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Topic Title: Operator Balance Chart and Cycle Time
Topic Summary: How to use OBC when your cycle times are in the form of batches
Created On: 05/25/2017 01:06 PM
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05/25/2017 02:38 PM
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ELS2017
Esai Munoz Bonet



Hi All,

I am struggling to come up with a solution for a particular cell.

The current cell runs with batches, this is a result of having a washer that run on a conveyor and parts nee to be placed on baskets.

The baskets run 20 pcs at a time and takes 15 min for a full cycle but once the machine is running and parts are placed to wash at a constant pace you start to see parts at about every 70 seconds.

Once the parts leave the washer the operators continue to work in batches of 20, then once a specific inspection is completed they move them to a basket that holds 30pcs.

In my solution I want to eliminate most of the double/triple handling of parts because once the parts are placed at the 30 pcs basket they are inspected and moved multiple times but every time the operators lift each part one by one and place them on another 30 pcs basket. The new layout would require the first batch of 20 to be inspected and then all the consecutive inspections are done 1 piece at time but all in sequential order instead of 30 at a time. Lift the parts once and take it all the way to the final basket. (I hope this is enough background info)

I am trying to put this data into a operator balance chart to validate if operators task would fit inside my talk time. However because everything is at a batch process and at different amounts, 20 pcs or 30 pcs. How do I go about building the OBC?

The only thing I can think of is to divide all the batching process by the total amount of parts, this way I have the time it would take to process that 1 part trough that 1 element of inspection. Is this the right thinking?

Also when I look at takt time for the operation I need to produce 1 pc every 20 seconds. The was takes 15mins for 20 pcs so 45 sec/pcs, but once the conveyor starts to get loaded at a frequent rate I am seeing batches of 20 every 70-80 seconds. At this point my cycle time is 80sec/20pcs = 4 sec/pc? Same mentality as the mentioned above?
05/26/2017 11:11 AM
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Robert_Simonis
Robert Simonis



My suggestion would be to decouple the operations and try to run at closer to takt. Just because the operation before, and the operation after, are in baskets or set quantities does not mean the operator has to do anything other than single piece flow. Material can come into a cell and leave a cell in a variety of ways but the cell should run one at a time, and the transfer of parts in and out are transparent to the operator. This is know as a "black curtain" operation.
05/30/2017 11:59 AM
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ELS2017
Esai Munoz Bonet



So the plan is to break all the batching process and 1 piece flow each part into the final basket. This plus a modification to the layout will eliminate traveling and all the double handling of parts. Ex, lift them to place them in a different tray, lift them from that tray and put them back again on a different tray, then walk the tray to final inspection.
06/02/2017 04:13 PM
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41674
David Apple



Esai,
Your thinking is sound. Finding a way to eliminate the use of baskets and 1 pc flow through the inspection step is a good goal.

From your description,it takes 15 minutes for a basket to travel through the washer, but the baskets come out every 70-80 seconds, so your cycle time is 4 sec/pc.

You state your takt time is 20 seconds, so the washer is producing 5 times faster than takt time, is that correct? Then the washer is not running all day, I suppose, or you are running other parts through the washer, too. There must be a large stack of baskets on either end of the washer.

Do you want the inspection operation to run at the same rate as the washer (4 sec/pc) or takt time (20 sec)?
It is counter intuitive to space out loading baskets in the washer 1 every 400 sec (400 seconds / 20 per basket = 20 seconds which you state is your takt time.), but this would eliminate stacking baskets between washer and inspection if you want to run at takt.

If you want to process parts through Inspection in 1 pc flow, your OBC should have 20 seconds as the target and load inspection tasks up the 20 second mark.

Best Wishes, David
06/12/2017 03:55 PM
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ELS2017
Esai Munoz Bonet



The idea is to have 1 operator run the inspection portion, it is possible but I still have to work the math. For now I am planning on a event to improve the layout and eliminate all the walking in the process. Then I will look into how to balance the work.
06/12/2017 03:55 PM
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Kaizenguy
jason libby



Does it make sense to reduce the amount of parts in the baskets to 4 per basket? Since you say your machine cycle is 80 sec, then that 80 sec would provide you time to process 4 parts before the next basket comes out of the machine.
06/16/2017 10:07 AM
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David Apple



Jason, Good idea. that keeps parts flowing at an even pace.
Esai - Is the washer a shared resource or dedicated to the parts in question? If the washer is a shared resource, that means you may need to have a WIP queue before and after. That depends on whether there is a changeover required, and what % capacity is used by other parts.
06/26/2017 02:16 PM
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ELS2017
Esai Munoz Bonet



Yes, The washer is a shared resource.

Most of the time it is available and on some occasions you will have one operator from a different process camp at the washer loading parts.
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