bottleneck - different line capacity 1

[Salvatio]

Dear all, I'm having some troubles, hope you guys could help me here. For current plant situation, each line has different capacity, with a ratio as below:
line 1 - 7
line 2 - 8
line 3 - 4
line 4 - 4.4
line 5 - 6
line 6 - 4

The process is from line 1 - line 2 - line 3 - etc. However, line 2 can provide WIP directly to either line 3 or/and line 4.
Problems start as soon as it reaches line 2. I've tried to arrange the production with smaller batch size, but still unable to provide any optimum solution. Is there any method to calculate or to simulate this? Thanks

 

[PSE]

Are these values the number of items run through the line in X amount of time or are these values the amount of time it takes to finish one of the process steps?

If I were to take a guess since you indicate the problems arise in line 2 that the values are times. Since lines 3 and 4 can both utilize product from line 2, they would end up waiting for line 2 to produce. Shutting down line 4 and running line 3 at half capacity would alleviate this; though from an efficiency standpoint (and managerial viewpoint) is likely to be perceived as going in the wrong direction. Your "cycle" times would be (assuming no other effects), 7, 8, 8, 6, 4. Likewise, running line 6 at half capacity would give 7, 8, 8, 6, 8.

Increasing the output of line 2 either through multiple shift operation or actual line duplication would reduce the cycle time. Since the two downstream lines (3 and 4) have approximately half the cycle time, you would need a 4 fold improvement in output from line 2. This in turn would cause line 1 to be the bottleneck requiring similar attention to increase throughput there.

In short, do the best you can to balance the ratio's in as simple a manner as practical. Line optimization is an ongoing process as long as it is fiscally justifiable. Eventually you can find that further refinement is more expensive than what it is worth.

Regards,

 

[tomwalz]

Wow,

Nice clear, simple accurate explanation.

I like Goldratt for reading in this area.

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[Salvatio]

PSE,

line 1 - 7 produce - FG and line2 WIP
line 2 - 8 produce - FG & line3,line4 WIP (main process)
line 3 - 4 produce - line4 WIP
line 4 - 4.4 produce - line5 WIP
line 5 - 6 produce - line6 WIP
line 6 - 4 produce - FG (main product)

as I've stated before it is refering to the production capacity; unit/time. i.e. line 1 - 7unit/time (e.g. unit/year), line 2 - 8unit/time. However, these all are just an approximation ratio. As shown,we have 3 types of Finish Goods, coming from line 1,2 and 6. Line3 and Line4 have the longest cycle time.
Since line4 receives WIP from both line2 and line3, it's already over it's capacity limit.
The current solution is only to lower down the production rate (nett throughput, unit/unit-time) of the first 2 lines such that downstream can cope with the production, like you've mentioned so.
However, we've tried using smaller lot size for each production cycle, especially in line1, as it is running a product mix. The result shows that the bottleneck effect on Line4 and Line6 has slightly reduced.
Further increasing the capacity of Line4 and Line6 shows rather impractical, since it requires modification of the over plant layout, and I dont think management will approve it anyway.
As it's seen, this has caused the overall plant utilization factor near to it's critical value, with Line1 and Line2 running below half of its capacity.

 

[tgeorge]

Not a big fan of lowering production speed downstream, myself. It only serves to maks problems that are occurring upstream. I would just keep them where they are currently, and use their idle time to really gage if the improvements you are making in the lengthiest cycle time are actually working. An idle worker is real incentive for actually making improvements. Plus you know exactly who to turn to if emergencies pop up and you need to allocate resources away from somewhere.

Some people like to do this to "make the line flow smoother," but sure, while your line is "flowing smoother," its also operating at a reduced capacity, that is all too easy to become, "status quo production."

I see the point they make though.

 

[PSE]

Since you are already working on lot sizes, also pay close attention to scheduling and any setup/changeover times needed for doing the various mixes. Lines 1 and 2 especially. Since line 3 can apparently pace line 6 on the main product production it looks like line 2 is caught in a balancing act of trying to fill in with additional volume as needed.

Regards,