High speed cutting and electric discharge machining as complementary processes in the die and mould industry

Treurnicht, N. F. (2003-04)

Thesis (MScEng) -- Stellenbosch University, 2003.

Thesis

ENGLISH ABSTRACT: High Speed Cutting (HSC), specifically milling is a significant contemporary development in machining. The Die and Mould industry is experiencing a difficult business climate. There is competitive pressure for shorter lead times and lower prices. Companies worldwide, are under financial pressure, to meet the challenges of a globalised business environment. The conventional position of milling and Electric Discharge Machining (EDM / Erosion) is discussed with the proposal to use HSC and EDM as complementary processes. Among new developments the progress in computer infrastructure is prominent. There is also a paradigm shift that should be made from experience based process planning to modern, up to date knowledge based process planning. High Speed Cutting is now a mature process capable of acceptable process security. The examples detailed include crankshaft-forging tooling, injection moulding tooling and powder sintering tooling. A process chain is proposed for the complementary HSC / EDM process with estimated illustrative time saving over the conventional EDM dominated process. HSC will be the first process removing the bulk of the material, finishing as far as possible and with EDM finally machining the features that will be difficult or impossible with HSC. To facilitate the use of the complementary processes a decision model to determine the crossover point between HSC and EDM is proposed. The decision model is firstly presented as a flow diagram to determine whether the task is a candidate for HSC only, EDM only, or the complementary HSC / EDM process. The key parameters e.g tool H d ratio are variables. This is in order that the flow diagram may be adapted to a specific machine tool infrastructure and expertise level in a company. The second part is a HSC machining time estimation model. The time is estimated per segment roughed, semi-finished, or finish machined. The model is in an empirical form with constants that can be adapted to the practices of a specific company. It is intended that the constants also be periodically revised to reflect the development in HSC expertise that will occur during the use HSC in the company. The model is practically evaluated with a case study, including the detail steps, not included in the model. Conceptual guidelines are given for software implementation. It is concluded that HSC and EDM are suitable complementary processes. It is a necessary prerequisite to use pallets to avoid multiple set-ups. Complementary HSC and EDM is especially appropriate for the gradual deployment and skill development for HSC. HSC and complementary HSC / EDM is considered the opportunity for companies to make a major breakthrough in lead time and operating expense if the necessary pallet/fixturing equipment, CAx infrastructure and human capability is available.

AFRIKAANSE OPSOMMING: Hoe Spoed Masjinering (HSC), spesifiek frees is ‘n betekenisvolle ontwikkeling in masjinering. Die Gereedskap en Gietvorm bedryf ervaar ‘n moelike besigheidsklimaat. Daar is kompeterende druk vir korter lewertye en laer pryse. Maatskappye wereldwyd is onder finansiele druk om in die geglobaliseerde besigheidsmilieu te presteer. Die posisie van frees en Elektriese Ontladingsmasjinering (EDM / Vonkerosie) word bespreek met die voorstel om HSC en EDM as komplementere prosesse te gebruik. Onder die nuwe ontwikkelings is daar prominente vooruitgang in rekenaarinfrastruktuur. Daar is ook ‘n paradigmaverskuiwing nodig van ondervinding gebaseerde na op datum kennis gebaseerde proses beplanning. HSC is nou ‘n ontwikkelde proses met voldoende prosessekerheid. Die voorbeelde sluit krukas smee gereedskap, inspuitgiet gereedskap, en poeier-sinter persgereedskap in. ‘n Prosesketting word voorgestel vir die komplementere HSC / EDM proses met ‘n beraamde illustratiewe tydbesparing oor die konvensionele EDM gedomineerde proses. HSC sal die eerste proses wees wat die meerderheid van die materiaal verwyder en oppervlaktes so ver as moontlik afwerk, met EDM wat die finale afwerking doen en ook die masjinering wat vir moeilik haalbaar of onmoontlik is vir HSC. Om die gebruik van die komplementere prosesse te fasiliteer, word ‘n beluitnemingsmodel vir die oorgangspunt tussen HSC en EDM voorgestel. Dit word eerstens as vloeidiagram gebruik om die taak te klassifiseer vir HSC alleen, EDM alleen of vir komplementere HSC en EDM. Die sleutelparameters, bv die beitel 116 verhouding, is veranderlikes. Dit is sodat die vloeidiagram aangepas kan word by ‘n spesifieke masjienvermoe en ‘n kundigheidsvlak in ‘n maatskappy. Die tweede deel is ‘n HSC masjineringstyd model. Die tyd word beraam per segment uitgerof, afgewerk, of finaal afgewerk. Die model is in empiriese vorm met konstantes wat kan aangepas word by die praktyke van ‘n firma. Dit is die bedoeling dat die konstantes periodiek aangepas word om die ontwikkeling te weerspieel wat in die maatskappy plaasvind. Die model word prakties evalueer met ‘n gevallestudie, insluitend die detailstappe, wat nie in die modelformulering ingesluit is nie. Konseptuele riglyne word gegee vir programmatuur implementering. Die gevolgtrekking word gemaak dat HSC en EDM geskikte komplementere prosesse is. Dit is ‘n voorvereiste om pallette te gebruik om veelvuldige opstellings te vermy. Komplementere HSC / EDM is veral toepaslik om HSC geleidelik in ‘n firma te ontplooi en kundigheid te bou. Die HSC / EDM kombinasie word ook die geleentheid geag vir firmas om ‘n deurbraak te maak in lewertyd en bedryfsuitgawes as die nodige pallettoerusting, CAx infrastruktuur en menslike vermoe beskikbaar is.

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