One-Piece-Flow aims to reduce process inventory. In other words, it eliminates the accumulation of semi-finished products between one machining operation and the next. One consequence of applying One Piece Flow is a significant reduction in the duration of production cycles (lead times). This is because many non-value-added activities, which in most cases coincide with product handling times, are minimised.
The literal meaning of One Piece Flow is 'one piece at a time'. In a nutshell, suppose a product has to go through 3 different processes A, B and C. Instead of producing 50 pieces during process A, then 50 pieces during B and finally 50 pieces during C - which would lead to an accumulation of inventory and an increase in the duration of the production cycle (known as lead time) - with One Piece Flow, each product is processed one by one from A to B to C, as opposed to batch processing.
One of the pillars on which lean production is based is undoubtedly 'just in time' (producing what is needed, at the right place, at the right time, at minimum cost). However, to work 'just in time', it is necessary to apply one-piece flow - an application that is particularly suited to assembly processes.
The advantages of this method are
- Reduction of circulating stocks, in this case of semi-finished products
- Reduction in production lead times
- A reduction in the specialisation of workers and a consequent increase in their polyfunctionality. Let me explain this last point in more detail. If we work with batches and queues, taking the example of the company with three processes A, B and C, we will probably have three workers, one for each of these processes. We will reach a situation where one person will be able to do all the work by implementing one piece flow, especially in the assembly cells. To sum up: One-piece flow reduces the specialisation factor of operators, who become multifunctional by being able to carry out several operations.
To implement the One-Piece-Flow methodology, what are the requirements?
- The process must be able to do a good product consistently, if there are a lot of quality problems, this lean tool cannot be in place.
- The cycle time must be repeatable, if there are many variations we cannot implement it.
- The equipment must have very high uptime (close to 100%). It must always be available and dedicated to single piece flow.
- The processes must be able to match the time taken or the rate of customer demand.
- For example, our processes should be able to produce a product in less than 1 minute if the time taken is 1 minute.
What are the requirements for implementing the One-Piece-Flow methodology?
- The process must be able to produce a good product on a consistent basis - if there are a lot of quality problems, then this lean tool cannot be implemented.
- The cycle time must be repeatable. If there are many variations, we cannot implement it.
- The equipment has to have very high uptime (close to 100%), it has to be always available and dedicated to single piece flow.
- The processes must be able to match the time taken or the rate of customer demand.
- For example, our processes should be able to produce a product in less than 1 minute if the time taken is 1 minute.
How can this methodology be in place?
The guide to follow consists of eight steps:
1. Definition of the product or product family.
2. Demand analysis and takt time calculation.
3. Analyse the product by performing a value stream mapping.
4. Determine the cycle time of the different work phases. This is done by analysing and optimising each elementary operation with the involvement of the operators.
5. Assessment of whether the equipment is in compliance with the takt time.
6. Design a lean layout (U-shaped cell). Involve the operators.
7. Determination of the number of operators required.
8. Balance between users
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