Page 26 - MetalForming July 2016

Straightening AHSS
However, in many cases, say Ward and Grant, just replacing the top half of the straightener suffices, to equip an existing coil-feed line to reliably feed AHSS. This includes a new head with the structural design and component content able to deliver the force needed for the application. Using the aforemen- tioned software utilities, the stamper can be assured that the retrofitted straight- ener will be able to sufficiently backbend the material and apply the required roll- depth penetration. And, there’s assurance that the machine will have the required rigidity and structural integrity.
For example, Ward describes use of such a utility to prove-out the capa- bilities of a straightener for flattening 1⁄4-in. 90-ksi-yield steel fed from 48-in.- wide coils. The software utility predict- ed for the customer that the application required roll force of 38,000 lb. (rated force of the machine was 60,000 lb.), pinch-roll gear torque of 31,400 in.-lb. (compared to a rated torque of 45,100 in.-lb.) and straightener-roll torque of
21,200 in.-lb. (compared to a rated torque of 31,500 in.-lb.)
Smaller Rolls, Tighter Spacing
Changing out components in the straightener often involves use of small- er-diameter straightening rolls than those typically specified for shaping mild steels, and use of tighter center distances to improve force transfer to the material. The gearing typically is upgraded to handle the increased forces and torque.
“In one recent retrofit project,” says Grant, “we upgraded a 1995-vintage straightener for feeding AHSS into a progressive die. The requirement was to feed 100,000-psi material from 60- in.-wide coil. Using our software tools and FEA, we were able to illustrate for the customer that the new support bridges designed for the straightener would provide sufficient structural sup- port for the new straightening rolls. We also proved out, using simulation software, the new gearing system designed for the application.”
“We often see the need to increase roll pressure by two or three times when upgrading from mild steel to AHSS,” adds Ward. “This requires upgrades to many straightener com- ponents, including the bearings, roll journal, roll supports and the machine structure, including the weldments. Still, we often can cost-effectively meet the needs of the stamper by retrofitting the straightener for one-third or less of the total cost to replace an entire feed line. And, in many cases the stam- per can pay for the retrofit from its maintenance budget rather than mak- ing a big-ticket purchase from its cap- ital-equipment budget.”
So, what should stampers look for, and ask for, when approaching equip- ment providers for help upgrading their operations to handle AHSS and other high-strength materials?
“Ask for the data,” says Grant. “Do your homework, and seek to understand the science behind the technology being proposed. Study the FEA analyses to
24 MetalForming/July 2016
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