Thesis (MScEng) -- Stellenbosch University, 2003. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53448 |
| Date | 04 1900 |
| Creators | Treurnicht, N. F. |
| Contributors | Fourie, C. J., Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 141 p. : ill. |
| Rights | Stellenbosch University |
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