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Rapid Prototyping Material Degradation: a Study of Mechanical Properties
6th IFAC Conference on Management and Control of Production and Logistics The International Federation of Automatic Control September 11-13, 2013. Fortaleza, Brazil
Rapid Prototyping Material Degradation: a Study of Mechanical Properties Carlos A. Costa*, Paulo Roberto Linzmaier*, Felipe M. Pasquali**
*Research Group on Engineering Design and manufacturing, University of Caxias do Sul, Caxias do Sul-RS, Brazil (Tel: +55 5432182160; e-mail: [email protected]; [email protected]). **Undergraduation student in Mechanical Engineering, University of Caxias do Sul, Caxias do Sul-RS, Brazil (e-mail : [email protected]) Abstract: This work presents a study on rapid prototyping material degradation through the time. The material degradation used was Veroblue840 resin from Objet and was analyzed by its mechanical properties. Two types of tests were realized: tensile strength test (standard tests ASTM) and an experimental cantilever beam. The specimens were tested with 0, 30, 60, 90 and 120 days aging. Mechanical properties such as tensile strength, Young’s modulus, strain at Yield Point and deformation (microstrains) were analyzed. Results show the aging degradation process was not linear through the time, being more accentuated at the first 30 days. Keywords: rapid prototyping, mechanical properties, resins, degradation.
virtual prototyping (VP) is that due to the inconsistency of the materials behaviour, mainly polymeric materials, is related to the difficulty in the capture of material properties and consequently its simulation.
1. INTRODUCTION Rapid prototyping technology (RP) became an important tool to support and assist product development process (PDP) providing shorter product life cycle and time-to-market, better product quality and reliability, and elimination of wastes (Onuh and Yusuf, 1999). It combines technological and organizational tasks in a single structure, from product design to manufacturing (Grimm, 2004). This kind of technology enables the manufacturing of parts directly from a 3D CAD model without any kind of tooling, with different types of materials, and it has been used by different industrial sectors, e.g. automotive, aerospace, electronic, etc. Campbel et al. (2012) discuss rapid prototyping, or more recently called additive manufacturing, on three major dimensions: its application in industries, materials development and implications for product design.
Previous works were carried out to capture the mechanical properties of the resins used in prototyping and insert them into virtual systems to support the project, such as CAE systems (Pasquali et al., 2013). In this case, the proposal was to allow that components produced by RP technology could be effectively scaled to replace the original part. However, in the case where the RP manufacturing process is done by means of photo polymerization, there is an additional factor in this analysis, which is the material degradation over time. Next section presents a brief review on RP and VP, followed by section 3 where materials and method are presented. Section 4 addresses the results of this work and finally the conclusions are presented.
Despite the limitations in mechanical properties of RP materials produced by this type of technology, the intense need for agile and efficient product development has required projects proof increasingly rapidly. At present, designers are experiencing severe market pressure to develop a variety of complex products in a short period of time, which associated to the need to reduce manufacturing costs leads companies to focus on the integration of product development with rapid manufacturing processes (Atzeni et al., 2010). Based on the advances of materials properties produced by RP technology, increasingly appears the interest in using parts produced by this type of technology to functional validation of the final product, and not just for validation visual aspects.
2. RAPID PROTOTYPING AND VIRTUAL PROTOTYPING FOR PRODUCT DEVELOPMENT Literature presents different RP systems based on different technologies of adding material usually classified according to the raw material before processing: liquid-based, solidbased and powder-based (Volpato et al., 2007). The work presented in this paper uses IJ-polyjet (Objet) technology. According to Balic et al. (2006), the rapid prototyping process IJ-polyjet (Objet Geometries Company) works with photopolymer material printed in 16 to 32 micrometers layers. The process uses an ink jet system for droplets resin deposition on a tray followed by a UV (Ultraviolet) light that cures each deposited layer. The resin is fully cured during the deposition process with no need for post-processing. It is a closed architecture technology, as no intervention on the material composition can be made and there are no major changes in the process parameters.
The joint use of rapid prototyping and analysis, i.e. virtual prototyping, of geometric models allow project validation at the early stages. The union of both technologies capabilities can provide advantages mainly in situations of one of kind products (Dhakshyani et al., 2012). Chua et al. (1999) state that the only problem the rapid prototyping simulation in 978-3-902823-50-2/2013 © IFAC
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IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
Many RP processes achieved great popularity in the area of product development and components customization due to the fact that almost every type of piece regardless of its complexity can be manufactured directly from a 3D model (Dotchev and Eyers, 2010). For Hague et al. (2003) one of the greatest benefits of rapid prototyping is to generate complex parts at no extra cost, once the traditional manufacturing processes have variables associated with the manufacturing cost and complexity of the piece. This view is also discussed by Atzeni et al. (2010).
materials behaviour especially related to limitations of polymeric materials (Chua et al., 1999), causing difficulties in finite elements simulations. In addition to this, considering the aspects related to the lifetime of the part and/or environmental conditions, some work has been done in order to evaluate the degradation of the mechanical properties of parts prototyped over time (Puebla et al., 2012). Commercial technologies with proprietary materials usually present limitations with respect to this level of degradation, especially in the case of photosensitive materials.
According to Chua et al. (1999), while RP is a relatively new technology, the virtual prototyping (VP) has been around since the 70s. The VP has the main objective to reduce the iteration cycles between tests on prototypes, that is why automotive, aerospace and manufacturing companies have developed complex systems of virtual prototyping to simulate components and reduce the time and cost of physical prototyping (Choi and Samavedam, 2001). Thus, VP can be considered as an initial stage for the testing product development and evaluation processes, minimizing the traditional prototyping.
The work presented in this article addresses this area of research, where the level of degradation of a polymer resin used by the process IJ-polyjet (Objet Geometries Company) is studied. 3. MATERIALS AND METHOD 3.1 Parameters and Attributes The specimen parts used in this study were produced on an Objet Eden 350V machine with Ink Jet Printing (IJP) technology. The resin used to manufacture the specimens was VeroBlue 840. Table 1 shows the mechanical properties of the resin according to the manufacturer (Objet, 2012).
Chua et al. (1999) stated also that rapid prototyping process is directly linked to virtual prototyping during product development cycle. In accordance with Tseng et al. (1998), there are basically two types of virtual prototypes, prototype analytical and aesthetic. The aesthetic prototype aims to integrate the user, or designer, with the visual effects of the part created in 3D program, providing the user the feeling that the prototype actually exists. This technique is used when there is a need to sell the concept or the idea of a product in the conceptual phase of the project.
Table 1 – VeroBlue 840 Mechanical Properties (Objet, 2012) Tensile Strength Elongation at Break Modulus of Elasticity
The analytical prototyping allows simulation of actual use, manufacturing or assembling of the final part. One of the techniques used in design for initial analysis of components is the FEM (Finite Elements Method), which is a widespread method in academia and industry (Bathe, 1996). Usually, each application, or finite elements software has its own structure, but all of these have the same basic steps: preprocessing, processing and post-processing. For FEM the reliability of the final results depends on the elements used, i.e. behaviour and degree of refinement appropriate. Also, it is important to clearly understand the problem under study to achieve the correct use of the modelling and to avoid possible errors.
50-60 MPa 15-25 % 2000-3000 MPa
The specimens were manufactured with layer deposition thickness of 16μm (High Quality), matte finishing type and in a longitudinal printing direction (Fig.1). Two types of specimens were produced: one based on ASTM D638 for tensile tests and another with dimensions of 165x20x4mm for cantilever tests. Specimens were produced to be evaluated at 0, 30, 60, 90 and 120 days of lifetime, which will be called, in this article, as specimen age.
Aspects related to the characteristics and properties of the materials used for RP technology has been discussed in the literature. This is primarily due to the nature of the process that is based on a layered construction along the "Z" axis. Among these aspects are: surface roughness (Onuh e Yusuf, 1999; Upcraft e Fletcher, 2003; Becker et al., 2005), mechanical properties of materials (Dickens e Hopkinson, 2001; Hague et al., 2003; Ahn et al., 2002; Gibson and Shi, 1997; Bellini e Güçeri, 2003) and more recently composite material (Bassoli et al., 2012; Marchelli et al., 2011; Berti et al., 2010), and dimensional accuracy (Upcraft e Fletcher, 2003; Dickens e Hopkinson, 2001). Thus, one of the main issues when dealing with joint application of rapid prototyping in virtual prototyping is the inconsistency of
Fig.1 – Longitudinal layer deposition representation
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3.2 Stress-Strain Tests
Beams were loaded with standard weights of 0.05kgf, 0.1kgf, and 0.2kgf 0.3kgf for 100 seconds, resulting in strain-time curves as shown in Fig. 4. The measurement was performed for each 100 seconds interval, where the maximum deformation value corresponds to 100 seconds time. This test was carried out for ages 0, 30, 60 and 90 days. In addition to the maximum strain in the 100s time, also it was measured the ratio strain/time (Δy/Δx). For this test, the beams used were always the same, and after each set of tests they were stored in the same environment protected from light.
The stress-strain tests were performed on a universal testing machine EMIC DL2000, according to the ASTM D638 test for I type specimens, with a reference length of 50mm and speed of 50mm/min. A set of five (5) specimens were used to each test at 0, 30, 60 and 120 (days) age. Since this type of material has a nonlinear behaviour, the parameter used as a comparison variable was the point of maximum stress of the material (yield strength) (Fig. 2). 40 35
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Fig. 2 – Stress-strain curves for specimens 0 days old
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3.3 Cantilever beam Test
Fig. 4 – Strain-time curves for cantilever beams
To measure the behavior of the material and its resistance to bending in relation to its age, a cantilever beam test was developed. A specimen with dimensions of 165x20x4mm was prototyped. This type of test was chosen based on results obtained in previous work, in which a virtual model was compared to the experimental model (Pasquali et al., 2013). Figure 3 depicts a representation of the experiment performed where two cantilever beams built in at one side. One of the beams was used to perform measurements of loads, while the other (reference) was used to compensate possible temperature variations. The measurement process was alternated to each load, i.e. two measures for each load. Each beam was instrumented with a Kyowa strain gage KFG-2-120-C1-11 with a half bridge type configuration with adjacent arms. The Data Acquisition System 5000 (Vishay - Micro Measurements) was used to capture the data.
For this experiment, it was also performed a test for a long period of time, checking the beam strain limit for a static load of 0.1kgf. The same test was used to analyze the reverse situation, i.e., the beam returning to its initial state without load. 4. RESULTS AND DISCUSSIONS 4.1 Mechanical resistance versus specimens age Figure 5 shows the evolution of maximum stress average for the specimens with different ages. Also the errors, for each age, based on the five (5) results are shown.
Tensile Streght at Yield [MPa]
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Fig. 5 – Maximum stress-age variation It can be observed that the tensile strength value for the age of zero (0) days, i.e. just prototyped, is close to the one presented by the resin manufacturer. As the age increases, i.e. number of days in which the specimen was produced, the
Fig. 3 – Cantilever beam experiment representation
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reduction of the maximum stress values can be noticed. This is more pronounced in the first 30 days, where the reduction was approximately 29% of initial value. Between the ages of 30 to 60 days the reduction registered is about 6% compared to initial value. For the ages between 60 and 120 days the value remains within a stable range with a variation about 2%.
both beams were tested for each load, always using the other beam as a reference to compensate any temperature variations. Thus the final result was based on an average. 2400
2306 Young Modulus [MPa]
A small variation with respect to errors can be observed, demonstrating a homogeneous behaviour of each set of specimens. The errors were calculated as the standard error, i.e. the ratio between the standard deviation and the square root of the number of samples (σ / √ n). Regarding to the strain average of the specimens at the point of maximum tensile strength (Yield Point), values were kept in the range of 4.5 mm/mm (Fig. 6). Basically, the performance was the same for all sets of samples, with no variation of this property over time, even with the reduction of the maximum tensile as shown in Fig. 5.
Strain at Yield Point [% mm/mm]
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52
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Fig. 7 – Young Modulus variation through the specimens age
7
6 5
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Figure 8 shows the maximum strain (at time 100 seconds) versus specimen ages for different loads. The strain in this case was measured in microstrain (με), which means 10 -6 mm/mm or 10-4 in percentage (%). In most of the cases, the strain grows with the age, particularly to the 0 to 60 days age. To the loads of 0.2 and 0.3 kgf this phenomenon was more remarkable. On the other hand, to the ages of 60 to 90 days the strain decreased to all loads in 22% approximately, i.e. at this range the specimens were less susceptible to bending by static loads. An exception was detected for the load of 0.1 kgf, where the largest deformation was detected at 30 days of age.
0.06 4.79
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4
4.41
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4.51
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3 2 0
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60 Time [days]
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Fig.6 – Nominal elongation variation (Yield Point) through the time
2500 Maximun Strain [uɛ]
With regard to the Young Modulus (ASTM D638) variation over time, the behavior identified is the same observed on maximum tensile strength curve (Fig. 7). There is a slightly drop in the first 30 days, with a small increase for the 60 days and returning the range of 1800 MPa at 120 days. As this value is obtained by the proportionality between force and displacement, it can be assumed that the results identified after 30 days are within an average range based on errors found.
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4.2 Cantilever Beam Results
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The results for the cantilever beam experiment are described based on different loads applied in different moments (specimen ages). This experiment has been also used in a previous work for the capture and simulation of data in a virtual model – CAE Tool (Pasquali et al, 2013), however it is not the main focus of this paper.
Fig. 8 – Maximum strain versus time for different loadings In the scope of this experiment, i.e. cantilever beam, a test was performed with 0.10 kgf load for an extended period time. The purpose was to check the time required for significant strain occurred in the specimen. The beams used for this experiment were zero (0) days age, or just prototyped, and two experiments were made: one with a load (5 hours)
To conduct this experiment, the weights were loaded in crescent order, respecting a minimum time interval between one experiment and another, allowing the specimen reaches back to its initial state (with no loads). As already mentioned, 353
IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
and other, just in a sequence, without loading allowing the part to return to its initial state (3.7 hours).
Future work should be performed by means of a real product with known boundary conditions, to assess the reliability of the results. Also, another important variable to be included in further work is the environment temperature.
Figure 9 shows the strain versus time for both situations: statically loaded beam and just after the beam returning to its initial position. Although graphically to appear a high strain variation, there is a stabilization tendency of the strain-time ratio (Fig. 10).
7. ACKNOWLEDGENMENT Authors would like to thanks the financial support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico); FINEP (Financiadora de Estudos e Projetos) Proc: 4873/06.
It is observed that, for both cases, the rate drops sharply during the first 1.5 hours and then will decrease homogeneously for the subsequent hours. These experiments were stopped at a rate of 3%.
REFERENCES Ahn, S-H.; Montero, M.; Odell, D.; Roundy, S.; Wright, P.K. (2002). Anisotropic material properties of fused deposition modeling ABS. Rapid Prototyping Journal, v.8, n.4, p.248-257. Atzeni, E. Iuliano, L., Minetola, P., Salmi, A. (2010). Redesign and cost estimation of rapid manufactured plastic parts. Rapid Prototyping Journal, Vol. 16 Iss: 5 p. 308-317 Balic, J.; Brezocnik, J.; Vaupotic, B. (2006). Use of Polyjet technology in manufacture of new product. Journal of Achivements in Materials and Manufacturing Engineering, v.18, n. 1-2, p.319-322. Bassoli, E., Gatto, A., Iuliano, L. (2012). Joining mechanisms and mechanical properties of PA composites obtained by selective laser sintering, Rapid Prototyping Journal, Vol. 18 Iss: 2 p. 100-108 Bathe, K.-J. (1996) Finite Element Procedures, first ed., Prentice Hall, New Jersey. Becker, R., Grzesiak, A., Henning, A. (2005). Rethink assembly design. Assembly Automation. v.25, n.4. p. 262-266. Bellini, A., Güçeri, S. (2003). Mechanical characterization of parts fabricated using fused deposition modeling, Rapid Prototyping Journal, Vol. 9 Iss: 4 p. 252-264 Berti, G., D'Angelo, L., Gatto, A., Iuliano, L. (2010). Mechanical characterization of PA-Al composites obtained by selective laser sintering, Rapid Prototyping Journal, Vol. 16, Iss: 2, p. 124-129 Campbell, I, Bourell, D., Gibson, I. (2012). Additive manufacturing: rapid prototyping comes of age, Rapid Prototyping Journal, Vol. 18, Iss: 4, p. 255-258. Choi, S.H., Samavedam, S. (2001). Visualization of rapid prototyping. Rapid Prototyping Journal, v.7, n.2, p. 99114. Chua, C.K., Teh, S.H., Gay, R.K.L. (1999). Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing, Int. J. of Adv. Manufacturing Technology. v.15. p. 597-603. Dhakshyani, R. Nukman, Y., Azuan, A.O.N. (2012). FDM models and FEA in dysplastic hip, Rapid Prototyping Journal, Vol. 18, Iss: 3 p. 215-221. Dickens, P.; Hopkinson, N. (2001). Rapid prototyping for direct manufacture. Rapid Prototyping Journal, v.7, n.4, p.197-202. Dotchev, K.; Eyers, D. (2010). Technology review for mass customization using rapid manufacturing. Assembly Automation, v.30, n.1, p.39-46.
1,80E+03 Load 0.1 kgf
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1,20E+03
9,00E+02 6,00E+02 3,00E+02 0,00E+00
0
500
1000
1500
Time (s)
Fig. 9 – Cantilever beam strain versus time 60,0% Load 0.1 kgf
Strain-Time Ratio (uɛ/uɛ)
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Unload 40,0% 30,0% 20,0% 10,0% 0,0% 0,0
1,0
2,0
3,0
4,0
5,0 Time (h)
Fig. 10 – Cantilever beam strain-time ration 5. CONCLUSIONS The work presented in this article explored the influence of time in the variation of the mechanical properties of the resin Veroblue 850 (Objet Geometries produced with a EDEN 350V Machine). It was analyzed the properties of maximum stress, strain at maximum stress, modulus of elasticity and flexural deformation with static load, with 0, 30, 60, 90 and 120 specimens ages. The results show, as expected for photo polymerization by ultraviolet light materials, the reduction of all properties examined over time, mainly in the first 30 days of age. After this age it was perceived a stabilization of the values. In relation to the strains identified in the cantilever experiment, the same situation was perceived to strain-time rate for the first 2 hours. The results allowed the improvement of virtual models for the design of parts "one of kind" prototypes into products, taking into account the lifetime of the part. 354
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Gibson, I., Shi, D. (1997). Material properties and fabrication parameters in selective laser sintering process, Rapid Prototyping Journal, Vol. 3, Iss: 4 p. 129-136. Grimm, T. (2004). User's guide to rapid prototyping. 1st ed., Society of Manufacturing Engineers, Dearborn. Hague, R., Mansour, S., Saleh, N. (2003). Design opportunities with rapid manufacturing. Assembly Automation. v.23 n.4, p. 346-356. Marchelli, G., Prabhakar, R., Storti, D., Ganter, M. (2011). The guide to glass 3D printing: developments, methods, diagnostics and results, Rapid Prototyping Journal, Vol. 17, Iss: 3, p. 187-194 Objet (2012). Objet Materials Data Sheets. http://objet.com/3d-printing-materials/polypropylenelike. Accessed on May/2012. Onuh, S.O., Yusuf, Y.Y. (1999). Rapid prototyping technology: applications and benefits for rapid product development. J. of Intelligent Manufacturing, v.10, p. 301-311. Pasquali, F.M., Bareta, D.R, Corso, L.L. Costa, C.A. (2013). Integrated Application of RP and FEM to Support “One of a Kind” Component Design Using Prototyped Materials. Materials Science Forum, v. 730-732, p 531536. Trans Tech Publications, Switzerland. Puebla,K., Arcaute,K., Quintana,R., Wicker, R.B. (2012). Effects of environmental conditions, aging, and build orientations on the mechanical properties of ASTM type I specimens manufactured via stereolithography, Rapid Prototyping Journal, Vol. 18, Iss: 5, p. 374-388. Tseng, M.M., Jiao, J., Su, C.J. (1998). Virtual prototyping for customized product development. Integrated Manufacturing Systems. v.9, n.6, p. 334-343. Upcraft, S., Fletcher, R. (2003). The Rapid Prototyping technologies. Assembly Automation. v.23, n. 4, p. 318330. Volpato, N.; Ahrens, C.H.; Ferreira, C.V.; Petrush, G.; Carvalho, J.; Santos, J.R.L.; Silva, J.V.L. (2007). Prototipagem rápida: tecnologias e aplicações. SãoPaulo: Edgard Blücher (port.).
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Rapid Prototyping Material Degradation: a Study of Mechanical Properties Carlos A. Costa*, Paulo Roberto Linzmaier*, Felipe M. Pasquali**
*Research Group on Engineering Design and manufacturing, University of Caxias do Sul, Caxias do Sul-RS, Brazil (Tel: +55 5432182160; e-mail: [email protected]; [email protected]). **Undergraduation student in Mechanical Engineering, University of Caxias do Sul, Caxias do Sul-RS, Brazil (e-mail : [email protected]) Abstract: This work presents a study on rapid prototyping material degradation through the time. The material degradation used was Veroblue840 resin from Objet and was analyzed by its mechanical properties. Two types of tests were realized: tensile strength test (standard tests ASTM) and an experimental cantilever beam. The specimens were tested with 0, 30, 60, 90 and 120 days aging. Mechanical properties such as tensile strength, Young’s modulus, strain at Yield Point and deformation (microstrains) were analyzed. Results show the aging degradation process was not linear through the time, being more accentuated at the first 30 days. Keywords: rapid prototyping, mechanical properties, resins, degradation.
virtual prototyping (VP) is that due to the inconsistency of the materials behaviour, mainly polymeric materials, is related to the difficulty in the capture of material properties and consequently its simulation.
1. INTRODUCTION Rapid prototyping technology (RP) became an important tool to support and assist product development process (PDP) providing shorter product life cycle and time-to-market, better product quality and reliability, and elimination of wastes (Onuh and Yusuf, 1999). It combines technological and organizational tasks in a single structure, from product design to manufacturing (Grimm, 2004). This kind of technology enables the manufacturing of parts directly from a 3D CAD model without any kind of tooling, with different types of materials, and it has been used by different industrial sectors, e.g. automotive, aerospace, electronic, etc. Campbel et al. (2012) discuss rapid prototyping, or more recently called additive manufacturing, on three major dimensions: its application in industries, materials development and implications for product design.
Previous works were carried out to capture the mechanical properties of the resins used in prototyping and insert them into virtual systems to support the project, such as CAE systems (Pasquali et al., 2013). In this case, the proposal was to allow that components produced by RP technology could be effectively scaled to replace the original part. However, in the case where the RP manufacturing process is done by means of photo polymerization, there is an additional factor in this analysis, which is the material degradation over time. Next section presents a brief review on RP and VP, followed by section 3 where materials and method are presented. Section 4 addresses the results of this work and finally the conclusions are presented.
Despite the limitations in mechanical properties of RP materials produced by this type of technology, the intense need for agile and efficient product development has required projects proof increasingly rapidly. At present, designers are experiencing severe market pressure to develop a variety of complex products in a short period of time, which associated to the need to reduce manufacturing costs leads companies to focus on the integration of product development with rapid manufacturing processes (Atzeni et al., 2010). Based on the advances of materials properties produced by RP technology, increasingly appears the interest in using parts produced by this type of technology to functional validation of the final product, and not just for validation visual aspects.
2. RAPID PROTOTYPING AND VIRTUAL PROTOTYPING FOR PRODUCT DEVELOPMENT Literature presents different RP systems based on different technologies of adding material usually classified according to the raw material before processing: liquid-based, solidbased and powder-based (Volpato et al., 2007). The work presented in this paper uses IJ-polyjet (Objet) technology. According to Balic et al. (2006), the rapid prototyping process IJ-polyjet (Objet Geometries Company) works with photopolymer material printed in 16 to 32 micrometers layers. The process uses an ink jet system for droplets resin deposition on a tray followed by a UV (Ultraviolet) light that cures each deposited layer. The resin is fully cured during the deposition process with no need for post-processing. It is a closed architecture technology, as no intervention on the material composition can be made and there are no major changes in the process parameters.
The joint use of rapid prototyping and analysis, i.e. virtual prototyping, of geometric models allow project validation at the early stages. The union of both technologies capabilities can provide advantages mainly in situations of one of kind products (Dhakshyani et al., 2012). Chua et al. (1999) state that the only problem the rapid prototyping simulation in 978-3-902823-50-2/2013 © IFAC
350
10.3182/20130911-3-BR-3021.00118
IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
Many RP processes achieved great popularity in the area of product development and components customization due to the fact that almost every type of piece regardless of its complexity can be manufactured directly from a 3D model (Dotchev and Eyers, 2010). For Hague et al. (2003) one of the greatest benefits of rapid prototyping is to generate complex parts at no extra cost, once the traditional manufacturing processes have variables associated with the manufacturing cost and complexity of the piece. This view is also discussed by Atzeni et al. (2010).
materials behaviour especially related to limitations of polymeric materials (Chua et al., 1999), causing difficulties in finite elements simulations. In addition to this, considering the aspects related to the lifetime of the part and/or environmental conditions, some work has been done in order to evaluate the degradation of the mechanical properties of parts prototyped over time (Puebla et al., 2012). Commercial technologies with proprietary materials usually present limitations with respect to this level of degradation, especially in the case of photosensitive materials.
According to Chua et al. (1999), while RP is a relatively new technology, the virtual prototyping (VP) has been around since the 70s. The VP has the main objective to reduce the iteration cycles between tests on prototypes, that is why automotive, aerospace and manufacturing companies have developed complex systems of virtual prototyping to simulate components and reduce the time and cost of physical prototyping (Choi and Samavedam, 2001). Thus, VP can be considered as an initial stage for the testing product development and evaluation processes, minimizing the traditional prototyping.
The work presented in this article addresses this area of research, where the level of degradation of a polymer resin used by the process IJ-polyjet (Objet Geometries Company) is studied. 3. MATERIALS AND METHOD 3.1 Parameters and Attributes The specimen parts used in this study were produced on an Objet Eden 350V machine with Ink Jet Printing (IJP) technology. The resin used to manufacture the specimens was VeroBlue 840. Table 1 shows the mechanical properties of the resin according to the manufacturer (Objet, 2012).
Chua et al. (1999) stated also that rapid prototyping process is directly linked to virtual prototyping during product development cycle. In accordance with Tseng et al. (1998), there are basically two types of virtual prototypes, prototype analytical and aesthetic. The aesthetic prototype aims to integrate the user, or designer, with the visual effects of the part created in 3D program, providing the user the feeling that the prototype actually exists. This technique is used when there is a need to sell the concept or the idea of a product in the conceptual phase of the project.
Table 1 – VeroBlue 840 Mechanical Properties (Objet, 2012) Tensile Strength Elongation at Break Modulus of Elasticity
The analytical prototyping allows simulation of actual use, manufacturing or assembling of the final part. One of the techniques used in design for initial analysis of components is the FEM (Finite Elements Method), which is a widespread method in academia and industry (Bathe, 1996). Usually, each application, or finite elements software has its own structure, but all of these have the same basic steps: preprocessing, processing and post-processing. For FEM the reliability of the final results depends on the elements used, i.e. behaviour and degree of refinement appropriate. Also, it is important to clearly understand the problem under study to achieve the correct use of the modelling and to avoid possible errors.
50-60 MPa 15-25 % 2000-3000 MPa
The specimens were manufactured with layer deposition thickness of 16μm (High Quality), matte finishing type and in a longitudinal printing direction (Fig.1). Two types of specimens were produced: one based on ASTM D638 for tensile tests and another with dimensions of 165x20x4mm for cantilever tests. Specimens were produced to be evaluated at 0, 30, 60, 90 and 120 days of lifetime, which will be called, in this article, as specimen age.
Aspects related to the characteristics and properties of the materials used for RP technology has been discussed in the literature. This is primarily due to the nature of the process that is based on a layered construction along the "Z" axis. Among these aspects are: surface roughness (Onuh e Yusuf, 1999; Upcraft e Fletcher, 2003; Becker et al., 2005), mechanical properties of materials (Dickens e Hopkinson, 2001; Hague et al., 2003; Ahn et al., 2002; Gibson and Shi, 1997; Bellini e Güçeri, 2003) and more recently composite material (Bassoli et al., 2012; Marchelli et al., 2011; Berti et al., 2010), and dimensional accuracy (Upcraft e Fletcher, 2003; Dickens e Hopkinson, 2001). Thus, one of the main issues when dealing with joint application of rapid prototyping in virtual prototyping is the inconsistency of
Fig.1 – Longitudinal layer deposition representation
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IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
3.2 Stress-Strain Tests
Beams were loaded with standard weights of 0.05kgf, 0.1kgf, and 0.2kgf 0.3kgf for 100 seconds, resulting in strain-time curves as shown in Fig. 4. The measurement was performed for each 100 seconds interval, where the maximum deformation value corresponds to 100 seconds time. This test was carried out for ages 0, 30, 60 and 90 days. In addition to the maximum strain in the 100s time, also it was measured the ratio strain/time (Δy/Δx). For this test, the beams used were always the same, and after each set of tests they were stored in the same environment protected from light.
The stress-strain tests were performed on a universal testing machine EMIC DL2000, according to the ASTM D638 test for I type specimens, with a reference length of 50mm and speed of 50mm/min. A set of five (5) specimens were used to each test at 0, 30, 60 and 120 (days) age. Since this type of material has a nonlinear behaviour, the parameter used as a comparison variable was the point of maximum stress of the material (yield strength) (Fig. 2). 40 35
1800
1600
Yield Strength
25 15 10 5
0 0
0,05
0,1
Load Start
100s
0,15
0,2
0.30kgf 0.20kgf
Δx
1200
0.10kgf
2.98
1000
0.050kgf
800 600
1.56
400
0,25
Load Stop
= 4.52
Δy
1400
20 Strain [ue]
Stress [MPa]
30
0.73
200
Strain [mm/mm]
0
0
Fig. 2 – Stress-strain curves for specimens 0 days old
20
40
60
80 Time [s]
100
120
140
160
3.3 Cantilever beam Test
Fig. 4 – Strain-time curves for cantilever beams
To measure the behavior of the material and its resistance to bending in relation to its age, a cantilever beam test was developed. A specimen with dimensions of 165x20x4mm was prototyped. This type of test was chosen based on results obtained in previous work, in which a virtual model was compared to the experimental model (Pasquali et al., 2013). Figure 3 depicts a representation of the experiment performed where two cantilever beams built in at one side. One of the beams was used to perform measurements of loads, while the other (reference) was used to compensate possible temperature variations. The measurement process was alternated to each load, i.e. two measures for each load. Each beam was instrumented with a Kyowa strain gage KFG-2-120-C1-11 with a half bridge type configuration with adjacent arms. The Data Acquisition System 5000 (Vishay - Micro Measurements) was used to capture the data.
For this experiment, it was also performed a test for a long period of time, checking the beam strain limit for a static load of 0.1kgf. The same test was used to analyze the reverse situation, i.e., the beam returning to its initial state without load. 4. RESULTS AND DISCUSSIONS 4.1 Mechanical resistance versus specimens age Figure 5 shows the evolution of maximum stress average for the specimens with different ages. Also the errors, for each age, based on the five (5) results are shown.
Tensile Streght at Yield [MPa]
50 48.10
48
0.91
46 44
42 40 36.75
38
38.88
0.52
0.28
36 35.89
34
0.40
35.99
0.69
32 0
30
60
90
120
Time [days]
Fig. 5 – Maximum stress-age variation It can be observed that the tensile strength value for the age of zero (0) days, i.e. just prototyped, is close to the one presented by the resin manufacturer. As the age increases, i.e. number of days in which the specimen was produced, the
Fig. 3 – Cantilever beam experiment representation
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IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
reduction of the maximum stress values can be noticed. This is more pronounced in the first 30 days, where the reduction was approximately 29% of initial value. Between the ages of 30 to 60 days the reduction registered is about 6% compared to initial value. For the ages between 60 and 120 days the value remains within a stable range with a variation about 2%.
both beams were tested for each load, always using the other beam as a reference to compensate any temperature variations. Thus the final result was based on an average. 2400
2306 Young Modulus [MPa]
A small variation with respect to errors can be observed, demonstrating a homogeneous behaviour of each set of specimens. The errors were calculated as the standard error, i.e. the ratio between the standard deviation and the square root of the number of samples (σ / √ n). Regarding to the strain average of the specimens at the point of maximum tensile strength (Yield Point), values were kept in the range of 4.5 mm/mm (Fig. 6). Basically, the performance was the same for all sets of samples, with no variation of this property over time, even with the reduction of the maximum tensile as shown in Fig. 5.
Strain at Yield Point [% mm/mm]
2200 1990
52
2000
1800
1780 1803
73
127
1600
1400 0
30
60
90
120
Time [days]
Fig. 7 – Young Modulus variation through the specimens age
7
6 5
80
4.38
Figure 8 shows the maximum strain (at time 100 seconds) versus specimen ages for different loads. The strain in this case was measured in microstrain (με), which means 10 -6 mm/mm or 10-4 in percentage (%). In most of the cases, the strain grows with the age, particularly to the 0 to 60 days age. To the loads of 0.2 and 0.3 kgf this phenomenon was more remarkable. On the other hand, to the ages of 60 to 90 days the strain decreased to all loads in 22% approximately, i.e. at this range the specimens were less susceptible to bending by static loads. An exception was detected for the load of 0.1 kgf, where the largest deformation was detected at 30 days of age.
0.06 4.79
0.13
4
4.41
0.05
4.51
0.16
3 2 0
30
60 Time [days]
90
120
Fig.6 – Nominal elongation variation (Yield Point) through the time
2500 Maximun Strain [uɛ]
With regard to the Young Modulus (ASTM D638) variation over time, the behavior identified is the same observed on maximum tensile strength curve (Fig. 7). There is a slightly drop in the first 30 days, with a small increase for the 60 days and returning the range of 1800 MPa at 120 days. As this value is obtained by the proportionality between force and displacement, it can be assumed that the results identified after 30 days are within an average range based on errors found.
2000
1558 1053
1000
1053
1926
1723 1315
1366
1500
875
540
676
500
0
4.2 Cantilever Beam Results
2452
1753
274
0
442
454
347
30
60
90
300g 200g 100g 50g
Time [days]
The results for the cantilever beam experiment are described based on different loads applied in different moments (specimen ages). This experiment has been also used in a previous work for the capture and simulation of data in a virtual model – CAE Tool (Pasquali et al, 2013), however it is not the main focus of this paper.
Fig. 8 – Maximum strain versus time for different loadings In the scope of this experiment, i.e. cantilever beam, a test was performed with 0.10 kgf load for an extended period time. The purpose was to check the time required for significant strain occurred in the specimen. The beams used for this experiment were zero (0) days age, or just prototyped, and two experiments were made: one with a load (5 hours)
To conduct this experiment, the weights were loaded in crescent order, respecting a minimum time interval between one experiment and another, allowing the specimen reaches back to its initial state (with no loads). As already mentioned, 353
IFAC MCPL 2013 September 11-13, 2013. Fortaleza, Brazil
and other, just in a sequence, without loading allowing the part to return to its initial state (3.7 hours).
Future work should be performed by means of a real product with known boundary conditions, to assess the reliability of the results. Also, another important variable to be included in further work is the environment temperature.
Figure 9 shows the strain versus time for both situations: statically loaded beam and just after the beam returning to its initial position. Although graphically to appear a high strain variation, there is a stabilization tendency of the strain-time ratio (Fig. 10).
7. ACKNOWLEDGENMENT Authors would like to thanks the financial support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico); FINEP (Financiadora de Estudos e Projetos) Proc: 4873/06.
It is observed that, for both cases, the rate drops sharply during the first 1.5 hours and then will decrease homogeneously for the subsequent hours. These experiments were stopped at a rate of 3%.
REFERENCES Ahn, S-H.; Montero, M.; Odell, D.; Roundy, S.; Wright, P.K. (2002). Anisotropic material properties of fused deposition modeling ABS. Rapid Prototyping Journal, v.8, n.4, p.248-257. Atzeni, E. Iuliano, L., Minetola, P., Salmi, A. (2010). Redesign and cost estimation of rapid manufactured plastic parts. Rapid Prototyping Journal, Vol. 16 Iss: 5 p. 308-317 Balic, J.; Brezocnik, J.; Vaupotic, B. (2006). Use of Polyjet technology in manufacture of new product. Journal of Achivements in Materials and Manufacturing Engineering, v.18, n. 1-2, p.319-322. Bassoli, E., Gatto, A., Iuliano, L. (2012). Joining mechanisms and mechanical properties of PA composites obtained by selective laser sintering, Rapid Prototyping Journal, Vol. 18 Iss: 2 p. 100-108 Bathe, K.-J. (1996) Finite Element Procedures, first ed., Prentice Hall, New Jersey. Becker, R., Grzesiak, A., Henning, A. (2005). Rethink assembly design. Assembly Automation. v.25, n.4. p. 262-266. Bellini, A., Güçeri, S. (2003). Mechanical characterization of parts fabricated using fused deposition modeling, Rapid Prototyping Journal, Vol. 9 Iss: 4 p. 252-264 Berti, G., D'Angelo, L., Gatto, A., Iuliano, L. (2010). Mechanical characterization of PA-Al composites obtained by selective laser sintering, Rapid Prototyping Journal, Vol. 16, Iss: 2, p. 124-129 Campbell, I, Bourell, D., Gibson, I. (2012). Additive manufacturing: rapid prototyping comes of age, Rapid Prototyping Journal, Vol. 18, Iss: 4, p. 255-258. Choi, S.H., Samavedam, S. (2001). Visualization of rapid prototyping. Rapid Prototyping Journal, v.7, n.2, p. 99114. Chua, C.K., Teh, S.H., Gay, R.K.L. (1999). Rapid Prototyping Versus Virtual Prototyping in Product Design and Manufacturing, Int. J. of Adv. Manufacturing Technology. v.15. p. 597-603. Dhakshyani, R. Nukman, Y., Azuan, A.O.N. (2012). FDM models and FEA in dysplastic hip, Rapid Prototyping Journal, Vol. 18, Iss: 3 p. 215-221. Dickens, P.; Hopkinson, N. (2001). Rapid prototyping for direct manufacture. Rapid Prototyping Journal, v.7, n.4, p.197-202. Dotchev, K.; Eyers, D. (2010). Technology review for mass customization using rapid manufacturing. Assembly Automation, v.30, n.1, p.39-46.
1,80E+03 Load 0.1 kgf
Strain (ue)
1,50E+03
Unload - Return
1,20E+03
9,00E+02 6,00E+02 3,00E+02 0,00E+00
0
500
1000
1500
Time (s)
Fig. 9 – Cantilever beam strain versus time 60,0% Load 0.1 kgf
Strain-Time Ratio (uɛ/uɛ)
50,0%
Unload 40,0% 30,0% 20,0% 10,0% 0,0% 0,0
1,0
2,0
3,0
4,0
5,0 Time (h)
Fig. 10 – Cantilever beam strain-time ration 5. CONCLUSIONS The work presented in this article explored the influence of time in the variation of the mechanical properties of the resin Veroblue 850 (Objet Geometries produced with a EDEN 350V Machine). It was analyzed the properties of maximum stress, strain at maximum stress, modulus of elasticity and flexural deformation with static load, with 0, 30, 60, 90 and 120 specimens ages. The results show, as expected for photo polymerization by ultraviolet light materials, the reduction of all properties examined over time, mainly in the first 30 days of age. After this age it was perceived a stabilization of the values. In relation to the strains identified in the cantilever experiment, the same situation was perceived to strain-time rate for the first 2 hours. The results allowed the improvement of virtual models for the design of parts "one of kind" prototypes into products, taking into account the lifetime of the part. 354
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Gibson, I., Shi, D. (1997). Material properties and fabrication parameters in selective laser sintering process, Rapid Prototyping Journal, Vol. 3, Iss: 4 p. 129-136. Grimm, T. (2004). User's guide to rapid prototyping. 1st ed., Society of Manufacturing Engineers, Dearborn. Hague, R., Mansour, S., Saleh, N. (2003). Design opportunities with rapid manufacturing. Assembly Automation. v.23 n.4, p. 346-356. Marchelli, G., Prabhakar, R., Storti, D., Ganter, M. (2011). The guide to glass 3D printing: developments, methods, diagnostics and results, Rapid Prototyping Journal, Vol. 17, Iss: 3, p. 187-194 Objet (2012). Objet Materials Data Sheets. http://objet.com/3d-printing-materials/polypropylenelike. Accessed on May/2012. Onuh, S.O., Yusuf, Y.Y. (1999). Rapid prototyping technology: applications and benefits for rapid product development. J. of Intelligent Manufacturing, v.10, p. 301-311. Pasquali, F.M., Bareta, D.R, Corso, L.L. Costa, C.A. (2013). Integrated Application of RP and FEM to Support “One of a Kind” Component Design Using Prototyped Materials. Materials Science Forum, v. 730-732, p 531536. Trans Tech Publications, Switzerland. Puebla,K., Arcaute,K., Quintana,R., Wicker, R.B. (2012). Effects of environmental conditions, aging, and build orientations on the mechanical properties of ASTM type I specimens manufactured via stereolithography, Rapid Prototyping Journal, Vol. 18, Iss: 5, p. 374-388. Tseng, M.M., Jiao, J., Su, C.J. (1998). Virtual prototyping for customized product development. Integrated Manufacturing Systems. v.9, n.6, p. 334-343. Upcraft, S., Fletcher, R. (2003). The Rapid Prototyping technologies. Assembly Automation. v.23, n. 4, p. 318330. Volpato, N.; Ahrens, C.H.; Ferreira, C.V.; Petrush, G.; Carvalho, J.; Santos, J.R.L.; Silva, J.V.L. (2007). Prototipagem rápida: tecnologias e aplicações. SãoPaulo: Edgard Blücher (port.).
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