The Growing Demand for High-Strength Steel in the Automotive Industry

High-strength steel (HSS) is increasingly becoming a popular material choice in the automotive industry due to its superior tensile and yield strengths when compared to conventional mild steels. Initially, lighter-gauge HSS replaced heavier-gauge mild steel to reduce weight in various automotive parts, and this application remains the most common use for HSS. However, the emerging trend of utilizing thicker gauges of HSS has led to stamping fabricators reevaluating their press feeding and coil handling equipment, as well as press tonnage capacities and die designs, to ensure efficient forming of these more robust parts. The unique properties of HSS impact feeding, straightening, and coil handling equipment.

Adapting Coil Feeding Equipment for High-Strength Steel

As HSS is harder than conventional mild steel, various adjustments must be made to the coil feeding equipment to accommodate these materials.

Feeder Adjustments for HSS

Due to the increased hardness of HSS, it may be necessary to increase the space for the slack loop behind the feeder. This may require a review of the torque generated by the servo feeder and consideration of the following questions:

  1. Will more material be present in the loop?
  2. Will the loop be too tight, putting pressure on the feed rolls when they are closed?

If the answer to either or both questions is affirmative, it’s crucial to ensure there is adequate torque in the feeder to pull the heavier and tighter loop. The feed equipment manufacturer can provide the current torque output of the feeder and recommend appropriate adjustments.

Straightener Modifications for HSS

HSS demands more attention in the straightener than any other component of a press feeding system. Unlike conventional mild steels, HSS cannot be processed using the same straightener roll diameters and roll spacing for a given material’s width and thickness. The harder the material, the larger the rolls and wider the spacing required between the rolls.

A general guideline is that HSS necessitates straightener equipment capable of processing mild steel that is 50% thicker than the HSS. This ensures that the journals, or axles, of the straightener rolls are proportionally larger to prevent excessive stress from the added pressure needed to penetrate the harder material. Furthermore, deeper roll penetration is often required to remove coil set from HSS. Larger rolls, larger journals, and broader center distances protect the straightener from potential damage due to these additional stresses.

However, increasing roll size and center distance on straighteners to accommodate HSS also alters the range of materials that can be effectively straightened. To address this issue, conventional feed lines can have a smaller pull-through straightener installed behind the feeder in addition to the larger high-powered straightener designed for thicker HSS.

press feed line

Optimizing Coil Handling Equipment for High-Strength Steel

There are two primary designs of coil handling equipment: reels and cradles.

Reels for HSS

Reels offer greater versatility than cradles and are better suited for surface-critical materials as they engage the coil by expanding on its inner diameter. However, safety concerns arise when using reels for HSS. Heavy-duty hold-down and threading devices, especially for gauges thicker than 0.125 inches, are necessary. For material exceeding 0.250 inches in thickness, hydraulically actuated hold-down arms, peelers, and lead-edge debenders should be employed to ensure operator safety. Hands-free threading devices are also recommended for HSS. Space-saving designs using reels should include safety containment and threading devices.

Cradles for HSS

Cradles are simpler coil handling devices that use nest rolls to decoil material,either with pinch rolls or a powered straightener. The advantage of cradles lies in their ability to contain the coil’s clockspring, or unraveling, when the bands are cut within the cradle’s side plates. With very thick and hard materials, cradles also employ hold-down arms, peelers, and debenders to ensure smooth processing.

However, a drawback of using cradles is that they are often challenging to rewind when dealing with partially used coils due to the coil’s clockspringing during band cutting and threading. This limitation should be considered when choosing the most appropriate coil handling equipment for HSS applications.

Adapting to the High-Strength Steel Revolution

The increasing use of high-strength steel in the automotive industry necessitates adaptations and adjustments to press feeding, coil handling, and straightening equipment. By carefully considering the unique properties of HSS and implementing appropriate modifications to feeders, straighteners, and coil handling equipment, manufacturers can efficiently process and utilize these robust materials in automotive parts production.

Staying ahead of the curve and continuously optimizing equipment for HSS processing will prove advantageous for automotive manufacturers as the demand for stronger, lighter, and more durable materials continues to grow in the coming years. By embracing the high-strength steel revolution, manufacturers can ensure their place at the forefront of the automotive industry.

press feed line
press feed line