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Topic Title: Production Planning & Scheduling
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Created On: 05/17/2019 09:20 AM
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05/17/2019 11:56 AM
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SafarKhan
Safar Khan



Dear Community,

We are producing high variety low volume components in our company. Right now we suffer a lot of bottlenecks at several work centers.

Our ERP System is applying backwards-, infinite capacity planning which means that based on the shipping date all the work is counted back. By doing that the ERP System assumes work centers do not have capacity limits and thus are overloaded.

This means that the ERP System does not take the actual workload of the work centers into account.


Now my question:

Is there a good method that would help to take the actual work loads of work centers into accounat so that the Schedule Start Date and Schedule End Date of an operation is stretched out based on the workload?

Best Regards,

Safar Khan.
05/20/2019 01:08 PM
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altemir
David Altemir



Yes. That's called finite-capacity scheduling. You should check to see if your ERP supports that.
05/20/2019 01:08 PM
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Don_Guild
Don Guild



Stretching out the operation dates is not going to help; it will just cause you to release more material sooner, thus driving up work in process. Use a Type B pull system to control the rate of release to production, and the operation dates to control the priority of release.
05/28/2019 08:54 PM
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Robert_Simonis
Robert Simonis



ERP stands for Enterprise Resource PLANNING. Use it to PLAN the sequence and delivery of products. If you create limits to capacity, it can highlight when your orders exceed capacity. Do NOT use it to schedule or execute anything inside the manufacturing or assembly processes. Stop using a planning tool as an execution tool.
05/28/2019 08:54 PM
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114506
Scott Alexander



we let the erp system drive the supply chain to have the parts that production required. Then we let the production system provide the signals to the warehouse to meet the shipping schedule. That worked for use assuming your capacity is sufficient for your demand. And we adjusted assembly lead times to allow for lumpy demand (say we assumed everything took 5 days to produce even though nothing took more than a day to make). When there were giant lumps of demand that far exceeded normal production demands, we had to respond manually (as we would never have the parts on hand even with infinite capacity).
06/10/2019 10:06 PM
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PrasadVelaga
Prasad Velaga



Originally posted by: SafarKhan

We are producing high variety low volume components in our company. Right now we suffer a lot of bottlenecks at several work centers.

This means that the ERP System does not take the actual workload of the work centers into account.

Is there a good method that would help to take the actual work loads of work centers into account so that the Schedule Start Date and Schedule End Date of an operation is stretched out based on the workload?


In my opinion, any production scheduling method that ignores the existing limited capacity of resources produces wishful schedules which can cause a lot discomfort and confusion to shop floor people.

In my opinion, Finite Capacity Scheduling (FCS) is a right answer to your query. However, FCS is an approach not a specific method / algorithm. Some powerful, third-party scheduling software implement FCS very efficiently for high-mix, low-volume production systems. If you do not look for bells and whistles and features for meeting a variety of production information needs, there are some powerful and affordable FCS software for job shops like Schedlyzer Lite see YouTube video .

Originally posted by: Don_Guild

Stretching out the operation dates is not going to help; it will just cause you to release more material sooner, thus driving up work in process. Use a Type B pull system to control the rate of release to production, and the operation dates to control the priority of release.


When resource capacity cannot be enhanced as required, stretching out an operation date (in order to eliminate resource overloading) is inevitable unless the operation can be outsourced. The stretching gives a sensible production schedule in such case. Good implementation of FCS will automatically release material for orders at optimal times so that work in process is very much under control. Look at the web page Lean-Production for an illustration.
06/18/2019 01:29 PM
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leanwannabe
Brian Koenig



One of the challenges you'll run into with Finite scheduling is your accuracy of information driving the system.

If you're planning on getting 120 hrs machine and labor availability out of a work center 3 weeks in the future, will it be available?

How accurate are your routings? If you plan on 500 parts taking 120 hrs to produce, how accurate is your projection? +/- 5%? +/- 15%? etc.

As the finite system is planning, it will most likely move orders up if it calculates excess capacity and move orders back if it calculates insufficient capacity. This can influence the projection for multiple other work centers which in turn can influence scheduling in additional work centers.

Garbage in - Garbage Out can apply to both Finite and Infinite systems. You should consider the impact of your database accuracy and the potential impact on scheduling and output both ways while evaluating the move to Finite scheduling.

Don't quote me on this. I think Finite Scheduling was common with Theory of Constraints software. If you can find a seasoned TOC person, they might be able to share some experiences on this.

Good luck

Brian
06/21/2019 02:55 PM
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PrasadVelaga
Prasad Velaga



Originally posted by: leanwannabe

One of the challenges you'll run into with Finite scheduling is your accuracy of information driving the system.

How accurate are your routings? If you plan on 500 parts taking 120 hrs to produce, how accurate is your projection? +/- 5%? +/- 15%? etc.


Brian, how accurate should the routing information be for getting some practical benefit from finite capacity scheduling? Accuracy of routing information will gradually improve when the information is used for scheduling purpose and the resulting schedule gets the attention of top management.

Routing information does not have to be highly accurate when we can judiciously allow some buffer time in the schedule to absorb uncontrollable natural variation in the system. Finite capacity scheduling received some justifiable criticism in the past because this concept was not implemented in it earlier. The large yellow segments in the right hand side of Gantt chart shown on the web page, Lean Production represent such buffer times of work orders (jobs).

Originally posted by: leanwannabe

If you're planning on getting 120 hrs machine and labor availability out of a work center 3 weeks in the future, will it be available?


If you are scheduling production over several weeks, do it first by default with the knowledge of regularly available hours of resources. Such schedule over weeks is like a weather forecast which gets updated regularly. Update schedule in response to major changes in the system.

Originally posted by: leanwannabe
As the finite system is planning, it will most likely move orders up if it calculates excess capacity and move orders back if it calculates insufficient capacity. This can influence the projection for multiple other work centers which in turn can influence scheduling in additional work centers.


Why should a finite capacity system not calculate capacity as such?

Originally posted by: leanwannabe
You should consider the impact of your database accuracy and the potential impact on scheduling and output both ways while evaluating the move to Finite scheduling.


The potential adverse impact of database accuracy on scheduling can be minimized by incorporating buffer times into the finite capacity schedule judiciously.

Originally posted by: leanwannabe
Don't quote me on this. I think Finite Scheduling was common with Theory of Constraints software. If you can find a seasoned TOC person, they might be able to share some experiences on this.


In my experience with job shops over many years, a vast majority of high-mix, low-volume production systems (usually found in job shops) still create and update production schedules using software like Excel, ERP systems, project management software and best-of-breed scheduling software. This practice has been going on in job shop world in spite of strong criticism by people like you. In fact, Excel still seems to be the most widely used tool for production scheduling. Even though most schedulers of job shop production are not quite happy with quality of schedules generated in Excel, they are not still embracing Lean and TOC methods as better alternative approaches for production planning.

I am unhappy that many critics of FCS maintain a false concept of how to implement on shop floor the schedules generated on computer by FCS software and ignore the current developments in FCS.
07/16/2019 10:01 AM
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leanwannabe
Brian Koenig



Prasad,

My apologies if you interpreted my post as meant to endorse Finite or Infinite scheduling. Looking back on my post and trying to answer some of your questions...

An early MRP II implementation I was involved with an implementation that struggled mightily the first 1 - 2 years mostly due to lack of understanding and training from staff including receiving, shipping, supervisors, purchasing, sales entry, etc. that lead to resistance to the new system, then some interpersonal issues along the way.

Both Ollie Wight (MRP II) and Shingo brought up the need to plan and control capacity as a key to their methodologies. As I learned about capacity planning and control, we modified how we approached scheduling and improved our performance.

Do you agree that having inaccurate routings can lead to challenges with capacity mgt, whether one is using a Finite or Infinite system? In my post I indicted that Garbage In - Garbage Out applies to both Finite and Infinite systems.

As to your question related to how accurate should routings be? Someone I worked with once shared his opinion that in a highly manual environment he would hope that the slowest operators could produce parts within 20% of the fastest. Obviously during training curve, the gap might be wider, for instance a new operator might only be up to 60% of rate after 45 - 60 days.

The extent of the impact of 20% variation might be affected by the complexity in the system. How many work centers are feeding this operation, and how many work centers is it feeding. If one of 5 centers feeding into me gets behind, I'm in trouble.

For whatever it's worth, in some ways it seems ironic that in a forum related to the stabilization of flow (Lean), I am discussing work centers with +/- 20% capacity / flow variation and uncertainty.

If I'm feeding into one work center and suddenly this week I'm 40+% behind due to absenteeism, material availability, and a machine breakdown, it possibly isn't as big of a deal as if I am feeding into 5. (how complex is the system?)

I agree that you hope to be able to improve routing accuracy, but the user (both finite and infinite) needs to put a system in place to update them.

Another challenge with routing accuracy seems to stem from, repeat business and the learning curve. What percent of your orders are ran more than 3 times per year? If it's less than 20%, the capability to maintain high levels of routing accuracy would seem to be more of a challenge than in an organization that has over 80% of their parts ran more than 3 times a year.

Hopefully you agree that a new Finite user who has limited experience and understanding of formal manufacturing software systems would want to understand:

A. Demand and Capacity management
B. Different variables that can impact such as variation in machine availability & efficiency, labor availability & efficiency, material availability, etc.
C. How to go about maintaining a level of currency of these.

If they don't, I would assume they'll struggle with most systems which can be frustrating. Sorry for the misunderstanding.

Brian
08/11/2019 09:18 PM
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Team_EP
Chetan Rao



Safar, this is usually the problem with ERP systems - it takes a lot of effort to keep them useful, and not every organisation has the resources to do that.

You probably already have seen this, but have you checked out the resources by Tony Rice over at his website called production scheduling? (Please look up the website, not sure if it's okay to plug links here). The folks there propose using a simple spreadsheet as an alternative to planning and scheduling.

Obviously, it won't be the right solution for every organisation, but I know some of my colleagues swear by it, and it aligns well the LEAN philosophy of reducing waste.

If you think the idea might be useful, it might be worthwhile getting someone to customise a spreadsheet to suit the specific requirements of your organisation.

Hope this helps.
08/11/2019 09:18 PM
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PrasadVelaga
Prasad Velaga



Brian Koenig,

Many manufacturing consultants who criticize finite capacity scheduling (FCS) in general seem to have some decades-old negative experience with FCS in MRP systems. But they also seem to be totally unaware of the power, flexibility and versatility of the current, best-of-breed FCS software.

Inaccurate routings can pose some problem in implementing FCS. But, we should also see how much inaccuracy the current, powerful FCS software can absorb while giving some practical benefits to production units. Would you think of such possibility? There is a way to get practical benefit from FCS even if routing accuracy is not perfect. It requires allowing some buffer times in the flow of jobs judiciously at certain stages of system. Those buffer times will absorb routing inaccuracy to a good extent.

Regarding the known variation in speed among operators, some of the current FCS software allows the users to specify speeds of machines and operators. For example, see a YouTube video of an FCS software, Schedlyzer Lite. Those FCS software also address the complexity you pointed out. They can also address the uncertainty that cannot be eliminated when that uncertainty is not at a chaotic level.

Good FCS tools help understand capacity management better because they facilitate what-if analysis with respect to changes in capacity. Similarly, they help users manage the variables you listed. Being away from sensible applications of the current FCS software, you might maintain a strong belief that there is no truth in what I have said here.

I take inaccuracy in the data as part of system uncertainty. If such uncertainty is at a chaotic level, I would not propose FCS software for production scheduling. I always say this on internet forums. Fortunately, the level of uncertainty is not so terrible for many production systems nowadays. However, I always insist that users must evaluate the practical merit of any FCS software on shop floor for weeks before purchasing it.

If we don't start using routings in calculations concerning production, their inaccuracy will never improve. Continuous pessimism about inaccurate routings does not help. If wrong results based on inaccurate data are brought to the notice of top management, then data quality will gradually improve.
09/25/2019 08:21 AM
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94286
David Pring



Hello Chetan,

Thanks for that information on the Tony Rice website and production scheduling. It is quite timely, I am a small manufacturer in Australia and operate in a job shop environment. Following the philosophy of Lean and TOC
has helped our production. We are now at the stage where we have an inhouse Access DB which fulfills some of the aspects of ERP and scheduling, but reporting is clunky and I do not have any connectivity to the factory floor.
My developer wants to retire and another custom development and or conversion of our system is probably uneconomic. We have been recommended to look for a cloud based solution, which will be a compromise. Maybe the integration of spreadsheets might be a cost effective solution both in the interim and into the future with another ERP platform?

Again thanks and I look forward to investigating the material on the Tony Rice website further.

Regards

David
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