This study focused upon the manufacturing lead time management in California's electrical and electronic machinery, equipment, and supplies industry. Manufacturing firms with one hundred or more employees were invited to participate in the research. Six subproblems relating to manufacturing lead time were selected and six appropriate null hypotheses were tested. The subproblems identified (1) factors influencing manufacturing lead time, (2) production planning processes influencing manufacturing lead time accuracy, and (3) techniques reducing manufacturing lead time. These factors, production planning processes, and techniques were then IV investigated to determine the importance of each of them in two environments: (1) high-volume continuous-production (HVCP) and (2) job-shop production-to-order (JSPTO).

Enquanto alguns indivíduos preferem processar informações no mundo exterior (extrovertido/extrospectivo), outros preferem processá-las de forma reflexiva (introvertido/introspectivo). Tal diferença induz vivências distintas e portanto gera aprendizados distintos, mesmo para estudantes no mesmo ambiente de aprendizagem. O problema examinado nesta pesquisa foi a assimetria no aprendizado de Planejamento e Controle da Produção (PCP) por estudantes com diferentes Estilos de Aprendizagem (EA) do modelo Ativo/Sem-preferência/Reflexivo em ambiente dinamizado pelo jogo de empresas (JE) Politron. A pergunta problema da pesquisa foi: a vivência com JE gera uma experiência mais efetiva para o aprendizado dos estudantes com EA Ativo? O objetivo central foi testar a hipótese de entrosamento do EA Ativo-Reflexivo com o ambiente de aprendizagem. O aprendizado no domínio cognitivo foi verificado com uma prova objetiva. Pela taxonomia de Bloom (ANDERSON; KRATHWOHL, 2001), a prova testou o desempenho escolar para os objetivos de aprendizagem dos processos cognitivos (recordar, entender, aplicar e analisar) e dos tipos de conhecimento (fatual, conceitual e processual). Os EA Ativo-Reflexivo foram mapeados com o modelo index of learning styles (ILS) de Felder e Silverman (1988). Foram conduzidos dois quase-experimentos de teste antes e depois com amostras separadas. No primeiro, com 375 estudantes, buscaram-se evidências de assimetria no aprendizado de estudantes com diferentes EA Ativo-Reflexivo. No segundo, com 100 estudantes, estudou-se o efeito do aumento de ênfase nas atividades reflexivas sobre a assimetria no aprendizado dos estudantes. No primeiro quase-experimento observou-se menor aprendizado dos estudantes com EA Ativo. Os resultados observados foram interpretados sob a ótica da teoria de aprendizagem vivencial de Kolb, D. (1984, p. 42) em que a aprendizagem depende de quatro etapas de um ciclo: existência imediata e concreta, observação reflexiva, conceitualização abstrata e experimentação ativa. Supôs-se que o menor aproveitamento dos estudantes com preferência Ativa, tenha decorrido da falta de atividades reflexivas, o que teria limitado o fechamento do ciclo de aprendizagem. Os Reflexivos, que preferem a transformação do conhecimento pela observação reflexiva (introspecção), foram estimulados a experimentar ativamente os conhecimentos no jogo de empresa fechando o ciclo de aprendizagem mais efetivamente que os Ativos: na reflexão, apoiados nas suas preferências pessoais, e na ação, pelas situações impostas pelo jogo. Para testar esta suposição, desenvolveu-se o segundo quase-experimento, ampliando-se as atividades reflexivas da vivência. O resultado levou à aceitação da igualdade das médias dos estudantes Ativos, Reflexivos e Sem preferência. Baseado nas referências e nos resultados observados sugere-se que agentes de aprendizagem incorporem em seus planos de ensino e aprendizagem o caráter cíclico da aprendizagem vivencial (KOLB, D. 1984). Em concordância com as observações de Felder e Spurlin (2005), Seno e Belhot (2009) e Felder (2010), sugere-se a criação de oportunidades de aprendizagem balanceadas aos estudantes com diferentes EA. Aos educadores que já adotam o jogo de empresas, ressalta-se a importância dos momentos reflexivos, sobretudo para os estudantes Ativos serem estimulados a analisar os resultados do JE e fazer observações reflexivas diminuindo assim a assimetria de aprendizado. / While some people prefer to process information upon the outer world (extroverted), others prefer to process it reflectively (introverted). This difference leads to distinct experiences and therefore to distinct learnings, despite the students being in the same learning environment. The research problem was the learning asymmetry in Production Planning and Control (PPC) by students with different Active-Reflective learning styles in a business game-based learning environment. The research question was: does the use of a business game generate a more effective learning process for students with an Active learning style? The main objective was to test the meshing hypothesis of the Active-Reflective learning style with the learning environment. The learning outcomes were assessed by means of an exam. Using Bloom\'s taxonomy (ANDERSON; KRATHWOHL, 2001) the exam assessed learning outcomes of the cognitive processes (remembering, understanding, applying, and analyzing) and of the types of knowledge (factual, conceptual and procedural). Active-Reflective learning style of each student was assessed using the Felder and Silverman (1988) inventory of learning style (ILS). Two quasi-experimental pre-test and post-test with separate samples were conducted; the first one, with 375 students, to evaluate the differences in the learning of students with different learning styles (Active-Reflective). The second one, with 100 students, aimed to study the effect of the increase of reflective activities on asymmetry of students learning due to their learning styles (Active-Reflective). The first quasi-experiment showed lower learning by Active students. To explain the results, the Kolb, D. (1984, p. 42) experiential learning theory was used. The experiential learning relies on the four stages of a cycle: concrete experience, reflective observation, abstract conceptualization and active experimentation. It was assumed that, the lower learning of the students with Active learning style, was caused by the lack of reflective activities during the business game. The Reflective students, who prefer the transformation of knowledge by reflective observation (introspection), were encouraged, by the game, to experiment actively the knowledge. They would have been able to close the learning cycle more effectively than the Active students: by reflecting, due to their personal preferences, and, by acting, due to the circumstances imposed by the business game. To confirm this assumption the second quasi-experiment was developed increasing the reflective activities of the experience. The results, then, led to the acceptance of the learning equality of students regardless of their Active-Reflective learning style. Based on the references and data observed in this study, it is suggested that the learning agents consider, in their teaching and learning plans, the cyclical nature of experiential learning, as defined by Kolb, D. (1984). In accordance with the studies of Felder and Spurlin (2005), of Belhot and Seno (2009) and of Felder (2010), it is suggested providing learning opportunities in a balanced way to students with any learning style. To the educators that already use games, it is important to encourage students, especially the Active ones, to review the results of the game and make reflective observations.

O problema de planejamento da produção integrado ao problema de corte de estoque surge em várias indústrias de manufatura, tais como indústria de papel, móveis, aço entre outras, e consiste em um problema de otimização combinatória bastante complexo, devido ao fato de integrar dois problemas conhecidos na literatura de difícil resolução. As aplicações práticas deste problema vêm aumentando em muitas empresas que buscam tornar seus processos produtivos mais eficientes. Neste trabalho, estudamos o problema de otimização integrado que surge em pequenas indústrias de móveis, em que placas de MDF disponíveis em estoque devem ser cortadas em itens menores, de diversos tamanhos e quantidades para comporem os produtos demandados. O modelo matemático de otimização linear inteiro proposto permite que alguns produtos sejam antecipados e estocados. Essa antecipação da produção aumenta os custos de estoque, porém com o aumento da demanda de peças é possível gerar padrões de corte melhores e diminuir os custos com a perda de material. Consideramos no modelo dois tipos de variáveis de antecipação, uma de estoque convencional para atender uma demanda em carteira e outra para aproveitar a produção e atender uma demanda prevista, chamada variável oportunista. A função objetivo consiste em minimizar os custos dos processos de produção e de corte. Para resolver a relaxação linear deste problema, propomos um método lagrangiano e utilizamos a estratégia de horizonte rolante. Alguns testes computacionais são realizados e os resultados apresentados / The integrated problem of cutting stock and production planning arises in a several manufacturing industries, such as paper, furniture, steel among others, and it is a complex combinatorial optimization problem, due to the fact that it integrates two well-known NP problems of the literature. The real world applications of this problem have increased in many industries that search for more efficient production process. In this work, we studied an integrated optimization problem that arises in small furniture industries, where MDF boards available in inventory must be cut into enough quantities of items to compose demanded finish-goods. The model of integer linear optimization proposed allows anticipating some products and keeping them in inventory. This production anticipation makes increase the inventory costs, although makes it possible to determine better cutting patterns and decreases the costs of the cutting process. We consider in the model two types of anticipation variables, the first one to the ordinary inventory to meet ordered products and an other one, called chance variables, to meet a forecasting demand. The objective function is to minimize the costs of production process and waste of material. To solve a linear relaxation of this problem, we proposed lagrangian approach and used a rolling horizon strategy. Some computational tests are performed and results shown

På senaste tiden har leveransprecision blivit allt viktigare eftersom kunder idag kännetecknas av att vara mer tidskänsliga och ständigt söker efter produkter som är specifikt anpassade till kunden. Tid har därmed betraktats som ett kriterium för konkurrens och är betydande för företag att kunna konkurrera på marknaden. Osäkerheter i marknaden har en stor påverkan på leveransprecision och det är en stor utmaning för företag att planera produktion utifrån dessa osäkerheter. När produktion för en artikel planeras måste en planerare ta hänsyn till osäkerheter som exempelvis att en maskin kan sluta fungera, att en defekt produkt måste omarbetas eller att det tar längre tid än planerat för att utföra ett arbetsmoment som leder till att en ledtid blir längre. Syftet med studien var att identifiera orsaker till skillnaden mellan planerad och verklig produktionstid samt ge förbättringsförslag för att minska skillnaden. Syftet har uppfyllts med hjälp utav en fallstudie på AQ Group i Pålsboda och genom intervjuer där planerad och verklig produktionstid har undersökts. En litteraturstudie har utnyttjats och tre frågeställningar har formulerats till studien. Dessa frågeställningar lyder: Hur ser skillnaden ut mellan planerad och verklig produktionstid? Vad är orsakerna till dessa skillnader? Hur kan dessa orsaker elimineras? Under det teoretiska avsnittet har fokuset varit på cykeltider, ställtider, produktionstid, Lean och produktionsplanering. Resultatet visar en total skillnad på 24 % mellan den planerade och verkliga produktionstiden över en 5-dagarsperiod. Några orsaker som påträffats är att de standardiserade arbetssätten inte är uppdaterade, inte är tvingande för operatörer att utföra och att det inte existerar några illustrationer för standardiseringen. En annan orsak är onödiga arbetsmoment där verktyg ligger långt ifrån arbetsstationerna och ibland fattas som gör att produktionstiden blir längre än planerat. Avslutningsvis presenteras kritiska förbättringsförslag som specifikt påverkar skillnaden i produktionstiderna och allmänna förbättringsförslag som AQ Group i Pålsboda kan ta nytta av för att effektivisera verksamheten. / In recent times delivery precision has become more important to customers, which today are characterized by being more time sensitive and constantly looking for products that are specifically tailored to the customer. Time is being seen as a criterion for competitors and it is important for companies to be able to compete in the market. Uncertainties in the current market have an effect on delivery precision and it is a major challenge for companies to plan production based on these uncertainties. When production for an article is planned, it should be planned in consideration of uncertainties, for example, a machine may break down, a defective product may need a rework or that it takes longer than planned to carry out an operation leading to a longer lead time. The purpose of the study was to identify causes of difference between planned and actual production time and to provide improvement suggestions to reduce the difference. The purpose has been achieved through a case study in AQ Group in Pålsboda with help of interviews where planned and actual production time has been investigated. A literature study has been used as well as three questions. These questions are: What is the difference between planned and actual production time? What are the causes of these differences? How can these causes be eliminated? During the theoretical section, the focus has been on cycle times, setup times, production time, Lean and production planning. The results show a total difference of 24% between the planned and actual production time over a 5-day period. Causes that have been found are that the standardized working methods are not up to date, are not mandatory for operators to perform and that there exist no illustrations for the standardization. Another cause is unnecessary work steps where tools is far away from the workstations and sometimes missing which leads to the production time being longer than planned. Lastly the study provides critical improvement suggestions that specifically affect the differences between planned and actual production times and general improvement suggestions that AQ Group in Pålsboda can take part of to streamline operations.

Thesis (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The main proposition of this study is that the notion of a single set of universal success factors (enablers) of innovation is naïve. Rather, the importances of different enablers are contextually based and dependent upon different kinds of projects and their attributes. By investigating the roles of project radicalness and maturity in governing the importance of enablers of innovation in the process industries, two major conclusions were made, viz. (1) the importance of enablers are significantly moderated by project attributes, and (2) the mutual interactions between moderators of enabler importance prevent the formulation of middle-range theories of innovation radicalness or maturity, which propose normative relationships between innovation attributes and enabler importance. Although a number of previous studies have posited such outcomes, this study provides empirical evidence thereof for a set of generic enablers of innovation. These findings have suggested that the modelling of innovation at the project level should follow a contingent approach. While contingency theory has widely been applied to correlate structural and environmental attributes when the unit of analysis is the organisation, the literature on project management has largely ignored the importance of project contingencies, assuming that all projects share a universal set of managerial characteristics. This void is addressed through the development of a contingency model of the influence of secondary contingencies (project radicalness and maturity) on the importance of enablers. It represents an integrative perspective of the contextual importance of a number of enablers (and constructs thereof) that have previously been investigated and reported independently. Given that theory development in project management is still in its early years, it may therefore be concluded that the study contributes to the validity of classical contingency theory arguments in the context of the project. Although it does not consider an exhaustive list of all possible contingencies, and findings thereof strictly pertain only to process innovation, it does represent a considerable step in the evolving process of theory development on the modelling of innovation at the project level. / AFRIKAANSE OPSOMMING: Die studie poneer in hoofsaak dat die idee van ‘n enkele stel universele suksesfaktore (drywers) vir innovasie, eng is. Dit word eerder voorgestel dat die belangrikheid van verskillende drywers kontekstueel is en bepaal word deur verskillende tipes projekte en hul eienskappe. Na gelang van ‘n ondersoek na die rolle van projek radikaalheid en stadium van ontwikkeling in die bepaling van die belangrikheid van drywers van innovasie, is twee hoofgevolgtrekkings gemaak, naamlik dat (1) projekeienskappe ‘n beduidende invloed op die relatiewe belangrikheid van drywers het, en (2) die onderlinge interaksies tussen moderators van die belangrikheid van drywers dit verhoed om middelomvang teorieë van innovasie radikaalheid of stadium van ontwikkeling te formuleer, wat normatiewe verhoudings tussen die eienskappe van innovasies en hul drywers voorstel. Alhoewel sulke resultate deur ‘n aantal vorige studies gepostuleer is, verskaf hierdie studie empiriese bewyse daarvan in terme van ‘n generiese stel drywers van innovasie. Bevindinge in hierdie verband het getoon dat innovasie op die projek-vlak deur ‘n voorwaardelikheidsmodel gemodelleer moet word. Alhoewel voorwaardelikheidsteorie algemeen gebruik word om strukturele en omgewingseienskappe op organisatoriese vlak te korrelleer, het die projekbestuur-literatuur tot dusver grootliks die belangrikheid van projekvoorwaardelikhede geïgnoreer deur aan te neem dat alle projekte ‘n universele stel bestuurseienskappe deel. Hierdie leemte word geadresseer deur die ontwikkeling van ‘n voorwaardelikheidsmodel vir die invloed van sekondêre voorwaardelikhede (projek radikaalheid en stadium van ontwikkeling) op die belangrikheid van drywers. Dit verteenwoordig ‘n geïntegreerde perspektief van die kontekstuele belangrikheid van ‘n aantal drywers (en konstrukte daarvan) wat voorheen onafhanklik nagevors en gepubliseer is. Aangesien teorie ontwikkeling in projekbestuur steeds jonk is, word die gevolgtrekking gemaak dat die studie bydra tot die geldigheid van klassieke voorwaardelikheidsteorieargumente in die konteks van die projek. Alhoewel dit nie ‘n veelomvattende lys van alle moontlike voorwaardelikhede beskou nie, en die bevindinge daarvan streng gesproke slegs betrekking het op proses-innovasie, verteenwoordig die studie ‘n beduidende stap vorentoe vir teorie-ontwikkeling in die modellering van innovasie op die projek-vlak.

Thesis (MBA)--Stellenbosch University, 2002. / Some digitised pages may appear illegible due to the condition of the original hard copy / ENGLISH ABSTRACT: The Fruit Unit of Tiger Brands is annually responsible for the canning of 75 000 tons of fruit of which apricots constitutes approximately twenty percent. The canning of apricots is subject to a few unique challenges with regard to production planning. The challenges are the unpredictable fruit sizes, unpredictable fruit quality, unpredictable fruit degradation in cold storage, unknown starting date for production and the uncompromisable end of production before Christmas day. These uncertainties led to the fact that no formal production planning for apricots had been done in the previous years of operation. The primary aim of this study is to reduce the risks with regard to production, apricot size and apricot quality by effectively forecasting the expected nett result thereof. This will quantify the resultant products available to marketing personnel and give a measure to evaluate and control production performance. The problem is addressed by organising and presenting historical data such that forecasts of future outcomes would become possible. Clear trends are present on throughput and fruit degradation over time, making forecasting of these two uncertainties quite simple. The forecasting of fruit size is however more problematic, especially because of the lack of sufficient data. It was proposed that the four main fruit size categories be described by using probability distributions fitted over the actual data of the last four years. The large variation on these distributions, probably caused by the lack of sufficient data, rendered this method unsuitable. It was decided that the best estimate of the percentage of each fruit size to be expected, was the average of the derived distributions. The model constructed of the above forecasts is suitable for the estimating of the quantities of specific products that would be available as output from the production process. The model is however not suitable for the evaluation and control of production processes. It is proposed that evaluation and control of production be achieved by using control charts derived from the same historical data. The production control charts are constructed from actual, cumulative production output from the last four years. Linear regression was done on this data to establish a trend line with two sigma limits plotted on the same chart. These charts could be used effectively to monitor daily production output to establish if the commitment towards marketing would be achieved. The lack of data for analysis puts a question mark on the statistical significance of the model. The model is viewed to be a first step in the elimination of uncertainties of raw materials and production variances by making use of historical performance data. The model and control charts will become more and more statistically significant if future actual performance data is incorporated. The model could also be drastically improved if detailed agricultural models for the prediction of apricot size and quality, based on climatic and soil conditions during the growing period were available. The development of such models could be the subject of future studies. / AFRIKAANSE OPSOMMING: Die Vrugte eenheid van Tiger Brands is jaarliks verantwoordelik vir die inmaak van naastenby 75 000 ton vrugte. Appelkose maak twintig persent van hierdie volume uit. Die inmaak van appelkose is onderhewig aan unieke uitdagings ten opsigte van produksiebeplanning. Die uniekheid is gesetel in die onvoorspelbaarheid van vruggrootte, die jaarlikse verskille in vrugdegradering tydens opberging, die onvoorspelbaarheid van die begindatum van produksie en die absolute vereiste om voor Kersdag produksie te voltooi. Hierdie onvoorspelbaarhede het tot gevolg dat daar tot op hede geen formele produksiebeplanning vir appelkose gedoen is nie. Die primêre doelwit van die studie is om die risiko's ten opsigte van produksie, appelkoosgehalte en appelkoosgrootte te verminder, deur die impak daarvan vooruit te skat. Sodoende sal die produkte wat vir bemarking beskikbaar gestel behoort te word ook beter bekend en beheerbaar wees. Die probleem word aangespreek deur geskiedkundige data sodanig te verwerk en te organiseer dat vooruitskattings daarmee gedoen kan word. Baie duidelike tendense ten opsigte van deurset en vrugdegradering oor tyd is deur middel van die geskiedkundige data waarneembaar, wat vooruitskatting van die twee faktore redelik vergemaklik. Die vooruitskatting van vruggrootte bly egter problematies, veral as gevolg van die gebrekkige geskiedkundige data wat beskikbaar is. Daar is gepoog om die vier gespesifiseerde vruggrootte kategorieë deur middel van waarskynlikheidsverdelings te beskryf, maar die gebrekkige data en groot variasie van die data en verdelings maak die tegniek ongeskik. Gevolglik is daar besluit om slegs die gemiddeld van hierdie verdelings as 'n beste raming te gebruik van die verwagte hoeveelheid van elke vruggrootte. Die model wat uit bogenoemde manipulering van data afgelei word, word gereken geskik te wees vir die raming van hoeveelhede van spesifieke produkte wat vir verkope beskikbaar sal wees. Die model is egter onvoldoende vir produksiebeheer en evaluasie. Produksie evaluasie sal egter met behulp van produksiebeheer kaarte wat ook van geskiedkundige prestasie afgelei is, gedoen word. Die produksiebeheer kaarte is kumulatiewe werklike fabrieksprestasie waardeur 'n regressielyn gepas is, met twee sigma afwykingslyne weerskante van die regressielyn geplot. Hierdie kaarte sal gebruik word om daaglikse produksie prestasie te plot en te interpreteer of die kommitment teenoor bemarkingspersoneel steeds haalbaar sou wees. Die model en die produksiebeheer kaarte is afgelei van slegs vier vorige seisoene se produksiedata. Die tekort aan relevante data plaas die betekenisvolheid van die afleidings dus onder verdenking. Die model en kaarte word beskou as 'n eerste poging om die risiko van grondstof- en produksievariasies te verminder deur die vooruitskatting van die uitsette met behulp van geskiedkundige prestasie. Die model en kaarte sal met die inkorporering van toekomstige seisoenale data meer statisties beduidend word. Die model sou ook verbeter kon word deur detail landboukundige modelle wat appelkoos gehalte en grootte verbind met klimatologiese en grondkundige kondisies tydens die verbouingsproses van die vrugte. Hierdie verbetering word egter voorgestel vir 'n verdere studie onderwerp.

Thesis (MBA)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Volkswagen of South Africa (Pty) Ltd. (VWSA) is part of the Volkswagen Group, which originated in Germany. VWSA’s production plant is situated in Uitenhage in the Eastern Cape and produces ± 100 000 cars per year with ± 5 800 employees. At the time of writing this report, VWSA had three platforms on which it produced the Citi Golf, Polo/Polo Classic and Golf 5/Jetta 5. It takes on average four days to produce a vehicle, but up to 17 weeks lead time is required before production can start. This lead time is needed to procure, transport and receive the single parts from suppliers in South Africa, Europe and other countries. The time window required in order to manufacture a vehicle is therefore relatively long. For this reason it is important that VWSA’s production schedule is firstly planned properly and secondly optimised continuously and timely, as circumstances change and unforeseen conditions arise. VWSA assemble vehicles “to stock” and not “to order”. This means that a production schedule is planned and executed, based on forecasted volumes and not on actual customer orders. The monthly production offline demand is received from marketing, which includes both the volume requirements for domestic and export units. Currently the production scheduling process of VWSA is performed manually in an Excel spreadsheet. This is a time consuming process that could be exposed to mistakes. Much iteration is performed manually in order to achieve the best solution. The aim of this research report was to develop an optimisation model for production after the fixed lead time period in order to ensure finished products on time as per the local and export demand. VWSA requires a 52 week rolling production schedule, which should take all the various constraints into account. The objective of the production schedule is to determine shift patterns and production units per shift that will provide some consistency, by avoiding short time, overtime, plant closures, variations in production rates, etc. as far as possible. More importantly, the production schedule must optimise the use of resources and minimise costs. A scheduling model was developed for each of the three model lines, making use of Mixed Integer Programming. The constraints and applicable costs were built into each individual model. Each model was solved with the use of Premium Solver Platform software, due to the fact that it has advance capabilities and includes a Nonlinear GRG Solver. Optimal solutions were found, satisfying all the various constraints, within seconds compared to the hours and days required for the current manual scheduling process. A summary sheet was developed, combining the individual model line schedules for distribution and presentation purposes. This summarises the required production units per day, week and cumulative. In addition it includes the required export units that are first priority to be produced per week. To improve decision making, a column was included to indicate the quantity of units of each model type that must be produced during overtime. This model provides management with the information required to make decisions regarding detailed production scheduling. / AFRIKAANSE OPSOMMING: Volkswagen van Suid-Afrika (Pty) Ltd. (VWSA) is deel van die Volkswagen Groep, wat onstaan het in Duitsland. VWSA se produksie aanleg is geleë in Uitenhage in die Oos-Kaap en vervaardig ± 100 000 voertuie per jaar deur gebruik te maak van ± 5 800 werknemers. Ten tyde van die skryf van hierdie verslag het VWSA drie platforms gehad waarop dit die Citi Golf, Polo/Polo Classic en Golf 5/Jetta 5 vervaardig het. Dit neem gemiddeld vier dae om ’n voertuig te vervaardig, maar kan tot 17 weke leityd benodig voordat produksie kan begin. Die leityd is nodig om enkel komponente van verskaffers in Suid-Afrika, Europa en ander lande te bestel, vervoer en te ontvang. Die tydperk wat benodig word om ’n voertuig te vervaardig is dus relatief lank. As gevolg van hierdie rede is dit belangrik dat VWSA se produksie skedule eerstens deeglik beplan word en tweedens aanhoudend en betyds ge-optimeer word soos omstandighede verander. VWSA vervaardig voertuie vir voorraad en nie op bestellings nie. Dit beteken dat ’n produksieskedule beplan en uitgevoer word, gebasseer op vooruitgeskatte volumes en nie op konkrete bestellings van kliënte nie. Die maandlikse produksie aanvraag word ontvang vanaf die Bemarkings-departement en sluit beide binnelandse en uitvoer aanvraag in. Die produksie skedulering van VWSA word tans in ’n Excel sigblad verrig. Dit is ’n tydrowende proses wat blootgestel is aan moontlike foute. Baie iterasies word benodig om uiteindelik die mees gepaste oplossing te vind. Die doel van hierdie navorsingsverslag was om ’n optimeringsmodel vir produksie na die vaste leityd tydperk te ontwikkel, met die doel om te verseker dat klaarprodukte betyds volgens die binnelandse en uitvoer aanvraag gelewer word. VWSA benodig ‘n 52 week rollende produksieskedule wat al die verskeie beperkings in ag neem. Die doel van die produksieskedule is om skofpatrone en volumes per skof te bepaal wat uiteindelik konsekwentheid verskaf deur korttyd, oortyd, aanlegsluitings, variasies in lynspoed, ens. te beperk. Meer belangrik, die produksieskedule moet die gebruik van bronne optimeer en kostes minimeer. ’n Skeduleringsmodel is ontwerp vir elkeen van die drie modellyne, deur gebruik te maak van Gemengde Heeltal Programmering. Die toepaslike beperkings en kostes is by elke individuële model ingebou. Elke model is opgelos deur gebruik te maak van “Premium Solver Platform” sagteware, as gevolg van die feit dat dit gevorderde vermoëens het asook “Nonlinear GRG Solver” insluit. Binne sekondes is optimale oplossings gevind, wat ook die beperkings bevredig, in teenstelling met die ure en dae wat benodig word vir die huidige skeduleringsproses. ‘n Opsommende blad is ontwikkel wat die individuële skedules saamvat vir verspreidings- en voordrag doeleindes. Dit bevat die beplande produksievolumes per dag, week en kumulatief. Addisioneel bevat dit ook die vereiste uitvoervolumes per week wat eerste prioriteit geniet. Om besluitneming te verbeter is ‘n kolom ingesluit wat aandui hoeveel eenhede van elke model tipe word benodig gedurende oortydproduksie. Die model verskaf aan bestuur die inligting wat benodig word om detail besluite oor produksieskedulerings te neem.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006. / In order to plan the engineering work of large construction projects efficiently, a model of the engineering process is required. An engineering process can be modelled by sets of persons, tasks, datasets and tools, as well as the relationships between the elements of these sets. Tasks are more often than not dependent on other tasks in the engineering process. In large projects these dependencies are not easily recognised, and if tasks are not executed in the correct sequence, costly delays may occur. The homogeneous binary relation “has to be executed before” in the set of tasks can be used to determine the logical sequence of tasks algebraically. The relation can be described by a directed graph in the set of tasks, and the logical sequence of tasks can be determined by sorting the graph topologically, if the graph is acyclic. However, in an engineering process, this graph is not necessarily acyclic since certain tasks have to be executed in parallel, causing cycles in the graph. After generating the graph in the set of tasks, it is important to fuse all the cycles. This is achieved by finding the strongly connected components of the graph. The reduced graph, in which each strongly connected component is represented by a vertex, is a directed acyclic graph. The strongly connected components may be determined by different methods, including Kosaraju’s, Tarjan’s and Gabow’s methods. Considering the “has to be executed before” graph in the set of tasks, elementary paths through the graph, i.e. paths which do not contain any vertex more than once, are useful to investigate the influence of tasks on other tasks. For example, the longest elementary path of the graph is the logical critical path. The solution of such path problems in a network may be reduced to the solution of systems of equations using path algebras. The solution of the system of equations may be determined directly, i.e. through Gauss elimination, or iteratively, through Jacobi’s or Gauss-Seidel’s methods or the forward and back substitution method. The vertex sequence of an acyclic graph can be assigned in such a way that the coefficient matrix of the system of equations is reduced to staggered form, after which the solution is found by a simple back substitution. Since an engineering process has a start and an end, it is more acyclic than cyclic. Consequently we can usually reduce a substantial part of the coefficient matrix to staggered form. Using this technique, modifications of the solution methods mentioned above were implemented, and the efficiency of the technique is determined and compared between the various methods.

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy