One Piece flow discussion 1

[IHaveNoSpaceBar]

Hello all, helpful forum.

Does anyone here utilize the one piece flow concept?

I am doing some reading about the topic, but a few things confuse me. It seems that batches are a big no-no, for reasons such as detecting quality problems early.

Does 1 piece flow really mean 1 piece flow? so producing lets say 10 items in every cell and passing it(crate of 10 items) down to the next cell would not be considered 1-piece flow? Or would each cell send down 1 unit as soon its cycle is complete? Does that really make sense? all the time lost in travel? Or is this what conveyor belts are made?

My team's assignment is to eliminate cell pile up. Which is why I am trying to understand 1-piece-flow or other possible solutions.

 

[PSE]

One company that I worked for utilized what I would consider 1 piece flow though I would consider it a bad example. As the company was so small 1 piece flow was due to financial necessity rather than actual intent. We did end up doing a significant amount of customization as each machine had to accommodate the facilities layout for hookups as provided by the potential customer. Assembly was time consuming as well as documenting each of the unique features for future servicing etc.

Another company I have worked with had the product assembler do the build from start to finish. That way they "owned" any quality problems that arose during its production.

1 piece flow might be nice in theory but take an actual look at your products/processes to see if it may be appropriate. Long setup time operations are likely to be better off as batch processes. Assembly operations may be amenable such efforts. Treat it as a goal but not as an absolute measure of success. Improvement efforts can have diminishing returns. You can reach a point where further refinement is just too expensive.

Detecting quality problems early? Yes as the theoretically shuts down every time. This can be a painful process. Hopefully the company can absorb the hit on cash flow (which may be only an internal "political" hit).

Communication is paramount to eliminating cell pile up. If no one flags a problem, no one is likely to respond to it until it becomes "obvious". Look at Kan-Ban as a way to shut down upstream operations from "over producing" and then attack your bottlenecks. Every product has some unique aspects about it and I do not feel that there is a single cure-all methodology that could be used.

Regards,

 

[nate2003]

My company practices "continuous flow" within a cell. For example, we have two cnc lathes, one VMC and three gear shapers in the same cell. Rather than run the first lathe op, then the second, then the mill, etc., we set up all the machines and run the parts continuously through the machines. That way if there is a problem with the first part, we catch it right away and fix it with maybe only one scrap part. Also, even though the part has 12 min. of machining with four operations, we balance our run times to 3 min. ea. That way the cell pumps out one piece every three minutes, rather than batching at each machine. If we batched, the total manufacturing time for 100 pcs would be 100 pcs x 12 min or 1200 min. plus setups. This way the time for 100 pcs is 12 min + (3min x 99 pcs) or 309 minutes plus setups.

Advantages: catch quality issues faster, faster overall manufacturing time, therefore faster lead times, therefore fewer past dues, smaller lot sizes, more inventory turns, ...

"I have had my results for a long time, but I do not yet know how I am to arrive at them." Karl Friedrich Gauss

 

[GerryMoore]

"Does 1 piece flow really mean 1 piece flow? so producing lets say 10 items in every cell and passing it(crate of 10 items) down to the next cell would not be considered 1-piece flow? Or would each cell send down 1 unit as soon its cycle is complete? Does that really make sense? all the time lost in travel? Or is this what conveyor belts are made?"[\color]

To answer your questions:
Yes
Correct
Yes
Yes
To have a correct "lean operation" using one piece flow travel needs to be minimized or it won't work.
Setups also need to be minimized. Setups correlate to batch size. Short setup=short batch.

My company has some one piece flow, some batching. The one piece flow is one person handing the part to the next person, or having one-part of inventory in between. not much travel maybe a step or a short piece of conveyor. Conveyor does not always support one piece flow, because as a wise man once said "If conveyor is there it will be full of parts, so keep it short".

To understand this principal in simple language along with lean in general read "The Goal". I forgot the author's name. It's an easy read.

 

[MikeHalloran]

This example may be tangential, or not:

My machinist friend Elmer was able to effect tremendous productivity improvements as the sole occupant of what used to be a dozen- person machine shop. Somehow the accountants there had not managed to sell off all the machinery for scrap prices, so it was still connected and usable. Elmer left each machine set up for a particular kind of operation, so no matter what process he used on any particular part, there was essentially zero setup time.

Zero setup time beats fast setup time, every time.

Of course this tactic is not available to a greenfield startup, but in an outfit that's just been reamed ... er, downsized, you might be able to justify not liquidating all the tooling right away.

Okay, I've tried. The only way I've found to keep accountants from selling off tools in a downturn is to keep them ignorant of the tools' existence.



Mike Halloran
Pembroke Pines, FL, USA

 

[BillPSU]

Hey Mike,

The accountants aren't the ones to blame. Upper management are the ones who hold the reins.

 

[MikeHalloran]

They always _say_ that they're just the point of the spear, and really just regular guys.

Which does not explain why they're over- represented in upper management.







Mike Halloran
Pembroke Pines, FL, USA

 

[Trad016]

In order for single piece flow to work efficiently, you'll need to set up your processes in a U-flow configuration. That way, you won't have as much transportation waste. If you want some good info on the subject, research Lean, JIT, or Kaizen. Good Luck.

 

[TechyC]

Ok here we go

Yes one piece flow does mean 1 piece flow. Though don't be tempted to introduce this throughtout the facility. The Handle that inventory is evil has become all to prevelant recently. Inventory should be used strategically to protect bottlenecks and be controlled.

Depending on the product it might be feasible to introduce 1 piece flow at certain points in the production process. If using batches a good rule of thumb is to make them equal to the average customer order size. Improving set up times etc will then allow you to reduce the batch size even further.

I assume by this point you've already completed a value stream map and this should show you clearly where 1 piece flow can be utalised and where it can't. If you havn't done a VSM then do this first. it will give you a much clearer goal and a better idea of the expected benefits instead of just guess work. It also prevents tinkering with production and shows where the greatest benefits can be reached.

Best books on this are

Learn to See - value stream mapping (avaliable on amazon)
The Goal - E Goldratt
Check out the American goldratt institute at

http://www.goldratt.com

or the lean enterprise acadamy or lean aerospace society websites (type into google) for some great free downloads of tool kits etc.

Also the WEAF (west of england aerospace forum) website has loads of case studies about companies undergoing this type change. Almost certian you'll be able to find a similar product - remeber what you make isn't important look for exaples of similar complexity, product range, lot sizes, customer requirements etc.

If after that your still struggling then your best bet is to get a grant and have a few sessions with one of the many subsidised copnsultancy firms, at least to get you started. As much as I dislike consultants they can get things moving.

Alternativly you could hire me I'm very reasonable ;-)

Hope this helps

 

[sigtan]

SPF concept can be misleading at times. If you try to implement it right away, you will fail most likely.

What I would suggest is that you should set single piece flow as an ideal and start working by reducing your batch size by half every time untill all your processes becomes tightly coupled with no inventory/WIP in between. Flow in very small batches without queues is what I have always tried to achieve in regards to single piece flow.

 

[ddbyrd3]

IHaveNoSpaceBar

One peice flow is exactly as stated.

The 1st step to modifying ANY process is you need to see it. I would recommend you spend the time necessary and document each step in the process, document the cycle time at each station/machine, the travel distance between stations/machines, etc.

Call it a process map, or a current state map, you cant make an educated decision unless you see it.

From there create what is called a future state map, or what would you like it to be.

This typically identifies bottle necks, extended travel distances, etc.

One peice flow is great, however NOT ALL products and processes can conform to one peice flow.

Look at your process, draw it out, you can also do a spagetti diagram.

Use these tools first to see your process, than make the educated decision if it will add value to redesign the current flow.

 

[edspearman]

Sound like you are experiencing a line balance problem; if your line in backing up; or Constraints.

JIT or Just-In-Time is one piece pull. "It Does Work" if you understand the rules; and enforce them with KAIZEN techniques. ( TPS or Toyota Production System ).

1) Know your customer demand
2) Establish TAKT Time
3) Design the work cell "UCell Concept" use correct footprints in Plant Layout.
4) Layout the cell by the numbers; Not always possible with Brown Field Projects.
5) Capacity Studies, Utilization Studies are completed.

My e-mail is:
edgarspearman@insightbb.com
I can walk you through this.

Remember; Don't Push; You Pull.

Materials Delivery is very important for any Thru-Put operation. "TYPE OF KANBAN SYSTEM"

Ed Spearman

 

[quartermeter]

Great site.

What type of processed don't work well wit

h "One Piece Flow"

I'm not talking about long setup time machining processes. I realise they don't.

Give me some examples and I will give more information.

 

[Bill07]

Hello All!

I have a few questions, maybe someone could help me answer or give some direction. Our company is currently working towards the goal of coverting from a push system to a pull system with implementing the Kanban concept. I have been in many meetings and the main topic has been one-piece flow over batch. Within in our production we do not make 100's of parts at a time. We manufacture equipment that is customized to the customer needs. There are some parts that are standard and have been implemented within the Kanban system. I feel giving our current operation that a one-piece flow will not work for our process. We focus alot on our load leveling and planning and "Q" times and has been working very well for us. It use to take us 60 days from start to finish to complete one machine. Now through our process & planning we can deliver a machine with the assist of the Kanban within 2-3 weeks. We appprox move 10-12 pieces of equipment per month. So we currently really are useing a batch system instead of a one-piece flow concept. Given some of the facts, is this the right direction?

 

[sigtan]

Bill,

This seems like you are going in the right direction. Next step would be further dividing the current batch size by 2 and improve processes to overcome the problems that arise there after. If you keep on this process as a continuous improvement process, you can achieve a very near true one piece flow.

Other than the setup times and changeovers there is a great deal that needs to be done in terms of station layout and standard work also. I feel that unless you layout your processes in such a way that it is the only best way to do it, you will not be able to achieve a perfect one piece flow.

 

[BillPSU]

What kind of a business model is your company?
Build to stock?
Build to order?
Engineer to order?

The purchased components which you cannot get pull delivery for, what are you doing about these? Is this maybe why you are batch building?

Your purchase parts probably makes up 65-75% of your product. Can the suppliers support 1-piece flow with your low quantities of production?

There are parts which do not meet the 1-piece flow model. Lets talk about fasteners, parts sold by the case, a half a bar/sheet of steel or other materials, or lots of other parts. The kanban size for your parts must make sense not just 1-piece flow.