Release characteristics of polymer surface when moulding polyurethane foam

The polyurethane (PU) foam moulding process involves the use of sacrificial release agents (SRAs) that are both costly and harmful to the environment. This research proposes the use of low surface energy, polymer substrates, as a means of eliminating SRAs from the foam moulding process. Previous work identified the major factors affecting the ability of a polymer surface to release a PU foam part as being the surface energy and surface roughness of the substrate, and the proportion of isocyanate in the foam. The research described here has built upon these results and quantified the effects of each factor by using a D optimal design of experiment structure. Crucially it has also been shown that, given the surface energy of a polymer substrate, its roughness and the composition of the foam, it is possible to predict whether or not unaided release should be possible, and a model has been produced in order to allow this prediction for the foams under consideration. This capability will provide the PU foam moulding industry with the possibility of identifying polymeric mould materials, and levels of finishing for these moulds, which have the potential to allow the elimination of SRAs from the production process

Utilising Additive Manufacturing technology for the development of knife resistant soft body armour to UK performance requirements

Utilising Additive Manufacturing technology for the development of knife resistant soft body armour to UK performance requirement

Effect of bed temperature and infra-red lamp power on the mechanical properties of parts produced using high-speed sintering

High-speed sintering is a new, layer-based, manufacturing process, based on printing consecutive cross-sections with a radiation-absorbing material, and exposing to an infra-red lamp, in order to initiate sintering of polymer powder particles in the appropriate profile. Research was carried out to determine the effects of varying process parameters on the mechanical properties of parts produced using this process. Results showed that increasing the temperature of the part bed led to an increase in the mechanical properties of the parts produced, and that increasing the infra-red lamp power had the same effect, but to a lesser degree. It was also found that these increases in process parameters led to a corresponding increase in the hardness of the unsintered powder, which could lead to difficulties with post-process powder removal

Effect of infra-red power level on the sintering behaviour in the high speed sintering process

Purpose: To investigate the effects of the infra-red power level on sintering behaviour in the High Speed Sintering process. Design/methodology/approach: Single-layer parts were produced using the High Speed Sintering process, in order to determine the effect of the infra-red power level on the maximum achievable layer thickness, and the degree of sintering. The parts were examined using both optical microscopy and contact methods. Findings: Whilst it was expected that an increase in the infra-red lamp powder might allow an increase in the depth of sintering that could be achieved, as a result of increased thermal transfer through the powder, results in fact indicated that there is a maximum layer thickness that can be achieved, as a result of part shrinkage in the z direction. Optical microscopy images have shown that a greater degree of sintering occurs at higher power levels, which would be expected to correspond to an improvement in the mechanical properties of the parts produced. These images also indicate that the RAM forms in small ‘islands’ on the powder bed surface. However, these islands begin to merge as sintering progresses, to a greater degree as the infra-red lamp power is increased. Research limitations/implications: These results are based only on single layer parts. Further work will examine the sintering characteristics of multiple layer parts. Practical implications: Results have shown that, whilst it is not possible to increase the achievable layer thickness of the parts produced by modifying the infra-red lamp power, the degree of sintering can be improved greatly by increasing the power. Originality/value: High Speed Sintering is an entirely new process which is currently still under development; the results presented here will directly impact the direction of further development and research into this process

Surface modification of the laser sintering standard powder polyamide 12 by plasma treatments

Polyamide 12 (PA12) powder was exposed for up to 3 h to low pressure air plasma treatment (LP-PT) and several minutes by two different atmospheric pressure plasma jets (APPJ) i.e., kINPen (K-APPJ) and Hairline (H-APPJ). The chemical and physical changes resulting from LP-PT were observed by a combination of Scanning Electron Microscopy (SEM), Hot Stage Microscopy (HSM) and Fourier transform infrared spectroscopy (FTIR), which demonstrated significant changes between the plasma treated and untreated PA12 powders. PA12 exposed to LP-PT showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from the surface functionalization and materials removal during the plasma exposure. However, it showed poor melt behavior under heating conditions typical for Laser Sintering. In contrast, brief PJ treatments demonstrated similar changes in porosity, but crucially, retained the favorable melt characteristics of PA12 powder

Surface modification of the laser sintering standard powder polyamide 12 by plasma treatments

Polyamide 12 (PA12) powder was exposed for up to 3 h to low pressure air plasma treatment (LP-PT) and several minutes by two different atmospheric pressure plasma jets (APPJ) i.e., kINPen (K-APPJ) and Hairline (H-APPJ). The chemical and physical changes resulting from LP-PT were observed by a combination of Scanning Electron Microscopy (SEM), Hot Stage Microscopy (HSM) and Fourier transform infrared spectroscopy (FTIR), which demonstrated significant changes between the plasma treated and untreated PA12 powders. PA12 exposed to LP-PT showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from the surface functionalization and materials removal during the plasma exposure. However, it showed poor melt behavior under heating conditions typical for Laser Sintering. In contrast, brief PJ treatments demonstrated similar changes in porosity, but crucially, retained the favorable melt characteristics of PA12 powder

Investigation and modelling of release behaviour of polymer moulds for polyurethane foam moulding

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The Effect of Layer Thickness on Ejection Forces for Injection Moulded Parts Made Using DMLS Tools

Direct metal laser sintered (DMLS) parts have previously been shown to be suitable for some tooling applications, in particular for injection moulding of plastics. This work shows that recent developments in materials have increased the suitability of DMLS tools for injection moulding processes, in terms of the force required to eject a part from a tool. Tools were manufactured for testing from two bronze (DirectMetal 50 and DirectMetal 20) and two steel (DirectSteel 50 and DirectSteel 20) powders, and the forces required to eject ABS parts from these tools were recorded. It can be seen that the more recent powder developments, sintered in 20 µm layers, showed a dramatic improvement over the older powders, sintered in 50 µm layers.Mechanical Engineerin

Investigation and modelling of release behaviour of polymer moulds for polyurethane foam moulding

In recent years the use of polymers has become increasingly significant in almost all areas of industry. Polyurethanes in particular can be produced in an extremely large range of formulations, and with a wide range of properties. The research carried out here was based on polyurethane foams used within the automotive industry for seating and insulation. One of the biggest problems facing the manufacturers of polyurethane foam is that of releasing a part from its mould without causing damage to either the part or the mould itself. Traditional methods of manufacture involve the use of a steel or aluminium mould, coated with a sacrificial, normally wax-based, release agent in order to allow effective part removal. Various environmental and financial issues are associated with the use of these release agents, and this research, therefore, aimed to provide an alternative to their use. Many companies use moulds manufactured from polymeric materials for short run production, and occasionally it has been observed that in certain cases a PU foam part can be released without using a sacrificial release agent. However, the issue of predicting release of PU foam from a polymer mould is something of a 'black art', and in most cases a company will continue to use a sacrificial release agent in order to prevent any possibility of parts sticking in the mould. The author of this work has shown that the low surface energy of a polymer allows un-aided polyurethane foam release under certain conditions. It has also been shown that, contrary to a large school of thought, the roughness of the substrate had a large effect on the ability of a polymer surface to release. The foam composition was also significant. Crucially it has been shown that, given the input of the surface energy of a polymer substrate, its roughness and the composition of the foam, it is possible to predict whether or not un-aided release should be possible, and a model has been produced in order to allow this prediction for the foams under consideration. This model will provide a company with the ability to identify possible polymeric mould materials, and levels of finishing for these moulds, which have the potential to allow un-aided release of polyurethane parts

Effect of tool finishing on ejection forces for injection moulded parts made using direct metal laser sintered tools.

With the continuing development of Rapid Prototyping technologies, there has been a move into areas of Rapid Tooling. This takes advantage of the shorter lead times and lower costs associated with the production of tooling, particularly for injection moulding. This paper analyses the effectiveness of using direct metal laser sintering to produce injection-moulding tools, in terms of the force required to eject a part from a tool. Different levels of finishing were applied to test tools, and the results show that in some cases the forces required to eject parts from direct metal laser sintered tools were comparable with those from machined tools