Tool Axis Research Articles

Characteristics of Dissimilar AA5083 and AA7050 Aluminium Alloys Friction Stir Butt Welded with Different Tool Axis Offsets

Characteristics of Dissimilar AA5083 and AA7050 Aluminium Alloys Friction Stir Butt Welded with Different Tool Axis Offsets

Research on the Magnetorheological Finishing Technology of a High-Steepness Optical Element Based on the Virtual-Axis and Spiral Scanning Path.

Magnetorheological finishing (MRF) of aspherical optical elements usually requires the coordination between the translational axes and the oscillating axes of the machine tool to realize the processing. For aspheric optical elements whose steepness exceeds the machining stroke of the equipment, there is still no better method to achieve high-precision and high-efficiency error convergence. To solve this problem, an MRF method combining virtual-axis technology and a spiral scanning path is proposed in this paper. Firstly, the distribution law of the magnetic induction intensity inside the polishing wheel is analyzed by simulation, the stability of the removal efficiency of the removal function within the ±7∘ angle of the normal angle of the polishing wheel is determined, and MRF is expanded from traditional single-point processing to circular arc segment processing. Secondly, the spiral scanning path is proposed for aspherical rotational symmetric optical elements, which can reduce the requirements of the number of machine tool axes and the dynamic performance of machine tools. Finally, an aspherical fused silica optical element with a curvature radius of 400 mm, K value of -1, and aperture of 100 mm is processed. The PV value of this optical element converges from 189.2 nm to 24.85 nm, and the RMS value converges from 24.85 nm to 5.74 nm. The experimental results show that the proposed combined process has the ability to modify curved optical elements and can be applied to ultra-precision machining of high-steepness optical elements.

Wheel path planning for flute grinding of non-cylindrical solid end-mills based on circular arc projection

Flute grinding is a crucial process in solid end-mill manufacturing, because the generated flute parameters, i.e. helix angle, rake angle, core radius, and flute width, have significant effects on the cutting performance of end-mills. However, the flute grinding of non-cylindrical solid end-mills is still challenging due to the variation of the flute parameters along the tool axis. This paper proposes an accurate and efficient method of wheel path planning for flute grinding of non-cylindrical solid end-mills based on circular arc projection. The wheel path determined by the new method can accurately generate the designed helix angle, rake angle, core radius, and flute width, even if all of these parameters vary along the tool axis. The helix angle and rake angle are ensured by the conjugate condition between the wheel surface and the cutting-edge curve. Based on circular arc projection, equivalent errors of the core radius and flute width are introduced to quantify the machining errors of the two parameters, without the need to predict the flute profile. Simulations and experiments are conducted to validate the proposed method. Three types of non-cylindrical end-mills i.e. tapered end-mill, tapered barrel end-mill, and barrel end-mill, are considered in the validation. The measured results indicate that the generated flute parameters coincide well with the designed ones at different axial positions of the end-mills.

Influence of material position and tool axis offset on the stir zone material flow and joint integrity of friction stir welded dissimilar AA5083 and AA7050 alloys

The present investigation aims to establish the influence of tool axis offset and the relative position of materials on the stir zone (SZ) material flow and joint characteristics of friction stir (FS) butt welded dissimilar AA5083-H111 and AA7050-T7651 aluminium alloys. The FS welding trials were conducted by systematically varying the tool axis offset from zero to 1 mm, with an increment of 0.25 mm, to both the advancing side (AS) and retreating side (RS) of the joint by keeping AA7050 and AA5083 alloys at the AS and RS of the joint, respectively. The welding speed, tool rotational speed, axial force and tool tilt angle were held constant. The results showed that for the given relative position of the alloys, the tool axis offset has significant influence on the SZ material flow pattern and the evolution of microstructure in the joint zone. The microhardness has a heterogeneous distribution across the joint and it is found to be sensitive to the tool axis offset. The highest hardness values are observed for the joints FS welded at 1 mm tool axis offset to the AS and the lowest for the joints welded at 1 mm tool axis offset to the RS of the joint. The joint fabricated at 0.5 mm tool axis offset to the AS has exhibited the highest joint strength of 303 MPa (joint efficiency of 98.4 %). Also, within the limits of tool axis offset experimented, the joint integrity is less sensitive to the variation of tool axis offset to both the AS and RS of the joint. The softening of the HAZ on the weaker AA5083 alloy side (for high heat generation cases) and the weakening of the SZ towards the bottom (for low heat generation cases) are the main factors limiting the joint strength. The studies showed that in FSW of dissimilar 5xxx and 7xxx alloys, appropriate selection of tool axis offset and relative position of the alloys are critical for producing joints with excellent joint efficiency.

OPC UA-based Force Control for Deep Rolling with Mechanical Tools

Deep rolling can increase the service life of components under cyclic loads. This is achieved by plastic deformation of the component surface using a roller. The degree of plastic deformation depends on the rolling force. For a maximum increase in service life, the rolling force applied to the roller must stay within defined limits. When performing deep rolling using mechanical deep rolling tools, the rolling force is applied via an elastic element such as a leaf spring. The deep rolling force therefore depends on the deflection of leaf spring. It varies when the workpiece bends or has a varying diameter. These variations in the deep rolling force are not desired. They must be reduced to achieve optimum process results. To achieve this, a novel deep rolling force control for mechanical deep rolling was introduced in this paper. To control the rolling force, the force was measured with a sensory tool and machine tool axes were adjusted accordingly. The adjustment of the axes was implemented using the OPC UA standard. It is shown that this can reduce the force error during mechanical deep rolling by 90%. This ensures a constant process result and improves the mechanical deep rolling process.

Optimization of machining path for integral impeller side milling based on SA-PSO fusion algorithm in CNC machine tools

The five axis linkage Computer Numerical Control machine tool for integral impeller can achieve blade machining through side milling, which is of great significance for improving the machining accuracy, production efficiency, and long-term stability of integral impeller blades. This study is based on non-uniform rational B-spline curves and aims to reduce the surface over cutting or under cutting of integral turbine blades. The path planning of non deployable ruled surfaces was analyzed in depth through side milling, and the path planning model of the side milling cutter axis was solved through a fusion algorithm of simulated annealing algorithm and particle swarm optimization algorithm, in order to find the optimal path through iterative process. As the number of iterations increased, the error values of particle swarm optimization algorithm and simulated annealing particle swarm optimization fusion algorithm gradually decreased, with convergence times of about 7 and 6, respectively. The stable error value of the fusion algorithm was 0.253, which is 30.45% lower than that of the particle swarm optimization algorithm. The optimal number of iterations for solving the model using particle swarm optimization algorithm and fusion algorithm was the 7th, with range values of 0.0213 and 0.0165 mm, respectively. The tool axis trajectory surface optimized by the fusion algorithm was closer to the tool axis motion state compared to the initial tool axis trajectory surface. The range of the sum of mean squared deviations for single and global cutting was 0.0011–0.0198 and 0.046–0.0341, but the overall error value was relatively small. This study effectively reduces the envelope error of machining tools and improves machining accuracy, thereby solving the principle error of non expandable ruled surfaces in the motion trajectory of the blade axis of the integral turbine. This provides new research ideas for the intelligent development of Computer Numerical Control machining technology.

Non-interference slow tool servo turning method for complex surfaces with large undulation changes

Complex curved surface parts are integral to the mechanical industry, demanding precise machining techniques. Multi-axis slow tool servo turning has emerged as an efficient method due to its high precision and quality. However, the challenge of severe tool flank interference arises, especially on surfaces with large undulation changes. Conventional methods, such as increasing tool clearance angles or adding extra tool axes, detrimentally affect machining precision and stability. To address this, a non-interference toolpath planning method is proposed for complex surfaces with large undulation changes. The approach begins with establishing geometric models of the single-point diamond turning tool and typical complex surfaces, followed by analyzing the mechanism and evolution of tool flank interference. By considering geometric parameters and vector relationships, the practical tool clearance angles are calculated. And then a criterion for subregion division is introduced and the non-cutting stroke is designed, accounting for the maximal acceleration of machine tool axis. Multi-pass toolpaths are generated to navigate different subregions while avoiding interference by transforming spindle rotation direction. Furthermore, a method is proposed to optimize toolpath stitching in practical machining regions, ensuring continuous and smooth transitions while maintaining machining precision and surface quality. Experimental validation, conducted on a hyperbolic paraboloid surface with large undulation changes, demonstrates a significant reduction in surface roughness (Sa) from 380.503 nm to 75.664 nm—a reduction of 80.115 %. The proposed method not only enhances machining precision and surface quality but also extends tool life and improves working conditions. This research offers vital guidance for non-interference toolpath planning in engineering practice.

Geometric Error-Based Multi-Source Error Identification and Compensation Strategy for Five-Axis Side Milling

Based on a multi-source error model, this paper discusses the principle of error element identification and uses the mirror bias method to compensate the geometric errors of a process system. Firstly, a nine-line measurement method to determine the geometric error of the linear feed axes of machine tools is introduced, and the geometric error identification model based on the “nine-line method” is established. Then, using a ballbar mounted in the axial, tangential, and radial directions of the machine, the geometric error elements of the rotation axis are identified by three simple measurements in each direction. Subsequently, for the more common flat vise clamping workpiece in actual production, the workpiece position error is identified by using the traditional process of dimensional chain, and the workpiece attitude error is identified by fitting the angle between the positioning plane and the horizontal plane by the least squares method. Finally, based on the tool position points and tool axis vectors obtained from the multi-source error model, the error compensation value is solved using inverse machine tool kinematics to offset the machining error by mirroring the error value of the same size, and based on the “S-shaped specimen” to compensate the processing experiments, after compensation, the processing error is reduced by 30~45%, verifying the effectiveness of the compensation method.

Influence of Tool Inclination and Effective Cutting Speed on Roughness Parameters of Machined Shaped Surfaces

Free-form surfaces in the automotive or aviation industry where the future shape of the product will contain complex surfaces raises the question of how to achieve the necessary shape of the required quality in the milling process. One of the methods of their production is the use of 5-axis milling, in which it is necessary to consider not only the input data of the process itself, but also the methodology for evaluating the desired results. Correctly answered questions can thus facilitate the choice of the inclination of the tool when machining parts of the surfaces defined in the experiment. The primary goal of the paper was to monitor the influence of tool inclination on the quality of the machined surface and effective cutting speed by evaluating surface roughness and surface topography. The experiment was designed to show the effect of different tool positions while the feed per tooth fz for the finishing operation remained constant. The best result in terms of surface quality was achieved with a tool inclination of 15° in the cutting process. The most unfavorable result was obtained with a tool axis inclination of zero degrees due to unfavorable cutting conditions.

An integrated method for compensating and correcting nonlinear error in five-axis machining utilizing cutter contacting point data

In current five-axis computer numerical control (CNC) machining, the use of minute linear path segments as an approximation for the ideal cutter contacting (CC) point trajectory is still prevalent. However, introducing rotation axes leads to a deviation of the actual CC point trajectory from the ideal, resulting in nonlinear errors. An integrated method is proposed in this paper for compensating and correcting both the contour error, associated with the approximation of the part surface by the ideal CC point trajectory and the nonlinear error of the CC point trajectory based on the information in the CC point data. By analyzing the spatial relationship between the tool posture and the CC point path during the five-axis linear interpolation process, two adjacent machining tool positions containing CC point data information are selected as the starting and ending points of the five-axis linear interpolation machining. The ideal tool center point and the actual CC point are calculated during the interpolation process, as well as the distance and the unit vector in the perpendicular direction between the actual CC point and the ideal CC point trajectory segment. In the comprehensive error compensation and correction phase, the obtained unit vectors are used as direction vectors for error compensation, and the tool center point during interpolation is first compensated and corrected. This ensures the actual CC point and the contour curve are on the same plane. The compensation direction for contour error is calculated using the start/end tool axis vectors and the ideal CC point trajectory vectors. The size of the contour error approximating the contour curve is calculated through the chord error. A second compensation and correction are applied to the tool center point for interpolation, ultimately achieving comprehensive compensation and correction of nonlinear errors. The data calculations were conducted in the MATLAB environment using actual machining data. After compensation and correction, the contour error was reduced by 76%, the nonlinear error of the CC point trajectory decreased to below 0.88 μm, and the comprehensive nonlinear error of the CC point trajectory was reduced from 19 to 1.5 μm, a reduction of 93%. This demonstrates significant practical value in enhancing the accuracy of five-axis CNC machining. Through actual machining verification, after using the method described in this paper, the average surface roughness decreased from 1.133 to 0.220 μm, and the maximum surface roughness decreased from 6.667 to 1.240 μm. This significantly demonstrates that the compensation and correction method proposed in this paper can significantly improve the surface quality of machined parts.

The residual stress state in meso- and micro-milling processes with a ball-end mill in Ti–6Al–4V titanium alloy

An experimental investigation and comparative analysis of the residual stress state between micro- and meso-milling processes with a ball-end mill on the Ti–6Al–4V titanium alloy were carried out. A methodology to study the characteristic kinematics of a five‑axis machining process in a three-axis vertical machining centre was proposed. The study considers the chip formation process according to the lead and tilt angles of the tool axis concerning the normal vector of the surface. When using the up‑milling cutting strategy, the defect of smeared/adhered material to the surface occurs in both the micro- and meso-milling levels, associated with the build-up edge and build-up layer phenomenon. The residual stress tensor of the surface was obtained through the X-ray diffraction technique. The down-milling cutting strategy produced the best surface finish and higher compressive residual stresses. The experiments showed higher compressive residual stresses in the feed direction than in the cross-feed direction. The micro-milling process produced higher compressive residual stresses than those observed in the meso-milling process.

Analysis of heat generation during friction stir welding of aluminum alloy 2024-T4 and its impact on joint characteristics

Friction stir welding (FSW) is a successful welding technique for joining of aluminium and many other materials with the required joint configurations. During this welding process, large amount of heat is generated, which influences the integrity, performance, and microstructure of the weld joints. In this study, both experimental and numerical approaches are adopted to analyse the influence of heat generation on the metallurgical and mechanical properties of friction stir-welded joints of AA2024-T4. A computational fluid dynamics (CFD) model is constructed for quantitative analysis of heat flux, heat generation, temperature distribution, strain rate and viscosity. The model is validated by experimentally measured temperature data, and both agree well. The results showed that both heat flux and strain rate are more or less symmetric about the tool axis whereas plastic material flow is asymmetric. Heat flux affects the grain size and mechanical properties of the joint.

A continuous oscillating milling strategy based on uniform wear theory for improving the service life of the ball-end cutter

The rapid deterioration of ball-end cutters leads to a shortened lifespan when milling difficult-to-cut materials. This research introduced a continuous oscillating milling approach aimed at enhancing the consistency of cutting-edge wear by dynamically adjusting the tool axis oscillation angle, thus prolonging the tool life. Initially, key processing parameters were determined according to the actual processing conditions. Subsequently, a tool wear model, rooted in continuous oscillating milling, was developed. Using it, an optimization framework for the tool oscillating angle, based on uniform wear theory, was established. Then, the CNC code was compiled according to optimization results. Finally, the proposed milling strategy was demonstrated by cutting tests on Ni-based superalloy GH4169. The results demonstrated that this approach notably extended the tool life.

Determination and Analysis of Working Diameters and Working Angle of the Torus Cutter Blade in Multi-axis Machining in the Aspect of Tool Wear

The aim of this study is to provide a theoretical and experimental analysis of the multi-axis milling process by the torus milling cutter of nickel-based superalloy parts in terms of surface quality and tool wear. In the analytical part, using, among other things, matrix calculus and trigonometric relationships, mathematical models were developed to describe the relationships between the tool axis orientation and the geometric parameters of the cutting layer at the contact point. On this basis, mathematical relationships for contact diameter and effective diameter were derived. The basis for these considerations is the very rarely considered working angle of the cutter blade. In part of the experimental study, machining tests were carried out for selected kinematic variants of multi-axis cutting. Based on the results obtained, it was found that as the tool axis inclination angle increases, the contact diameter increases. The effective diameter at the upper characteristic point of the cutting layer increases up to a certain angle of inclination, after which it begins to decrease. The rotational angle of the tool axis does not affect any of the diameters, but it does affect the displacement of the contact point, the values of the working angle of the tool blade and the feed-related component decrease. The result of this displacement is a change from climb milling to conventional milling, which has significantly degraded surface quality and tool life. The best results of the machining test were obtained when only the angle of inclination of the tool axis was used. It was concluded that the parameter tool blade working angle can be a control variable in a multi-axis milling process and has a major impact on the physical aspects of the cutting process.

Evaluating the Influence of the Disc Tool Axis Position Errors on the Machined Helical Gear Surface

This work has presented advanced methods for determining disc tool profiles for machining helical gears and how to evaluate gear errors, as well as the influence of tool axis position errors on the machined gear surface by 3D comparing the tool surfaces corresponding to the tool axis positions. Experimental results for ISO standard helical gears confirm that the precision of the disc tool determined by the proposed method is very high (0.01 mm), with a helix angle greater than 20 degrees, undercutting is likely to occur, the influence of the angle between the tool axis and the machined gear axis on the gear surface deviation is on the order of 0.05 mm per 0.5 angular deviations.

Influence of the width of cut in ultrasonic vibration superimposed face milling of X46Cr13 and X40CrMoV5-1 on the surface microstructure and CVD diamond coating adhesion

Ultrasonic vibration superimposed milling (UVSM) with an oscillating movement of the specimen in the direction of the tool axis is an efficient method for the generation of microstructured functional surfaces. The application of end milling cutters with a diameter smaller than the length and the width of the surface to be structured generally results in recuts and path overlaps. In order to avoid surface recutting, a small lead angle was realized by slightly tilting the ultrasonic system with the specimen. The overlapping area of two adjacent paths was kinematically simulated for different widths of cut (from 70% to 90% of the tool diameter). Cutting experiments were carried out by UVSM of X46Cr13 and X40CrMoV5-1 steel specimens to investigate the influence of the width of cut on the surface generated in the overlapping area and also the adherence of a subsequently deposited CVD diamond layer. For this purpose, 3-D laser scanning microscopy and SEM analysis were applied. The knowledge gained allows for designing UVSM processes, especially regarding 3-D freeform surfaces with defined microstructures subjected to CVD diamond coating.

Features of using the over-skiving method for multi-pass cutting of external gears

Problem. There is a problem of determining the working parameters, including axial feed and cutting speed, as well as the helix angle of the teeth of the disc cutter and the tool spindle, the geometry of the cutting part, and the cutting depth per pass in Power skiving technology.Objective. It is necessary to investigate the cutting process using the Power Skiving method for generating external gears over multiple passes and develop recommendations for selecting its optimal parameters.Implementation methodology. The cutting force and its tangential component acting on the cutter are presented based on the fundamental principles of cutting theory, using the function of the cross-sectional area of the cut, the material strength limits of the workpiece for shear, and the intensity of plastic deformation of the chip. Calculations of the cut area are based on a graphoanalytical 3D model of the undeformed chip. The coefficient of shear intensity is determined depending on the thickness of the cut layers using the Deform 2D system. The study of the force factors is conducted in the initial stage for single-tooth cutting, considering the operation of a single tooth of the tool, and for multi-tooth cutting conditions, corresponding to real cutting and forming conditions in this method.Results. Analysis of harmonic vibrations with different frequencies of the investigated forces indicates that, under average loading, the maximum principal component of the cutting force occurs on the third pass, and the tangential force on the tool axis occurs on the first pass. The variation in the frequency of these signals is explained by changes in the contact angle between the tool and the gear wheel in the machine engagement and the different number of teeth involved in cutting.Conclusions. The obtained data allowed the development of a methodology for selecting rational parameters - axial feed values, the number of passes with different cutting depths to minimize time consumption, and achieve the desired accuracy of gears. It has been demonstrated that to reduce processing errors, it is most rational to decrease cutting force by increasing the number of passes, rather than reducing the axial feed.

Toolpath smoothing with reduced curvature and synchronized motion for hybrid robots

G01 commands are the most commonly used toolpath format in Computer Numerical Control (CNC) machining. Due to the discontinuity between adjacent linear segments, toolpath smoothing is necessary to improve machining efficiency and machined surface quality. This paper proposes an analytical C3 continuous local toolpath smoothing and synchronization method for a five-axis hybrid robot. Position and orientation smoothing are decoupled, with quintic B-spline segments replacing the original linear segments. The curvatures of the toolpath are reduced under constrained smoothing errors by weaving transition splines along the linear segments instead of confining them within the corners. A synchronization method based on arc length parameterization tailored to the smoothing method is also proposed. Tool tip position and tool axis orientation are synchronized using another monotonic, C3 continuous spline, which achieves smoother joint motion along the toolpath. For the hybrid robot with highly nonlinear kinematics, improved results in feedrate scheduling considering joint constraints can be realized. Simulations and experiments validate the effectiveness of the proposed method.

In-situ measurement and control of the tool-workpiece interface temperature during friction stir processing of 304/304L stainless steel

Friction stir processing of 304/304L stainless steel is an area of interest for repair of spent nuclear fuel canisters. To enable repair without canister deflection or fracture, it is necessary to define the limitations for the depth of the processing zone which will be critically dependent on the thermal history of the material. This work provides the first direct measurement of the interface temperature for friction stir processing of steel. The measured temperature is in the range of 850–1050 °C which is 20–30 % higher than previously reported values. Notably, the peak temperature occurs at the pin tip which is attributed to a higher sticking fraction and subsequently higher strain rate near the tool axis of rotation. Furthermore, a clear correlation between the temperature, grain size, and hardness is established within a single weld nugget and across different processing conditions. In the future, this data may lead to improved process modelling through direct validation and allow for property optimization through direct microstructure control.

Friction stir welding of dissimilar AA7050 and AA5083 aluminium alloys: Microstructural and mechanical characterization

In this study, dissimilar aluminium alloys, AA7050-T7651 and AA5083-H111, with 5 mm thickness were friction stir butt welded and the microstructural and mechanical properties of the joints are investigated. The experiments were carried out at tool rotational speeds of 800, 1000 and 1200 rpm while keeping the tool traverse speed, axial force and tool tilt angle, respectively, at constant values of 30 mm/min, 3.5 kN and 1.5°. A tool axis offset of 0.25 mm towards the 7xxx alloy side that fixed by a detailed preliminary study was used in all the trials. All the fabricated joints were externally defect-free and the fractured tensile specimens showed that the joints have fractured in the thermo-mechanically affected zone (TMAZ) at the AA5083-H111 alloy side. The highest ultimate tensile strength of 294 MPa (96% joint efficiency) was observed for the joint fabricated at tool rotation speed of 1000 rpm. The location of fracture together with the microstructure observation at the joint zone showed that the coarsening of grains and loss of cold work are the causes of fracture of the tensile specimen at the TMAZ of the 5083-alloy side. In addition, significant grain coarsening and dissolution of precipitates are observed at the heat-affected zone and TMAZ at the 7050-alloy side at tool rotational speeds of 1000 rpm and 1200 rpm. The study testified that the tool rotational speed has a significant influence on the microstructure and tensile properties of the dissimilar joints.