Production smoothing

Many months ago, we held a Kaizen program with external consultant for production smoothing. Below is the study from me to summarize the concept of production smoothing for your reference.

It came from Japanese term "Heijunka" (平準化), sometime, some people called it as "production balancing" or "production leveling". It is a system designed to achieve a more even and consistent flow of work. Heijunka as a concept is closely related to lean production and just in time manufacturing. It also means two different, but related, things. One is the leveling of production by volume. The other is leveling production by product type or mix. Use for level the resource of production in machine capacity, working space, operation capital and manpower arrangement including supporting departments.

According to the figure shown above, the red line represents the customer demand and the green line represents the production capacity. If we plan for production schedule as red line, because of its high variance of demanding, due to the resource issue, it will cause much of waste in manpower or machine capacity. Production smoothing is using to plan and try to lower down the variance of scheduling but achieve the target for customer demand. Offcause, it is no way to retain the capacity in a straight line profile, but versus the red line, it becomes more consistent and easiler for planning.

The slower but consistent tortoise causes less waste and is much more desirable than the speedy hare that races ahead and then stops occasionally to doze. The Toyota Production System can be realized only when all the workers become ortoises. ~~~ From Ohno, 1988

Leveling by volume: Toyota's view is that production systems that vary the required throughput suffer from mura and muri with capacity being 'forced' in some periods. So their approach is to manufacture at the long-term average demand and carry an inventory proportional to the variability of demand, stability of the production process and the frequency of shipments. The advantage of carrying this inventory is that it can smooth production throughout the plant and therefore reduce process inventories and simplify operations which reduces costs.

Leveling by product: Most value streams produce a mix of products and therefore face a choice of production mix and sequence. It is here that the discussions on economic order quantities take place and have been dominated by changeover times and the inventory this requires. Toyota's approach resulted in a different discussion where it reduced the time and cost of changeovers so that smaller and smaller batches were not prohibitive and lost production time and quality costs were not significant. This meant that the demand for components could be leveled for the upstream sub-processes and therefore lead time and total inventories reduced along the entire value stream.

At last, we adjusted the customer demand forecast and production schedule in the program. But, one thing so important we must remember that, "the world is changing everyday". The requirement from customer is also changing as well. Production smoothing is not a improvment program, at some point of view, it should be said as a scheduling concept. We can not fix all the resource planning problem in one program, actually, it imply the concept needed to be combined with daily planning job.

Benefits of leveling the schedule,
1. Flexibility to make what the customer wants when they want it.

2. Reduced risk of unsold goods.

3. Balanced use of labor and machines.

4. Smoothed demand on the upstream processes. (people, machine, suppliers)