Methods for Measuring Cycle Time in Assembly and Machining Activities

[praveenraaaj]

Hello,

We are doing assembly and machining activities.

Can anyone please explain the various methods to evaluate the cycle time for operations to estimate capacity ?

Does it depends on the type of operation ?

Thank you!

Kind Regards,
R Praveen

 

[Bev D]

in general all cycle times are calculated the same way:

• some timing mechanism (I typically use the transaction times in our workflow software, but I've also used paper logs
• include both queue time prior to the operation and the time at the operation until it is complete.
• you can extract the 'touch time' from point 2 to understand how much of the overall cycle time is spent waiting, but remember that cycle time for cpaacity is the total time including all of the wait time.
• you will have a choice of calculating the average, teh median or whatever statistic is most applicable for your capacity model

does this help?

 

[praveenraaaj]

in general all cycle times are calculated the same way:

• some timing mechanism (I typically use the transaction times in our workflow software, but I've also used paper logs
• include both queue time prior to the operation and the time at the operation until it is complete.
• you can extract the 'touch time' from point 2 to understand how much of the overall cycle time is spent waiting, but remember that cycle time for cpaacity is the total time including all of the wait time.
• you will have a choice of calculating the average, teh median or whatever statistic is most applicable for your capacity model

does this help?

Thanks for the reply.

It would be helpful if you clarify the following :

Whats the best method for measuring cycle time ?
a) clock cycle time for 10 parts (whats the std qty ?) then take average for one part.
b) Monitor the no. of parts for prescribed time (say half an hour) then calculate the average for each part.

also pl mention others if any.

Praveen R

 

[Bev D]

Like all sample size determinations, there is no single answer. The correct sample size will be dependent on how much variation in cycle time you have. When you sample will be dependent on your volumes. In most cases a sample of 10 units or a single half hour period is not sufficient - even for very high volume. Look at the factors that can affect cycle time: operators, equipment state (needs set up, maintenance, no set up required, mold change) material replenishment, etc. Your sample size should encompass changes in these factors. Typically cycle time is measured for days and weeks for all units to capture the full range of variation.

There are several measures for the central tendency of cycle time and depends on risk and use. For the constraint I typically use the 75th percentile value or higher. (once you fall behind, you can never catch up without adding capacity somehow, usually overtime. And any operation that is targeted at it's average cycle time will fall behind in quantity half the time...). If the operation isn't the constraint I will typically use the median as cycle time is skewed to the high side and the average is too susceptible to one or two extreme values...


Of course this assumes that you are after true cycle time and not just touch time for the operation.

 

[lightaudio]

As Bev has mentioned, it depends on the variability within your process. In my past experiences, working with electro-mechanical assemblies, I often get involved and perform the function myself; of course doing this takes practice to overcome the learning curve. Another approach I have used is through interviewing operators. Inform them what and why you are doing it and ask them for a number. In most cases, they will low ball you by about 30%, but it gives you a starting point.
Depending on the number of parts per hour, you could do the old fashion way of picking an operation and using a stop watch in your pocket. This approach conceals your actions and I believe, by not alarming the operators of your actions, the result is more accurate.
The last and not least is to look at you MRP or manufacturing system and do some simple math. If your employee’s clock into jobs, the information should be ready for the taking.