iSixSigma

Cycle Time Question

  • This topic has 15 replies, 5 voices, and was last updated 6 years ago by Jay.
Viewing 16 posts - 1 through 16 (of 16 total)
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  • #55194

    68rs327
    Participant

    I need help… I work for a company who’s lean group calculates cycle time by timing the line 40 cycles and chooses the fastest cycle of the 40 cycles and post this as the cycle time of the assembly line. I have to disagree with this.
    My reason why I disagree is the assembly line has manual load time of machine and auto time of machine. Workers are going from machine to machine to load parts. As a worker works the 8 hour shift through out the day, workers get tired and are moving slower by the end of the shift. At the start of the shift people are rested, toward the end of the shift they are tired and moving slower. So how can you say the cycle time of the line is the fastest cycle? To me it like running a fifty yard dash 40 times. The first few races, I am pretty fast. But, by the time I get to the 40th race, I am tired and slower. I would love to hear your thoughts.

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    #199071

    Shelby Jarvis
    Participant

    If you plan a line to be 100% efficient based upon your fasted observed time, you will overstate your capacity. So in my experience, your intuition is good. However, it doesn’t seem like your lean group is very far what your intuition.

    I use the fastest repeatable time. As you are noting, fastest is not always representative of reality. Typically, the fastest repeatable time will be in the fastest quartile, but not the fastest.

    To address your concern of the difference in speed from start to finish, never assume 100% efficiency. Knowing the working conditions and some time observations may help you know how much of a factor to apply.

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    #199072

    Strayer
    Participant

    I think your intuition is right on. It seems that your lean group is confusing capability with performance. It would be much better to have both numbers and then ask why average performance is below capability, and what could be changed to bring performance up to capability. If you can collect time-bound data to confirm your suspicion that cycle time decreases during the shift this could be persuasive.

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    #199074

    Chris Seider
    Participant

    They may be doing this cycle time to get the denominator for the production line’s OEE. You want to know best technical speed with NO losses and this technique is a great first start at calculating best output capability–yes, they are including some losses but quick hits at improving output can use this technique.

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    #199078

    68rs327
    Participant

    The problem we are facing is over the last 10+ years the company has based their sales on the cycle times they were given for the assembly lines. They based the cycle times off the Lowest time in 40 cycles. This has caused the company to over sell their capacity, which has caused shortages to customers and 7 day week work. Our machines are 10 to 20 years old, which are not as reliable. On top of that they based the cycle times off one worker and taking their lowest cycle time. Then on top of that, they have started rotating operators on the lines every two hours. They weren’t thinking about through out the day people get tired and begin to slow down, they also didn’t think about the rotation every two hours and the person that was timed many be faster than the person who will be running the machine the next two hours. We work in 4 person work cells and have a lot of manual assembly work.
    My problem is: How do I change this and what is the proper way to determine the cycle time of the line with the stated conditions. If I were only timing machine, this would be easy, if everyone was a robot, this would be easy. But we have a Lot of manual assembly work with people being rotated every two hours. So operator “A” may be slower or faster than operator “B”, “C” or “D”. The second question is, how do we tell our customer that our cycle times were wrong and we over sold our capacity? On top of ALL this, this is a Japanese company who preaches TPS which isn’t a bad thing, but the way we have been taught to do cycle times and taking the lowest cycle, no matter who’s running the machine will be difficult to change. They will say “Kaizen the process to where everyone can do it the same at the same speed”,, but in reality people are not robots and some people are just faster than others and are not robots.

    Thank you

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    #199079

    Paul Madix
    Guest

    I think you know the answer already to your question. The bigger question is how to sell your production or engineering management team on why it is important to look at all of the data. Have them (with Mktg. dept. approval) contact your paying customers who have complained about long lead times to get the product or service you offer. Tie those orders to the data you are collecting (probably is not associated with the fast cycle times for the data you are collecting). You know the rest of the story…

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    #199080

    Sunil
    Guest

    Hi,
    You cannot use the fastest clocked time as the std. time for the complete shift.
    Fastest time can be used as Pacemaker for your line & set this time as your Kaizen target.
    To arrive at std. cycle time, have the average & give the allowances as per the kind of industry you are working in.

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    #199081

    Guy Paterson
    Guest

    Will try to post this for the second time. The theory of what your lean group is doing is sound. The logic is to look at the minimum cycle time and use that as a benchmark to shoot at. When doing standard work it is important that the team also look at the waste (muda) and variation (mura) that stops the cycle time being the same and minimum every time. Of course there is the human fatigue factor, part of the observations for mura should include fatigue and the corrective actions should be to identify ways to make the work less fatiguing for the workers and hence reduce the variation seen during the course of the day. If standard work is done correctly,y there is a “give back” allowance that is add in that can help with that too.

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    #199082

    Alex Pamatat
    Participant

    The replies above pretty much hit the nail on the head. Specifically regarding Guy Paterson’s reply, he is correct, there is typically a lot that can be done to make one’s job less fatiguing.

    At my company we spend a lot of time and money improving work space to address worker fatigue. This type of work sometimes goes as far as ripping down walls and rebuilding complete areas, building custom shelving and designing and building custom material transport carts. We’ve also created a web based system which allows for prompt feedback from people on the floor, these pieces of feedback are assigned an individual owner (typically an engineer) and the metric which tracks the feedback is reviewed every morning meeting with the factory managers. The feedback stays open until the person who submitted it meets with the owner and they agrees that the appropriate corrective action has been taken and they collectively close it.

    This should all come out in the kaizen, just make sure you have at last a couple operators from the manufacturing floor participate.

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    #199086

    Chris Seider
    Participant

    @68rs327

    Remember, in Lean and TPM or TPS methodology, the first step to improve a process is to identify the wastes, then pareto those wastes, then tackle the largest sources of waste. Of course, the waste reduction should align with the business needs at the time.

    Don’t worry about the ability to always get the best cycle time rate but look at the losses and how to get there.

    Good luck.

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    #199087

    68rs327
    Participant

    Thank you all for your replies, helped a lot.
    I thought I knew the answer, you all gave me peace of mind with your replies.
    I am going to talk with management and see how they want to move forward with this. I hope we can discuss this with our suppliers, who are the automotive industry. Sometimes they are a little hard to deal with.
    Thank you again.

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    #199103

    68rs327
    Participant

    Update: The company is warming up to the idea of the cycle time adjustments needed.
    Also, They are wanting to put a Production Display on the assembly lines. The display needs to show “Shift Production Target”, “Hourly Production Target”, “Running Production Output Per Shift” and “Running Hourly Output”
    Have any of you used a display like this and do you know a good supplier in the USA?
    I found this company http://www.vorne.com/xl/xl600-lean-manufacturing-tool.htm
    Any of you familiar with this product?
    I researched the web, and found only a few companies that had these products.

    Thank again.

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    #199104

    Chris Seider
    Participant

    See below.

    I’ve used them personally and you can get great results from this.

    http://www.vorne.com/

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    #199113

    Devender Malhotra
    Guest

    @68rs327, I think Strayer has stated it right & clear. Its Capability Vs Performance. Your Lean group is working on capability, but to Quote to the customer, the Standard Time of any product is given, which is not The Minimum cycle time.
    Standard Time which is the average time (of 5 or 10 cycles as per operation/ company) taken by an Average operator (trained to a certain eff level- 90% or 100% decided by company based on manual/ auto work) to perform the operation.
    Our lines are designed on ATT (Actual Tact Time) which is a few percent (2 ~ 5%) lesser than TT (TactTime) taking care of comapny’s benchmarked Downtimes/ Preventive schedules & so on..
    Minimim cycle time for benchmarking & Kaizen activities 1st target.

    Hope, i added some value :)

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    #199114

    68rs327
    Participant

    Devender Malhotra ,
    thank you very much for your reply, I agree with your comment.
    Our lean team in the past always took the fastest cycle out of 40 cycles and stated this as the cycle time of the assembly lines. Our sales group sold capacity of the line based off this at 100% efficiency. Now our problem is we can’t produce enough based on the information our sales team was given. This has put us into 7 days a week when the line has any downtime. This leaves us no room for PM work, so if the line goes down, we put a band aid on the problem because we can’t afford to shut the line down to fix properly. The band aid’s keep breaking which causes a snowball effect. This has caused us to expedite shipments to customers so we don’t shut them down. So, with the overtime cost for Saturday/Sunday work and the cost of expedites, we are loosing money, a lot of money. Now management is saying speed the lines up, reduce the downtime and get profitable….. Easy to say, hard to do under the current conditions.
    I am trying to reverse this thinking, but it has proven to be difficult.

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    #199141

    Jay
    Guest

    A better estimate of adjusted (true)
    cycle time is fastest cycle time X OEE. Calculating in this manner offers 2 benefits. First,a more realistic representation of cycle time is achieved. Second, using the OEE, the company can determine where to focus efforts to improve performance. Typically in LEAN manufacturing operations, adjusted takt time is calculated using theoretical takt time X OEE. The aforementioned approach (I.e, using cycle time instead of takt time) should be suitable as well as it seems your lines are running at near capacity and so the fastest cycle time is being used in lieu of takt. In any event, using the approach will adjust the cycle time for line availability, first pass yield, and actual machine speed versus design speed.

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