Sep 3 2018
“Lean manufacturing as it is traditionally practiced is of benefit to machine shops, but the extent of its benefit is often limited. The Toyota Production System on which lean manufacturing is based was designed for assembly plants that produce automobiles by the thousands. While an assembly plant focuses on low-mix, high-volume production, a typical machine shop focuses on high-mix low-volume production. A machine shop and assembly plant cannot expect to realize the same lean benefits with the same lean tools.”
Source Modern Machine Shop
Michel Baudin‘s comments: Shahrukh and I have long disagreed on these issues and I still take exception to many of his general statements. On the other hand, I agree with most of his recommendations.
Machining is not all about High-Mix/Low Volume
While there may be many small machine shops doing high-mix/low-volume production, the bulk of machining is done in larger Automotive and Aerospace & Defense shops that don’t fit this description. Automotive machine shops remove small amounts from hundreds of thousands of aluminum castings/year with product lives on the order of 4 years; aerospace machine shops, large amounts from forgings in exotic alloys in the hundreds/year with product lives in decades.
“Typical” has no precise, technical meaning and, to me, the pictures that come to mind on this subject are shops machining engine blocks at Honda and aircraft landing gears at Boeing, not the shop down the road that I used to hack the fittings of Ikea closet doors. Shahrukh lists one-piece flow cells, mixed-model production with takt time, and pull-based scheduling as “tools to avoid” but, in the machine shops I have been in, these tools have been quite useful.
Cells and Focused Factories are Different Concepts
Figure 2 in Shahrukh’s article is described as showing part flows in a cell:
What he shows here, however, differs from the concept of a Lean machining cell in the following ways:
- It doesn’t have an operator work area inside, with work flowing in a consistent direction around this area. In this picture, operators cannot assist each other, and you cannot run this line at half-speed with half the people.
- The entrance and exit points are not collocated. In a Lean machining cell, they are, so that the same operator who sees workpieces coming out releases new blanks into the cell. This directly helps prevent WIP buildup inside the cell and raises the operators’ quality consciousness.
Manufacturing professionals often confuse machining cells with Wickham Skinner’s focused factories, which contain dedicated resources to make a product or a product family from start to finish. As the parts go straight to Shipping after the cell, Figure 2 looks more like a focused factory than a cell. Sometimes machining cells are focused factories; most often, they are not, and only handle a process segment, for example, soft machining from blank to heat treat.
Recommendations I Support
I agree, however, with the following recommendations. Please read Shahrukh’s article for details:
1. Segment the Product Mix
2. Rationalize the Product Mix Annually
3. Split One Machine Shop into Two
4. If the Shop Currently Uses a Process Layout, Change It
5. Implement a Cellular Layout in Shop 1
6. Right-Size Non-Machining Processes
7. Purchase a Multifunction Machine Tool
8. Standardize Routings within Part Families
Recommendations I Disagree With
On the other hand, the issue of make-to-stock versus make-to-order strikes me as an issue for Sales to decide on, not Manufacturing. Sales is Manufacturing’s single customer. Manufacturing’s job is to make what Sales wants, regardless of whether Sales’ intent is to put it in inventory to sell later or to fill an actual order. Fundamentally, it makes no difference to Manufacturing.
As for Water Spiders, I mostly see them in assembly operations. In machining cells, Cell Leaders perform the tasks described by Shahrukh.