Originally posted by: zman
The Blown Film Process is perhaps the hardest process to control gauge variations (i.e. in 3 layered constructions).
Does anyone know of the typical +/- variances one can set realistic variations for each layer at?
Zman, I would think the first thing you would need to establish is what you are capable of measuring. A gauge R&R may be in order to break down the variablity between device/operator/process.
Once you establish what you can measure, then you can set up your tolerances accordingly. If your measureable tolerances do not reflect what is needed for product performance, I would look into less variable equipment, attempt to make the people less variable through training in the use of equipment (difficult to do), or redefine the process (depending on where the most variability is found). In our case, using compound stereo microscopy, 60% of our variablity is operator (of course, our tolerances are out to the 4th decimal place).
The more capability you have in measuring on line, the less non-value added steps you will need post extrusion, IMO.
Even in medical device, we have systems that allow us to take product off line and directly to inventory, foregoing costly post process inspection. Out of the 80MM ft we produce each year, less than 10MM actually goes through any kind of QC inspection.
<b>Be One With The Extruder, Luke</b>
[This message has been edited by Larry A. (Edited: 01/25/04).]