PA12 Parts Research Articles

On the influence of inter-layer time and energy density on selected critical-to-quality properties of PA12 parts produced via laser sintering

Laser Sintering (LS) of polymers is an Additive Manufacturing technique progressively used to produce functional parts. However, LS parts still present a certain quality variability. Efficient consolidation of the polymeric powder, necessary to obtain a dense part, mainly depends on the viscosity of the molten polymer and on the time given for the polymer to coalesce. The polymer viscosity is a function of the temperature and, consequently, of the energy density (ED) input by the laser. The sintering time strongly depends on the surface area to be laser-scanned in each layer, which in turn is strongly related to the product complexity and the number of parts within one build. The aim of this work is to investigate how this thermo-temporal effect, influenced by the ED and the inter-layer time, influences the resulting LS PA12 part quality at both micro-level (e.g., porosity, crystallinity) and macro-level (e.g., dimensional accuracy, mechanical performance).

Correlation of Process Parameters with Mechanical Properties of Laser Sintered PA12 Parts

Selective laser sintering (SLS) is an additive manufacturing technique that enables the production of customized, complex products. SLS has proven itself a viable prototyping tool and production method for noncritical products. The industry has picked up on the potential of SLS, which raised the question whether it is possible to produce functional products with reproducible mechanical properties for application in critical sectors. Properties of SLS parts highly depend on the applied process settings. Hence, present work examined the influence of key process parameters (preheating temperature, laser power, scan spacing, scan speed, layer thickness, and part build orientation) on the properties (tensile strength, tensile modulus, elongation at break, and part density) of SLS produced parts. A design of experiments (DoE) approach was used to plan the experiments. Test samples according to DIN EN ISO 527-2 were produced on a sintering system (EOSINT P395) using polyamide 12 powder (EOS PA2200). Regression models that describe the relation between the process settings and resulting part properties were developed. Sensitivity analysis showed that mechanical properties of sintered parts were highly affected by layer thickness and scan spacing variations.

Fatigue behaviour of laser-sintered PA12 specimens under four-point rotating bending

Purpose – The purpose of this paper was twofold: first, to determine if rotating bending could be used as an effective way of determining the fatigue behaviour of laser-sintered nylon, and second, to examine whether the fatigue behaviour of laser-sintered PA12 showed any significant anisotropy. Design/methodology/approach – Specimens were measured to obtain dimensional accuracy, density and surface roughness levels. Then, uniaxial tensile and rotating-bending fatigue tests were performed. A purpose-built test-jig has been used to subject hourglass-shaped specimens to reversed bending at two frequencies: 50 and 30 Hz. Additionally, thermal and microstructural analyses were performed to understand the underlying mechanisms of failure. Findings – The experiments suggest PA12 specimens will fail in fatigue following the conventional fatigue mechanisms observed in previous research with ductile polymers. Although high-frequency loading caused a heat build-up in the specimen, temperatures stabilised between 20 and 30°C, suggesting that rotating-bending fatigue at frequencies of up to 50 Hz is a valid way of determining the fatigue behaviour of laser-sintered PA12 specimens. Stresses below 20 MPa led to fatigue lives above 1 million cycles. Some anisotropic behaviour was observed in the fatigue test results, with specimens made orientated with the Z axis showing the lowest fatigue lives on average, but an endurance limit of approximately 15 MPa seems to be common for all specimens regardless of their build orientation. Practical implications – The observed endurance limit of 15 MPa did not depend significantly on the orientation at which a part was built – meaning that it may be possible to guarantee a service life for a part which does not depend on part orientation within a build. Clearly, good-quality control will also be required to ensure performance, but this has important implications for the design of laser-sintered PA12 parts for realistic service conditions. Originality/value – To our knowledge, this is the first paper to present rotating-bending fatigue data for laser-sintered PA12 parts, and the first to identify an endurance limit which is independent of part orientation.

Studies on morphology and crystallization of polypropylene/polyamide 12 blends

Abstract Scanning electron microscopy (SEM) and an image analyser are used to study morphologies of the fractured surface, etched by hot phenol, of polypropylene/maleated polypropylene/polyamide 12 (PP/PP-MA/PA12)=65/10/25 blend and PP-MA/PA12=75/25 blend. The particle dimension and its distribution of PA12 dispersed phase in these blends are much lower and narrower than that of the PP/PA12 blends. Especially, most of the particles in the PP-MA/PA12 = 75/25 blend are smaller than 0.1 μm. The effect of the morphology of PP/PA12 blends on their crystallization behaviour is studied using differential scanning calorimetry and SEM. PA12 dispersed phase coarsens during annealing in the PP/PP-MA/PA12 = 65/10/25 blend. The mechanism of coarsening of the PA12 dispersed phase is a coalescence process. The intense mixing between the PP component and the PA12 component through reaction of PP-MA and PA12 leads to a change of dynamic mechanical behaviour of the components. A separation method is used to separate the polyolefin parts (precipitated from hot phenol), from PA12 parts (hot phenol filtrate). Of PP/PP-MA/PA12 = 65/10/25 blend, infra-red measurements and elementary analysis show that the precipitate has a lower PA12 content than the feed, whereas the filtrate has a higher PA12 content. From PP-MA/PA12 = 75/25 blend, PA12 contents in the precipitate and the filtrate are the same as in the feed. This implies that all PA12 has reacted with all PP-MA in the latter case while not in the former case. Using the method of interface exposure, interfacial reaction of PP-MA with PA12 is studied by X-ray photoelectron spectrometry (X.p.s.).