Abstract
Additive manufacturing is traditionally used to manufacture either prototypes or very small-scale demonstrators. In recent years though, it is being increasingly used to make low volume parts for the aeronautical and defence industry. One concern with laser sintered parts is that their relatively porous nature, means that they may be more susceptible to ageing than injection moulded parts. Parts were aged for 6 months in at different temperatures (18°C, 40°C, 50°C, 60°C, 80°C and 100°C) and in a humidity chamber at 60°C and 80% relative humidity. Each month samples were removed for characterisation. The testing included tensile testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and gas pycnometry. During ageing the samples displayed visible discolouration and embrittlement over the 6-month test period. This embrittlement was not observed in those samples aged at room temperature or an elevated humidity. The observed yellowing in the samples aged above ambient temperature is likely a result of the build-up unsaturated degradation products. No significant differences as a result of ageing were observed via DSC, TGA, SEM or gas pycnometry.
Highlights
Additive manufacturing requires no tooling, complex shapes can be produced and costing is straightforward, based on the material and time required
Void levels of 2–10% depending upon the material choice and laser power have been previously reported for laser sintered PA12.3 in a comparison of laser sintered and injection moulded PA12, Van Hooreweder et al reported that the ultimate tensile strength and tensile modulus were broadly similar for both production methods.[3]
While there is noticeable variation in the data, which may be due to the degree of variability inherent in laser sintered parts; the stiffness of the samples stored at evaluated temperature and ambient humidity tends to increase during ageing
Summary
Additive manufacturing requires no tooling, complex shapes can be produced and costing is straightforward, based on the material and time required. 3D printing is much slower than alternative thermoplastic processing techniques and as such is poorly suited to high volume production. Even laser sintering which enables several parts to be produced simultaneously is still orders of magnitude slower than injection moulding. The use of additive manufacture in commercial production has increased in recent years, outside of the historical use in prototyping. In the defence and aerospace sectors, companies including Boeing are using additive manufacture to produce low volume parts for the F18 fighter jet and 787 aircraft.[1,2]. In the case of laser sintered components, incomplete bonding between particles, together with the presence of air pockets may reduce the mechanical properties as compared to solid extruded or moulded parts. It was reported that laser sintered PA12 parts
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