Just in Time (JIT)

This document describes our personal view of what Just in Time should encapsulate. It includes references to flexible plant, manufacture in cells formed into natural groups (group technology), production smoothing, Takt times, (line balancing), level scheduling, the SMED system (Single Minute Exchange of Die), for set up reduction, standard working, simple visible controls, and low inventory pull systems such as Kanban (Kamban).

Links to other best practices and training at bottom of page.

Just-in-Time originally encapsulated the logistics aspects of the Toyota Production System. Our current view of what it should encapsulate incorporates some of the principles of "leanness" because by itself and specifically detached from Kanban and continuous improvement it begins to loose its meaning. Also to implement these techniques without flexible, reliable processes and appropriate organisation is impossible. However at this point it begins to blur with agile manufacturing principles. This section should therefore be read in conjunction with these others and as a minimum JIT should include:

• Strategic Capacity Management for example the use of multiple small machines (rather than "efficient" expensive machines that have to be kept busy).
• Group Technology (Also commonly called "Cellular" manufacturing). This is based on the principle that segmented (possibly product focused) manufacture is much simpler, with less interference of material flows, than factories where similar processes are grouped together, such as heat treatment. This principle has also been applied to other processes where natural groups are formed to perform a complete process aligned to customer needs in manufacturing and other industries, and "category management" in procurement. However we have shown in some circumstances that the benefits of cellular manufacturing can be gained by creating "virtual cells" (without moving the plant). (See Business Process Reengineering / Organisational Redesign). This thinking was based on our early experience of forming cells, which demonstrated, at least to our satisfaction, that cell stability can be poor if volume and / or mix change, with the need to review cell integrity at regular intervals.
• Production smoothing, avoids the problems associated with poor demand tracking (See Demand Management) and unnecessary interference of the production schedule. In a recent consultancy assignment we established that whilst customer orders were highly volatile, the underlying demand was extremely stable. The volatility downstream in the supply chain was in fact being artificially induced by poor customer planning, resulting in late changes to the order schedule, to bring the orders back in line with the very stable underlying demand! However many companies experience cyclic or seasonal demand, where it is beneficial, and in some cases vital, to flex or move resources to respond to fluctuating demand, the alternative being to pre-build stock to a forecast to afford some production smoothness, at some risk and tying up of capital. A refinement of this process is, in addition, to use "Takt" times (See Previous Technique of the Week T021: "Takt Time, Measuring Throughput Time") to set rates of production. I.e. the hourly rate of demand from customers (as opposed to coarser units of time and uncorrupted by planning parameters).
• Levelled schedules, bring more stability and regular patterns of production (See Previous Best Practice of the Week 005: Level Scheduling).
• Labour balancing when used in conjunction with Takt time (Previous Best Practice of the Week 046: "Using Takt Time to Manage Your Business") highlights process / line imbalance from the cycle time of one operation to the next and indicates the need to balance the manning for each operation (and the opportunity to improve the slowest to achieve balance). There are some dangers here in achieving balance. (See the "lean question" at the end of this article.) This is the guiding principle of lean manufacturing where the problem would be permanently solved as opposed to the traditional approach of buffering the uncertainty with stock.
• Set-up reduction, which is based on the principle that small is beautiful as far as batch sizes are concerned and that what is required, is made that day without inflating batch sizes. (In the article Previous Technique of the Week T019: Avoiding Set Ups and Reducing Changeover Times (SMED) (and thereby reducing batch sizes)) we show that there is in fact much more to this than the set-up reduction techniques proposed by Shingo. But there are a number of techniques available to do this stated by Shingo. His SMED techniques give rise to the opportunity to reduce batch sizes by up to a factor of 50. It should be remembered however that this should be applied to the bottleneck first and maybe even stop there.
• Standard working. Defined by the operator, not the industrial engineer, it is a prescribed sequence of production steps done by one operator and balanced to the required rate of demand. It becomes the basis of understanding the job and therefore what can be improved. (Will be covered by a future article)
• Visual controls. Characteristic of JIT factories are simple visible controls, held locally where they are used to monitor key performance indicators and used as a spur to improvement. This is a deliberate attempt to give eyeball control rather than the over-sophistication provided by remote computer systems. Examples include:

• Standard container sizes replacing irregular sizes such that stockholding is a simple question of counting containers rather than the parts within them. The reorder point in this case is a chalk mark on the wall rather than it being hidden in a computer system and appearing on a reorder report the following morning.
• The graphs of quality, productivity, safety and delivery performance updated daily and discussed at the daily stand-up meeting.
• A small segregation area for quality defects kept deliberately small to ensure that problems are solved quickly and rejects are not allowed to accumulate.
• The flip chart to write down today’s problems while they are still fresh.

• Minimising inventory, Minimising Work in Process, and synchronising production by the use of replenishment systems such as Kanban. The principle of Kanban operation is extremely simple but there are a number a detailed considerations to make in design and implementation which are not trivial including:

• Positioning of buffers
• Buffer sizing
• Signalling mechanisms
• Prioritisation of signals
• Priming the system
• Accounting aspects
• Ongoing integrity of cell design

Summary

JIT can only be achieved by a combination of strategic capacity considerations, strategic supply chain management and detailed ways to make work flow using pull systems such as Kanban. This can only be achieved by a holistic view such as is given by Business Process Reengineering, followed by a focused approach to continuous improvement.

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The following further best practice articles were also mentioned in this paper:

The following public training courses and in-house workshops provide solutions to Just In Time & methods of implementing it:

To discuss your consulting or training needs with one of our independent consultants or trainers please Contact Us.

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Ó SM Thacker & Associates (Consultancy and Training Specialists) Original April 2000 Version 8 November 2009