The problem is that many plants produce multiple products on the same assembly line, for example, all GM X cars. The right part must be at the right place at the right time and any program to control this process must run in real time. Many schemes have been devised to improve the flow of parts and resources because substantial savings are possible through reduction of inventory and wastage. The US contribution is called manufacturing resource planning, MRP, which schedules the flow of parts as part of the forecasted production schedule. A more advanced form of MRP is manufacturing resources planning, MRP II. MRP II also considers the cash flow required to order the parts and pay expenses in the forecasted manufacturing plan. It is important to note that both MRP and MRP II are future oriented plans.
The most advanced plan, which was developed by Toyota, is JIT, just-in-time, where the order for a final product generates the orders for parts as they are needed (demand pull). Toyota created this system using order cards without computers. The ideal of JIT is that there should be no inventory; consequently, every part must be perfect when it reaches the assembly line. At Toyota parts are ordered from suppliers only as they are needed. Obviously to make this work the suppliers must be located adjacent to the Toyota factory. While some Japanese firms have been able to goad their suppliers into this level of quality control and obtain instantaneous coordination with suppliers, few firms outside of Japan have been able to successfully implement JIT.
A common feature of both MRP and JIT is the emphasis on reducing inventory and making factories more efficient. JIT places more emphasis on efficiency and quality.
Another aspect of automation in parts manufacturing is how parts are delivered to their assembly point in a factory. In many older manufacturing plants parts are handled as many as 10 to 15 times from the time they enter the factory until they reach their assembly station. Obviously, the more a part is handled the greater the chance for a fiasco. One advance in manufacturing automation is to automate the delivery of parts to their final destination.
Ideally, parts from outside suppliers are handled twice. Once when they are arrive at the factory and once when they are assembled into the product. One of the first firms in the US to do this was Apple in the production of the first Macintosh. Jobs and the chief engineer, Irwin, spent two years (probably part time) studying Japanese production methods. The original Macintosh factory incorporated three basic concepts:
a. Just in time parts delivery
b. Linear production system
c. Good environment for workers.
The first Mac had about 500 parts. To supply the parts to the linear assembly line, Apple installed three automatic parts delivery systems and one manual system:
a. Totes or plastic bins: These stored electronic parts
b. Overhead rail: This delivered bulkier items.
c. Automatically guided vehicles(AGV): Delivered other items
d. Humans delivered screws once a month or so because automating this delivery would be too expensive.
The trend in automatic delivery of parts is in making advances in AGV systems and automatic warehouses.