Page 24 - MetalForming January 2010

Tooling Technology
Peter Ulintz has worked in the sheetmetal-forming industry since 1978. His background includes tool and die making, tool and process engineering, engineering management and product devel- opment. Peter also operates the website ToolingbyDesign.com, a source for the transfer of modern metalforming and tool-and-die technology, and which promotes the use of “Performance-Based Die Engineering Strategies.”
Peter speaks at PMA seminars and roundtables focusing on tool and die design, die maintenance, deep drawing, stamping simula- tion, tooling for stamping high- strength steels and problem solv- ing in the press shop.
Peter Ulintz pete.ulintz@toolingbydesign.com www.toolingbydesign.com
Question: There seems to be some confusion, not to mention vigorous debate, within our company regard- ing coil-straightening equipment. I have two questions that I hope you can answer. First, is there any difference between a coil flattener and a coil straightener, or are they just two differ- ent ways of saying the same thing? My second question concerns levelers. A coworker claims levelers are basically straighteners with back-up rollers that provide additional support behind the straightening rolls. I know that levelers and straighteners are different but I can’t explain how they differ. Can you explain the difference to me?
A: Without a doubt, one of the most frustrating experiences we encounter in the metal-stamping industry is trying to find common terminology that is used consistently and understood broadly. Technical terms like flatten- ing, straightening and leveling are good examples. These terms can be used so loosely that they eventually become interchangeable. When this happens it is difficult to know if there is any real difference in their meanings. This cre- ates significant communication prob- lems for all of us.
Flattening, straightening and leveling are terms commonly used to describe various coil-straightening methods. Coil straightening is accomplished by bend- ing and unbending the incoming coil strip around several sets of rolls. The rolls alternately stretch and compress the upper and lower surfaces of the sheetmetal past its yield point until both surfaces have the same surface length. Technically speaking, this process is correcting surface-to-surface length differentials within the coil strip.
Surface-to-surface differentials include coil set and crossbow. Coil set occurs when the steel sheet is coiled. The inside surface of the sheet compresses during winding while the outside sur- face is placed in tension, causing it to stretch slightly. As a result, the inside of the sheet ends up shorter than the out- side but it is consistent across the width of the coil. Cross bow occurs when the bottom side of the material is shorter than the top side when measured across the width of the coil. This condition is usually induced during coil slitting. Fig.1 illustrates both conditions.
The number of rolls in a straighten- ing device correlates to the number of yielding strains (bends) it can produce.
TOOLING BY DESIGN
Flattening, Straightening and Leveling
PETER ULINTZ
22 METALFORMING / JANUARY 2010
www.metalformingmagazine.com
Fig. 1—Coil Set and Cross Bow