Reduce the Footprint, Flatten and Feed

December 1, 2015

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Ducker Research predicts that use of advanced high-strength steels (AHSS) for automotive body and closure applications will nearly double by 2025. These higher yield- and tensile-strength steels allow automakers to maintain structural integrity while using a lighter-gauge material to reduce weight. However, processing AHSS grades continues to challenge stampers, including how to feed them into presses.

Listen to the Customer

Nahanni Steel Products’ new compact coil line (a Coe SpaceMaster Series 4) unwinds, straightens and feeds coil stock in yield strengths to 1000 MPa at speeds to 60-70 strokes/min, within 23 ft. of floor space. Key to the design is its unique approach to pilot release. Shown in the insert photo: Powered coil guides that feature a tapered roll design for effective coil guiding of higher-yield materials.

For the past few years, representatives from Coe Press Equipment have spent significant time meeting with customers to understand their needs and identify gaps in current product offerings, especially in terms of processing AHSS grades. Case in point: Nahanni Steel Products, Brampton, Ontario, Canada, a metal stamper with 12 press lines ranging from 60 to 800 tons. Nahanni, a Tier Two automotive supplier that has been expanding into other industries and product lines, has faced a set of unique challenges. In addition to processing thinner-gauge higher-strength materials, it also must stamp a diverse product mix, while facing a cost premium on floor space and increasing safety requirements. Says general manager Sebastijan Zupanec:

“The move to higher-yield, higher-tensile material requires higher loads, which were really beating up our feed lines as well as our tooling. We were required to run these materials on larger equipment than we normally would use, which reduced our efficiencies.”

With these higher-strength materials also comes safety concerns. Notes Coe sales representative Mike Foster:

“When you’re dealing with the high-strength material in coil form, it’s like a giant coiled spring. The stamper must contain the coil with devices that control the direction of material flow, so it will thread hands-free through the equipment into the feeder-straightener.”

Advanced Equipment for Advanced Materials

To overcome these issues, Nahanni began looking to invest in technology to help improve safety, processing times and quality, and reduce setup times, all while reducing the footprint required for manufacturing. In particular, Nahanni had been experiencing difficulty in obtaining the required material flatness prior to feeding the press. In addition to the common coil-set issues, it also consistently experienced crossbow issues—where the material is curved across the width of the coil.

After extensive discussions, Nahanni agreed, in 2013, to run some of its material on Coe equipment featuring the firm’s advanced HD-straightener head, at its Sterling Heights, MI, facility. “Crossbow correction has always been in the realm of leveler capability,” says Zupanec. “We viewed Coe’s ability to address coil set and crossbow on the same machine as a real accomplishment.”

To optimize slack-loop storage and maximize feed speed (the coil line can support press speed to 70 strokes/min.), the coil line employs lasers to track material location.

Nahanni next laid out its requirement wish list, which included a solution that could run a broad range of materials, material thicknesses (0.030 to 0.300 in.), and increased material strengths; optimize floor space; and enable simple and safe threading.

“At that point,” Foster adds, “we focused on overcoming the technical hurdles of condensing a line that would normally stretch 45 to 50 ft. long and to less than 25 ft.”

Building on a Good Foundation

Starting with the capabilities of the advanced HD-straightener head, the Coe engineering team continued to design the rest of the solution from the ground up, developing several new concepts. Engineers verified design feasibility with solid modeling, unique spreadsheet calculations and finite-element analysis, ensuring that the machine would have the right structures in the right places.

Ultimately, Nahanni Steel Products welcomed, in September 2015, a new coil line (Coe’s new SpaceMaster Series 4 compact coil line) that unwinds, straightens and feeds coil stock in yield strengths to 1000 MPa at speeds to 60-70 strokes/min, within 23 ft. of floor space. Key to the design is a unique approach to pilot release—the act of momentarily releasing the strip to allow it to be aligned by pilot pins in the die. This momentary release relieves built-up stress and binding of the strip through the feed and die, caused by feed-length variation, misalignment and coil camber.

Most servo-driven roll feeds and feeder-straighteners feature air- or hydraulic-operated pilot-release mechanisms. Here, Coe provided what reportedly is the industry’s first servo-driven pilot-release mechanism, able to achieve higher speeds than conventional mechanisms. As explained by Coe director of engineering Jim Ward, “A servo motor rotates an eccentric mechanism to drive the pilot-release mechanism. This design allows us to achieve 60 to 70 strokes/min. with full pilot release.”

The servo-driven feeder-straightener has 4-in.-dia. straightening rolls and 6.3-in.-dia. pinch rolls, selected for processing heavy-gauge and high-strength materials. The small straightener rollers provide a small radius around which to bend the material to accommodate AHSS, which needs to be bent more severely in order to exceed its high yield point.

Adds Ward, “The straightener-head design has close centers to effectively yield thinner yet stronger material, as well as increased force delivery so a wider range of materials can be processed and flattened.”

Another unique feature of the new line is a pivoting pull-off roll assembly. This allows tension to be maintained on the coil to prevent clock-springing, and it enables higher line speeds for the compact coil-line process. Additionally, the roll system is self-leveling to accommodate a wide range of material thicknesses.

Proof is in the Performance

Describing the benefits Nahanni has realized with its new coil line, Zupanec notes significantly reduced coil changeover time, improving efficiencies. Coil handling and safety also have been improved, he says, with reduced trial-and-error times to meet required specifications that had previously challenged the company. And, whereas press rate once exceeded feed-line capability, the new line promises to help improve throughput.

“We now can deliver products from high-strength materials,” concludes Zupanec, “that require a higher flatness tolerance, allowing us to obtain more of this type of automotive work with the hope that as we continue to evaluate this new product line, we’ll be able to expand and add additional metalforming technology.” MF

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See also: Coe Press Equipment Corporation