Lean manufacturing

8 Common Lean Manufacturing Waste Types

Describing something as “lean” suggests it’s been slimmed down to just the essential elements needed for it to function. It also implies an absence of excess or waste, and this is exactly the objective of lean manufacturing. If manufacturing is about making things that customers want to buy, “lean” means doing it without waste.

Waste is anything the customer doesn’t want or isn’t prepared to pay for. Customers don’t spell these things out because it’s implicit. They only want to pay for the product — and the functions the product performs for them — and nothing else.

This identification of value is one of the fundamental principles of lean manufacturing. Anything that doesn’t contribute to the process or add value to it is therefore wasteful. Eliminating waste starts with learning how to recognize it. In his book, “Toyota Production System” (one of the first books on lean manufacturing), Taiichi Ohno, the “Father of Lean” identifies seven types of waste, or “muda” in Japanese:

  • Transportation
  • Defects
  • Excess processing (sometimes called “over-processing”)
  • Overproduction
  • Waiting
  • Inventory
  • Motion

In recent years, lean practitioners have added an eighth type of waste to this list: the waste of human potential or skills.

1) Transportation

During the manufacturing process, moving raw materials or partly finished products from one location to another doesn’t get them any closer to the form the customer wants. This movement does take time though, and usually requires equipment, such as forklifts or conveyors, and some expenditure of energy (human, mechanical, or both). These are unnecessary costs — or in other words, waste.

Transportation is wasteful in other ways, too. There’s the risk of the product being damaged as it’s moved, which results in unsellable goods. To move things, you also need the physical space to do so. This is space that could otherwise be used more productively. In addition, conveyors make it difficult to move around a factory while forklifts are often responsible for delays.

Transportation waste extends beyond the materials being processed or products being manufactured. Lean thinking views any time spent moving anything as a wasteful activity. This can include tools, people, and even information.

Real-Life Examples of Transportation Waste

  • Moving baskets of castings from the foundry into the machine shop
  • Moving stamping dies from the storage area out to the press, and back again when the batch or production run is over
  • Taking partially empty drums of resin back into the stores so they can be used for the next production run

Tools For Eliminating Transportation Waste

  • Value stream mapping (VSM)
  • Gemba walks, or routing by walking around (going to see the manufacturing process and following the route material takes)
  • Laying out “U-shaped” cells where each part is handed off from one workstation directly to the next

2) Defects

A defect in the product means there’s something about it that doesn’t meet specifications or customer expectations. In the event such a defect is discovered before it gets to the customer, the product will either be sent for rework or scrapped and replaced. Both mean that time and materials were wasted.

If the customer discovers the defect, they may insist on an investigation and corrective actions. This consumes more man hours, which could have been spent on more productive activities.

“Defects” can also refer to mistakes made during production that don’t show up in the product. While material may not be wasted, doing things wrong and having to do them again still consumes time and resources.

Real-Life Examples of Defects

  • Metal was poured at the wrong temperature so the castings have internal flaws and may fail in-service.
  • Knotted yarn was incorporated into woven material, so the product can only be sold at a lower margin.
  • A pallet of parts was delivered to the wrong assembly station. It then had to be found and relocated.
  • Inventory errors meant more material was ordered than was needed.

Tools for Eliminating Defects

  • Poka-yoke devices (simple fixtures or other tools that ensure a task can only be done one way)
  • Standardized work
  • Continuous improvement (kaizen) efforts, specifically using Pareto analysis to find the most frequent defects, followed by fishbone analysis to identify causes

3) Excess Processing (Over-Processing)

This waste refers to doing more work than needed to satisfy the customer. This may translate into the product looking or performing better than expected.

The waste of excess processing is not always obvious. It’s a waste because perhaps a more expensive machine was used than was needed, or more time was taken than required. To put it simply, the customer’s desired result could have been achieved with less time and effort.

Real-Life Examples of Excess Processing

  • Grinding a non-functional surface to a very fine finish
  • Grading by size, rather than manufacturing to the tolerances the customer needed
  • Inspecting 100% when SPC/sampling would be sufficient to maintain process control

Tools for Eliminating Excess Processing

  • Voice of the Customer (a tool for understanding customer requirements)
  • Process mapping, to understand what processes are actually needed

4) Overproduction

This is sometimes called the “Just in Case” waste. It’s what happens when you make more than is needed at that particular moment, often to ensure there are extras for set up or in case of defects. Some people may argue overproduction is not a waste because the products will be sold eventually, but that’s incorrect. It’s wasteful in at least two ways:

  1. The machines and people could have been occupied doing something else, such as making products that were needed more urgently, or identifying process improvements. Similarly, the material could have been used elsewhere rather than focus on overproduction.
  2. Overproduction creates excess inventory that must be put somewhere until needed. This requires handling and space, with the associated risks of damage and deterioration.

Real-Life Examples of Overproduction

  • A press with a long setup time is used to make a large batch that is subsequently broken into smaller batches with some being stored for use later.
  • There is no other work for the machine, so it’s kept running to avoid downtime impacting utilization statistics, or to keep workers busy.
  • Changing over to another product would hit output numbers, so the change is delayed until the next shift takes over.

Tools for Eliminating Overproduction

  • Takt time: Creating a “drumbeat” which gears the rate at which products are manufactured to customer demand
  • Kanban: Using visual signals to initiate production of a specific quantity just in time with downstream operations “pulling” work from upstream processes
  • Single Minute Exchange of Dies (SMED): A methodology for reducing setup time, thus removing the incentive to run larger batches

5) Waiting

Another way of looking at waste is as delays or idle time. People may be waiting because a job hasn’t arrived or a machine isn’t available. A machine may be delayed because there’s no operator to load it. Material is waiting any time it’s not being processed. Queues are one of the biggest reasons for material delays during the manufacturing process.

The problem with people or machines waiting is that these are expensive resources, and the time they spend doing nothing can never be recouped. With material delays, the problem is slightly different. These delays signify that the material is waiting for processing. The more material that is waiting, the longer it will take a specific product to get through. Material delays correlate with lead time.

Real-Life Examples of Waiting Waste

  • A large cage of cut fabric pieces arrives at a sewing machine. However, the machinist can only sew one at a time and the batch can’t move on until it’s complete, so the rest wait to have labels sewn in.
  • A stamping press is set up and ready to run, but the first piece produced must be measured and inspected before full-scale production can begin.
  • A forklift isn’t immediately available to move a pallet off a shrink wrapper in the packaging area, so work stops until the space is cleared.

Tools for Eliminating Waiting Waste

  • Single piece flow
  • U-shaped cells

6) Inventory

This refers primarily to material, which may be in the form of raw material, works-in-progress, and finished goods. It can also refer to the inventory of manufacturing equipment, spare parts inventories, and tool inventories.

Inventory takes up space that could be used for something else. Some materials will deteriorate if stored for any length of time, and storage increases the risk of inventory being damaged. Another risk is that customer tastes change continuously, and there may no longer be a demand for the product you’re holding in inventory, rendering it obsolete.

Although quantified as an asset, inventory is a form of waste with direct, measurable financial impact. There is a cost to holding inventory, and in addition, it reduces cash flow. To look at it in another way, reducing inventory improves cash flow.

Work-in-progress inventory is material waiting for processing, so the more there is, the longer the lead times will be. It’s usually particularly acute at bottlenecks. Taiichi Ohno argued that inventory hides problems in manufacturing because it allows machines and people to be busy, even if they’re not working on something the customer needs at that moment.

Real-Life Examples of Inventory Waste

  • Keeping spare parts for machines that are no longer in use is a type of inventory waste often seen in maintenance department storage.
  • Purchasing larger quantities than can be consumed in a reasonable amount of time in order to qualify for quantity discounts.
  • Producing large batches and maintaining long machinery runs to dilute the impact of setup time and support Economic Order Quantity (EOQ) thinking.

Tools for Eliminating Inventory Waste

  • Implement kanban/pull systems
  • Use one-piece flow and U-shaped cells
  • Review safety stock policies

7) Motion

Motion waste is different from transportation waste. It refers to movements that would be unnecessary if the task was redesigned or laid out differently. Bending to pick things up, stretching to take items from a shelf, and walking to obtain an item of equipment are examples of this type of waste.

Unnecessary movements are a type of waste because they take time to perform and increase operator fatigue. They can lead to musculoskeletal disorders that cause employee absences. Even when motion is mechanized or automated, it’s wasteful because the machine is expending unnecessary energy.

Real-Life Examples of Motion Waste

  • An assembly cell where workers must walk to fetch parts
  • Passing a tape dispenser between two packaging cells
  • Going into the office to get a printout of the daily production schedule

Tools for Eliminating Motion Waste

  • Use the 5S methodology to ensure tools are always in the right place.
  • Apply good ergonomic principles to workplace design.
  • Put production control terminals on the factory floor.

8) Human Potential or Skills

The waste of human potential is a recent addition to the original seven wastes. It recognizes that manufacturing workers are often able to do far more than they are asked.

This waste represents acceptance that no one has a monopoly on good ideas, and that engineering alone is not responsible for finding and making improvements in manufacturing. All workers have skills, talents, and creativity that should be used to help improve production and address the other seven wastes.

Real-Life Examples of Skills Waste

  • Not asking setters for ideas on ways to speed up machine changeovers
  • Operators not being involved in writing work instructions, even though they may know better ways of doing things
  • Not sharing defect paretos or performing kaizen activities

Tools for Eliminating Skills Waste

  • The 5 Whys
  • Brainstorming
  • Ensure training records are visible and accessible so workers can be trained to rotate between tasks.

Reduce Waste With Amper’s Factory Operating System

The eight wastes of lean explain where to look for opportunities to improve manufacturing. What they don’t do is prioritize, and in this regard every factory is different.

In a batch manufacturing environment, the greatest improvements may come from attacking delays, inventory, and transportation. You might achieve this by focusing on layout improvements and reducing work-in-progress inventory. Conversely, a highly automated factory with continuous flow may reap greater rewards by reducing defects, motion, and over processing.

Prioritization requires data about what’s happening in the factory. This is where Amper’s Factory Operating System can help. Amper provides visibility into factory operations, in real time. This gives managers the information they need to focus kaizen efforts in the areas that yield the biggest returns. Learn more about how Amper supports waste elimination through a free 30-day pilot.

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