Production line balancing Yes or No

The “fundamentalists” of lean and the Toyota Production System are always defending line balancing.

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Line balancing consists in balancing operator and machine time to match the production rate to the takt time.

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Takt time is the rate at which parts or products must be produced in order to meet customer demand.

On a production line perfectly balanced the production time is exactly equal to takt time.

The production operations are rearranged to remove bottlenecks or excess capacity.

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The benefits are supposed to be:

1. Reduce waiting waste – that occurs when operators or machines are waiting for materials from a previous task.
2. Reduce inventory waste – that is an excess of raw materials, work in progress (unfinished goods), or finished goods.
3. Absorb internal and external irregularities – a balanced production line is expected to be stable and flexible enough to adapt to changes, reducing variation.
4. Reduce production costs and increase profits - no operator is standing idle, machines are used to their full potential.?

But

about 20 years ago I read the book "The Goal" from Eliyahu M. Goldratt and the theory of "statistical fluctuations".

Well I am an Engineer and as such I use mathematics to find answers and guarantees.

So I created an Excel file to do some mathematical simulations.

?Process assumptions:

• 3 consecutive operations
• parts are moved between operations every hour
• 1 shift (8 hours) per day

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Scenarios:

1. All production rates equal, as hourly production rate variations equal
2. Production rates increasing, as hourly production rate variations equal
3. Production rates decreasing, as hourly production rate variations equal

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With ±2% hourly production rate variation

Balanced process does not achieve target daily production, during 220 days average, with an average deviation of -84 units per day.

With ±10% hourly production rate variation

Balanced process does not achieve target daily production, during 220 days average, with an average deviation of -398 units per day.

With ±20% hourly production rate variation

Balanced process does not achieve target daily production, during 220 days average, with an average deviation of -802 units per day.

Both remaining scenarios (increasing production rates and decreasing production rates) are always better than the balanced process.

The best end of the day WIP level is always attained by the increasing production rates process.

These calculations and simulations raise many doubts about one of the main lean concepts.

#productivity ;#processimprovement ;#lean ;#leanmanufacturing