Tool development

The altered formability and strain‑hardening behavior of new sheet metal materials have a decisive impact on component quality, springback behavior, and dimensional accuracy, thereby placing increased demands on tool design. To achieve an acceptable tool life when forming and trimming sheet metal components made from advanced lightweight materials, the selection of suitable tool materials and the use of load‑optimized coatings are of particular importance.

In recent years, together with our industrial partners, we have conducted extensive investigations into the application of tool coatings for forming and cutting tools, taking into account the behavior of the entire tribological system. Load‑appropriate coating design requires a holistic consideration of the complete system, consisting of sheet material and coating, or lubricant and tool material. This includes the analysis of the actual load conditions acting on the tool surface, the alignment of tool surface finishing with the coating process, the consideration of altered coating behavior under thermally assisted forming conditions, and the adaptation of the coating system to the specific temperature field.

Provided that the tool material offers sufficient resistance to plastic deformation, crack initiation, fracture, and catastrophic failure during forming, abrasive and adhesive wear are the dominant factors limiting tool lifetime. To address these challenges – particularly in the forming of high‑strength sheet metal materials – effective wear protection measures are indispensable and represent a key focus of research at Fraunhofer IWU.

Due to the wide range of application conditions and the resulting, often highly complex requirement profiles, tools are specifically adapted to the respective process. Tailored solutions are developed in close cooperation with project partners and end users.

The application of hard coatings is an effective means of mitigating both abrasive and adhesive wear. Established solutions primarily include tool coatings deposited by CVD, PVD, and PACVD processes. In selected cases, wet‑chemical coatings such as hard chromium are still used.

In metal forming applications, titanium‑based hard coatings (TiN, TiCN, TiC, TiAlN) and chromium‑based coatings (CrN, CrC, CrAlN), including their modified variants, as well as amorphous carbon coatings (a‑C:H, a‑C:H:Me), are most widely applied. The highest load‑bearing capacity under predominantly abrasive wear conditions is still provided by titanium‑based coatings deposited via thermal CVD processes, such as TiC/TiN. Comparable hard coatings applied by PVD or PACVD often exhibit significantly lower wear resistance in practice, particularly under high localized loads.

The key advantage of PVD and PACVD processes lies in their substantially lower coating temperatures (below 500 °C), which eliminate the need for subsequent re‑hardening of the tools by multiple tempering steps.

To enhance the load‑bearing capacity of PVD and PACVD coatings, they are frequently combined with plasma nitriding treatments. Nitrogen diffusion into the tool steel results in a hardened surface layer that provides improved load support, avoids excessive hardness gradients, and significantly enhances both coating adhesion and mechanical support. For forming tools, the combined application of both processes in a single sequence (duplex process) has become well established.

Another surface treatment method with considerable potential is gas and plasma boriding, which can meet demanding requirements in terms of hardness, wear resistance, load‑bearing capacity, temperature stability, and – most importantly – adhesion behavior. In particular, the interaction of the tool surface with strongly adhesive aluminum can be significantly improved, especially with regard to contact with the AlSi coating on press‑hardening steels such as 22MnB5.

Conventional heat treatment processes for steel materials are carried out at elevated temperatures and typically involve hardening and tempering, depending on the alloy composition and the targeted property profile. In order to further extend tool lifetime –particularly for highly demanding forming and machining operations –the effects of cryogenic treatments have been intensively investigated in recent years within various research projects. Depending on the selected tool steel and the specific process design, exceptional improvements in material performance can be achieved. Significant enhancements have been demonstrated in hardness, impact toughness, retained austenite content, residual stress state, wear resistance, fatigue strength, and dimensional stability.

To fully exploit the material potential, Fraunhofer IWU has systematically studied the influence of innovative cyclic cryogenic treatments in the temperature range from −180 °C to +200 °C for a wide variety of tool materials. Particular emphasis has been placed on combinations with surface engineering treatments and different coating systems. The cryogenic treatment facilities available at Fraunhofer IWU Chemnitz cover this entire extreme temperature range and offer sufficient chamber volume to treat large tools or multiple tools and components simultaneously.

As a result of such cryogenic heat treatment of tool steels, tool lifetime can be significantly increased (by up to 100 percent) while additional performance benefits, such as improved corrosion resistance, can also be achieved.

The increasing demand for a wide variety of product variants – particularly in the automotive industry – leads to disproportionately high tooling costs, as the production volume per derivative decreases at the same time. In most cases, the components differ only in specific details. With a modular tool design, therefore, only the relevant segments need to be exchanged.

A tool base concept developed at Fraunhofer IWU enables very short changeover times between two or more geometries while maintaining a high level of component accuracy and reproducibility.

Monitoring the manufacturing process enables a significant reduction in scrap parts during tool try‑out, ramp‑up, and series production. Quality deviations are often caused by gradual changes in material properties within a coil or a production batch. By employing appropriate sensor systems, virtually all stages of the manufacturing process can be monitored. Evaluation algorithms detect significant deviations from the optimal process state and generate corrective values accordingly.

By using tool‑integrated actuators (e.g. piezoelectric elements), minor adjustments to process parameters can be applied automatically. This ensures consistent component quality throughout the entire production run.