Page 26 - MetalForming February 2010

Tooling Technology TOOLING BY DESIGN
PETER ULINTZ
The combination of high forming pressures and surface friction results in significantly higher tool-wear rates than those used to form carbon steels. These higher wear rates increase tool maintenance, downtime and produc- tion costs. As a result, proper processing methods, tool coatings and lubricants must be chosen in order to improve overall tool performance.
Extreme-pressure (EP) additives in lubricants provide excellent anti-galling tendencies under extreme heat and pressure conditions. EP additives (see below) commonly used in metalform- ing lubricants are chlorine, sulfur, and phosphorus compounds. When chlori- nated hydrocarbons, for example, are added to stamping lubricants, the heat
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
Issues with Stainless Steel
Question: I’m looking for a bit of enlightenment regarding lubricants, tool steels and die surface coatings for stainless-steel applications. A couple of months back you wrote about lubri- cants having EP additives and wetting agents; could you elaborate? What base materials and surface coatings would you recommend for stamping stainless steels? Should we avoid D2 with stain- less due to the chromium content in both materials? We have recommended this on some of our tool builds but most tool shops would prefer to stay with D2 and many say they have not had adhesion issues with their other customers.
A: The Specialty Steel Industry of North America (SSINA), a trade asso- ciation representing virtually all of the producers of specialty steels in North America, claims that working with stainless steel is not difficult, it’s just dif- ferent. With that in mind, let’s first con- sider how stamping stainless steels dif- fers from plain carbon steels.
Ferritic and austenitic stainless steels work-harden at a faster rate than do carbon steels. As a result, higher pres- sures are required to form stainless steel as compared to plain carbon steel of the same thickness and temper.
The chromium in stainless steel reacts naturally with oxygen in the air to create a passive chromium-oxide (Cr2O3) film on the sheet surface. Pas- sive simply means the surface no longer reacts chemically to its surrounding environment. It is this passive film to which stainless steels owe their superi- or corrosion resistance. Even though this layer is very thin, it significantly increases the level of friction between the tool and the workpiece.
Operating-Temperature Ranges of
Extreme-Pressure (EP) Additives
°C 1000
950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100
50 0
24 METALFORMING / FEBRUARY 2010
www.metalformingmagazine.com
Soaps and Esters
Synthetic, Polymeric Esters
Chlorinated Paraffins
Organo-Phosphorous cpds
Sulfur cpds