4b. Flow-Time Reduction

Here’s a little more detail on the Flow-Time Reduction Method mentioned in the Flow-Optimise Anything! post.  It combines elements of Lean Thinking with the TOC Production and Critical Chain solutions.

TL;DR

1. Reduce the duration of the biggest lead-time contributors (critical path; critical path changes; critical path delays and critical resource delays) –
2. By identifying a comprehensive set of reduction solutions for each of their contributing elements (e.g. wait-time; rework-time; processing-time and; travel-time).

Use time-wheels to make it easy to identify the biggest opportunities and then use simple techniques for manipulating the levers.

What is Flow-Time Reduction?

Flow-Time Reduction is about getting each product, job, process project completed sooner and faster.  It’s about reducing the lead-time of the system.

It’s natural to think that accelerating flow-rate (increasing  capacity) is the only way to reduce lead-time.  It does play a part – and it’s a good place to start – but it’s only one of many things that have a dramatic impact on lead-time.

Flow-Time Reduction views things from the perspective of the work-item being processed (how long the end-to-end process takes), while Flow-Rate Acceleration views things from the perspective of the system that’s processing the work-items (how many/much of demand volume can we satisfy).

Lead-Time Contributors

Lead-Time is comprised of the following contributors:

1. The Critical Path
   The longest sequence of dependent steps in the flow-system.  (The term originated in the project world, but applies to any flow system.)
2. Critical Path Changes
   When a step that’s not on the Critical Path is so delayed that the next Critical Path step can’t start or continue.  The Critical Path now has to include the step that was previously not on it.
3. Critical Handover Delays
   Delays between consecutive steps on the Critical Path caused by lack of synchronisation between Critical Path Resources (mostly as the result of process/task/step duration unpredictability).
4. Critical Resource Delays
   Delays caused by Critical Resources having to work on non-Critical Path steps in parallel with Critical Path Steps.
   (In some situations, non-Critical Resources that process parallel steps that aren’t on the Critical Path can become Critical Resources and create changes in the Critical Path – similar to point 2. above).

(The use of the word “Critical” is significant here: we’re not interested in reducing the duration or frequency of all steps, changes and delays  – only those that contribute to total lead-time.)

How to shorten the Critical Path

Build a time-wheel with estimates of each of the following common contributing elements:

1. Wait-time.
2. Rework-time.
3. Setup-time.
4. Processing time.
5. Travel time.

Here’s a starting set of simple solutions for addressing each of them:

1. Reduce Wait-Time
   1. Reduce the transfer batch-size.
   2. Reduce queue lengths – i.e. reduce WIP and other inventory at non-bottleneck steps.
   3. Use Flow-Rate acceleration.
   4. Right-size the bottleneck buffer.
   5. Process in first due order.
   6. Reduce setup-times, if they contribute significantly to wait-times
2. Reduce Rework
   1. Make sure that the product specs or process or task requirements are correct, up front.
   2. Ensure that in-progress and completed work isn’t damaged.
   3. Optimise the rework process.
   4. Inflate batch-size numbers in cases where the low cost of materials justifies it.
3. Reduce Processing Time
   1. Use Flow-Rate Acceleration.
   2. Streamline the processing process.
   3. Reduce the process batch-size.
   4. Make to (e.g.) 50% of forecast for high volume items.
   5. Standardise components, where possible.
   6. Minimise unnecessary multitasking at the bottleneck.
4. Minimise Travel Time
   1. Hold small stocks on the fringes and replenish from central warehouse frequently.
   2. Locate production and warehouse close to each other.
   3. Mix product flows (stationery resources) with resource flows (stationery products) appropriately.

How to Reduce the Number & Impact of Critical Path Changes

Draw a time-wheel to compare the incidence and impact of the primary ways in which the Critical Path can be changed unexpectedly.

1. Reduce the likelihood and impact of Non-Critical Tasks on the Critical Path
   1. Add feeding time or inventory buffers at convergence points on Non-Critical Paths with the Critical Path.
   2. Ensure that Non-Critical paths start on time
2. Prevent Non-Critical Resources from becoming Critical Resources
   1. Deliberately check for unexpected Critical Resources
   2. Add feeding time or inventory buffers at convergence points

How to Reduce Critical Handover Delays

Work out where the Critical Handovers are delayed most often (it’s normally in the handover between the most unpredictable steps) and select from or add to the following solutions:

1. Improve due-date performance, by minimising unnecessary multitasking by Critical Resources.
2. Ensure increasingly frequent updating and synchronisation between Critical Path steps the close to handover we get.
3. Minimise the number of handovers – move towards constant flow.
4. Design handovers to be recipient-ready.

How to Reduce Critical Resource Delays

Work out where Critical Resource Delays are most likely to happen – draw a time-wheel, if it helps and use or add to the following solutions.

1. Minimise Critical Resource / Bottleneck multitasking.
2. Schedule all Critical Resource activities, to enable appropriate batching and sequencing.

The next post will focus on freeing up 10 hours a week that you don’t even realise you’re wasting.

I’m certain to have missed some dimensions and opportunities: help me out with the ones that spring to mind, in the comments below.