Algoritam planiranja operacija "flow shop" u cilju smanjivanja vremena izvršenja kod problema n-poslova i m-strojeva

In multi stage job problems, simple priority dispatching rules such as shortest processing time (SPT) and earliest due date (EDD) can be used to obtain solutions of minimum total processing time, but may not sometimes give sequences as expected that are close to optimal. The Johnson\u27s algorithm is especially popular among analytical approaches that are used for solving n-jobs, 2-machines sequence problem. In this paper the presented algorithm is based on converting an m-machine problem to a 2-machine problem. Based on testing and comparison with other relevant methods, the proposed algorithm is offered as a competitive alternative for practical application when solving n-jobs and m-machines problems.U problemima posla s više faza, mogu se koristiti jednostavna prioritetna dispečerska pravila kao što su najkraće vrijeme obrade (PT) i najraniji datum dospijeća (EDD) za dobivanje rješenja najmanjega ukupnog vremena obrade. Međutim, ona ponekad ne daju slijed za koji se očekuje da je blizu optimalnom. Johnsonov algoritam je posebno popularan među analitičkim pristupima koji se koriste za rješavanje problema slijeda n-poslova i 2-stroja. Algoritam prikazan u ovom radu se temelji na pretvaranju problema m-strojeva u problem 2-stroja. Na temelju ispitivanja i usporedbe s drugim relevantnim metodama, predloženi algoritam se nudi kao konkurentna alternativa za praktičnu primjenu pri rješavanju problema n-poslova i m-strojeva

Supplier evaluation and selection: a fuzzy novel multi-criteria group decision-making approach

Suppliers’ evaluation and selection is a subject widely explored through many different kinds of approaches and multi-criteria decision methods, and more recently also through group decision making ones. This paper addresses these problems by proposing an easy-going two-phase supplier selection decision model that uses a scientific approach and incorporates performance criteria in screening and selecting the potential suppliers for further optimal supplier selection. The first phase of the model determines the performance of the suppliers on both quantitative and qualitative criteria and the relative importance weights of the criteria. Fuzzy set theory is utilized to deal with the imprecision and vagueness involved with the subjective judgment of both the qualitative data of the decision-matrix and the relative importance weights of the criteria. In the second phase, the suppliers are screened using their efficiencies and an agreed threshold. Then, the optimal supplier for corporation is selected from the limited potential suppliers set. To illustrate the applicability and validate the proposed model, a case study of a beverage producing company located in Ghana, the Sub-Saharan Africa is proposed. The results of the study can provide valuable clues and guidelines to decision-makers and analyst in pre-contract negotiations. The proposed model will assist practicing managers to effectively reduce their supply-base and efficiently select the optimal supplier for corporation. Implications of the study to the theory and practice and future research directions are also outlined.info:eu-repo/semantics/publishedVersio

Manufacturing technology of composite materials-principles of modification of polymer composite materials technology based on polytetrafluoroethylene

The results of the investigations into the technological formation of new wear-resistant polymer composites based on polytetrafluoroethylene (PTFE) filled with disperse synthetic and natural compounds are presented. The efficiency of using PTFE composites reinforced with carbon fibers depends on many factors, which influence the significant improvement of physicomechanical characteristics. The results of this research allow stating that interfacial and surface phenomena of the polymer-solid interface and composition play a decisive role in PTFE composites properties. Fillers hinder the relative movement of the PTFE molecules past one another and, in this way, reduce creep or deformation of the parts, reducing the wear rate of parts used in dynamic applications as well as the coefficient of thermal expansion. The necessary structural parameters of such polymer composites are provided by regimes of process equipment.Web of Science104art. no. 37

DESIGNING AND EFFECTIVENESS OF VIRTUAL LOGISTICS CENTERS

Abstract: This paper investigates the creation, benefits, obstacles and further development areas of virtual logistics centers. Its main focus is on designing and effectiveness of multi-integral logistical centers. Also other aspects, like impacts of ICT on the development of virtual logistical centers and the development stages of SCM are presented. Moreover, the paper outlines some pitfalls of this development trend in an effort to provide pertinent practitioners and other involved with a more complex view of this issue

A CASE STUDY ON MEASUREMENT EFFECTIVENESS

Ensuring the measurement effectiveness of Cost of Quality (COQ) implementations presents steadily a practical managerial problem. Even though there are many approaches to measurement COQ optimal methods for this purpose in real conditions often depend on confrontation and evaluation of different calculation models. The paper based on a case study describes a procedure for comparison between so called controllable costs and incurred cost of poor quality. Presented study confirms assumption of a propitious influence of preventive costs on an overall COQ and a change of structure of separate cost of quality items

Study of a tap failure at the internal threads machining

The article aims to study a tap failure during the internal threads making. Within the research, the synergic effects of cutting speed and helix angle on the durability of selected taps have been investigated including detection of the types tool wear that occurred during the machining. The C45 steel has been selected for the study as a standard machined material used at the long-term durability tests. Three types of taps for M12 thread making with three different helix angles ω = 0° 15° and 35° all with cutting cone type C, were used during the experiments. The experimental study was carried out in several steps. At the beginning, the preliminary tests were done to be verified the input parameters related to both machined material and tool geometry. In the main phase of the experiments, tool life was investigated at the cutting speed recommended by the tool supplier and after that also at the higher cutting speeds. Within the research, the equations that describe the dependencies of tool durability and threaded length on both observed parameters have been developed based on the experimentally obtained data. The vibro-diagnostic of the taps was carried out because of process stability monitoring and the possibility to predict the tool behavior at the machining with early identification a tool failure. The results have shown that the intensity of tool wear is affected not only by cutting speed but also by the pitch angle of the tap. Next findings confirmed that the tap failure can appear in various forms and that it is possible to identify the presence of tap wear by means of vibro-diagnostics. © 2019 Elsevier LtdMinistry of Education, Science, Research and Sport of Slovak Republic [KEGA 007TUKE-4/2018, VEGA 1/0795/19