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Lean Improvement: Pull

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About this lesson

The benefits of Lean improvements rely on changing the process schedule management approach in addition to process redesign. Pull scheduling and visual management are used to maintain smooth flow in the process.

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Lean Improvement: Pull

When to use

Once the Lean flow improvements have been made to a process, it is time to consider whether to implement Pull Scheduling techniques. They are very powerful for improving customer responsiveness.

Instructions

There are two primary approaches for scheduling items to flow through a process – push scheduling and pull scheduling. Push scheduling relies on a forecasted schedule. Based upon the forecast, new items are started into the process so that they will be completing at the time of the forecasted demand. Pull scheduling relies on an actual order from a customer, based upon that demand, an item is pulled through the process.

Pull scheduling is much more responsive to the customer demand, but it requires a process with a very short cycle time. Push scheduling was developed to accommodate long process cycle times. However, since the forecast is never perfectly accurate and the estimated lead times often have uncertainty, the push system is normally characterized by large amounts of unneeded inventory and inventory shortages of what customers are currently demanding.

The shortened cycle times of Lean enables many processes to operate with the flexibility and lower cost of pull scheduling and still remain responsiveness. Additionally, several techniques are used by Lean to implement pull scheduling.

Visual Scheduling

Visual scheduling is a set of scheduling principles that relies on the operators and supervisors to schedule the flow of items through a process based upon the demand and how each process step is performing. The operators and supervisors are able to see all workstations in the process and can recognize when one station needs assistance and others are free. It is often used with pull scheduling because it allows everyone in the process to see what is needed next based upon customer demand. There are many ways of showing the schedule need and performance including charts, lights, and inventory containers/areas.

JIT

Just In Time inventory scheduling is an approach that can be used with either pull or push scheduling. In this approach, the materials and documentation needed to complete an item at a work station arrive at the workstation just as work is set to begin. This reduces confusion at the workstation since there is only one item to work on. It is normally partnered with Batch Size of 1 or Kanban. When used with push scheduling, everything arrives at the workstation based upon the assigned schedule time. When used with pull scheduling, items are pulled from the preceding step where they have been held in a small inventory buffer or Kanban.

Kanban

Kanban is a signal-based scheduling system that relies on a communication signal from a succeeding process step to notify it when to do the next item. It's the most popular method for implementing a pull system with visual scheduling. A visual signal is telling a particular work station what to make and how many based upon the level of usage that has occurred at the succeeding workstation. There are often lights or messages between workstations. Another common approach is to use bins, or temporary storage containers that are sent to a preceding step. When the step gets the signal container, they fill it and send it back. Most push systems using signals are relying on barcode signals through ERP or other central scheduling systems.

Hints & tips

Be creative with the visual scheduling system and Kanban, the key is a visual signal providing real-time schedule status and direction.
Many companies have invested millions of dollars in ERP systems to plan and track manufacturing schedules. These systems are push systems. Expect resistance if you try to get “off the ERP” system and go to visual scheduling.
The greater the uncertainty in the customer demand, the more practical and powerful is a good visual scheduling system.

00:04 Hi I'm Ray Sheen, there's another improvement methodology that's been
00:09 popularized by the lean six sigma approach, and that is pull scheduling.
00:14 You may be asking yourself, what is pull scheduling?
00:17 Well, let's compare a pull scheduling system with a push system.
00:22 First, the schedule's based upon actual customer needs or
00:24 demands, not a forecasted schedule.
00:27 A unit is only loaded into the process,
00:29 when there is a customer who is asked for it.
00:32 Second, everything is scheduled from the customer end date or time backwards.
00:36 A day is promised to a customer by looking backwards, and
00:39 seeing how soon the next unit can be made they will meet the customer's demand.
00:44 Pull often uses visual scheduling in particular Kanban,
00:47 which I'll discuss more in other slide.
00:49 This allows the end of the process to see just where things are in the process, and
00:53 how soon the item will finish.
00:56 One of the most interesting changes that happens with a pull system,
00:59 is that when there is a problem with the unit in the process.
01:02 What changes, is the priorities of the units that are moving through.
01:06 We don't need to start a whole new unit at the beginning.
01:09 We just repurpose something all ready in the flow, as close to the end as possible,
01:13 and possibly cascade this repurposing through all the other preceeding steps,
01:18 until we get to step one, and then start a new item in the process.
01:22 Now let's compare this with push scheduling.
01:25 Rather than scheduling based upon the actual demand,
01:27 pushed schedule based upon a forecaster estimate.
01:30 And these are always wrong.
01:32 Hopefully, I'll be a little bit wrong, but sometimes they are terribly wrong.
01:37 The schedule is based upon the start date looking forward, so
01:40 all the step duration times are also guesses.
01:43 Again, some of those will be wrong.
01:45 The forecast schedule is often updated daily or weekly, but
01:49 that means in can't react in real time to processor item problems.
01:53 We must wait for the next published schedule, and try to address those then.
01:58 Finally, when problems occur, it accommodates this by telling the customer,
02:02 wait, we're not ready yet.
02:05 So how do you do pull scheduling?
02:08 Well, the most popular approach is to do Just In Time, or JIT scheduling.
02:13 Just In Time means that, a process step gets the material and
02:17 any other information or control documents at the workstation,
02:21 just before workstation is scheduled to do that work.
02:24 In other words, as soon as something arrives at the workstation
02:27 it's completed and then awaits for the next thing to arrive.
02:31 If my process was designed according to the tech time, and
02:34 I am using a batch time of one,this is very easy to plan and manage.
02:39 There are a number of benefits of JIT.
02:42 One is that, the opportunity for obsolescence is minimized,
02:45 both product obsolescence, but even more importantly, information obsolescence.
02:50 I'm not working on last week's schedule.
02:52 I'm working on the most important thing right now.
02:55 Another benefit is that,
02:57 there's much less whip inventory, which reduces operating costs.
03:01 A benefit that is sometimes overlooked, is that it reduces the opportunity for
03:05 something to get lost in the process.
03:07 It can't get put in with the wrong batch or overlooked.
03:10 It's the only item being worked on at that workstation.
03:13 Finally, it reduces the chances of the operators, or
03:16 system working on the wrong item.
03:18 When there's only one thing to do, you can't choose the wrong one.
03:22 Now JIT and Pool make it very easy to implement visual scheduling.
03:26 I've all ready talked about visual scheduling.
03:29 It's an approach that uses both active and
03:31 passive means, to provide immediate feedback to both the process operators,
03:35 and process managers when there is a problem in the process flow.
03:39 Everybody knows what's going on.
03:42 There are a few principles to follow when implementing visual control.
03:45 First, since it's sensitivity visual system,
03:48 you must have line of sight to every work station.
03:50 This includes both operators and managers.
03:53 Nothing could be hidden from others.
03:55 Second, each work station can signal, when it is done and ready for the next item.
03:59 This may be with lights or flags, or even a simple as the item is placed in
04:03 the hand off location for the next step in the process.
04:07 Third, in addition to showing when ready to move the process operators, or
04:12 systems provide a visual signal when they have a problem.
04:15 This notifies those that can help to solve the problem, where it is, so
04:19 they can quickly participate in the solution.
04:22 Finally, the system provides a passive signal about constraints,
04:26 by showing where work is stacking up at a bottleneck.
04:29 If the bottleneck step is known,
04:30 and planned process constraint, then there is no problem, and
04:33 that step continues to be actively managed to prioritize items through the step.
04:38 If it is not the constraint step, then you know that there's a problem there, and
04:42 process management can quickly react.
04:45 The last point to discuss will pull scheduling is Kanban.
04:49 Kanban is an implementation element for demand-based scheduling.
04:53 A kanban is a communication signal that tells a work station, that the next step
04:57 in the process is ready for them to do another item, and feed it to them.
05:02 The next thing about Kanban is, it's a communications signal.
05:05 Even if you don't have visual scheduling, you can communicate with Kanban.
05:09 I've often used Kanban with suppliers of other departments, who are not co-located.
05:14 You just need to figure out what type of signal will be used.
05:18 Let me go through some of the examples of common signalling approaches.
05:21 A favorite technique in manufacturing, or with suppliers is the Kanban container.
05:27 When you get an empty container, fill it and send it back.
05:30 If you don't have a container for
05:31 a particular item in your process, then don't do that.
05:34 I often see this approach used, to schedule parts and
05:36 supplies from stock rooms to the workstations.
05:40 Another technique is a light, email, or a cue that someone is asking for
05:44 the next item.
05:45 I like to use the email version of this with administrative processes.
05:50 Another technology that is a great enabled for Kanban is barcoding.
05:54 With barcoding, the schedule system knows when an item has been used,
05:57 it's bar code has been swiped.
05:59 The system then orders a replacement.
06:01 Many retail stores use this approach to keep their shelves stacked.
06:07 With today's information management systems, and a well designed lean process,
06:11 pull scheduling is easy to implement, and can pay big dividends for
06:15 the organization.

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Lean Improvement: Pull

About this lesson

Exercise files

Quick reference

Lean Improvement: Pull

When to use

Instructions

Visual Scheduling

JIT

Kanban

Hints & tips