The Keys To Quick Changeover
Reducing changeover times will eliminate waste, moving a shop closer to becoming lean.
Lean manufacturing is operating your facilities with the least amount of waste at the highest state of efficiency with the least amount of investment and the lowest number of employees, the highest state of quality, the shortest timeline from order to delivery of the finished products, that you neither over nor under produce, and that you deliver the products to your customer neither early nor late—just exactly on time.
Reducing changeover times is one way to eliminate waste and one area that contributes to a shop becoming lean. The keys to quick changeover are as follows:
- Rethink the idea that machines can be idle, but workers cannot be idle.
- The ideal setup change is no setup at all or within seconds.
- Ensure that all tools are always ready and in perfect condition.
- Blow a whistle and have a team of workers respond to each changeover.
- Establish goals to reduce changeover times, record all changeover times and display them near the machine.
- Distinguish between internal and external setup activities and try to convert internal to external setup.
One day in the late 1960s Taiichi Ohno came over to Dr. Shigeo Shingo and said, "I want you to see if you can reduce the changeover time on this punch press from four hours to two hours." This was a magical moment. Imagine if your client or your boss came over to you and asked that question of you and you knew that it had always taken close to four hours to do that changeover. What would you think?
Dr. Shingo said, "Okay!" And then he sat, watched and studied various changeovers in the plant. A few days later Ohno came over again and said to Dr. Shingo, "Two hours is not good enough we need to lower it to 10 minutes." And Dr. Shingo said, "Okay." With patience Dr. Shingo sat in front of a punch press and watched operators change the molds. As he watched, slowly, light bulbs went off in his head and he found ways to reduce setups, virtually all setups at Toyota, from hours to less than 10 minutes.
Changeover Lessons for Moldmakers
Dr. Shingo’s first trip to America included a visit to Dresser, Inc.—a manufacturing plant that produced gasoline fuel dispensing systems—during which he toured the plant floor with a small group of engineers and managers. He stopped in front of a punch press, asked everyone to look at the operation and determine the percentage of value adding time (time when materials are being converted, altered by either machines or labor). He then took out his stopwatch to time the operation.
Two workers in front of the punch press proceeded to bend down and pick up a large sheet of thin stainless steel from the left side of the press. They placed the steel into the bed of the press. Then they removed their hands to press buttons outside the press, which indicated that their hands were out and clear of the press. The large press came down and formed the metal into a side of a gasoline pump. Then the two workers reached into the press, removed the formed sheet and placed the formed sheet at the right side of the press.
"What was the value adding percentage?" Dr. Shingo asked. One engineer said, "100 percent, the workers never stopped working." Another engineer said, "75 percent," and another said, "50 percent." Dr. Shingo laughed and looked at his stopwatch and said, "Only 12 percent of the time was the process adding value.
Adding value is only when the dies are pressing against the metal to create the formed sheet, the rest of the time is waste." Waste is defined as that which does not add value to the product—excess inventory, excessive motion, transportation, defects (producing scrap), waiting time (workers watching machines), overproduction, incorrect processing and the underutilization of people’s creative talents.
Then Dr. Shingo asked, "What can you do to improve the value adding time?" An engineer immediately said, "You can place a table over here and put the raw inventory sheets on top of the table, so they wouldn’t need to bend down; they could just slide the sheets directly into the press." Another engineer said, "We could install a leveler to automatically raise the sheet metal to keep it at a constant height." A third engineer said, "We could put a spring into the back of the punch press to force the formed metal to leap forward after the stamping." "Yes," Dr. Shingo said. "You all know what to do, so do it!"
This demonstrated the importance of stimulating others to think about how they could bring change to the production process without spending a lot of money.
Another punch press operation was observed. Now, Dr. Shingo asked, "How long does it take you to make this changeover when you go from one product to another?" "Around two hours," was the answer. "I want you to do it in less then 10 minutes," said Dr. Shingo. There was a lot of grumbling—especially from a worker who had been working on the press for the past four years and it always took him around two hours to do the changeover.
Dr. Shingo proceeded to explain the process, "First, I want you to make a shim; cut out a piece of metal and attach it to the top of the next die that you are going to use. This shim will make each die the exact same height so that when you do the changeover, you will not have to adjust the cam. You can then just pull out the old die and slide the new one in without any height adjustment. Second, when the previous process is complete and you are ready to do the next changeover, blow a loud whistle to attract the changeover team, time it with a stopwatch, chart the results, and post those results near the punch press machine. Third, put a metal block under the inventory so the sheet metal slides in quickly. If the thickness of the metal changes you can easily put in another metal block to meet that thickness."
Dr. Shingo discussed the value of examining each part of the changeover process to reduce the time it takes. He explained external activities (outside exchange of die)—things you can do while the machine is running—including making sure all of the tools and inventory needed are ready and close by; checking to see that the next die is ready with all of the necessary parts; pre-heat the die if necessary, etc.; and internal activities (inside exchange of die)—things that can only be done when the press stops—including the use of cranes to lift the die or pneumatics to move the die around; change the clamping method to reduce the number of bolts and hoses, etc.
Dr. Shingo then requested to see the new changeover process. It was completed in 12 minutes.
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