Precision Meets Sustainability

Whether in vehicle and machine construction, the building industry or shipbuilding – wherever load-bearing structures and components with high strength and corrosion resistance are used, aluminum alloys are in demand as a material. They also play an important role in tool and mold making. For example, they are used to manufacture injection molds for both small and large-scale production of a wide variety of components, from lightweight structural components to the smallest components and miniaturized components for medical technology, electronics, and microsystems technology. Manufacturing injection molds from aluminum alloys for micro-production requires the highest level of precision to ultimately produce very complex or very small structures with micrometer accuracy.

In practice, high-precision milling processes using uncoated carbide tools are often employed for this purpose. The quality of the milling tools directly impacts the quality of the results. Even the slightest change in tool geometry can affect the machining process, resulting in suboptimal machining of the workpiece. Carbide consists of tungsten carbide as the hard phase and a cobalt binding phase. Due to the high temperatures involved in milling, however, this binding phase weakens during the process, causing the tools to wear out quickly.

This economic disadvantage is compounded by an ecological one. While tungsten carbide is readily available for industrial use, the European Commission classifies cobalt as a critical raw material. The metal is mined in only a few regions, often under difficult political, ecological, and social conditions. This results in dependencies on volatile supply chains, fluctuating prices, and potential export restrictions for the German industry.

This was reason enough for a research team at the IWF of the Technical University of Berlin to search for a technologically sound and sustainable material for producing micro injection molds. Their goal: to significantly increase the efficiency and cost-effectiveness of high-precision milling of aluminum alloys and to expand its application in industrial environments.

Novel material put to the test

The scientists opted for binderless cemented carbide (bWC) as the cutting tool material. Unlike conventional cemented carbides, bHM consists of 99 percent tungsten carbide and contains almost no cobalt. This eliminates the weakening intrinsic stresses of the cobalt binder phase, which arise at process temperatures above 450 degrees Celsius. This makes binderless cemented carbide 52 percent harder than conventional tungsten carbide-cobalt materials (WC-Co), making it significantly more resistant to abrasive wear caused by hard or sharp-edged particles and wear caused by changing stresses on the surface. On the other hand, reducing the cobalt binder phase to less than 0.2 percent makes binderless cemented carbide more brittle, meaning its fracture toughness is significantly lower than that of conventional tungsten carbide-cobalt materials. In other words, cracks can spread more easily in bWC, thereby reducing the material’s stability.

To qualify binderless carbide as an alternative cutting material, the researchers collaborated with Sommertools to develop a practical manufacturing concept for milling tools made of binderless carbide, as well as technologies for their economical use. To this end, cylindrical semi-finished products made of binderless carbide were brazed onto tool shanks made of conventional tungsten carbide-cobalt powder (WC-10Co) and further processed as composite blanks in multi-stage grinding processes to produce radius milling cutters for the finishing of complex surfaces.

The researchers evaluated the sharpness of the milling tools produced in this manner based on their cutting edge rounding. They found that, while the tools correspond to the level of conventional carbide tools, they are significantly more homogeneous. The average chipping of the cutting edge decreased by 60 percent, to less than 0.1 micrometers. Since cutting edge characteristics directly reflect the produced surface, this indicates that cutting edges made of binderless carbide enable significantly improved surface quality.

The research team then tested the performance of the binderless carbide cutting material by machining an AlMgSi1 aluminum alloy. They conducted 125 tests using five conventional milling strategies: high-speed cutting, high-performance cutting, micro milling, and high-feed cutting. On average, the binderless carbide tools achieved 34 percent lower surface roughness than the tungsten carbide-cobalt milling tools across all strategies, ranging from 15 percent in micro milling to 64 percent in conventional milling. Only in high-feed cutting were the two types of tools comparable.

Based on these test results, the scientists were able to determine suitable process parameters for machining the AlMgSi1 alloy with the tungsten carbide-cobalt cutting and binderless carbide cutting materials. These parameters, in turn, served as the basis for subsequent wear tests. The tests showed that binderless carbide had a 25 percent lower wear value than conventional milling tools when the process parameters identified for bWC were applied. Even under the conditions designed for tungsten carbide-cobalt, the wear value was approximately 20 percent lower than that of WC-Co milling tools. In both cases, the homogeneity and sharpness of the cutting edges made of binderless carbide could be maintained over a longer period of time, enabling more stable and precise machining of the AlMgSi1 alloy and increasing tool life compared to conventional WC-Co milling tools.

Technologically and ecologically best-in-class

»The results show that binderless carbide is much more than just an alternative material to those currently used for machining aluminum alloys,« says Niklas Maschke, research assistant at the IWF at the Technical University of Berlin. Binderless carbide combines the cutting edge sharpness necessary for micro and precision manufacturing with high stability. Maschke and his team demonstrated that their binderless carbide milling tools can produce injection molds with high-quality surfaces, reduced wear, and greater process reliability. The resulting improvement in the service life of the new tools also significantly reduces costs and resource consumption. Additionally, eliminating cobalt as a binder makes the tools more sustainable and reduces industrial dependencies for manufacturers and users. Thus, binderless carbide combines technological excellence with strategic relevance, opening up new perspectives for tool and mold makers in producing parts and components using injection molding.