Changeover means a certain kind of set-up that we must make before beginning a different set of operations. Often, a changeover’s set-up procedure involves rearranging things. Changeover can be changing of dies & tools, Change of standard parameters, change of parts for assembly. Changeover time is loss of capacity while shifting from one product to another product. Many factories still believe in Obsolete idea of “economic lot size.” Economic lot sizes are thought to be whatever lot size helps to minimize the sum of changeover costs and inventory costs. Factories traditionally have tried to keep their lot sizes as close to the ideal “economic lot size” as possible. These money-saving efforts probably had some value during the bygone days of limited product variety and large-scale mass production. However, today the trend is for diverse product models and small-lot production with short delivery deadlines. These radically different circumstances require a new approach to economic lot sizes. The conventional idea of economic lot size assumes that inventory costs and changeover costs are constant; but changeover costs can vary significantly. Moreover, changeover improvements can drastically reduce the changeover costs.
Technique of SMED (Single Minute Exchange of Die) has helped many organisations to reduce changeover times. First of all we must understand how to calculate changeover time.
Changeover time begins when the current processing task is finished and ends when the next processing task produces a defect-free. To understand concept of SMED, we must understand Internal & External Activities. Internal Activities are those activities that can be done only when the equipment is not running. External Activities are those activities which can be performed even when the equipment is running
There are 6 steps in SMED approach to reduce changeover time.
- Measure Total Job Time
- Separate Internal & External Tasks
- Convert Internal Tasks to External Tasks wherever possible
- Eliminate Internal Waste
- Eliminate External Waste
- Standardise & Maintain Best Practice