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Lean process improvements are designed based on problems found in the value stream map that show the new flow. The flow improvements are concerned with overall process design and constraints along with the design of individual steps.

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Quick reference

Lean Improvement: Flow

Lean process improvements are designed using a “to be” value stream map that shows the new flow.  The data box on this map estimates the impact of the elimination and redesign of process steps and the removal of system constraints

When to use

Lean flow improvement techniques are used when the goal of the Lean Six Sigma project is cycle time improvement.   With the flow improvement, the techniques will often increase capacity, lowering total costs.  

Instructions

The Lean analysis should have identified opportunities for improvement.  Starting with the As-Is Value Stream Map, the team can prioritize which opportunities to address and the nature of the changes to create a Should-Be Value Stream Map.  This becomes both the vision and guide for implementing the improvements.  Many of the changes can be made independently of each other.  As soon as a change is ready for implementation, it should proceed.

There are a number of Lean techniques that focus on improving the flow of an item through the process.

Flow Design

This technique is a reflection of how the steps are connected. Seek to eliminate non-value added time, especially that associated with movement and handling. Also, consider eliminating paper-based systems and reports and rely on electronic reporting. Locate the loops, also known as backwards flow. Determine the reasons for loops and minimize those. This is often done by eliminating decision points, which can derail an item. Create one significant decision point at the beginning of the process to either follow the process or divert to a special “non-lean” process to address exceptional conditions.

TAKT Time Step Design

In this technique, any step that takes longer than the TAKT time for the process is redesigned to shorten the step.  When all the steps are operating at the speed of the TAKT, the process will flow smoothly at its needed capacity.  One method of shortening the step is to split the step into several sub-steps, each of which is shorter than the TAKT time.  In some cases, the activities at the step can be changed to a different technology or approach that is faster.  If the step cannot be shortened to the TAKT time, then the step resources will need to be duplicated so that multiple items can be processed simultaneously.

Batch Size of 1

This technique is self-explanatory.  The batch size of items flowing the process is reduced to the smallest possible number, preferably one.   This item is processed at one step and immediately moved to the next step.  This approach accelerates items through the process by eliminating waiting, makes the process more responsive to customers, and is easier for process management as it quickly identifies problems.  The challenge with this technique occurs when the step requires a large amount of unique setup for each item.  If multiple items were done on one setup, it would lower setup cost and time.  Implementing this technique often requires a trade-off decision between setup effort and the speed and responsiveness of the small batch.

Theory of Constraints

Dr. Goldratt developed this technique for improving process capacity by focusing the flow improvement actions on the constraining step in the process.  Since the constraining step is what ultimately limits the process capacity, increasing flow through that step will increase the overall process capacity and improve flow.  This technique is a five-step analysis and response approach.

  1. Identify the constraint – increasing capacity at any other step is pointless
  2. Focus the constraint – the constraint should be doing the activities that can only be accomplished at that step.  Move all other activities to other steps or resources.
  3. Subordinate everything to the constraint – ensure the preceding steps are scheduled to maintain a buffer at the constraint.  That way the constraint is always working.  An idle constraint is lost capacity that can never be made up.
  4. Increase the constraint- if the step is still constraining the process, increase resources to add capacity (Note: this is the first step requiring any financial outlays)
  5. As soon as a constraint is broken, go to the next constraint – continue this approach until the process has sufficient capacity.

Hints & tips

  • TAKT time design is an enabler of many other improvement opportunities.  Do this first.
  • Local optimization will destroy flow.  Making one step very efficient, such as running equipment 24/7 to lower absorption costs, can create havoc for flow.  Causing big bubbles of WIP.  Expect resistance when trying to do Batch Size of 1 from those measuring local optimization.  You must show the overall process flow and responsiveness to convince them.
  • Theory of constraints can be difficult in a heavy mix operation where the constraining step is different for different categories of process items. 
  • To get the maximum process capacity and customer responsiveness, the constraining step must be actively managed to prioritize items through that step – first in, first out is not the way to manage it.
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  • 00:05 Hi, I'm Racine.
  • 00:06 Now let's turn our focus to improving the flow of the lean process.
  • 00:11 >> So let's look at different categories of flow improvements.
  • 00:15 You may not use all of them on the same project,
  • 00:17 but you're likely to use at least a few of them.
  • 00:20 The focus of these is to reduce waste in the value stream.
  • 00:24 All the measurements and analyses so far have been defined waste,
  • 00:28 now it's time to get rid of it.
  • 00:30 The most obvious is to reduce the non-value added activities.
  • 00:34 Try to eliminate those steps or at least shrink them.
  • 00:37 And then, of course, look to get straight line flow.
  • 00:40 Get rid of your decision points and branches.
  • 00:43 Another technique is to redesign the steps so that they fit within the tact time.
  • 00:48 This may mean splitting some steps and
  • 00:50 indicate an opportunity to combine some others.
  • 00:53 If you can't get a step below the tact time,
  • 00:56 you'll need to duplicate the workstation and all the resources so
  • 00:59 that multiple units can go through in parallel.
  • 01:03 When I do that, I try to stagger the start of each of those units so that as they're
  • 01:08 coming off, I can continue to have a unit available at each tacked interval.
  • 01:13 Another change is to reduce setup and change over time so
  • 01:17 that you can get to a batch size of 1.
  • 01:19 I've been amazed at the results at the benefit of this technique and
  • 01:23 leads to an immediate understanding of problems within steps,
  • 01:25 more about this in the next slide.
  • 01:28 Finally, apply the theory of constraints to improve total process cycle time by
  • 01:32 eliminating bottlenecks.
  • 01:34 Again, I'll talk more about this later in this lesson.
  • 01:38 Let's discuss what we mean by the term flow.
  • 01:42 Keep in mind that our lean process goal is straight-line flow, no stops for
  • 01:46 decisions to branch off or other delays, and
  • 01:49 we want each step to be composed of value-added effort.
  • 01:53 So an obvious improvement is to get rid of as much non-value-added work and
  • 01:57 activity as you can.
  • 01:59 Often, this will entail changing the flow, so the product doesn't move as often,
  • 02:03 which then saves effort and reduces inventory.
  • 02:06 Also, take a look at all the reports being written.
  • 02:09 Are they still needed?
  • 02:10 Lots of people now have access to data dashboards and
  • 02:13 don't need to have reports to be generated.
  • 02:16 So, hopefully, there are some things that you can completely eliminate.
  • 02:20 In addition, there are some things you should try to minimize.
  • 02:24 Look in the process for any loops where you are redoing something.
  • 02:29 And I do mean re-, re-pair, re-turn, re-work, re-inspect,
  • 02:33 re-issue, and the list can go on.
  • 02:36 Each of these are non-value-added loops.
  • 02:38 Find out what starts a product on the loop and seek to reduce or eliminate the cause.
  • 02:45 Another thing to eliminate is decision points.
  • 02:47 Each decision point is a bottleneck and a chance to make a bad decision.
  • 02:52 If something is unique or special, take it out of the main flow, but
  • 02:56 don't bog down 95% of the product because 5% need special processing.
  • 03:02 Keep your main flow decision-free.
  • 03:05 You can also do some work cell redesign to optimize flow within a work cell,
  • 03:10 your industrial engineer can help you with this.
  • 03:13 Some of the ideas here are to have immediate notification of a problem, so
  • 03:17 we can stop and fix things before we've created dozens or
  • 03:20 hundreds with the same error.
  • 03:23 Also, work cell design can get rid of a lot of the movement and improve handoffs.
  • 03:27 And further, it enables visual scheduling, which is more flexible and
  • 03:32 responsive to customer needs.
  • 03:35 Now, let's talk about batch size of 1.
  • 03:38 Batch size of 1 leads to huge reductions in cycle time and
  • 03:41 the level of work in process inventory.
  • 03:45 I've seen processes that routinely took weeks to accomplish,
  • 03:48 be accelerated to get done within a few hours.
  • 03:50 Now, the technique of batch size of one is self explanatory, but
  • 03:54 there are several major implications so that this will actually work well.
  • 03:58 First, the process must be simple.
  • 04:01 This also includes simplifying the setup and changeover of equipment.
  • 04:06 Second, there is an implication for process control.
  • 04:09 Schedule and tracking systems must be real-time, or at least, nearly so,
  • 04:13 otherwise a preceding step may shove items into the next step,
  • 04:16 not knowing that there's a problem there and creating a bottleneck.
  • 04:20 More about this when we discuss visual controls in another lesson.
  • 04:26 The last thing I want to talk about is constraint management.
  • 04:29 This is based upon the theory of constraints developed by Dr.
  • 04:33 Eliyahu Goldratt and made famous in his book, The Goal.
  • 04:37 He outlines a five-step process for managing the process constraints, and
  • 04:42 the first step is pretty obvious, identify the constraints.
  • 04:45 This is the bottleneck, if we can increase flow through this point,
  • 04:50 we speed up the entire process.
  • 04:51 One of the easiest ways to do this is to watch where processes and
  • 04:56 items such as inventory start to stack up.
  • 04:59 Something is constraining them at that point.
  • 05:02 Step 2 is to focus the constraint.
  • 05:04 Make sure the constraint resources are focused doing that part of the process
  • 05:08 that only they can do.
  • 05:10 Offload any non-essential items or
  • 05:13 generic activities to other resources with excess capacity.
  • 05:18 Step 3, subordinate everything to the system constraint.
  • 05:23 Schedule all preceding activities to provide a small surplus of inventory items
  • 05:28 at that point, so that the constraint step is never able to get caught up.
  • 05:33 Since a constraint step limits the total output from the process,
  • 05:37 an idle constraint is lost process capacity to last forever.
  • 05:42 I know creating an inventory backup is countered to some
  • 05:44 of the other lean improvement approaches.
  • 05:47 But it's only at this one spot in the process, and
  • 05:50 only if that process step is capacity constrained.
  • 05:54 Now notice that so far, doing steps 1, 2, and 3,
  • 05:56 we've not actually hired anybody new and we've not bought any new equipment,
  • 06:01 in fact, we probably haven't spent any money at all.
  • 06:04 Yet often, I find that by doing steps 1, 2, and 3,
  • 06:08 I get a 50% increase in process output.
  • 06:12 Well, now it's time to look at spending money.
  • 06:15 If the first three steps did not break the constraint,
  • 06:18 now add additional resources to increase the capacity at the constraining step.
  • 06:24 You'll add people or equipment to increase the capacity.
  • 06:27 Finally, once that step is no longer the constraint, go back to your process and
  • 06:32 determine what's the next constraint and
  • 06:35 do the five steps again, there is always a process constraint.
  • 06:39 Something will limit how much the process can do.
  • 06:42 Keep moving from constraint to constraint until the capacity exceeds the demand.
  • 06:48 >> When cycle time, cost, or flow are issues, applying these flow
  • 06:53 improvement tools can significantly improve your process performance.

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