Two types of heuristic capacity control policies a·re evaluated with a SLAM simulation model of a materials requirements planning production system. The control policy decisions are based solely on the size of the queue, as measured in standard hours of work, at each work center in the production system. Several classes of product mixes and product structures are investigated, as well as several levels of the control parameters of each control policy. The results indicate that each control policy gives rise to a unique population of weekly labor, work in process, and inventory level. Product structure is also identified as a major variable in Materials Requirements Planning systems performance. Sensitivity analysis of the cost functions for each policy indicate the conditions under which it will minimize the sum of labor costs, work in process holding costs, and inventory holding costs. The simulation model, MRPSIM, is included with a user's guide. / M.S.

One of the main assumptions in conventional production process is that each component or part of the production process can be controlled separately as if they are not dependent on anything. This assumption gives rise to problems such as need of effective collaboration with different actors and constraints in budgets. Conventional planning process also causes delay as well as cost overruns which ultimately leads to reduction in productivity.The Last Planner system, LPS, is a tool used in the construction sector with the goal of streamlining production. The tool has several advantages, for example, to make collaboration between different actors more efficient, achieve a better workflow and increase production efficiency. The purpose of this masters’ thesis is to explore how two construction projects in Stockholm work with LPS. Apart from the fact that LPS provides many advantages in the production planning of the projects, this study aims to explore the challenges that they face while working with LPS. The goal of this study is to be able to suggest improvement measures for the challenges that the projects are facing.Semi-structured interviews were conducted on both projects to understand how they work with LPS and what challenges they face. The results section contains the information from the interviews. That is then discussed against the theory on which the Last Planner system is built.The conclusion of this study is that the production planning in the projects differs from how the tool should be used according to the framework of LPS. Learning, which emphasizes what has been done during the project, is a phase in LPS's framework. According to one of the founders of the LPS system, ‘learning’ is the most important phase. However, due to the lack of time, the studied projects were not able to involve the learning phase into their production planning. The projects faced several challenges, including repeated changes from the design teams, which entailed new actions during the project. Also, the involvement of the construction workers in the planning phases came out as a big challenge for the managers. Furthermore, communication problems and lack of cooperation with subcontractors is also present. Some of the improvement measures suggested to meet the challenges are that managers should increase commitment to involve especially construction workers in the planning phases, create nucleus teams, create a standard protocol for how production planning should be implemented, and improve visual planning to enhance communication. / I de traditionella produktionsprocesserna har det antagits att olika komponenter kan styras separat d.v.s. att de är oberoende. Detta antagandet har gett upphov till problem som till exempel försämrat samarbete mellan olika aktörer. Den traditionella produktionsprocessen har också lett till förseningar och kostnadsöverskridanden i projekt.Last Planner-systemet, LPS, är ett verktyg som används inom byggsektorn med målet att effektivisera produktionen. Förutom att effektivisera produktionen är syftet att involvera byggarbetare i planeringsfaserna. Verktyget har flera fördelar, till exempel att effektivisera samarbeten mellan olika aktörer, uppnå ett konstant arbetsflöde och ökad effektivitet i produktionen. Syftet med denna uppsats är att utforska hur två byggprojekt i Stockholm arbetar med LPS. Bortsett från att LPS tillför många fördelar i projektens produktionsplanering har denna uppsats som mål att utforska vilka utmaningar projekten står inför kring arbetet med LPS. Målet är att kunna föreslå eventuella förbättringar för att möta utmaningarna som projekten står inför.Semistrukturerade intervjuer genomfördes på båda projekten för att förstå hur de arbetar med LPS och vilka utmaningar de står inför. Resultatavsnittet redovisar informationen från intervjuerna, som sedan diskuteras i relation till teorin som LPS bygger på.Slutsatsen av denna uppsats är att det skiljer sig mellan hur verktyget används i praktiken jämfört med vad ramverket för LPS står för. Att ta lärdom av vad som gjorts under projektet är en fas i LPS ramverk. Enligt en av grundarna av LPS-systemet är ’lärande’ den viktigaste fasen. Men på grund av tidsbrist har inte projekten som denna studie undersökte kunnat genomföra den fasen. Projekten stod inför flera utmaningar, bland annat upprepade ändringar från designteamen, som ledde till nya åtgärder under projektet, att involvera byggarbetare i planeringsfaserna, kommunikationsproblem mellan aktörer och bristande samarbete med underentreprenörer. Några förbättringsåtgärder är att chefer borde engagera sig mer för att involvera byggarbetare i planeringsfaserna, skapa ett standardprotokoll för hur produktionsplanering bör genomföras och förbättra den visuella planeringen för att uppnå bättre kommunikation.

The purpose of this study was to investigate the impact of the maintenance management system (MMS) on production output and profitability (PO&P) at the Petroleum Oil and Gas Corporation of South Africa (PetroSA) GTL Refinery as a source of competitive advantage. State-Owned Companies and, or more specifically the PetroSA GTL Refinery must maintain its strategic importance for government fuel security but, at the same time, it must compete against private refineries in terms of achieving high production volumes, maximising profitability and to maintain its stake of 6.5% of the available production capacity. The literature review for this study suggested that the maintenance management system (MMS) impacts positively on production output and profitability (PO&P). The MMS has a tremendous influence on PO&P at the PetroSA GTL Refinery. Using a quantitative research design, cross-sectional research survey and the Maintenance Scorecards (MS) assessment tool, this study was conducted on six areas of the PetroSA GTL Refinery. Two population groups, namely production and maintenance groups participated in the survey. Fifty-six respondents belonged to the maintenance group and thirty-eight respondents belonged to the Production Group. All the Maintenance and Production Group respondents completed the MS questions designed to fit the characteristics of these population groups. Correlation analysis in terms of the means, standard deviations, gap analysis, Pearson product moment correlation coefficient (r) as well as the coefficient of determination (R²) was used to analyse the data. The findings of the study indicated a moderate positive linear correlation between the MMS and PO&P. Recommendations based on the findings were tabled in chapter 7 to improve and enhance production perspective (asset health gap), safety perspective (asset prioritisation gap) and the learning and growth perspective (skills and working condition gap). / Business Management / M. Com. ((Business Management)

Thesis (MScIngwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis is a case study in optimal inventory control, applied to Clickabox factory, a South African cardboard box producer from whom cardboard boxes may be ordered at short notice via the internet. The problem of developing a decision–support system for optimal stockholding at the factory, in order to minimize cardboard off–cut wastage subject to required service levels, is addressed in this thesis. Previously a simple replenishment policy, based largely on experience, was implemented at the factory. The inventory model developed for and applied to Clickabox in this thesis takes account of a raw materials substitution cascade, as well as the stochasticity of demand, and other factors such as cost, service level and spatial requirements for the storage of stock. This combination of stochastic demand and product substitution has not, to the author’s knowledge, previously been dealt with in the literature. There are two primary deliverables of this study. The first is a suggestion as to the suitable stock composition (cardboard types from which boxes may be manufactured) to be kept in inventory at the factory. The second deliverable is a computerised decision–support system, based on the inventory model developed, to aid in future inventory replenishment decisions at Clickabox. Some of the results of this thesis have, at the time of writing, already been implemented with success at the factory. These include the suggestions given to the management of Clickabox as to the suitable stock types to be held in inventory, which have been implemented in stages since March 2003. The suggested stock composition has proven to be superior to the previous stock types held, in terms of a reduction in off–cut wastage and increased availability of suitable boards. / AFRIKAANSE OPSOMMING: Hierdie tesis is ’n gevallestudie in optimale voorraadbeheer, toegepas op Clickabox fabriek, ’n Suid–Afrikaanse kartondoosprodusent by wie kartondose op kort kennisgewing via die internet bestel kan word. In hierdie tesis word ’n besluitnemingsteunstelsel ontwikkel vir optimale bestuur van voorraad by die fabriek, wat karton afknipselvermorsing onderhewig aan vereiste diensvlakke minimeer. Vantevore is ’n eenvoudige voorraad aanvullingstrategie, wat hoofsaaklik op ondervinding gebaseer was, by die fabriek toegepas. ’n Wetenskaplike gefundeerde voorraadmodel word vir Clickabox ontwikkel en toegepas, waarin ’n rou–voorraad kaskade– substitusie proses in aanmerking geneem word, asook die stogastiese vraag na kartondose en faktore soos prys, diensvlakke en benodigde stoorruimte. Hierdie kombinasie van stogastiese vraag en rou–voorraad kaskade–substitusie is, tot die skrywer se kennis, nog nie in die literatuur behandel nie. Die studie het twee hoof–uitkomste ten doel. Die eerste is ’n aanbeveling ten opsigte van ’n geskikte rou–voorraad samestelling (kartontipes waaruit kartondose geproduseer kan word) wat by die fabriek in voorraad gehou moet word. Die tweede is ’n rekenaarmatige besluitnemingsteunstelsel, wat op die ontwikkelde voorraadbeheermodel gegrond is, en wat vir toekomstige besluite in verband met voorraadaanvulling by Clickabox bedoel is. Van die resultate wat in hierdie tesis vervat is, is reeds ten tyde van die opskryf daarvan doeltreffend by die fabriek ge¨ımplementeer. Ondermeer is die aanbeveling in verband met die geskikte voorraadsamestelling, geleidelik vanaf Maart 2003 by die fabriek ingefaseer. Dit het duidelik geword dat hierdie samestelling beter as die vorige voorraadprofiel funksioneer, in terme van ’n verlaging in afknipselvermorsing en ’n verhoging in die beskikbaarheid van geskikte kartonne.

The purpose of this study was to investigate the impact of the maintenance management system (MMS) on production output and profitability (PO&P) at the Petroleum Oil and Gas Corporation of South Africa (PetroSA) GTL Refinery as a source of competitive advantage. State-Owned Companies and, or more specifically the PetroSA GTL Refinery must maintain its strategic importance for government fuel security but, at the same time, it must compete against private refineries in terms of achieving high production volumes, maximising profitability and to maintain its stake of 6.5% of the available production capacity. The literature review for this study suggested that the maintenance management system (MMS) impacts positively on production output and profitability (PO&P). The MMS has a tremendous influence on PO&P at the PetroSA GTL Refinery. Using a quantitative research design, cross-sectional research survey and the Maintenance Scorecards (MS) assessment tool, this study was conducted on six areas of the PetroSA GTL Refinery. Two population groups, namely production and maintenance groups participated in the survey. Fifty-six respondents belonged to the maintenance group and thirty-eight respondents belonged to the Production Group. All the Maintenance and Production Group respondents completed the MS questions designed to fit the characteristics of these population groups. Correlation analysis in terms of the means, standard deviations, gap analysis, Pearson product moment correlation coefficient (r) as well as the coefficient of determination (R²) was used to analyse the data. The findings of the study indicated a moderate positive linear correlation between the MMS and PO&P. Recommendations based on the findings were tabled in chapter 7 to improve and enhance production perspective (asset health gap), safety perspective (asset prioritisation gap) and the learning and growth perspective (skills and working condition gap). / Business Management / M. Com. ((Business Management)

A multistage production system consists of a number of production stages that are interrelated, that is the output from one stage forms input to the next stage. There are constraints associated with each stage as well as constraints imposed by the overall system. Besides, there are multiple objectives that need to be satisfied, and in numerous cases, these objectives conflict with each other. What is required is an efficient technique to allocate and schedule resources so as to provide a balance between the conflicting objectives within the system constraints. This study is concerned with the problem of scheduling multistage production systems in food processing industry. The system and products have complex structure and relationships. This makes the system difficult to be solved analytically. Therefore, the problem is solved by developing a heuristic algorithm that considers most of the constraints. The output generated by the algorithm includes a production schedule which specifies the starting and completion times of the products in each stage and the machines where the products are to be processed. In addition, a summary of system performances including throughput times, resources' utilizations, and tardy products is reported. / Graduation date: 1992

This dissertation is composed of three major parts, each studying a problem related to semiconductor manufacturing. The first part of the dissertation proposes a high-level scheduling model that serves as an intermediate stage between planning and detailed scheduling in the usual planning hierarchy. The high-level scheduling model explicitly controls the WIP over time in the system and provides a more specific guide to detailed scheduling. WIP control is used to balance the WIP (Work In Process) level and to keep the bottleneck station busy to maintain a high throughput rate. A mini-fab simulation model is used to evaluate the benefits of different approaches to implementing such a high-level scheduling model, and to compare different WIP control policies. Extensive numerical studies show that the proposed approaches can achieve much shorter cycle times than the traditional planning-scheduling approach, with only a small increase in inventory and backorder costs. With increasing worldwide competition, high technology product manufacturing companies have to pay great attention to lower their production costs and guarantee high quality at the same time. Advanced process control (APC) is widely used in semiconductor manufacturing to adjust machine parameters so as to achieve satisfactory product quality. The interaction between scheduling and APC motivates the second part of this dissertation. First, a single-machine makespan problem with APC constraints is proved to be NPcomplete. For some special cases, an optimal solution is obtained analytically. In more general cases, the structure of optimal solutions is explored. An efficient heuristic algorithm based on these structural results is proposed and compared to an integer programming approach. Another important issue in manufacturing system is maintenance, which affects cycle time and yield management. Although there is extensive literature regarding maintenance policies, the analysis in most papers is restricted to conventional preventive maintenance (PM) policies, i.e., calendar-based or jobbased PM policies. With the rapid development of new technology, predictive maintenance has become more feasible, and has attracted more and more attention from semiconductor manufacturing companies in recent years. Thus, the third problem considered in this dissertation is predictive maintenance in an M/G/1 queueing environment. One-recipe and two-recipe problems are studied through semi-Markov decision processes (SMDP), and structural properties are obtained. Discounted SMDP problems are solved by linear programming and expected machine availabilities are calculated to evaluate different PM policies. The optimal policy can maintain a high machine availability with low long-run cost. The structures of the optimal PM policies show that it is necessary to consider multiple recipes explicitly in predictive maintenance models. / text

Call number: LD2668 .T4 1979 L39 / Master of Science

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

Research report submitted in partial fulfillment of the requirements for the degree Master of Commerce in Development Theory and Policy at The University of the Witwatersrand 2016 / This study investigates the nature of labelling and regulation in South African free-range dairy production. It aims to reveal the complexities of designing and implementing regulation on process characteristics and policy’s failure to address the heterogeneous needs of consumers and producers. In parallel, the tensions that arise in the policy-production interaction are considered. This research addresses a gap in the theoretical and industry literature regarding understanding and explaining labelling, certification and regulation of credence attributes, such as animal welfare, within food systems. It provides interesting and important insight into regulation’s role in developing alternative production structures and niche markets as a response to variety in consumers’ needs and tastes. It is therefore relevant more broadly for understanding drivers for and governance of other niche production structures such as organic, fair-trade and religious or cultural influences. / MT2017