DLC-coated Tools Research Articles

Evaluation of the performance of DLC Coatings (ta-C) of WC-Co tools while machining Al7075 alloy

This study investigates the performance of DLC-coated 3-flute Ø 12 mm WC-Co (10%) end mills in the high-speed machining (226 m/min) of Al7075 Aluminum alloy, with high-pressure (20 bar) cooling applied in all tests focused on the cutting zone. Rolled blocks with dimensions of 150 × 350 × 150 mm were used as workpiece material. Slot milling was preferred as a test method for machining tests. Each end mill machined 757 slots with a length of 350 mm at a depth of 3 mm, and a total volume of 9150 cm3 was removed with each tool. In total, three groups of endmills were tested. A1 is a specially designed endmill for aluminum machining and was tested in an uncoated state, while A2 has the exact same geometry as A1 and was coated with tetrahedral amorphous carbon (ta-C), which is a form of Diamond-Like Carbon (DLC) coating. Finally, the A3 endmill was tested as an industrial comparative designed for aluminum machining, which was also ta-C coated. Performance tests have shown that ta-C coating significantly prevented the formation of the built-up edge. In addition, it reduced the average bending moment on the tool by 20%–25% by acting as a lubricant. It has been observed that DLC coating reduces tool wear. It was determined that flank wear was reduced by 28% and rake wear by approximately 58% in the A2 tool compared to the uncoated tool. The DLC-coated tools also provided smaller chips and improved chip control.

Study of the Industrial Application of Diamond-Like Carbon Coatings Deposited on Advanced Tool Steels

The utilization of diamond-like carbon (DLC) coatings has emerged as a promising strategy to enhance the performance, durability, and functionality of industrial tools and components. Recognized for their exceptional attributes such as hardness, wear resistance, low friction, and biocompatibility, DLC coatings have achieved widespread acclaim for their potential to improve the capabilities of tool steels for different applications. This present study shows a comprehensive investigation into the application of DLC coatings on a diverse range of tool steel substrates, encompassing 1.2379, 1.2358, Caldie, K340, HWS, and Vanadis 4. The main aim is to show the effects of DLC coatings on these substrates and to provide an in-depth analysis of their properties during forming processes. Furthermore, this study explores the practical utilization of DLC-coated tool steel components, with a particular focus on their role in cold forming dies. Additionally, the study reviews the application of duplex treatments involving plasma nitriding to enhance DLC coating performance. To sum up, this study pursues a threefold objective: to investigate DLC coatings’ performance on diverse tool steel substrates; to assess the potential for improvement through nitriding; and to evaluate the behavior of DLC coatings in the cold stamping of S235 steel, which is of great technological and industrial interest to the cold forging sector.

Tool wear and surface finish analysis after drilling Al-SiC metal matrix composite with DLC-coated tools at varying feed

Metal matrix composites (MMCs) show enhanced mechanical and physical properties compared to monolithic alloys, which make them attractive for various engineering applications. However, their actual use in industry is limited due to their low machinability. The hard reinforcements present in the matrix may lead to high tool wear and poor surface integrity. In this context, the paper aims at studying the drillability of an Al-SiC MMC when using DLC-coated tungsten carbide tools at varying feeds. After the machining trials, a quantitative evaluation of the tool wear as well as the analysis of the hole surface roughness and damage was carried out. The results demonstrate that, at increasing feed, the tool wear, surface roughness, and surface defect density decrease, leading to the counterintuitive conclusion that increasing feed when drilling causes an increase in the MMC drillability.

Analysis of MRR, Thrust Force, and Torque in Drilling Al/BN/Al2O3 Composites using Hybrid Grey–Taguchi Technique

The demand for hybrid composite materials has been expanding globally in all kinds of mechanical industries. Drilling is one of the basic operations required in manufacturing of various components and choosing optimum parameters of drilling is vital for getting good quality holes. The main objective of our work is to determine the ideal parameters of drilling and tool coatings required to minimize the thrust force and torque in drilling and to maximize the material removal rate (MRR) using Grey–Taguchi technique. Hybrid composite specimen made by reinforcing Al7075 alloy with 4% of aluminum oxide and 2% of boron nitride in stir casting process and drilling was carried out in a sequence at different drilling feed rates (40, 80, and 120 mm/min) and spindle speeds (1,200, 2,400, and 3,600 rpm) in a vertical machining center attached with drill tool dynamometer, using twist drills of diameter 5 mm and point angle 118° made of uncoated carbide, diamond-like carbon (DLC)-coated carbide and high carbon (HC)-coated carbide. The recorded thrust force and torque from the dynamometer and the computed MRRs during each drilling operation are tabulated as per Taguchi’s L27 orthogonal array and the results are analyzed using hybrid Grey–Taguchi technique. In our analysis, the optimum thrust force of 62.12 N and torque of 0.766 Nm were obtained when using a DLC-coated tool at a maximum speed of 3,600 rpm and minimum feed rate of 40 mm/min. An optimum MRR of 178.79 mm3/s was obtained while using DLC coated at a maximum speed of 3,600 rpm and a maximum feed rate of 120 mm/min.

Modification Methods of Diamond like Carbon Coating and the Performance in Machining Applications: A Review

The ideal cutting-tool coating material is characterized by unique chemical and physical properties to achieve excellent cutting performance, a good thermal barrier effect, and a high-quality machined surface. Diamond-like carbon (DLC) coating, as a kind of cutting-tool coating material, has been used in cutting various materials due to its low coefficients of friction and thermal expansion, high hardness, and good chemical inert and thermal conductivity. This article mainly focuses on the modification methods for the DLC coating and their application in machining different materials. Firstly, the methods employed to improve the mechanical properties of DLC coating are reviewed and analyzed, including the multilayer structure design, transition layer, and doping other elements. Secondly, the machining performances of DLC-coated tools in the application of different materials are summarized. This review provides knowledge of modification mechanisms regarding DLC coating and its effects on mechanical properties. For machining different materials, it provides a reference to make a suitable selection and design of DLC coating to obtain better machining performance.

An experimental investigation on tool wear behaviour of uncoated and coated micro-tools in micro-milling of graphene-reinforced polymer nanocomposites

Nanomaterials such as graphene have been added to various matrices to enhance mechanical, thermal and electrical properties for various applications requiring intricate designs at the micro-scale. At this scale, mechanical micro-machining is utilised as post-processing to achieve high surface quality and dimensional accuracy while still maintaining high productivity. Therefore, in this study, the machinability of polymer nanocomposites in micro-scale (micro-machinability) is investigated. Graphene (0.3 wt%)-reinforced epoxy nanocomposites were fabricated using traditional solution mixing and moulding. The samples were then subjected to micro-milling at various cutting speeds using three different micro-tools, including uncoated, diamond and diamond-like carbon (DLC) tools. Mechanical and thermal properties of nanocomposite were also used to support the discussions. The result indicates that the DLC-coated tool shows better performance than the other tools for less tool wear, improved surface quality and less cutting forces.

Improving Precision in Aluminum Alloy Machining Due to the Application of Diamond-Like Carbon Thin Film

Abstract Cutting precision is extremely affected by a phenomenon known as built up edge (BUE) that occurs on tungsten carbide tools during low cutting speed of aluminum alloy. BUE is responsible for early tool breakage due to excessive material build up from the machined part on the cutting face, leading to problems of shape irregularity and tool-tip breakage. Thus, diamond-like carbon (DLC) was deposited and tested to verify cutting precision in aluminum alloy by using tungsten carbide tools. The characterizations of the film were morphology analysis through scanning electron microscopy (SEM), structural atomic analyze of chemical bond from Raman backscatter spectroscopy, the distribution of carbon atoms on the film surface by X-ray photoelectron spectroscopy (XPS), and the evaluation of Young’s modulus and hardness using the Oliver–Pharr method. To analyze the cutting precision, drilling tests were performed on coated/uncoated drills at two cutting speeds (340 and 430 m/min). As an evaluation parameter in the aluminum alloy, the hole diameter deviation was measured after pre determined numbers of drilling operations. Statistical comparisons between the diameter deviation as a function of the number of drilling test indicated better cutting accuracy for the DLC-coated tool. The factors identified in this work, such as the reduction of the friction coefficient, and the hardness and Young’s modulus of the DLC helped in the performance of the tool, mainly in the lower cutting speed.

Mechanical and cutting performance of cemented carbide tools with Cr/x/DLC composite coatings

Diamond-like carbon (DLC)-coated tools are suitable for the machining of various aluminum alloys, graphite, and other non-ferrous metals. The shortcomings of DLC-coated tools such as high internal residual stress, low toughness, and poor adhesion strength limit their application. In order to reveal the mechanical and cutting performance of DLC-coated tools, a DLC monolayer coating, Cr/CrN/DLC composite coating, and Cr/W-DLC/DLC composite coating had been prepared on the cemented carbide cutting tools. The influences of transition interlayer on the microstructure and mechanical properties of DLC coatings were analyzed. Tool lives, wear mechanism, and machined surface roughness obtained with uncoated cemented carbide tool, DLC monolayer–coated tool, and Cr/x/DLC-coated tool during the machining of Al-Si alloys were investigated. Compared with DLC monolayer coating, the strength ratio (ID/IG) of the DLC composite coatings with Cr/x transition structure was improved, while the sp3 covalent bond contents was decreased. The results show that the adhesion strength and toughness of the Cr/x/DLC composite coating were enhanced, and the residual stress was greatly reduced. The cutting tests further indicate that the DLC coating significantly improved the tool life. Based on comprehensive evaluation, the Cr/W-DLC/DLC composite coating has the highest adhesion, highest toughness, the lowest residual stress, and the longest tool life, and it is suitable for the machining of non-ferrous metal.

Effect of Graphene Nanoplates Dispersed in Ethanol on Frictional Behaviour of Tool Steel Running Against Uncoated and DLC-Coated Tool Steel

Friction tests conducted between two tool steel surfaces sliding under boundary-lubricated condition in ethanol containing 5 × 10−4 wt% graphene nanoplates (GNP) under the boundary-lubricated condition showed a low coefficient of friction (COF) of 0.18, compared to 0.31 without the addition of GNP, and generated graphene incorporating tribolayers at the contact surfaces. Oxidation of the steel surfaces at high-sliding cycles increased the COF. When a diamond-like carbon (DLC)-coated counterface was used against the tool steel in GNP-containing ethanol a low steady-state COF (µS) of 0.06 was observed, and the wear rates of the DLC-coated steel were decreased by 70% compared to sliding against an uncoated tool steel counterface. Tribolayers that consisted of graphene flakes formed on top of and within the iron oxide layers that were generated on the steel surfaces. The graphene layers were deformed and damaged according to Raman spectroscopy. Cross-sectional high-resolution TEM revealed that sliding contact caused bending and occasional fragmentation of graphene layers. The graphene layers deposited on top of the tribololayers provided low friction.

Fundamental evaluation of burnishing process with DLC-coated carbide tool targeting aluminum mold for plastic injection molding

Fundamental evaluation of burnishing process with DLC-coated carbide tool targeting aluminum mold for plastic injection molding

Influence of helix angle on tool performances of TiAlN- and DLC-coated carbide end mills for dry side milling of stainless steel

This work reports the influences of helix angle on tool performances of titanium aluminum nitride (TiAlN)- and diamond-like carbon (DLC)-coated carbide end mills for dry side milling of 304L stainless steel. The study results revealed that the number of axis contact points and effective cutting length increased with increasing helix angle, leading to less tool wear and thinner milled chips but higher workpiece temperature. In addition, DLC-coated tools exhibited relatively high workpiece temperature, rapid chipping wear due to thermally induced graphitization, and chip-built-up on side edge while TiAlN-coated end mills displayed less severe abrasive wear on cutting and side edges. Moreover, the DLC-coated end mill with a high helix angle of 60° gave the lowest surface roughness of 0.26 μm within the cutting length of 20 m while the corresponding TiAlN-coated tools offered longer tool cutting length of more than 50 m with comparable surface finish. Consequently, the TiAlN-coated end mill with a high helix angle of 60° offered high-quality surface finish with long tool life time and would be more useful for dry milling of stainless steels.

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.

An investigation on the micro cutting performance of diamond-like carbon coatings using finite element method

In an effort to prolong the tool life and improve the tooling performance in micro cutting, it is attractive and promising to apply diamond-like carbon (DLC) coatings on micro tools. Comprehensive understandings of micro cutting performance under various coating circumstances are essential for choosing optimum coating conditions so as for potentially improving cutting tool designs. In the study, the cutting characteristics of a DLC-coated tool has been extensively evaluated and compared with those of an uncoated tool under constant and various uncut chip thickness (UCT) using 2D plane-strain finite element method (FEM). The thermo-mechanical modelling approach has been validated at different UCT in micro milling. Besides, the influence of coating friction coefficient, coating thickness as well as UCT on the cutting forces and tool temperatures has been determined and analysed through design of experiment. It is found that appropriate UCT in micro cutting is of the greatest importance for achieving desirable coating performance of micro tools.

Recycling of DLC-Coated Tools for Dry Machining of Aluminum Alloys via Oxygen Plasma Ashing

DLC coated tools have been widely utilized in the dry milling and cutting of aluminum alloy parts and components for automotive industries and cellular phone makers. Most of these tools are inevitably exchanged with new ones to preserve high quality of machined products. Then, the used DLC coating must be removed or ashed away before grinding and polishing. Complete removal of used DLC coating plays a key to make DLC-recoating onto the ashed surface of tools for their reuse. High density oxygen plasma ashing provides a solution to make perfect ashing of DLC coating together with metallic interlayers before recoating. In the present paper, this plasma system with quantitative diagnosis instrumentation is first stated to describe the effect of processing conditions on the ashing behavior. Two types of end-milling tools were prepared to prove that the whole DLC-coating should be completely removed with fast rate. This ashed tool substrate was ground and DLC-recoated to demonstrate that the reused tools have the same machinability in dry as the original virgin tools through dry milling experiments.

Wear Behavior of a DLC-Coated Blanking and Deep Drawing Tool Combination

In macro forming a DLC-coating can increase durability and decrease wear of a deep drawing tool. Due to size effects, the behavior in micro range can differ from the behavior in macro range. To investigate durability and wear in micro deep drawing a blanking and deep drawing tool combination was developed, capable of maximum stroke rate of 200 parts per minute. Experiments with copper foil (E-Cu58) of 0.05 mm thickness were performed to produce cylindrical micro cups with a diameter of 1 mm using the lubricant Lubrimax Edel C. The tool material is stainless steel (German standard 1.2379). The punch has a diameter of 0.9 mm and the die diameter is 1.06 mm. To increase durability and decrease wear in micro deep drawing a DLC-coated tool is used. DLC-coated and uncoated tools are compared in long term test regarding wear behavior. Furthermore, the die radii of the tools are measured optically and cross-sections of the tools are made to analyze the microstructure. Experiments show, that the DLC-coating starts to delaminate during the first 5000 strokes. By analyzing the cross section it can be recognized a high density of scattered carbides and pores with different sizes up to 35 μm in the tool material are visible, causing delamination. Furthermore, higher load and stress in micro forming provides delamination. Thus a high influence on the durability of the DLC-coatings base material can be reported in micro range.

Initiation of Galling in Metal Forming: Differences Between Aluminium and Austenitic Stainless Steel Studied In Situ in the SEM

High friction and transfer of work material to tool surfaces constitute important industrial problems in forming of many metals and alloys. However, it is very hard to gain a deeper understanding of these phenomena by studying real forming operations. In this paper, we have tried to gain fundamental understanding by avoiding as much as possible of the complexity of real forming. This has been realised by studying the friction and material transfer between well-defined tool material surfaces; uncoated and DLC-coated tool steel, and a needle shaped austenitic stainless steel tip, in situ in the SEM. The tool materials were tested in two conditions; well polished and well polished with local intentional scratches. It was found that work material was immediately transferred to the tool steel surface. When passing an intentional scratch, the local transfer was on a much larger scale, and the friction was higher, but the effect was mostly local. For the polished DLC-coated surface, almost no work material was transferred and the friction was low. An intentional scratch in the polished DLC surface barely influenced the galling behaviour. The present results are discussed in the light of previously published results from an analogous study with aluminium as work material.

環境に優しいDLCコーテッド工具・金型・機能部品の開発

環境に優しいDLCコーテッド工具・金型・機能部品の開発

Tool Wear of Diamond-Like Carbon-Coated High-Speed Steel with a Cr-Based Interlayer in Cutting of Aluminum Alloys

In cutting aluminum alloy 6061, continuous chips have a negative influence on the machining operation. Usually, Pb is added in order to break continuous chips. However, from the standpoint of environmental protection, it is necessary to improve chip breakability without adding Pb. One effective measure to improve chip breakability is by adding Si to aluminum alloy 6061. However, the influence of Si content on tool wear has not been fully examined. In this study, in order to clarify the influence of a diamond-like carbon (DLC) coating layer with a Cr-based interlayer, namely (Al,Cr)N, on cutting performance, aluminum alloys having different Si contents were turned. The substrate of the tool material was high-speed steel (1.4%C). The tool wear and the surface roughness were experimentally investigated. The following results were obtained: (1) In cutting two kinds of Al-Si alloys, namely the Al-2%Si alloy and Al-4%Si alloy, the progress of wear of the DLC/(Al,Cr)N-coated tool was slower than that of the DLC-coated tool. Therefore, the (Al,Cr)N interlayer was effective for decreasing the tool wear of the DLC-coated tool. (2) The wear progress of the two kinds of DLC-coated tools in cutting of Al-4%Si alloy was faster than that in cutting of Al-2%Si alloy. (3) In cutting of Al-2%Si alloy with the (Al,Cr)N/DLC-coated tool, the surface roughness was almost constant in the range of a cutting distance from 0.1 km to 9.5 km.

Tribological behaviour of DLC-films and their application in micro deep drawing

In this work, the tribological behaviour of DLC-coated as well as uncoated tools was characterized by tests on a tribometer. Special attention was paid to assess how the failure mechanisms of the films proceed, for example, whether the so-called “eggshell effect” plays a role in the failure of the films. Compared to the uncoated tools, the DLC-coated tools showed a significantly lower friction coefficient to the work piece material stainless steel X5CrNi18-10. As the contact pressure was varied from 215 to 330 N/mm 2, which is comparable to the maximum contact pressure in deep drawing, no damages in form of cracks or flaking were observed. Furthermore, lubricant-free micro deep drawing was performed with DLC-coated tools made of tool steel X153CrMoV12. Though no lubricant was used, the experimentally measured punch force was lower than that from experiments using lubricant with uncoated tools. This indicates that the DLC-coating has a great application potential in micro forming.

Cutting Performance of Diamond-Like Carbon Coated Tool in Cutting of Aluminum Alloys

In cutting aluminum alloy 6061, continuous chips have a negative influence on the machining operation. Usually, Pb is added in order to break continuous chips. However, from the standpoint of environmental protection, it is necessary to improve chip breakability without adding Pb. One effective measure is improving chip breakability by adding Si in aluminum alloy 6061. However, the influence of Si content on tool wear has not been fully examined. In this study, in order to clarify the influence of a diamond-like carbon (DLC) coating layer on cutting performance, aluminum alloys having different Si contents were turned. The substrate of the tool material was high speed steel (1.4%C). The chip configuration, cutting force and tool wear were experimentally investigated. The following results were obtained: (1) The DLC coating layer was effective for decreasing the cutting force. (2) In cutting Al-2mass%Si alloy, the wear progress of the DLC-coated tool was slower than that of the un-coated tool. The length of a chip with the DLC-coated tool was shorter than that with the un-coated tool.