Volume 26 (2018): Issue 42 (June 2018)

Electric cables can contribute to the spread of fire through the insulating layer. This paper focuses on their properties characterizing the initiation of fire. Samples of ethylene-based cable insulation were tested using a cone calorimeter by exposing them to external heat flows of six different values (25 kW m⁻² – 50 kW m⁻²). Time to initiate flame burning was observed. The critical heat flux (depending on the method of calculation was in the range 2.94 kW m⁻² – 4.59 kW m⁻²) and the thermal response parameter (342 kW s^−0.5 m⁻²) was calculated from the time of initiation and external heat flow dependence.

This paper deals with the fire risk of a selected halogen-free electrical cable. The research was objected to a three-core power electric cable for a fixed installation CHKE J3x1.5 (cross section of each copper core was 1.5 mm²) with a declared class of reaction to fire B2_ca, s1, d1, a1. The electrical cable was manufactured and supplied by VUKI, a. s., Slovakia. The fire risk of the electric cable was evaluated based on the heat release rate, total heat release, smoke release rate, total smoke release and effective heat of combustion. These parameters were measured using a cone calorimeter at 50 kW m⁻² (specimens and cone emitter were placed horizontally during the test). The measured electrical cable showed a maximum heat release rate of nearly 150 kW m⁻², a maximum average heat emission rate of almost 100 kW m⁻², a total heat release of almost 130 MJ m⁻², a maximum smoke release rate of almost 2.5 s⁻¹, a total smoke release of more than 800 m² m⁻², an effective heat of combustion (cable as a whole) of nearly 9 MJ kg⁻¹ and an effective heat of emission (polymeric parts of the cable) of 26.5 MJ kg⁻¹.

The purpose of this article is to describe the methodology to define coefficient of friction between a tool and a forming material during tube cold draw technology process. In this regard, an experimental drawing process was done by using the tensile testing machine. The tensile testing machine was modified by additional equipment that allows drawing the tube. During the drawing, the force was recorded. Subsequently, the finite element simulation of cold draw forming was used to generate load-stroke curves with different friction coefficient. The friction coefficient was estimated by comparing the load stroke and the force recorded curves.

An important point in Tribology is mechanical-dynamic testing of lubricants and materials under stress and the interpretation of the results obtained therefrom. Widely-used test methods are often applied to test the performance of lubricants e.g. test results determined by tribometers should be treated carefully when using marketable oils. A closer evaluation of these results is part of this research paper. Within this study, several marketable oils were used and experimentally investigated. These were a gear oil, two engine oils, one hydraulic oil, one metal working fluid and one forming oil. There were several distinct differences. On the one hand, the used oils differ significantly in terms of their performance in the individual test methods. This is not surprising but has a clear reason in the different compositions of the lubricants resulting from their respective application. By subjecting these oils to diverse test methods with different test equipment, the results can vary widely and result in completely dissimilar results from the tests. Thus, a metalworking oil appears excellently when determining the welding force in the four-ball apparatus. In the high frequency liear oscillation tester, on the other hand, barely usable results are generated. Thus, there are two contradictory statements that should be the same.

In practice, pipe products are often produced. The surfaces of these components are often turned. The three-jaw chuck is often used to clamp the components for turning. It is a universal clamping fixture. The main advantage of three-jaw chuck is its high flexibility. However, its disadvantage is the inappropriate influence of the clamping forces on the geometrical accuracy of the produced components. This article deals with research of the influence of clamping forces on the roundness of turned pipes. A universal three-jaw chuck was used. The chuck was tightened using a torque wrench. The applied tighten torques were determined by monitoring the commonly used torques for a manually tightened chuck. The article presents the results of experimental research.

In the changing economic environment, global competition where the customer demands are changing continuously, the enterprises have to focus on cost reduction, efficiency improvement, higher productivity and profitability. In the production, the resources (raw materials, humans, machines, equipment, etc.) are always limited. It is very important for the manufacturing companies to produce cost effective final products in a short lead time which can be achieved by minimized cost and higher effectiveness, and therefore, efficiency improving methods are needed. There are lot of tools and sophisticated methods for design, analysis and improvement of production and logistical processes. The author introduces the most often applied methods for it, which are the simulation, Lean method and layout design. The paper summarizes the characteristics, typical application fields of these methods and the reasons for application of these. Main aims of logistics process improvement and the main steps and advantages of the described methods are introduced.

Paper deals with the design of assembly workplaces and systems. The aim is to provide a solution to the problems in the field of the assembly systems design and planning. One of the goals is to design a solution to the design of assembly workplaces. The focus of the research is therefore a proposal of the design methodology of the assembly workplaces and systems, and thus the development of integrated methodological procedure and tools. The introductory part is devoted to the current state of assembly workplaces, assembly systems and their planning. On the basis of the theoretical knowledge, an analysis of the assembly systems and workplaces is carried out according to the pre-selected criteria. It is necessary to develop the classification of assembly systems and workplaces in terms of product or assembled entities. Individual sections of the paper are devoted to the design of databases for the needs of designing the assembly workstations and systems.

The article deals with main research direction in the field of assembly process analysis and assembly workstation design. The basic applied methods and tool in the mentioned research direction are a part of digital factory concept. The paper presents the application of knowledge system for DFA analysis, computer aided assembly, workstation design and application of virtual reality.

Coordinate measuring machines are devised for most complex measurements. Besides their dimension measuring abilities, the CNC operated machines can measure geometrical characteristics of form, such as straightness, roundness, cylindricity, etc. These are vital features currently, when inspection needs to submit very thorough reports not only on the form, but also on the geometrical features of the given workpiece. Yet the question arises: are these measuring data regarding roundness received from the CMM accurate and reliable enough to be exploited? In order to confirm this statement, the geometrical roundness characteristics were measured on three types of coordinate measuring machines, the results of which were analyzed from several aspects. The results showed a special importance of specific measuring parameters and proved to be independent of the type of measuring machines.

The present article focuses on the possibilities of using Virtual Reality (VR) as a supporting tool by using the offline programming method for industrial robots. The philosophy of using such a process is hierarchically linked to the observance of methodological procedures for the proposal new workstations with using industrial robots. First, it is necessary to develop CAD models of the projected workplace, which can be imported into a suitable simulation environment for the creation of robotic simulations with support for visualization to the immersive VR environment. In our case, the CAD software Catia was used to develop a workstation, followed by integration of the CAD database into the simulation environment of Process Simulate (PS). Support for the visualization in the immersive environment of the Virtual Reality of Process Simulate was vested using the glasses headset HTC VIVE.

With the rise of the Industry 4.0 and the digitization increase in the field of design of the automated devices and systems, raises the requirements to digitize all stages of the design processes, including Virtual Commissioning. This technology allows to verify the functionality of the device and/or systems, generate OLP programs for robots and test the functionality of the PLC code on the virtual model. The article presents research into the possibility of implementing a robotic cell into a real flexible production system in the Laboratory in order to eliminate defective products after an automatic control through the Quality-handling station. This technology was verified on the basis of a methodology through a virtual system model and a virtual control system in the Software-in-Loop using the Siemens Tecnomatix Process Simulate software.

The system with short circuiting metal transfer in comparison to common MIG/MAG process was introduced as CMT (Cold Metal Transfer) process by the Fronius company in 2004. The paper deals with the arc current analysis of the CMT process during MIG brazing of automotive components. The TPS 5000 CMT power source together with VR 7000 CMT wire feeder, Robacta Drive CMT welding torch and CuAl 5 Ni 2, Ø1 mm filler metal were used. In order to monitor the welding current, the galvanic separator WS 1.0, digital oscilloscope ETC M621 and IBM notebook with software applications ETC Scope M621 were engaged. A current waveform in the stage D at the time of 5s from the brazing process beginning within duration of 50 ms was closely analysed. The analysis revealed the total ratio of the arc burning to the total brazing time to be approximately 26%. The starting and ending phases of short-circuit were performed at decreased current (approximately 34 to 38 % of the current value during arc burning), which was very positive from the transient effect point of view, and could not be proclaimed for the conventional short-circuit droplet transfer modes.

This contribution focuses on the topic of the Production–Maintenance integration at the tactical level and what it presents to the correct functioning and success of companies. For these purposes, a general framework for the integration of production and maintenance planning at the tactical level is introduced and described within this paper. It considers the key elements from the Value Analysis, Fuzzy Control and the Reliability-Centered Maintenance theories and implements them into the context of an existing method for selecting maintenance strategies. The proposal mainly focuses and addresses the definition of 1/ the roles played by the fixed assets that do really add value to the production system, 2/ the best maintenance strategy for each asset, and also addresses 3/ the modifications that, may be needed in the tactical production plan due to potential capacity problems in the maintenance subsystem.

The present paper discusses the impact of the speed of an abrasive water jet cutting process on some surface properties and morphology of the S235JRG1 steel. The values of the cutting speeds used for the analysis were of 100, 150 and 200 mm.min⁻¹respectively. A contact profile method was used to analyze the surface roughness during the conducted tests. In this study, the observed surface roughness parameters were the Ra, Rt and Rz, respectively. At the same time, these parameters were measured in three positions, i.e.: at the inlet (A), in the middle (B) and at the exit position (C) of the water jet nozzle with respect to the machined material. The experimental study showed that the roughness of the surface reached higher peaks and was more pronounced at the exit position (C) of the water jet. Similarly, it was also concluded that a better quality of the surface was achieved at a speed of 150 mm.min⁻¹.

The article presents a constructive heuristic for the integrated programming of production orders and preventive maintenance (PM) interventions in an environment of identical parallel machines, aimed at minimizing the completion time of the last scheduled job (makespan). Unlike other proposals found in the literature, the one here considers that the time between preventive interventions is not previously known, but instead, this is assumed as one of the decision variables of the system in the beginning of each of these interventions; in addition, the proposal also considers the possibility that not all jobs have the same release time. The design of the heuristic algorithm is based on the general approach of the Longest Processing Time dispatch rule, with a slight modification in its conception to consider the random character of the equipment failures and their impact on the execution time of the tasks. Consequently, a simple dispatch rule called rj - LPT was also proposed to comply with one of the steps of the heuristic, as well as an algorithm to determine the minimum dimension for the makespan, which constitutes the basis of the stop criterion linked to the initial solution.

In these days, the maintenance process, as a part of the operation of manufacturing systems, is also developing while following the changes in the production area. Maintenance, in many of the cases, is operating as an individual service task, which requires many changes from the related handling processes. To follow the changes and the development in the field of the maintenance, we need many new concepts, methods and ideas. Main objective of our research was to uncover the relations between the effectivity of the maintenance processes and the material handling parameters. In this paper, we summarise the development of the maintenance processes and give an overview about the topical handling tasks, which must be solved.

To achieve quick response of production, it is necessary to abandon the traditional form of production process planning. Nowadays, most of the products are designed by using CAx software. The product design 3D model contains not only the geometrical data of product, but may contain a part of the process plan and technological data as well. The process plan is important to enter the process of manufacturing of various precision engineering components of complex shape. Using the highest level of programming through graphical engineering system, a 3D model and the ISO programs using CNC machine tools were designed.

Porosity distribution in the spin cast zinc alloy castings was observed. Results shows that it is influenced by rotations per minute and by the centrifugal and Coriolis’ forces. The influence of Coriolis’ force is higher at low rotation speed. Porosity in castings can be eliminated by high rotation speeds.

The growing pressure to increase productivity and production quality is one of the reasons for the growing interest in using automated production facilities, such as robots. In many enterprises, automated lines are introduced that partially or completely replace the human factor. The automotive industry was one of the first to start using automated robots and still is the one of the largest users of these devices. Flexibility and affordability enabled robots to become part of the industry’s automation strategy. In order to achieve the desired goals, it is necessary to modernize and automate workplaces or to create completely new concepts of grouping of machines and industrial robots. An increasing trend in the use of robotic technology has caused several factors that have changed significantly in the recent years in favor of automated workplaces. The main changes made by industrial robots to the fore are improving their technical parameters, high reliability, affordability, reduced operating and maintenance costs.

The paper discusses the use of 3D digitization and additive manufacturing technologies in the field of medicine. In addition, applications of the use of 3D digitization and additive manufacturing methods are described, focusing on the design and manufacture of individual medical aids. Subsequently, the process of designing and manufacturing of orthopedic aids using these technologies is described and the advantages of introducing the given technologies into the design and manufacturing processes in the medicine sector are presented.

The technology of plasma polishing in electrolyte is considered as environmental friendly alternative to the common electrochemical polishing process. The solutions of the electrolyte use no acids or toxicants, but the environmental safe, low concentrated aqueous solutions of various inorganic salts are used instead. The dependence of the gloss level of the treated surface upon the electrolyte concentration as well as upon the voltage is examined in this paper. The specimens of stainless steel were used for plasma polishing in ammonium sulphate based electrolyte. The influence of the voltage on the overall properties of the process is discussed, as well.

This paper deals with the influence of the end mill helix angle on the flatness and surface quality of aluminium (EN AW 6082) thin-walled parts. The three teeth solid end mills of 12 mm diameter with same and different helix angle of third tooth were designed. The tests were performed using the HSC 105 linear CNC machine and following cutting parameters: cutting speeds (800, 100 and 1200 m.min⁻¹), feed per tooth (0.12 mm), cutting depth (for roughing 10 mm and for finishing 5 mm). Evaluation of surface quality of the processed thin-walled parts shows that the helix angle of the end mills has a significant influence on the surface quality of the thin-walled parts. The best results were obtained in the case of end mill with different 35° helix angle of third tooth and cutting speed 1000 m.min⁻¹.

The paper deals with the design of replaceable jaws on pneumatics gripper of the CNC milling machine EMCO Concept MILL 105, which is part of the iCIM 3000 manufacturing and assembly system. When designing replaceable jaws to allow firm and safe clamping of rotating and non-rotating parts, it was based on limiting factors such as parameters of the pneumatics gripper, dimensions, shape and material of the clamped parts and the like.

The article deals with the tool life of ball nose end mills during finish milling of weld deposit. The aim was to determine and compare the wear of ball nose end mill for different types of ball end milling strategies, as well as to specify particular steps of the measurement process. For tool life test, DMG DMU 85 monoBLOCK 5-axis CNC milling machine was used. In the experiment, the cutting speeds, feed rates, axial and radial depth of cut were constant. The coated cemented carbide was used as tool material. The cutting tool wear was measured on Zoller Genius 3s and laser Blum Micro Compact NT. The results show different achieved tool life of ball nose end mills depending on the finish milling strategy.