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Tact Time Estimates



Tact Time Estimates | 8 March, 2003

My two Process Engineers are at odds with each other.

One says that the Tact Time is only the actual Pick-n-Place time to build a board, and the other says it needs to include the load/unload time as well as the Fiducial reading time.

Example: So when we balance the line and we get a Tact Time of 2:30 per machine (for example), you would think that you would get 24 boards an hour. This is assuming no downtime. But in reality we get 23 boards an hour. This is a basic example and when we run kits from 5K - 25K+ piece kits, this will add up.

So based on this I always need to de-rate my tact time by 5 or 6 seconds to allow for the loading/fiducials/unloading?

Sounds like PE#2 has proven the case and we need more accurate balancing software? This software is accurate for optimizing and balancing the line based on Tact Time only(and it does a good job), but it can not be used to estimate actual production times. So we would use this software for balancing and use another to gauge production times?

We can not quote to our customers that we will run their boards at 58,000 CPH based on the Tact Time alone, well I guess we could...

Any thoughts?

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Tact Time Estimates | 9 March, 2003

"Tact time" has to do with pick, move, and place. It has nothing to do with loading and unloading feeders. [Not to say a measure like that isn't good and useful, it just isn't called "tact time".]

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Tact Time Estimates | 9 March, 2003

Tact time is a poor measure of your throughput capability. The Number of boards produced per hour or shift or 24 hour period is the true measure of what you are really doing. Your theoretial "tact time" can be used as a metric to judge performance, but you need to develop a manufacturing model which is epresentative of your factory.

Your software can not predict: 5K reels or 10K feel quantaties? How many feeder changes per hour? Decalibrated feeders causing pick erors, Down time per hour and the attribute of each event. Also, your quoting accuracy is a function of your software constants. That is, what you have assigned as time constants vs. part type. Chip = 0.1 sec, tand D = 0.4 sec etc.

There are a hundred reasons for a machine to stop. It's your ME's job to eliminate the road blocks and attempt to achieve the theoretical PPH rating. Quoting should reflect what you actually do, not your theoretical capability.

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Tact Time Estimates | 10 March, 2003

Tact time as defined by the IPC 9850 standard is "the average time required to place a single component while maintaining the specified placement process capability. Excludes transfer time, fiducial time and nozzle change time." Sounds like what you are really interested in is "net throughput". This is the number of components placed (on a panel) multiplied by 3600 and then divided by the sum of the "build time" plus the "transfer time". This will give you your throughput in components per hour. Build time includes fiducial read, nozzle exchange and total tact time (time to place all components on the panel). Transfer time includes panel transfer and clamping. Your balancing software need to be machine specific so that times for transfer, fiducial read and nozzle change (even during the run) are all accurate. I think your are on the right track with a de-rating factor so long as it is based on actual data.

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Tact Time Estimates | 10 March, 2003

Tact times published by placement equipment suppliers usually do not account for board load/unload. Placement time standards set for your boards must include load/unload time. I measure from first fiducial read on board 1 to first fiducial read on board 2. This is pure machine tact time for that given board. Ensure there are no "pick recovery" during the cycle. Then you burden the "pure" machine tact time for that given board based on your efficiency. Feeder changeovers, when a feeder runs out, do you: a. remove that feeder and reload it on the bench, which is a variable time, or b. do you have a feeder standing by already loaded to replace the empty one on the machine, which is a standard time. Do your machines stop for emply feeders or are they smart enough to alert the operator and continue building allowing the operator to change out the feeder while the machine is running. In that senerio, no production is lost during feeder reloads. These are factors that will effect the degree of burden you apply the the "pure" tact time for the placement machine time standard for a given board.

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Tact Time Estimates | 10 March, 2003


You really received some good replies.

It seems like the best replies are a BLOW to one of your engineers, at least from a terminology view point. "No cake tonight". Yet it doesn't mean (s)he is better or worse than the other.

Tact Time from a manufacturing/industry group perspective (aka IPC) tends to be defined so that equipment can be compared (kind of) yet you still need to know more about the entire process to really compare equipment. It is one of those games they play so that one mfg doesn't compare themselves apples to apples with another.

So my advice is to teach them both what Tact Time means in terms of industry wide definitions and then move on to what really matters to your operation. Us Engineers do like to quibble about our expertese.

YiEng MA/NY DDave

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Tact Time Estimates | 10 March, 2003

You can call it anything you want. At the end of the day what matters is what you are able to produce in a given period, say 8 hours. How many components where placed during that time. Most engineers do not fully understand that there is generally more down time on a typical line than uptime.

The best, most accurate and simplest way to track and create a benchmark to work towards improvement is.

1. run job one, track total time on the smt line until finished.

2. how many components where placed to run that job

3. divide the hours by components, that is your actual placement time.

4. run multiple jobs and job sizes and keep track of this on a spread sheet, very simple since most lines will not run more than a few different jobs in a shift.

5. you can then see what the impact is of a small job versus a very large job and how many placements can be expected in an hour, 4 hours 8 hours.

6. Start looking at how long your pick and place machine is down during changeovers and reloads. As you find ways to reduce this you will see you placements per hour go up.

Your wasting you time using machine manufactures specs for running costs. their specs are great for comparing machines only and to guide you at time of purchase.

Only reality is worth trackiing, call it anything you want.

Hope that helps

Ken Bliss Bliss Industries, Inc.

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Tact Time Estimates | 10 March, 2003

This touches on one of my pet peeves. Management types demand something, that is not feasible or practicle. So the manufacturers put something together to pass off as what was asked for. In this case a way to put hard numbers on what a machine can do. Mydata at least pushes, that tact time is not what's most important, it's how much you get out in a day. The worst case I saw was a manger asking me about why production on a particular board was way below his calculations. When the machine was transfering boards the turret was stopped for a full 5 seconds. The machine populated the panel in about 15 seconds. I told the manager that the problem was the time transferring the panels, he replied that no as long as there was a board waiting and the next station was empty transferring was not a problem. I didn't argue but then told also that the panel was very sparce and that lowered efficiency. He said that then the program had to optimized. I didn't bother telling him that most of the parts were ceramic caps that were not put on at the turrets top speed.

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