Application-oriented implementation of cutting-edge steel materials

Time and flexibility are key factors in product development today. “Short product life cycles increase the pressure on all stages of the value chain, from steel production to steel strip production to manufacturing the final product,” explains Dr. Michael Hellmann from Waelzholz’s Materials Technology department. In light of this fact, there is an increasing demand for materials that offer customized performance, both in terms of the final application and the manufacturing processes within the individual stages of the value chain. This requires close collaboration between the engineering team and the material supplier at a very early stage of product development.

When selecting materials, the focus is often on the typical properties like spring force, resistance to wear, corrosion resistance, magnetizability, or a favorable strength-to-weight ratio. Dr. Hellmann explains why this approach often falls short in many projects: “The conventional properties are really just the tip of the iceberg. These are the factors that are immediately considered relevant. These core features often mask other requirements, however, some of which directly become more important during the development stage, but sometimes also indirectly after the start of mass production.” In order to precisely identify the aforementioned factors and customize the material accordingly, Waelzholz has developed a three-step procedure:

1. Development project
2. Processing behavior
3. Series testing

A development project often begins with the conventional properties that are presumed to be necessary for an application. The fact that these only cover a fraction of the materials that may be suitable is illustrated by the chart in Figure 1 showing elongation as a function of tensile strength. According to Dr. Hellmann: “The chart shows our range of materials for the properties of yield strength and tensile strength in the range 150 – 1,700 MPa (22 – 247 ksi) at an elongation of 10 – 60%. This results in a total of 280 different material variations available from Waelzholz.” The overlaps in the material properties are of particular importance to us in this context, however. They show that several material variations fall into identical yield strength and tensile strength ranges. This means that we need to look at further properties to differentiate between them. “We have tremendous potential here to perfectly cover the entire range of requirements by taking other factors into account when selecting materials,” says Dr. Hellmann. The earlier the material supplier is involved in the development process, the more flexibility and freedom the manufacturer will gain through this holistic approach.

Example spring steel: When manufacturing springs, the spring steel strip is often formed using complex, multi-stage punching/bending processes. According to Dr. Hellmann: “Due to the complicated tooling arrangements, manufacturers can’t use process technology that allows them to react to changes in material properties. This makes predictable processing behavior and guaranteed reproducibility that much more important.” In order to achieve this, Waelzholz tests different material and implementation concepts in a process that closely replicates the final production process. “For spring steel strip, a bending test that involves analyzing spring-back behavior has proven to be a good indicator (Figure 2). We conduct this material test on different production batches and examine random samples over the entire length of the core of a coil,” explains the materials engineer. In Figure 3, we see the spring-back behavior of two materials – both with very narrow scattering across the samples. This ensures predictable processing behavior with a high degree of reproducibility.

The third step focuses on assessing uniformity in serial production. According to Dr. Hellmann: “When integrated into mass production, we inspect the tolerance uniformity over the length and width of each coil. In this process, our highly sensitive measuring devices can even detect when a parameter tends to move in the direction of a tolerance limit, but is still well away from it. This gives us the ability to fine-tune the process at a very early stage.” In connection with numerous analyses of the mechanical properties as well as statistical tests over the entire coil length, this guarantees serial production quality and identifies potential areas of improvement early on. “Our comprehensive testing technology offers a considerable advantage, both during the development stage as well as in serial production. Our laboratories are capable of conducting all of the essential testing methods, from macroscopic examinations to microscopic testing using a scanning electron microscope.”

“In the past ten years, Waelzholz has almost tripled the percentage of custom-developed materials. And more than 85% of them were created working directly with our customers,” says Dr. Hellmann. Highly collaborative development partnerships lead to material solutions that perfectly meet all of the respective customer’s requirements, from the process to the application – creating real value in the process. According to Dr. Hellmann: “Our customers develop groundbreaking products and inspire us with their ideas. We use our materials expertise to help them bring these ideas to life. And thanks to having locations on four continents, our materials expertise is available worldwide exactly where our customers need it – locally.”