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Guest Editorial

Fact check

By Bruce Grant

Data helps companies ensure equipment can handle advanced steelsFFJ 1017 guest lead

November 2017 - With the focus on lightweighting across industries, especially in automotive, the use of advanced high-strength steels (AHSS) with tensile strengths of 1,000-plus MPa has increased exponentially. Recent analyst forecasts predict that these steels will represent 40 percent of vehicle content on body and closures by 2025. Although proven as a reliable solution for reducing weight while retaining crashworthiness standards, the properties of AHSS present significant challenges in terms of formability. These higher-yield-strength grades have a greater tendency to retain coil set and tighter tolerances between yield and tensile strength.

Nearly a decade ago, Coe Press Equipment observed its customers struggling to flatten these materials adequately for effective press feeding. We realized most of the existing equipment was not providing enough force delivery to the work rolls to adequately back bend AHSS material nor did the equipment offer the design and structural features required to effectively process these materials.

Anticipating the increasing use of dual-phase steels, we began researching better ways to flatten and feed high-strength materials. We met with our customer base to gain a comprehensive understanding of how these new steels were affecting traditional coil processing equipment. We found that even if a straightener can apply the force needed, it may not provide sufficient roll support. Another issue was gear train reliability. The roll-force delivery required for feeding AHSS results in roll deflection, causing gear wear and snapping journal ends.   

Crucially, what we discovered is that our customers were being led to buy new equipment that promised to handle these high-tensile materials. Yet, the equipment often could not manage the increased force needed to straighten these advanced materials—some components failed within a year of installation.

Coe invested in making significant design modifications to its heavy-duty straightener head, launching a new product line in 2014 specifically focused on AHSS materials.  Conventional straighteners typically incorporate a series of seven to 11 large-diameter work rolls. Our design, however, borrowed from precision straightener technology by incorporating a series of relatively small-diameter work rolls. Other design enhancements included higher-strength construction materials, tighter straightener roll spacing and increased roll depth penetration. These new straightener heads also offer increased roll force delivery, stronger gears and bearings, and an improved straightener roller backup mechanism to provide the rigidity needed to effectively process AHSS materials.

The field application success of these heavy-duty (HD) series straighteners has led us to redesign our entire line of straighteners using these same enhancements.

A critical part of the success was due to the development of our performance spreadsheets. These spreadsheets represent a combination of engineering utilities and finite element analysis (FEA), which ensure the equipment can handle the forces needed to bend and straighten the higher-strength materials as they feed from coil through the feed line to the press. These tools also calculate the torque required to drive the straightening rolls in order to deliver the required forces on the material.

So, before any equipment is finalized, its performance has been proven to the customer. This is what Coe refers to as “the science behind the solution.” Before we build any equipment, we prove to the customer it is capable of running the specified materials.  And, we encourage any company to ask for this kind of factual support.

So, to effectively straighten AHSS, involve your equipment supplier early in the process. Ensure that your vendor can demonstrate the following:

• Engineering prowess behind straightening continuous coil steel,

• Experience with designing machines capable of generating the forces necessary to process AHSS as well as the robustness to withstand the forces over the long term,

• Application tools that can predict suitability of a machine design for a particular application, and

• A proposed machine that is suitable for your processing needs.

In Coe’s case, its HD straightener design has opened new pathways of opportunity for our customers. Basically, it’s a precision straightener with the ability to process a wide range of material, removing both coil set and crossbow from coiled materials. But additionally, it can achieve flatness typically only accomplished with a corrective, and more expensive, leveler. This level of flatness is appropriate for high-precision applications, potentially saving money for customers while enabling them to handle tight-tolerance orders. But, the bottom line is, equipment buyers should require any press equipment builder to prove its claims backed by facts. FFJ

Bruce Grant, R&D manager, has led Coe Press Equipment’s new product development efforts including the redesign of heavy-duty straighteners. He authored the Coil Feeding Equipment chapter of the Handbook of Metalforming Processes, which provides hands-on experience of materials, equipment, tooling and processes used in the industry. 

More in this category: « Horizon unclear

Sources

  • Coe Press Equipment
    Sterling Heights, Michigan
    phone: 586/330-0011
    www.cpec.com

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