Nikola Gjeldum

Investigation and modelling of process parameters and workpiece dimensions influence on material removal rate in CWEDT process

Cylindrical wire electrical discharge turning (CWEDT) is a special form of wire electrical discharge machining (WEDM) process, which uses submerged rotation spindle as a clamping device for workpiece rotation in order to produce cylindrical parts. This study aims at determining influence on material removal rate (MRR) of CWEDT as an objective function. In the preliminary experiments, the widely used X5CrNi18–10 (DIN) and hard machinable S390PM (DIN) were used. The results of preliminary experiments showed that the type of steel is not the factor that has a significant influence on MRR. Pulse maximum current, pulse pause time, rotation speed, length of discharge area and cutting radius were used in MRR mathematical modelling by neural network programming. The results of the study exhibit that among the machining parameters, the pulse maximum current has the strongest influence on MRR. When the pulse maximum current increases, MRR increases as well. The discharge area length has an influence on MRR only on higher pulse maximum current values, and by the increase of the discharge area length, the MRR also increases. The derived mathematical model for MRR, which was finally validated and tested, enables calculation of complex cylindrical part production machining time for the given experimental set-up condition.

Solving partner selection problem in cyber-physical production networks using the HUMANT algorithm

The idea of non-hierarchical production networks consisting of autonomous enterprises has been present in scientific community for more than 20 years. Although some global corporations are using their own production networks across continents, they are not similar to the original idea of non-hierarchical production networks in many aspects. It seems that this idea waited for production systems to acquire proper information and communications technology (ICT) or new industrial platforms, like Industry 4.0. The result is a new type of production network called Cyber-Physical Production Network (CPPN). The CPPN is, from ICT point of view, ready to act as non-hierarchical production networks consisting of autonomous production systems with many automated processes. One of the most important processes of the CPPN is a selection of optimal partners (enterprises) to be part of a new virtual enterprise, created inside production network. An optimisation problem emerges in this process, and it is called Partner Selection Problem (PSP). It is non-polynomial-hard combinatorial problem. Since metaheuristic algorithms are well-proven in solving that kind of problem, a specially designed metaheuristic algorithm derived from ant colony optimisation and named the HUMANT (HUManoid ANT) algorithm is used in this paper. It is multi-objective optimisation algorithm that successfully solves different instances of PSP with two, three, four or more objectives.

Selection of the Basic Lean Tools for development of Croatian Model of Innovative Smart Enterprise

The research within project Innovative Smart Enterprise (INSENT) was conducted in order to improve scientific understanding of the current state of Croatian manufacturing industry by promoting empirical, enterprise-level research on technological and non-technological processes and organizational innovation. The aim was to understand how manufacturing enterprise in Croatia acquire new manufacturing technologies, ICT integration within processes, new organizational concepts in production such as group work or relocation of production, new products that emerge from process and organizational innovation such as production-related services, and other demands related to Industry 4.0. In order to develop Croatian model of Innovative Smart Enterprise (HR-ISE model), analysis of global and local enterprises, based on literature review and questionnaires, has been made. A selection of six basic Lean tools is made, and foundations of generic configuration of HR-ISE model are defined. In further research, interviews with CEOs of leading Croatian manufacturing enterprises should help creating completely defined HR-ISE model.

Application of AHP, Fuzzy AHP and PROMETHEE Method in Solving Additive Manufacturing Process Selection Problem

Additive manufacturing is a technology of making a three-dimesional solid object of any shape from a digital model. Today on the global market exist various additive manufacturing processes. All of these processes build parts by applying material layer by layer. In a wide range of different processes there is a problem of selecting an adequate process for a user or company interested in additive manufacturing technology. Solving of such a problem is possible by using multicriteria decision methods which result in ranking of alternatives. Thus the user or company can easily select one of the available additive manufacturing processes. In this paper basic methodology of application of three different multicriteria decision methods in solving the mentioned problem was shown. These methods are: Analytic hierarchy process (AHP), Fuzzy AHP and Preference ranking organization method (PROMETHEE). Available alternatives are processes: 3D printing, Fused Deposition Modeling, Selective Laser Sintering and Photopolymer Jetting.

Simulation of Bullwhip Effect in a Supply Chain for Lean Learning Factory Purposes

A mission of the Learning Factory (LF) is a development of practice-based engineering curriculum through the simulation of a real factory by specialized equipment. In this paper, supply chain network simulator is developed, as a replacement for the traditional board Beer Game. The board Beer Game could be misused by participants in order to avoid significant bullwhip effect, which occurrence is the Beer Game main aim. The disadvantage of the board Beer Game, that participants have insight in inventory levels and placed orders and thus strategically act upon their knowledge or even activate a sort of decentralized information sharing policy, is avoided. Further considerations prove the mandatory occurrence of bullwhip effect without decentralized information sharing policy on three case studies. Optimal mathematical model for placing orders within supply chain was defined according to multi-criteria optimization process using spreadsheet simulation. As even optimal model results with the bullwhip effect, newly developed system will always lead to the tremendous bullwhip effect during the learning process.

Modeling of Control Loop in Production Scheduling for Overall Inventory Cost Reduction

Performance of manufacturing organization depends on production scheduling which is an essential part of the management of production systems. Effective scheduling can lead to performance which results in reducing work in process inventories [1]. According to the lean production principles, excessive production and high inventory level are the biggest waste in production process [2]. Inventory level higher then it is necessary for fulfilling the costumer demands, leads to additional costs in warehouse. Objectives of production control are graphically represented over time in diagrams: inventory, lead time, input orders and output of production process. In this paper, the fact that the input and output amount of work coming from released orders of one product are not equal in every period, results with a technique to balance input against output continuously, to establish a control loop.