Evonik Resource Efficiency GmbH, Essen, Germany, has developed a polymer powder for applications in higher temperature range as part of its polyamide 6 series. 

Temperature-Resistant PA Powder for 3D Printing 

Polyamide

Additive Fertigung

Selektives Lasersintern von Kunststoff, Metall, Keramik

Thermal Properties Modified 

PA66 and PBT considerably expand the field of applications for laser sintering by showing better properties than classic PA11 and PA12 materials in most cases.

PA66 and PBT for Laser Sintering

Polybutylenterephthalat

Kunststoff Werkstoffe

Thermoplaste

Technische Kunststoffe

Verfahren für die additive Fertigung

Pulverbettverfahren

Kunststoff

Bauwesen

Baustoffe

From Injection Molding to  Additive Manufacturing

After the explosion of developments in polymer formulations over the last year, it is worth taking a closer look during Fakuma at details such as functional additives or application-specific modifications. Overall, lightweight design continues to spur development but defined surface characteristics are also in demand. The reported innovations do not just follow current consumer trends but also provide ideas for advanced product and process developments. 

Functional Modifications Characterize Developments in Additives and Compounds 

Hochleistungskunststoffe

Polypropylen

Compound

Verbundwerkstoffe / Werkstoffverbunde

Additive

Farbstoffe

Pigmente

Füllstoffe für Kunststoffe

Oberflächentechnik

Medizintechnik

Compoundeure

Distribuenten

Polymers Can Be Expected Everywhere 

3-D printing is increasingly being touted as the ultimate solution for the production world of the future. It remains to be seen whether that is justified – at any rate the bandwidth of applications and technical developments continues to grow steadily. That applies particularly to the possibilities of additive manufacturing with thermoplastics – recently also with endless-fiber-reinforcement. 

Additive Manufacturing with Thermoplastics 

Rapid Manufacturing

Faserverarbeitung

3-D Printing for Production 

With K 2016 in Düsseldorf, Germany, and formnext in Frankfurt/Main, Germany, professionals with an interest in additive manufacturing had two opportunities last year to gain a sense of the spirit of innovation in the industry. One issue was particularly prominent: the increase in production efficiency. This improves the economy of using the different 3D printing processes. 

A Diversity of Suppliers and Physical Cross-Linking Make Possible New Business Models and Application Scenarios for Additive Manufacturing  

Steuern, Regeln

Werkstoffe für additive Verfahren

Rapid Prototyping

Selektives Laserschmelzen von Kunststoff, Metall, Keramik

Spritzgießwerkzeuge

Industrieroboter

Qualitätssicherung

All Elements at a Glance 

At the beginning of May, Jürgen Becky took over the helm of BASF’s European plastics business. He is steering the ship in the direction of polyamides, 3D printing, and digitalization. In the interview, he explains why BASF is not just a material supplier, why business could not be going better, and why the company will not get everything it would have liked from Solvay. 

Interview with Jürgen Becky on Goals, Markets, and Trends for BASF Plastics 

Industrie 4.0

"Service Requires Trust" 

Much as when injection molding materials were being developed 30 years ago, the current trend in additive production is toward higher melting materials and materials with improved mechanical properties. The latter can be achieved, for example, by fiber embedding. In machine technology, the developments are increasingly aimed at adapting processing times, sensor systems, and quality monitoring to the demands of high-tech companies.  

Materials Manufacturers and Process Developers Face Growing Demands in 3D Printing  

Biokunststoffe

Kohlenstofffasern / -matten

Rapid Tooling

Pulver-Spritzgießen

Schleifen, Polieren

Additive Adolescence 

As part of a collaborative initiative, the Brightlands Chemelot Campus focuses on the development and implementation of advanced additive manufacturing technologies. Three current biomedical projects illustrate the multiple possibilities for start-up companies in this market. 

Medical Device Developments at the Brightlands Chemelot Campus 

Breeding Ground for Additive Manufacturing 

A new joint venture is getting a hybrid manufacturing cell ready for market. A screw-based plasticizing unit is mounted on a 6-axis robot. The novel processing approach facilitates additive manufacturing of structural parts from granular and fiber-reinforced standard compounds.   

High-Speed Additive Manufacturing of Fiber-Reinforced Structural Parts 

Flexible Fertigungssysteme

Layer-by-Layer from Granulate to Part 

Bavarian Minister of Science Bernd Sibler handing the notification of funding for the ¿FAB-Weld¿ research project to FAU Erlangen-Nürnberg, FIT and other partners  

¿FAB-Weld¿ Research Project to Investigate Welding Processes 

Kunststoffverarbeitung: Maschinen und Komponenten

Vibrationsschweißen

Technik Trend

kunststoffe-international.com

Connecting SLS Parts to Injection Molded Components 

To extend the range of polymer powders for selective laser sintering, Paderborn University in collaboration with the Maag Group has developed an extrusion line that can produce round particles with good flowability.

Research Project to Manufacture Powder for Selective Laser Sintering of Plastics

Compoundieren

Kunststoffverarbeitung: Verfahren

Kunststoff-Aufbereitung

Perfectly Round

On account of the many different components involved and high quality and design requirements, automotive interiors continue to be a challenge for plastics. Both materials and processes are becoming more diverse and sophisticated. At the present time, the focus is on lightweight components, metal replacement in design elements, and surface decoration.  

Current Trends and Developments in Automotive Interiors 

Display im Automobil

Polyurethan

Oberflächenveredelung

Increasingly Complex Innovations 

Scratches and marring limit the potential applications of thermoplastics, which is why many processors are searching for approaches to protecting surfaces from such damage. To address this issue, various thermoplastics have been combined with additives based on modified clay and then had their properties compared. 

Modified Clay-Based Additives Improve the Surface Properties of Polyamides, Acrylates and Polycarbonate 

Polyacrylate

Polycarbonat

Organoclay Imparts Scratch Resistance 

Visible components in vehicle engine rooms increasingly have to satisfy not just technical requirements, but design expectations, too. An engine cover thus has to have an attractive and distinctive surface. A series part by Volkswagen demonstrates that this is possible not only with polyamide, but with glass-fiber-reinforced polypropylene as well.  

Optimizing Properties and Costs in the Production of Designer Engine Covers 

Glasfasern / -matten

Eye-Catchers Under the Hood 

Digitalization, electromobility, energy and resource efficiency are making their mark on future vehicles. These trends were also reflected at this year¿s PIAE, the branch¿s get-together in Germany. Plastics are an important key to mastering ecological and economic challenges in the coming years. 

New Polymers, Efficient Processes, and Advanced Parts for the Automotive Industry 

Schaumstoffe und Vorprodukte

Plastics for the Mobility of Tomorrow  

Influence of Chemical Post-Treatment on Glass-Filled Polyamide 12 Samples

In many technical applications, laser-sintered components still have inadequate surface topology. New methods of cost-effective and geometry-independent surface finishing of the laser-sintered specimens are therefore needed. Chemical post-treatment of laser-sintered PA12 components imparts enhanced mechanical characteristics as well as a reduction in roughness to ~85 %.

In many technical applications, laser-sintered components still have inadequate surface topology. New methods of cost-effective and geometry-independent surface finishing of the laser-sintered specimens are therefore needed.

The growth in additive manufacturing (AM), and particularly laser sintering (LS) processes, has resulted in the development of new material systems. Polyamide 12 (PA12), which is widely used in LS, has the advantages of good suitability as well as relatively high mechanical strength and stiffness. However, in the specific areas of application in which the part is required to have high stability and endurance, its mechanical properties are not always competitive with those produced by conventional manufacturing processes. The addition of various fillers to the PA12 contributes to enhancing its material properties and opens up additional areas of application. In this study, PA12 filled with borosilicate glass beads was processed via laser sintering. One part of the manufactured samples was chemically post-treated, while the other was left untreated.

Growing Demand for Post-Treated Additive Manufacturing Components

Prominent applications of laser sintering can be found above all in the aviation and automotive industries [1]. LS is an additive manufacturing process, which enables the production of parts with modest mechanical characteristics [2]. These characteristics can be improved by reinforcing LS polymer materials with various fillers, which differ in their properties, shape, and size [3–7].

However, due to the layered structure, the process-related resolution, and powder adhesion, the LS components do not have a smooth surface. The development of methods for reducing surface roughness is, therefore, a necessary step toward widespread adoption of LS technology. In this study, chemical post-treatment was examined concerning its effect on sintered parts made of glass-filled PA12. As a filler, borosilicate glass (E-glass) was chosen for reinforcing the PA12. Compared to common lime glass (A-glass) it offers better elastic modulus along with better thermal resistance [8–11]. Regarding the filled LS materials, no chemical post-treatment has been performed so far. The aim of this study was therefore to investigate the influence of treatment with trifluoroacetic acid (TFA) on the mechanical and topological characteristics of the additively manufactured glass-filled PA12 specimens.

LS materials with various fillers have already been studied regarding their suitability for LS and effect on the characteristics of the manufactured parts. Some of the fillers that were investigated for their possible use in LS included carbon fibers, aluminum, various nanomaterials, and glass beads. All of them modified the tensile and flexural properties of the laser-sintered specimens. [10, 12, 13]

According to the state of the art, vibratory finishing offers an already investigated method for smoothing the surfaces of PA12 components and reduces the roughness to one third of its initial value using ceramic or plastic abrasives [14,15]. However, depending on the parts’ geometry, the grinding bodies may not be able to reach all of the surface, particularly in slits or small openings.

Promising approaches to high-quality finishing of AM plastic components are post-treatment methods using a liquid or vapor active medium [15–17]. Compared to other post-treatment options, a liquid or vapor medium offers the advantage of near-contour surface modification. It is essential to select the active medium using the solubility parameter [15,18]. Depending on the solubility of the chemicals used – this can be influenced by changing the concentration by heating – smoothing of the surface takes place [19]. Since the solubility parameters are not always given in the literature and are generally difficult to determine, the post-treatment times are usually selected independently of the acid [18]. Since these data are only available for a few acids, the immersion time was investigated as a parameter.

In earlier research, Wiedau et al. [20] treated laser-sintered PA12 samples with trifluoroacetic acid (TFA) and reduced the surface roughness Rz to ~10 µm. This active medium was considered a sound alternative for the finishing of components of any geometry, so that even fine structures were successfully post-treated without any damage. Furthermore, the dimensional accuracy of the post-treated laser-sintered PA12 specimens was retained.

In this study, two materials were investigated, unfilled and filled PA12. The unfilled PA12 (PA2201, EOS) was used as reference material. The filled PA12 was a mixture of PA2201 and 30 vol.  % of borosilicate beads (Spheriglass 3000E CP03, manufacturer: Potters Industries). Glass-filled PA12 was processed on an upgraded LS machine Sinterstation 2500 ATG (manufacturer: DTM) with an advanced heating and laser scanner system. Unfilled PA12 was sintered on a Vanguard HiQ HS (manufacturer: 3D Systems). For the mechanical tests, tensile specimens of type 1A (DIN EN ISO 3167 [21]) were sintered in the x-direction, with the parameters listed in Table 1. Hatch distance and layer thickness were kept constant at 0.2 and 0.1 mm, respectively. A laser scanning speed was set at 10.16 m/s for both materials.

In the chemical post-treatment, the component can either be directly immersed in the liquid acid or exposed to a vapor medium. During post-treatment with acid, dissolution of PA12 molecules together with equalization of the amorphous surface area of the semi-crystalline structure occurs [20,22,23].

In previous studies, PA12 samples were already chemically post-treated with various acids [20]. Immersion in a TFA bath for 120 s caused a reduction of the surface roughness Rz of laser-sintered PA12 samples of 87 % [24]. TFA dissolves PA12, so that the surface softens. To prevent softening of the PA12 surface, the acid on the sample’s surface should be neutralized immediately after the post-treatment.

Post-treatment with the vapor has the advantage that small quantities of the corrosive acid can be used [25]. That is why, in this study, the samples were post-treated by the acid vapor. TFA was chosen as a chemical medium due to its high volatility. The examined PA12 samples were post-treated in a special post-treatment station, the bottom of which was completely covered with TFA. The propeller integrated into the chamber contributed to the air circulation inside the station for effective vaporization of the acid. In a preliminary experiment, samples were exposed to the acid vapor for 5, 6, and 7 min. After the roughness measurement, the post-treatment time for the tensile samples was set at 6 min.

The roughness measurements were carried out with a SJ-400 roughness measuring instrument (manufacturer: Mitutoyo) in accordance with DIN EN 4288 with an accuracy of 0.001 mm. Subsequently, tensile tests were conducted under DIN EN ISO 527–1 [26] with a testing speed of 5 mm/min on a Z020 M tensile testing machine (manufacturer: Zwick).

Initially, the samples of unfilled PA12 were examined. For the untreated samples, the roughness Rz was ~83 µm. With increasing post-treatment time, the roughness of the samples decreased gradually, resulting in a roughness of ~18 µm after chemical post-treatment.

A graphic demonstrates the elastic modulus and tensile strength of PA12 specimens and their dependence on the post-treatment time (Fig. 1). The results were compared with those of the untreated PA12. Post-treatment times of 6 and 7 min led to a slight increase in elastic modulus in comparison to the post-treatment time of 5 min. However, all the post-treated values were still lower than the elastic modulus of the untreated PA12. Nevertheless, this reduction of the elastic modulus was insignificant. At the same time, the tensile strength remained almost constant. This showed that the post-treatment did not have any apparent negative influence on the tensile strength of the laser-sintered PA2201 specimens either. Post-treated samples performed a slight increase in values of elongation at break: From 20.1 % (untreated) to 19.7 % (5 min), 24.4 % (6 min), and 22.1 % (7 min).

In the next step the glass-filled PA12 was laser-sintered and examined before and after the post-treatment. Figure 2 shows the surface roughness of the top and bottom sides of untreated and post-treated samples at the different manufacturing settings (see Table 1). After exposure of the samples in TFA vapor for 6 min, the surface roughness of the samples was reduced almost twofold.

The process parameters showed a significant influence on the modulus of elasticity of the untreated glass-filled specimens. After the post-treatment with the TFA vapor, the glass-filled PA12 demonstrated the same tendency as in the case of the unfilled PA12: elastic modulus was reduced slightly due to the post-treatment, e. g., elastic modulus of the V1 samples was reduced from 3650 to 3320 N/mm². In contrast to the unfilled PA12, the glass-filled PA12 demonstrated the decline of the tensile strength after the post-treatment, e. g., the tensile strength of V1 samples reduced from 30.5 to 25.5 N/mm². The results are shown in a graphic (Fig. 3).

Examination of the elongation at break showed a slight decrease in the values with increasing energy density. After the post-treatment, all acquired values of the elongation at break were almost constant at ~1.43 % (Fig. 4).

Influence of Process Parameters and Chemical Post-Treatment

This study demonstrated the influence of TFA vapor on the mechanical and surface properties of the virgin and glass-filled PA12 specimens manufactured via LS. After the chemical post-treatment, the roughness Rz of the bottom surface was reduced to 17 % of the initial value for the unfilled PA12 and almost twice for the glass-filled one. The same trend was observed for the top surface.

Glass-filled PA12 demonstrated an enhancement of elastic modulus of 140 %. However, its elongation at break reduced significantly, which is known behavior among reinforced materials.

The exposure to the TFA vapor resulted in a slight reduction of elastic modulus of both unfilled and glass-filled PA12 samples by 5 and 8 %, respectively. No influence of the TFA post-treatment on the tensile strength of the unfilled PA12 was observed. However, the tensile strength of the glass-filled PA12 decreased from 30.8 to 28.6 MPa after the post-treatment. The influence of the TFA vapor on the elongation at break of both materials could not be accurately assessed due to the scattered results. Further investigation of the effect of post-treatment with TFA vapor on the properties of the LS parts is therefore required.

[1]  B. Sheppard, C. Shaw, B. Williams, J. Persaud, J. Bromberger, Factory of the Future: Advanced manufacturing technologies, including 3-D printing, will disrupt how we manufacture. Are you ready to implement them?; 2014

[2] M. Schmid, Selektives Lasersintern (SLS) mit Kunststoffen: Technologie, Prozesse und Werkstoffe. Carl Hanser Verlag, München; 2015

[3] EOS GmbH, <a href="https://www.eos.info">https://www.eos.info</a>. Accessed January 25, 2019

[4] 3D Systems, Inc., <a href="https://de.3dsystems.com">https://de.3dsystems.com</a>. Accessed January 25, 2019

[5] S. R. Athreya, K. Kalaitzidou, S. Das, Mechanical and microstructural properties of Nylon-12/carbon black composites: Selective laser sintering versus melt compounding and injection molding, Composites Science and Technology 71, 506–510 (2011)

[6] H. Zweifel, R. D. Maier, M. Schiller, Plastics Additives Handbook. Carl Hanser Verlag, Munich; 2009

[7] M. Xanthos, Functional Fillers for Plastics. WILEY-VCH Verlag, Weinheim; 2010

[8] PQ Corporation, <a href="https://www.pqcorp.com">https://www.pqcorp.com</a>. Accessed October 22, 2019

[9] A. A. Mousa, Experimental investigations of curling phenomenon in selective laser sintering process, Rapid Prototyping Journal 22, 405–415 (2016)

[10] K. Wudy, L. Lanzl, D. Drummer, Selective Laser Sintering of Filled Polymer Systems: Bulk Properties and Laser Beam Material Interaction, Physics Procedia 83, 991–1002 (2016)

[11] A. J. Cano, A. Salazar, J. Rodriguez, Effect of temperature on the fracture behavior of polyamide 12 and glass-filled polyamide 12 processed by selective laser sintering, Engineering Fracture Mechanics (2018)

[12] M. Karevan, S. Eshraghi, R. Gerhardt, S. Das, K. Kalaitzidou, Effect of processing method on the properties of multifunctional exfoliated graphite nanoplatelets/polyamide 12 composites, Carbon 64, 122–131 (2013)

[13] C. Yan, L. Hao, L. Xu, Y. Shi, Preparation, characterisation and processing of carbon fibre/polyamide-12 composites for selective laser sintering, Composites Science and Technology 71, 1834–1841 (2011)

[14] M. Schmid, G. N. Levy, Inspire AG, Finishing und Coating von SLS-Teilen für Additive Manufacturing (AM)

[15] T. Reinhardt, Entwicklung einer ganzheitlichen Verfahrenssystematik bei der Qualifizierung neuer Werkstoffe für das Laser-Sintern am Beispiel Polypropylen, <a href="http://duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/Derivate-41992/Reinhardt_Diss.pdf">http://duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/Derivate-41992/Reinhardt_Diss.pdf</a>. Accessed March 6, 2019

[16] O. Baier, Optimierung von FLM – Bauteilen durch chemische Nachbearbeitung sowie deren Einsatz in der Galvanik: Lehrstuhl Fertigungstechnik, Universität Duisburg-Essen, Dissertation (2016), <a href="https://duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/Derivate-40945/Baier_Oliver_Diss.pdf">https://duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/Derivate-40945/Baier_Oliver_Diss.pdf</a>. Accessed October 15, 2018

[17] Cunico M. W. M., Cunico, M. M., de Carvallo, J., ed., Study of Vapourised Solvent Attack on Additive Manufacturing Part Surface; 2015

[18] E. Bagda, Bestimmung der Lösungsgeschwindigkeit und Löslichkeitsparameter von Polymeren; 1977

[19] U. Zorll, E.-C. Schütze, Kunststoffe in der Oberflächentechnik. Kohlhammer, Stuttgart; 1986

[20] L. C. Wiedau, L. Meyer, A. Wegner, G. Witt, Chemisches Nachbehandeln von Laser-Sinter-Proben – Einflussuntersuchung von verschiedenen Säuren auf die Oberflächentopologie. In: M. Kynast, M. Eichmann, G. Witt (eds.). <a href="http://Rapid.Tech">Rapid.Tech</a> + FabCon 3.D, 267–282. München: Carl Hanser Verlag; 2018

[21] DIN Deutsches Institut für Normung e. V., Plastics – Multipurpose test specimens 83.080.01 (November 2014)

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[24] L. C. Wiedau, L. Meyer, A. Wegner, G. Witt, Einflussuntersuchung von verschiedenen Nachbehandlungsmethoden auf die Oberflächentopologie von laser-gesinterten Polyamid 12 Proben. In: M. Kynast, M. Eichmann, G. Witt (eds.). <a href="http://Rapid.Tech">Rapid.Tech</a> + FabCon 3.D, 228–243. München: Carl Hanser Verlag; 2019

[26] DIN Deutsches Institut für Normung e. V., Plastics – Determination of tensile properties – Part 1: General principles 83.080.01 (August 2018)

Universität Duisburg-Essen Inst. f. Produkt Engineering 

https://www.uni-due.de/kkm/

Ausgabenartikel

Table 1. Process parameters for tensile specimens made of glass-filled and unfilled PA12

Fig. 1. Elastic modulus and tensile strength of PA12

Fig. 2. Influence of post-treatment on glass-filled PA12

Fig. 3. Elastic modulus and tensile strength of glass-filled PA12

Fig. 4. Elongation at break of glass-filed PA12

Wiedau - Hauptartikel

Livia Carmen Wiedau is a research assistant at the Institute of Manufacturing Technology at the University Duisburg-Essen, Germany; <a href="mailto:livia.wiedau@uni-due.de">livia.wiedau@uni-due.de</a>

Anna Tarasova worked as a research assistant at the Institute of Manufacturing Technology, University Duisburg-Essen.

Prof. Dr.-Ing. Habil. Gerd Witt is Head of the Institute of Manufacturing Technology, University Duisburg-Essen.

This paper is the result of two projects: The iGF project (19623 N) with the title “Resource-saving Small Series Production by Polymer Laser Sintering – Influence of the Anisotropy and Surface Structure on the Long-term Dynamic and Mechanical Properties of Laser- sintered Parts” of the research association Institute of Energy and Environmental Technology e.V. (iUTA).

The iGF project (19646 N) with the title “Influence of the Material Composition and Surface Structure of Laser-Sintered Model Propellers on Predicting the Accuracy of Propulsion Experiments” of the research association Development Centre for Ship Technology and Transport Systems e. V. (DST).

Both were sponsored by the Federal Ministry of Economics and Energy via the AiF within the program for funding industrial joint research based on the resolution of the German Bundestag.