Milling Titanium Alloy Research Articles

Cutting parameters and tool geometry selection for plunge milling - Analysis of cutting forces at the bottom of deep titanium workpieces

• Plunge milling of titanium alloy. • Comparative study of tools in plunge milling. • Study of the cutting forces in plunge milling. • Study of the increase of cutting forces at the bottom of the pocket in plunge milling. Plunge milling is a machining process recognized to be efficient for roughing deep workpieces. This is due to the distribution of cutting forces on the tool. Important axial forces and reduced radial forces lead to more rigidity, and eventually productivity. It is commonly used in the case of machining hard to cut materials, like titanium alloys. However, plunge milling process can exhibit a problem at the end of plunging phase, which is the increase of cutting forces. Within this paper, the study considers the case of wet plunge milling process applied to Ti-6Al−4 V alloy, that is the most generally used titanium alloy and applied in a wide range of applications. The authors investigate the effects of the geometrical parameters and the cutting parameters on the amplification of the cutting forces at the bottom of deep pockets. The study shows that the augmentation of the chip cross-section is the cause of the increase of the cutting forces, and a geometrical model is set up so as to predict the enlargement of the chip cross-section depending of several parameters. The results indicate that the entering angle and the nose radius of the insert are the main influential geometrical parameters. Furthermore, is was found that for cutting parameters, the principal influential parameter is the radial offset. Thus, proper cutting parameters and type of insert should be carefully chosen in order to avoid high levels of cutting forces at the bottom of deep titanium workpieces in plunge milling operations.

Thermal analysis in MQL end milling operations

The impact of various additives such as Al2O3, polycrystalline diamond (PCD) and graphite as well as water in MQL oil has been investigated on convective heat transfer and machinability in end milling Ti6Al4V for the first time. The analysis indicated that suspending PCD in oil improves heat transfer by 43% from 557 W/m°K in conventional MQL to 970 W/m°K resulting in 1.6 times increased tool life in high speed machining of Ti6Al4V alloy. This can potentially allow for high speed end milling of Ti6Al4V titanium alloy resulting in increased productivity.

Milling of aerospace alloys using supercritical CO2 assisted machining

Novel “sub-zero” cooling methods are an emerging technology employed in machining of aerospace alloys that has been the focus of substantial ongoing research. A series of different cooling media have been used in an effort to decrease the friction and the amount of heat generated in the cutting zone. This study focused on the use of supercritical carbon dioxide (scCO2) as a coolant in the face milling of titanium alloy Ti-6Al-4V. Traditional flood emulsion coolant was compared with through tool scCO2 as well as scCO2 with minimum quantity lubrication (MQL).

Optimising milled titanium alloy concave surface quality with micro-textured ball-end milling cutters

Optimising milled titanium alloy concave surface quality with micro-textured ball-end milling cutters

Substantiation of the parameters of the process of plasma-mechanical milling of titanium alloys and alloyed steels

The article is devoted to the development and scientific substantiation of the method of processing high-strength materials using surface plasma heating. A method for determining the parameters of the plasma-mechanical milling process has been formed, which includes: thermal calculations of the plasma arc power; thermal field characteristics in the part material; determination of residual stresses and hardness of the surface layer of the part. The choice of technological parameters of a plasma heating source is grounded. Criteria are formulated to which the source of plasma heating must correspond. Calculations are performed to determine the dependence of the performance of the milling process on titanium alloy Ti-6Al-4V with the achievement of a certain microstructure of the part being cut off under the influence of plasma heating. A new scheme of plasma-mechanical milling is proposed, which provides for arc scanning in a magnetic field in the direction of the minute vector filing cutters and additional cyclical movement across the plasma torch feed vector with an amplitude of approximately equal to width milling. The proposed method of plasma heating a cut off layer allows lowering costs of processing time, and solve the problem of shortening ships' construction time.

Simulation and Experimental Research into Combined Electrochemical Milling and Electrochemical Grinding Machining of Ti40 Titanium Alloy

Simulation and Experimental Research into Combined Electrochemical Milling and Electrochemical Grinding Machining of Ti40 Titanium Alloy

Improvements to machining surface quality by controlling the flow direction of electrolyte during electrochemical sinking and milling of titanium alloy

Electrochemical milling is eminently suitable for machining aerospace parts (which usually have complex structures) because of its great flexibility. However, titanium alloys are particularly sensitive to changes in the flow field, which often cause severe pitting corrosion of the machined surface. Although electrochemical sinking and milling (ESM) can restrict the flow of electrolyte and reduce pitting corrosion, the quality of the machined surface is not ideal because the latter are susceptible to stray corrosion. To reduce such corrosion and improve the surface quality, the internal flow channel of the tool electrode and the cutting depth were investigated thoroughly. Extensive experiments revealed that stray corrosion could be reduced significantly and surface quality improved by controlling the electrolyte flow direction in the machining area, which was achieved by changing the style of the internal flow channel of the tool electrode. These reductions in corrosion and surface roughness were achieved using a tool electrode with a triangular internal flow channel. In addition, the main components and micro-hardness of the machined surface were close to that of the TB6 titanium alloy substrate, which helped to maintain the inherent high strength of the titanium alloy. The surface of the workpiece changed from being hydrophilic to being hydrophobic, which reduced the flow resistance.

Investigation on PCD cutting edge geometry for Ti6Al4V high-feed milling

Some new research challenges are connected to new high-feed milling tools, developed recently to reduce the cutting time. The main objective of this article is to analyze if PCD tools could be used for high-feed face milling of Ti6Al4V. As its performance depends significantly on cutting edge geometry, different tool geometries were evaluated regarding tool life and cutting forces. Experimental investigations demonstrate that the tool profile, which has a discontinuity on chip flow direction along the cutting edge, presents an intense local tool wear and, consequently, a smaller tool life. The PCD tool having a straight edge has a longer tool life but, contrarily to the carbide tool theory, local wear behavior on the cutting edge is not constant when depth of cut increases. The cutting force magnitude, and its dynamic, affects drastically the tool life of PCD tools in milling and it is a limitation to the increase of the material removal rate. In conclusion, it is possible to use specific PCD tools for milling titanium alloy in high feed with low depth of cut (smaller than 1 mm), which is not economically practicable.

Influence of the application of wear-resistant coatings on force parameters of the cutting process and the tool life during end milling of titanium alloys

The studies were focused on the process of end milling of VT20 titanium alloy with uncoated end milling cutters and cutters with the Ti-TiN-(Ti,Cr,Al)N and Zr-ZrN-(Zr,Cr,Al)N coatings. The investigation of the coating microstructures has revealed that the coatings have nanolayer structures, with the thicknesses of nanolayers within a range of 2–20 nm and the period λ = 75–92 nm. Curves of instantaneous cutting force components (Fp,Fx,Fy) were built. According to the results of the cutting tests, tools with the coatings under study demonstrate the tool life of 2.5–3 times higher compared to the tool life of an uncoated tool. The studies were conducted to investigate the wear and fracture patterns on the coatings during the end milling, and the differences in the processes of coating wear and fracture were revealed.

Questions of generalization of statistical modeling results on the example of face milling of titanium alloys

The article presents the results of the experiment on face milling of titanium alloy Ti-6Al-4V in coarse-grained and ultra-fine-grained states. The nanostructured state of the alloy was obtained by equal-channel angular pressing that leads to higher strength characteristics of material. The experiment was carried out on a universal milling machine PROMA model FHV-50PD. During the three-factor experiment, the cutting modes were varied: cutting depth (t = 0.4; 0.6; 0.8 mm), feed (s = 65; 100; 185 mm/min) and the rotation speed of the mill (n = 580; 720; 875 rpm). The cutting force was determined indirectly by measuring the displacement of the mill holder using a vibration sensor. The simulation of the dependence of the main component of the cutting force on the processing modes was performed by linear regression for exponential dependence. The model adequately describes the experimental data. A comparison of the results of regression analysis obtained during full and short experiments is presented. The questions of generalization of the results of the obtained force dependencies for processing conditions that differ from the basic ones are considered. The analysis is carried out using a modern method of statistical analysis – bootstrap.

Investigation on influence of hybrid nozzle of CryoMQL on tool wear, cutting force, and cutting temperature in milling of titanium alloys

The titanium alloy has a low thermal conductivity of 1/8th that of common metals and half that of stainless steel. The heat dissipation is poor during dry cutting, so the cutting temperature rises above about 600°C. Due to this, the quality of the cutting surface decreases during machining, and rapid tool wear occurs. To solve this, the use of cutting fluid is essential, but the chemical composition of the cutting fluid has a negative effect on the body and the environment. In the current cutting process, in order to minimize this effect, eco-friendly processing using minimum quantity lubrication (MQL) is performed. The machining method using both MQL and a cryogenic gas separately applies the MQL and the cryogenic gas to both sides of the cutting tool. In this case, the oil mist cannot penetrate the cutting zone due to the spray pressure of the cryogenic gas. Therefore, it is necessary to design a hybrid nozzle that can spray oil mist and cryogenic gas into a single flow. Besides, although the study on the effect of MQL and cryogenic machining on the cutting temperature should be preceded, most of the titanium MQL processing papers only study the material surface and tool wear. Accordingly, in this study, we designed and fabricated the hybrid type nozzle of CryoMQL which combined MQL and a cryogenic gas to improve the spraying concentration. And the cutting temperature generated by the process was measured, and the effectiveness of the proposed nozzle on decreasing the cutting temperature was evaluated. Besides, cutting force and tool wear were analyzed according to each cutting method.

Axial contact points method for improving end-milling productivity

The article analyzes results of a study on the effects of cutting data on cutting forces when end milling titanium alloys. A solid carbide mill was used. Stability of the milling process is ensured by optimal values of axial depth of cut using the axial contact points (ACP) method. The radial depth of cut and feed were varied to achieve a required level of milling productivity. Cutting forces and vibrations were measured when milling. Vibrations were measured in the frequency and time domains. Possibilities of reducing cutting forces without decreasing the productivity level by choosing optimal values ​​of cutting parameters were studied. The practical significance of the research results for planning milling processes in real production conditions was demonstrated. Ways to improve end milling productivity for titanium alloys by reducing loads on the technological system were identified. Avenues for further research on high-productivity end milling of titanium alloys were proposed.

Development of the innovative differential tool wear modeling for high-feed milling and its experimental verification

During the high-feed milling process, the vibrations generated by interrupted cutting cause changes in the instantaneous tool posture, as well as in the working angle and the distribution of the thermal stress coupling fields of each tool blade. These changes result in significant differences in the wear distribution of each tool blade. In this research, well-designed experiments for the high-feed milling of titanium alloys were carried out to identify the key factors affecting the differential wear on the milling tool insert blades. A differential tool wear model for the tool blades was developed in order to comprehensively describe the effects of the location error of the blades, the vibrations in the tool posture, and the working angle of each tool blade. The wear status of the milling tool was simulated based on the dynamic tool trajectories and postures derived by the model, and the entire simulated wear distribution was investigated with an innovative wear boundary recognition method. The differential tool wear model was evaluated and validated by the milling experiments and further supported by simulations.

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.

Thermo-mechanical coupling behaviour when milling titanium alloy with micro-textured ball-end cutters

The high-speed milling of titanium alloy is a very complex nonlinear dynamic cutting process, and there are mutual coupling effects between multiple physical fields of the tool. Therefore, the thermo-mechanical coupling behavior of micro-textured ball-end milling cutters during the cutting of titanium alloy was studied in depth, combined with theoretical calculations, milling experiments and simulation analysis. First, based on the experimental data of milling titanium alloy, the stress field of the micro-textured ball-end milling cutter was solved. Then, the dimensional method was used to solve the temperature field of the micro-textured ball-end milling cutter. Finally, the thermo-mechanical coupling simulation analysis of the micro-textured ball-end milling cutter was carried out, and the stress concentration area and tool breakage area of the micro-textured ball-end milling cutter under the thermo-mechanical coupling effect are obtained. This in turn gives a theoretical basis for further improving the performance and tool life of micro-textured cutters.

Обеспечение качества поверхности и производительности обработки при фрезеровании титановых сплавов ВТ20 и ВТ22

The investigations of output parameters of titanium alloy milling at cutting mode control are presented. The works were carried out on a milling processing center with the use of high-performance milling cutters with replaceable cutting inserts. There are shown optimum modes of high-performance milling titanium alloys VT20 and VT22 ensuring the minimum value of a roughness parameter of the surface Ra.

Tool Quality Life during Ball End Milling of Titanium Alloy Based on Tool Wear and Surface Roughness Models

The prediction and control of milling tool service performance is critical for milling tool design and machining. However, the existing prediction model can hardly quantify tool performance, or precisely describe the relationship between the tool performance and the design or milling parameters. This study redefines the tool lifetime as a function of surface roughness and proposes a new geometric analysis method based on a time-varying wear model. The proposed method can be utilized to evaluate the relationship between tool wear and lifetime. The surface roughness, with respect to tool service performance, is expressed as a time-varying model of the tool and processing parameters. After experimental validation, the influence factors were analyzed through simulation. A generalized method for milling tool design was proposed and successfully applied to a tool performance design case, on a theoretical level. Additionally, the research results prove that basing the tool milling quality life on the surface roughness is extremely feasible and necessary.

Study of the effect of sharpness of cutting tools on the formation of defects in the surface finish in micro cutting titanium alloys

The quality of machining of titanium alloys in the aviation and medical fields, characterized by the presence of micro vias, scales and surfacing on the treated surface, as well as the level of roughness is important in the manufacture of key parts. The quality parameters of the treated surface are influenced by many factors - cutting modes (cutting speed, depth and feed), cutting tool parameters (geometry of the cutting part, hardening coating, sharpness of the cutting wedge, etc.), technological equipment parameters (rigidity and accuracy), etc. The aim of the work was investigation of treated surface of titanium alloy VT1-00 when milling with small thicknesses of the shear layer, commensurate with the sharpness of the cutting wedge of the cutter. Method. The method of investigation of the treated surface during milling of titanium alloy on the micro level with the use of standard and high-quality carbide cutting tools is proposed. Results. Operating experience of the received carbide tool has shown that sharpness of a cutting wedge influences quality of the processed surface characterized by microwaves, scales and burrs, also by the roughness of the treated surface. On the basis of carried out researches it is established that for maintenance of conditions of normal cutting and chip formation it is necessary to provide sharpness of the cutting wedge characterized by the conditional entered radius of a blade rounding having values less than values of the sizes of grains of a processed material, that is re < 5 μm. Field of application. The obtained results of work allow to substantiate the recommendations on the required sharpness of carbide cutting tools used for milling of titanium alloys at the micro level. Conclusions. Experiments on the study of the process of cutting of titanium alloy VT1-00 at the micro level to determine the effect of cutting tool sharpness on the quality of the treated surface (microwaves, scales and burrs), allow to form recommendations on its initial state and determine performance.

The design and performance evaluation of assisted chip removal system in helical milling of CFRP/Ti stacks

Hybrid structures consisting of carbon fiber reinforced plastics (CFRP) and metal have been widely applied in aircraft manufacturing. Numerous holes need to be made in order to assemble the structures. Due to the small size of CFRP chips and the dry cutting conditions, improperly dealing with chips can increase tool wear, degrade hole quality, and contaminate to environment and health. In this study, an assisted chip removal system, mainly including an exhaust hood, a vacuum cleaner, and a tool holder, was used for helical milling of CFRP and titanium alloys (CFRP/Ti stacks). The geometry of the chip exhaust hood model was designed and optimized to clear and collect cutting chips using finite element method (FEM). Based on this system, pressurized air was pumped into cutting areas through the inner cooling channels in the tool. Then, the performance of the assisted chip removal system was evaluated in helical milling of CFRP/Ti stacks under different chip collecting conditions. Results showed that this system had a good ability of chip removal and preventing chips returning into the hole. And the pressurized air could promote chips remained in the hole to be removed and provide cooling effect to cutting tool. As a result, tool wear was reduced, the cutting force and cutting temperature were decreased, and hole quality was improved. Results proved the assisted chip removal system can help to further improve the hole-making process of CFRP/Ti stacks.

Optimizing milled titanium alloy concave surface quality with micro-textured ball-end milling cutters

The cutting speed at the lowest point of a ball-end milling cutter is zero, which results in poor workpiece surface quality and serious cutter wear. To alleviate this problem, a micro-texture can be processed on the rake face of a ball-end milling cutter to provide an anti-friction and anti-wear mechanism. The objective of the work reported here is to reduce cutter wear and optimise workpiece surface quality. By using a mathematical model of row spacing to analyse the differential geometric relationship between cutters and surfaces at their contact point, we have been able to obtain optimal cutter orientation. This was verified by simulating concave surface machining. Experiments were then conducted to verify the approach and the results showed that when the cutter orientation is adjusted to its optimum, the surface quality of the workpiece processed by a micro-textured ball-end milling cutter is at its best. [Submitted 10 May 2018; Accepted 28 July 2019]