Page 34 - MetalForming May 2015

Automotive Steels
of AHSS (the area under true stress-strain curve) also increase part temperature. Mill oils will not provide the required lubricity for most applications; therefore stampers need to employ pre-lubes, die-process lubricants or dry-film lubricants.
A properly performing stamping lubricant must protect the tooling, tool coating and part from the abrasive effects of friction. The lubricant also should assist the flow of materi- al to prevent wrinkles, necks and fractures. In simple oper- ations, the lubricant requires little more than a boundary film and slip agents. More difficult operations require the use of extreme-pressure (EP) additives.
The boundary protection provided by die-process lubri- cants must remain intact throughout the forming process. If friction degrades the boundary film, the associated heat must activate the EP additives intended to provide additional protection. Ideally, the lubricant will delay the need for this EP protection by dissipating the die and deformation heat, protecting the boundary film and fluid viscosity.
The two most viable lubricant technologies for high- strength steel applications consist of some petroleum-based and some water-based synthetic lubricants. The most eco- nomically significant EP additives are oil-soluble and are only feasibly blended into oil-based formulas. However, the petro- leum content of the lubricant retains heat and therefore provides poor cooling and heat transfer. This problem is magnified as increased friction develops as the blank mate-
rial workhardens during forming.
Oils present post-processing problems such as cleaning,
painting and welding. Housekeeping and environmental impact also are concerns.
Several lubricant manufacturers have developed water- based synthetics specifically for AHSS applications. These advanced synthetics comprise polymers, boundary films, thermal-resistant additives and special wetting agents. Recent- ly, some proprietary additives have been developed to increase film tenacity, giving these lubricants “multiphase” charac- teristics. As frictional heat is generated during forming, the fluid forms a residual film that coats the part and the tooling. This tenacious film provides new boundary protection for later forming processes and protects punches during withdrawal.
Synthetic lubricants provide significant advantages for post-process operations, housekeeping, plant safety and environmental compliance. Often, cleaning operations can be eliminated between stamping operations and welding.
Press Equipment
The increased forces needed to form, pierce and trim higher-strength steels create significant challenges for press- room equipment and tooling. Excessive tooling defections, damaging tipping moments, amplified vibrations and snapthrough forces can shock and break dies, and sometimes presses. Stamping higher-strength steels can affect the size,
Power / Speed / Value Since 1937
J21 One Point
JIER C Frame Stamping Presses
J23 Inclinable
JIER North America, www.jier-na.com, Plymouth, MI USA, 734-404-6751 JIER Machine-Tool Group, www.jiermt.com, Jinan, China, 86-531-81616654
J25 Two Point
J35 Front Support
32 MetalForming/May 2015
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