Probably of no help but here it is anyway
This is a tuff one. Attrition is due to many factors. You have machine rejects (visual fail, no pick), feeder set-up loss each time a reel is removed you lose X number of parts depending on feeder design (we lose 10 comps. each time we unload a 4mm pitch tape)you will lose some during reel loading. You will lose more parts during a first build while your techs are "dialing in". There is also the feeder/machine that screws up during production (assignable cause probably shouldn't be used for attrition calc.)
I would recommend that you get data from your machine as to its reject rate by package/feeder or whatever you can get. then allow for set-up/teardown loss whatever that may be.
but here is what we use for attrition when possible
discreets - 2% overage or 10 extra whichever is more Big$$ - 0% sometimes two extra in case of damage. Big parts (Dpacks, coils, etc...)- < 1% we retrieve from scrap bins and handplace
also keep in mind that when you build one assy. and the quantity of a certain component is for example, 1 per, the percentage thing obviously doesn't work (you need 10 extra parts to ensure that you do not go line down) Also make sure that all reels have adequate leader tape.
Russ
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