Modern Machine Shop gives you ten ideas on how to create a more lean shop floor:
In addition to the right mix of traditional strategies, a new lean manufacturing toolkit can make high-mix, low-volume machining faster, more predictable and less expensive.
Figure 1: On left, a machine shop’s initial Product-Process Matrix; on right, the final Product-Process Matrix after identifying and grouping by part families. (Courtesy of Strategos Lean Manufacturing.)
Figure 2: An example of material flows for a part family after implementation of a machining cell. Before, the parts machined followed a spaghetti diagram that sent them to different stations throughout the facility.
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.
What tools are those? Today, many machine shops have realized the gains from implementing one or more of the methods listed in the “Lean Tools to Use” list below. In contrast, the lean tools in the “Lean Tools to Avoid” list are ineffective or inapplicable in a machine shop. They cannot handle the complexity of a high-mix low-volume shop, especially if it is a job shop!
Lean Tools to Use
Lean Tools to Avoid
- Strategic planning
- Top-down leadership
- Gemba walks
- Employee engagement
- Workplace design with 6S
- TPM (Total Productive Maintenance)
- Setup reduction (SMED)
- Error-proofing (Poka-yoke)
- Quality at source
- Visual workplace
- Product and process standardization
- Standard work
- Continuous problem solving
- Pencil-and-paper problem solving
- Value stream mapping
- Assembly line balancing
- One-piece flow cells
- Product-specific Kanbans
- FIFO sequencing of orders
- Pacemaker scheduling
- Inventory supermarkets
- Work order release based on pitch
- Production based on level loading
- Mixed-model production with Takt Time
- Pull-based production scheduling
- Manual scheduling with whiteboards
With this article, I would like to describe a different toolkit. Even for machine shops that are lean today, there are benefits yet to be gained by implementing some or all of the tools described in this article to replace the lean tools in the “Tool to Avoid” list.
Here are some of the new tools that belong in the machine shop’s lean manufacturing toolkit:
1. Segment the Product Mix
Most machine shops choose to make a diverse range of products that differ in their respective annual production volume, demand pattern and margin. Based on these three business attributes, divide the products into two segments: Runners/Repeaters and Strangers.
For parts in the Runners/Repeaters segment, batch sizes will tend to be medium or large with many parts having long-term agreements. In contrast, for parts in the Strangers segment, batch sizes will trend small. These orders tend to be one-offs, repairs, prototypes, or start- or end-of-lifecycle jobs. Different order fulfillment strategies, rules for CRM (customer relationship management), business practices and so on need to be used for either of these two segments. A job shop can think of itself like a hospital wherein the Emergency Department operates as a separate “mini-hospital” within the main facility for rapid care delivery. Ideally, the average lead time to deliver care to any given patient is short.
2. Rationalize the Product Mix Annually
At the end of each year, eliminate the “cats and dogs”—those products that are losing money. As a machine shop manager quipped to me years ago, “We are happy to send our difficult parts, and sometimes our difficult customers, too, to our competitors. It does not hurt our business if their production efficiencies and profit margins are affected!”
3. Split One Machine Shop into Two
In Shop 1, produce orders for parts or products that are in the Runners/Repeaters segment of the product mix. In Shop 2, produce orders for parts or products that are in the Strangerssegment of the product mix. Set up Shop 2 to operate as a quick-turnaround shop with resources such as additive manufacturing, flexible automation, multitasking machines and machining centers with pallet-changers that can produce any part in a single setup, no matter how small the quantity. Even the skill levels of the employees in the two shops will be different. Employees in Shop 1 will tend to prefer production runs of mature parts, whereas employees in Shop 2 will prefer the challenges of manufacturing complex one-offs and mastering new technology.
4. If the Shop Currently Uses a Process Layout, Change It
In a process layout, similar machines are co-located in functional departments (manual lathes, CNC lathes, manual mills, CNC mills and so on). Any machine shop that has a process layout will always operate in a batch-and-queue production mode.