Multi-Process Operations
Building up one-piece flow production is the best way to get rid of defects, waste, and production delays. The basic concept in one-piece flow production is to send workpieces along the processing sequence one at a time, adding process-ing (value) to the workpieces at each process. As such, flow production is a very basic ingredient in JIT production. (For further description of flow production, see Chapter 5.)
Lack of respect for workers Minutely specialized job tasks
“Human robots”
Productivity and Humanity in the Factory
Productivity Humanity
Lack of concern over economic matters Selfish production Corporate deterioration The joy of constructive activities Multi-skilled workers handling several processes
Corporate development
Figure 6.1 Relationship between Productivity and Humanity.
The following are the main things we must have in order to establish flow production.
Equipment.
◾ We need specialized machines that include only the essential required functions, are inexpensive, and are small enough to fit right in to the production line.
Equipment layout.
◾ Equipment must be arranged
accord-ing to the processaccord-ing sequence. Workshops should be of the “flow shop” type (as opposed to the “job shop” type) and should preferably consist of U-shaped manufactur-ing cells.
Operational procedures.
◾ We must give up “shish-kabob”
production and learn one-piece flow in which work-pieces are fed to and from processes one at a time. All workers must stand while working and learn to handle several processes in order to synchronize their work with the cycle time.
People.
◾ We must train workers in the multiple skills they will need to handle several processes.
Multi-process operations are the key that opens the door to one-piece flow production. Without multi-process opera-tions, there can be no JIT production system.
We are not likely to find much worker enthusiasm for multi-process operations if we introduce such operations in conventional “job shop” type workshops (workshops laid out according to function). Multi-process operations can be achieved in such workshops, but the amount of conveyance the workers would have to do themselves by walking and carrying workpieces makes it hard to find time for process-ing the workpieces. Therefore, we first need to change the equipment layout to the “flow shop” arrangement (equipment arranged according to the product). This changes the work-shop from being a unit process station to being a multi-process production line.
Obviously, we cannot change a multi-unit process station to a multi-process production line unless we change the equipment. A group of presses are only good for pressing and a group of drilling machines are only good for drilling.
There is no way we can arrange multiple press units or drill-ing machine units into a multi-process production line. That is why we need to make the distinction between the group-ing of machines that all serve a certain processgroup-ing function (multi-unit process stations) and the grouping of machines that provide a sequence of processing functions needed to build a certain product (multi-process production line).
Figure 6.2 illustrates this distinction.
The concept behind multi-unit operations (that is, opera-tions at multi-unit process staopera-tions) is to have one worker handle several processing machines that perform the same type of process. By contrast, the concept behind multi-process operations is to have one worker handle several processes (arranged according to the processing sequence).
No matter how many machines multi-unit operators handle, they only need one skill to operate them since the machines are all similar (presses, drilling machines, or whatever). Since multi-unit operations all take place at the same processing stage in the overall production line, we refer to multi-unit operations as “horizontal operations.”
Conversely, operators who handle multi-process operations must have skills in several types of processes, such as presses, drilling machines, bending machines, and so on. We there-fore refer to such workers as “multi-skilled workers.” Since multi-process operations occur along a sequence of processes that include several stages along the overall production line, we refer to multi-process operations as “vertical operations.”
Once we have established flow production that uses multi-process operations, we can be sure to expect higher quality . Almost all surface defects on products—such as dents, cracks, or missing parts—will disappear. One-piece flow will ensure that when the occasional defect does occur, the line
can be stopped before an entire lot of defective products is turned out.
Best of all is the fact that this improvement enables us to track down the causes of defects and take appropriate counter measures. In conventional shish-kabob production, anywhere from 500 to 1,000 defective units are produced
One worker handles four similar machines.
Zero dented, damaged, or missing items
Zero defective lots
Causes of defects are tracked down and arrested.
Production workers do their own inspecting.
Quality is built in at each process.
Zero waste
Costs are steady regardless of volume fluctuation.
Workshops try to reduce manpower.
Dented, damaged, or missing items Defective lots
Causes of defects remain a mystery
“I make the products, you inspect them.”
Inspectors are responsible for sorting out all the defective products.
Creates lots of waste related to in-process inventory, space, man-power, and conveyance Costs vary depending upon volume.
Workshops try to save labor.
Long lead-times Chronically late deliveries Not very adaptive to schedule revisions
Short lead-times Zero late deliveries
Adaptive to schedule revisions Quality
(Q)
One worker handles five different processes.
Figure 6.2 Difference between Unit Process Station and Multi-Process Production Line.
before anyone notices the defect. Since the people who dis-cover the defects are usually several stages down the line from the operators at the defect-causing process, it is very difficult to trace where that process is, and therefore it is very likely the defect will occur again.
By contrast, flow production using multi-process opera-tions usually includes self-inspection by the multi-process operators. These operators not only turn out products, they objectively inspect them for defects. The inspection results reflect directly on their work and remind the operators that quality is built into products at each process.
In conventional shish-kabob factories, the general attitude among line workers is: “I just make them. It’s up to the inspectors to inspect them.” When we stop to think of the way the quality “buck” gets passed to the inspectors, we can recognize just how flawed the conventional approach is. The inspectors do what they can to sort out defects, but they do little or nothing to stop them from recurring.
We have been comparing shish-kabob production and flow production using multi-process operations only in terms of their quality aspects. But there are other important aspects, such as costs and punctual delivery. The cost impact of these two very different approaches includes the cost of in-process inventory waste, space-related waste, conveyance waste, and waste caused by putting things down and picking them up again. Flow production using multi-process operations can completely eliminate all of these kinds of waste.
One way to eliminate these kinds of waste is the prac-tice of manpower reduction. (Chapter 7 describes manpower reduction in detail). Manpower reduction means using the minimum number of workers needed to produce the amount of products ordered by the client. When work is divided into single-skill tasks, more workers are needed to operate a pro-duction line and it is more difficult to reduce the number of workers when client orders shrink. Multi-process operations
enable us to easily determine the minimum number of work-ers needed for any particular amount of output.
As for the delivery aspect, the lead-time for multi-process operations is remarkably shorter than for conventional shish-kabob operations. The former method not only prevents delivery delays, but reduces lead-time to where it is much better able to adapt to schedule revisions than the latter con-ventional method.