JIT/Lean Defined

When people who should know are asked to define JIT, the typical response is that JIT “is getting your materials deliv­ered just when you need them.” Probing a little deeper may elicit a response that suggests JIT manufacturers let their sup­pliers keep their materials inventory until the manufactur­ers need it. The first statement demonstrates an inadequate understanding of JIT/Lean, and the second is simply wrong. Even so, many companies under the auspices of JIT/Lean have indeed pushed their warehousing back to the suppliers for a net gain of zero. If these are not the right answers to the question “What is JIT/Lean?” then what is it? Although not exactly what was originally intended, just-in-time/Lean manufacturing, by any of its names, has become a manage­ment philosophy that seeks to eliminate all forms of waste in manufacturing processes and their support activities. JIT/ Lean permits the production of only what is needed, only when it is needed, and only in the quantity needed. This must apply not only to the just-in-time/Lean manufacturer, but also to its suppliers if the system is to eliminate all possible waste. Those companies that have required their suppliers to do their warehousing clearly have not gotten the point. The supplier should not produce the material until the JIT/Lean manufacturer needs it. In that mode, there is no warehousing and, therefore, no wasted resources for buildings, mainte­nance, people to care for the material, spoilage, obsolescence, or other related problems.

JIT/Lean is not so much related to supplier activities, although they are important, as to events on the manufac­turing floor. For example, assume that a company manu­factures motion sensors. There are five discrete processes involved, each carried out by one worker, as illustrated in Figure 21.1a. The traditional production process places a big supply of input materials in the warehouse, doling them out to the production line at the rate of so many pieces per unit time. The electronic assembly and the mechanical assembly processes convert their respective input materials into input materials for the electronic module assembly process. The electronic module assembly and the frame fabrication pro­cesses then convert their input materials into input materials for the final assembly process, which, in turn, converts them into completed motion sensors. Each of the five work areas produces at the rate necessary to meet a quota, or to con­sume all the input materials. The completed sensors are sent to the warehouse for storage until someone buys them.

Figure 21.1a is the simplest possible depiction of this par­ticular combination of the steps required to manufacture the motion sensors. What happens in the traditional manufactur­ing setting takes on a much more complicated and convoluted series of events. This is depicted in Figure 21.1b. In Figure 21.1b, the materials warehouse sends kits of appropriate ma­terials and parts to the first three assembly/fabrication stations (1, 2, and 3) according to a predetermined schedule. Working to their own assigned schedules, each of the three stations con­verts the kits into semifinished assemblies or parts and pushes that output to the succeeding stations, 4 and 5. At this point, we may run into a problem. Ideally the output of stations 1, 2, and 3 would go directly to stations 4 or 5, but for a variety of rea­sons, it is common that the local staging areas for stations 4 or 5 may, at any given time, be unable to accept more input. When that happens, the excess partially built goods, also known as work-in-process (WIP), must be sent to a remote staging area, as shown in Figure 21.1b. The same thing can happen between stations 4 and 5. A comparison of Figure 21.1a with Figure 21.1b reveals how complicated a simple manufacturing job can become. What is not obvious from Figure 21.1b is the expense involved in this kind of waste in traditional manufac­turing. All of that WIP that cannot go straight through the sys­tem, as it appears to do in Figure 21.1a, must be transported to a suitable area for storing it; someone has to keep track of its completion status, and where it is; withdrawal from the WIP staging area must be managed; salaries must be paid for the extra people involved; overhead costs for the staging area must be absorbed; and carrying costs for the WIP itself has to be paid. Even finished goods may go to a warehouse to await customer orders, adding even more costs. Not one of those costs add value to the product, therefore, it is pure waste. All these functions have costs that add up to making the company uncompetitive and are targets for elimination in a JIT/Lean or­ganization. A similar case can be made for competitive dam­age caused by time lost in the process, which can easily add an order of magnitude to the manufacturing cycle time.

Just-in-time/Lean approaches the manufacturing process from the opposite end of the line. Rather than pushing materi­als into the processes and storing them whenever they cannot be accommodated, JIT/Lean controls the line from the output end. Indeed, it can be said that the customer controls the line because nothing is built until there is an order for it. After an order is received for a product, the final assembly process is turned on to put together the required number of units. The assembler pulls the required input materials from the elec­tronic module and frame fabrication processes—only enough to make the required number. Similarly, the electronic module assembly and frame fabrication processes pull input materials from their preceding processes, and so on back up the line. At the top of the line, input materials are pulled from suppliers in the exact quantity needed, and no more.

Following the JIT/Lean procedure, no step in the produc­tion process ever overproduces or produces before a demand is made. Therefore, there is no need for a staging area or the people required to move materials into it and out of it, account for it, and so on. No money is tied up in inventory of raw ma­terials, WIP, or finished goods. If there are no stored materials, there is no spoilage or obsolescence. The elimination of these wastes alone makes JIT/Lean the most powerful manufactur­ing concept to come along since Henry Ford’s moving assem­bly line of 1913. JIT/Lean contributes to the elimination of many more forms of waste, as discussed later in this chapter.

So, the definition of JIT/Lean as used in this book is this:

Just-in-time/Lean is producing only what is needed, when it is needed, and in the quantity that is needed.

Source: Goetsch David L., Davis Stanley B. (2016), Quality Management for organizational excellence introduction to total Quality, Pearson; 8th edition.