Computer Solutions
Design freedom from a bottom up approach
Robin Weston looks at the benefits designers can achieve with additive manufacturing.
A
dditive manufacturing is empowering designers with a whole new approach - particularly to the design of parts where complex voids and internal features have historically led to restrictions in materials or
method of manufacture, long lead times and heavy overheads. The challenge of designing ‘what’s not there’ – often the starting point for many projects - can now be addressed by designing for a process which creates hidden features and complex internal geometries as a by-product of its bottom up build style.
The original additive manufacturing (AM) processes were developed using CO2
lasers for the production of pseudo
plastic parts using photo cure resins or sintered polymers. AM in metal became a possibility as ytterbium infrared fibre lasers were developed with the ability to melt metal. Selective Laser Melting or SLM, the metal AM process being developed by MTT Technologies, builds parts from a range of fine metal powders that are fully melted by a laser in a tightly controlled atmosphere. It uses an industry standard 3D CAD file in .stl format, from which the system’s software creates a file that can be read by the machine in 2D layers. Once the file is loaded, the dense metal part is built layer by layer in thicknesses from 20–100 microns.
Medical sector
SLM is already widely used commercially in the dental industry for the creation of patient specific crowns and bridging units. In the medical sector it has been used to build bespoke as well as non-patient specific medical implants, but the most exciting research is leading towards the creation of implants which incorporate a surface which encourages osseointegration. Currently these surfaces have to be post applied, but SLM has the imminent potential to produce implants with an integral surface into which bone will grow. For the aerospace sector, 360mm rocket propulsion test
parts are being produced as part of a development project, between MTT and a major US aerospace manufacturer, using an extended SLM250 machine. At the University of Liverpool the worlds largest SLM machine, the SLM500 with a 500mm (x,y,z) part building envelope is being developed to overcome the perceived productivity issues with the technology. The process is also being used to trial the production of other lightweight aircraft parts. While certification of the process for use in the industry is progressing, manufacturers are striving to speed up the process in order to address economic issues. MTT for example is working on the commercialization of higher power lasers in order to increase productivity rates.
Waste handling
The SLM process uses a range of gas atomised metallic powders. The first to be qualified were Stainless Steel (316L and 17-4 PH) and Cobalt Chrome. MTT then met additional challenges in the development of special powder and waste handling systems to enable the safe processing of reactive materials such as Titanium and Aluminium. Materials nearing the end of process qualification include Nickel alloys such as Inconel and Hastalloy X and Tool Steel (H13). MTT uses a unique method to ensure the quality of its
Fig. 1. Heat exchanger produced using SLM technology by The Welding Institute (TWI) for Rolls Royce.
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SLM build atmosphere - a crucial factor in any metals AM process if part quality and mechanical performance is to be
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