Page 64 - MetalForming October 2009

Tooling Technology TOOLING BY DESIGN
PETER ULINTZ
the ability to deform. But oxides found on aluminum surfaces are quite differ- ent. Aluminum oxide is very hard, brit- tle and tightly adhering. The brittle oxide tends to break, allowing highly adhesive metal-to-metal contact.
Did you know the most commonly used grinding-wheel abrasives are alu- minum-oxide compounds? That’s right, the same oxide that forms on the surface of your aluminum sheetmetal.
Several studies have shown that the surface hardness of tools does not have a statistically significant affect on tool buildup when forming aluminum stampings without lubricants. Even with very hard surface coatings, the alu- minum-oxide film is still hard enough to cause die damage. In deep drawing, a very small surface scratch (damage) will result in galling after just a few hits.
When forming aluminum it is imperative to separate the sheetmetal from the die surface. Lubricants for- mulated specifically for aluminum stamping operations provide a tena- cious barrier between the die surface and the oxide film on the blank. With the proper stamping lubricant, the blank avoids intimate contact with the tool surface. Common practice should include lubricating both sides of the blank to reduce galling tendency.
Here’s an alternative option for you to consider: Polyethylene (PE) or polyvinylchloride (PVC) plastic films can be applied to the aluminum surface to aid drawing and protect the surface finish. These films provide excellent lubrication with friction coefficient val- ues below that of oil. PE suffices for most applications but PVC may be required for severe draws and multiple forming operations. Unfortunately, both can be difficult to remove.
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
Pressing Questions?
The next few issues of Tooling by Design will be presented in a ques- tion and answer format. This format allows the reader to actively participate in the column’s content. The intent is to more closely align the topics with the needs and interests of its readers.
In order for the Q&A format to work, I need your participation. I encourage readers having tool and die or metal- stamping-related questions, to e-mail me at: pete.ulintz@toolingbydesign.com. I will try to answer as many questions as possible in this column. If your question is not answered in this column, it will be answered by e-mail.
Here is a sampling of some ques- tions I have recently received:
Q: I recently read your column on forming aluminum stampings (May 2009). We manufacture commercial food service equipment. One of our products is an aluminum baking pan produced from 0.040-in.-thick 3003 material.Thepanis18x26in.x1in. deep and takes four operations to pro- duce the finished product: draw, trim, partial form and final form. A light lubricant (oil) is applied mechanically to the coil prior to the initial stamping. The residual oil must be cleaned prior to packing, which is done in a closed vapor-degreasing process. My question is, do you know of a “hard-coating” that could be applied to the forming dies to eliminate the lubricant? Our desire is to eliminate the cleaning process and the associated costs.
A: The short answer to your question is, no. Now the longer explanation.
In general, many steel parts can be produced using only the residual cor- rosion-inhibiting mill oil on the coil. The primary reason is that any ferrous oxide that develops on the surface has
62 METALFORMING / OCTOBER 2009
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