Wyniki wyszukiwania - BazTech

1

Cryogenic machining, surface integrity and machining performance

Kopac J., Krolczyk G.

Archives of Materials Science and Engineering

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2015

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Vol. 71, nr 2

83--93

EN

Purpose: Of this paper is to present state-of-the-art on cryogenic machining and delivery principles of liquid nitrogen to the machining/cutting zone. Additionally, the influence of cooling/lubrication conditions on the surface integrity, generated during turning of Inconel 718, are analysed and presented. Design/methodology/approach: Of the paper are to present the design of the cryogenic machining system and how the liquefied nitrogen is delivered to the cutting zone. Additionally, the system is used to evaluate the effect on surface integrity of machined Inconel 718 workpiece. Methodologies used for the surface integrity evaluation are: electro-polishing, X-ray diffraction and micro indentation hardness measurements, with the approach to evaluate the extent of cryogenic influence on machined surface. Findings: The results show that the cryogenic machining process generates larger compressive residual stresses, and prevail at deeper levels beneath the machined surface, thus resulting in improved product quality and performance characteristics in terms of fatigue life and wear resistance. Research limitations/implications: The solutions of the delivery and the evaluation results have been all performed for the turning process, while there is still a challenge for the implementation of findings on the milling and drilling process kinematics. Practical implications: Work shows that cryogenic machining is capable of improving surface integrity and with this, as practical implication, having high potential for improving the sliding conditions, fatigue life of the final product, corrosion resistance, etc. Originality/value: Originality of the paper is shown by novel solutions (patents) on cryogenic machining system (delivery) and in machined surface modification capabilities with alternative cooling/lubrication fluid.

2

Machining of near-net shape forged pinions

Kramar D., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

716--720

EN

The paper presents a machining of near-net shape (NNS) pinions with forged chamfer in automotive industry and compares it with an older procedure of turning pinions without forged chamfer as well as production of pinions in a classic mechanical way from steel bars. It contains a description, which focuses on a technological procedure, utilization of different types of tools, and machine tools. The last part of the paper deals with an economic analysis considering sub-assembly of car starter motors production, their treatment and pinion production in a classic mechanical way from steel bars and with NNS process. The calculations are presented for different batch sizes from prototype to mass production.

3

Effect of cutting on surface hardness and residual stresses for 12Mn austenitic steel

Cebron M., Kosel F., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 1

80--89

EN

Purpose: Austenitic steels are known for their high impact toughness and resistance against abrasive wear, yet their machining is difficult and limits their application. Since surface conditions resulting from production strongly affect the performance of finished products, any information linking the machining process to the mechanical properties of the surface is useful not only in production but also in the design phase of the product. Design/methodology/approach: The state of the cutting zone was researched using a quick-stop device for suddenly stopping the cutting process and so retaining the mechanical conditions developed during machining. Residual stresses were measured using X-ray diffractometry, while the standard Vickers micro-indentation hardness test was used for determining the material hardness in the cutting zone. Findings: It was confirmed that the analysed material hardens substantially during machining and that the wear of cutting tools can be related both to this phenomenon and to the material structure after heat treatment. Furthermore, it was found that inadequate machining conditions can lead to tensile stresses that alone can initiate cracks in the surface layer even before the material is additionally loaded. Research limitations/implications: Since measurements of temperature in the cutting zone were not performed, the effect of temperature on the final mechanical properties of the surface can only be estimated. The dislocation theory of hardening is briefly explained, while actual research of dislocations is limited. Since the orthogonal cutting process involves substantial plastic deformation, the study of dislocation motion in the cutting area could be of interest. Practical implications: The main reasons why highly hardening materials require an accurate assessment of the cutting conditions are outlined. It is shown that an apt choice of cutting conditions has a favourable influence both on the condition of the surface after cutting and on the tool life. Originality/value: This paper presents an account of some of the difficulties that are associated with machining austenitic and other highly hardening materials. Since the detailed composition of the material and all the important machining parameters are listed, the results presented can also be useful for checking or calibrating numerical models of the cutting process.

4

Turning conditions of Ck 45 steel with alternate hardness zones

Stoic A., Kopac J., Ergic T., Duspar M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 1

87-94

EN

Purpose: of this paper is investigation of dynamic impacts on cutting edge during machining of locally hardened steel. Alteration of hardness on a single work piece is a source of impact on tool, which could lead to breakage of cutting tool and work piece surface damage in turning. Influence of material properties (primary hardness) is important when work piece is hardened locally by induction and part of material is soft annealed. Design/methodology/approach: Experimental tests of cutting outputs have been done on specimens after induction hardening to evaluate the rate of variation of cutting forces, surface roughness and chip formation because of hardness alteration. Measured data of main cutting force were analyzed in frequency and time domain. Findings: It was found that chip formation condition, chip thickness and chip shape depends on cutting forces alteration in transition areas in the range of 10 to 15%. Much higher alteration of force signal is recorded when machining is performed with low depth of cutting value as a result of backlash in system. The most important value of cutting force correlates with depth of cutting, and roughness correlates oppositely to the hardness. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. other heat treatable steels or other hardening techniques or other single cutting point processes). There is evident force value alteration in the transition (hard to soft state) zone. Practical implications: Surface roughness is a consequence of both cutting impacts and of tool/work piece loading condition. Originality/value: Originality of the paper is in analysis for stability of turning to heat treatable steel influenced with alternating work piece hardness. It was recorded edge loading shock overcome from hard to soft machining. It was recorded and analyzed self-exited vibration. A new type of chips: horseshoe-type was found.

5

Development process and manufactu-ring of modern medical implants with LENS technology

Balazic M., Recek D., Kramar D., Milfelner M., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 32, nr 1

46-52

EN

Purpose: Research and development of modern medical implants is complex and demanding process focused on fulfilling requirements regarding materials, machining technologies and functionality. Typical example of modern medical implant is elbow nail for fixation of Caput radii fractures. It could be manufactured with classical machining technologies and with advanced Rapid Prototyping technologies such as highly targeted metal deposition technology LENS (Laser Engineered Net Shaping). Design/methodology/approach: Development of modern medical implants is a multi-stage design and manufacturing process primarily based on computer aided design (CAD), computer simulations, machinability of certificated biomaterials, in-vitro biofunctionality and in-vivo tests. Findings: LENS technology enables rapid and agile manufacturing, improved design flexibility, repair and re-manufacture. Material built with LENS technology has equal or even better mechanical and material properties. In medical application LENS technology enables development and rapid prototyping of special surgical instruments, trauma and orthopaedic high-performance implants which are hollow and thin walled. Research limitations/implications: To confirm assumption regarding better material and mechanical properties of products made with LENS technology additional static, dynamic (the High-Cycle-Fatigue test) and material (porosity and microstructure) tests will be carried out in the near future. Practical implications: Three different designs of bone fixation nail prototype made of titanium alloy had been manufactured with conventional machining techniques where some disadvantages due to the technology had been identified. To solve those problems LENS technology had been applied. As fourth design hollow thin walled fixation bone nail prototype made of titanium alloy powder (grain size 45 micrometers) had been manufactured and tested. Originality/value: Paper presents case study where LENS technology is being applied to manufacture modern medical implants. Particular focus of the paper is on material quality and quality benefits obtained in current and future medical application.

6

Achievements of sustainable manufacturing by machining

Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 2

180-187

EN

Purpose: Manufacturing industry is under increasing pressure of global competition, stricter environmental legislation and supply-chain demand for improved sustainability performance. The latter can be achieved through changes in products, processes and systems which are related to the sustainability issues. Sustainability in manufacturing is an appropriate approach; however it is still unified to a higher production rate and benefit. To encounter this problem academic, scientific, cultural and human organizations have to find the way, on a highest level of decision; maybe to rise the sustainability over production growth. This paper also presents some results from modelling and optimization of sustainable machining of Inconel 718. High temperature alloys, such as Nickel and Titanium alloys, pose significant difficulty in machining, due to their unique thermo-mechanical properties. Design/methodology/approach: In the paper are presented and evaluated two sustainable machining alternatives: cryogenic machining and high pressure assisted machining in comparison to conventional machining. The sustainability performance measures refer to environmental impact, energy consumption, safety, personal health, waste management and costs. The sustainability evaluation is supported with machining experiments on high-temperature Ni-alloy (Inconel 718). It is shown that tooling costs are presenting the major contribution to the overall production costs, when hard-to-machine materials are machined, what is contradictory with previous analysis. Findings: As a result, it is shown that sustainable machining alternatives offer economic, environmental and social performance improvement in comparison to conventional machining. The results of the experimental part show that appropriate cooling/lubrication application can provide improved overall machining performance while satisfying sustainable issues in terms of enhanced machined surface quality, tool-life, chip breakability, power consumption and increasing productivity. Research limitations/implications: The Faculty of Mechanical Engineering in Ljubljana, Slovenia is implementing two new cutting strategies for the machining of a special material – Inconel. The first one is cryogenic machining and the second is material cutting by assistance of high pressure jet cooling lubrication. Both machining strategy are in rang of sustainable manufacturing. The implications of processes like those are not only nature friendly, but also modern spirit for producers and users of products. Originality/value: Paper present the technical description of two modern machining processes, the comparison of them and benefit, advantages and disantvantages. Really new is the strategy and opinion of spirit, which can be included in product over sustainable manufacturing processes.

7

Influence of temperature and microstructure of the workpiece material on energy quanta in cutting process

Kisin M., Noc Razinger M., Pusavec F., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 30, nr 1

75-78

EN

Purpose: of this paper is on-line identification of the machinability based on the theory of energy quanta power spectra of the measured signal of the cutting force. Identification method is supported by measurements of the instantaneous temperature in the cutting zone for workpieces with the same chemical composition but different microstructure and mechanical properties. Design/methodology/approach: For measuring the temperature in the cutting zone the direct IFT (Instantly Formed Thermo element) method was used. Findings: Low carbon steel with a previously cold-deformed microstructure has a better machinability in lower cutting force, smaller energy quanta and lower temperature in the cutting zone as low carbon steel with the normalized microstructure. Research limitations/implications: The theory of energy quanta as a basis for on-line identification of cutting parameters for optimization and adaptive control of the cutting process in the industry praxis is not yet in use. But it was developed in laboratory research up to the stage when testing in the industry is already possible, where are because of high productivity the demands on work load of machines and the quality of final products much higher. Originality/value: The method on-line identification on the theory of energy quanta used for that has to be accomplished in real time and has to have the required reliability. The choice of the measured parameter has to be suitable and relevant.

8

Improvements of medical implants based on modern materials and new technologies

Balazic M., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 25, nr 2

31-34

EN

Purpose: Modern medical implants are products with pretentious requirements regarding materials, machining technologies and their functionality. In general they are divided into two main groups which are permanent and temporary medical implants. To improve implant's performance in the working environment one of the main goals of research and development process is to improve implant's biofunctionality, biocompatibility, corrosion resistance, bioadhesion, processability and availability. Design/methodology/approach: Development of modern medical implants is a multi-stage design and manufacturing process primarily based on computer design, computer numerical simulations and in-vitro tests. Findings: Some improvements could be done with reverse engineering technology which generates a numerical model from the workpiece in order to get a replica or geometric variant for the scanned data. Practical implications: The surgical treatments of bone fractures (osteosynthesis) are divided into external fracture fixation or internal fracture fixation. One of the most common used medical implant for internal fracture fixation is bone fixation plate which holds together the bone fragments. In some cases the improved shape of the plate could results into better biofunctionality and bioadhesion. Originality/value: In this contribution few examples of machining technologies based on CAD-CAM principle, modern materials and research/development process of modern medical implants is presented.

9

Identification of scanning errors using touch trigger probe head

Sokovic M., Cedilnik M., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

383-386

EN

Purpose: Creation of a mathematical model, which combine ball tip radius error and small tilt of the stylus to determine translational motion (in two directions) of the stylus ball centre, due to the surface slope. Design/methodology/approach: First error is described on two dimensional model, thus is very simple. Second model is based on 3D-mathematical model, which is a basis to determine (and plot) translational movement of the stylus ball according to surface slope. Findings: Accurate scanning process on freeform surface with touch trigger probe head could not be performed, due to number of reasons connected to the stylus ball and trigger probe head errors. Research limitations/implications: According to nature of this problem, 4D, 5D and 6D-graphs could not be plotted, which would define translational motion of the stylus ball centre at any slope surface. Practical implications: Understanding the physical model for described error is a basis to create mathematical compensation error model. Originality/value: No such mathematical model to determine translational motion (in two directions) of the stylus ball centre was published in any paper before.

10

Rapid tooling in sand casting applications

Dolinsek S., Kopac J., Brtoncelj G., Kosic P.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

30-34

EN

Rapid tooling refers to process and technologies that help shorten time from planning to producing tools and with which the production costs are reduced. Classic technological procedures, such as turning, milling or casting are still the most common way of producing products from a wide range of available materials; rapid tooling is an option how to make those procedures faster, cheaper and better. On the example of the casting model we present the analysis of time and costs savings between separate procedures of rapid tooling according to classic production of casting application with high-speed cutting.

11

Radial basis function simulation and metamodelling of surface roughness in centreless grinding

Krajnik P., Sluga A., Kopac J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 14, nr 1-2

104--110

EN

Purpose: The purpose of this study was to investigate the efficiency of artificial neural networks and the related metamodels to simulate and identify complex centreless grinding process. Design/methodology/approach: The modeling is founded on the system approach, which is efficiently dealing with the complexity of the grinding process. The unknown process transfer function is identified via artificial neural network that requires fewer assumptions and less precise information about the process modeled than other conventional modeling techniques. The developed metamodel is a response surface (polynomialfit) of the simulated process that is achieved by the computer model. Findings: The metamodel quality is strongly related to the prediction accuracy of the underlying simulation model. The generalization capability of an artificial neural network is sensitive to the training samples (design of experiments). The predictive ability of a metamodel is comparable to the accuracy of the response surface regression model. Research limitations/implications: Improved simulation model and application of unconventional metamodels (Gaussian process regression) will significantly improve the presented preliminary results. Originality/value: Metamodelling of computer experiments is an expansion of response surface methodology and the classical designs of experiments and represents a new paradigm in empirical modelling of machining operations.

12

Intelligent system for machining and optimization of 3D sculptured surfaces with ball-end milling

Milfelner M., Kopac J., Cus F., Zuperl U.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 14, nr 1-2

171--177

EN

Purpose: This paper describes about intelligent machining system which is applied in a high speed machining robot with on-line monitoring and optimization for ball-end milling process. Design/methodology/approach: Manufacturing of 3D sculptured surfaces on high speed machining robot involves a number of machining parameters and tool geometries. The system collects machining data and cutting parameters which are necessary for genetic algorithm optimization. Findings: An intelligent machining system is developed for the simulation and testing on the PC machine. It is based on a main PC computer, which is connected to the high speed machining robot main processor so that control and communication can be realized. The system collects the variables of the cutting process by means of sensors which are optimized with the genetic algorithms. Research limitations/implications: 3D sculptured milling covers a wide range of operations. In 3D metal cutting processes, cutting conditions have an influence on reducing the production cost and time and deciding the quality of a final product. Practical implications: Simulated results show that the proposed intelligent machining system is effective and efficient, and can be integrated into a real-time intelligent manufacturing system for solving complex machining optimization problems. Originality/value: The paper describes about intelligent machining system which can applied in intelligent manufacturing process.

13

Struktura i własności wielowarstwowych powłok CVD na podłożu z narzędziowej ceramiki azotkowej

Dobrzański L.A., Pakuła D., Kopac J., Sokovich M.

Inżynieria Materiałowa

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2003

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R. XXIV, nr 6

461-464

PL

W pracy przedstawiono wyniki badań struktury i własności wielowarstwowych powłok CVD na podłożu z narzędziowej ceramiki azotkowej Si3N4. Przedstawiono wyniki badań na skaningowym mikroskopie elektronowym, wyniki badań przyczepności naniesionych pokryć do podłoża oraz wyniki mikrotwardości i chropowatości. Wykonano również badania składu chemicznego wytworzonych powłok za pomocą spektrometru energii rozproszonego promieniowania rentgenowskiego EDS oraz składu fazowego przy użyciu dyfraktometru rentgenowskiego. Płytki z Si3N4 pokryto wielowarstwowo w wysokotemperaturowym procesie CVD kombinacją powłok TiC, Ti(C, N), Al2O3 i TiN, które następnie porównano z komercyjnymi płytkami różnych producentów oferujących kombinację pokryć CVD typu Al2O3+TiN.

EN

In the paper results of examinations of structure and properties of multilayer CVD coatings on the tool nitride ceramics substrate Si3N4 have been presented. The results of examinations in a scanning microscope, the one of adhesion of deposited coatings and microhardness and roughness have been presented. Moreover, the examination of chemical composition of coatings created by means of a spectrometer of energy of dispersed X-ray EDS and phase composition by means of a X-ray diffractometer. Inserts including Si3N4 have been covered multilayerly by the combination of TiC, Ti(C, N), Al2O3 and TiN in high temperature CVD which next have been compared with the commercial inserts of different producers offering the combination of Al2O3+TiN CVD coatings.