You may have experienced this dilemma: You’re forming an auto part using AHSS/UHSS, the steel has met all of your specifications, the part looks good to the human eye — but when measured with high precision tools you discover that 20% of your final formed parts are out of specification. How can your AHSS/UHSS supplier help?
Inconsistent AHSS/UHSS flatness is a major contributor to parts becoming out-of-tolerance for their specified shapes. Out-of-tolerance shape issues include profile straightness, end flare, positional control problems, and punched features and datum holes not aligning properly from the front to the back of the part. Can precision levelers help?
Precision levelers have been used to address flatness issues in AHSS coils, including coil set, crossbow, and so-called “heat pockets” problems. Precision levelers have their place in metalworking, but to quote a recent WorldAutoSteel article:
"Correcting edge waves and distortion requires exceeding the yield strength of the (AHSS) steel strip at levels of 50% or more of the cross section of the strip; this may increase the potential for workhardening the steel strip, negatively affecting the formability . . . . The progressively higher yield strength for AHSS steels are challenging the capabilities of straighteners and precision levelers that were not designed for flattening these high-strength materials."
The progressively higher yield strength for AHSS steels are challenging the capabilities of straighteners and precision levelers that were not designed for flattening these high-strength materials.
Precision levelers are also very large pieces of equipment that are difficult to place in front of blanking operations. However, the alternative of outsourcing the precision leveling has its own drawbacks: The part manufacturer cannot be sure that the mechanical properties of the AHSS/UHSS steel have been preserved (e.g., no workhardening) by the outsourced leveler.
SSAB is continually refining our mill processes so recipients of our Docol® AHSS/UHSS coils won’t need to use a precision lever. For example, for the problem of “heat pockets” — the less-than-flat conditions that can result from internal stresses during the quenching process — we’ve developed several proprietary steps at our mills to reduce those stresses.
SSAB also offers its own, very precise conversion of AHSS/UHSS coils into sheets or slit coils, done to our Docol specifications, so work hardening, and the resulting reduction to ductility, is minimized. Customers find this service particularly useful for our higher strength martensitic grades.