Edited by Elizabeth Engler-Modic
As automakers increasingly rely upon lightweighting and advanced structural materials as key technologies, the use of advanced high-strength steels (AHSS) with tensile strengths of more than 1,000MPa continues to grow. AHSS is forecast to be the fastest growing material in automotive applications and will represent 40% of vehicle content on body and closures by 2025.
However, the thermo-mechanical properties of AHSS that improve strength and ductility also come with formability challenges. Higher-yield-strength materials have a greater tendency to retain coil set. The American Iron & Steel Institute has published guidelines to help with stamping and forming AHSS, but the flatness required to feed advanced steels to the press has been largely ignored.
COE Press Equipment engineers understand the struggle that customers were having in uncoiling, straightening, and feeding AHSS. Equipment as new as five years old was not providing enough delivery force to the work rolls to back bend AHSS, nor the design and structural features required to effectively process the new materials.
Anticipating the increasing use of dual-phase steels, COE specialists began researching better ways to process high strength materials nearly a decade ago. The COE team met with customers to understand the challenges associated with running the new steels and how they were impacting traditional coil processing equipment.
Straightening materials with yield strengths of 1,000MPa or higher requires greater forces, impacting straightener design. Even if a straightener can apply the force needed, it may not provide sufficient roll support. Another issue is gear-train reliability as roll-force delivery required for feeding AHSS results in roll deflection, gear wear, and snapping journal ends.
COE’s HD Series heavy-duty straighteners tackle AHSS material processing, ofering a wider range of materials than conventional metal-stamping straighteners.
Conventional straighteners typically incorporate a series of 7 to 11 large-diameter work rolls; HD straighteners incorporate a series of relatively small diameter work rolls. Design enhancements include higher-strength materials, tighter straightener-roll spacing, and increased roll-depth penetration. Straightener heads have increased roll force delivery, stronger gears and bearings, and an improved straightener roller backup mechanism to improve rigidity.
By 2016, COE had installed multiple AHSS straighteners at customers throughout the country. To support those systems, COE engineers developed performance spreadsheets – a combination of engineering utilities and finite element analysis (FEA) – to ensure the equipment can handle the forces needed to bend and straighten higher-strength materials. These tools calculate the torque needed to drive the straightening rolls to deliver forces on the material. FEA data verifies that the machine design and gear train will withstand the forces generated.
Following the launch of the HD line, COE engineers started redesigning the company’s entire line of heavy-duty straighteners to adopt the improvements. The technology is being incorporated into machines such as COE’s SPACEMaster Series of compact coil lines, one piece of equipment that unwinds, straightens, and feeds coil stock in yield strengths up to 1,000MPa.
The transition began with the SPACEMaster Series 4, developed by working closely with Nahanni Steel Products in Brampton, Canada, a Tier 2 automotive supplier challenged by processing thinner gauge, high-tensile steel as well as a diverse product mix. Nahanni was facing challenges in obtaining the material flatness prior to feeding the press. In addition to the typical coil set (curves in steel resulting from being wound into a coil), a consistent crossbow issue led the material to curve across the width of the coil. Increasing use of advanced steels were taking a toll on Nahanni’s feed lines and tooling, and managers had been seeking technologies to overcome processing challenges.
Managers wanted better safety, throughput, quality, and setup times as well as a reduced footprint. COE ran the problematic materials on its HD series straightener at COE’s headquarters to show that its equipment could address coil set and crossbow issues from one piece of equipment.
The HD straightener head provides the foundation for the SPACEMaster series, including the Series 5, capable of handling 24"-to-72" rolls up to 0.40" thick. A pull-off roll allows tension to be maintained on the coil during the pull-off process with slack material provided at a constant speed.
Though developed for coil strengthening, COE’s team has applied the technology to other industries. This includes coil-processing lines for fineblanking, which normally require a leveler for the flatness and tight tolerances needed for near-net-shape blanked parts. Fineblanking has been in the market for more than 40 years, and a modern vehicle contains more than 200 fineblanked components, but it requires tight tolerances in external product dimensions and flatness.
COE presented its HD series to Concord, Canada-based, a maker of backing plates and brake shoes. Braking components have tight tolerances since deviations can interfere with caliper performance. UTIL officials wanted a straightener with good value, constant output, and, most importantly, flatness. A solution needed to stabilize production and eliminate stopping the line to adjust material.
COE’s fineblanking solutions can process coil at widths from 1" to 36", thickness up to 0.500", weights up to 40,000 lb, and yield strengths up to 1,000MPa while holding flatness tolerances of 0.003" total indicator reading (TIR) per square foot. Fineblanked parts are often made from thick, high-strength material that can be dangerous to handle manually, so lines feature coil reels with hydraulic hold downs and motorized endwheels. The mandrel and motorized endwheels rotate in unison for threading and rewinding. A pivoting alligator-style peeler-debender offers hands-free, modular threading.
UTIL presented COE with a list of materials – AISI 3040, 4040, and 5149 at 80mm thick – and the feed-and-speed parameters required from new equipment. Because its bid was higher than some competitors, COE officials introduced UTIL’s team to Nahanni’s engineers and showed them the SPACEMaster system in action. Although a significantly different configuration than the proposed UTIL fineblanking coil reel and straightener, the demonstration illustrated COE machines’ robust construction. Machines were installed at UTIL in early 2017, and the equipment has been used successfully for fineblanking since then.
COE Press Equipment