Martin Necpal - Academia.edu (original) (raw)

Papers by Martin Necpal

Journal of physics, Dec 1, 2022

The cold drawing process produces high-quality tubes with precise dimensions, good surface qualit... more The cold drawing process produces high-quality tubes with precise dimensions, good surface quality, and higher strength due to cold forming. The tube drawing is used to reduce the cross section of the produced tubes. Depending on the reduction size, the outer diameter and wall thickness of the final tube changes. Due to the fact that cold drawing of tubes is mostly the last operation of production, it is necessary to pay attention to the process parameters and geometry of the forming tools. This paper presents a statistical evaluation of the influence of the wall thickness of the pre-tube, die diameter, and pre-tube diameter on the measured responses, which were the outer diameter and wall thickness of final tube, after the FEM simulations of the drawing process. For these purposes, a factorial design with three input factors was implemented. The goal of using the simulations was also to investigate whether the single-pass type of tube drawing would guarantee useful statistical results that could lead to significant time and cost reductions. The FEM simulations were executed using DEFORM software of Scientific Forming Technologies Corporation with Design of Experiment application module of this software. A factorial design of experiment has been processed in Minitab v. 17 software. The results show that most of the factors significantly influenced the response variables.

Research Papers Faculty of Materials Science and Technology Slovak University of Technology

Titanium grade 2 plates were modified by a pulsed nanosecond laser beam. The aim was to determine... more Titanium grade 2 plates were modified by a pulsed nanosecond laser beam. The aim was to determine the surface properties after the machining process in two different liquid media. The samples were processed in distilled water and paraffin oil. It was found that a surface with half-surface roughness values with a number of cracks was formed in distilled water. The presence of water reduced the size of the heat-affected zone.

IOP Conference Series: Materials Science and Engineering, 2021

The analyses of the tube drawing process can be divided into two basics parts of investigations -... more The analyses of the tube drawing process can be divided into two basics parts of investigations - macro-scale and micro-scale. Macro-scale analyses involve investigation of dimensional accuracy of the formed specimen, drawing forces, strain, stress, etc. The analyses of the tube drawing process in the macro-scale have been studied experimentally or theoretically using numerical methods for many years. For the final product of drawing process is also important to know the surface quality for example. For this purpose, it is important to know micro-scale material properties (spatial distribution of grain neighbourhood orientation etc.), and examine the context of micro forming material. There has been a trend in the last decade to make a link between macro-scale forming and micro-scale material properties and name it Multi-scale modelling. This research illustrates the possibility to use Voronoi tessellation grain microstructure model in DEFORM FEM software to predict grain plasticity...

A steel tube drawing process is a cold forming method to reduce the tube dimension and improve th... more A steel tube drawing process is a cold forming method to reduce the tube dimension and improve the surface quality simultaneously. The profiles and shape of drawing tools are key factors to achieve the requirements of tube geometric precision and surface quality. Production of multi-rifled seamless steel tubes by cold draw process using multi-rifled mandrel is quite a new technology. The important characteristic of the tube drawing process, unlike the tube with internal rifling, is the corner filling which influences the dimension accuracy of the internal shape of the tube. In order to ensure the reliability of the forming process and to achieve the desired product quality, FEM computer simulation and modeling are used to design forming tools and determination of forming process parameters [1,2] . A number of FEM applications are used in the manufacturing industry. DEFORM developed by Scientific Forming Technologies Corporation is an engineering software that enables designers to an...

Materials, 2021

We prepared overlap soldered joints of high-temperature superconducting tapes, using various mate... more We prepared overlap soldered joints of high-temperature superconducting tapes, using various materials and preparation conditions. In order to select the joints with optimal performance, we correlated their electrical properties (derived from current–voltage curves) with the microstructure of the respective joint cross-section by scanning electron microscopy. With the first group of joints, we focused on the effect of used materials on joint resistivity and critical current, and we found that the dominant role was played by the quality of the internal interfaces of the superconducting tape. Initial joint resistivities ranged in the first group from 41 to 341 nΩ·cm2. The second group of joints underwent a series of thermal cyclings, upon which the initial resistivity range of 35–49 nΩ·cm2 broadened to 25–128 nΩ·cm2. After the total of 135 thermal cycles, three out of four joints showed no signs of significant degradation. Within the limit of 100 thermal cycles, reliable soldered join...

Solid State Phenomena, 2020

The most comprehensive steel tube portfolio is used to produce all kinds of modern energy product... more The most comprehensive steel tube portfolio is used to produce all kinds of modern energy production and the corresponding auxiliary unit such as boilers and heat exchangers. Multi-rifled seamless steel tubes are distinguished by maximum pressure, heat resistance, strength and durability. Production of multi-rifled seamless steel tubes by cold draw process using multi-rifled mandrel is quite a new technology. Shape and dimension of the drawing tool depend on drawing tube reduction degree, i. e. on the original diameter of the initial tube and final diameter of the tube. The technology of drawing tubes is influenced by process parameters, dimensions of tools and cold forming process conditions. Optimization of the whole forming process naturally involve the FEM analyses and simulation. One of the most important information of the cold drawing process is the load stroke of the tools. The contribution is concerned at the usability of FEM simulation on an evaluation of cold draw forming...

Proceedings of the 30th International DAAAM Symposium 2019, 2019

The cold forming method and the process of the die drawing tubes are ranked among frequently used... more The cold forming method and the process of the die drawing tubes are ranked among frequently used methods of production. The aim of this paper is the research of using Finite Element Method for analyses of the cold drawing process to produce tubes with the contoured internal surface. This is the process of pulling the tube through a die using a fixed mandrel whose shape is designed to achieve the shape of the inner finned tube. Commercial software DEFORM 3D is used for numerical simulation. The size and shape of the forming tools are designed by following the real requirements of industrial production for the shape of the resulting tubes. The input parameter, such as the material model and the initial boundary conditions of the simulation, is determined based on previous real experiments and investigations. The result of the analysis is an assessment of the stress-strain process of the forming as well as the resulting tube in the individual cross-sections of the tube ribs. The result of the numerical simulation assists in the understanding of the technological processes of forming, defining the necessary plastic properties of the formed material as well as in the construction of the forming tools.

MATEC Web of Conferences, 2017

This paper deals with the deformation of precision seamless tubes during the cold drawing process... more This paper deals with the deformation of precision seamless tubes during the cold drawing process, using Finite Element Methods. The value of strain obtain by stereology measurement of degree grain boundaries deformation are compared with simulation result for each drawing pass. The material chosen was the E235 and E355 steel grade, which is drawn from the initial dimension of Φ70 x 6.3 mm to the final dimension of Φ 50 x 3.75 mm by two passes. FEM Software DEFORM 2D with the Lagrangian method is used to numerical analyses of the cold drawing process. 2 Experimental Material In this work, steel grade E235 and E355 (ferritic-pearlitic carbon steel, see Table 1 [1]) was considered; as a feedstock for cold drawing, hot rolled tube with dimensions of ∅70 x 6.3 mm was selected. Mechanical properties of E235 steel are as follows: yield stress Re = (226 ÷ 245) MPa, tensile strength Rm = (343 ÷ 441) MPa, ductility A5 = 24 %, mechanical properties of E355 steel are as follows: yield stress Re = (335 ÷ 355) MPa, tensile strength Rm = (490 ÷ 630) MPa, ductility A5 = 24 % [2].

Research Papers Faculty of Materials Science and Technology Slovak University of Technology, 2016

The article is focused on optimization of four-facet drill for 3D drilling numerical modelling. F... more The article is focused on optimization of four-facet drill for 3D drilling numerical modelling. For optimization, the process of reverse engineering by PowerShape software was used. The design of four-facet drill was created in NumrotoPlus software. The modified 3D model of the drill was used in the numerical analysis of cutting forces. Verification of the accuracy of 3D models for reverse engineering was implemented using the colour deviation maps. The CAD model was in the STEP format. For simulation software, 3D model in the STEP format is ideal. STEP is a solid model. Simulation software automatically splits the 3D model into finite elements. The STEP model was therefore more suitable than the STL model.

Applied Mechanics and Materials, 2015

This paper deals with precision seamless tube drawing process in Železiarne Podbrezová, consideri... more This paper deals with precision seamless tube drawing process in Železiarne Podbrezová, considering a three-pass drawing technology without the intermediate annealing. The material chosen was the E235 steel grade, cold-drawn from the initial dimension of ∅ 70 x 6.3 mm to the final dimension of ∅ 44 x 3.0 mm. Strength and deformation analyses for each drawing pass were made, based on simulation results in numerical modelling software DEFORM 2D. The deformations calculated for all passes served as a guideline for further process optimization. Furthermore, the effect of a particular reduction on mechanical properties was investigated (yield point Re, ultimate tensile strength Rm, ductility A, and hardness HV). The research shown here is a part of the Research Project No. 3-2014/ŽPVVC “TUMIFORM – Optimization of precision tube drawing technology considering dislocation theory, microstructure, and plasticity limit“, being solved at ŽP VVC s.r.o. in Podbrezová, Slovakia. This project deal...

Advanced Science, Engineering and Medicine, 2015

Key Engineering Materials, 2013

An article deals with a measurement of flatness of thin-walled parts with low rigidity. The flatn... more An article deals with a measurement of flatness of thin-walled parts with low rigidity. The flatness is important for quality thin-walled parts made by milling. Measurement of the variation in the flatness of thin-walled components conventional 3-axis, high-speed 3-axis milling was done. In the first part is description of flatness and definition of thin-walled parts. Second part characterizes the measuring system, the principle of measurement and experimental setup. The last part of this work is evaluation of the experiment, which compares different factors to determinate flatness during machining of thin-walled parts.

DAAAM Proceedings, 2018

The article is divided into two main experimental parts. The screening experiment setting is desc... more The article is divided into two main experimental parts. The screening experiment setting is described in the first part and settings of the main experiment is described in the second part. The aim was to clarify the impact of input parameters on the cutting process and to find those parameters to make the process as fast and stable as possible. Sintered carbide type K (PCG GMBH F10) was used as the sample. The experiment was performed on the machine Agie Charmilles Robofil 310. As input factors were selected pulse width, the time between two pulses, servo voltage, pulse current, short pulse time and frequency. Due to the fact that it is necessary to assess the impact of several input parameters, the Taguchi experimental design was selected. L27 matrix was used. Screening experiment was used in the first part of the experiment.

Materials, 2022

The paper deals with the issue of cutting zone and chip compression. The aim was to analyse the m... more The paper deals with the issue of cutting zone and chip compression. The aim was to analyse the microstructure transverse section of the cutting zone on a metallographic cut, due to determined values of chip compression and plastic deformation, which affect the cutting process efficiency. The tested cutting tool material was coated with cemented carbide. The selected workpiece materials were C45 medium carbon steel of ISO grade and 62SiMnCr4 tool steel of ISO (W.Nr. 1.2101) grade. In the experiments, a DMG CTX alpha 500 turning centre was used. The cutting speed and feed were varied, and the depth of the cut was kept constant during the turning. The plastic deformation and chip compression determine the efficiency of the cutting process. The higher compression requires more work to perform the process and, therefore, it requires more energy for doing so. With the increase of the cutting speed, the deformation for C45 steel is decreased. The rapid deformation reduction was observed w...

DAAAM Proceedings, 2017

A lot of nowadays researches are focused on increasing strength of the components and decreasing ... more A lot of nowadays researches are focused on increasing strength of the components and decreasing their weight, or obtaining unique properties. Composite materials are one of the results of the researches. However, different material properties of matrix and reinforcing material usually cause certain difficulties during conventional machining, such as rapid tool wear and delamination of composite. Therefore, focusing on machinability of this kind of materials is necessary. Scientists have discovered several ways of how to satisfactorily machine different composite materials. Seco Tools Company starts developing a new design of the cutting tools. Researchers of the Stanford University have devised a diamond-like carbon (DLC) coating available to effectively cut matrix as well as reinforce fibres. DMG Mori Company has implemented ultrasonic assistance into machining process and reached enhanced machinability. This article compares conventional milling and ultrasonic assisted milling of the composite materialsglass fibre reinforced plastic (GFRP) and two types of carbon fibre reinforced plastics (CFRP) by using a special designed cutting tool. The results could be applied to determine when ultrasonic assistance is advantageous and what advantages it brings about. The purpose of this study is to determine ways to increase efficiency and productivity of machining different types of composite materials.

Proceedings of the 29th International DAAAM Symposium 2018, 2018

The paper deals with the issue of cutting edge radius sizes their influence on the tool life of c... more The paper deals with the issue of cutting edge radius sizes their influence on the tool life of coated cemented carbide drills. Theoretical analysis was focused to the issue of cutting edge microgeometry, discussing the classification and importance of cutting edge microgeometry. The most famous and used edge preparation methods are summarized in this article. The tool lives of cemented carbide drills were compared when cutting edge radius was varied. Cemented carbide drills were deposited by TiAlN coating. Tool life tests were carried out on EMAG VSC 400 machining centre. These results were investigated in the process of machining of EN-GJL-250 grey cast iron (equivalent to DIN GG25, equivalent to ASTM A48).

Many nowadays researches are focused on decreasing the weight of components and increasing their ... more Many nowadays researches are focused on decreasing the weight of components and increasing their strength, or obtaining unique properties. One of the results of the researches are composite materials. However, different material properties of matrix and reinforcing material cause certain problems during conventional machining, such as rapid tool wear and delamination of composite. Therefore, other researches start focusing on machinability of this kind of materials. Scientists have discovered several ways of how to satisfactorily machine composite materials. Seco Tools Company starts developing a new design of the tools. Researchers of the Stanford University have devised a diamond-like carbon (DLC) coating available to effectively cut matrix as well as reinforce fibers. DMG Mori Company has implemented ultrasonic assistance into machining process and reached enhanced machinability. This article compares conventional milling and ultrasonic assisted milling of the carbon fiber reinfo...

Laser machining is one of the most widely used advanced machining processes used for creating new... more Laser machining is one of the most widely used advanced machining processes used for creating new surfaces, structures, cavities and also complex electro-mechanical devices, usually with very small dimensions, by laser radiation. Optimal selection of process parameters is highly critical for successful material removal and high machine surface quality. In the paper the relation between process parameters and machined surface quality characteristics is experimentally studied applying the five axis highly dynamic laser precision machining centre Lasertec 80 Shape equiped with the pulsed ytterbium fibre laser (wave lenght 1064 nm, maximal average output power 100 W) and CNC system Siemens 840 D and commercionally pure titanium (Grade 2) as working material. The influence of the pulse frequency and energy, laser scanning speed and stepsize (spacing between adjacent passes) on the machined surface roughness is evaluated using Taguchi experimental design approach. The influence of process...

In this paper a method for creating chip breaker on cutting insert is described. For cutter inser... more In this paper a method for creating chip breaker on cutting insert is described. For cutter inserts the powder is compressed into the molds, in a process. After pressing and sintering the cutting tools chip breaker looks like negative molds shape. For experimental cutting insert prototype is important to design and make molds with specific shape. Designing and production of new molds is time and cost consuming. Another way is to make insert with flat rake face and make chip breaker by an advanced machining method. Hard carbide material may be machined by laser ablation. This paper deals with possibility of laser ablation machine LASERTEC 80 Shape usage for creating of comprehensive chip breaker surface on the carbide insert.

Journal of Engineering Research, 2021

The article deals with the local plastic deformation analysis after cold forming. The technology ... more The article deals with the local plastic deformation analysis after cold forming. The technology of drawing seamless steel tubes was used to obtain cold-formed samples. The tubes were manufactured by a Tinius Olsen 300ST tensile tester with a 6 ° and 12 ° die drawn without and with an inner mandrel. Based on orientation size recalculated by stereology and applying Monte Carlo method a mathematical conversion model was developed. Implemented model together with surface measurements and structure characteristics were used to get the orientation to the size of the deformation. Thus, the actual (logarithmic) deformations and local stresses were determined. Comparison of experimentally measured values of the actual local plastic deformation with the deformation calculated found on the model simulation in the Deform program defined the significance of the differences assessed by means of a statistical T-test. All differences in the values of the local plastic deformation with respect to t...