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Additive Manufacturing for Reactive Metals

May 21, 2012
Laser melting system produces Al, Ti parts; designed for rapid material changeover
Renishaw’s new system is installed in a fully welded vacuum chamber, for an ultra-low oxygen build atmosphere.

RENISHAW INC. offers a new laser melting additive-metal manufacturing process it reports will produce fully dense metal parts direct from 3D CAD data using a high-powered fiber laser. Parts are built in layers, in thicknesses ranging from 20 to 100 microns, using a range of fine metal powders that are fully melted in a tightly controlled atmosphere. The new machines represent a third-generation design with features that include variable powder delivery, ultra-low oxygen content in the build atmosphere, and a safe-change filter system that minimizes user contact with materials.

Two systems are available, the AM125 and the AM250. Both models feature vacuum technology and low-gas consumption, and both adopt "machine tool" engineering in design, operation, and serviceability, emphasizing ruggedness and ease of operation. The touch-screen operator interface includes menu options for machine preparation and clean down. Consumable costs are minimized through features such as the soft re-coater blade that can be rotated several times before replacement, use of low-cost filter elements, and low gas consumption. All these reportedly improve system reliability and reduce cost of ownership.

Renishaw additive-metal systems process a variety of materials, including 316L and 17-4PH SS, H13 tool steel, aluminum Al-Si-12, titanium CP, Ti-6Al-4V and 7Nb, cobalt-chrome (ASTM75), and Inconel 718 and 625. Both systems are designed for rapid material changeover: the AM125 uses a cassette-type materials delivery system; and the AM250 uses a removable hopper, which the developer said is particularly useful for materials development or when using a range of materials. To improve system productivity, a valve interlock on the AM250 allows addition of extra powder while the process is running. Safe processing of reactive materials (e.g., titanium or aluminum) is ensured with features like a gas knife that clears away reactive, sooty emissions, and a heated build plate.

The AM125 provides a part-build volume of 125×125×125 mm (X×Y×Z). The AM250 provides a build volume of 250×250×300 mm (X×Y×Z), with Z axis extendable to 360 mm. Both have build rates of 5 to 20 cm3/hour, according to the material, part density, and part geometry. The AM125 offers a choice of 100- or 200-W laser. The AM250 has a 200- or 400-W laser.

Both designs have a fully welded vacuum chamber, so they’re capable of low-pressure evacuation followed by a recharge with high-purity argon gas. The developer said gas consumption after the initial chamber flood is very low, so it’s possible to operate at oxygen concentrations below 50 ppm – which is critical for processing reactive materials — and contirbutes significantly to material integrity and mechanical performance.

Product designs are completed off-line and the build files are delivered to the machine via a secure network or direct connection. Product traceability has been improved by the addition of process data and event logging as standard, with various additional process control options on request.