Sheet metal forming is a central process in the production of car body parts, housings and household appliances. The design and material selection of the forming tools plays a decisive role in the process stability of the respective forming process. It influences the possible cycle time and therefore productivity, tool life and workpiece quality. High-strength aluminum bronzes (Cu-Al alloys) are becoming established, particularly for dies and blank holders in deep drawing, as they have a number of advantageous properties compared to conventional tool steels. They are available not only as plates but also as rings, offering not only technical advantages but also material and processing time savings for the toolmaker.
Advantages of hard bronzes in sheet metal forming
Deep drawing enables the production of complex shapes from sheet metal in a single work step. Three-dimensional structures are created by cold forming using controlled forces. Aluminum, steel and stainless steel sheets are preferred due to their excellent deep-drawing properties. The construction and design of the tools are decisive for the success of the deep drawing process. A well-designed tool minimizes wear and extends service life, resulting in higher productivity and cost efficiency.
If cold welding (adhesive wear) occurs with the tool during sheet metal forming, scratches, cracks or surface defects occur in the workpiece. These faults are exacerbated by deposits on the tool or workpiece in the subsequent forming steps. Dies or hold-down devices made of aluminum bronze have a clear advantage here: their surface hardly tends to adhere to sheet material, whether steel, stainless steel or aluminum. The service life of hard bronzes is also significantly longer than that of uncoated tool steels due to their high mechanical strength. Even in comparison to coated steels (e.g. TiN, CrN), aluminum bronzes offer constant process stability without the risk of spalling of a coating.
In addition, the good thermal conductivity of the copper-based alloys (CuAl) leads to more efficient dissipation of the forming heat, which reduces temperature fluctuations in the contact zone. This increases dimensional accuracy and process reliability.
Material characteristics of high-strength aluminum bronzes
Aluminum bronzes are copper alloys with an aluminum content of between approx. 8 and 12 %. Other typical additives are iron, nickel or manganese, which specifically influence the mechanical properties. The high-strength aluminum bronzes, such as ALBROMET-A340, usually contain an even higher aluminum content of up to 14 %. This allows the very hard β-phase to form in the bronze during quenching from the melt.
The additional iron and manganese additives act as stabilizers and refine the structure. Fine, disperse precipitates form in the copper-aluminum matrix and cause classic precipitation hardening. The result is a very strong but still tough structure. Rockwell hardnesses of up to 40 HRC and tensile strengths of up to 750 MPa are achieved, which corresponds to classic heat-treatable steels. In contrast to steel, aluminum bronzes have no tendency to cold welding with low-alloy steels or aluminum sheets and have good corrosion resistance. In addition, the significantly higher thermal conductivity compared to tool steel leads to a more even temperature distribution in the tool.
Limits of use
Despite the many advantages, aluminum bronzes also have limitations. Aluminum bronze reaches its limits with very high pressing forces – high-strength tool steels or carbide are still required here. The material price of aluminum bronzes is higher than that of standard steels, but the longer service life of the tools clearly pays for itself. The mechanical processing (e.g. milling, turning) of hard bronzes requires some experience and must be carried out with carbide tools and an adapted cutting speed.
Forged hard bronze rings – additional benefits in pot production
In the production of saucepans from thin, high-strength stainless steel sheet (e.g. 0.6-0.8 mm), the material is formed from the blank into the pot shape in several drawing stages. This results in high sliding movements between the sheet and the tool – especially at the blank holder and the die. If these are made of aluminum bronze, the stainless steel does not adhere to the tool due to the very low adhesion and the pot wall becomes smooth. The forming process can run stably, scoring and scratches in the formed sheet metal are avoided and process reliability is increased. The service life of the tools can be doubled compared to tool steel and the reject rate of the workpiece is significantly reduced. This means that the investment in the higher-priced tool material pays for itself after just a few weeks of production.
Rings are often required for the construction of dies and blank holders for forming stainless steel sheets into pots, e.g. as inserts or complete blank holder rings. These rings can either be machined from solid material, such as plates, or obtained as forged blanks.
Albromet GmbH offers the high-strength aluminum bronzes, e.g. ALBROMET-A300 or -A340, as plates, plate blanks and as forged or rolled rings. These rings can also be produced in customized dimensions on request. This reduces material loss and machining time during subsequent turning to finished size. In addition, forging or ring rolling thickens the microstructure of hard bronzes and refines the grain structure. This leads to higher strength, toughness and wear resistance compared to cast semi-finished products. This in turn further increases the service life and process reliability in forming operations. In addition to the aforementioned economic advantage, there is also technical added value.
ALBROMET also has manufacturing expertise and produces all the necessary components from hard bronze, also according to customer drawings, from a quantity of 1 up to series production.
Further application examples can be found in the automotive industry. Hold-down devices and other tools made of aluminum bronze are used there to prevent aluminum or steel sheets from sticking to the forming tools. With hard bronze inserts in steel bodies at the most stressed points, costs can be reduced and the advantages can be used exactly where they are needed.
Conclusion
Aluminum bronzes offer an attractive alternative to classic tool steels in sheet metal forming, especially for applications with high friction and wear loads. Their combination of hardness, wear resistance, thermal conductivity and anti-adhesion properties make them predestined for dies and hold-down devices. Although the acquisition costs and machining effort are higher, the increased tool life, process reliability and workpiece quality justify their use in many cases.
Published online on 02.10.2025 in Blech, read more here.
