Tool Surface Layer Research Articles

Hardness Assessment Considering Nitrided Layers Based on Tempering Tests for Numerical Wear Prediction for Forging Processes.

The nitriding of forging tools is an industrially established standard used to increase the hardness of the tool surface layer and reduce wear. However, this modification of the tool surface layer, as well as the microstructural changes that occur during this operation due to the thermo-mechanical load, cannot be considered during wear calculations with the widely used Archard wear model in the context of FE simulations. Based on previous work, this study further develops two tempering tests for the investigation of the hardness evolution of two nitride profiles based on H11 tool steel. Here, significant tempering effects could be observed depending on temperature, mechanical stress superposition and time. The results are used for setting up a new material model that is implemented in an existing numerical wear model. The validation is carried out in two laboratory forging test series. The evaluation shows that the hardness development in terms of tempering effects of a nitrided forging tool can be numerically predicted, especially for high forging cycles. However, due to the unexpected occurrence of adhesion effects, only limited applicability of the wear prediction then carried out is achieved.

Strengthening the Surface Layer of Tools with State-of-the-Art Technologies

Increasing both the service life and the wear resistance of the tool by surface hardening is an urgent issue. Its solution contributes to a significant increase in the performance of products. Available methods of surface hardening of tools, based on coating or changing the surface condition, are becoming increasingly important due to the complexity of the operation of products. Plates made of the T5K10 (85%WC–6%TiC–9%Co) and T15K6 (79%WC–15%TiC–6%Co) hard alloys as well as cylindrical samples made of the W6Mo5Cr4V2 and W18Cr4V high-speed steels are used for the study. Studies have shown that, after processing the T15K6 alloy plates with a pulsed magnetic field, the cutting tool life improved by more than 200% as compared to the untreated ones. The proposed method will increase the strength of carbide plates and stabilize the physical and mechanical properties of the cutting tool. For tools made of alloy steels, the hardening treatment is carried out by the boron method in pastes with nanodisperse powders. As shown, the thickness of the boride layer for high-speed steels increases with the duration of the process; however, its growth rate depends on the composition of the steel. An increase in the holding time of the chemical and thermal treatment leads to the growth of boride layers. The layer thickness changes quadratically (as a second-degree polynomial) with duration time. A feature of formation of diffusion layers is revealed. The dependences of both the surface hardness and the thickness of boride layer on the borating time for high-speed steels are also shown. Studies have shown that boriding in a nanodisperse medium can significantly increase the wear resistance of steels. The method of expert assessments of the maximum values of the surface properties of the studied steels is carried out. As shown, it is more rational to use W6Mo5Cr4V2 steel as a cutting tool after hardening the surface layer by boriding in a nanodisperse boron-containing powder. The proposed processing method demonstrates the prospects of using it to improve the performance of products. In addition, this method of hardening can significantly increase the wear resistance of materials (by ≈3.38–3.75 times) as compared to steels without processing.

Advanced Complex Analysis of the Thermal Softening of Nitrided Layers in Tools during Hot Die Forging.

This article is devoted to the issues of thermal softening of materials in the surface layer of forging tools. The research covers numerical modeling of the forging process, laboratory tests of tempering of nitrided layers, and the analysis of tempering of the surface layer of tools in the actual forging process. Numerical modeling was supported by measuring the temperature inside the tools with a thermocouple inserted into the tool to measure the temperature as close to the surface as possible. The modeling results confirmed the possibility of tempering the die material. The results of laboratory tests made it possible to determine the influence of temperature on tempering at different surface layer depths. Numerical analysis and measurement of surface layer microhardness of tools revealed the destructive effect of temperature during forging on the tempering of the nitrided layer and on the material layers located deeper below the nitrided layer. The results have shown that in the hot forging processes carried out in accordance with the adopted technology, the surface layer of working tools is overheated locally to a temperature above 600 °C and tempering occurs. Moreover, overheating effects are visible, because the surface layer is tempered to a depth of 0.3 mm. Finally, such tempering processes lead to a decrease in the die hardness, which causes accelerated wear because of the abrasion and plastic deformation. The nitriding does not protect against the tempering phenomenon, but only delays the material softening process, because tempering occurs in the nitrided layer and in the layers deeper under the nitrided layer. Below the nitrided layer, tempering occurs relatively quickly and a soft layer is formed with a hardness below 400 HV.

The application of a new, innovative, hybrid technology combining hardfacing and nitriding to increase the durability of forging tools

The article deals with the wear of forging tools used in hot forging processes. The research presented in the work includes analysis of tool life used in a selected industrial hot die forging process. Multiple treatment variants were used to increase wear resistance, including thermo-chemical treatment (nitriding), welding methods (surfacing) and an innovative new hybrid technology combining surfacing and nitriding. First of all, the research focused on determining the impact of the phase structure of the nitrided layers used and the surfacing layer on resistance to destructive factors occurring in the analyzed process. Next, hybrid treated tools combining surfacing and nitriding were also subjected to operational tests. Each of the tools analyzed in this work was operated until it was withdrawn due to excessive wear, and then subjected to comprehensive analysis. The tests of tools after operation included: surface scanning to determine the amount of wear of the analyzed tools after work, microhardness measurement, and microscopic tests. A detailed analysis of changes in the surface layer of tools in selected areas was made using a scanning microscope. The aim of the study was to assess the effectiveness of the hybrid surface treatment process used to increase the wear resistance of the surface layer of tools and thereby improve the durability of the forged tools analyzed. The obtained research results indicate a beneficial effect of using the new technology resulting in 300% increase in the durability of the analyzed tools. The effect of improving durability confirmed by obtained results arises from the use of hybrid layers, which are more resistant to abrasive wear and to cracking due to thermo-mechanical fatigue. Moreover, the study shows that nitriding may have a beneficial influence on improving the lifetime of forging tools, under the condition that the nitrided layer has an α diffusive layer structure, without a larger amount of γ’ and ε nitride precipitates.

Wear Resistance and Titanium Adhesion of Cathodic Arc Deposited Multi-Component Coatings for Carbide End Mills at the Trochoidal Milling of Titanium Alloy

The work was devoted to the study of the effectiveness of the application of multi-component coatings, TiN–Al/TiN, TiN–AlTiN/SiN, and CrTiN–AlTiN–AlTiCrN/SiN, obtained by cathodic arc deposition to increase the wear resistance of 6WH10F carbide end mills in trochoidal milling of titanium alloy. The surface morphology of the tool with coatings was studied using scanning electron microscopy, and surface roughness texture was estimated. Microhardness and elastic modulus of the coated carbide tool surface layer were determined by nanoindentation. The process of sticking titanium to the working surface of the tool and quantitative evaluation of end mill wear with multi-component coatings at the trochoidal strategy of milling titanium alloy was studied. The CrTiN–AlTiN–AlTiCrN/SiN coating showed the maximum value of the plasticity index at the level of 0.12. The maximum effect of reducing the wear rate was achieved when using a tool with a CrTiN –AlTiN–AlTiCrN/SiN coating when the operating time to failure of end mills was increased by 4.6 times compared to samples without coating, by 1.4 times compared with TiN–Al/TiN coating and 1.15 times compared with TiN–AlTiN/SiN coating.

Study of effect of technological lubricant type and parameters of tool surface layer on characteristics of multitoothed mandrelling methods of holes

The regularities of the change in the mandrelling forces and the geometric quality parameters of the obtained holes depending on the type of technological lubricant and the parameters of the tool surface layer that implements the scheme of sequential multi-tooth mandrelling are experimentally studied.

Improving efficiency of machining the geometrically complex shaped surfaces by milling with a fixed shift of the cutting edge

In order to improve efficiency of machining by milling geometrically complex shaped surfaces, mainly the methods related to improvement of properties of the tool material, change of composition and properties of the tool surface layer, application of thin film coatings, reduction of roughness of the working surfaces and improvement of operating conditions of the tool using lubricant-cooling media are mainly used. Proceeding from the above stated, scientifically grounded technical and technological solutions consisting in development of a new highly effective method for machining geometrically complex shaped surfaces by means of disk rotary cutters with a reciprocatively rocking feed motion were studied and set forth in this work. This machining method can increase the period of durability of tools by 1.7 times and milling performance by 1.6 times by means of a fixed kinematic shift of the cutting edge relative to the machined surface. A mathematical apparatus of the method of milling with a fixed shift of the cutting edge was proposed. Analysis of this method with the help of numerical functions has enabled establishment of analytical dependences for determining thickness and volume of a unit cut-off layer. Thickness of the cut-off layer is mainly affected by feed per tooth, Sz, and the angle υ influences its volume which determines normal cutting conditions. A model of distribution of heat flows in the cutting wedge for the method of milling with a reciprocatively rocking feed motion taking into consideration the amplitude of rocking motion of the workpiece was studied. A temperature decrease to 330.2...395.5 °C was established, that is by 80.6...181.6 °C for the stamp steel 9CRSI and to 193.8...285 °С, that is, by 56.6...120.2 °C for steel 45 compared to conventional milling. It was found that total length of the cutting edge increases 2.4 times with 1.5 times temperature decrease

Технологические особенности формирования нанокомпозитных структур на поверхностях сложного профиля воздействием низкотемпературной плазмы

The paper reports the consideration of plasma technologies for surface layer strengthening in products, in particular, the strengthening by the impact of low-temperature plasma of the combined discharge allowing the formation of nano-composite structures in a surface layer. By the example of a cutter made of steel R6M5 there are defined basic technological peculiarities of low-temperature plasma strengthening the account of which is possible at the expense of the optimization of parameter values defining the impact of plasma upon a surface. A chart of optimum parameters of a low-temperature plasma strengthening process is obtained. There are presented results of the study of a tool surface layer strengthened with the use of a chart and also tool operation at manufacturing parts made of different materials allowing the establishment of wear resistance increase.

Surface Layer Properties of Low-Alloy High-Speed Steel after Grinding

Abstract Investigations of the surface layer characteristics of selected kinds of low-alloy high-speed steel after grinding were carried out. They were carried out on the flat-surface grinder with a 95A24K grinding wheel without cooling. The influence of grinding parameters was defined especially for: the quantity of secondary austenite, surface roughness, microhardness and grinding efficiency with a large range of grinding parameters: grinding depth 0.005–0.035 mm, lengthwise feed 2–6 m/min, without a cross-feed on the whole width of the sample. It was found that improvement of grinding properties of low-alloy high-speed steels is possible by efficient selection of their chemical composition. The value of the grinding efficiency is conditioned by grinding forces, whose value has an impact on the grinding temperature. To ensure high quality of the tool surface layer (i.e. a smaller amount of secondary austenite, lack of wheel burn and micro-cracks) in the case of sharpening of tools made of low-alloy high-speed steel, the grinding temperature should be as low as possible.

The failure mechanisms of hot forging dies

This paper describes the phenomena taking place on the surface of the dies used for hot forging. Because of this paper’s limited space only changes in the tool surface layer during the forging of a gear wheel, as most representative, are presented. Similar changes were observed in the case of the other two investigated closed die forging processes, i.e. the forging of a cover and a yoke, respectively. The research was aided by FEM, which supplied a lot of information about the forging conditions. The most intensive wear of the tools occurs in the place of their longest contact with the material being forged, regardless of the number of produced forgings. The research has shown that the one of the most adversely factor affecting the investigated forging process is thermomechanical fatigue which results in fine cracks quickly developing into a network of cracks extending over the entire tool/forged material contact surface. Also the abrasive wear of the investigated die is high due to the intensive flow of the material in the presence of abrasive oxide particles and tools bits created by thermomechanical fatigue. An attempt to model the abrasive wear using the Archard model is presented.

The Innovative Directions In Development And Implementations Of Hybrid Technologies In Surface Engineering

AbstractThe dynamics of the development of modern technology depends, to a great extent, on the possibilities of producing the innovative materials with high functionality parameters, which could be used in modern, highly advanced technological processes. Surface engineering plays a very important role in this area. This is mainly due to the fact that, for many structural materials, the possibilities of classical formation of their properties (e.g., by heat treatment or the selection of the microstructure, chemical and phase composition) have been practically used up. The material and technological achievements in the surface engineering area allow the modification of the properties of the surface layer of tool and machine components. As a result, they may be better suited to work in increasingly difficult and more demanding conditions. The hybrid technologies, combining several different methods of surface treatment in one complex technological process, are the most advanced solutions compared to already known surface engineering methods. In the article, the authors present the possibilities of shaping the functional properties of the surface layer. The authors describe problems associated with the development of the hybrid technology and provide the examples of physical modelling, design, technological development, and the practical application of a hybrid technology. In this work, the authors also identify the areas whose development is needed for more effective transfer of surface engineering innovations to business applications.

Working Features of Surface Layer of Tool Reinforced with Dispersed NbC Particles

Working Features of Surface Layer of Tool Reinforced with Dispersed NbC Particles

Estimation of Roles of Matrix and NbC Particles Dispersed in Surface Layer of Tool by PTA Welding

Investigation has been carried out to estimate the roles of the matrix and NbC particles in the reinforced layer of a tool surface. In the last decade of the last century/In the 1990s it was reported that the reinforced layer of a tool surface by plasma-transferred-arc (PTA) welding using coarse NbC particles showed 10 times longer tool life in hot rolling of stainless steel and titanium. However, the roles of the matrix and NbC particles have not been investigated separately until now. In order to maximize the performance of the tool, it is important to optimize the structure of the welded surface layer, and for this purpose an optimum set of welding parameters of PTA should be selected. In the present work, major welding parameters are changed to clarify the roles of the matrix and NbC particles. The parameters changed are the size of NbC particles in the parent powder, the weight fraction of NbC in the parent powder, and the times of re-melting after PTA welding. For evaluation two types of sliding test are carried out: sliding tests under room temperature and at elevated temperature.

Analysis of Degradation and Failure Mechanisms that Develop in Hot Forging Die

A failed die, used to forge gas valves, was analyzed using macroscopic and microscopic equipment on some specimens. Fatigue cracks on the die were evidently observed on all the surfaces of the die. Many processes were found to be major contributors to have caused the die failure. Oxidation was observed in some areas, especially on plane surfaces and thin sections. Surface layers of tools at the tool-workpiece interface were not only exposed to high mechanical stresses but also to severe temperature cycles, which could have led to loss of strength and hardness. Metallographic analysis revealed that the oxide layers consisted of different diffusion layers which accelerated thermal fatigue mechanisms.

Effects of simulation conditions on evaluation of tool temperature in hot extrusion-forging

High thermal loading causes severe wear and plastic deformation at the tool corners in hot forging. The quick evaluation of temperature in the tool surface layer is required for the prediction of tool life in the tool design. In this study, the effects of simulation conditions including simulation procedures on the evaluation of tool temperature were investigated. When unsteady state analysis of thermal effects is conducted only for important parts of the die, a combined method of steady and unsteady state thermal analysis, which was introduced to estimate a steady heat cycle required to evaluate die life, was more efficient at reducing computation time. The combination of three-dimensional analyses of steady state temperature fields, and two-dimensional analyses of localized unsteady state temperature fields was efficient for practical simulation. The maximum temperature, the softening of die and the depth of thermally softened layer were effectively evaluated.

Prediction of wear in hot forging tools by means of finite-element-analysis

The intention of the work presented in this paper is the estimation of abrasive tool wear, as the major cause of failure of tools used for hot forging. Experiments are carried out to determine the wear amount after several numbers of forging cycles. For tool wear estimation, the analysed forging process in consideration of all process stages is represented with a finite-element model to compute the wear relevant parameters. A separate program is developed to calculate the tool wear by using the Archard wear model taking into account the hardness change of the tool surface layer with increasing number of forging cycles. In the end, the applied wear model is verified by comparing with the experimental results.

A newly designed laboratory hot forging test for evaluation of coated tool wear resistance

A computer controlled equipment for testing and studying the wear of coated tools (dies) in hot forging processes has been designed. Physical simulation of the hot forging process was carried out on a Gleeble 1500 testing machine which was additionally equipped with a heating system and a system for feeding workpieces. The abilities of the testing equipment were well demonstrated by the results of wear testing on four tools with differently treated surfaces: two different heat treated tools, a plasma nitrided tool and a duplex treated tool (plasma nitrided + PVD multilayer coating (Futura)). Besides microhardness, indentation modulus for all those tools was measured. Plasma nitriding improved hardness of the surface layer significantly, while indentation modulus of the diffusion layer is the same as that of bulk H11 tool steel. Microhardness of the Futura coating was ca. 3000 HV while the indentation modulus was ca. 425 GPa. After a certain numbers of strokes, we made optical micrographs or SEM images of the tested tool surfaces and on their cross-sections, and additional measurements of roughness on the tool surface and of microhardness in the tool surface layer were carried out. The duplex treated tool improved the load-bearing capacity, the fracture resistance, the oxidation resistance and the wear resistance of hot forging tools since on few tool surface parts removal of coating occurred. On plasma nitrided and heat treated internally cooled tools considerably higher surface roughness were found in comparison to duplex treated tool. Non-cooled heat treated tool showed very high wear amounts.

Temperature profiles and conditions for thermal fatigue cracking in brass die casting dies

In this study, the temperature variations in the surface layer of a hot work tool steel was experimentally evaluated during actual brass die casting. A special method was developed to measure the temperature in the surface layer of the mould at different depths. Untreated, borided, and physical vapour deposition (PVD) coated (CrN) tools were included. Temperature profiles in the surface layer of the mould were recorded and details of the thermal cycling were obtained. Starting with a tool of room temperature, the tool temperature range averages during the initial 20 casting events. Simultaneously, within a surface layer of about 2 mm thickness, the maximum stress is reduced to a constant level. Based on the temperature profiles, the maximum surface temperature of the mould and the thickness of the tool surface layer within which fatigue damage can occur were estimated to about 826 °C and 1.5 mm, respectively. This limited thickness results from the decrease in temperature range and, consequently, stress from the tool surface and inwards. Finally, no notable influence of the investigated surface engineering on the thermal conditions was found.

ＭＴ‐ＣＶＤ法を用いて製作したＴｉ（Ｃ，Ｎ）コーテッド工具の長寿命化に関する一考察

A Ti(C, N) coated tool which has a balanced performance of the expected high wear resistance in the coated layer with high toughness of the substrate, has been widely used for machining of ferrous materials. Applying this tool to the machining of the nodular cast iron, however, formation of the adhered layer at the tool tip occurred intensively, tool-tip failure and or separation of the coated layer tends to take place especially in semi-final and/or rough finishing. It is also indicated that there is possibility to yield a finished product with some faults caused by continued cutting operation without noticing serious damage occurred on the tool-tip. In the present investigation, effects of reducing the pre-existing cracks in tool surface layer, thickness of the coated layer and the existence of the η phase in substrate material (WC-Co) on the tool life were extensively investigated in order to increase efficiency and to stabilize the tool life on the cutting process for semi-final finishing of nodular cast iron. As the results, it is clarified that the thinner the coated layer the lower became the tensile residual stress on the surface, resulting in the extension of the tool life without taking place separation of the coated layer. The separation is also able to suppress by controlling the surface roughness of the tool substrate to several μm with certain homogeneity.

Experimental evaluation and FE simulation of thermal conditions at tool surface during cooling and deformation phases in hot forging operations

In hot and warm forging operations, surface layers of tools at the tool-workpiece interface are not only exposed to high mechanical stresses but also to severe temperature cycles, which often lead to loss of strength and hardness and thermal fatigue failure as well. This paper offers an approach for determining heat transfer conditions at the surface of punches and dies during both the deformation and the cooling-lubrication phases of forging cycles. The approach is based on temperature readings inside the tool, FE simulation and inverse analysis. An application case is illustrated where operating conditions reproduce hot forging of turbine airfoil sections.