GEOMETRIC COMPLEXITY ANALYSIS IN AN INTEGRATIVE TECHNOLOGY EVALUATION MODEL (ITEM) FOR SELECTIVE LASER MELTING (SLM) #

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1 GEOMETRIC COMPLEXITY ANALYSIS IN AN INTEGRATIVE TECHNOLOGY EVALUATION MODEL (ITEM) FOR SELECTIVE LASER MELTING (SLM) # S. Merkt 1*, C. Hinke 2, H. Schleifenbum 3 & H. Voswinckel 4 1, 2 Deprtment of Lser Technology RWTH Achen University, Germny 1 simon.merkt@ilt.frunhofer.de; 2 christin.hinke@ilt.frunhofer.de 3 Frunhofer Institute for Lser Technology (ILT), Germny henrich.schleifenbum@ilt.frunhofer.de 4 Institute of Metl Forming (IBF) RWTH Achen University, Germny voswinckel@ibf.rwth-chen.de ABSTRACT Selective lser melting (SLM) is becoming n economiclly vible choice for mnufcturing complex seril prts. This pper focuses on geometric complexity nlysis s prt of the integrtive technology evlution model (ITEM) presented here. In contrst to conventionl evlution methodologies, the ITEM considers interctions between product nd process innovtions generted by SLM. The evlution of mnufcturing processes tht compete with SLM is the min gol of ITEM. The pper includes complexity nlysis of test prt from Festo AG. The pper closes with discussion of how the expnded design freedom of SLM cn be used to improve compny opertions, nd how the complexity nlysis presented here cn be seen s strting point for feture-bsed complexity nlysis. OPSOMMING Selektiewe lsersmelting word geleidelik n gngbre ekonomiese keuse vir die vervrdiging vn opeenvolgende komplekse onderdele. Die nvorsing is toegespits op die ontleding vn meetkundige kompleksiteit s n gedeelte vn n integrerende tegnologiese evlueringsmodel. Gemeet teen konvensionele evlueringsmodelle behndel die genoemde metode interksies tussen produkte- en prosesinnovsies wt gegenereer word. Die nvorsing behndel n kompleksiteitsontleding vn n toetsonderdeel vn die firm FESTO AG. Die resultt toon hoe kompleksiteits-nlise gebruik kn word s die vertrekpunt vir eienskpsgebseerde nlise. 1 The uthor is enrolled for PhD degree t the RWTH Achen University. 2 The uthor is enrolled for PhD degree t the RWTH Achen University. 3 The uthor ws enrolled for PhD degree t the RWTH Achen University. 4 The uthor is enrolled for PhD degree t the RWTH Achen University. * Corresponding uthor. # This rticle is n extended version of pper presented t the 2011 RAPDASA conference South Africn Journl of Industril Engineering, July 2012, Vol 23 (2): pp

2 1. INTRODUCTION: STATE-OF-THE-ART / MOTIVATION SLM is mnufcturing process tht builds up metllic or cermic prts lyer by lyer directly from 3D-CAD dt [1]. The prts re fbricted from metl or cermic powders on substrte. The powder on the substrte is selectively melted by lser bem ccording to the sliced CAD model (see Fig. 1). After the first lyer is melted, the substrte plte is lowered, nd new powder is deposited on top of the first lyer. This new lyer is selectively melted, nd the lyers (pproximtely 50µm) re metlliclly bonded. The finl component is thus built of mny single lyers. The density of the prts is bout 100%, nd the mechnicl properties cn even bet conventionl mnufcturing processes such s diecsting [2]. In ddition, novel geometries cn be generted (the only limittion being the imgintion of the designer) nd cn be used to improve the performnce of conventionl product designs [3, 4]. Selective Lser Melting Deposition of powder Melting of the powder ccording scn strtegy 3D-CAD model in slices, determintion of best scn strtegy nd process prmeters Novel geometric products Metllic powder, powder hndling Preprocessing Lowering substrte plte Build process Postprocessing Figure 1: Schemtic SLM process Typicl build rtes re round 1.2 mm 3 /s nd depend on mteril nd qulity requirements. To improve the build rte by fctor of ten, the Frunhofer Institute for Lser Technology (ILT) designed nd built n innovtive lser. To rech the desired build rte improvement, it investigted incresing the lser power from 200/400 W to 1 kw (high power selective lser melting), nd implementing new scnning strtegy (skin-core strtegy) [5]. These process improvements helped to build luminium prts quickly tht re suited for eco-design (due to their low weight nd superior mechnicl nd chemicl properties). Stte-of-the-rt build-rtes for luminium (5 mm 3 /s) could be improved by fctor of four to five; up to 21 mm 3 /s by using high power selective lser melting (HPSLM) [6]. These improvements resulted in higher process productivity, nd enbled the economic production of series components (direct mnufcturing) in smll btch sizes. SLM cn even bet conventionl processes if complex products with high mount of functionl integrtion need to be fbricted [7]. New methods to exploit the potentil of SLM for mss customistion re investigted to further enhnce the ppliction field. Trends tht follow globlistion nd the sturtion of consumer demnd, such s mss customistion nd individulistion, will further rise the need for highly flexible nd individulised production. These requirements re seen s one of the big chllenges in mnufcturing technology [8]. SLM is suitble solution to fcing this chllenge by producing highly individulised products t low prices. Incresing complexity leds to exponentilly incresing costs of conventionl production technologies for smll series production (see Fig. 2). In contrst to conventionl production 98

3 technologies, mnufcturing costs for dditive mnufcturing (AM) technologies like SLM do not normlly increse with higher geometric complexity. In some cses, higher geometric complexity leds to higher preprocessing costs of SLM (e.g. pltform ssembly, bcking, scnning strtegy, etc.). At the sme time, high geometric complexity often mens lower build volumes: this decreses the process time for SLM nd equlises the dditionl preprocessing costs. Costs (for smll lot sizes, high dependnce of process nd dimensions) Additive Mnufcturing Conventionl mnufcturing technologies tody complexityfor free Sme costs Higher mrgins Higher profits topology optimiztion functionl integrtion etc. tomorrow complexity brek even Stndrd Design Design for conventionl mnufcturing technologies Design for Additive Mnufcturing Utiliztion of dditionl design freeddom Figure 2: The ide of Complexity for Free ccording to [9] Geometric complexity For products tht exceed stndrd design, SLM cn be economiclly superior due to pprent cost drivers of conventionl technologies. Functionlly-optimised designs ( design for AM ) cn improve product performnce t the sme cost. This ide of complexity for free, using the dditionl design freedom of SLM, is shown in Figure 2. Tody severl pplictions exceed certin mount of economicl stndrd design ( complexity brekeven ) nd re mnufctured more economiclly with SLM. The dditionl design freedom through SLM could be used for future pplictions tht use geometric complexity to improve product performnce t the sme costs (see Fig. 2). Furthermore, SLM enbles innovtive business models through product individulistion becuse costs re independent of lot size in contrst with conventionl mnufcturing processes. 2. INTEGRATED TECHNOLOGY EVALUATION MODEL (ITEM) The generl objective when evluting technologies is to determine the impct of technology decisions on given vlution stndrd [9]. Technology evlution is n importnt tool for technology mngement; it supports the selection, plnning, controlling, nd positioning of technology. Without trgeted technology mngement, it is difficult for compnies to succeed when their surroundings chnge, nd to fulfil incresing mrket/product requirements. Adpttion to these chnges needs to be performed t the technologicl level. Long-term strtegic technology decisions cn led to significnt competitive dvntges, nd build key point for the future vibility of compnies. There re severl pproches to generl technology evlution in production tht focus on different evlution criteri. None of them cn integrte ll the criteri relevnt to supporting comprehensive decision-mking process. None of the decision methods listed by [10] cn support the decision-mking process if highly innovtive mnufcturing methods re evluted becuse of their focus either on product or process. Highly innovtive mnufcturing technologies such s SLM hve n 99

4 impct on both product nd process design t the sme time. Most pproches do not cover interctions between product nd process innovtions [11]. To consider these interctions, n ITEM for SLM will be introduced to extend stte-of-the-rt decision frmeworks (see Fig. 3). Unlike conventionl technology evlution methods, the ITEM mtches (mong other things) mnufcturing process limittions nd product requirements, to determine suitble mnufcturing method. The ITEM focuses on the min decision prmeters, nd helps to ensure systemtic plnning cycles, s well s prllel design nd mnufcturing ctivities, to shorten the development times of new products. Since the process limits re considered inflexible, t lest in the short term, the individul product design is of mjor importnce for product development [12]. 1. Level: Productprocess nlysis (technicl level) Integrted product process model (PPD-model) Mtching process limittionsnd product requirements Result: Technicl design relted rnking of mnufcturingprocesses 2. Level: Economicnlysis (economiclevel) Product design nd mnufcturingprocess considered inflexible Economiccomprison of mnufcturingprocesses with finncil rtios / complexity nlysis Result: Economic Rnking of mnufcturingprocesses 3. Level: Economicpotentil nlysis (potentil level) Product design nd mnufcturingprocess considered flexible Innovtion nlysis to improve product performnce Cost / benefit rtio s key indictor Result: Rnking fter redesign 4. Level: Technology potentil nlysis(potentil level) Portfolio nlysis Consideringof compny specificpotentil nd strtegy potentil Result: Compny relted decision of ppliction technology Figure 3: Evlution levels of the integrtive technology evlution model for SLM In order to use the potentil of innovtive mnufcturing processes, four different levels of the ITEM need to be considered to determine the suitbility of mnufcturing processes on ny specific ppliction (see Fig. 3). The integrted product process design model (PPD-model) builds the first level of the ITEM, nd covers ll techniclly-relted decision prmeters. Severl key indictors re mtched with product requirements to determine ll techniclly-suitble mnufcturing technologies. On the second level, n economic rnking is determined by compring mnufcturing technologies with finncil rtios. A complexity nlysis helps to group products into different mnufcturing groups to derive first economic ssumptions. The product design nd mnufcturing process is considered flexible in the economic potentil nlysis on Level 3 of the ITEM. This llows the designer to improve product performnce by using the potentil of innovtive methods nd to compre them using cost/benefit rtio. A technology potentil nlysis ends the evlution process of the ITEM by considering compny-specific mnufcturing potentils (e.g. expnsion on other products) nd strtegic possibilities (e.g. mss customistion) tht re generted through innovtive technologies like SLM. 100

5 After completing ll four stges of the ITEM, decision cn be mde regrding the most suitble production technologies. The complexity nlysis from Level 2 is the focus of this investigtion. 3. GEOMETRIC COMPLEXITY ANALYSIS OF A TEST PART Complexity nlysis my help to determine the right mnufcturing technologies for specific pplictions. As shown in Figure 4, geometric complexity nd lot size re importnt criteri for the selection of mnufcturing process. Figure 4: Two-dimensionl selection pttern for mnufcturing processes [7] Highly complex products re generlly more suitble for SLM becuse geometric complexity leds to incresed costs when conventionl technologies re used [7, 13]. Geometric (shpe) complexity, for exmple, increses the mnufcturing time (costs) for mchined prts due to dditionl set-ups, the number of tool chnges, nd the mount of removl volume. High speed cutting (HSC) nd csting processes hve lower limits in chievble geometric complexity thn dditive mnufcturing technologies like SLM. SLM is not yet pplicble to high lot size, for resons relted to productivity. Thus mnufcturing gps exist for highly complex prts s well s for high lot size, nd t certin complexity level even tht cnnot be chieved by SLM (see Fig. 4). Bsed on 3-D CAD models in the STL-formt, severl rtios cn be pplied to determine the geometric complexity of test prt from Festo AG (see Fig. 5). Vlentn [14] hs introduced rtios to determine geometric complexity bsed on the STL formt. The following rtios re pplied to the Festo test prt, nd compred with selection of typicl mchined, cst, nd SLM prts: Prts volume/number_of_fcets Prts volume/surfce re Prts volume/block volume 101

6 1 cm Figure 5: Festo test prt The STL formt is fcet-bsed representtion tht pproximtes surfce nd solid entities only. Difficult surfces nd solids re represented by high number of fcets in the STL formt. A low rtio of volume/number_of_fcets mens high geometric complexity. As shown in Figure 6, the Festo test prt hs the second lowest prts volume/number_of_fcets rtio. Only typicl SLM prts hve lower rtio. Note tht the die-cst Festo prt hs four-time lower rtio thn the verge vlue of the investigted csting prts. This indictes reltively high geometric complexity of the test prt. 102 Figure 6: Complexity nlysis bsed on prts volume/number_of_fcets rtio The second rtio tht cn be used to estimte geometric complexity is prts volume/surfce re. This rtio cn differentite mssive prts from prts with high number of free-form surfces nd curved surfces [15]. Agin, the Festo test prt hs lower vlue thn the verge reference vlue of cst nd mchined prts (see Fig. 7). The verge of SLM prts is significntly lower thn the vlue of the Festo test prt. In contrst to cst prts tht need dditionl volumes due to design restrictions, lmost no dditionl volume needs to be built up by SLM. In comprison with mchined prts, only functionl volume is built up by the genertive mnufcturing process SLM. This leds to extremely low vlues for prts volume/surfce re in comprison with other mnufcturing

7 techniques. For the Festo test prt, prts volume/surfce re rtio still indictes medium high geometric complexity. Figure 7: Complexity nlysis bsed on prts volume/surfce re rtio The lst rtio for estimting geometric complexity is the prts volume/block volume rtio. The block volume cn be clculted by multiplying the mximum vlues in the x-, y- nd z- directions. Similrly to the rtio of prts volume/surfce re, this rtio cn be used to differentite mssive prts from complex prts with high number of free-form surfces. The Festo test prt shows reltively high vlue of prts volume/block volume (see Fig. 8). The high vlue for prts volume/block volume indictes tht the Festo test prt is compct one with reltively low geometric complexity. Figure 8: Complexity nlysis bsed on prts volume/block volume rtio All in ll, the geometric complexity nlysis of the three rtios s prt of the ITEM indictes medium-high to high geometric complexity of the Festo test prt. The nlysis suggests tht the prt is suitble for economic mnufcturing by SLM. 103

8 4. CONCLUSION AND OUTLOOK Specific cost drivers of mnufcturing processes re minly influenced by the geometric complexity of the product. The complexity nlysis presented here s prt of the ITEM helps to determine geometric complexity, nd supports the selection of suitble mnufcturing process. In generl, highly complex products hve low rtios of volume/number_of_fcets, prts volume/surfce re, nd prts volume/block volume, nd re more suitble for SLM. Products cn be grouped by compring their rtios with the verge rtio vlues of the production technology groups (csting, mchining, nd SLM). In ddition to the complexity nlysis, technicl nd economic nlysis (included in the ITEM) is necessry to mke n overll decision regrding the best mnufcturing process. Geometric complexity nlysis llows severl ssumptions to be mde, which re summrised in the following wy. Besides the well-known dvntges of the design flexibility of SLM, functionl integrtion cn led to significnt improvements in compny opertions. The ide of complexity for free illustrtes the possibility of integrting dditionl fetures in products to improve product performnce t the sme costs (see economic potentil nlysis on Level 3 of ITEM). According to the well-known Kno model, SLM gives dditionl spce to integrting excitement fctors, thus improving product performnce nd customer stisfction. Functionl optimised designs nd more individulised designs follow this ide to better fulfil mrket demnds. Figure 9 summrises the economic leverge effect of SLM in the three dimensions of cost, time, nd qulity enbled by the possibility of integrting dditionl complexity (e.g. functionl integrtion) into product designs. These leverge effects significntly reduce process complexity. Lower costs Assembly time reduction Joining time reduction Qulity control time reduction Inventory time reduction Process chin shortening Functionl integrtion using geometric potentil of Selective Lser Melting Lbour costs reduction Process costs reduction Mteril svings through e.g. downsizing Shorter times Better qulity Simplifiction of qulity control Reduction of mnufcturing deepness Increse of product functionlity Higher customer stisfction 104 Figure 9: Economic levers through functionl integrtion by SLM The complexity nlysis of test prt s presented here cn be used s strting point for more detiled complexity nlysis. Key indictors like prts volume/number_of_fcets, prts volume/surfce re, nd prts volume/block volume need to be extended to obtin comprehensive overview of product complexity. The geometric complexity of product design is dependent upon the chosen mnufcturing process, nd single geometric fetures cn boost geometric complexity drmticlly. For csting processes, undercuts result in high geometric complexity, lthough they cn be mnufctured esily by SLM. Even when most of the product geometry contins simple

9 geometric fetures, single fetures cn cuse mjor problems due to individul restrictions of the mnufcturing processes. These individul restrictions need to be considered when evluting the specific geometric complexity for mnufcturing process. For conventionl mnufcturing techniques, there is good evidence bout geometric design restrictions, nd design engineers use this informtion to develop their products. Although in the pst few yers gret efforts hve been mde to develop design for dditive mnufcturing prctices, there is still no comprehensive collection of design rules for SLM. As consequence, only mnufcturing engineers experienced in using SLM re ble to use its technologicl potentil to the full. Feture-bsed recognition systems re used to determine the mnufcturing costs for mchining [17]. Recognition systems re ble to detect geometric fetures including feture properties (e.g. surfce requirements). These feture-bsed recognition systems cn be used to determine geometric complexity utomticlly, by detecting specific geometric cost drivers relted to the mnufcturing process. A better understnding of geometric complexity nd how it reltes to different mnufcturing processes cn be improved by these systems in future investigtions. 5. ACKNOWLEDGEMENTS The uthors would like to thnk the Germn Reserch Foundtion (DFG) for supporting this reserch within the Cluster of Excellence Integrtive Production Technology for High-Wge Countries. REFERENCES [1] Meiners, W Direktes Selektives Lser Sintern einkomponentiger metllischer Werkstoffe. Shker Verlg Achen. [2] Wohlers, T Wohlers Report Wohlers Assocites. [3] Gebhrdt, A Genertive Fertigungsverfhren. Crl Hnser Verlg. [4] Gibson, I., Rosen, D.W. & Stucker, B Additive mnufcturing technologies. Springer Verlg. [5] Schleifenbum, H., Meiners, W., Wissenbch, K. & Hinke, C Individulized production by mens of high power Selective Lser Melting. CIRP Journl of Mnufcturing Science nd Technology (2), [6] Buchbinder, D High power selective lser melting (HP SLM) of luminum prts. LIM Proceedings. Munich [7] Levy, G.N Rpid mnufcturing nd rpid tooling with lyer mnufcturing (LM) Technologies, stte of the rt nd future perspectives. Annls of the CIRP, 52(2). [8] Wiendhl, H.-H., Rempp, B. & Schnz, M Turbulenzen erschweren Plnungssicherheit. IO- Mngement, 69, [9] Wegener, K Vorwort Additive Fertigung. SWISS RPiD Forum, St. Gllen. [10] Kröll, M Methode zur Technologiebewertung für eine ergebnisorientierte Produktentwicklung. Disserttion, Universität Stuttgrt, Jost-Jetter Verlg Heimsheim. [11] Bilsing A.P Kennzhlengestützte Bewertung der technologischen Leistungs-fähigkeit der Fertigung im Werkzeug- und Formenbu. Disserttion, RWTH Achen, Shker Verlg. [12] Voswinckel H Design for mnufcture bsed on n integrted product process design model, Key Engineering Mterils, 473, [13] Zäh, M Wirtschftliche Fertigung mit Rpid-Technologien. Crl Hnser Verlg GmbH & Co. KG; Auflge: 1. [14] Vlentn, B Bsic solutions on shpe complexity evlution of STL dt. Journl of Achievements in Mterils nd Mnufcturing Engineering, 26 (1). [15] Vlentn, B Evlution of shpe complexity bsed on STL dt. Journl of Achievements in Mterils nd Mnufcturing Engineering, 17 (1-2). [16] Shh, J.J Fetures in design nd mnufcturing: Intelligent design nd mnufcturing. John Wiley & Sons, Inc. [17] Ngrjn, S. & Venkt Reedy, N Step-bsed utomtic system for recognising design nd mnufcturing fetures. Interntionl Journl for Production Reserch, 48 (1), A A 105