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Application of additive manufacturing for improved thermal management of hot sheet metal forming tools

dc.contributor.advisorMatope, Stephenen_ZA
dc.contributor.advisorHarms, T. M.en_ZA
dc.contributor.advisorDimitrov, D. M.en_ZA
dc.contributor.authorMuvunzi, Rumbidzaien_ZA
dc.contributor.otherStellenbosch University. Faculty of Industrial Engineering. Dept. of Industrial Engineering.en_ZA
dc.date.accessioned2020-02-10T12:55:24Z
dc.date.accessioned2020-04-28T12:08:25Z
dc.date.available2020-02-10T12:55:24Z
dc.date.available2020-04-28T12:08:25Z
dc.date.issued2020-03
dc.identifier.urihttp://hdl.handle.net/10019.1/107899
dc.descriptionThesis (PhD)--Stellenbosch University, 2020.en_ZA
dc.description.abstractENGLISH ABSTRACT: In hot stamping, a blank or sheet of metal at high temperature (800-900 °C) is formed and cooled simultaneously by the tools. The rapid cooling of the blank causes transformation to a martensitic microstructure with high tensile strength (1 500 MPa) which enables the parts to acquire crash resistant properties. Accordingly, the process is used to produce vehicle components for improving safety of passengers. However, the hot stamping tools are exposed to high thermal load as they come into contact with the hot blanks. To aid in the cooling, the tools have a network of drilled channels in which a coolant circulates to extract heat. Due to machining restrictions, the straight drilled channels are unable to ensure consistent cooling of geometrically complex parts. If the tools are not evenly cooled, thermal stresses are induced and this compromises the tool service life and quality of parts (hardness properties). Moreover, the average cooling time in hot stamping occupies at least 30 % of the total cycle time. Thus, one of the major challenges in hot stamping research is to find ways of reducing the cycle time. The above mentioned challenges can be resolved through exploiting the design freedom offered by Additive Manufacturing technologies in the producing of tools with cooling channels which conform to the shape of tools. This has already been extensively investigated in the injection moulding and die casting tooling industry. However, there is limited information on the design and manufacturing parameters of hot stamping tools with conformal cooling channels. The aim of this research was to apply Additive Manufacturing as a tool for improving thermal management of hot stamping tools. The first objective was to identify the parameters required for an effective thermal management system of hot stamping tools. A method for identifying the structural conformal cooling system parameters was developed based on the technical limitation of the Selective Laser Melting process, principles of mechanics and heat transfer. The developed method was validated using finite element analysis simulation on a typical benchmark component. The second objective of the study was to develop a model for predicting minimum cycle time in hot stamping under ideal conditions. The model was developed using heat transfer principles and study of the stages in hot stamping. The model is a useful benchmark tool which is applicable in cycle time prediction. The third and fourth objectives were to design and manufacture a hot stamping tool with conformal cooling channels for a benchmark part. The fifth objective was to investigate the impact of the tool with conformal cooling channels on cycle time. In view of that, experiments were conducted to compare the performance of the optimised tool and the conventional one under typical industry like conditions. According to the results, the conformable tool shows the potential of reducing cooling time by 29%.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Gedurende warmstempeling word ’n ru-stuk of plaat metaal by ’n hoë temperatuur (800-900 °C) deur gereedskap gevorm en terselfdertyd afgekoel. Die vinnige afkoeling van die plaat veroorsaak omskakeling na ’n martensitiese struktuur met hoë treksterkte (1 500 MPa), wat die gestempelde onderdele plettervaste eienskappe gee. Daarom word hierdie proses gebruik vir die vervaardiging van voertuigonderdele om passasiersveiligheid te verbeter. Nietemin word die warmstempelingsgereedskap weens die hoë temperatuur van die metaalplaat aan ’n hoë termiese las blootgestel. Om afkoeling aan te help, beskik die gereedskap oor ’n netwerk boorkanale waarin ’n koelmiddel sirkuleer om hitte te onttrek. As gevolg van masjineringsbeperkinge kan die reguit boorkanale egter nie gelykmatige afkoeling van geometries komplekse onderdele verseker nie. Indien die gereedskap nie gelykmatig afkoel nie, veroorsaak dit termiese spanning, wat die gebruiksduur van die gereedskap verkort en die gehalte van onderdele (hardheidseienskappe) verlaag. Daarbenewens neem gemiddelde afkoelingstyd gedurende warmstempeling ten minste 30% van die algehele siklustyd in beslag. Een van die groot uitdagings van warmstempeling is dus om na maniere te soek om die siklustyd te verkort. Bogenoemde uitdagings kan die hoof gebied word deur gebruik te maak van die ontwerpvryheid wat additiewe vervaardigingstegnologieë bied vir die vervaardiging van gereedskap met pasgemaakte, konforme koelkanale. Dít is reeds uitvoerig ondersoek in die inspuitvorming- en matrysgietingsgereedskapbedryf, maar inligting oor die ontwerp- en vervaardigingsparameters van warmstempelingsgereedskap met konforme koelkanale is nog beperk. Die doel van hierdie navorsing was om additiewe vervaardiging te gebruik as ’n metode om die termiese bestuur van warmstempelingsgereedskap te verbeter. Dít is bereik deur eers die vereiste parameters vir ’n doeltreffende termiese bestuurstelsel vir warmstempelingsgereedskap te bepaal. ’n Metode vir die vasstelling van die strukturele parameters vir ’n konforme afkoelingstelsel is derhalwe op grond van die tegniese beperking van die selektiewe lasersmeltproses, beginsels van meganika sowel as warmteoordrag ontwikkel. Die ontwikkelde model is gestaaf met ’n eindige-elementontledingsimulasie van ’n tipiese standaardonderdeel. Die tweede oogmerk van die studie was om ’n model te ontwikkel vir die voorspelling van minimum siklustyd vir warmstempeling in ideale omstandighede. Die model is met behulp van warmteoordragbeginsels en ’n studie van warmstempelingsfases ontwikkel, en is ’n nuttige standaardmetode vir siklustydvoorspelling. Die derde en vierde doelwitte was om ’n warmstempelingsinstrument met konforme koelkanale vir ’n standaardonderdeel te ontwerp en te vervaardig. Die eindproduk is ’n warmstempelingsinstrument met innoverende konforme koelkanale op grond van ’n werklike standaardonderdeel. Die vyfde doel was om die impak van die instrument met konforme koelkanale op afkoeltyd te ondersoek. Vir dié doel is eksperimente uitgevoer om die werkverrigting van die geoptimaliseerde instrument met dié v van die konvensionele een in soortgelyke omstandighede as in die bedryf te vergelyk. Die resultate toon dat die instrument met konforme koelkanale afkoeltyd moontlik met 29% kan verkort.af_ZA
dc.format.extentxxii, 223 leaves : illustrations (some color)
dc.language.isoenen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.subjectAdditive manufacturingen_ZA
dc.subjectHeat -- Transmissionen_ZA
dc.subjectHot stampingen_ZA
dc.subjectMartensitic transformationsen_ZA
dc.subjectSheet-metal work -- Coolingen_ZA
dc.subjectMetal stampingen_ZA
dc.subjectUCTDen_ZA
dc.titleApplication of additive manufacturing for improved thermal management of hot sheet metal forming toolsen_ZA
dc.typeThesisen_ZA
dc.description.versionDoctoralen_ZA
dc.rights.holderStellenbosch Universityen_ZA


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