The application of a photopolymer material for the manufacture of machine elements using rapid prototyping techniques

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Logistyka nauka Artur Andrearczyk1, 2 The Szewalski Institute of Fluid-Flow Machinery, Gdańsk University of Technology The application of a photopolymer material for the manufacture of machine

This technology has a wide spectrum of application which ranges from ornaments or housing for a device to functional limb prostheses [1].

1 Logistyka nauka Artur Andrearczyk1, 2 The Szewalski Institute of Fluid-Flow Machinery, Gdańsk University of Technology The application of a photopolymer material for the manufacture of machine elements using rapid prototyping techniques Introduction Currently, rapid prototyping technology itself develops at a fast pace. This technology has a wide spectrum of application which ranges from ornaments or housing for a device to functional limb prostheses [1]. Recent research are focused mainly on essential biomedical areas such as transplantation, bionic body parts or artificial organs. Typical applications in mechanics include manufacturing machine bodies and preparing prototypes which are then tested for proper operation. Depending on the materials applied and print quality, there are five prevailing technologies in rapid prototyping techniques. Fused deposition modeling (FDM) is a technology which is suitable for 3D prints that do not require high accuracy of printing (e.g. building concept models, functional prototypes or end-use parts). 3D printers that run on FDM technology build parts layer-by-layer (0.1 to 1 mm in thickness) from the bottom up by heating and extruding thermoplastic filament. ABS or PLA are the materials used in the process of product manufacture. FDM technology enables much faster printing compared to other technologies, which translates into a lower quality. However, this 3D printing technology allows you to produce parts that are good in thermal strength and outstanding in mechanical strength. Multi-Jet Printing (MJP) is a rapid prototyping process that can be used everywhere where there is a necessity of very high resolution. MJP technique has been successfully used for printing hard plastic parts with smooth surfaces and highly complex geometries. For the time being, this technology definitely stands out from other technologies in the market. This technology uses only one type of building material photopolymer in the form of resin. The 3D printers, based on the two above-mentioned technologies are being used increasingly on the premises of the IFFM PASci [2] (see Fig. 1). Fig.1. 3D printers based on MJP (on the left) and FDM (on the right) technologies, situated in the IFFM laboratory 1 1 Artur Andrearczyk, The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Gdańsk, Poland, aandrearczyk@imp.gda.pl 2 Artur Andrearczyk, Gdańsk University of Technology, Gdańsk, Poland 8628

2 Logistyka nauka The original predecessor of MJP, the stereolitography (SLA or SL; also known as resin printing) is a 3D printing technology that uses the same type of material. While it closely resembles MJP technology, it provides a much lower printing accuracy. The two remaining technologies are similar to each other, but they only vary in terms of laser application and materials used. Selective Laser Sintering (SLS) involves the use of a high power laser to fuse small particles of plastic, metal, ceramic, or glass powders into a mass that has a desired three-dimensional shape. Selective Laser Melting (SLM) follows a similar concept, but in this technique the material is fully melted rather than sintered. SLM is often used in the development of commercially usable prototypes, manufactured in metallic materials. Very common are metal powders of the metals such as titanium, stainless steel or cobalt-chromium alloy. The last two technologies offer printing accuracy about 3 times lower than the MJP technology, which is available in the Rapid Prototyping Laboratory, at the IFFM PASci. Applied technology and material properties The MJP technology has been selected for prototype manufacturing from the technologies described in the previous chapter, which is available on the spot and offers very high accuracy of printed elements. The minimal thickness of the layer of material is 16 µm. The printouts were carried out with ProJet 3500 Max, a 3D printing device which was placed in the Rapid Prototyping Laboratory in the institute's building. The manufacturing of prototypes using Multi-Jet Printing technology is characterised primarily by putting material layers through printhead nozzles distributed throughout the whole printing platform. During the additive manufacturing (AM) process, the printer uses two types of materials, each of them having a different function. The first one serves as a support material occurring in the form of hot wax, pre-heated in a cartridge. It is put in liquid form onto a printing platform to form some kind of supporting structure for target material. It allows for printouts of any geometry, while keeping with details of complicated shapes. A polymer resin, in its various varieties (varying in material properties), was employed as a building material. The process of depositing liquid photopolymer onto the supporting structure takes place using the same nozzles as in the case of material of the first kind. Once a layer has cooled and hardened (by means of UV lamps), the next layer can be built until the model is complete. This constitutes the first phase of the process to obtain a fully functional prototype. In the second stage the model should be subject to wax melting process (using oven) and then the remaining wax layers are removed by means of an ultrasonic bath. The properties of the material called VisiJet M3 Crystal (used as a building material) are presented in Table 1. The two photopolymers (both UV cured), marketed under trade names VisiJet M3 Crystal and ABS have closely resembling characteristics. Table.1. Basic properties of the material called VisiJet M3 Crystal Density(liquid) at 80 C Heat distortion temperature Tensile strength (at 20 C) 1.02 g/cm 3 56 C 42.4 MPa UV curing of a material substantially affects printing quality in comparison to curing in the presence of oxygen. There is no vaporisation of a building material, so the volume does not change which keeps the exact dimensions of a printed element. The process is based upon the photochemical reaction in which monomers and oligomers (integrated in photopolymers) are being mixed with photoinitiators under UV light, taking suitable and permanent form. However, this method should not be applied at elevated ambient temperature, as it generally leads to errors in the printing process. This problem will be described in a more detailed way in the following part of the article (see chapter An example of application of rapid prototyping technique). 8629

Logistyka nauka Fig.2. On the left: Screenshot from Autodesk Inventor program.

Design) programs. The model written to.stl file was subsequently sent to the 3D printer over a LAN (or over the internet). Then, the process for manufacturing the prototype can be launched.

Testing of the building material Static tensile strength testing has been performed for the previously selected building material in order to use it during the manufacturing process of functional

3 Logistyka nauka Fig.2. On the left: Screenshot from Autodesk Inventor program. On the right: Printed elements of a fully functional prototype (after removing the wax) According to the Figure 2, the design of prototype elements was prepared by means of CAD (Computer Aided Design) programs. The model written to.stl file was subsequently sent to the 3D printer over a LAN (or over the internet). Then, the process for manufacturing the prototype can be launched. The final version of the exemplary parts of a fluid-flow machine prototype was presented on the right-hand side of Figure 2. Testing of the building material Static tensile strength testing has been performed for the previously selected building material in order to use it during the manufacturing process of functional prototypes. It was decided to carry out these tests because the values concerning material properties, given in catalogue, provided no information on the printout direction of a model which affects mechanical strength of the prototype. It is important especially under the circumstances when working machine component has to withstand heavy stress. The model of the element intended for tensile strength testing was created in Autodesk Inventor program, which is illustrated on the left-hand side in Figure 3, while the right-hand side shows the sample printed on the basis of this model. The samples were designed according to PN EN ISO 527 1/1998 standards. Fig. 3. Model of the sample for tensile strength testing. On the left: schematic drawing in Autodesk Inventor program. On the right: printed sample They were printed in two configurations: their longitudinal plane was parallel (configuration no. 1) or perpendicular (configuration no. 2) to the surface of the printing platform. By using two printout config- 8630

4 Logistyka nauka urations, it was possible to examine the anisotropy of building material in two directions in which all subsequent layers are put during printing process. The selected results of the tensile tests were shown in Figures 4 and 5. Fig.4. Force strain curve, sample in configuration no. 1 [3] Fig.5. Force strain curve, sample in configuration no. 2 [3] The strain measurements were carried out with an extensometer. The initial sample length was 15 mm and its surface area was 40 mm 2. The tensile stress was calculated from the following equation: F [MPa] A (1) where σ is the stress, F is the force and A is the surface area. On the basis of the research results and the equation (1), the values of tensile stress has been estimated, and were around 47 MPa or 41 MPa for printout configuration no. 1 or no. 2, respectively. It can be concluded that the material printed in different directions has similar stress characteristics, and the results have been satisfactory. The building material (sold under the commercial name VisiJet M3 Crystal) manifests hardly noticeable anisotropic behaviour. The conducted analysis suggests that this material is suitable for manufacturing of functional 8631

An example of application of rapid prototyping technique In recent months, work has been performed at the IFFM PASci laboratory involving the use of rapid prototyping technologies for manufacturing

5 Logistyka nauka prototypes intended for use in difficult operating conditions. It is also capable of withstanding high loading and its good strength characteristics are close to those of ABS (a strong plastic for professional applications) [4]. An example of application of rapid prototyping technique In recent months, work has been performed at the IFFM PASci laboratory involving the use of rapid prototyping technologies for manufacturing machine components. Up to now, many functional models have been printed allowing for the verification of effective functioning of devices or durability of certain materials as well as preparation of reference models. During the course of preparation of the models, certain anomalies affecting the printouts were observed. In some models with thin edges or even in the thick-walled ones which were printed subsequently, various degrees of curvilinearity were present resulting from unsticking of the supporting structure from the working platform in the way presented in Figure 6. The problem affected only the rectangular shaped parts. Fig. 6. Photo of parts manufactured using rapid prototyping technology, with apparent defects. Given the presence of negative effects of shrinkage caused by UV-curing, it was decided that the two planes of the model were inclined at a slight angle in the software, which led to the reduction in number of defects, but it did not eliminate them entirely. The elements attached to the surface of a printing platform are exposed to elevated ambient temperature (especially operating in offices without air-conditioning) during a printout. Wax adhering closely to the printing platform can operate under thermal stress, which leads to unsticking the edges of a supporting structure (also being able to transfer heat to the building material. The supporting structure itself becomes elastic due to the effect of the heat. The solution to this problem would be temperature reduction inside the printing chamber by means of additional cold source or an appliance which will ensure sufficient circulation of air. The element acting as a powder shield (seen in the upper part of Figure 6) does not unstick, since the building material (dark color between the wax) takes too small surface in relation to the wax, so that material shrinkage affects its detaching from the platform. In addition, problems have been encountered while removing wax. After taking out the elements from the oven (after the heat treatment process) it turned out that the elements with thin edges underwent thermal deformations according to the direction of printout. Even though the temperature in the oven did not exceed the heat distortion temperature indicated in the catalogue thermal deformation phenomenon have occurred 8632

Logistyka nauka here. It turns out that the amount of time spent in the oven is an important factor, which was quite long in case of application of many supporting material layers.

The problem has been addressed by mechanically removing the bulk of wax, leaving only a thin layer adhering to model surface.

6 Logistyka nauka here. It turns out that the amount of time spent in the oven is an important factor, which was quite long in case of application of many supporting material layers. As a result, the material exhibited permanent distortion under the influence of temperature. The problem has been addressed by mechanically removing the bulk of wax, leaving only a thin layer adhering to model surface. This reduced the amount of time needed for melting down of wax, and in consequence prevented thermal distorsions. One example of the application of rapid prototyping techniques is the replacement of components manufactured with conventional methods by elements printed out using a high quality 3D printer. The technique of this type is described below along with an exemplary use of the newly printed functional model (a machine component). The geometrically optimised blade have been designed and printed on the basis of the original machine part in order to test its flow parameters. The blade was modeled with the use of 3D CAD software (Autodesk Inventor) and then printed in the laboratory. The printed blade together with the blade used as a reference model are presented in Figures 7 and 8. Fig. 7. The blade printed using rapid prototyping techniques (on the right) together with the blade used as a reference model (on the left) view from above. Fig. 8. The blade printed using rapid prototyping techniques (on the right) together with the blade used as a reference model (on the left) side view. As you can see by looking at the above figures, the blade manufactured by the means of MJP technology accurately represents the actual reference model. In this case, it was decided to change the geometry in such a way that additional pressure nozzles were placed across the entire width of selected surface (for research 8633

The newly printed blade can be mounted in the transonic wind tunnel as replacement (see Figure 9). It is one of many printouts carried out by means of 3D printing technology.

7 Logistyka nauka purposes). The printout can be considered satisfactory. The created computer model allows for fast geometry changes and gives the possibility to print out further variants of the blade. The newly printed blade can be mounted in the transonic wind tunnel as replacement (see Figure 9). It is one of many printouts carried out by means of 3D printing technology. Beside the manufacture of functional elements, rapid prototyping techniques also allows you to prepare casting moulds used to produce various elements according to future requirements. Fig. 9. The photo of a reference blade placed in the transonic wind tunnel. Summary and conclusions The article presents several 3D printing technologies currently available on the market. Employing the Multi-Jet Printing (MJP) technology available in the premises of the IFFM PASci, samples were printed for static tensile strength testing. Then, the tests were carried out for the selected material (with a trade name VisiJet M3 Crystal), used as a building material at a later stage of the work. The values of tensile strength were 47 MPa and 41 MPa for the printout configurations no. 1 and no. 2, respectively. The results were satisfactory, providing a sound basis for further research activities. The functional prototypes have been developed using rapid prototyping technology. It is intended that they will be used for research and it is possible that they may prove useful in certain industrial applications. The paper deals with the problems (e.g. thermal distorsions) occurring during a printout as well as in the process of melting down of wax. Technical problems which caused that some elements were printed with defects were almost completely eliminated. The polymer resin was the only material employed as a building material for printouts. In the very near future it is planned to perform experimental research on the building material of a different type (which has higher heat distortion temperature). Its strength properties and thermal behaviour will be examined. This new material is to be used in manufacturing of functional prototypes which will be components of rotating machinery. It is also planned to design and print a pattern of casting moulds allowing faster production of machine parts with predefined geometry. Abstract The paper discusses the application of polymer resin for 3D printing. The first section focuses on rapid prototyping technique and properties of the photopolymer, used as input material in the manufacture of ma- 8634

8 Logistyka nauka chine components. Second part of the article was devoted to exemplary 3-D-printed elements for incorporation in machines. The article also contains detailed description of problems encountered in implementation of the selected rapid prototyping technology and the ways to deal with them. Keywords: photopolymer, polymer resin, rapid prototyping WYKORZYSTANIE FOTOPOLIMERU DO BUDOWY MASZYN Z ZASTOSOWANIEM TECHNIK SZYBKIEGO PROTOTYPOWANIA Streszczenie W artykule omówiono zastosowanie żywicy polimerowej w wydruku przestrzennym. W pierwszej części przedstawiona została technologia szybkiego prototypowania oraz właściwości fotopolimeru wykorzystywanego do tworzenia elementów maszyn. Druga część artykułu została poświęcona przykładowym wydrukom i ich zastosowaniom w maszynach. Artykuł zawiera również opis problemów na jakie napotkano się w trakcie korzystania z wybranej technologii szybkiego prototypowania oraz ich eliminację. Słowa kluczowe: fotopolimer, szybkie prototypowanie, żywica polimerowa References [1] Wichniarek R., Górski F., Kuczko W.: Rapid prototyping in the design proces, Projektowanie i Konstrukcje Inżynierskie 6(81)/2014, [2] Andrearczyk A., Żywica G., Czoska B.: Development of the method of creating geometric models for 3D printing by means of a device used to manufacture functional prototypes. The description of preparatory activities and finishing processes. IFFM PASci, registered under number 141/2014, internal paper registered in the IFFM database, only in Polish. [3] Andrearczyk A., Żywica G.: Rapid prototyping techniques in mechanical engineering, Mechanik 07/2015, accepted for publication in Polish scientific journal. [4] Miazio Ł.: Tensile strength test of samples printed in FDM technology with different filling density, Mechanik 07/2015, accepted for publication in Polish scientific journal. 8635

Sharif University of Technology. Session # Rapid Prototyping

Advanced Manufacturing Laboratory Department of Industrial Engineering Sharif University of Technology Session # Rapid Prototyping Contents: Rapid prototyping and manufacturing RP primitives Application