A 5-axis C 40 U machining centre is the host platform for the addition of an AM process, which it calls metal powder application. The hybrid machine, known as an MPA 40, has a thermal spray nozzle mounted alongside the vertical milling spindle and a heater built into the fourth/fifth axis rotary swivelling table.
A production cycle involves clamping an application-specific faceplate onto the rotary table, importing the CAD model of the component to be produced, and converting the 3D data into successive AM builds and milling cycles, which can be followed by water quenching and heat treatment, if necessary.
In the metal powder application process, a high-energy jet of super-heated steam propels metal powder suspended in nitrogen through a nozzle onto the workpiece at high temperatures (up to 1,000°C) and pressures (local pressures up to 10 GPa), forging the powder particles together and onto the component surface.
Powder grain size is between 25-75 micron and deposition rate for tool steel, for example, is 4 to 5 cm3/min. The process allows dissimilar metals to be layered, with either a sharp or a smooth transition between them. Up to six materials can be made available, stored in sealed drums within the machine. Each metal powder requires its own process parameters, which are stored in a knowledge database within the machine control. Materials currently available are 1.2344 and 1.2367 hot-working steels, 1.4404 stainless steel, copper, bronze, titanium and aluminium.
Components produced can be up to 550 mm in diameter, 460 mm deep and weigh up to 600 kg. Almost any internal geometry is possible, as there is an option to use a water-soluble filler material to create internal features, such as conformal cooling channels in plastic injection moulds, that would be impossible to machine conventionally. The filler is subsequently dissolved to leave the desired void.
For writing programs that alternate material deposition and cutting cycles, Hermle has developed MPA-Studio CAM software. Simulation of the sequence and quality assurance functions for checking the finished components are included.
