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On the occurrence of weld bead porosity during laser vacuum welding of high pressure aluminium die castings
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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 74 (2018) 438–441 www.elsevier.com/locate/procedia th 10th CIRPConference Conferenceon onPhotonic PhotonicTechnologies Technologies [LANE [LANE 2018] 2018] 10 CIRP
On the occurrence weld bead porosity laserFrance vacuum welding of 28thof CIRP Design Conference, Mayduring 2018, Nantes, high pressure aluminium die castings A new methodology to analyze the functional and physical architecture of a, a Fabian *, Sebastian Müller , Klaus family Dilgera identification existing products for Teichmann an assembly oriented product a
Technische Universttät Braunschweig, Langer Kamp 8, 38106 Braunschweig, Germany
Paul Stief *,; fax: Jean-Yves Dantan, Alain Etienne, Ali Siadat * Corresponding author. Tel.: +49-0531-391-955-73 +49-0531-391-955-99. 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]
Due to porosity and incomplete fusion, aluminium high pressure die castings are materials that are known to be difficult to weld. Hereby porosity is mainly caused by hydrogen which is trapped within the weld bead during solidification as a result of insufficient degassing. To Abstract enhance degassing and to reduce the influence of surrounding air, laser vacuum welding was applied within the current study. The main goal was to investigate the occurrence of porosity during laser beam welding of aluminium high pressure die castings. To reach this aim, die casting Inplates today’s business environment, trend towards product variety and customization is unbroken. to thisofdevelopment, the need of were laser welded at variedthe ambient pressuremore and investigated by x-ray computed tomography. TheDue analysis the welds focuses on the agile reconfigurable production emerged to cope with various productspressure and product families. design andshowed optimize production size, and position, amount and shape of systems the detected defects depending on the ambient during welding.ToThe results a dependency systems as well asoftoporosity choose and the optimal product matches, analysis methods are needed. Indeed, most of the known methods aim to of the occurrence the ambient pressure whilstproduct welding. analyze product or one product family on the physical Different families, may differ largely in terms of the number and © 2018aThe Authors. Published by Elsevier Ltd. This islevel. an open accessproduct article under the however, CC BY-NC-ND license © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/) (https://creativecommons.org/licenses/by-nc-nd/4.0/) system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of the the Bayerisches Bayerisches Laserzentrum GmbH. Peer-review under responsibility of Laserzentrum GmbH. these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based Laser on Datum Flow Chain, the physical structure the products analyzed. Functional subassemblies are identified, and Keywords: Laser welding; vacuum welding; Aluminium; Aluminium die of castings; Porosity;isX-ray computed tomography a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation 1. Introduction whereofittheisproposed trappedapproach. during solidification. Thus, weld bead © 2017 The Authors. Published by Elsevier B.V. porosity results [4]. Welding in the region of inclusions can Peer-review underhigh responsibility scientific ofhard the 28th Design Conference 2018.or porosity due to the rapid thermal Aluminium pressure of diethe castings arecommittee known as to CIRP cause incomplete fusion
weld materials, due to the occurrence of porosity and incomplete fusion [1]. The limited weldability is mostly caused by the high pressure die casting process. During the casting process, the die casting mould is filled rapidly with aluminium. As a result of the highly turbulent mould 1.liquid Introduction filling process, release agent residues and other impurities are carried casting part. In addition, solubility of of Due into to the the diefast development in thethe domain hydrogen in aluminium strongly depends on the temperature communication and an ongoing trend of digitization and and increasesmanufacturing by a factor ofenterprises 20 [2] when the temperature digitalization, are facing important exceeds the melting point. During the die casting the challenges in today’s market environments: a process, continuing aluminium is mostly present in the liquid phase, which leads tendency towards reduction of product development times and to an increased hydrogen content. Thethere resulting hydrogen shortened product lifecycles. In addition, is an increasing contaminations and the inclusions affect the weldability in a demand of customization, being at the same time in a global negative way. During welding, the occurring porosity competition with competitors all over the world. This trend,is predominantly caused the dissociation of macro hydridesto[3]. The which is inducing thebydevelopment from micro dissociation process releases hydrogen which diffuses towards markets, results in diminished lot sizes due to augmenting the region of a higher temperature, in particular the melt pool, product varieties (high-volume to low-volume production) [1]. Keywords: Assembly; Design method; Family identification
expansion of the inclusions. In prior research many different welding processes were investigated to reduce welding defects when welding aluminium high pressure die castings. Hereby, electron beam welding was identified as the most feasible welding processrange and laser beam welding manufactured as the most sensitive of the product and characteristics and/or welding process [4]. Aiming to enhance laser beamchallenge welding in of assembled in this system. In this context, the main aluminium high pressure die castings, other studies applied modelling and analysis is now not only to cope with single high frequency beam deflection dual beam welding [6] or products, a limited product range[5], or existing product families, magnetic degassing [7, 8]. Considering laser beam welding of but also to be able to analyze and to compare products to define ferrous metals, laser welding under reduced ambient pressure new product families. It can be observed that classical existing has been investigated precisely during of theclients last or years. The product families are regrouped in function features. investigations have shown that laser vacuum welding has However, assembly oriented product families are hardly to find. various favorable effects, such as an increase of penetration On the product family level, products differ mainly in two depth,characteristics: an calming effect onnumber an meltofpool, a reduction main (i) the components andof (ii)weld the spatter and an enhanced degassing behavior [9–11]. type of components (e.g. mechanical, electrical, electronical). Consequently, the underlying study deals the Classical methodologies considering mainly singlewith products
or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 Theoptimization Authors. Published by Elsevier is an opencauses access article under theregarding CC BY-NC-ND license identify potentials in Ltd. the This existing difficulties an efficient definition and (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 Bayerisches Laserzentrum GmbH.
2212-8271 © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the Bayerisches Laserzentrum GmbH. Peer-review under responsibility of the committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.163
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Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
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investigation on pore formation during the laser beam welding under varied ambient pressure. 2. Materials and Methods
3. Results and Discussion Fig. 1 shows boxplots of the loss of porosity detected within the test specimen using 3D-XCT. Furthermore, the plot contains the mean loss of porosity for each specimen tested as scatter plot as well as median values indicated as horizontal lines. The plot shows that the mean loss of porosity sinks when welding under reduced ambient pressure after reaching a peak at 100 hPa. Additionally, the graph shows that median, mean and span of the loss of porosity fall below the level detected for atmospheric welding when welding at or below 10 hPa.
Fig. 1. Boxplot graphs of the loss of porosity measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values, horizontal lines median values and stars outliers.
Fig. 2 shows the number of pores detected within each sample as scatter plot and boxplots of the mean number of pores to compare the results of each ambient pressure level. From the graphs it can be derived that the average number of pores rises when welding under vacuum condition. The average number of pores per sample steeply increases for welds performed under a vacuum of 100 hPa and decreases with a further reduction of ambient pressure up to 0.1 hPa. The minimum number of pores was found for weldings performed under atmospheric conditions. 800 Average number of pores
Aiming to investigate the influence of the ambient pressure on the occurrence of porosity during laser beam welding, laser welding trails at varied ambient pressure were carried out. The welding trials were performed using casted aluminium plates of the dimensions 260 x 150 x 4 mm made from EN AC-AlSi10MgMn(Fe). Several measures, such as rotor degassing of the melt and evacuation of entrapped air in the mould cavity were taken to achieve a relatively low melt density index (DI) of 0.8 %. Hereby, the density index is a quality measure for the gas content, which is relatively proportional to the hydrogen content, as described in [12]. On the casted plates, bead on plate welds of 250 mm length were processed with a welding speed of 2 m/min. Since the penetration depth in laser vacuum welding is a function of ambient pressure (p) and laser power (P) [13, 14], the welding trials were carried out with four different combinations of ambient pressure (1000 hPa / 100 hPa / 10 hPa / 0.1 hPa) and laser power (3,2 kW / 2,96 kW / 2,8 kW / 2,8 kW). The laser power was adjusted for each pressure level to achieve full penetration welding. The laser beam welding trials were carried out using a solid state disk laser (TRUMPF TruDisk6002D) with a wavelength of λ = 1030 nm and a beam parameter product of BPP = 8.0 mm × mrad. Moreover, a TRUMPF BEO D70 processing optic with a focal length of 300 mm and an aspect ratio of 1.5:1.0 was used. Thus, the resulting focal spot size was 300 µm for the applied optical fiber diameter of 200 µm. From each weld bead, seven test specimen of 13 mm width were taken and tested by x-ray computed tomography (XCT) analysis. All XCT-scans were carried out using a GE v|tome|x x-ray computed tomography scanner and a proprietary analysis software package. The scans were conducted with a beam current of IB = 250 mA, an accelerating voltage of UB = 220 kV and an exposure time of tex = 100 ms. Every scan consisted of 1440 images, sized 1000 x 1000 pixels and a resulting voxel size of vx = 45 µm.
700 600 500 400 300 200 100 0
1000
100 10 Ambient pressure / hPa
0,1
Fig. 2. Boxplot graphs of the average number of pores measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
The boxplots shown in Fig. 3 present the mean pore diameter per probe as a function of the ambient pressure during laser beam welding. The mean pore diameter for welds performed under vacuum and atmospheric condition shows a decline of the median values from ~ 0.41 mm for p = 1000 hPa to ~ 0.35 mm for p ≤ 100 hPa. In addition, the spread and the inter quantile range of the mean pore diameter drop steeply
Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
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3
when welding below atmospheric pressure. Hereby the absolute reduction seems to have no significant influence on the average pore size.
0,48 0,45
a)
Ψ = 0.51
0,43 0,38 0,35 0,33 0,30
1000
100 10 0,1 Ambient pressure / hPa
Fig. 3. Boxplot graphs of the average pore diameter measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
The graphs presented in Fig. 1, Fig. 2 and Fig. 3 show the mean loss of porosity, the average number of pores and the mean pore diameter as functions of the ambient pressure during the laser welding process. The figures indicate that welding under reduced ambient pressure causes a diminution of the average loss of porosity. Thereby, welding below atmospheric pressure (p ≤ 100 hPa) leads to an increased number of pores and a reduced average pore diameter. To describe the geometry of the pores detected by 3D-XCT, the sphericity ψ of the pores was calculated and analyzed for each test specimen. Hereby, the sphericity is a measure of how far a given object equals a perfect sphere. Equation 1 gives the definition of the sphericity as a function of the volume (VP) and the surface area (AP) of a particle the according to [15]. As it can be taken from the formula, a perfect sphere is calculated to 𝛹𝛹𝛹𝛹 = 1. For values smaller than 𝛹𝛹𝛹𝛹 = 1 the shape becomes correspondingly more fractured and irregular. 1
b)
Ψ = 0.56
c)
Ψ = 0.67
Fig. 4. Sample pores of different sphericity
0,40
2
𝜋𝜋𝜋𝜋 3 ∗ (𝑉𝑉𝑉𝑉𝑝𝑝𝑝𝑝 )3 𝛹𝛹𝛹𝛹 = 𝐴𝐴𝐴𝐴𝑝𝑝𝑝𝑝
(1)
Fig. 4 presents three isometric images of sample pores extracted from a 3D-XCT scan as well as the calculated values for the sphericity. From the images in Fig. 4 it can be seen that a change of the sphericity of about 0.11 from Fig. 4a) to Fig. 4c) results in a visual impact on the appearance of the pore.
The mean sphericity for each welding trial and the corresponding boxplots are given in Fig. 5. The figure shows that specimen welded under atmospheric conditions contain more pores with a low sphericity while other samples welded under reduced ambient pressure contain more spherical pores. Moreover, the sphericity is sensible to a further reduction of ambient pressure below p ≤ 100 hPa. In addition, spread and inter quantile range of the mean sphericity are lower when welding under vacuum condition. 0,59 Mean sphericity
Mean pore diameter / mm
0,50
0,58 0,57 0,56 0,55 0,54 0,53
1000
100 10 Ambient pressure / hPa
0,1
Fig. 5. Boxplots of the mean sphericity per sample measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
4. Conclusions The findings presented above indicate that laser beam welding under reduced ambient pressure leads to a significant drop of the mean loss of porosity. Thereby, the loss of porosity is mainly driven by a reduction of the pore size despite an increase of the number of pores. In addition, it was found, that the sphericity of the pores rises when welding under reduced ambient pressure.
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Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
Acknowledgements The IGF research project no. 18.156 N of the German Welding Society (DVS), Aachener Straße 172, 40223 Düsseldorf has been funded by the German Federation of Industrial Research Associations (AiF) within the programme for sponsorship by Industrial Joint Research (IGF) of the German Federal Ministry of Economic Affairs and Energy based on an enactment of the German Parliament. References [1] Schulze, G.: Die Metallurgie des Schweißens. Eisenwerkstoffe, nichteisenmetallische Werkstoffe, 4., neu bearb. Aufl. Heidelberg [u.a.] 2010. [2] Ostermann, F.: Anwendungstechnologie Aluminium, 3rd ed (OnlineAusg.). Berlin, Heidelberg 2015. [3] Wiesner, S.: Wirtschaftliche Herstellung von gasarmem, schweißbarem Aluminium-Druckguß, Dissertation. Braunschweig 2003. [4] Herrmann, C.; Pries, H.; Hartmann, G.: Energie- und ressourceneffiziente Produktion von Aluminiumdruckguss. Berlin, Heidelberg 2013. [5] Dittrich, D.; Standfuß, J.; Jahn, A.: Neuartiges Verfahren zum druckdichten Laserstrahlschweißen von Aluminium aus AtmosphärenDruckguss. In: DVS Media GmbH (Hrsg.): DVS Congress 2016. Große Schweißtechnische Tagung, DVS Studentenkongress. Vorträge der Veranstaltungen in Leipzig am 19. und 20. September 2016. Düsseldorf 2016. [6] Winkler, R.: Porenbildung beim Laserstrahlschweissen von AluminiumDruckguss, Dissertation. Stuttgart 2004.
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[7] Fritzsche, A.; Hilgenberg, K.; Teichmann, F.; Pries, H.; Dilger, K.; Rethmeier, M.: Improved degassing in laser beam welding of aluminum die casting by an electromagnetic field. In: Journal of Materials Processing Technology 253 (2018), S. 51–56. [8] Fritzsche, A.; Hilgenberg, K.; Teichmann, F.; Pries, H.; Rethmeier, M.: Electromagnetic porosity reduction in laser beam welding of die-cast aluminum alloy. In: Wissenschaftliche Gesellschaft Lasertechnik e.V. (WLT) (Hrsg.): Lasers in Manufacturing 2017 2017. [9] Börner, C.; Garthoff, C.; Pries, H.; Dilger, K.: Possibilities of Improving Weld Seam Quality in Laser Welding of Aluminium Die Cast. Paper 404: ICALEO. The 33rd International Congress on Applications of Lasers & Electro-Optics: October 19-23, 2014. Orlando, F.L. 2014. [10] Reisgen, U.; Olschok, S.; Jakobs, S.; Turner, C.: Laser beam welding under vacuum of high grade materials. In: Welding in the World 60 (2016) 3, S. 403–13. [11] Longerich, S.: Untersuchung zum Laserstrahlschweißen unter Vakuum im Vergleich mit dem Elektronenstrahlschweißen, Dissertation. Aachen 2011. [12] BDG - Bundesverband der Deutschen Gießerei-Industrie: P 230: Unterdruck-Dichteprüfung - P 230 Bestimmung des Dichte - Index für Aluminiumgusslegierungen (2015) 230. Düsseldorf. Abrufdatum 31.05.2017. [13] Katayama, S.; Kobayashi, Y.; Mizutani, M.; Matsunawa, A.: Effect of vacuum on penetration and defects in laser welding. In: Journal of Laser Applications 13 (2001) 5, S. 187. [14] Katayama, S.; Abe, Y.; Mizutani, M.; Kawahito, Y.: Deep penetration welding with high-power laser under vacuum. In: Transactions of JWRI 40 (2011) 1, S. 15–19. [15] Wadell, H.: Volume, Shape, and Roundness of Quartz Particles. In: The Journal of Geology 43 (1935) 3, S. 250–80.
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Procedia CIRP 00 (2018) 000–000
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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 74 (2018) 438–441 www.elsevier.com/locate/procedia th 10th CIRPConference Conferenceon onPhotonic PhotonicTechnologies Technologies [LANE [LANE 2018] 2018] 10 CIRP
On the occurrence weld bead porosity laserFrance vacuum welding of 28thof CIRP Design Conference, Mayduring 2018, Nantes, high pressure aluminium die castings A new methodology to analyze the functional and physical architecture of a, a Fabian *, Sebastian Müller , Klaus family Dilgera identification existing products for Teichmann an assembly oriented product a
Technische Universttät Braunschweig, Langer Kamp 8, 38106 Braunschweig, Germany
Paul Stief *,; fax: Jean-Yves Dantan, Alain Etienne, Ali Siadat * Corresponding author. Tel.: +49-0531-391-955-73 +49-0531-391-955-99. 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]
Due to porosity and incomplete fusion, aluminium high pressure die castings are materials that are known to be difficult to weld. Hereby porosity is mainly caused by hydrogen which is trapped within the weld bead during solidification as a result of insufficient degassing. To Abstract enhance degassing and to reduce the influence of surrounding air, laser vacuum welding was applied within the current study. The main goal was to investigate the occurrence of porosity during laser beam welding of aluminium high pressure die castings. To reach this aim, die casting Inplates today’s business environment, trend towards product variety and customization is unbroken. to thisofdevelopment, the need of were laser welded at variedthe ambient pressuremore and investigated by x-ray computed tomography. TheDue analysis the welds focuses on the agile reconfigurable production emerged to cope with various productspressure and product families. design andshowed optimize production size, and position, amount and shape of systems the detected defects depending on the ambient during welding.ToThe results a dependency systems as well asoftoporosity choose and the optimal product matches, analysis methods are needed. Indeed, most of the known methods aim to of the occurrence the ambient pressure whilstproduct welding. analyze product or one product family on the physical Different families, may differ largely in terms of the number and © 2018aThe Authors. Published by Elsevier Ltd. This islevel. an open accessproduct article under the however, CC BY-NC-ND license © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/) (https://creativecommons.org/licenses/by-nc-nd/4.0/) system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of the the Bayerisches Bayerisches Laserzentrum GmbH. Peer-review under responsibility of Laserzentrum GmbH. these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based Laser on Datum Flow Chain, the physical structure the products analyzed. Functional subassemblies are identified, and Keywords: Laser welding; vacuum welding; Aluminium; Aluminium die of castings; Porosity;isX-ray computed tomography a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation 1. Introduction whereofittheisproposed trappedapproach. during solidification. Thus, weld bead © 2017 The Authors. Published by Elsevier B.V. porosity results [4]. Welding in the region of inclusions can Peer-review underhigh responsibility scientific ofhard the 28th Design Conference 2018.or porosity due to the rapid thermal Aluminium pressure of diethe castings arecommittee known as to CIRP cause incomplete fusion
weld materials, due to the occurrence of porosity and incomplete fusion [1]. The limited weldability is mostly caused by the high pressure die casting process. During the casting process, the die casting mould is filled rapidly with aluminium. As a result of the highly turbulent mould 1.liquid Introduction filling process, release agent residues and other impurities are carried casting part. In addition, solubility of of Due into to the the diefast development in thethe domain hydrogen in aluminium strongly depends on the temperature communication and an ongoing trend of digitization and and increasesmanufacturing by a factor ofenterprises 20 [2] when the temperature digitalization, are facing important exceeds the melting point. During the die casting the challenges in today’s market environments: a process, continuing aluminium is mostly present in the liquid phase, which leads tendency towards reduction of product development times and to an increased hydrogen content. Thethere resulting hydrogen shortened product lifecycles. In addition, is an increasing contaminations and the inclusions affect the weldability in a demand of customization, being at the same time in a global negative way. During welding, the occurring porosity competition with competitors all over the world. This trend,is predominantly caused the dissociation of macro hydridesto[3]. The which is inducing thebydevelopment from micro dissociation process releases hydrogen which diffuses towards markets, results in diminished lot sizes due to augmenting the region of a higher temperature, in particular the melt pool, product varieties (high-volume to low-volume production) [1]. Keywords: Assembly; Design method; Family identification
expansion of the inclusions. In prior research many different welding processes were investigated to reduce welding defects when welding aluminium high pressure die castings. Hereby, electron beam welding was identified as the most feasible welding processrange and laser beam welding manufactured as the most sensitive of the product and characteristics and/or welding process [4]. Aiming to enhance laser beamchallenge welding in of assembled in this system. In this context, the main aluminium high pressure die castings, other studies applied modelling and analysis is now not only to cope with single high frequency beam deflection dual beam welding [6] or products, a limited product range[5], or existing product families, magnetic degassing [7, 8]. Considering laser beam welding of but also to be able to analyze and to compare products to define ferrous metals, laser welding under reduced ambient pressure new product families. It can be observed that classical existing has been investigated precisely during of theclients last or years. The product families are regrouped in function features. investigations have shown that laser vacuum welding has However, assembly oriented product families are hardly to find. various favorable effects, such as an increase of penetration On the product family level, products differ mainly in two depth,characteristics: an calming effect onnumber an meltofpool, a reduction main (i) the components andof (ii)weld the spatter and an enhanced degassing behavior [9–11]. type of components (e.g. mechanical, electrical, electronical). Consequently, the underlying study deals the Classical methodologies considering mainly singlewith products
or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 Theoptimization Authors. Published by Elsevier is an opencauses access article under theregarding CC BY-NC-ND license identify potentials in Ltd. the This existing difficulties an efficient definition and (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 Bayerisches Laserzentrum GmbH.
2212-8271 © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the Bayerisches Laserzentrum GmbH. Peer-review under responsibility of the committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.163
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Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
439
investigation on pore formation during the laser beam welding under varied ambient pressure. 2. Materials and Methods
3. Results and Discussion Fig. 1 shows boxplots of the loss of porosity detected within the test specimen using 3D-XCT. Furthermore, the plot contains the mean loss of porosity for each specimen tested as scatter plot as well as median values indicated as horizontal lines. The plot shows that the mean loss of porosity sinks when welding under reduced ambient pressure after reaching a peak at 100 hPa. Additionally, the graph shows that median, mean and span of the loss of porosity fall below the level detected for atmospheric welding when welding at or below 10 hPa.
Fig. 1. Boxplot graphs of the loss of porosity measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values, horizontal lines median values and stars outliers.
Fig. 2 shows the number of pores detected within each sample as scatter plot and boxplots of the mean number of pores to compare the results of each ambient pressure level. From the graphs it can be derived that the average number of pores rises when welding under vacuum condition. The average number of pores per sample steeply increases for welds performed under a vacuum of 100 hPa and decreases with a further reduction of ambient pressure up to 0.1 hPa. The minimum number of pores was found for weldings performed under atmospheric conditions. 800 Average number of pores
Aiming to investigate the influence of the ambient pressure on the occurrence of porosity during laser beam welding, laser welding trails at varied ambient pressure were carried out. The welding trials were performed using casted aluminium plates of the dimensions 260 x 150 x 4 mm made from EN AC-AlSi10MgMn(Fe). Several measures, such as rotor degassing of the melt and evacuation of entrapped air in the mould cavity were taken to achieve a relatively low melt density index (DI) of 0.8 %. Hereby, the density index is a quality measure for the gas content, which is relatively proportional to the hydrogen content, as described in [12]. On the casted plates, bead on plate welds of 250 mm length were processed with a welding speed of 2 m/min. Since the penetration depth in laser vacuum welding is a function of ambient pressure (p) and laser power (P) [13, 14], the welding trials were carried out with four different combinations of ambient pressure (1000 hPa / 100 hPa / 10 hPa / 0.1 hPa) and laser power (3,2 kW / 2,96 kW / 2,8 kW / 2,8 kW). The laser power was adjusted for each pressure level to achieve full penetration welding. The laser beam welding trials were carried out using a solid state disk laser (TRUMPF TruDisk6002D) with a wavelength of λ = 1030 nm and a beam parameter product of BPP = 8.0 mm × mrad. Moreover, a TRUMPF BEO D70 processing optic with a focal length of 300 mm and an aspect ratio of 1.5:1.0 was used. Thus, the resulting focal spot size was 300 µm for the applied optical fiber diameter of 200 µm. From each weld bead, seven test specimen of 13 mm width were taken and tested by x-ray computed tomography (XCT) analysis. All XCT-scans were carried out using a GE v|tome|x x-ray computed tomography scanner and a proprietary analysis software package. The scans were conducted with a beam current of IB = 250 mA, an accelerating voltage of UB = 220 kV and an exposure time of tex = 100 ms. Every scan consisted of 1440 images, sized 1000 x 1000 pixels and a resulting voxel size of vx = 45 µm.
700 600 500 400 300 200 100 0
1000
100 10 Ambient pressure / hPa
0,1
Fig. 2. Boxplot graphs of the average number of pores measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
The boxplots shown in Fig. 3 present the mean pore diameter per probe as a function of the ambient pressure during laser beam welding. The mean pore diameter for welds performed under vacuum and atmospheric condition shows a decline of the median values from ~ 0.41 mm for p = 1000 hPa to ~ 0.35 mm for p ≤ 100 hPa. In addition, the spread and the inter quantile range of the mean pore diameter drop steeply
Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
440
3
when welding below atmospheric pressure. Hereby the absolute reduction seems to have no significant influence on the average pore size.
0,48 0,45
a)
Ψ = 0.51
0,43 0,38 0,35 0,33 0,30
1000
100 10 0,1 Ambient pressure / hPa
Fig. 3. Boxplot graphs of the average pore diameter measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
The graphs presented in Fig. 1, Fig. 2 and Fig. 3 show the mean loss of porosity, the average number of pores and the mean pore diameter as functions of the ambient pressure during the laser welding process. The figures indicate that welding under reduced ambient pressure causes a diminution of the average loss of porosity. Thereby, welding below atmospheric pressure (p ≤ 100 hPa) leads to an increased number of pores and a reduced average pore diameter. To describe the geometry of the pores detected by 3D-XCT, the sphericity ψ of the pores was calculated and analyzed for each test specimen. Hereby, the sphericity is a measure of how far a given object equals a perfect sphere. Equation 1 gives the definition of the sphericity as a function of the volume (VP) and the surface area (AP) of a particle the according to [15]. As it can be taken from the formula, a perfect sphere is calculated to 𝛹𝛹𝛹𝛹 = 1. For values smaller than 𝛹𝛹𝛹𝛹 = 1 the shape becomes correspondingly more fractured and irregular. 1
b)
Ψ = 0.56
c)
Ψ = 0.67
Fig. 4. Sample pores of different sphericity
0,40
2
𝜋𝜋𝜋𝜋 3 ∗ (𝑉𝑉𝑉𝑉𝑝𝑝𝑝𝑝 )3 𝛹𝛹𝛹𝛹 = 𝐴𝐴𝐴𝐴𝑝𝑝𝑝𝑝
(1)
Fig. 4 presents three isometric images of sample pores extracted from a 3D-XCT scan as well as the calculated values for the sphericity. From the images in Fig. 4 it can be seen that a change of the sphericity of about 0.11 from Fig. 4a) to Fig. 4c) results in a visual impact on the appearance of the pore.
The mean sphericity for each welding trial and the corresponding boxplots are given in Fig. 5. The figure shows that specimen welded under atmospheric conditions contain more pores with a low sphericity while other samples welded under reduced ambient pressure contain more spherical pores. Moreover, the sphericity is sensible to a further reduction of ambient pressure below p ≤ 100 hPa. In addition, spread and inter quantile range of the mean sphericity are lower when welding under vacuum condition. 0,59 Mean sphericity
Mean pore diameter / mm
0,50
0,58 0,57 0,56 0,55 0,54 0,53
1000
100 10 Ambient pressure / hPa
0,1
Fig. 5. Boxplots of the mean sphericity per sample measured by 3D-XCT analysis for varied ambient pressure. Squares indicate mean values and stars outliers.
4. Conclusions The findings presented above indicate that laser beam welding under reduced ambient pressure leads to a significant drop of the mean loss of porosity. Thereby, the loss of porosity is mainly driven by a reduction of the pore size despite an increase of the number of pores. In addition, it was found, that the sphericity of the pores rises when welding under reduced ambient pressure.
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Fabian Teichmann et al. / Procedia CIRP 74 (2018) 438–441 Author name / Procedia CIRP 00 (2018) 000–000
Acknowledgements The IGF research project no. 18.156 N of the German Welding Society (DVS), Aachener Straße 172, 40223 Düsseldorf has been funded by the German Federation of Industrial Research Associations (AiF) within the programme for sponsorship by Industrial Joint Research (IGF) of the German Federal Ministry of Economic Affairs and Energy based on an enactment of the German Parliament. References [1] Schulze, G.: Die Metallurgie des Schweißens. Eisenwerkstoffe, nichteisenmetallische Werkstoffe, 4., neu bearb. Aufl. Heidelberg [u.a.] 2010. [2] Ostermann, F.: Anwendungstechnologie Aluminium, 3rd ed (OnlineAusg.). Berlin, Heidelberg 2015. [3] Wiesner, S.: Wirtschaftliche Herstellung von gasarmem, schweißbarem Aluminium-Druckguß, Dissertation. Braunschweig 2003. [4] Herrmann, C.; Pries, H.; Hartmann, G.: Energie- und ressourceneffiziente Produktion von Aluminiumdruckguss. Berlin, Heidelberg 2013. [5] Dittrich, D.; Standfuß, J.; Jahn, A.: Neuartiges Verfahren zum druckdichten Laserstrahlschweißen von Aluminium aus AtmosphärenDruckguss. In: DVS Media GmbH (Hrsg.): DVS Congress 2016. Große Schweißtechnische Tagung, DVS Studentenkongress. Vorträge der Veranstaltungen in Leipzig am 19. und 20. September 2016. Düsseldorf 2016. [6] Winkler, R.: Porenbildung beim Laserstrahlschweissen von AluminiumDruckguss, Dissertation. Stuttgart 2004.
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