Can you apply DFM to winding?
David Roisum, Ph.D., Consulting Technical Editor -- Converting Magazine, 1/1/2008 12:00:00 AM
Of course you can. However, you really have to think outside the box so that the winder is considered a vital step in manufacturing instead of an after-thought. DFM (or Design For Manufacturability) recognizes the futility of making a product that the end-user really likes if manufacturing costs prohibit profitability. It recognizes that sometimes waste and delays can be reduced by slight changes in product design that would be acceptable by the customer.
So, this is not really a new idea in itself. It's just that, until recently, winding was not considered on par with upstream manufacturing. That is, until winding defects forced a rethinking of this narrow view. There are scores of products which have been redesigned to make them more windable. Papermakers change clay suppliers to reduce crepe wrinkles and change soaps to reduce winder vibration. They may add frictionizers to cut paperboard slipperiness and thus avoid telescoping. They may reduce frictionizers to avoid vibration of kraft paper. In all these cases, material costs rise noticeably, and the chemistry consequences are far-reaching. Even so, the paper people recognize the payback. You can't sell what you can't wind. Film makers have also started to modify the outer molecule of their products to keep them from being too tacky or too slippery.
Some properties, such as gauge variation, you always want to minimize. For others, you want to avoid extremes. COF is a great example, where problems arise at either end of the scale. The following Characteristics/Action List gives just a few examples to consider for DFM applied to winding.
Thickness: Minimize intentional variation such as ink add-on; minimize unintentional variation such as gauge variation; maximize symmetry with any variations that are otherwise unavoidable.
Coefficient of web-web friction: Low friction risks telescoping; high friction risks blocking, out-of-round and vibration.
MD modulus: Extremely low and extremely high stiffness products may pose runnability issues.
MD strength: Avoid low strength to prevent runnability problems such as web breaks.
ZD resilience: Avoid low durability or else suffer from vibration and/or permanent bulk loss.
Dimensional instability of any kind: Even 1 part in 1,000 is truly frightening.
Roll size: Small cores, large finish diameters and tall aspect ratios can all be risky.
The major problem is seldom technical; usually, it's people. You have different people responsible for product design, manufacturing and winding. At best, they just don't understand each other. More often, they don't communicate well. Thus, it usually falls to management or the web handlers to explain the issues and how they relate to product and process design choices.
More often the problem is with attitudes such as complacency (let the winder guy work it out), fear (we've not done that before) or paralyzing fright (don't upset the customer). That, coupled with a remarkable lack of understanding of winding, always has the same results. Continuous problems in the winding department and with the customer related to wound-roll defects. Ever see anything like that?
920/312-8466, drroisum@aol.com, www.roisum.com
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