Friday, April 16, 2010
Why Not Manufacture in Easy Batches?
During a workshop, a manager resisted the idea that batches are always to be avoided if possible. He used the example of paying his bills by check (this was before the days of online bill-paying). It was easiest for him, he said, to sit down at the kitchen table, open all the bills and take them out, write all the checks, stuff all the envelopes, put stamps on all the envelopes and drop them in the mail.
I asked the group if there was anyone present who had ever sent the wrong check to a payee. A couple of people admitted that it had happened to them.
If you practice one-piece-flow, processing one unit at a time – in this case one bill—you practically eliminate that particular mistake. You open one envelope, read the bill, write the check, put it in the envelope with the bill stub, seal the envelope and put a stamp on it. If you wait to put stamps on the envelopes until all have been sealed and stacked, there is more of a chance of skipping an envelope and mailing it without a stamp.
The manager still protested that it would take less time to process his bills in batches. That may be the case, but the extra time can be minimized if you organize the work station for one-at-a-time. What would that take? To begin, a place for everything and everything in its place: the checkbook, the stack of bills, the letter opener, the stamps. In the factory one of the sources of waste is having to hunt for and go get what you need, stopping your value-adding activity while you do it.
In an auto industry factory, the product required a length of rubber hose about six inches long. There was an elegant machine that chopped the lengths of hose from a large roll. I watched it working very fast, spitting out short lengths of hose in less than a second a piece. These fell into a large barrel. The machine did not require an operator, unless it stopped automatically due to a problem, or when the current barrel was nearly full and an operator had to stand ready to shut it off and the full barrel with an empty one.
There were two barrels beside the machine that had large reject tags on them. I asked why. Either through human error or a mechanical problem, the machine had cut the lengths too short. There was no way they would work. If they had been too long, they could at least be reworked, buy trimming off the excess. These hoses would have to be scrapped.
I asked what they had done to keep this problem from happening again. The answer: more frequent inspections. Inspections are an activity that does not add value and are therefore wasteful. We gathered the improvement team that was involved in the workshop and I gave them a challenge. How could we cut the length of hose each time we needed it?
The team experimented with various cutting devices and improvised a tree-trimming lopper as a guillotine, through which the hose could be threaded. A stop at exactly the right distance made it possible to cut a single piece to the exact size when it was needed in less than a second. There were details to be worked out so that this could be done at several assembly stations. This included receiving smaller rolls of hose from the supplier to make it easy to mount this operation at each place in the factory where the short length of hose was needed.
When making changes of this type we often run into the question of whether the supplier will cooperate without charging more. Sometimes some negotiation is required, but there have been many times when the supplier sees the point and is happy to oblige, even seeing advantages for himself.
At another client, a specialized hydraulic pump was being assembled to fill orders in quantities of four to seven units per day. Each pump was shipped bolted to a wooden pallet measuring two feet by two feet. While I was in the factory a delivery of pallets arrived and took up a space along a wall that was two feet wide, several yards long, and ten feet high. The plant was receiving a supply of pallets that would last approximately two months.
When the improvement team asked the purchaser to see if the supplier would deliver small quantities more frequently, the purchaser was sure that the supplier, a local sole proprietor with a pallet making business, would not want to change his practice. Grudgingly he agreed to invite the supplier in to meet with the team.
We showed the pallet maker the space that all his pallets took up under the current arrangement. He recognized it, as he had had to fill a space of equal size at his shop. When we said that we wanted to have much smaller delivers more frequently, he suggested daily deliveries. What was more, he said, he drove by the plant every day. He would put the seven needed for a day in the back of his pickup and drop them off. We would eliminate the requirement and cost of transporting them by the trailer load.
All we had to do was ask.
Batches hide errors and quality problems, sometimes in large numbers. They have to be tracked, managed, counted and recounted. They take up space. The can become obsolete. They sit there with all the expense so far tied up and no further value being added. When batch processing seems easy, the hidden costs should be remembered.
Notes: For more on manufacturing in batches, see the post, “Keeping it Simple,” in this blog (March 25, 2010).