Locked lesson.
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.
Exercise files
Download this lesson’s related exercise files.
Lean Improvement Pull - Exercise.docx61.6 KB Lean Improvement Pull - Solution.docx
61.4 KB
Quick reference
Lean Improvement: Pull
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.
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 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 enable 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 on 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 on customer demand. There are many ways of showing the schedule needs 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 workstation 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 on 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 workstation what to make and how many based on 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 rely 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.
- 00:05 Hi, I'm Ray Sheen.
- 00:06 There's another improvement methodology that has been popularized
- 00:10 by the Lean Six Sigma approach, and that is pull scheduling.
- 00:14 You may be asking yourself, what is pull scheduling?
- 00:18 Well, let's compare a pull scheduling system with a push system.
- 00:22 First, the schedule is based upon actual customer needs or demands,
- 00:26 not a forecasted schedule.
- 00:27 A unit is only loaded into the process when there
- 00:30 is a customer who has asked for it.
- 00:32 Second, everything is scheduled from the customer end date or time backwards.
- 00:36 A date is promised to a customer by looking backwards and
- 00:39 seeing how soon the next unit can be made that will meet the customer's demand.
- 00:44 Pull often uses visual scheduling, in particular, Kanban,
- 00:47 which I'll discuss more in another slide.
- 00:49 This allows the end of the process to see just where things are in the process, and
- 00:54 how soon the item will finish.
- 00:56 One of the most interesting changes that happens with a pull system is that when
- 01:00 there is a problem with a unit in the process,
- 01:03 what changes is the priorities of the units that are moving through.
- 01:07 We don't need to start a whole new unit at the beginning.
- 01:09 We just repurpose something already in the flow as close to the end as possible.
- 01:14 And possibly cascade this repurposing through all the other preceding 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 actual demand,
- 01:28 push schedule is based upon a forecast or an estimate, and these are always wrong.
- 01:32 Hopefully only 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.
- 01:46 The forecast schedule is often updated daily or weekly, but
- 01:49 that means it can't react in real-time to process or item problems.
- 01:53 It must wait for the next published schedule and try to address those then.
- 01:59 Finally, when problems occur,
- 02:01 it accommodates this by telling the customer, wait, we're not ready yet.
- 02:06 So how do you do pull scheduling?
- 02:08 Well, the most popular approach is to do just in time, or JIT, scheduling.
- 02:14 Just in time means that a process step gets the material and
- 02:17 any other information or control documents at the workstation just before
- 02:22 the workstation is scheduled to do that work.
- 02:24 In other words, as soon as something arrives at the workstation,
- 02:28 it's completed, and then it waits for the next thing to arrive.
- 02:31 If my process was designed according to the tack time and
- 02:35 I'm using a batch size 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 both product
- 02:46 obsolescence and 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 there's much less WIP inventory,
- 02:59 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 pull make it very easy to implement visual scheduling.
- 03:27 I've already talked about visual scheduling.
- 03:29 It's an approach that uses both active and
- 03:31 passive means to provide immediate feedback in both the process operators and
- 03:36 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.
- 03:46 First, since it is a visual system,
- 03:48 you must have line of sight to every workstation.
- 03:51 This includes both operators and managers, nothing can be hidden from others.
- 03:55 Second, each workstation can signal when it is done and ready for the next item.
- 03:59 This may be with lights or flags or even as simple as the item is placed in
- 04:04 the hand-off location for the next step in the process.
- 04:07 Third, in addition to showing when ready to move,
- 04:10 the process operators or 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 that they can quickly prticipate in the solution.
- 04:22 Finally, the system provides a passive signal about constraints by showing where
- 04:27 work is stacking up in a bottleneck.
- 04:29 If the bottleneck step is known in a plan process constraint,
- 04:32 then there's no problem, and
- 04:34 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
- 04:43 process management can quickly react.
- 04:45 The last point to discuss with 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 workstation that the next step
- 04:58 in the process is ready for them to do another item and feed it to them.
- 05:02 A nice thing about Kanban is that it is a communication signal.
- 05:05 Even if you don't have visual scheduling, you can communicate with Kanban.
- 05:10 I've often used Kanban with suppliers and 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 signaling approaches.
- 05:22 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 a particular item in your process,
- 05:33 then don't do that.
- 05:34 I often see this approach used to schedule parts and
- 05:37 supplies from stock rooms to the workstations.
- 05:40 Another technique is a light email or a queue 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 enabler for Kanban is barcoding.
- 05:54 With barcoding, the schedule system knows when an item has been used,
- 05:58 its barcode has been swiped.
- 05:59 The system then orders a replacement.
- 06:02 Many retail stores use this approach to keep their shelves stocked.
- 06:06 With today's information management systems and
- 06:09 a well-designed Lean process, pull scheduling is easy to implement and
- 06:14 can pay big dividends for the organization.
Lesson notes are only available for subscribers.
PMI, PMP, CAPM and PMBOK are registered marks of the Project Management Institute, Inc.