Ball End Research Articles

Nonlinear dynamic modeling and vibration analysis of whole machine tool

The machine tool structure vibration during machining operation is directly linked to machining quality, production efficiency as well as machine reliability. Hence, this research focuses on the dynamic modeling of the whole machine tool considering the milling process to predict vibration response and dynamic characteristics during machining. Applying the lumped parameter and finite element hybrid method, in order to improve virtual simulation efficiency, the analytical models of the workpiece clamping worktable system and the tool clamping column spindle system are theoretically developed considering the nonlinearity of moving joints and the position-dependent dynamics. The integrated model of the whole machine tool dynamics is established by coupling the models of two subsystems with the generated nonlinear dynamic load in the ball end milling process including the effects of vibrations and tool system errors. Subsequently, the frequency response functions and the instantaneous cutting forces and vibration responses under different cutting conditions are measured and compared with simulation results to evaluate the prediction ability of the proposed model. Finally, the experimentally confirmed model is used to carry out the parameter analysis of machine tool. The investigations reveal that the worktable system dynamic characteristics vary with the joint assembly preload, but the change becomes no longer significant when the preload increases to a certain value. Besides, cutting conditions have a significant influence on the vibration characteristics of machine tool during machining.

Design of surface micro texture in the cutter-chip contact area of a cemented carbide cutter

Placing micro textures on a cutter surface can enhance the cutter-chip and cutter-workpiece contact, improving the cutter performance and machined surface quality. However, both the proper placement of micro textures and careful modeling of their density function are required for optimizing the cutting performance. In this study, a ball end milling cutter was utilized to demonstrate how these can be achieved. Initially, the theoretical cutter-chip contact length of the was calculated based on the chip curl theory and the theoretical cutter-chip contact area was obtained by combining the theories of cutter contact area and micro texture placement. Then, a mathematical model describing the micro texture distribution was established using a uniform density function, which allowed the determination of the specific distribution model for the micro textures. Finally, both simulations and experiments were used to validate the accuracy of the theoretical solution for the cutter-chip contact area and the uniformity of the micro texture density function. The results showed that the theoretical cutter-chip contact area and the uniform micro texture density mathematical model are consistent with the simulation and experimental results. The results reported in this paper provide a theoretical basis for the accurate preparation of micro textures.

Determination of force coefficient based on instantaneous forces and linear mechanistic model in ball end milling

Due to the intricate geometry, force prediction in the ball end milling process (BMP) is a challenging task. Cutting forces generated during BMP have an impact on important aspects of machining characteristics such as form error, chatter and vibration, surface finish, tool wear, and dimensional accuracy. These machining problems might be resolved by foreknowledge of the cutting forces. In the present research, a new and quick mathematical model based on the linear mechanistic method is reported to determine the force coefficients. The cutter’s hemispherical part is discretized into five discs along the axis at 0.4 mm uniform spacing in the range of 0.2–1.8 mm. For one cutter revolution, forces in the tangential, radial, and axial directions are measured for each disc to prevent radial runout. The current disc makes use of the preceding disc’s cutting force. To derive the shear and edge force coefficients, these are further divided into edge and shear forces. Validation experiments have been conducted and compared with the simulated forces to assess the predictive power of the developed force coefficient model. The predicted results are found to be remarkably close to the experimental results with an error of 5.5%, −8.6%, and 8.9% at 6631 rpm and 2.8%, −4.4%, and 2.21% at 10,052 rpm in tangential, radial, and axial forces, respectively.

Research on design and fabrication of micro ball end milling tool with flat edge and conical flank

The microball end mills are widely used in the processing of micro parts in the fields of aerospace. These micro parts are often made of hard to machine materials with high hardness and strength, such as martensitic stainless steel. As the main processing tool of these parts, the micro cutting tools wear fast and have a short service life. At the same time, because of the small diameter and complex structure of the micro ball end milling tool, its preparation process is complex, and its quality is difficult to guarantee. In order to solve the above problems, a micro ball end milling tool with a flat edge and conical flank (FC-MBMT) made of cemented carbide is proposed, which reduces the difficulty of tool preparation through the design of the flat edge, and reduces the friction between the flank and the machined surface through the design of the conical flank. Firstly, based on the theory of the spherical helix, the mathematical model of FC-MBMT was established. Then, the motion expression of each axis of the machine tool in the grinding process of FC-MBMT is obtained by deriving the transformation matrix between the machine tool coordinate system and the tool coordinate system. The precision grinding of the FC-MBMT is realized, and its geometric parameter error is less than 8%. Finally, based on the above methods, two kinds of FC-MBMT with a flank width of 16 μm and a flank width of 24 μm were prepared, and their cutting performance was verified by micro groove milling experiments of martensitic steel. Ordinary equal guide cutting edge ball end milling tool participated in the machining as a comparison item. The milling experiment results show that the surface roughness of the FC-MBMT is less than 0.52 μm and the total cutting force is less than 7 N. The machining quality of the FC-MBMT with a conical flank width of 16 μm is better than the FC-MBMT with a flank width of 24 μm, and its cutting force is smaller than the FC-MBMT with a flank width of 24 μm, which indicates that it has better cutting performance with a conical flank width of 16 μm. The wear morphology shows that the wear forms of the FC-MBMT are chip adhesion on the conical flank and slight cutting edge wear. The anti-wear ability of the FC-MBMT with a conical flank width of 16 μm is obviously better than the FC-MBMT with a flank width of 24 μm. Compared with the ordinary micro ball end milling tool, the cutting performance and wear resistance of the FC-MBMT with a flank width of 16 μm are not significantly different. The experimental results verify the feasibility of the proposed tool structure.

Development of magnetic nanoparticle based nanoabrasives for magnetorheological finishing process and all their variants

Efficacy and the outcome of the magnetorheological finishing (MRF) related processes depends on two crucial factors, (i) a finishing abrasive and (ii) a magnetic particle. However, the magnetic particles although necessary, become a hindrance for non-magnetic abrasive particles in directly reaching the surface to be finished. This study relates to the development of SPION-based smart material for MRF and all their variant processes. The SPION particles possess dual nature such as nanoabrasives and magnetic nanoparticle. The superparamagnetic property of the developed SPION particle has been confirmed by alternating gradient magnetometer with the saturation magnetization value of 82.23 emu/g. The polishing performance of the developed SPION-based particle as abrasive has been investigated on a BK-7 optical glass and the polishing is done via a 5-axes automated ball end magnetorheological finishing (BEMRF). The developed SPION abrasive enhanced the finishing process of the BEMRF technique and provided surface finishing on the BK-7 substrate up to the surface roughness (Ra) values of 22.3 nm with the Ra improvement of 88.14%.

The Effect of the Machining Strategy on the Surface Accuracy When Milling with a Ball End Cutting Tool of the Aluminum Alloy AlCu4Mg

The article discusses the effect of milling strategies on surface quality and geometric deviations during pocket milling when the perpendicular position of the tool is used. For experimental research, an aluminum alloy, AlCu4Mg, was used. For the production, a three-axis milling machine was used, and consequently, the geometric deviations and roughness parameters of the machined surface were evaluated. Also, the surface texture from each strategy was compared. For the production strategy, the constant Z, circular pocket, constant stepover pocket auto border, and spiral strategies were used. The geometric characteristic evaluation showed the influence of the ball end mill used in the machining process. Constant Z strategy achieved the lowest shape deviations. In the spiral strategy, it was possible to observe an effect of plowing, where the cutting tool crushed the material at the tool center. There was a minimal effect on the surface texture in the circular pocket and constant stepover pocket auto border strategies. Using the constant Z strategy, a non-oriented surface texture was obtained. 3D maps of the extracted residual scallop height for each strategy were observed when examining the surface texture. The roughness parameters Ra and Rz for the circular pocket and constant stepover pocket auto border strategies were the lowest.

Tool Orientation Optimization Based on Spatial Tractrix Method for Five-Axis CNC Machining with Ball End Cutters

Tool Orientation Optimization Based on Spatial Tractrix Method for Five-Axis CNC Machining with Ball End Cutters

Effect of Ball End Cutter Tilt Milling on Path Interval of Blade Surface

Different milling posture of ball-end cutter will alter path interval and affect surface scallop-height, which was an important problem to be considered to enhance the quality and efficiency of blade surface. In view of ball end cutter tilt milling of blade surface, the relation equation between path interval and scallop-height was established by constant scallop-height method, based on the determination of collision boundary and milling sensitivity, the optimal tilt angles and path interval of blade surface milling were solved, moreover, by means of cutting simulation method, the differences between tilt milling and traditional non-tilt milling were compared and analyzed from the perspective of scallop height and processing time, and verified through comparative experiments. The results show that the optimal tilt angles of blade surface milling is 36.9°, when the path interval is fixed, the surface roughness of non-tilt milling and tilt milling are 0.719 µm and 0.561 µm respectively, the surface processing quality of tilt milling is 28.2% higher than that of non-tilt milling, when scallop-height is fixed, the total time of non-tilt milling and tilt milling are 31.21 min and 25.46 min respectively, the machining efficiency of tilt milling is 17.1% higher than that of non-tilt milling. The effectiveness of tilt milling method is verified, which can provide reference basis for high-quality and efficient machining of similar blade surfaces.

Dynamic modeling and nonlinear vibration analysis of spindle system during ball end milling process

Dynamic modeling and nonlinear vibration analysis of spindle system during ball end milling process

Study on material removal and cutting analysis in ball helical milling process

In the ball helical milling (BHM), when the ball end mill follows an orbital path around the center of the hole, it plunges into the workpiece material with a helical motion, and the movement of the tool is relatively complex. In order to deeply understand the material removal and cutting characteristics in the BHM process, kinematics of BHM technology is introduced first, then material removal is analyzed according to the shape and relative position relationship between the tool and the workpiece at different typical moments, material removal behavior is discussed through the cross-sectional area, and the cross-section features of the workpiece material. In addition, the change of cutting forces is analyzed through microelement force, and then entry and exit zones are discussed in detail. BHM experiments of titanium alloy were carried out; cutting forces were measured; and burrs around the hole and surface roughness of the hole are analyzed. The results show that the ball end mill can remove materials uniformly in the helical milling with stable cutting forces and high hole-making quality.

A roughness calculation method based on milling topography simulation

The surface texture and roughness parameters of the workpiece after milling have a greater impact on the performance of the workpiece, so the analysis of the milling topography is particularly important. Firstly, the edge line of the ball end milling cutter was modeled. According to the movement law of the milling process, a complete set of milling topography simulation model was established, and a new influencing factor phase difference is proposed. In addition to the conventional cutting parameters, the model also considers the phase difference and tool inclination. Secondly, through the topography analysis and the calculation of the height of the convex peak H max, the comparison with the experiment was carried out to further verify the accuracy of the model. Finally, the point cloud data obtained from the topography simulation is processed, the roughness Sa is calculated according to the least square method. and the influence of the phase difference Δφ and the tool inclination β on the milling topography, surface texture and roughness Sa are respectively analyzed. The conclusions obtained provide guidance and reference for industrial parts designers who have specific texture requirements.

Experimental Investigation into Residual Stress in Ball End Magne-Torheological Finishing

Ball end magnetorheological finishing (BEMRF) is a novel finishing process used to finish variety of surfaces ranging from flat, curved, complex, two dimensional, three di-mensional and non linear. The residual stress and surface finish play an important role in overall efficiency and durability of the components. The present work is aimed to relieve the residual stress of work-piece surface with the improvement in surface finish using pulse DC power supply (PDCPS) in BEMRF process. The preliminary experiments have been conducted on flat EN-31 steel with and without pulse DC power supply (WPDCPS). The process parameters during experiments were considered as magnetiz-ing current (MC) of 2.5A, tool rotational speed (TRS) 500 rpm, and working gap (WG) 1.5 mm with finishing time 35 minutes and 55 mm/minute feed rate given to the work-piece. The responses such as residual stress and surface roughness have been measured before and after experimentation. Residual stress of EN-31 surface was measured with X-ray residual stress analyzer using Cosα method. It has been observed that the residual stress was found reduced from 130 to 66 MPa and surface roughness was reduced drastically wit h the use of pulse DC power supply in BEMRF process. After preliminary experi-mentation, the statistical analysis with design of experiment has been conducted with pulse DC power supply on EN-31 steel to visualize the effect of various process parame-ters on residual stress using RSM technique.

Characterization and functional evaluation of surface texture of micro eccentric shaft based on multi-index

Micro eccentric shaft has important application in many high-tech fields because of its small specific gravity, material, and energy saving. The machined surface texture has an indispensable influence on the surface integrity and the final functional capability. However, due to the micro scale and weak rigidity, it is difficult to characterize the surface texture and evaluate the functionality by traditional quantitative parameters. In order to comprehensively realize the surface texture characterization and functional analysis, a mathematical model is established to simulate the surface texture machined with different cutting tools. Then the surface microscopic profile and functional performance of the surface texture are analyzed by amplitude distribution function (ADF) and bearing area curve (BAC), and the surface texture is also evaluated by fractal dimension, which can avoid the negative effects of scale and resolution. Furthermore, power spectrum density (PSD) is utilized to analyze the relationship between the process dynamic state and geometrical specification of the surface texture. The validity of experimental results shown that the microscopic height distribution of surface machined by flat end milling cutter tends to be more random and there are more microscopic geometric features than that of the ball end milling cutter. The machined surface obtained by the flat end milling cutter has better load bearing, wear resistance, and liquid retention capability.

The Effectiveness of Diamond-like Carbon a-C:H:Si Coatings in Increasing the Cutting Capability of Radius End Mills When Machining Heat-Resistant Nickel Alloys

The main purpose of this paper was to study the efficiency of using diamond-like carbon (DLC) coatings based on a-C:H:Si with a pre-formed CrAlSiN sublayer to increase the cutting ability of ball end mills made of KFM-39 cemented carbide at a speed of 150–250 m/min in milling aircraft-grade Inconel 718, and to assess the DLC coating effect on the quality of the machined surface. DLC coating performance was quantified against uncoated carbide ball end mills and the proven TiN–AlN–TiAlN gradient multilayer coating at elevated temperatures measured by the natural thermocouple method. The temperature near the cutting edge is the factor determining the wear intensity in the tool contact surfaces in milling hard-to-machine nickel alloys to the greatest extent. Thermo-EMF (electromotive force) was recorded and converted into temperatures by calibration charts. The behavior of CrAlSiN–DLC and TiN–AlN–TiAlN coatings was compared with the results of high-temperature tribological tests on a ball-on-disc friction machine. For the CrAlSiN–DLC coating at cutting speeds of 150 and 200 m/min (<650 °C), the milling time until critical flank face wear (0.4 mm) was more than 67 and 50 min, respectively (1.4–1.5 times longer than an uncoated tool and about 1.3 times longer than the TiN–AlN–TiAlN coating). The CrAlSiN–DLC coating was characterized by a minimum adhesion amount.

Experimental and theoretical investigation into surface roughness and residual stress using ball end magnetorheological finishing

The generation of residual stresses by grinding process on the surface for a soft material results in poor performance and diminished life. In this paper, grinding-induced residual stresses is addressed and an attempt is made to relieve these residual stresses while achieving nano level surface finish using ball end magnetorheological finishing (BEMRF) process. BEMRF is a recently developed process that is effectively used to for fine figuring and polishing of a variety of magnetic and non-magnetic materials. In our present work we will demonstrate the relieving of residual stresses and reduction in surface roughness generated after surface grinding of Aluminium 7075 workpiece using BEMRF process. The impact of various BEMRF variables on reduction in surface roughness and residual stresses are discussed statistically and graphically. Residual stresses of workpiece surfaces have been measured by using portable X-ray residual stress analyzer. Significant process parameters affecting the residual stresses during polishing of workpiece are obtained using Analysis of variance (ANOVA) and F-test. It has been observed that reduction in residual stress is achieved along with nano level surface finish on aluminium workpiece surface using BEMRF technique.

Cutting characteristics of implant materials in milling

The demand of implant parts has recently been increasing with aging of the population progresses. In terms of biocompatibility and mechanical strength, stainless steels and cobalt chromium molybdenum (CoCrMo) alloy have been applied to implant parts. Laser sintering parts processed in additive processes have also been manufactured to adapt for each human body. However, the machinability of these materials is much lower than the conventional ones such as carbon steels. Residual stresses are also associated with the cutting forces for long lives of implant parts. This paper discusses the cutting processes of CoCrMo alloy, sintered stainless steel (SUS420J2), and wrought stainless (SUS304) in ball end milling with the cutter axis inclination. The cutting characteristics are compared in the cutting force, the surface finish and the residual stress. The cutting force of the sintered stainless steel includes large dynamic components due to non-uniformity of material with voids. Z component in the cutting force becomes large in milling of CoCrMo alloy. The surface finishes, then, are discussed in terms of the cutting force and the vibration. The surface finish also depends on the tool vibration associated with the dynamic response of tool and adhesion. The residual stresses measured in the feed direction of the tool and the width direction of the groove for some cutting parameters and the testing materials. In order to discuss the mechanical effect on the residual stress, the residual stresses are associated with the resultant cutting force in the feed and the width directions. The sensitivity of the residual stress to the cutting force is discussed for the testing materials. The residual stress in the width direction has large dependency on the cutting force, which may be controlled by the cutting parameters and the tool geometry. The residual stress of the feed direction depends on the material behavior controlled by the material properties.

Effect of micro tool-tips in electrochemical micromachining

Electrochemical micromachining (EMM) is an anodic dissolution process which governs by Faraday’s laws of electrolysis. The accuracy of the machining de-pends on the tool design as the streamline of current density formed in between the tool and the workpiece (electrodes) depends on it. In the present paper, two different tool-tips namely flat and ball end are considered for investigation. The complete set-up is modeled in the COMSOL Multiphysics® software coupling electrochemistry and fluid flow. The current density develops during EMM for both the tool-tips are used for analysis. The tool material is tungsten and work-piece material is stainless steel. Keeping parametric conditions constant for the two, simulation was performed. It was observed that more uniform current developed for ball end compared to flat end. It leads to a decrease in overcut of 120 µm in ball tip than the flat end. The fluid flow shows flushing of debris particles from the interelectrode gap is more effective in ball end than the flat end tooltip.

5-axis double-flank CNC machining of spiral bevel gears via custom-shaped tools\u2014Part II: physical validations and experiments

Recently, a new methodology for 5-axis flank computer numerically controlled (CNC) machining, called double-flank machining, has been introduced (see “5-axis double-flank CNC machining of spiral bevel gears via custom-shaped milling tools—Part I: Modeling and simulation”). Certain geometries, such as curved teeth of spiral bevel gear, admit this approach where the machining tool has tangential contact with the material block on two sides, yielding a more efficient variant of flank machining. To achieve high machining accuracy, the path-planning algorithm, however, does not look only for the path of the tool, but also for the shape of the tool itself. The proposed approach is validated by series of physical experiments using an abrasive custom-shaped tool specifically designed for a particular type of a spiral bevel gear. The potential of this new methodology is shown in the semifinishing stage of gear manufacturing, where it outperforms traditional ball end milling by an order of magnitude in terms of machining time, while keeping, or even improving, the machining error.

Automated insular surface finishing by ball end magnetorheological finishing process

ABSTRACT Ball end magnetorheological finishing (BEMRF) is a process employed for precision finishing of flattened, intricate form complex 3D surfaces up to the nano level. Roughness of a surface determines the quality of results produced, which is usually measured by stylus-based instruments, with some optical methodologies also being adopted. These conventional methods when used for BEMRF tend to introduce errors in the part, which have to be removed from its fixture for measurement, and it is not feasible to remount it in the exactly same orientation again. Applications such as insular finishing (i.e., confined to a narrow region on the workpiece) demand the workpiece to be kept in the same orientation throughout, leading to requirement of measuring roughness in situ during the BEMRF process. A confocal sensor fits the requirement because of its confined design and lightweight capabilities. This work presents integration of a confocal sensor into the BEMRF setup for in situ roughness measurement. An initial Ra value of 352 nm was reduced to 289 nm just by insular finishing before finishing the full surface down to 78 nm in the case of a grinding error, from 420 nm to 342 nm by insular finishing, and finally down to 142 nm in the case of lapping error.

Tool Path Generation for Five-Axis Controlled Machining of Free-Form Surfaces Using a Barrel Tool Considering Continuity of Tool Postures

This study aims to improve the efficiency of free-form surface machining using a five-axis controlled machine tool and a barrel tool. The barrel tool has cutting edges with curvatures smaller than its radius; thus, its pick feed width is larger than that of a conventional ball end mill with the same tool radius. Therefore, the machining efficiency can be improved. Barrel tools can be effectively utilized in a five-axis controlled machine tool. When five-axis controlled machining, tool interference may occur, which should be avoided during actual machine operation. Additionally, a sudden change in tool posture adversely affects the quality of the machined surface. This paper proposes a method to obtain the cutting points that render cusp heights below the target value. A method for generating an interference-free tool path, in which the tool posture changes continuously, is also proposed. The usefulness of the developed methods was confirmed through machining simulations.