Dietmar Drummer

Suitability of PLA/TCP for fused deposition modeling

Purpose – Fused deposition modeling (FDM) is a layer by layer technology with the potential to create complex and individual parts from thermoplastic materials such as ABS. The use of Polylactic acid (PLA) and tricalcium phosphate (TCP) as resorbable composite is state of the art in tissue engineering and maxillofacial surgery. The purpose of this paper is to evaluate the processing conditions and the performance of parts (e.g. mechanical properties) manufactured with a FDM machine.Design/methodology/approach – In this paper, the general suitability of PLA for the processing with FDM is evaluated and material specific effects (e.g. crystallization and shrinkage) are shown. Therefore, the characterization of the semi‐crystalline biodegradable material by thermal, mechanical and microscopic analysis is carried out.Findings – Facts, which affect the functional properties of the samples, are analyzed. Among them, the processing temperature and sample size significantly affect the morphology of the final compo...

New aspects of process induced properties of microinjection moulded parts

Abstract The microinjection moulding process is subject to microspecific phenomena, such as rapid cooling or high shear rates, which greatly affect part properties. While the correlations between morphology, crystallinity and the mechanical properties are well known for parts of usual macroscopic dimensions, there is less information available for microparts. In this paper, these correlations are discussed, related to the dimensions of semicrystalline thermoplastic parts. Results indicate that, if submitted to rapid cooling, microparts exhibit a fine structure, with low crystallinity, low yield strength and low elastic modulus. Experimental investigations have shown the influence of process parameters to be negligible. More important are the materials rate and ability to crystallise, which allow for properties to be significantly enhanced. Another possibility to considerably improve the performance of microparts independent of the used polymer is processing with slow cooling in thermally conductive moulds.

Characterization of Polymer Materials and Powders for Selective Laser Melting

Concerning individualization, the requirements to products have increased. The trend towards individualized serial products faces manufacturing techniques with demands of increasing flexibility. Additive manufacturing techniques generate components directly out of a CAD data set while requiring no specific tool or form. Due to this additive manufacturing processes comply, in opposite to conventional techniques, with these increased demands on processing technology. With a variety of available additive manufacturing techniques, some of them have a high potential to generate series products with reproducible properties. Selective laser melting (SLM) of powder materials shows the highest potential for this application. If components made by SLM are desired to be applied in technical series products, their achievable properties play a major part. These properties are mainly determined by the processed materials. The range of present commercially available materials for SLM of polymer powders is limited. This paper shows interrelations of various material properties to create a basic understanding of sintering processes and additional qualifying new materials. Main properties of polymer materials, with regard to their consolidation are viscosity and surface energy. On the one hand the difference of the surface energy between powder and melt influences, the wetting behavior, and thus the penetration depth. On the other hand, a high surface tension is fundamental for good coalescence of bordering particles. To fulfill these requirements limits of the surface tension will be determined on the basis of a reference material. For these reason methods for determining surface tension of solids, powders and melts are analyzed, to carry out a possible process-related material characterization. Not only an insight into observed SLM phenomena is provided but also hints concerning suitable material selection.

Fundamental investigation of laser beam melting of polymers for additive manufacture

By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam–matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.

Derivation of heating rate dependent exposure strategies for the selective laser melting of thermoplastic polymers

The selective laser melting of polymer powder is for rapid prototyping applications an established technology, although a lack in basic process knowledge appears. Considering demands of series production the selective laser melting technique is faced with varies challenges concerning processable material systems, process strategies and part properties. Consequently basic research is necessary to shift from rapid prototyping to rapid manufacturing of small lot sized series. Based on basic research the high potential of selective laser melting for the production of complex parts without any tools can be opened up. For the derivation of part quality increasing process strategies knowledge about interactions between sub-processes of selective laser melting and resulting part properties is necessary. The selective laser melting consists of three major sub-processes: Geometry exposure, tempering and powder feeding. According to the interaction of sub-processes resulting temperature fields during the selective laser melting process determine the part properties by changing micro structural pore number and distribution. Beneath absolute temperatures also the time-dependency of the thermal fields influences the porosity of molten parts. Present process strategies tend to decrease building time by increasing scanning speed and laser power. Although the absolute energy input into the material is constant for increasing scanning speed and laser power in the same ratio, time dependent material effects are neglected. The heating rate is a combined parameter derived from absolute temperature and time. Within the paper the authors analyze the basic interactions between different heating rates and part properties (e.g. porosity, mechanical strengths). Therefore with different heating rates produced specimens are analyzed with imaging technologies as well as mechanical tests. Based on the done basic investigations new heating rate dependent process strategies can be established considering time dependent material behavior.

Modelling of the aging behavior of polyamide 12 powder during laser melting process

Concerning individualization, the requirements to products have increased. Additive manufacturing technologies, such as selective laser melting allow manufacturing of complex parts without tools and forms. Due to this additive manufacturing processes comply, in opposite to conventional techniques, with these increased demands on processing technology. Due to the high temperature during processing, a degradation of the used plastic powder occurs. The non-molten material in the building chamber, the so-called partcake, can be removed after building from the finished component and reused for another process. To realize reproducible part properties refreshing of partcake powder with 30 up to 50 % virgin powder is necessary. However, these refreshing strategies lead to varying component properties due to an undefined aging state. Previous investigations on oven aged powder for selective laser melting showed for short periods of storage near the melting point thermally induced post condensation is the predomina...

Influence of Mold Temperature on Mold Filling Behavior and Part Properties in Micro Injection Molding

Abstract A variety of polymer parts used in microsystems technology is manufactured by injection molding processes. Particularly the high cooling velocity negatively affects the process and the resulting part properties. The scope of this paper is to investigate the influence of the mold temperature during the injection phase on the melt flow and the mold filling as well as on the resulting part properties. The results indicate that an increasing mold temperature supports the filling behavior, although the injection pressure has more impact. An increasing mold temperature also influences the part properties. It was found that a higher mold temperature leads to a more homogeneous and spherulitic structure as well as to an increasing degree of crystallinity. As a consequence the mechanical part properties are affected, too.

Correlation of Processing, Inner Structure, and Part Properties of Injection Moulded Thin-Wall Parts on Example of Polyamide 66

In micro- and thin-wall injection moulding the process conditions affect the developed internal structures and thus the resulting part properties. This paper investigates exemplarily on polyamide 66 the interactions of different cooling conditions on the morphological and crystalline structures. The investigations reveal that a slow cooling rate of the melt results in a homogeneous morphology and a higher degree of crystallinity and also a favoured crystalline structure. Consequently, the dielectric behaviour and light transmitting part properties are affected.

The Influence of Moisture and Laminate Setup on the De-Consolidation Behavior of PA6/GF Thermoplastic Matrix Composites

Abstract Thermoplastic matrix composites enable production in short cycle times suitable for high volume production of lightweight design parts. While heating fully consolidated semi-finished products (“organo-sheets”) internal stresses from their production emerge, thus causing voids. Such de-consolidation must be undone or obviated for void-free parts. In this article the influence of moisture and the laminate setup on the de-consolidation behavior of twill-weave PA6/GF laminates is investigated. The results show that moisture leads to a higher void content during de-consolidation. The laminate setup in terms of fiber-volume content preponderances the influence of moisture on the de-consolidation.

Affecting the Ageing Behaviour of Injection-Moulded Microparts Using Variothermal Mould Tempering

The fast cooling of the melt in an injection moulding process for manufacturing polymer microparts can lead to a modified inner structure, resulting in minor mechanical properties. Furthermore, the ageing can be also dependent on the process-induced properties. The results indicate that especially physical ageing processes occur in parts with unpropitious inner properties. Chemical ageing processes seem to occur independently of the process conditions in microparts. Tensile tests indicate that a process-induced favoured morphology can reduce the ageing-based change of mechanical properties.