Page 34 - MetalForming November 2019

FABRICATION
Resistance Welding
A Fastening Option for Hot Stamping
BY LOUIS A. KREN, SENIOR EDITOR
As hot stamping gains a foothold in North America among automotive OEMs and their Tier suppliers, other technologies, such as capacitive discharge (CD) resistance weld- ing, can be applied to optimize the effectiveness of the process.
Employing advanced and ultra-high-strength steel (AHSS, UHSS), hot stamping has been revealed as the process that most efficiently produces—and many times the only process that pro- duces—complex, safety-critical components. Common hot stamped components include A and B pillars, and roof reinforce- ments, and as the technology becomes more ubiquitous, more part applications surface.
During the hot stamping process, steel blanks feed into tunnel or stacked furnaces for heating to a temperature (above 1500 F or so) that makes the blanks malleable. Blanks move into a press capable of controlling stroke rate and dwell time for forming, followed immediately by in-die quench- ing for 3 to 10 sec.—in-die water chan- nels often serve this purpose. The heat-
ing and quenching processes—the for- mer shifting the steel to a full austenitic phase followed by the latter for trans- formation to a full martensitic phase— create the hardened material while not overly stressing the tooling, thus the material can be formed more easily prior to reaching its final hardened state.
Attendees of MetalForming mag- azine’s Hot Stamping Experience and Tech Tour, held this past Sep- tember in Michigan, had an up- close look at capacitor discharge (CD) resistance welding, courtesy of this CD welding machine. The process promises quality welds of softer fasteners to harder hot stamped steels.
A major aspect of hot stamp- ing concerns joining, including the projection welding of fasten- ers, as these parts make their way into larger components and assemblies. Installing fasteners on hot stamped aluminum-sili- con (AlSi)-coated parts can be tricky business owing to a num- ber of factors, according to offi- cials from Weld Systems Integra- tors ( WSI), which provides
systems for CD resistance welding in hot stamping applications. Bob Kollins, senior application engineer with Tech- nical Sales & Solutions, which works with end-users to set up and operate stand-alone Amada Miyachi-powered CD welding units from WSI, along with Allen M. Agin, WSI Midwest regional sales manager, described and demon-
32 MetalForming/November 2019
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