7 wastes of lean manufacturing
Increase the efficiency of your production by identifying and eliminating the 7 wastes of lean manufacturing in your production process.
General Overview
In classical lean management according to the teachings of Taiichi Ohno, 7 types of waste are distinguished. Numerous examples of these 7 wastes of lean manufacturing (known as “Muda” in Japanese) can be found in every production environment. Therefore, it should not be misunderstood: a complete elimination of waste is not possible. In fact, they can sometimes cause each other, such as a reduction in inventory triggering waiting times for resupply. At the same time, they can multiply: overproduction increases inventory, and consequently, the transportation effort. Knowledge of the 7 wastes of lean manufacturing is intended to help identify process weaknesses and efficiency losses more easily and reduce them more effectively.
A quick overview over the 7 wastes of lean manufacturing:
- Transport
- Inventory
- Motion
- Waiting
- Overproduction
- Over-Engineering / Incorrect Technology
- Defects/Rework
A useful mnemonic for remembering the 7 wastes of lean manufacturing is the acronym TIM WOOD (Transport, Inventory, Movement, Waiting, Over-Production, Over-Engineering, Defects).
All seven types of waste share the characteristic of being non-value-adding processes in production. Strictly speaking, only the primary utilization time of the operational resources is value-adding. Therefore, in a project, the activities that are non-value-adding and thus represent waste must be identified.
The scope of the project should include the assessment of waste. For example, the transport of components to hardening furnaces in another hall is a non-value-adding activity. However, if considered at the operational level, such as within the framework of a continual improvement process (CIP), the rough layout of the production is assumed to be fixed, and the transport is mandatory. To reflect this situation, the category of value-enabling processes can be introduced, as transport enables the value creation brought by the hardening furnaces. On a strategic level, this would still be critically examined as a non-value-adding activity.
In addition to the above-mentioned “basic types of waste“, further types of waste are distinguished depending on the literature. These include:
- Unused talents of employees
- Variations/non-harmonized production processes
- Overburdening of people, machines, and materials
- Energy
- Complexity
Transport
Description:
Transport is not a value-adding activity. However, it is very prevalent and is an integral part of manufacturing processes within companies, often referred to as intralogistics. Transport encompasses any movement, whether of (raw) materials, semi-finished and finished products, tools, or equipment.
Due to process-related, physical, and structural conditions, transport is often unavoidable and thus frequently falls into the category of necessary value-enabling waste. Nonetheless, the goal should be to reduce transport as much as possible and to keep walking and transport distances as short as possible.
Examples:
- Transport within process steps
- Transport of intermediate products to and from intermediate storage
- Transport to and from external warehouses
Impact:
- Transport binds employee capacities and operational resources (containers, forklifts). Unnecessary transport can cause waiting times for other processes.
- Transporting incorrect quantities can lead to a lack of material availability or unnecessarily large inventories.
Possible Solutions:
- Kanban or Pull Production: Production and transport of the Kanban quantity are triggered only when an (internal) customer consumes it.
- Layout Optimization of Manufacturing: Using tools such as value stream mapping or path analysis through spaghetti diagrams to minimize transport distances.
Inventory
Description:
Any type of inventory can be considered waste, whether it is raw materials and semi-finished products within the production process or finished goods after completion. These inventories incur holding costs, such as opportunity costs for the tied-up capital and, depending on the item, potential depreciation due to aging or perishability. In extreme cases, a complete loss of value can occur if certain processing deadlines are not met. Therefore, inventories should be reduced to an appropriate minimum. The appropriateness is determined by process-related conditions, required service levels, and batch sizes of preceding and subsequent processes.
However, it can also be a competitive advantage for companies to have inventory on hand and always be ready to deliver. Overall, there should always be a balance between the costs of holding inventory (storage costs, tied-up capital, depreciation) and the costs of not meeting customer demand.
Examples:
- Extensive finished goods inventory for products that are rarely ordered
- Intermediate storage between production steps
Impact:
High inventories can conceal other issues in production. For example, a lack of process harmonization can be masked by high safety stocks.
Possible solutions:
- Kanban or Pull Production: Production is triggered only when an internal customer consumes the Kanban quantity, reducing inventory to a few Kanban quantities.
- ABC Analysis and Service Level Determination: Analyzing items based on their importance and setting appropriate service levels to optimize inventory management.
Motion
Description:
Unnecessary movement and travel reduce productivity. Unnecessary movement starts with the inconvenient placement of two tools that are used consecutively and escalates to having to walk across the shop floor to bring material or tools to the workstation.
Examples:
- Reaching for tools
- Centralized tool distribution
- Lack of workplace ergonomics
Impact:
- Movement ties up employees’ time that could be used productively.
- Inadequate and unfavorable workplace ergonomics reduce efficiency and can also lead to workplace accidents and poor quality.
Possible solutions:
- Observation and Documentation of Workflows: Followed by the arrangement of equipment to minimize movement.
- Provision of Frequently Used Tools and Equipment Near Workstations: Ensuring tools and materials are readily accessible to reduce unnecessary movement.
Waiting
Description:
Waiting refers to the time when a worker is not adding value, such as waiting for the completion of a production process or for material replenishment.
Similarly, material can also “wait,” meaning idle times during which a product is not undergoing value-adding processes, leading to increased lead time.
Examples:
- Waiting for the availability of production equipment
- Waiting for material replenishment
- Waiting for feedback from supervisors, colleagues, or (internal) customers
- Batch sizes greater than one, as this forces material to have idle times
Impact:
- Waiting times directly increase the lead time.
- They also reduce the productivity of employees.
- Longer lead times can result in delayed orders and economic inefficiencies.
Possible solutions:
- Kanban or Pull Production: Trigger production only when the Kanban quantity is consumed by an internal customer, thereby reducing waiting times.
- Combining Equipment and Processes: Fill waiting times with value-adding activities by handling multiple machines or processes (“Multi-Machine/Process-Handling”).
- U-shaped Material Flow Layout: Optimize material flow to reduce waiting times.
- Setup Time Optimization (SMED): Reduce setup times to minimize waiting.
Overproduction
Description:
Overproduction occurs when more is produced than what is currently demanded by customers. In the case of make-to-stock production, this is common and leads to inventories. As previously discussed regarding inventories, this can also be a competitive advantage. However, overproduction always creates a need for storage space and incurs storage costs. In the production of perishable goods, the impacts are particularly critical, necessitating optimization to minimize overproduction as much as possible. Additionally, the future demand for produced quantities is not guaranteed, and the revenue that can be achieved is uncertain.
Examples:
- Production of Products for Stock
- Producing in batch sizes that exceed immediate demand.
- Selling Stocked Goods at Discounts
Impact:
- Creates storage requirements and incurs storage costs.
- In the case of perishable goods, leads to spoilage risks.
- Extension of lead times and delivery times directly when inappropriate batch sizes are chosen, and indirectly through the allocation of equipment and resources.
Possible solutions:
- Measuring utilization metrics to harmonize production
- Optimizing batch sizes, e.g., with One-Piece-Flow
Over-Engineering / Incorrect Technology
Description:
Over-Engineering or incorrect technology and unsuitable processes refer to unnecessarily complex or inadequate designs and manufacturing processes. In addition to the examples mentioned below, this could be due to a machine that is capable of producing a much higher quality than actually needed for a component. However, unnecessarily complex designs can also be wasteful if a simpler solution equally meets customer requirements. It is essential to identify the critical voice of the customer and develop or select corresponding processes and products accordingly.
Examples:
- Higher quality of a workpiece than necessary due to enjoyment of technical feasibility
- Lack of knowledge about the actual purpose of the component
- Maintaining existing processes and hierarchies without economic necessity
- “We have always done it this way”
Impact:
The effects can vary from immediate negative impacts to hindering additional positive influences. Depending on the individual case, additional costs, time loss, higher scrap rates, or lower margins may occur.
Possible solutions:
- Capturing the Critical Voice of the Customer (e.g., House of Quality (QFD))
- Critical evaluation of the processes used
- Change management
Defects / Rework
Description:
Defects and rework are certainly the most immediate and obvious of the 7 types of waste. Particularly when scrap and defects occur late in a manufacturing process, a large portion or even all of the added value is lost. Here, all previous wastes that may have been introduced into the process are also magnified.
Beispiele:
- Component fails End-of-Line QA
- Processing produces errors, and parts must be reworked
- Process parameters are incorrectly selected, leading to scrap
Impact:
- In make-to-order scenarios, scrap and rework directly lead to delays in delivery to customers, while in make-to-stock, the impact may be less severe
- Production costs for all batches of the product increase, and margins decrease
- Systematic errors can affect an entire batch, having particularly severe impacts
Possible solutions:
- In-line quality control
- Poka-Yoke and other Lean Management methods to reduce errors
- One-Piece-Flow to limit the impact of systematic errors
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