From Traditional Manufacturing to cellular manufacturing is a journey from ‘Mass Manufacturing’ conceived of during 1909 – 1915, to ‘Lean Manufacturing’, which evolved during the 1950’s and 1960’s in Toyota, Japan.
This is one of the secrets that caused emergence of Japan from the ruins of the second world war to a world economic power within a matter of 3 decades!!!
Historic Evolution of manufacturing cells
Preparation for cell designing
- Part/ Quality Analysis
- Process Route Analysis
- Group Parts by Process
- Material flow Diagram (Spaghetti Diagram)
Rules for cell designing
- Lay out Machines/ operations in sequence of operations
- Machines close together
- Input to cell close to output
- Anticlockwise movement of material
- Operators work inside the cell
- Multi – Operation handling by operators
- Standing work
- One piece flow
- Work of ‘Takt Time’
Comparison: Straight Line & U – Shaped Line
Linking operations/ machines together is the best way to reduce work-in-process inventory, waiting & transportof material and improve work balancing.
There is no thumb rule whether U-shape is better or Straight line. U-Shaped cells only make sense when the size of the cell is at a human scale and a person’s work sequence permits him to work on both sides of the cell.
U-Shaped cells offer flexibility to arrange and carve up the work content among different operatives. This means that as demand changes, it is possible to balance the cell workload with different manning. The maximum manpower is determined by the capacity of the cell & the total manual work content. Generally, this is accomplished by use of Yamazumi charts.
However, if the product must be accessed from all sides for work, and/ or is too big to handle, straight lines make more sense. Lines are easier to pace (one can use a moving conveyor), and are more intuitive.
Hence, rather than say one is “better” than the other, it is preferable to try things out practically, & use the approach that fits the requirement better. Levelled production (or Heijunka), is one reason we might need to use a U-shaped cell. By balancing the work content to ensure that output meets the customer takt time, we may need to run slower, with less operators than machines. This situation will require operators to perform multi-machine operations.
Data to be evaluated (Before & after)
- Throughput time
- Space used
- Rejections (Scrap/ Rework)
- Man power productivity
- Distance travelled
- Space used
Expected benefits from cells
- Throughput time reduction – – – 90% +
- WIP inventory reduction – – – 90% +
- Space release – – – 50% +
- Rejects/ Rework reduction – – – 50% +
- Manpower productivity up – – – 100% +
Standard work in a cell
Three elements of the standard work
- Cycle time
- Sequence of work
- Standard WIP
Evaluation criteria for manufacturing cell