Lean manufacturing defines seven types of waste that make a production system inefficient and costly. These are:
- Over-production: Producing too much, too soon.
- Inventory: Extra production required to buffer process variability.
- Transportation: Movement of materials without adding value.
- Waiting: Increasing production cycle time without adding value.
- Movement: Movement of operators without adding value.
- Defects: Product that does not conform to customer specifications.
- Over-processing: Processing a material more than necessary to meet customer specs.
The first three types of wastes above relate to a lack of material flow. By the very nature of process manufacturing, material flows in a continuous stream from one process to the next, without periods of stopping and waiting in between (the possible exceptions being some batch processing in the chemical and steel industries). Therefore, the Lean ideal of flow occurs by default. As a result, over-production, inventory, and transport are either non-issues or only minor issues in process manufacturing. Movement waste is also less relevant to process manufacturing because operators typically monitor automated equipment.
However, three types of waste— waiting, defects, and over-processing— do exist in process manufacturing and are fertile ground for the application of Lean and Six Sigma methodologies. For instance, product changeovers, which in process manufacturing can sometimes take 18 hours or more, are an example of waiting waste. Defects are the result of production of material that does not meet the specifications of the downstream internal/external customer. Over-processing occurs when the material is processed to a greater extent than is required by the downstream customer. All of these add to costs and can be reduced/eliminated through the use of these methodologies.
In the perfect value stream, products are produced reliably, efficiently, with good quality, and in sufficient quantity at the individual process level and throughout the entire value stream. A suboptimal condition with respect to any of these characteristics constitutes a type of waste. Since no production value stream is perfect, all real-world process-manufacturing value streams will contain one or more of these wastes. These are targets of opportunity for any process-improvement effort.
The root causes of these wastes may be identified by means of fish-bone (Ishikawa) diagrams (Figure 1). They can be used as “straw models” to identify the root causes of wastes in your specific value stream and then the appropriate methodology/tool can be applied to address it.
While the causes of process manufacturing waste vary, a few occur regularly:
- Equipment condition.
- Suboptimal operation.
- Design and technology.
- Availability due to changeover and set-up time.
Equipment condition refers to machines that are not properly maintained. Equipment in poor mechanical condition has poor availability, produces poor-quality product in inadequate quantities, and operates inefficiently. A maintenance kaizen event is the appropriate process-improvement tool to return the machine to an optimum mechanical condition. To sustain the improvement, a long-term maintenance program such as Asset Health Care (AHC) or Total Productive Maintenance (TPM) must be installed.
Suboptimal Operation is a second major cause of waste. Typically process manufacturing involves a combination of physical parameters. These could be a combination of temperature, pressure, density, flow rate, moisture level, and chemical concentration that are set at the machine to process the material. If these settings are suboptimal, then the process operates sub-optimally in terms of throughput, quality, and efficiency. These types of problems are ideally solved using Six Sigma.
Design and technology are two other major causes of waste. In brown-field plants that have been in operation for many years, it’s not uncommon to find equipment that is obsolete with regard to both design and technology. Such equipment can operate wastefully in terms of availability, quality, throughput, and efficiency, much like those in poor mechanical condition. Improving/upgrading equipment design/technology is an engineering problem requiring technical analysis and designed experimentation.
Availability can also be adversely affected by product changeovers and by long setup times after a process has been taken down for maintenance. In this case, quick changeover techniques such as Single Minute Exchange of Die (SMED) may be applied to reduce setup times and improve availability.
There is, however, a word of caution before applying these methodologies and tools. In many companies, becoming Lean seems to be primarily concerned with implementing tools such as “one piece flow,” “value stream mapping,” “standardized work,” or “kaizen events,” but the expected results have not always followed.
By contrast, Toyota has stayed focused on its principles and not the tools. At most Toyota plants, there are no dedicated change agents or black belts. Value stream maps are rare and only used in problem areas. There are no value stream managers and only small portions of the plants contain actual standardized work charts and many of the daily tracking systems are highly computerized.
For the last 50 years, “TPS at Toyota has been primarily concerned with making a profit, and satisfying the customer with the highest possible quality at the lowest cost in the shortest lead-time, while developing the talents and skills of its workforce through rigorous improvement routines and problem solving disciplines.” This stated aim is mixed in with the twin production principles of Just in Time and Jidoka (build in quality at the process). This emphasis on process improvement to obtain results rather than the implementation of tools is the main reason why Toyota has continued to see success on so many dimensions.