Diamond-coated Tools Research Articles

Comparative study of the performance of diamond-coated drills on the delamination in drilling of carbon fiber reinforced plastics: Assessing the influence of the temperature of the drill

Drilling processes are a topic of great importance for the manufacturing of carbon fiber reinforced plastics parts. The characteristics of the carbon fiber reinforced plastics contribute to the appearance of a phenomenon called delamination during drilling, which is responsible for the greater part of the rejected parts in various industries. The present work aims to study and characterize the phenomenon of “peel-up” and “push-out” delamination, which occurs in drilling of carbon fiber reinforced plastics laminates at the entrance and exit of the drill, respectively. The work focuses on the study of the influence of the machining parameters: feed rate and spindle speed on the delamination damage. In addition, the influence of the temperature at the entrance of the tool was also studied. For this purpose, three different tools: one conventional and two specific for drilling carbon fiber reinforced plastics laminates were used. The results of the work recognised as the most influential factors the feed rate and the tool, at the entrance and at the exit, respectively. Regarding the tools, the diamond-coated tools were the best to diminish the delamination damage. Finally, for the range of parameters tested, the peel-up delamination decreases as the temperature reached at the beginning of the drilling process increases.

Interface delamination study of diamond-coated carbide tools considering coating fractures

Interface delimitation is one of the major failure modes of diamond-coated carbide tools in machining. On the other hand, diamond coatings are prone of cracking easily due to its brittleness, which may affect interface delaminations. To study any influence between the two failure modes, micro-scratch testing on diamond-coated carbide tools was conducted and finite element (FE) modeling was developed to simulate the scratching process. In scratch testing, normal and tangential forces as well as acoustic emission signals were recorded to detect coating delaminations and crack initiations. Scratched samples were also observed by optical microscopy to determine the corresponding critical load of delaminations and cracking initiations. In the FE scratch simulation, a cohesive-zone interface and the extended finite element method (XFEM) were applied to investigate delamination and coating fracture behaviors, respectively. The cohesive elements were based on a bilinear tractionseparation model and XFEM was implemented to model cracking behavior in a diamond coating with a damage criterion of the maximum principal stress.The major findings are summarized as follows. The coating fracture energy has a negligible effect on the critical load for interface delaminations, and similarly, the interface fracture energy has no effect on the critical load for coating cracking, indicating that the two failure modes are mostly uncoupled for the testing range in this study. From the experiments and simulations, it is estimated that the coating fracture energy of the samples tested in this research is in the range of 120 to 140J/m2, and the diamond-carbide interface fracture energy is from 77 to 192J/m2. Moreover, increasing the coating Young's modulus will increase the critical load for coating delaminations, but decrease the critical load of coating cracking.

Cutting Performance of Diamond Coated, TiAlN Coated and Carbide Cutting Tools in High Speed Milling Graphite

This paper focusing on cutting performance high speed milling Electrical Discharging Machining (EDM) graphite with diamond coated、Carbide (WC) and TiAlN coated cutting Tools. tools wear, cutting force and machined surface had been researched. Experiment study including cutting speed, feed rate per tooth, radial depth of cut, axial depth of cut, and material of tools factors effects on the cutting forces. Cutting parameters are optimized based on the orthogonal experiment. Experiment in high speed milling with diamond coated tools all comparison with TiAlN coated and Carbide (WC) tools. On the surface quality, cutting forces and tool wear influence graphite cutting tool materials research, process parameters, tool design and optimization of processing parameters to provide supportive data. The minimum cutting force as the goal, through the orthogonal experiment for the optimization of cutting parameters obtained for the high speed milling graphite with diamond-coated tool: cutting force 360m/min,feed per tooth 0.15mm/z, radial depth of cut 0.9mm, axial depth of 9mm.

Comparison of two models for predicting tool wear and cutting force components during high speed trimming of CFRP

Because of the low thermal conductivity of Carbon Fibre Reinforced Polymers (CFRPs) during high speed-trimming, cutting forces and tool wear significantly increase the temperature at the contact zone, which is then completely transferred to the cutting tool and exceeds the permitted thermal stability limit of the cutting material. This then leads to a drastic reduction of the tool life, thermal damage, poor quality, and in some cases, rejection of machined parts. This paper presents the development of tool wear and cutting force prediction models in the trimming of CFRPs. A 3/8 in. diameter CVD diamond-coated carbide tool with six straight flutes was used to trim 24-ply carbon fibre laminates. The results obtained using a scanning electron microscope (SEM) showed increasing defect rates with increased tool wear. Two models were adjusted to predict tool wear and cutting force for different values of cutting speed, feed and cutting length. One of them is a multiplicative statistical model, and the other, an exponential model. Outcomes from the two models were analysed and compared. The ANOVA approach was also used to test the overall significance of the models by applying F-tests. The results obtained show that the exponential model is better capable of accurately predicting the cutting force and tool wear under the conditions studied. To enhance the prediction accuracy of the tool wear model, the cutting force was added as a variable in the tool wear model. Results show that the enhanced multiplicative model provided higher predictive capabilities than the exponential model.

Tool wear and hole quality when single-shot drilling of metallic-composite stacks with diamond-coated tools

This article details experimental work performed to evaluate the effects of varying feed rate (0.08 and 0.15 mm/rev) and tool coatings (diamond-like carbon and chemical vapour–deposited diamond) on tool wear modes and hole quality when drilling 30-mm-thick Ti-6Al-4V/carbon fibre–reinforced plastic/Al-7050 stacks in a single-shot operation. At a feed rate of 0.08 mm/rev, the diametrical accuracy of holes produced by both the chemical vapour–deposited diamond and diamond-like carbon–coated drills (6.38 mm diameter) was comparable within a tolerance of ±0.04 mm even after 70 holes. However, in terms of cylindricity, holes machined with chemical vapour–deposited diamond were significantly better than those produced using the diamond-like carbon–coated drills by a factor of ∼2 (65.7 vs 140.6 µm). A similar trend was also observed for hole out of roundness. Burr height at hole entry locations (Ti layer) ranged from ∼0.03 to 0.08 mm for all trials undertaken at the lower feed rate level; however, the diamond-like carbon–coated drills generated exit burrs which were ∼4 times larger than their chemical vapour–deposited diamond-coated counterparts. Subsequent wear analysis showed that diamond-like carbon–coated drills operating at 0.08 mm/rev typically exhibited progressive abrasion, workpiece adhesion and chipping leading to fracture of the tool corner, while fracture due to fatigue was prevalent in tests carried out at the high feed rate level. In contrast, poor adhesion of the chemical vapour–deposited diamond coating to the carbide substrate led to premature flaking, severe chipping and fracture of the drill cutting and chisel edge.

Implementing a Cohesive Zone Interface in a Diamond-Coated Tool for 2D Cutting Simulations

The interface properties and deposition residual stresses may have significant effects on the diamond-coated tool performance. However, it is still not fully understood how the interface mechanical behavior and deposition residual stress together influence the thermo-mechanical behavior of a diamond-coated tool during machining. In this study, a two-dimensional (2D) cutting simulation incorporating both deposition residual stresses and an interface cohesive zone model has been developed to demonstrate the feasibility of evaluating coating delamination of a diamond-coated tool during cutting. It has been shown that even the residual deposition stresses alone may result in failure initiations in the cohesive zone (i.e., the interface). In addition, the study further demonstrates the implementation of a cohesive zone interface in a diamond-coated tool in 2D cutting simulation. An example of cohesive failures occurred during the cutting simulation is presented. The result further shows that a larger uncut chip thickness will result in cohesive delamination of the coating-substrate interface during cutting.

Comparative analyses on tool wear in helical milling of Ti-6Al-4V using diamond-coated tool and TiAlN-coated tool

Comparative analyses on tool wear in helical milling of Ti-6Al-4V using diamond-coated tool and TiAlN-coated tool

Temperature of internally-cooled diamond-coated tools for dry-cutting titanium

The role of cutting fluids is well known for the importance of removing heat from the cutting edge, lubricating the sliding chip contact and transporting the metal chips away from the cutting zone. Dry machining leads to increased cutting temperatures and higher wear rates resulting in shorter tool life; this is particularly evident in the cutting of high strength materials. Diamond coated cutting inserts are not usually considered for machining titanium due to rapid oxidation of the coating at the temperatures typical of titanium machining. This paper examines the formation of hot-spots on the rake face during dry and near-dry turning of titanium using conventional cemented carbide inserts. Machining performance is assessed by measurement of tool wear and tool life. Trials with an internally cooled tool with a specially designed, diamond coated insert have shown that the heat from the cutting operation can be rapidly diffused over the entire surface of the insert and thus successfully drawn away from the tool via closed loop recirculation of coolant through the tool holder. This enables wear to be inhibited by management of rake face temperature to keep it below the critical temperatures at which these prominent wear mechanisms operate. Measurements of change in coolant temperature before and after circulation are used to quantify the heat removed from the cutting process. The low friction coefficient and high thermal conductivity of diamond, assisted by the indirect cooling, results in longer tool life whilst maintaining high standards of surface finish.

SIMULATION AND EXPERIMENTAL STUDIES ON SUBSTRATE TEMPERATURE AND GAS DENSITY FIELD IN HFCVD DIAMOND FILMS GROWTH ON WC–Co DRILL TOOLS

Uniform temperature and gas density field inside the reactor play an important role on synthesis of high-quality diamond films using hot filament chemical vapor deposition (HFCVD) method. In the present study, the finite volume method (FVM) is adopted to simulate the temperature and gas density distribution during the deposition process. Temperature–measuring experiments are conducted to verify the correctness of the simulation results. Thereafter, the deposition parameters are optimized using this model as D (filament separation) = 35 mm, H (filament–substrate distance) = -10 mm and N (number of gas inlet) = 3. Finally, experiments of depositing diamond films on WC– Co drill tools are carried out with the optimal deposition parameters. The results of the characterization by SEM and Raman spectrum exhibit that as-fabricated diamond-coated tools present a layer of high-quality diamond films with homogeneous surface and uniform thickness, further validating the accuracy of the parameter optimization using the simulation method.

A Comparative Evaluation of the Wear Resistance of Various Tool Materials in Friction Stir Welding of Metal Matrix Composites

Friction stir welding (FSW) is the preferred joining method for metal-matrix composites (MMCs). As a solid-state process, it precludes formation of the intermetallic precipitates responsible for degradation of mechanical properties in fusion welds of MMCs. The major barrier to FSW of MMCs is the rapid and severe wear of the welding pin tool, a consequence of prolonged contact between the tool and the harder reinforcements which give the material its enhanced strength. This study evaluates the effectiveness of harder tool materials to combat wear in the FSW of MMCs. The tool materials considered are O1 steel, cemented carbide (WC-Co) of the micrograin and submicrograin varieties, and WC-Co coated with diamond. The challenges which accompany the application of harder tool materials and diamond coatings in FSW are also discussed. This study represents the first use of diamond-coated tools in FSW and the first comparative evaluation of tool materials for this application.

The Development of Decision-Making Maps for the High-Speed Machining (HSM) of Rhyodacite (Carijó Basalt) in Milling-Based Processing Applications

The demand for innovative products that overcome competitive pricing and conquer market shares can be met by interdisciplinary approaches that bridge product design, engineering and technology. Ornamental and covering stones stand out among the materials in need of innovation and are commonly used in architecture and construction as coverings in urban elements, funerary art, and art and decor. In spite of the many applications of ornamental stones, products with low added value are typically observed. Although Brazil displays significant geological potential for ornamental stones, its actual market participation is as a supplier of un- or semi-processed stones. Even with the market’s visible expansion and Brazil’s increased representation in the market, the technological advances used in the final processing of stones are restricted to improve the tools used for cutting, especially the durability of diamond-coated tools, and for polishing, which, in the short-term, meets the demands for marketing, producing and distributing semi-finished products. Accordingly, a little exploited aspect of ornamental stones appears, especially for “carijo basalt” (rhyodacite), that is, the inclusion of new processing and value-adding technologies or the inclusion of non-conventional processes in the sector. The goals of this work are to study and develop HSM (high speed machining) CNC (computer numerically controlled) milling processes that are applicable to rhyodacite, specifically to determine the milling parameters that give the best results for machining time with respect to tool wear and material abrasion and to replicate the results obtained in the samples. The results show that the raw material used in the present study, because it is natural, presents significant variations in composition and hardness, which prevent specific milling parameters from being determined. However, using a post-processor specifically developed for this study, it was possible to draft a decision-making map that aids in the execution of this process. Additionally, equipment failure occurred during every attempt and with every adjustment of the milling process. This indicates that the application of multipoint tools to rhyodacite milling is difficult in this industry. Thus, the use of single-point tools should be the natural path to follow for a potential practical industrial application in Brazil.

Coating thickness and interlayer effects on CVD-diamond film adhesion to cobalt-cemented tungsten carbides

In this study, diamond coating adhesion on cobalt-cemented tungsten-carbide (WC–Co) substrates was investigated using scratch testing. In particular, a methodology was applied to evaluate the effects of the coating thickness and the interlayer on diamond coating delaminations. In the coating thickness effect research, substrate surface preparations, prior to diamond depositions, were common chemical etching using Murakami solutions. On the other hand, to study the interlayer effect, Cr/CrN/Cr and Ti/TiN/Ti, were deposited to WC–Co substrate surfaces (no chemical etching) by using a commercial physical vapor deposition (PVD) system in a thickness architecture of 200nm/1.5μm/1.5μm, respectively. Diamond films were synthesized by using a hot-filament chemical vapor deposition (HFCVD) reactor at a fixed gas mixture with varied deposition times.Scratch testing was conducted on the fabricated specimens using a commercial instrument. It is noted that the onset of coating delamination can be clearly identified by high-intensity acoustic emission (AE) signals and high tangential force fluctuations when such events occur, which can be used to determine the critical load for coating delaminations. Scratched track morphology was also characterized by scanning electron microscopy and white light interferometry.The results show that the adhesion of diamond coatings on WC–Co substrates increases with the increased coating thickness, with a nearly linear relation. The trend is consistent with the findings from a previous study that experimentally evaluated the coating thickness effect on the diamond-coated tool performance. Scratched tracks were characterized by diamond coating cracking and coating delaminations once the adhesion critical load is reached. For the two types of interlayer materials tested, neither of them seems to be effective and the diamond coating with the Ti-interlayer shows poor adhesion compared to the Cr-interlayer coatings.

An investigation on the cutting performance of nano-crystalline diamond coatings on a micro-end mill

In conventional milling, appropriate coatings can be used on tools to enhance their cutting performance and efficiency of the production process. In an effort to improve the tooling performance in micro-scale milling, nano-crystalline diamond films were applied on a micro-end mill by a hot filament chemical vapour deposition process. The cutting performance of the nano-crystalline diamond-coated tool, including cutting forces, tool integrity, surface roughness and burr formation, were evaluated in slot milling of aluminium 6061-T6 against that of an uncoated tool in dry cutting conditions. Reduced cutting forces, free chip adhesion, lower tool wear, improved surface roughness, as well as smaller burrs, were observed using the nano-crystalline diamond-coated tool. The investigation illustrates the possibility of applying nano-crystalline diamond coatings on micro-milling tools for dry cutting and better tooling performance.

ダイヤモンド膜の付着特性評価のための押込み試験機の開発

Diamond-coated tools are intended for use in machining of carbon fiber reinforced plastics and dry processing of metals such as aluminum alloys and stainless steel. To guarantee the reliability of the coated tool, quantitative evaluation of the adhesion strength of the film onto the substrate is necessary. This study examines the development of an indentation tester for the evaluation of diamond film adhesion properties. The indenter point shape resembles that of the Rockwell C scale. This tester detects acoustic emissions continuously during the indentation of the diamond indenter against the film. This method defines the critical load to yield a crack on the film as the adhesion property of the film. Results show that the tester works satisfactorily for the quantitative evaluation of peeling or cracking strength of the film. The effect of the diamond material on the indenter lifetime is also discussed according to the longest lifetime for the binderless polycrystalline diamond.

On measurements of tool edge geometry of diamond-coated tools

In this study, a white-light interferometer (WLI) was used to acquire tool edge surface data, and MATLAB-based algorithms were developed to characterise the tool edge geometry. Commercial cobalt-cemented tungsten carbide (WC-Co) cutting inserts with different edge radii were evaluated. In addition, the carbide tools were further subject to controlled diamond film depositions and then were evaluated again in the tool edge geometry to evaluate the coating thickness. The tool geometry and coating thickness will enable a quantitative model correlating the deposition stresses with the tool geometry edge. The major results are summarised as follows. 1 The combination of WLI and the developed algorithms is capable of efficient tool edge geometry measurements. 2 For the straight edges, the variations of edge radii among different tool samples in a single batch are reasonably small. 3 Comparing coated and uncoated edge results, the coating thickness can be estimated. It is also noted that the coating is thicker at the rake and the edge than the flank faces. 4 Tools with a large edge radius ( > 50 mm) showed a greater variation in coating thickness estimates.

Interface characterizations of diamond-coated tools by scratch testing and simulations

In this study, micro-scratch tests were conducted on diamond-coated tungsten-carbide substrates to investigate coating adhesion. During the scratch testing, high intensity acoustic emission (AE) signals can be clearly detected when the coating delamination occurs. It is also found that the tangential force increase gradually with the normal force, but fluctuates significantly when the critical load of coating delamination is reached. A three-dimensional (3D) finite element (FE) model with a cohesive-zone interface was developed to simulate the scratch process, and by comparing with the delamination critical load from the experiment, the interface characteristic length, the maximum strength and the fracture energy can be obtained. The preliminary results indicate that it is feasible to use the FE simulation combined with scratch tests to evaluate the coating interface behaviors.

Characterisation of surface micro-topography by power spectral density in high speed precision planar milling of SiCp/Al composite

This paper presents an experimental study in high speed precision planar milling of SiCp/Al composites. Machining tests were carried out on a high speed milling machine (ops 650) by using chemical vapour deposition (CVD) diamond-coated tools. The surface micro-topography was tested by the OLS3000 confocal laser scanning microscope. The Gaussian filtering method and the least square fitting method were used to treat the measured results. Two methods are compared according to the effect on keeping important original character of the machined surface, as original character of the machined surface such as surface defects affect the surface micro-topography seriously. The treated surface data was analysed using the method of power spectral density. The three-dimensional root-mean-square deviation of the surface Sq was also calculated. The results showed that the least square fitting method is suitable due to its good accordance to the original characters of the surface. Cutting speed is found to be the main fa...

Machining Behavior of Green RBSC Body Prepared by Gel-Casting

In this paper, the green RBSC was prepared by gel casting process. The influences of the monomer content (MBAM and AM) and monomer ratio (MBAM to AM) on the flexural strength were investigated. The results indicated the flexural strength of green body was up to 8MPa and the micro- structures were homogeneous. The green RBSC bodies were machined by CNC grinding machine with diamond-coated grinding tools. Machining tests showed the green component could be machined without appended defects. It was found that green machining as a ‘top-down’ approach was a potential alternative for the rapid fabrication of complex-shaped ceramics, especially for some one-of-a-kind products.

Precision and micro CVD diamond-coated grinding tools

Both for ultra-precision and for micro-machining diamond is used very often as tool material. The reason is the very high dimensional stability of diamond due to its extreme hardness. Diamond is used for two kinds of machining processes: for cutting, like turning, drilling or milling, as well as for abrasive processes, like grinding. Diamond cutting tools can be made with massive diamond (monocrystal, CVD diamond, PCD) or with diamond coatings. Standard diamond abrasive tools are made by bonding diamond monocrystals onto a base body. A new grinding layer technology is presented: chemical vapour-deposited microcrystalline diamond layers have crystallite tips with very sharp edges that can act for grinding processes. Base body materials and coating technology is presented. Application results of grinding experiments show that very high workpiece quality can be reached, e.g. a roughness Ra of 5 nm with glass workpieces. Truing and recoating techniques are discussed for reuse of worn CVD diamond grinding wheels. Micro grinding tools (abrasive pencils, burrs) can be manufactured with the same coating technology. Very small tools with diameters of 50 μm have been made and successfully tested.

Delamination wear of nano-diamond coated cutting tools in composite machining

Nanostructured diamond (nano-diamond) coated cutting tools have a potential to supplant costly polycrystalline diamond tools. However, coating delaminations remain the primary wear mode that often results in catastrophic tool failures. Studying tool wear will help to understand machining parameter effects on coating delaminations. Moreover, monitoring coating delamination events can prevent production loss and assist process planning. In this study, nano-diamond coated cutting tools were investigated in machining aluminium matrix composites. Outside-diameter turning with a wide range of cutting conditions was conducted. Tool flank wear-land was periodically measured by optical microscopy and worn tools were examined using scanning electron microscopy. A dynamometer and an acoustic emission (AE) sensor were also used to monitor tool conditions during machining operations. The results are summarized as follows. (1) Tool wear evolutions include a low wear rate followed by an abrupt increase of flank wear due to coating delaminations. Such behaviour is consistent in all machining conditions tested. (2) Once coating is delaminated, cutting forces increase sharply along cutting with a high level of dynamic forces, especially for the radial and axial components. (3) AE signals including raw data, root-mean-square (RMS) values, and frequency responses all show distinct features before and after coating delaminations. Significant conclusions drawn from this study include the following. (1) The feed has a more dominant effect on cutting durations prior to coating delaminations because of the increased mechanical load. (2) Nano-diamond coating tools have greater coating delamination wear resistance than conventional microcrystalline diamond-coated tools. (3) AE signals may be used to identify if coating delaminations occur, which are recognized by significant reductions of AE-RMS values.