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Effect of dwell time and press speed on the forming quality of the press formed wood plastic composite product
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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 81 (2019) 524–528
52nd CIRP Conference on Manufacturing Systems 52nd CIRP Conference on Manufacturing Systems
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Effect of dwell time and press speed on the forming quality of the press CIRP Conference, Maythe 2018, Nantes, France Effect of dwell 28th time andDesign press speed on forming quality of the press formed wood plastic composite product formed wood plastic composite product A new methodologyAmir to analyze theSami functional architecture of Toghyani*, Matthews, and Juha physical Varis Amir Sami Matthews, Juha Varis Laboratory offor Production Engineering, LUT University, Skinnarilankatu 34, Lappeenranta 53850 Finland existing products anToghyani*, assembly oriented product family identification Laboratory of Production Engineering, LUT University, Skinnarilankatu 34, Lappeenranta 53850 Finland * Corresponding author. Tel.: +358 50 379 6959. E-mail address: [email protected]
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
* Corresponding author. Tel.: +358 50 379 6959. E-mail address: [email protected] École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Abstract Press forming of the Wood Plastic Composite (WPC) allows the use of recycled materials in the production of the sustainable consumer products. This paper evaluates key factors in the forming quality of a complex draft angled consumer product. The forming quality dependents to the Press forming of the Wood Plastic Composite (WPC) allows the use of recycled materials in the production of the sustainable consumer products. pressing parameters, specifically the speed and dwell time of the press, which are investigated as variables in this paper. The investigated WPC Abstract This paper evaluates key factors in the forming quality of a complex draft angled consumer product. The forming quality dependents to the material in this article includes 45% wood fiber, 50% high-density polyethylene (HDPE) thermoplastic and 5% of other additives. The pressed pressing parameters, specifically the speed and dwell time of the press, which are investigated as variables in this paper. The investigated WPC were assessed using a 3D profilometer to determine the shape accuracy and surface roughness of the product. It was found that the Inplates today’s environment, the trend more product variety and customization is unbroken. Duefinal to of this development, the need of material inbusiness this article includes 45% wood towards fiber, 50% high-density polyethylene (HDPE) thermoplastic and 5% other additives. The pressed forming quality is heavilyproduction dependentsystems on the dwell time and partially affected by pressing speed of thefamilies. formingTo unit. Basedand on the research findings, agile and reconfigurable emerged to cope with various products and product design optimize production plates were assessed using a 3D profilometer to determine the shape accuracy and surface roughness of the final product. It was found that the selecting an improper range of these parameters may lead to significant deformation in the final product. Determined ranges of pressing force systems well as to choose the optimal matches, productaffected analysisbymethods needed. the on known methodsfindings, aim to formingasquality is heavily dependent on theproduct dwell time and partially pressingare speed of theIndeed, formingmost unit. of Based the research and dwell time found inproduct this article can on help toDifferent start the press forming of WPCs and let them have faster production rampage. analyze a product or one family themanufacturers physical level.to product families, differ largely in terms numberforce and selecting an improper range of these parameters may lead significant deformation inhowever, the final may product. Determined rangesofofthe pressing nature of components. impedes an manufacturers efficient comparison andpress choice of appropriate family combinations for therampage. production and dwell time found inThis thisfact article can help to start the forming of WPCs product and let them have faster production © 2019AThe Published by Elsevier Ltd. This is an open access CC BY-NC-ND license system. newAuthors. methodology is proposed to analyze existing products in article view ofunder their the functional and physical architecture. The aim is to cluster © 2019 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/) these products inaccess new assembly oriented product foropen the (http://creativecommons.org/licenses/by-nc-nd/3.0/) optimization existing lines and the creation of future reconfigurable © 2019 The Authors. Published by Elsevier Ltd.families This is license an access articleofunder theassembly CC BY-NC-ND license This is an open article under the CC BY-NC-ND Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on Manufacturing Systems. assembly systems. on Datum Chain, the physicalof structure the products is analyzed. FunctionalSystems. subassemblies are identified, and (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review underBased responsibility of Flow the scientific committee the 52ndofCIRP Conference on Manufacturing aPeer-review functional analysis is performed.ofMoreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the under responsibility the scientific committee of the 52nd CIRP Conference on Manufacturing Systems. Keywords: wood plastic composites; press forming method; forming quality; surface quality similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of awood nail-clipper is used topress explain the method; proposed methodology. An industrial Keywords: plastic composites; forming forming quality; surface quality case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach. © 2017 The Authors. Published by Elsevier B.V. 1. Introduction feasibility has investigated in the previous set of researches. In Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
this manufacturing method extrusion was selected as the 1. Introduction feasibility has investigated in the previous set of researches. In Recent changes to environmental legislation mandating primary method of material fabrication based on preliminary Keywords: Assembly; Design method; Family identification this manufacturing method extrusion was selected as the higher recycling targets have created additional interest. EU research and due to the well-recognized capabilities of the Recent changes to environmental legislation mandating primary method of material fabrication based on preliminary legislation has adopted a five-step waste hierarchy for waste method. Press forming is proposed for the shaping process of higher recycling targets have created additional interest. EU research and due to the well-recognized capabilities of the disposal and management [1]. post extrusion manufacturing based on analysis and evaluation legislation has adopted a five-step waste hierarchy for waste method. Press forming is proposed for the shaping process of 1. Introduction product range and characteristics manufactured and/or Wood-plastic composites (WPC) are a good example of a of of the possible secondary fabrication methods. disposal and management [1]. post extrusion manufacturing based on analysis and evaluation in this molding system. In thisextrusion context, are the the main challenge in modern material that has great potential, commercially and assembled Compression and most common Wood-plastic composites (WPC) are a good example of a of possible secondary fabrication methods. Due to the through fast development in the domain modelling analysis istonow not onlyplastic to copeand withpolymer single environmentally, the use of recycled materials [2]. of processingand techniques fabricate modern material that has great potential, commercially and Compression molding and extrusion are the most common communication and have an ongoing trend of application digitization areas, and products, product range or existing product families, WPC products several different compositea limited products. The compression molding process has environmentally, through the use of recycled materials [2]. processing techniques to fabricate plastic and polymer digitalization, manufacturingfurniture enterprises are facing important alsoused to be able analyze thermoset and to compare products including the construction, and automotive industries. but been for to molding powders andto define rubber WPC products have several different application areas, composite products. The compression molding process has challenges market technologies environments: continuing product [3], families. can be observed thatextrusion classical has existing Innovationsinintoday’s manufacturing havea enabled the new compounds whileItmaterial binding by been including the construction, furniture and automotive industries. been used for molding thermoset powders and rubber tendency towards reduction of product development timeswider and product families regrouped in function of clients orcomposite features. development of new products and utilization of a much the most usedare way to produce thermoplastic Innovations in manufacturing technologies have enabled the compounds [3], while material binding by extrusion has been shortened lifecycles.including In addition, there is materials an increasing oriented families are with hardly to find. range of product raw materials, recycled and However, materials.assembly Reinforcement of product the WPC materials glass and development of new products and utilization of a much wider the most used way to produce thermoplastic composite demand of hitherto customization, the same time in a global On the product differ [4]. mainly in two materials sent tobeing wasteat disposal. The novel postother fibers has family been level, widelyproducts researched However, range of raw materials, including recycled materials and materials. Reinforcement of the WPC materials with glass and competition with competitors all over therange world. This trend, main characteristics: the number ofstage components andreceived (ii) the production process for fabricating a wider of eco-friendly possibilities in the (i) post-processing have not materials hitherto sent to waste disposal. The novel postother fibers has been widely researched [4]. However, which is using inducing therecycled development from to and micro ofattention components (e.g. mechanical,ofelectrical, electronical). products mainly materials wasmacro proposed its type much in the improvement the material properties. production process for fabricating a wider range of eco-friendly possibilities in the post-processing stage have not received markets, results in diminished lot sizes due to augmenting Classical methodologies considering mainly single products products using mainly recycled materials was proposed and its much attention in the improvement of the material properties. product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the 2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which (http://creativecommons.org/licenses/by-nc-nd/3.0/) 2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND licensean efficient definition and identify possible optimization potentials in the existing causes regarding Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on difficulties Manufacturing Systems. (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on Manufacturing Systems.
2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an©open article Published under theby CC BY-NC-ND 2212-8271 2017access The Authors. Elsevier B.V. license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of scientific the scientific committee theCIRP 52ndDesign CIRPConference Conference2018. on Manufacturing Systems. Peer-review under responsibility of the committee of the of 28th 10.1016/j.procir.2019.03.149
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In the research by the authors it has been previously shown, that the pressing force has a clear influence on formability [5] In theory, as the composite material is above the melting temperature of the polymer, the forming resistance should be minimal. However, in reality, the tool temperature, environment and material aspects set a challenging environment for the material melt flow and a measurable press force is generated during the forming process. It has also been shown that moisture can affect the forming quality [6]. Online process is usually highly dependent on the production rate of the extruder while offline process is only dependent on the dwell time. One reason press forming is a promising method to produce composite products is the reason that shorter dwell times are needed compared to polymer injection molding, in which the duration may reach minutes. Defining the usable dwell time window enables significant time savings and improved efficiency in production. Fig. 1 Illustrates the role of the dwell time in the overall working cycle of an offline system.
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excellent weight to strength factor and has good availability, as recyclable plastic is the most commonly produced plastic in the world. The relatively low melting point of 130 °C enables the use of natural cellulosic fibers such as wood as fillers without significant thermal degradation. The tested composite material had a density of 1.24 g/cm3, which is similar to the densities of commercial high-density WPC materials. Table 1. Material properties of the selected WPC material.
Composite material
Composition
Hardness
Tensile strength
Modulus of elasticity
50% HDPE, 3% MAPE, 3% lubricant, 44% wood flour MESH 20
5.06 HB
21.5 MPa
4.5 GPa
15.0 MPa
0.8 GPa
40.0 MPa
11.0 GPa
HDPE Wood flour
2.6-7.0 HB
The Kompoline manufacturing system (Fig. 2) was used in the article because it enables faster press speeds than a typical hydraulic press. The setup comprises two moving press units with GSX60-1005 electric actuator with 55 kN press force on a linear table Tecnotion linear motor TL12 with 1 kN linear force. Both units move on the same linear magnetic track with a total length of 2 m.
Fig. 1. Typical working cycle of the post-process line. The durations of the different time zones for the post-process press unit are highlighted. The dashed line presents the speed and solid line presents the acceleration.
Surface roughness indicates the suitability of the material and process for certain products or types of products; different products have different surface quality requirements. In addition to absolute surface roughness, variability in surface roughness and consistency of surface roughness are important measurements in assessing the formability of a product and the feasibility of a forming process. It should be noted that surface roughness is only one of several surface quality characteristics. The effect of dwell time and pressing speed are generally known as two major forming parameters in press forming of any material[7-9]. With extruded WPC sheet material, the dwell time has not been investigated before and is investigated in this article in continuum to effect of strain rate and effect of temperature in previous work of the authors [10]. 2. Composite material and manufacturing system The WPC material (Table 1.) for the experiments was selected on the basis of promising preliminary forming results in previous research done by authors, wide availability and usability of this material as a reheated material, due to the used thermoplastic matrix. This matrix; polyethylene (PE); offers an
Fig. 2. The Kompoline manufacturing system used in post-production of the extruded composite products through press forming method.
The WPC sheets with a thickness of 3.2 mm ±0.1 mm were heated in an industrial electric oven. The selected temperatures were based on ASTM D3418-15 digital scanning calorimetry (DSC) test indicating material melting temperature of 135 ºC. The selected temperature was 160 ºC, to be sure that the material remained in a molten state during the press forming. Also, the selected temperature is a typical temperature in the extrusion of high-density polyethylene (HDPE) based WPC materials. Moreover, thermal degradation of wood particles caused in high temperature set an upper limit to the selected temperature.
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The preliminary forming tests at lower temperatures showed cracks and poor surface quality in the final product. Samples produced at the higher temperature of 150 °C were found to be acceptable visually. It was decided based on a visual and tactile inspection that product areas touched by customers should have less than 45 µm of surface roughness (Rz) for selected samples, to enable use in a wide range of products. This was set as the preliminary level of acceptance in the evaluation of roughness. A hybrid forming test tool designed for a circular plate product with a diameter of 150 mm was designed and manufactured. The tool is symmetrically circular to highlight the possible effects of fibre orientation along the direction of extrusion. A test specimen plate was produced utilizing the mentioned circular tools as shown in Fig. 3; with an overall diameter of 150 ± 0.5 mm. Selected forming tool tolerances are achievable in basic turning machining. Based on knowledge with polymers [11] the surface quality of forming surfaces of the tools should be considered important as the press forming copies the surface of the tools to the product piece in significant detail for a consumer product. Therefore, forming surfaces of the tools were polished in a way they end to a surface roughness of Ra 0.2 or smoother.
3
through visual assessment. In this process, no significant incline or curvature in the shape could be accepted similarly to the previous article [4] because of the suitability for many consumer applications that require a smooth surface. The press unit was set to the maximum power of 50 kN leading to theoretical forming pressure of 0.7 MPa. Following table presents the selected variable parameters. Table 2. Selected parameters in the forming process. (DT denotes dwell time; S denotes speed). Name
Dwell
Series DT0.2
Speed
0.2
150
Series DT2
2
150
Series DT5
5
150
Series DT10
10
150
Series S20
2
20
Series S150
2
150
Series S300
2
300
3. Results and discussion
mm
Following Fig. 4 and Fig. 5 highlight the effect of the speed in the geometry of upper surface of the specimen plates in fiber and cross fiber direction.
6 5 4 3 2 1 0 -1
0
20
40
60
80
100
mm
The surface roughness of the specimen was investigated with a hand-held surface roughness tester Innovatest TR-110 made by Innovatech Holding BV (Maastricht, Netherlands). Surface roughness was measured for a length of 2.5 mm of the surface of the sample. The temperature of forming tools was kept at room temperature during the tests. In this case using heated tools could increase the risk of material sticking to the tools and would increase complexity in the ejection of produced samples. Overall geometry was measured using a Keyence (Japan) VR-3200 3D laser measurement system with nominal repeatability of 0.5 µm and an accuracy of ±3 µm. The final surface roughness value was averaged from both fibre and counter-fibre direction. Each parameter set was repeated five times and from each set an average plate was visually selected for further investigation with the laser profilometer. In this paper, acceptable forming quality was defined
Dwell time 2s
Dwell time 5s
Dwell time 10s
Fig. 4. The geometry of upper surface of resulting specimen in fiber direction of different dwell times.
mm
Fig. 3. Forming tool composition and sample dimensions.
Dwell time 0.2s
7 6 5 4 3 2 1 0 -1 -2 -3 -4
10
30 50 Dwell Time 0.2s Dwell time 5s
mm
70
90 110 Dwell time 2s Dwell time 10s
Fig. 5. The geometry of upper surface of resulting specimen in cross-fiber direction of different dwell times.
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Amir Toghyani et al. / Procedia CIRP 81 (2019) 524–528 Amir Toghyani et al. / Procedia CIRP 00 (2019) 000–000
mm
The results provided in Fig. 4 and Fig. 5 are demonstrating the geometry differences in each set of produced samples. Setting a short dwell time of 0.2s caused significant warpage in the plate and its poor forming quality makes them unacceptable. In addition, the produced samples with a dwell time of 2s also have not acceptable accuracy in geometry due to the surface twist in the plates. On the other hand, the longer dwell time results (5s and 10s) are significantly better in terms of geometry but they still have small curvature of 0.5 mm in comparison to the ideal shape. It is also clear that increasing the dwell time over 5s did not lead to a better geometrical shape.
527
S20
28.5±6.9
40.0±6.5
S150
32.5±5.0
34.3±4.9
S300
29.4±2.9
29.2±3.5
The results provided in table 3 demonstrate that the average surface roughness for the produced samples are in similar range regardless of the variation in dwell time and pressing speed. The result is similar to the research that has been conducted previously [5]. Although the measurement was done on the flat side of the plate, the tapered section of the plates is significantly rougher. This phenomenon is usually caused by improper thickness of the material in comparison to the designed tool forming tolerance as highlighted in Fig. 8.
5 4 3 2 1 0 -1
0
20
40
Speed 20mm/s Speed 300mm/s
mm
60
80
100
Speed 150mm/s
mm
Fig. 6. The geometry of upper surface of resulting specimen in fibre direction of different pressing speeds.
Fig. 8. The highlighted areas in the lower image present thickness variation of the material in the process caused by forming tools while the upper image shows constant thickness.
A long dwell time leads to a low overall production speed which is not acceptable for many manufacturers of bulk products. To counter this, it is needed to set up many parallel pressing machines for more feasible production rate.
8 6 4 2 0 -2 -4
10
30
50
mm 70
Speed 20mm/s Speed 300mm/s
90
110
Speed 150mm/s
Fig. 7. The geometry of upper surface of resulting specimen in fibre direction of different pressing speeds.
Fig. 6 and Fig. 7 show that the forming results in 20 and 150 mm/s are quite similar, while the 300 mm/s sample is drastically deformed. Table 3. Resulting average values of surface roughness Rz. (± value denotes to standard deviation). Series
Fiber-Direction (μm)
Cross-Direction (μm)
DT0.2
30.9±1.6
28.1±8.1
DT2
30.4±6.2
33.5±7.5
DT5
32.2±1.7
32.7±3.2
DT10
31±4.4
33.4±3.5
Fig. 9. A sample produced in pressing speed of 300 mm/sec, which caused bumps to tapered section during backstroke due to material being partially stuck to the stationary bottom tool and moving upper tool.
The Fig. 9 and Fig. 10 indicate that the short dwell times of 0.2 s and 2 s lead to curvature in the form. This can be due to
Amir Toghyani et al. / Procedia CIRP 81 (2019) 524–528 Amir Toghyani et al. / Procedia CIRP 00 (2019) 000–000
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long polymer setting time or the material is stuck to cold tools and then ripped apart by the backstroke of the press. One reason can also be forming of partial vacuum do the deeper parts of the mould while backstroking.
• •
5
the more significant the difference to the ideal flat surface geometry. Dwell time of over 5 seconds did not lead to significant quality improvement in the final product. Due to the insignificant influence of speed in final quality, typical speeds of hydraulic presses can be used without loss of quality.
Acknowledgement This study was conducted in the Life IP on waste – Towards circular economy in Finland (LIFE-IP CIRCWASTEFINLAND) programme (LIFE15 IPE FI 004). Funding for the programme was received from EU LIFE Integrated projects, companies and cities. Fig. 10. A sample produced with the dwell time of 0.2 seconds. Uneven and bumpy surface shape in the bottom of the sample is clearly visible. Also there is roughness in the tapered section indicating insufficient material thickness.
In speed of 300 mm/s trapped air led to an uneven surface in the fiber direction. Otherwise, the convex curvature was similar to the results of speed 20 mm/s. Although in this paper the underside of the plate was ignored, the plate roughness and quality were always better facing the stationary tool, so it is recommended that the tool mounted to the stationary end plate of the press unit should be facing the customer side of the product. To validate this, it was trialed by changing the tools upside down. In every case, the stationary part was always better quality regardless of the attached tool. Since the air pressure and vacuum played an important role of determining the overall quality of research the addition of the air channels could be investigated in future research. 4. Conclusions In this article press forming quality in terms of geometry and surface roughness of a WPC material consisting of 45% wood fiber, 50% HDPE thermoplastic and 5% of other additives was investigated with profilometers. In the experiments pressing speed and dwell time were varied. In the tests it was found that: • .
Dwell time less than 2 seconds leads to a warped and curved geometry. The shorter the dwell time,
References [1] Varis J, Kärki T, Immonen V. A Novel Method for Producing Composite Products Based on Recycled Plastic and Wood – An Industrial Case. 24th International Conference on Production Research ICPR 2017. [2] Ashori A, Nourbakhsh A. Characteristics of Wood-Fiber Plastic Composites Made of Recycled Materials. Waste Management 2009; 29:1291-1295. [3] Park CH. Compression molding in polymer matrix composites. In Advani GS, Hsiao KT, editors. Manufacturing techniques for polymer matrix composites(PMCs). Oxford: Woodhead Publishing; 2012. p. 47-50. [4] Rizvi GM, Semeralul H. Glass-Fiber-Reinforced Wood/Plastic Composites. Journal of Vinyl & Additive Technology 2008; 14:4168-4185. [5] Toghyani A, Matthews S. Feasibility Assessment of a Wood-Plastic Composite Post-Production Process: Formability. BioResources 2016;11:4168-4185. [6] Matthews S, Toghyani A, Ovaska SSO. Role of moisture on press formed products made of Wood Plastic Composites. Procedia Manufacturing 2018;17:1090-1096. [7] Wang L, Zhu B, Wang Y, An X, Wang Q, Zhang Y. An Online Dwell Time Optimization Method Based on Parts Performance for Hot Stamping, Procedia Engineering, vol. 207, p. 759-764, 2017. [8] Wen H, Can T. Effect of Dwell Time and Heating Rate on Thermal Residual Stresses in Co-Cured Aluminum/Composite Hybrid Shaft. Applied Mechanics and Materials, vol. 723, p.485-488, Jan 2015. [9] Summerscales J, Green D, Guild F. Effect of processing dwell-time on the microstructure of a fiber-reinforced composite. Journal Of MicroscopyOxford, vol.169, pp.173-182, Feb 1993. [10] A. E. Toghyani, M. Amraei, S. Matthews, J. Varis, T. Kärki, and X.-L. Zhao, “Effect of strain rate and temperature on press forming of extruded WPC profiles,” Compos. Struct., vol. 180, pp. 845–852, Nov. 2017. [11] Harper, CA. Handbook of plastic processes. Hoboken, NJ: WileyInterscience; 2006.
ScienceDirect ScienceDirect Available online atonline www.sciencedirect.com Procedia CIRP 00 (2019) 000–000 Available at www.sciencedirect.com
ScienceDirect ScienceDirect
Procedia CIRP 00 (2019) 000–000
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia CIRP 00 (2017) 000–000 Procedia CIRP 81 (2019) 524–528
52nd CIRP Conference on Manufacturing Systems 52nd CIRP Conference on Manufacturing Systems
www.elsevier.com/locate/procedia
Effect of dwell time and press speed on the forming quality of the press CIRP Conference, Maythe 2018, Nantes, France Effect of dwell 28th time andDesign press speed on forming quality of the press formed wood plastic composite product formed wood plastic composite product A new methodologyAmir to analyze theSami functional architecture of Toghyani*, Matthews, and Juha physical Varis Amir Sami Matthews, Juha Varis Laboratory offor Production Engineering, LUT University, Skinnarilankatu 34, Lappeenranta 53850 Finland existing products anToghyani*, assembly oriented product family identification Laboratory of Production Engineering, LUT University, Skinnarilankatu 34, Lappeenranta 53850 Finland * Corresponding author. Tel.: +358 50 379 6959. E-mail address: [email protected]
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
* Corresponding author. Tel.: +358 50 379 6959. E-mail address: [email protected] École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Abstract Press forming of the Wood Plastic Composite (WPC) allows the use of recycled materials in the production of the sustainable consumer products. This paper evaluates key factors in the forming quality of a complex draft angled consumer product. The forming quality dependents to the Press forming of the Wood Plastic Composite (WPC) allows the use of recycled materials in the production of the sustainable consumer products. pressing parameters, specifically the speed and dwell time of the press, which are investigated as variables in this paper. The investigated WPC Abstract This paper evaluates key factors in the forming quality of a complex draft angled consumer product. The forming quality dependents to the material in this article includes 45% wood fiber, 50% high-density polyethylene (HDPE) thermoplastic and 5% of other additives. The pressed pressing parameters, specifically the speed and dwell time of the press, which are investigated as variables in this paper. The investigated WPC were assessed using a 3D profilometer to determine the shape accuracy and surface roughness of the product. It was found that the Inplates today’s environment, the trend more product variety and customization is unbroken. Duefinal to of this development, the need of material inbusiness this article includes 45% wood towards fiber, 50% high-density polyethylene (HDPE) thermoplastic and 5% other additives. The pressed forming quality is heavilyproduction dependentsystems on the dwell time and partially affected by pressing speed of thefamilies. formingTo unit. Basedand on the research findings, agile and reconfigurable emerged to cope with various products and product design optimize production plates were assessed using a 3D profilometer to determine the shape accuracy and surface roughness of the final product. It was found that the selecting an improper range of these parameters may lead to significant deformation in the final product. Determined ranges of pressing force systems well as to choose the optimal matches, productaffected analysisbymethods needed. the on known methodsfindings, aim to formingasquality is heavily dependent on theproduct dwell time and partially pressingare speed of theIndeed, formingmost unit. of Based the research and dwell time found inproduct this article can on help toDifferent start the press forming of WPCs and let them have faster production rampage. analyze a product or one family themanufacturers physical level.to product families, differ largely in terms numberforce and selecting an improper range of these parameters may lead significant deformation inhowever, the final may product. Determined rangesofofthe pressing nature of components. impedes an manufacturers efficient comparison andpress choice of appropriate family combinations for therampage. production and dwell time found inThis thisfact article can help to start the forming of WPCs product and let them have faster production © 2019AThe Published by Elsevier Ltd. This is an open access CC BY-NC-ND license system. newAuthors. methodology is proposed to analyze existing products in article view ofunder their the functional and physical architecture. The aim is to cluster © 2019 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/) these products inaccess new assembly oriented product foropen the (http://creativecommons.org/licenses/by-nc-nd/3.0/) optimization existing lines and the creation of future reconfigurable © 2019 The Authors. Published by Elsevier Ltd.families This is license an access articleofunder theassembly CC BY-NC-ND license This is an open article under the CC BY-NC-ND Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on Manufacturing Systems. assembly systems. on Datum Chain, the physicalof structure the products is analyzed. FunctionalSystems. subassemblies are identified, and (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review underBased responsibility of Flow the scientific committee the 52ndofCIRP Conference on Manufacturing aPeer-review functional analysis is performed.ofMoreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the under responsibility the scientific committee of the 52nd CIRP Conference on Manufacturing Systems. Keywords: wood plastic composites; press forming method; forming quality; surface quality similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of awood nail-clipper is used topress explain the method; proposed methodology. An industrial Keywords: plastic composites; forming forming quality; surface quality case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach. © 2017 The Authors. Published by Elsevier B.V. 1. Introduction feasibility has investigated in the previous set of researches. In Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
this manufacturing method extrusion was selected as the 1. Introduction feasibility has investigated in the previous set of researches. In Recent changes to environmental legislation mandating primary method of material fabrication based on preliminary Keywords: Assembly; Design method; Family identification this manufacturing method extrusion was selected as the higher recycling targets have created additional interest. EU research and due to the well-recognized capabilities of the Recent changes to environmental legislation mandating primary method of material fabrication based on preliminary legislation has adopted a five-step waste hierarchy for waste method. Press forming is proposed for the shaping process of higher recycling targets have created additional interest. EU research and due to the well-recognized capabilities of the disposal and management [1]. post extrusion manufacturing based on analysis and evaluation legislation has adopted a five-step waste hierarchy for waste method. Press forming is proposed for the shaping process of 1. Introduction product range and characteristics manufactured and/or Wood-plastic composites (WPC) are a good example of a of of the possible secondary fabrication methods. disposal and management [1]. post extrusion manufacturing based on analysis and evaluation in this molding system. In thisextrusion context, are the the main challenge in modern material that has great potential, commercially and assembled Compression and most common Wood-plastic composites (WPC) are a good example of a of possible secondary fabrication methods. Due to the through fast development in the domain modelling analysis istonow not onlyplastic to copeand withpolymer single environmentally, the use of recycled materials [2]. of processingand techniques fabricate modern material that has great potential, commercially and Compression molding and extrusion are the most common communication and have an ongoing trend of application digitization areas, and products, product range or existing product families, WPC products several different compositea limited products. The compression molding process has environmentally, through the use of recycled materials [2]. processing techniques to fabricate plastic and polymer digitalization, manufacturingfurniture enterprises are facing important alsoused to be able analyze thermoset and to compare products including the construction, and automotive industries. but been for to molding powders andto define rubber WPC products have several different application areas, composite products. The compression molding process has challenges market technologies environments: continuing product [3], families. can be observed thatextrusion classical has existing Innovationsinintoday’s manufacturing havea enabled the new compounds whileItmaterial binding by been including the construction, furniture and automotive industries. been used for molding thermoset powders and rubber tendency towards reduction of product development timeswider and product families regrouped in function of clients orcomposite features. development of new products and utilization of a much the most usedare way to produce thermoplastic Innovations in manufacturing technologies have enabled the compounds [3], while material binding by extrusion has been shortened lifecycles.including In addition, there is materials an increasing oriented families are with hardly to find. range of product raw materials, recycled and However, materials.assembly Reinforcement of product the WPC materials glass and development of new products and utilization of a much wider the most used way to produce thermoplastic composite demand of hitherto customization, the same time in a global On the product differ [4]. mainly in two materials sent tobeing wasteat disposal. The novel postother fibers has family been level, widelyproducts researched However, range of raw materials, including recycled materials and materials. Reinforcement of the WPC materials with glass and competition with competitors all over therange world. This trend, main characteristics: the number ofstage components andreceived (ii) the production process for fabricating a wider of eco-friendly possibilities in the (i) post-processing have not materials hitherto sent to waste disposal. The novel postother fibers has been widely researched [4]. However, which is using inducing therecycled development from to and micro ofattention components (e.g. mechanical,ofelectrical, electronical). products mainly materials wasmacro proposed its type much in the improvement the material properties. production process for fabricating a wider range of eco-friendly possibilities in the post-processing stage have not received markets, results in diminished lot sizes due to augmenting Classical methodologies considering mainly single products products using mainly recycled materials was proposed and its much attention in the improvement of the material properties. product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the 2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which (http://creativecommons.org/licenses/by-nc-nd/3.0/) 2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND licensean efficient definition and identify possible optimization potentials in the existing causes regarding Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on difficulties Manufacturing Systems. (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Peer-review under responsibility of the scientific committee of the 52nd CIRP Conference on Manufacturing Systems.
2212-8271 © 2019 The Authors. Published by Elsevier Ltd. This is an©open article Published under theby CC BY-NC-ND 2212-8271 2017access The Authors. Elsevier B.V. license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of scientific the scientific committee theCIRP 52ndDesign CIRPConference Conference2018. on Manufacturing Systems. Peer-review under responsibility of the committee of the of 28th 10.1016/j.procir.2019.03.149
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In the research by the authors it has been previously shown, that the pressing force has a clear influence on formability [5] In theory, as the composite material is above the melting temperature of the polymer, the forming resistance should be minimal. However, in reality, the tool temperature, environment and material aspects set a challenging environment for the material melt flow and a measurable press force is generated during the forming process. It has also been shown that moisture can affect the forming quality [6]. Online process is usually highly dependent on the production rate of the extruder while offline process is only dependent on the dwell time. One reason press forming is a promising method to produce composite products is the reason that shorter dwell times are needed compared to polymer injection molding, in which the duration may reach minutes. Defining the usable dwell time window enables significant time savings and improved efficiency in production. Fig. 1 Illustrates the role of the dwell time in the overall working cycle of an offline system.
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excellent weight to strength factor and has good availability, as recyclable plastic is the most commonly produced plastic in the world. The relatively low melting point of 130 °C enables the use of natural cellulosic fibers such as wood as fillers without significant thermal degradation. The tested composite material had a density of 1.24 g/cm3, which is similar to the densities of commercial high-density WPC materials. Table 1. Material properties of the selected WPC material.
Composite material
Composition
Hardness
Tensile strength
Modulus of elasticity
50% HDPE, 3% MAPE, 3% lubricant, 44% wood flour MESH 20
5.06 HB
21.5 MPa
4.5 GPa
15.0 MPa
0.8 GPa
40.0 MPa
11.0 GPa
HDPE Wood flour
2.6-7.0 HB
The Kompoline manufacturing system (Fig. 2) was used in the article because it enables faster press speeds than a typical hydraulic press. The setup comprises two moving press units with GSX60-1005 electric actuator with 55 kN press force on a linear table Tecnotion linear motor TL12 with 1 kN linear force. Both units move on the same linear magnetic track with a total length of 2 m.
Fig. 1. Typical working cycle of the post-process line. The durations of the different time zones for the post-process press unit are highlighted. The dashed line presents the speed and solid line presents the acceleration.
Surface roughness indicates the suitability of the material and process for certain products or types of products; different products have different surface quality requirements. In addition to absolute surface roughness, variability in surface roughness and consistency of surface roughness are important measurements in assessing the formability of a product and the feasibility of a forming process. It should be noted that surface roughness is only one of several surface quality characteristics. The effect of dwell time and pressing speed are generally known as two major forming parameters in press forming of any material[7-9]. With extruded WPC sheet material, the dwell time has not been investigated before and is investigated in this article in continuum to effect of strain rate and effect of temperature in previous work of the authors [10]. 2. Composite material and manufacturing system The WPC material (Table 1.) for the experiments was selected on the basis of promising preliminary forming results in previous research done by authors, wide availability and usability of this material as a reheated material, due to the used thermoplastic matrix. This matrix; polyethylene (PE); offers an
Fig. 2. The Kompoline manufacturing system used in post-production of the extruded composite products through press forming method.
The WPC sheets with a thickness of 3.2 mm ±0.1 mm were heated in an industrial electric oven. The selected temperatures were based on ASTM D3418-15 digital scanning calorimetry (DSC) test indicating material melting temperature of 135 ºC. The selected temperature was 160 ºC, to be sure that the material remained in a molten state during the press forming. Also, the selected temperature is a typical temperature in the extrusion of high-density polyethylene (HDPE) based WPC materials. Moreover, thermal degradation of wood particles caused in high temperature set an upper limit to the selected temperature.
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The preliminary forming tests at lower temperatures showed cracks and poor surface quality in the final product. Samples produced at the higher temperature of 150 °C were found to be acceptable visually. It was decided based on a visual and tactile inspection that product areas touched by customers should have less than 45 µm of surface roughness (Rz) for selected samples, to enable use in a wide range of products. This was set as the preliminary level of acceptance in the evaluation of roughness. A hybrid forming test tool designed for a circular plate product with a diameter of 150 mm was designed and manufactured. The tool is symmetrically circular to highlight the possible effects of fibre orientation along the direction of extrusion. A test specimen plate was produced utilizing the mentioned circular tools as shown in Fig. 3; with an overall diameter of 150 ± 0.5 mm. Selected forming tool tolerances are achievable in basic turning machining. Based on knowledge with polymers [11] the surface quality of forming surfaces of the tools should be considered important as the press forming copies the surface of the tools to the product piece in significant detail for a consumer product. Therefore, forming surfaces of the tools were polished in a way they end to a surface roughness of Ra 0.2 or smoother.
3
through visual assessment. In this process, no significant incline or curvature in the shape could be accepted similarly to the previous article [4] because of the suitability for many consumer applications that require a smooth surface. The press unit was set to the maximum power of 50 kN leading to theoretical forming pressure of 0.7 MPa. Following table presents the selected variable parameters. Table 2. Selected parameters in the forming process. (DT denotes dwell time; S denotes speed). Name
Dwell
Series DT0.2
Speed
0.2
150
Series DT2
2
150
Series DT5
5
150
Series DT10
10
150
Series S20
2
20
Series S150
2
150
Series S300
2
300
3. Results and discussion
mm
Following Fig. 4 and Fig. 5 highlight the effect of the speed in the geometry of upper surface of the specimen plates in fiber and cross fiber direction.
6 5 4 3 2 1 0 -1
0
20
40
60
80
100
mm
The surface roughness of the specimen was investigated with a hand-held surface roughness tester Innovatest TR-110 made by Innovatech Holding BV (Maastricht, Netherlands). Surface roughness was measured for a length of 2.5 mm of the surface of the sample. The temperature of forming tools was kept at room temperature during the tests. In this case using heated tools could increase the risk of material sticking to the tools and would increase complexity in the ejection of produced samples. Overall geometry was measured using a Keyence (Japan) VR-3200 3D laser measurement system with nominal repeatability of 0.5 µm and an accuracy of ±3 µm. The final surface roughness value was averaged from both fibre and counter-fibre direction. Each parameter set was repeated five times and from each set an average plate was visually selected for further investigation with the laser profilometer. In this paper, acceptable forming quality was defined
Dwell time 2s
Dwell time 5s
Dwell time 10s
Fig. 4. The geometry of upper surface of resulting specimen in fiber direction of different dwell times.
mm
Fig. 3. Forming tool composition and sample dimensions.
Dwell time 0.2s
7 6 5 4 3 2 1 0 -1 -2 -3 -4
10
30 50 Dwell Time 0.2s Dwell time 5s
mm
70
90 110 Dwell time 2s Dwell time 10s
Fig. 5. The geometry of upper surface of resulting specimen in cross-fiber direction of different dwell times.
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mm
The results provided in Fig. 4 and Fig. 5 are demonstrating the geometry differences in each set of produced samples. Setting a short dwell time of 0.2s caused significant warpage in the plate and its poor forming quality makes them unacceptable. In addition, the produced samples with a dwell time of 2s also have not acceptable accuracy in geometry due to the surface twist in the plates. On the other hand, the longer dwell time results (5s and 10s) are significantly better in terms of geometry but they still have small curvature of 0.5 mm in comparison to the ideal shape. It is also clear that increasing the dwell time over 5s did not lead to a better geometrical shape.
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S20
28.5±6.9
40.0±6.5
S150
32.5±5.0
34.3±4.9
S300
29.4±2.9
29.2±3.5
The results provided in table 3 demonstrate that the average surface roughness for the produced samples are in similar range regardless of the variation in dwell time and pressing speed. The result is similar to the research that has been conducted previously [5]. Although the measurement was done on the flat side of the plate, the tapered section of the plates is significantly rougher. This phenomenon is usually caused by improper thickness of the material in comparison to the designed tool forming tolerance as highlighted in Fig. 8.
5 4 3 2 1 0 -1
0
20
40
Speed 20mm/s Speed 300mm/s
mm
60
80
100
Speed 150mm/s
mm
Fig. 6. The geometry of upper surface of resulting specimen in fibre direction of different pressing speeds.
Fig. 8. The highlighted areas in the lower image present thickness variation of the material in the process caused by forming tools while the upper image shows constant thickness.
A long dwell time leads to a low overall production speed which is not acceptable for many manufacturers of bulk products. To counter this, it is needed to set up many parallel pressing machines for more feasible production rate.
8 6 4 2 0 -2 -4
10
30
50
mm 70
Speed 20mm/s Speed 300mm/s
90
110
Speed 150mm/s
Fig. 7. The geometry of upper surface of resulting specimen in fibre direction of different pressing speeds.
Fig. 6 and Fig. 7 show that the forming results in 20 and 150 mm/s are quite similar, while the 300 mm/s sample is drastically deformed. Table 3. Resulting average values of surface roughness Rz. (± value denotes to standard deviation). Series
Fiber-Direction (μm)
Cross-Direction (μm)
DT0.2
30.9±1.6
28.1±8.1
DT2
30.4±6.2
33.5±7.5
DT5
32.2±1.7
32.7±3.2
DT10
31±4.4
33.4±3.5
Fig. 9. A sample produced in pressing speed of 300 mm/sec, which caused bumps to tapered section during backstroke due to material being partially stuck to the stationary bottom tool and moving upper tool.
The Fig. 9 and Fig. 10 indicate that the short dwell times of 0.2 s and 2 s lead to curvature in the form. This can be due to
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long polymer setting time or the material is stuck to cold tools and then ripped apart by the backstroke of the press. One reason can also be forming of partial vacuum do the deeper parts of the mould while backstroking.
• •
5
the more significant the difference to the ideal flat surface geometry. Dwell time of over 5 seconds did not lead to significant quality improvement in the final product. Due to the insignificant influence of speed in final quality, typical speeds of hydraulic presses can be used without loss of quality.
Acknowledgement This study was conducted in the Life IP on waste – Towards circular economy in Finland (LIFE-IP CIRCWASTEFINLAND) programme (LIFE15 IPE FI 004). Funding for the programme was received from EU LIFE Integrated projects, companies and cities. Fig. 10. A sample produced with the dwell time of 0.2 seconds. Uneven and bumpy surface shape in the bottom of the sample is clearly visible. Also there is roughness in the tapered section indicating insufficient material thickness.
In speed of 300 mm/s trapped air led to an uneven surface in the fiber direction. Otherwise, the convex curvature was similar to the results of speed 20 mm/s. Although in this paper the underside of the plate was ignored, the plate roughness and quality were always better facing the stationary tool, so it is recommended that the tool mounted to the stationary end plate of the press unit should be facing the customer side of the product. To validate this, it was trialed by changing the tools upside down. In every case, the stationary part was always better quality regardless of the attached tool. Since the air pressure and vacuum played an important role of determining the overall quality of research the addition of the air channels could be investigated in future research. 4. Conclusions In this article press forming quality in terms of geometry and surface roughness of a WPC material consisting of 45% wood fiber, 50% HDPE thermoplastic and 5% of other additives was investigated with profilometers. In the experiments pressing speed and dwell time were varied. In the tests it was found that: • .
Dwell time less than 2 seconds leads to a warped and curved geometry. The shorter the dwell time,
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