Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Throughput Calculation

Rivkin

#24708

Throughput Calculation | 4 June, 2003

Hi Guys,

How do you calculate throughput? and what's the standard allowance for some hidden downtimes like pick-up miss, pick-up errors, parts/feeder replenishment etc.

say i have 4 machines that are not properly balanced in tact time:

A= 3 mins B= 3.5 mins C= 4 mins D= 4.5 mins

where will I base my throughput from the above tact? Is it proper to have at least 20% allowance for machine errors and replenishment? How do you calculate feeder replenishment allowance ? How do you measure the tact per machine as well? is it when the board starts to move in and up to leaving the placement table?

thanks,

rivs

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#24709

Throughput Calculation | 4 June, 2003

The tact time is determined by the slowest machine in the line. In your case it is 4.5 min. This is the time from the board leaving the output conveyor sensor to the next board leaving the sensor. The first machine, which finishes the job in 3 min. has to wait 1.5 min. to put its finished board onto the conveyor, because all boards will back up to the first machine. In practice, this time is even longer, because all other machines in line will impact the time of the first machine. If the line is that badly un-balanced, at least the last machine should be set up to be the fastest and the first the slowest. Even when the line is well balanced, you may want to calculate 10 % slower with each machine you are adding in line.

Station A does 8,000 comp/h, station B 8,000 � 800 = 7,200 comp/h, station C 7200 � 720 = 6,480 comp/h...

Replenishment time is dependent on the type of machine you are using. Can you re-fill, while the machine is running? Are you using stick magazines? Do you have extra feeders, which you could prepare with new components. Are you using full reels or do you get only a few inches long tape? Do you have only one operator and two feeder table sides on a 100 feet long line? However, 20% re-fill time is too high.

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Stephen

#24719

Throughput Calculation | 5 June, 2003

The most important thing to remember when measuring tact time for a machine is to pick a point in the cycle and start measureing from that point untill the next board reachs that point. What is best is to measure multiple consecutive cylcles, that is run say 5 boards and dont' stop the stop watch during the 5 boards. Make sure that the upstream has boards ready at all times and downstream is ready to recieve boards. And hope that nothing stops the machine during those 5.

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