Additive Manufacturing: the way forward?

The excitement surrounding Additive Manufacturing (AM) has grown as confidence in the technology builds, resulting in the increasing commercial application of the technology for parts production.

Kingsbury Principal – Hermle AG – has spent the last ten years undertaking pioneering research into AM technologies, culminating in the introduction of its new MPA 40 hybrid additive-subtractive vertical machining centre which uses an innovative cold spraying manufacturing process that is unique in the market.

Unlike other metal deposition techniques such as the welding-type process used in most hybrid machine tool solutions, the method developed by Hermle involves the supersonic propulsion of metallic powder grains. Propelled by superheated water vapour, the powder grains (below 100 micron diameter) slam into the substrate at supersonic velocities, creating locally enough energy in a process akin to forging. The particles are deformed into flattened disc shapes, but do not melt, which produces superior material characteristics compared to the other so-called fused metal deposition processes.

The result is a much higher and faster rate of deposition achieving, for example, rates of 200 cm³/hr for steel and 900 cm³/hr for copper. Where conformal cooling channels cannot fit into the part, such as in tapered areas, the Hermle machine has another trick up its sleeve: it can lay down a layer of pure copper, whose superior thermal conductivity can help dissipate heat more effectively than tool steel. Up to six materials – including hot- and cold-work tool steels, stainless steels, pure iron, Invar, copper, bronze and titanium – can be combined, due to six parallel powder conveyors.

The manufacturer currently has 4 machines that are employed on a sub-contract basis supplying real parts against real applications whilst the processes are perfected. The platform is based on a modified 5-axis machine, enabling the MP40 to reach every part of a component. It features a 420 mm diameter rotary swivelling trunnion table (maximum part size: 550 mm diameter, 460 mm high, length up to 650 mm depending on the shape), an AM head mounted next to the vertical milling spindle, with its trunnion having a built-in heater to pre-heat mould parts in the same set-up to avoid thermal stress.

Case Study

The potential for ongoing innovation is impressive. One such example is a joint exercise undertaken with German carmaker VW to develop hot-forming moulding jaws in tool steel that have internal conformal channels. In its so-called direct heat forming process, manganese-boron steel sheet formed at 950°C is cooled with water to about 200°C in a few seconds, producing high strength components from thinner material to offer weight savings. The MPA process has enabled the hot-forming tool’s cooling channels to better match the exterior contour than is possible with drilled ducts. A complete tool with generatively manufactured moulding jaws has been developed and trialled.

Along with the capability to handle increasingly complex and ever larger parts to meet the changing needs of the aerospace and automotive sectors, AM is redefining the parameters of modern production technology and offers a way to substantially reduce waste, by building up layers rather than stripping off material from metal stock to create the three-dimensional form.

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