SMT tact time

This is highly dependent upon your board, vision inspection, part rotation, part type, layout, number of P/Ns per (1 pers or 100 pers) feeder layout, optimization, nozzle changes, etc... all have significant impact on placement speed. I find if you get 50% you are doing well or average. Some boards will be faster, some might actually even be slower. Placement speed is sometimes calculated by the manufacturer using the maximum speed of pick time, place time, and seek time, maybe even vision inspection time. Others will use the IPC board and under ideal conditions, (ie perfect feeders and feeder layout since they don't necessarily have to place a different P/N in each location like we do) and can only really be used to compare one machine with another, These are not real life conditions on these test boards and setups. You need to ask how the speed was calculated and have them "run your product" and tell you what they got and how fast they got it going. Did they spend two days changing feeders around? or modifying step sequence? how did get this incredible speed? Show them a typical board if you can and have them guarantee a tact time and see what they do.

Is anybody getting 75% of advertised speed out there? I'm curious.

Russ

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Machine design plays a major factor in actual placement rate vs. the published tact time max speed. For example, random access horizontal turret head machines can vary greatly depending on nr. of different components and size ranges, while the dual gantry dual vertical turret head (the collect and place design) design achieves some of the most consistent rates regardless of nr. of components and component size range. Single gantry single head designs can also vary greatly from board component mix. There are also designs such as split axis where the head moves in X and the table/board moves Y. This design allows for maximum axis speeds and delivers good performance in max. cycle rate vs. actual rates. There is also the multi-head sequential design, which is the absolute fastest with rates in the hundreds of thousands per hour. In this design the machine is segmented in stages. Each stage has its own placement head(s) and feeders. The board steps from stage to stage. The proper method to measure actual placement rate on a given board is to time the machine from the first fiducial read on board nr. 1, then complete component assembly, then stop the clock at the first fiducial read on board nr. 2. This will account for board transport time. Ensure there are no feeder re-picks or errors during this test. What you time will be �real best case� for that given board. Now, how many placements you get at the end of the day for that board will depend on how efficient your operation is. Speed of feeder change outs and re-loading, how fast operators react to a machine stoppage- these are the human factors that will effect placement rate. Machine design can effect these times as well. Not all machines take the same time to re-load a feeder and mount it on the machine. Some machines are designed to not stop for a minor error, instead it will continue picking and placing (provided there is more to do) and alert the operator to the issue. The IPC9850 spec is a good start to differentiate machines in terms of what their actual placement rate is on the IPC board vs. what their published max rate. A good machine design should deliver 80% of max cycle rate or better on the IPC9850 board.

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