Scheduling is at the heart of lean. Flow scheduling is, or should be, the reason why we do all those activities – cells, changeover reduction, 5S, policy deployment, standard work, visual management, and so on. Flow scheduling ‘brings home the bacon’ in terms of lead time competitiveness, cash flow, and quality.
Thousands of pages have been written about lean. But does flow scheduling enjoy top priority attention? Ask a senior operations manager these ‘obvious’ questions:
- What is a pull system?
- Is MRP push or pull?
- Is pull the same as make to order?
- What are the advantages of pull over push?
- Is kanban the best pull system?
- Limitations of kanban?
- What variables affect flow?
- Where are your bottlenecks?
- What is your possible bottleneck rate compared with your demand rate (and where does the ‘danger zone’ of queue instability begin?)
We would hope that an experienced lean manager would have the answers to these at his or her fingertips. Test this out and see…
The ‘answers’ – such as they are – are given below in the form of questions:
- What is the essential difference between a pull system and a push system in terms of when orders or work are released? Since work-in-process is directly related to lead time, what does a pull system achieve that a push system does not?
- Does an MRP system consider the status of work in process before orders are released?
- The same questions as above should be asked for the third question. Surely, yes, make-to-order is preferable in a lean system, but how is a surge of orders to be dealt with?
- Certainly cost, quality, delivery. But how is that achieved? Surfacing problems is a central idea in lean, so how does pull help make this possible? (There are a few reasons….)
- Kanban requires both look-ahead authorisation, and look-back at part availability. So what might cause throughput to go down, and what are possible causes of this? Is Drum-Buffer-Rope and CONWIP push or pull?
- Toyota has words that relate to the first two – Mura and Heijunka. Contrast a stable order regime with unstable demand. Which will work best in terms of lead time? (And who causes this instability? Customers or self?) Why spend so much time and effort on activities such as 5S, standard work, six sigma? (What is the real and common aim of these activities?) When you know that Heathrow has a runway utilisation in the high 90%’s what is your experience in delays? And utilisation is determined by a numerator and a denominator. Each can have a significant effect. By the way, is the statement ‘Lean is about freeing up capacity’ entirely correct – in terms of scheduling?
- Many organisations, perhaps as part of ‘leader standard work’, hold daily shop floor meetings. Where on the shop floor is that meeting held?
- Goldratt told a story about this in The Goal. Of course the answer depends on variation, but do you believe in 100% loading? See Heathrow comment above. Toyota has a word for this – it is called Muri.