![]() JIT presumes that to achieve such reductions the system should deliver to every operator, in any conversion process, whatever he or she needs just when it is needed. It asserts that incremental reductions in lead times are crucial indices of manufacturing improvement. It underscores the importance of lead-time management in all aspects of manufacturing. Think of JIT as a statement of objectives. What does either method have to do with JIT? When you plan for a meeting, you are in the push mode. What Is JIT Anyway? When you drop everything to take care of a walk-in client, you are reacting, implicitly, to a pull system. In other words, the caterer gets a picture of production in his mind and pushes materials to where he expects them to be needed. ![]() He can account for the special event that he knows is scheduled to take place in midweek. He reckons roughly how long it takes to broil a steak or serve a party of four he figures out how many meals he can accommodate and commits to buying what he needs in advance. In a push system, the caterer estimates how many steaks or lobsters are likely to be ordered in any given week. In effect, the customer’s purchase triggers the pull of materials through the system the customer initiates a chain of demand. The manager orders more ground beef when the maker’s inventory gets too low. Thus a fast food restaurant like McDonald’s runs on a pull system, while a catering service operates a push system.Īt McDonald’s, the customer orders a hamburger, the server gets one from the rack, the hamburger maker keeps an eye on the rack and makes new burgers when the number gets too low. The basic difference between pull and push is that a pull system initiates production as a reaction to present demand, while push initiates production in anticipation of future demand. The question of how to manage inventory cuts quickly to the basics of manufacturing in an age of intense global competition: How much automation is enough? How should the factory respond to customers? How much can you load on workers? How do you deal with orders? What is waste? The shop floor is still a microcosm of the whole business. All managers can learn interesting strategic lessons from their choices. Indeed, most advanced manufacturing companies find that they require a hybrid system of shop floor control systems-tailored systems, including innovative pull systems like kanban, as well as time-tested, computer-driven push systems like MRP II.Īt the same time, shop floor managers should know just when MRP II is an unnecessary burden and when kanban can’t work-when push comes to shove and pull comes to tug. ![]() JIT principles should certainly not preempt the use of MRP II. The idealized conception of the shop floor one gets from some extreme JIT advocates-a line, inherently flexible, inventoryless, even computerless, replenished by infinitely responsive suppliers-may actually prevent manufacturing managers from using the tools they need to run their operations. This debate needs clarity, and then it needs to end. Worst of all, doesn’t kanban look suspiciously like the old order point, order quantity (OP, OQ) system that MRP once discredited and replaced? In crucial respects, MRP II aims to be a JIT system, while kanban cannot. What must be particularly confusing to manufacturing managers who get wind of this debate is that kanban systems are used most successfully by the same Japanese and American corporations that are famous for spearheading the use of advanced computer automation-Toyota or Hewlett-Packard, for example. For JIT, presumably, human pull is good, computer push is bad. In contrast, JIT people seem especially drawn to such computerless, “pull” techniques as kanban, the system used extensively in Japan’s auto and electronics industries. An MRP II program promises manufacturing managers more precision than it can deliver, requires unnecessary information, and demands more formal discipline than the shop floor needs. MRP, proponents of JIT explain, is merely a “push” technique. One recent ad put the choice this starkly: “JIT vs. Pick up virtually any manufacturing magazine these days and there will be some articles and pages of advertisements by consultants extolling the virtues of JIT over such computer-driven control systems as materials requirements planning (MRP) or materials resource planning (MRP II)-as if JIT principles were opposed to MRP and to the use of computers. Consider the curiously vexed debate about how to get materials to, and work in process through, the shop floor. It is also producing over reactions from people determined to make them stop. Like all good revolutions, just-in-time manufacturing is producing revolutionaries who don’t know when to stop.
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