Coated Tool Surface Research Articles

Generation of square micropattern using electrochemical micromachining

Surface microtexturing accomplishes a substantial role in enhancing the interfacial functional performance of machine-driven components. For producing good-quality square micropatterns, maskless electrochemical micromachining (EMM) is a viable option. Maskless EMM is employed for producing micropatterns, wherein the workpiece remains close by interaction with the mask tightly enclosed to the coated tool surface, and the electrolysis of job involves in the enclosed cell. The special micropatterning setup is developed to produce the good quality square micropatterns including micropatterning cell, pulsed electrical unit and perpendicular cross flow electrolyte system. The developed flow method on the job surface in this unit produces better good quality micropatterns. A reused textured tool and developed flow method is applied in maskless EMM in an enclosed unit, which eradicates the sludges and fabricate micropatterns with higher depth. This unique method is an efficient approach for improving the dimensional accuracy of micropatterns. The influences of input criteria, viz. voltage, duty ratio and frequency are studied on surface roughness, current efficiency, length overcut, and textured depth using this technique. The experimental outcomes show that the best parametric combination, viz. 30% duty ratio, 5 kHz frequency and 8 V voltage, enhances the micropatterned quality. A study has been approached based on micrographs for attaining the best input criteria combination.

Influence of Tool and Workpiece Properties on the Wear of the Counterparts in Contact Sliding

Abstract In a deep drawing process, the contact sliding between the surfaces of a metal sheet and a die/mold under high contact stresses brings about wear of both the counterpart surfaces. This paper aims to investigate the influence of tool and workpiece properties on the wear behaviors subjected to cylinder-on-flat sliding conditions. The effects of different tool materials (Cr12MoV, SKD11, and DC53), radii, surface hardness, and surface treatment processes including thermal diffusion (TD) coating, nitriding coating, and vacuum heat treatment (VHT) were investigated. Two types of workpieces with high tensile strength (DP980 and QP980) were also applied in the tests. The friction coefficient, surface morphology, and material removal were analyzed with the aid of load cells installed and microscopy measurements. It was found that the DC53 tool experiences the smallest tool wear and material transfer. The least material transfer is attributed to its low adhesion to workpiece material, which also results in more wear debris and a higher friction coefficient. The TD coated tool surface can further improve the wear resistance and bring about the lowest friction coefficient. The debris density associated with the TD coating is also the smallest. These findings provide a useful guideline for the design and optimization of molds/dies for the deep drawing processes of sheet metals.

Machinability Investigations on Aerospace Custom 450 Alloy Using TiAlN/TiCN, TiCN/TiAlN Coated and Uncoated Carbide Tools

In this present research, the machinability studies of TiAlN/TiCN, TiCN/TiAlN coated and uncoated inserts were investigated on machining custom 450 alloy. The machining input parameters such as feed rate (f), cutting speed (V) and depth of cut (d) are set using orthogonal array. The machining output parameters such as surface roughness, tool wear and cutting forces were studied for its parametric contribution and it was analyzed using Analysis of Variance (ANOVA). Further, the tool wear obtained was studied using scanning electron microscopic images and energy dispersive spectroscopy analysis was conducted to check the addition of work material elements to the coated tool surface. The results show that, the feed rate is the most contributing factor in deciding resultant forces, surface roughness and tool wear respectively. TiAlN/TiCN coated carbide tool has obtained improved machinability, when compared to TiCN/TiAlN coated carbide and uncoated carbide inserts. To obtain one optimal level for all three responses of three types of tools, multi criteria decision making approach, named utility concept approach is selected. Based on the MCDM analysis, it is found that trial number 4 gives better experimental output of improved surface integrity, lower resultant force and less tool wear for all types of tools.

Effect of Scale and Sequence of Surface Textures on the Anti-adhesive Wear Performance of PVD Coated Tool in Dry Machining SLM-Produced Stainless Steel

During the dry post-machining processing of selective laser melting (SLM)-produced stainless steel with TiAlN coated tool, the elements of stainless steel chips can diffuse and adhere into the coated tool surface, causing serious adhesive wear. In this study, to inhibit the adhesion problem at the tool-chip interface, surface textures with different scales (micro-, nano- and micro/nano-textures) are produced on tool rake face by laser processing before and after physical vapor deposition (PVD) TiAlN coatings deposition. To investigate the cutting performance of these developed coated tools, dry machining tests of the SLM-produced stainless steel are carried out. And, the mechanical properties of textured TiAlN coatings such as the hardness, elastic modulus and critical load are also studied to explain the results from the machining tests. It can be found that the anti-adhesive wear performance of TiAlN coated tool is improved by laser surface texturing. The texture dimension significantly affects the mechanical properties and dry cutting performance of the TiAlN coated tool, and the micro/nano-textures are found to be optimum. Meanwhile, the sequence of surface textures also has an effect on the wear performance of the developed TiAlN coated tools. In the experiment, laser surface texturing before coatings is effective in acting as a barrier against flaking of the TiAlN film, providing a higher active surface for the subsequent TiAlN coatings and presenting a higher compressive residual stress. Thus, the developed cutting tool which is textured before TiAlN coatings deposition presents a milder wear compared to the developed one which is textured after TiAlN coatings deposition.

Correlation of the fatigue impact resistance of bilayer and nanolayered PVD coatings with their cutting performance in machining Ti 6Al 4V

Abstract Titanium alloys are widely employed in aerospace and biomedical applications. During the cutting process of Ti 6Al 4V alloy, the material characteristics of high specific strength and poor thermal conductivity lead to a stress concentration occurred at the tool/chip interface, which may cause severe failure of the coated tools. Besides, the titanium alloy gives rise to serrated chips, whose thickness varies regularly in the cycle mode, which lead to the variation of cutting force and tool stress. So a cyclic impact with high frequency is applied on the coated tool surface, and this induces the fatigue fracture of coating. In this study, repetitive contact between the coating and Vickers diamond indenter through the high frequency cyclic impact tester was developed by employing the ultrasonic actuator device. High frequency cyclic impact testing has been used to study the impact resistance of the TiSiN/TiAlN bilayer coating and TiSiN/TiAlN nanolayered coating. Besides, stress concentration resulting in the failure of coatings can be generated by using the sharp Vickers indenter. The crack propagation in coatings was investigated by the scanning electron microscope (SEM), and the fracture processes of coatings were studied from the force measurement data acquisition system. In addition, the cutting performance of cemented carbide tools coated with these two coatings was evaluated in turning Ti 6Al 4V titanium alloy. The correlation between the fatigue impact resistance of coatings at high frequency and the wear behavior of coated tools under different cutting conditions was studied. It can be concluded that the TiSiN/TiAlN nanolayered coating showed better properties to resist fatigue impact at the lower impact load, but worse properties to resist fatigue impact at the higher impact load.

A Study on Machining Characteristics of KP4 Steel Using Alumina Coated Insert

In this study examine KP4 steel (HRC 32), a non-thermal treated material among plastic mold steels, a material widely used in the mold industry. The sample will be machined upwards and downwards at different angles (15°, 30°, 45°). To this end, it uses a multicoated carbide tool (1 to 4 layers of AlTiN using physical vapor deposition (PVD) and ion plating). This study presents basic processing data of the multi-coated ball end-mill and discuss the characteristics of high-speed machining. For measuring the roughness of the coated tool surface, this study uses Atomic Force Microscope (AFM) manufactured by PSIA, which can measure specimen surface in nm range. In this experiment, the specimen was scanned by 20×20 μm units, to observe and measure the surface roughness of the tools according to the layers of coating. Mechanical properties of the specimen are found to be the best when the carbide ball end-mill is coated in three layers, with the hardness of the coating layer being 29.7GPa and surface roughness 0.042 μm. The cutting component forces are better in the upwards direction than in downwards, and become smaller as the effective diameter of the tool increases as the angle of inclination of the material got bigger. DOI: http://dx.doi.org/10.5755/j01.mech.24.1.20216

Control of the material flow in sheet-bulk metal forming using modifications of the tool surface

Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous occurrence of different load conditions such as the stress and strain states. These conditions influence the material flow and often lead to a reduced geometrical accuracy of the produced components. To improve the product quality, a control of the material flow is required. One suitable approach, the local adaption of tribological conditions by means of surface modifications of tool or workpiece, so-called tailored surfaces. To control the material flow and thus to improve the component accuracy, methods to reduce and to increase friction are needed. The aim of this study is to determine requirements for necessary adaptions of the friction, the identification of tribological mechanisms for different types of tool-sided tailored surfaces as well as the verification of the effectiveness of these surface modifications to improve the results of a specific SBMF process. The numerical analysis of a combined deep drawing and upsetting process revealed that this process is characterized by two areas of varying tribological load conditions. Using a numerical analysis, the friction factor gradient between these two areas was identified as a main influencing factor on the material flow. Based on this finding, Chromium-based hard coatings for the reduction of the friction and high-feed milled surfaces for an increase of the friction were investigated regarding their frictional behaviour. The results of the ring-compression tests revealed that the carbon content and the post treatment of coated tool surfaces are relevant to reduce the friction. The increased profile depth of the milled surfaces was identified as the main influencing factor on the tribological behaviour of this kind of tailored surfaces. The effectiveness of both types of tailored surfaces was verified for the combined deep drawing and upsetting process.

Wear behaviour of coated carbide tools during machining of Ti6Al4V aerospace alloy associated with strong built up edge formation

In the machining of Ti alloys, it is challenging to optimise the cutting tool life and process productivity. It is not a trivial task to find an efficient strategy to improve the tool life during machining of Ti alloys using surface engineered tooling. In the case of rough turning operation with strong built up edge formation we establish that it can be achieved through the application of self-lubricating TiB2 PVD coating. It has been shown that the application of a TiB2 coating results in tool life improvement by over 60% compared to the uncoated tool and over 70% compared to the TiAlN coated tool. Comprehensive characterization of the coated vs. uncoated cutting tool wear performance was performed using optical 3D imaging, SEM/EDX and XPS methods. Various micro-mechanical characteristics of the TiB2 coating were evaluated. It was determined that tool life improvement using the TiB2 coating is mostly related to the ability of the coating layer to provide self-lubrication effect and in this way, very efficiently dissipate frictional energy. The coating also exhibited less substrate exposure as it fails indicating better protection of the coated tool surface. This is of particular importance for machining of materials like Ti, which have strong sticking intensity. It has been demonstrated that the TiB2 coating combines beneficial micro-mechanical characteristics and self-lubricating properties due to the formation of B-O tribo-films on the tool surface under operation. These tribo-films serve as a liquid lubricant formed in-situ on the tool surface under the elevated temperature of cutting. The formation of liquid tribo-films is an effective way to address intensive adhesive interaction followed by built up edge formation at the tool/chip interface, which is typical for roughing operations during Ti machining.

Investigation of the lubrication performance using WC: C coated tool surfaces for hot stamping AA6082

This paper presents the lubrication performance of WC: C coated tool surfaces used in hot stamping process of AA6082. A range of cylindrical deep drawing experiments were performed to determine the required minimal lubricant amount under coated and uncoated tooling conditions. In addition, effects of process variables, forming temperature and speed, on the lubrication performance were investigated. The results have shown that the advanced WC: C Diamond-like Carbon (DLC) coating could significantly reduce the use of lubricant for hot stamping. The required amount of lubricant for successful forming decreased with increasing forming speed and decreasing forming temperature. The lubrication mechanisms under different forming conditions were discussed also.

Numerical and experimental investigation of dry deep drawing of aluminum alloys with conventional and coated tool surfaces

Abstract The demand for light weight concepts in the automotive industry motivates a permanently increasing amount of aluminum alloys in the body in white. Aluminum alloys cause challenging tribological conditions in sheet metal forming due to their adhesion tendency towards tool steel. Therefore, in conventional deep drawing lubricants are applied to separate tool and workpiece to reduce friction and avoid wear. Global trends like increasing sustainability and a demand for an efficient usage of resources encourage the abandonment of environmental harmful lubricants. However, the realization of lubricant free – so called dry – deep drawing is accompanied by an intensive interaction caused by the direct contact between sheet and tool. Especially for aluminum alloys, this leads to increased friction and galling. Therefore, surface modifications are necessary for realizing dry forming. Due to the large batch sizes in the automotive industry surface modifications of the workpiece do not seem appropriate. In former studies, the tool-sided application of carbon based coatings revealed promising results in laboratory tribological tests without lubrication. However, these tests do not mirror the conditions of the entire deep drawing process. In this study, dry deep drawing was analyzed numerically and experimentally in comparison to lubricated tests. With conventional tools the direct contact led to adhesive wear and failure of the rectangular cup. Thus, deep drawing was not possible without lubrication. Applying a ta-C coating led to decreasing friction and thus lower forming forces under dry conditions. A tool- and workpiece-sided surface characterization revealed that ta-C coatings prevent adhesion and improved workpiece quality. The experimental results like punch force, part geometry and sheet thickness were used for validation of the finite element (FE) model. Comparing experimental and numerical results revealed that modelling of dry forming is possible with conventional FE methods as long as the friction coefficients are determined under the same tribological conditions without distinctive wear occurrence.

Effect of nano-scale textures on cutting performance of WC/Co-based Ti55Al45N coated tools in dry cutting

It is well known that topographical features on contact surfaces have a significant impact on friction and wear. Indeed, surfaces that entail a texture are being used to improve and/or control the performance of sliding surfaces. In this study, two kinds of novel WC/Co-based Ti55Al45N coated tools were developed utilizing femtosecond laser technology and cathode arc-evaporation technique: the first one, nano-scale surface texturing was produced on the rake face close to the main cutting edge of the WC/Co carbide tools, these textured tools were then deposited with Ti55Al45N hard-coatings; the second one, Ti55Al45N hard-coatings were deposited onto the carbide tools, nano-scale surface texturing was then produced on the coated tool surfaces. This paper details the effect of nano-scale textures and their processing sequence on cutting performance of WC/Co-based Ti55Al45N coated tools. Dry cutting tests were carried out on hardened steel with the firstly nano-scale textured and then Ti55Al45N coated tools (NCT), the firstly Ti55Al45N coated and then nano-scale textured tools (CNT), and the conventional coated tool (CCT). A reduction in cutting forces, cutting temperatures, friction coefficient at the tool–chip interface and tool wear that ensues from nano-scale textures is demonstrated, and the CNT tools are more effective compared with the NCT ones. In addition, the geometry of nano-scale textures has a profound effect, the coated tool with areal nano-scale textures shows better cutting performance compared to the one with partial nano-scale textures parallel to the main cutting edge. The possible effect mechanisms of nano-scale textures were discussed. Hence, it is expected that the results of this study can be applied to improve the performance and reduce the wear of coated tools in dry cutting.

Warm and Hot Upsetting Sliding Test: Tribology of Metal Processes at High Temperature

Identification of friction data at high temperatures is still a critical point in the optimization of forming processes. In the present paper the WHUST (Warm and Hot Upsetting Sliding Test) dedicated to the tribology of metal forming processes at high temperature is presented. The friction test is able to operate according to a large range of plastic strains, contact pressures and temperatures. The methodology to use the friction test to respect contact conditions encountered at the tool/workpiece interface of various industrial forming processes is discussed. Then three designs of experiments are achieved. The first set of experiments is performed to study the effects of the composition of graphite based lubricants on friction of hot forging tool. A particular attention is paid on the volume of lubricant used, the size of graphite particles and the amount of binding agents. The second set of experiments is performed to quantify the ability of two white lubricants to reduce friction and protect tool surface. The first lubricant is a mineral salt; the second one is an organic salt. Tests are performed at 1200°C on AISI 4820 steel specimens, with AISI H11 nitrided steel contactors. Results show the tested white lubricants lead to coefficient of friction in the same range of the graphite lubricant one, but white lubricants lose their ability to reduce friction as soon as the sliding lengths becomes greater to 10mm, where graphite lubricants can undergo sliding length greater than 30mm. The last experiments are performed to qualify a new sol-gel coating deposited on a common tool steel AISI H13. Tests are operated at 1100°C on AISI 4820 steel specimens. After each test, the ability of the coating to reduce friction and prevent metal transfer from specimens to the coated tool surfaces is established.

Innovative Tools to Improve Incremental Bulk Forming Processes

Sheet-bulk metal forming is an innovative process with a high potential to generate load-adapted parts with high precision. Bulk forming processes of sheet metals especially require high process forces, resulting in an intense contact pressure and, thus, in a very high abrasive and adhesive wear. As a method to reduce or avoid these common wear phenomena, even hardened or coated tool surfaces are not sufficient. The objective of this paper is to show an improvement of the tool resistance during an incremental forming process by an adapted tool design and the application of structured tool surfaces combined with coatings. For the tool surface the structure of the scarabaeus beetle serves as the basis for a bionic structure. This structure was manufactured by micromilling. Despite the high hardness of the tool material and the complex geometry of the forming tools, very precise patterns were machined successfully using ball-end milling cutters. The combination of bionic structures with coating techniques like physical vapor deposition (PVD) on plasma nitrided tool surfaces is very promising. In this work, the influence of process parameters (workpiece material, lubrication, tool design, stepwise infeed) on the tool resistance during the forming operation was analyzed experimentally. The results of the optimized forming tools were compared to conventional, unstructured, uncoated, and only plasma nitrided forming tools. The different tools were applied to 2 mm thick metal sheets made of aluminum (AlMg3) and steel (non-alloy quality steel DC04). As a result, the process forces could be reduced by a modified shape and surface of the tools. Thus, the lifetime of the tools can be enhanced.

An investigation on wear mechanism of high-speed turning of free-cutting steel AISI 1215 using uncoated and multi-layer coated tools

AISI 1215 is a new kind of green and non-toxic free-cutting steel with minimum environmental pollution and excellent machinability, which receives wide promotion, investigation, and application in manufacturing industries. In machining of AISI 1215 steel, tool wear has a close relation with the presence of manganese sulfide lubricant zone formed on the tool surface. In this work, with the aid of cutting temperature and tool Von Mises stress simulations, tool wear analysis on the uncoated and multi-layer (Al2O3/TiCN) coated carbide tools was performed in high-speed turning operation. Wear pattern and wear mechanisms were studied through the experimental results. The main findings showed that the uncoated tool suffered high cutting temperature and severe tool wear and was not conducive to form a manganese sulfide lubricant zone in the turning operation. In contrast, the multi-layer coated tool could form a manganese sulfide lubricant zone on the chip–tool contact area. The beneficial roles of the manganese sulfide lubricant zone formed on the coated tool surface can be summarized as lubrication and diffusion blocking. The main wear mechanisms of the uncoated tool were crater wear, oxidation wear, adhesive wear, and abrasive wear, whereas for the multi-layer coated tool, they were crater wear, adhesive wear, and abrasive wear.

Optimization of wet micro-blasting on PVD films with various grain materials for improving the coated tools’ cutting performance

The applied grains’ material in micro-blasting of Physical Vapour Deposition (PVD) films and the process conditions affect significantly the coated tools’ cutting performance. Through micro-blasting, compressive stresses are induced into the film, thus increasing the coating hardness, but its brittleness too. Simultaneously, abrasion phenomena are activated, which may lead to roughness augmentation, film thickness decrease and substrate revelation. The paper deals with the optimization of wet micro-blasting conditions for improving the coated tool's wear resistance. The explanation of the grains’ penetration into the coated tool surface and of the film deformation mechanisms renders the achievement of this target possible.

Computer Simulation of Orthogonal Cutting using a Tool with Multiple Coatings

The development and evaluation of an orthogonal cutting simulation model for carbide tools with multiple coating layers (1 µm-TiN/3 µm-Al2O3/6 µm-TiC) is presented. The chip geometry, cutting forces, tool temperatures and stresses were predicted using the Finite Element Method (FEM). The results were analyzed with a focus on the understanding of the thermal influence of coating upon tool temperatures at the tool-chip interface and in the substrate. In the simulation model used, the thermal effect of tool coating was considered by using two different models: (a) use of individual coating layers defined with intrinsic thermal properties and (b) use of a composite coating layer defined with equivalent thermal properties. The proposed models were evaluated by comparing the predictions with the experimental data available in the literature under the same cutting conditions. The steady state tool temperature solution was obtained by adopting a three-step simulation scheme. It consisted of an initial Lagrangian-type simulation until a stable chip shape was formed and a subsequent Eulerian-type calculation with update of the free surface and plastic strain field of the workpiece. The predicted results indicated that for the coated tool considered the thin-film surface coatings with an Al2O3 intermediate layer did not significantly alter the steady state temperature gradients between the chip and the tool substrate and provided little thermal insulation effect to the tool substrate. However, the modified thermal response of the coated tool surface caused lower cutting temperatures at the tool-chip interface as compared to that for an uncoated tool under the same conditions. Although these results are consistent with similar experimental observations in the literature, further validation work needs to be conducted.

Wear resistance and anti-sticking properties of duplex treated forming tool steel

The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB 2, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included. Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.

Geometry and coating parameters effect on cemented carbide sticks cutting performance used in bevel gear manufacturing

Wear phenomena affecting the coated tool performance in bevel gear manufacturing are still unexploited due to the restricted possibilities to investigate the influence of the extremely complicated cutting kinematics on the chip removal process. In the present paper the cutting process of bevel gear manufacturing was approached by means of two-axis milling. The cutting conditions and the chip formation of the bevel gear hobbing process were sufficiently considered in the applied milling experimental procedure. The coated tools cutting performance results at various cutting speeds and tool substrate and coating surface mechanical treatments is presented. The results extracted, demonstrate the extent of influence of coated tool surface preparation as well as its geometry on the overall tool life.