5.08 - Small Process Plant
Approach
Traditional Approach - buy ‘super machines’ and keep them busy. There is little emphasis on natural groupings, of component mix & demand frequency.
Japanese Approach - make or buy SMALL machines. Add more as needed. Only use CNC machines where product variety & batch size merit their use.
Reasons
The Traditional European View - Complex technology solves our problems.
The Japanese View - Small cheap machines allow:-
- Less emphasis on machine utilisation (recognising that high utilisation can lead to long lead times)
- Quick and easy end-user maintenance
- Purchase of duplicate machines - set up ready for changeovers
- Multi-purpose U-Shaped cells
- Internal machine tool development (which generates know how for changeover reduction times, etc)
- Flexibility
Example: Heat Treatment / Processing
- Small ovens strategically distributed instead of big ‘Super Ovens’
- Small wash tanks strategically distributed in factory instead of large centralised tanks
Project Scale Categorisation
- Reduced lead times (no batching up to send to heat treatment), reduced queues.
- Matches the needs of Kanban Production Systems (i.e. simpler control system).
- Reduces complexity (need for ‘gateways’, etc reduced)
- Enhances ‘ownership’ of problems.
Machinery Choice
Type |
Advantages |
Disadvantages |
2x capital cost at each stage
|
Dedicated specialised machinery |
- Suitable for a low variety of runners
- Very short cycle time (production rate high)
- One worker can operate a number of machines easily
- Ideal for multi-process cells
- Easy maintenance
|
- Not suitable for small lot production
- Low flexibility
|
Semi-dedicated, semi-flexible Machinery |
Suitable for repeaters:
Advantages and disadvantages lie between those outlined above and below. |
CNC
Expensive, highly flexible machinery |
- Suitable for strangers and a variety of runners.
- Effective for smaller batches
- Small lot production of a variety of products
- Highly flexibility of production
|
- Longer cycle time
- CNC skills required
- Expensive
- Specialist support (overhead) needed for maintenance and programming
- Complex fixtures and tooling, plus maintenance difficulties can lead to process incapability
|
Trade-offs
- Cycle time versus flexibility
- Flexibility versus capital cost
- Influenced by ability to modify for quick changeover