventory.

Reduced space required.

Reduced requirements for transportation and associated people and equipment.

Reduced lead times.

Reduced planning complexity.

Problems seen sooner and reacted to, not hidden by the inventory sea!

The benefits of lean manufacturing implementation can be very significant, normally far in excess of what most people believe possible, implementing the principles of Just In Time manufacturing along with the other main principles of Lean Manufacturing (Respect and involving all of your employees in a continual improvement drive towards perfection) will help your business not just to survive, but to flourish! It will help you to reduce costs and improve profits significantly.

The other lean principles relevant to implementing Just in Time manufacturing are detailed below with links to the relevant lean manufacturing tools to give you additional information on their implementation.

The reason for implementing Just in Time is not just to eliminate the obvious waste or muda as described by the 7 wastes but also to reduce the less known wastes of Mura - unevenness and Muri - overburden. Muri and Mura describe the problems created by production demand that varies excessively causing overburden on the operators in the system.

These problems can be tackled by implementing Just in Time principles such as Heijunka, heijunka is the process of smoothing production for JIT using tools such as the heijunka board for JIT. Work-cells can also be balanced to help you to achieve Takt time by using tools such as the Yamazumi chart.

The batch size reductions required to enable Just in Time and Heijunka are achieved through the use of SMED (Single Minute exchange of Die) to reduce change over and setup times to a fraction of the current times. We also need to improve our machine reliability through the use of TPM (total productive maintenance) and performance measurements such as OEE.

Once we have smaller batches we can work on the layout to give us flow and pull production through our manufacturing systems using Kanban to drive our JIT system.

All of these improvements at the gemba (workplace) can be built on through the use of kaizen continuous improvement principles.

The following are useful links for business support and lean manufacturing resources.

Manufacturing Improvements Institute for Manufacturing

Quality Institute Chartered Quality Institute

American Quality Society American Society of Quality

Manufacturers Association American National Association of Manufacturers

Business Innovation and Skills Improvement UK Department for Business Innovation and Skills

Trade Improvement International Trade Administration USA

Lean Manufacturing Improvements UK Manufacturing Advisory Service

Business Improvements UK Business Link

US Business Improvement US Business Link

Toyota Lean Manufacturing and TPS Toyota

Motor Manufacturers and Traders Society of Motor Manufacturers and Traders

Automotive Industry Action Group Automotive Industry Action Group

These Links will help you to find more information regarding Just in Time manufacturing (JIT) to help you improve your business by implementing lean manufacturing.