Single-minute exchange of die (SMED) is a manufacturing process that favors rapid changeovers between running different machines and producing different units. The term does not refer to changeovers of less than a minute, but rather ones that occur within single digits, or less than ten minutes. SMED is useful for streamlining production processes by removing bottleneck effects, reducing waste, and decreasing the inventory space needed at any given time.
During a typical manufacturing process, the machinery and equipment is turned off and reconfigured once all of the products have completed a run. In-progress products must be stored at this time until the new equipment has been prepared for a second run. This period of time, known as the changeover, is where SMED focuses to create lean manufacturing.
Manufacturers used to assume that it was the most cost effective to optimize the number of units produced in each step of the process, but in reality improving changeover and enacting lean production tactics can save time and money. Not only will this reduce the required inventory space to store in-progress units, also known as lot size, but it will also increase the return on investment (ROI) by using the equipment more efficiently. The number of works in progress (WIP) also decreases because products are turned out in smaller, faster batches.
A common example of SMED in practice is the Toyota® vehicle manufacturing process. The process initially focused on high numbers of units for each step, but the company found that rapid changeovers saved them money in the long run. This is because they were spending large sums of money storing WIP on expensive land, whose costs were higher than the cost of changeovers. By streamlining the equipment set-up times, the company was able to save money by reducing their economic lot size (EOQ), which had previously been large.
There are several targets for improving lean manufacturing that SMED tackles. First, the process requires the removal of steps or equipment that are not essential. This could involve anything from implementing new, more universal equipment to limiting adjustments on non-essential machines during changeovers. Second, the process should include all of the necessary materials for the next step, as well as records of their locations, to make sure that everything needed is present at the time of the changeover. Simplification of the necessary steps in the changeover and thorough measurement and testing are the last main steps in the SMED process.