Browsing by Author "Matope, S."
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- ItemAgent based job scheduling for a vehicle engine reconditioning machine shop(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Nyanga, L.; Van der Merwe, A. F.; Burawa, M.; Matope, S.; Dewa, M. T.ENGLISH ABSTRACT: Job scheduling at a machine shop is a multi-decision criteria problem whose skills are acquired after some years of experience. For Small, Medium to Micro Enterprises (SMMEs) with limited machinery the objective when scheduling jobs should not only focus on machine utilization but also on the increase of job through put. The paper presents an agent based job scheduling system for a vehicle engine reconditioning machine shop to assist decision makers in job scheduling. The Analytic Hierarchy Process (AHP) method was used to compute the relative weights of each decision criteria used for job scheduling considering the job priority. The value of the job, the number of operations to be performed, the engine type, the frequency of the customer and the company to customer relationship rating are used to prioritize the jobs. A Multi Agent System (MAS) comprising of the provider, job allocator and machine agents is developed using the Java Agent development framework (JADE) methodology and modelled using Unified Modelling Language (UML 2). The provider agent schedules all the jobs based on job weight and earliest due dates. The job allocator agent is responsible for making sure that all the scheduled jobs are allocated to all the machines after which they are registered as complete jobs and can leave the system.
- ItemA conceptual framework to create shared value in base of the pyramid communities with micro-containerised factories(Elsevier, 2019) Chihambakwea, Z. J .; Oosthuizen, G. A.; Matope, S.; Uheidaa, E. H.ENGLISH ABSTRACT: Shared value creation at the Base of the Pyramid (BoP) receives growing interest. The BoP is a socio-economic group characterised by people who have poor nutrition, limited income, inadequate technologies, lack of access to markets and poor infrastructure to produce valuable products and services. Possible methodologies and systems to successfully implement sustainable micro-containerised factories at the BoP are still very limited and remain unanswered. In this study a conceptual framework to create shared value in BoP communities with micro-containerised factories is developed. These factories provide portable, scalable technologies to produce valuable products from sustainable locally sourced resources or waste streams. Concepts from literature and case studies were evaluated to identify key elements for the conceptual framework. A proposed business model and conceptual framework were developed to guide business model prototyping in a case study in South Africa.
- ItemDesign of a multi agent system for machine selection(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Nyanga, L.; Van der Merwe, A. F.; Tsakira, C.; Matope, S.; Dewa, M. T.ENGLISH ABSTRACT: In a machine shop effective assignment of jobs to machines is a multi-criteria decision making problem which is usually done by professionals and experienced planners. The skill of job assignment becomes handy in machine shops which are in the Small, Medium to Micro Enterprises (SMMEs) category as they work on a variety of products with limited machinery. The paper presents a machine selection system for helping decision makers when selecting machines to be scheduled. Customer order parameters which include product weight, clamping force, mould dimensions, due date and lead time are used to select moulding machines suitable to manufacture the desired parts. The criteria for machine selection was developed using Analytical Hierarchy Process (AHP) were quality, time and cost were considered as the key parameters. The available machines which meet the requirements for moulding a desired part are then made to compete for the part using an English auction. A Multi Agent System consisting of a managing agent, administrator and bidding agents was developed to conduct the auction that takes place between machine agents viewed as potential contractors representing available machines in the production line. The multi agent system is developed using Java Agent Development framework (JADE). An injection moulding plant with 11 injection moulders was used as a case study for application of the system.
- ItemDevelopment of a model for predicting cycle time in hot stamping(Elsevier, 2018) Muvunzi, R.; Dimitrov, D. M.; Matope, S.; Harms, T. M.In manufacturing, reducing the cycle time results in lower production costs. The cycle time in a hot stamping process affects the quality characteristics (tensile strength) of formed parts. A faster cooling rate (˃27 K/s) of the blank guarantees the production of a part with the required microstructural properties (martensite). This compels researchers to continuously develop ways of increasing the manufacturing speed. On the other hand, it is important to predict the minimum cycle time for a given set of parameters which does not compromise the quality of formed parts. In this paper, a model for predicting the cycle time for a hot stamping process is presented. The lumped heat capacitance method is used in formulating the model since the temperature gradient across the blank and heat transfer within the plane of the blank are considered negligible. To validate the equation, a finite element simulation was conducted using Pam-Stamp software. The results show that the proposed model can be useful in further studies targeted towards cycle time reduction in hot sheet metal forming processes.
- ItemA holonic approach to reactive scheduling when rush orders emerge(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Dewa, M. T.; Van der Merwe, A. F.; Matope, S.ENGLISH ABSTRACT: Rush orders can complicate the life of project managers when they emerge especially if they are of a high priority. Initially prepared process plans and schedules become invalid while extra capacity may be needed to meet the new demands placed on the shop-floor. However, with the era of distributed manufacturing, skills and resources can be shared in an optimal manner. The paper presents an application for automated management of resources in response to varying demands experienced by an industrial cluster of tool and dies workshops. A set of holons are utilized to monitor progress of orders in process while responding in real time to new demands placed on the system. The system utilizes the Petri-net protocol for the bidding function and automatically organizes the manufacturing function in a cost effective and timely manner. The ARENA discrete event simulation platform was utilized to demonstrate system’s results in a virtual environment.
- ItemHolonic control system : a proposed solution for managing dynamic events in a distributed manufacturing environment(South African Institute for Industrial Engineering, 2014) Dewa, M. T.; Matope, S.; Van der Merwe, A. F.; Nyanga, L.ENGLISH ABSTRACT: Due to globalization, manufacturing of products is no longer a local activity done by a single company but rather a distributed venture as more firms are realizing the need to improve their flexibility and agility. The paradigm of e-manufacturing is gaining popularity among researchers and manufacturers who aim to improve their market share and shop floor visibility by belonging to larger collaborative networks. However, real-time events which lead to operational disturbances in a plant remain a challenge most manufacturers face since they result in deviation from initially prepared process plans and schedules, rendering them invalid before they can be launched on to the shop floor for implementation. The paper presents a Holonic Control System (HCS) as a proposed solution to managing this pandemic. The research focused on manufacturing firms in the Western Cape of South Africa which belong to the tooling industry. Cited in this paper are holonic architecture together with the success factors and barriers to implementing holonic control systems in South Africa. Results of the proposed system were generated by a simulation model and revealed that delivery time and resource utilization were improved by adopting the system.
- ItemInfluence of process parameters on residual stress related distortions in selective laser melting(Elsevier, 2018) Mugwagwa, L.; Dimitrov, D.; Matope, S.; Yadroitsev, I.ENGLISH ABSTRACT: Residual stresses pose a major setback in Selective Laser Melting (SLM) and limit the applicability of the process, particularly from the standpoint of form accuracy and mechanical strength. The purpose of this paper is to investigate the influence of SLM parameters namely laser power and scanning speed on thermal stress related warping distortions and porosity. In this study, residual stress related distortions and achievable density for different process parameter combinations are presented simultaneously due to the profound influence of the porosity on residual stress relaxation. The paper also discusses the implications of the process parameters on the sustainability of the SLM process.
- ItemThe learning factory : a didactic platform for knowledge transfer in South Africa(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Van der Merwe, A.; Hummel, V.; Matope, S.During the first years of their employment, the graduates are a liability to industry. The employer goes an extra mile to bridge the gap between university-exiting and profitable employment of engineering graduates. Unfortunately some cannot take this risk. Given this scenario, this paper presents a learning factory approach as a platform for the application of knowledge so as to develop the required engineering competences in South African engineering graduates before they enter the labour market. It spells out the components of a Stellenbosch University Learning Factory geared towards production of engineering graduates with the required industrial skills. It elaborates on the didactics embedded in the learning factory environment, tailor-made to produce engineers who can productively contribute to the growth of the industry upon exiting the university.
- ItemA methodology to evaluate the influence of part geometry on residual stresses in selective laser melting(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Mugwagwa, L.; Dimitrov, D.; Matope, S.; Becker, T. H.ENGLISH ABSTRACT: The subject of residual stresses induced by the Selective Laser Melting (SLM) process has been one of the main focus areas in literature over the past decade. It has been reported that residual stresses can be responsible for shape and dimensional distortions, cracking and compromised mechanical properties (reduced yield and fatigue strength). These shortfalls limit the applicability of SLM components in industry, particularly for the aerospace industry where part lifetime and hence fatigue life is of utmost concern. High temperature gradients have been reported to be responsible for the residual stress build up. A key aspect that has not been considered in literature is part geometry and orientation and its influence on residual stress levels. Thus, this study proposes a methodology for investigating this influence for different geometric features. In this work, samples were built from tool steel powders. The Hole Drilling Method (HDM) and X-Ray Diffraction (XRD) techniques are proposed for measuring residual stresses. Preliminary results show that the geometry of a part influences residual stress magnitudes and distributions, with sharper ends exhibiting higher stresses than less sharp specimen ends.
- ItemMicro-material handling employing e-beam generated topographies of copper and aluminium(Southern African Institute of Industrial Engineering, 2011-11) Matope, S.; Van der Merwe, A. F.; Nemutudi, R.; Nkosi, M.; Maaza, M.ENGLISH ABSTRACT: This paper focuses on the employment of copper and aluminium in a micro-material handling system actuated by Van der Waals forces. Electron beam (e-beam) evaporator deposited both materials on a silicon substrate at a rate of 0.6-1.2 Angstroms/second, vacuum pressure between 2x10-6 and 3x10-6mbar, and at a current less than 10mA. A Veeco NanoMan V Atomic Force Microscope with Nanoscope version 7.3 software was used to analyse the root mean square (rms) surface roughnesses of the generated topographies. Rumpf-Rabinovichs rms formula was used to determine the Van der Waals forces exerted by the surfaces. It was synthesised that an e-beam deposition of 7 minutes duration on both materials produced an optimum micro-material handling solution, with copper suitable for the pick-up position and aluminium for the placement position.
- ItemMicro-material handling, employing e-beam coatings of copper and silver(Southern African Institute for Industrial Engineering, 2012-05) Matope, S.; Van der Merwe, A. F.; Rabinovich, Y. I.ENGLISH ABSTRACT: Van der Waals forces and other adhesive forces impose great challenges on micro-material handling. Mechanical grippers fail to release micro-parts reliably because of them. This paper explores how the problematic Van der Waals forces may be used for micro-material handling purposes using surface roughnesses generated by e-beam coatings of copper and silver on silicon. An atomic force microscope, model Asylum MFP 3 D-Bio with version 6.22A software, was used to measure the forces exerted by the surfaces. A silver coating of 1.41 nm rms surface roughness value is found to exert the highest Van der Waals force, followed by a copper coating of 2.72 nm rms; a copper coating of 217 nm rms exerts the least force. This implies that, in a reliable micro-material handling system, these coatings are suitable for the interactive surfaces of the placement position, micro-gripper, and the pick-up position respectively.
- ItemSilver, copper and aluminium coatings for micro-material handling operations(Southern African Institute for Industrial Engineering, 2013-08) Matope, S.; Van der Merwe, A. F.; Rabinovich, Y. I.ENGLISH ABSTRACT: Micro-material handling has challenges accompanying it because of adhesive forces, which make the picking and placing of micro-parts difficult. The adhesive forces hinder the picking of a micro-part, and once picked, they pose even a greater challenge when attempts to release a micro-part are made. Van der Waals forces are part of the adhesive forces and are always present between interacting surfaces in a micro-material handling operation. However, Van der Waals forces can profitably be manipulated in a micro-material handling operation. The paper reveals how the Van der Waals forces can be advantageously used in micro-material handling operations involving silver, copper and aluminium coatings of rms surface roughness values ranging from 0.5 nm to 2.72 nm, which are produced by the electron beam evaporation (e-beam) method. These were found to exert Van der Waals forces ranging from 17 nN to 314 nN, which can be used for reliable micro-material handling operations.
- ItemStudy on applicability of adhesive forces for micro-material handling in production technology(Stellenbosch : Stellenbosch University, Department of Industrial Engineering, 2011-09) Neugebauer, R.; Koriath, H-J.; Van der Merwe, A. F.; Muller, M.; Matope, S.Micro-material handling and micro-assembly becomes increasingly important in largevolume manufacturing of products like sensors in automotive applications. Smaller dimensions of the micro-objects lead to problems with regard to the reliability of the manufacturing process because adhesive forces become predominant over gravity for objects whose dimensions are in the micro-range. In contrast to the common approach of minimizing those adhesive forces, this paper focuses on the use of the three main adhesive forces, van-der-Waals, electrostatic and surface tension forces, as gripping principles. These forces are compared to conventional vacuum grippers with regard to gripping forces and complexity of application. Modelling of the forces is executed for separation distances in the range of 1x10-12 m - 1x10-3 m. Even though vacuum forces dominate in magnitude over others within the whole range, there are several disadvantages of using them. On the other hand adhesive forces are advantageous in that they require little amount of energy and they do not mechanically strain the micro-parts being handled.