Chapter 04 - Reducing Lead-time
Q: Theory of constraints scheduling creates smaller lots to reduce lead-time. Are there any other methods for reducing lead-time?
A: The next method we will discuss for reducing lead-time is that of making the transported lots smaller.
The transport method (stacking method) described so far has been the ES method shown in the above diagram. It is called ES (end-start) because the next process begins right after the previous process ends. In contrast to this is the SS method, one in which the second process starts simultaneously with the first process. This method greatly reduces lead-time, but it may result in a schedule in which the subsequent process finishes earlier than the first process if the distance between the two is large. With this method, one cannot make job instructions that can be used on site. The method for getting around that is SSEE. This method adds to SS control that further synchronizes the end of the previous process with the end of the subsequent process. This results in a schedule that completes the first process before the next.
SSEE requires that every time the earlier process makes a product, it must be transported to the subsequent process. Consequently, when manufacturing is based on SSEE, the machines must be located close together so that no transport is necessary or certain employees have the job of doing nothing but going round and round transporting product. This method is also known as single-item flow production, because products are transported in units of one product each (or one palette each).