Cutting Edge Geometry Research Articles

A comparison between micro milling pure copper and tungsten reinforced copper for electrodes in EDM applications

In today's continuously growing demand for components with increasingly smaller dimensions and features, micro milling is gaining more significance. However, for the mass production of components with micro features, injection molding is still customary in order to keep target costs. Due to high requirements regarding lifetime and resistance to wear, the molds are made of hardened steel. The shaping of those molds involves electrical discharge machining (EDM), because the process is independent of the material hardness. As a work tool for EDM, electrodes made of pure copper (Cu) and tungsten reinforced copper (WCu) are commonly used. The quality and reliability of the eroded shapes are determined to a high extent by the quality of the electrode deployed. For this reason, micro milling is a crucial factor in the process chain and its impacts have to be evaluated. This paper explores the key factors which have to be considered in micro milling pure copper and tungsten reinforced copper for micro features of electrodes. Due to scaling effects, micro milling differs strongly from macro milling. For mastering this process, a new approach to identify cutting edge geometry and the influence of the common milling parameters and material properties is required. Two flute micro milling tools with diameters as low as 200 μm and a cutting edge as low as 3 μm are applied for examination. To generate suitable cutting conditions with such small tools, extremely high rotational speeds of the spindle are required. Here it is chosen to be 200.000 rpm. The size of the minimum uncut chip thickness for both materials is discussed. Optimal process parameters and conditions for micro machining both materials are derived concerning process forces as well as burr and wear formation.

Effect of saw blade geometry on crack initiation and propagation on the lateral cortical hinge for HTO: Finite element analysis

IntroductionThe hinge plays a primary role in the hold and healing of a high tibial osteotomy (HTO). Weakening of the hinge is a risk factor for failure. The aim of our study was to determine whether the geometry of the saw blade's cutting edge impacts crack initiation or propagation on the hinge. HypothesisA certain cutting edge geometry exists that will reduce this risk. Materials and MethodsA finite element model with transverse isotropic elastic bone properties was created. A 1.27-mm thick saw cut (full thickness in anteroposterior direction) was made leaving a 1cm lateral cortical hinge. Three different cutting edge geometries were compared: rectangular, U-shaped, V-shaped. Opening of the osteotomy was done over 1mm for 1 s by a load applied distally with the proximal portion fixed. In the first simulation, no crack was initiated at the hinge, while in the second simulation, the beginnings of a 2mm crack angled upward at 15° was added. These two simulations were used to identify whether a local stress riser was present at the hinge. This information was used to calculate the energy release rate to the hinge, which corresponds to the energy needed to initiate and propagate a crack on the hinge. ResultsIn the first simulation (no crack initiation), a rectangular saw blade geometry resulted in the lowest local stress concentration. In the second simulation (with crack initiation), the U-shaped geometry resulted in the lowest local stress concentration. The U-shaped geometry had the lowest energy release rate, meaning that it was the least likely to initiate and propagate a crack on the lateral cortical hinge. Discussion/ConclusionKeeping the inherent limitations related to computer modelling in mind, our findings show that a U-shaped cutting edge is least likely to initiate or propagate a crack since it has the lowest energy release rate. This confirms our hypothesis. Level of evidenceV, expert opinion.

Modelling and analysis of surface topography generated in face milling operations

This paper presents a model for predicting the surface topography generated in face milling operations. In these operations, when the face mill inserts remove the workpiece material, they leave marks on the machined surfaces. The marks depend on the face mill geometry, the geometry and runout of the face mill inserts, and cutting conditions, e.g. feed and step over. In order to predict the surface topography, the geometry of the face mill cutting edges must first be modelled. The modelling of the cutting edge geometry is for round insert face mills and for square shoulder face mills. Due to the influence of insert runout on the final surface topography, axial and radial runouts of the face mill inserts are also taken into account in the modelling of the cutting edge geometry. Next, the equations expressing the trajectory of any cutting edge point are derived as a function of the feed value, the rotation angle of the face mill, its axial position, and its radial position with respect to the face mill axis. Finally, given the cutting edge geometry and the trajectory of cutting edge points, a methodology based on the discretization of the milled surface in a grid with a finite number of points is developed in this paper for the simulation of the surface topography. The methodology is based on the fact that at each grid point, the final height of the topography will be the height of the workpiece material remaining at this point after many face mill revolutions. For this reason, the procedure initially estimates the rotation angles of the face mill for which the face mill cutting edges in their front-cutting and back-cutting motion pass by the grid point being considered. In order to achieve this, a transcendental equation that is only dependent on the rotation angle is derived from the cutting edge trajectory equations. This equation is transformed into an equivalent polynomial equation by means of Chebyshev expansions. The transformed equation is solved for the rotation angle using a standard root finder that does not require a starting value. Then, by means of the estimated rotation angles and the cutting edge trajectory equations, the radial positions of the cutting edge points passing by the grid point are obtained. Finally, based on these radial positions and the cutting edge geometry, the heights of cutting edge points, which can generate the surface topography at this grid point, are estimated. The final height of the surface topography will correspond to the lowest value among the estimated height values. The methodology can be easily extended and applied to face mills with other insert geometries or to face mills with central and peripheral inserts. In addition, the simulation of the surface topography generated by lateral passes in face milling operations is simplified. The procedure allows the influence of the face mill geometry, the feed value and the step over between passes to be analysed and the roughness values to be predicted. In order to validate the model predictions, a series of face milling tests are carried out. Predicted surface topographies are compared with measured topographies and a good agreement between them is observed.

Tool wear mechanism in low-frequency vibration–assisted drilling of CFRP/Ti stacks and its individual layer

In this paper, a novel tool wear mechanism in low-frequency vibration–assisted drilling (LFVAD) of carbon fiber–reinforced plastic (CFRP)/Ti stacks and its individual layer has been proposed. Firstly, the difference of the effective rake angle, effective clearance angle, undeformed chip thickness, and tool-workpiece contact length between low-frequency vibration–assisted drilling and conventional drilling (CD) was analyzed based on the kinematic model. Then, the strength at different positions of the cutting edge was evaluated. Furthermore, the drilling experiments of CFRP/Ti stacks, CFRP plate, and Ti plate individually were taken under LFVAD and CD processes. Finally, the tool wear mechanism and the benefit of CFRP/Ti stacks and CFRP plate processed by LFVAD were expounded by kinematic analysis results, the analysis of drilling force, SEM images, and the profile of the cutting edge. The results show that the inner edge close to the chisel edge could be the weakest position of the drill in LFVAD. As the mean drilling force of LFVAD is lower than CD, the total wear volume of LFVAD is smaller than CD. Due to the change in the resultant cutting speed angle and the undeformed chip thickness, LFVAD produces the longer tool-workpiece contact length on the rake face and the flank face, which directly leads to a more uniform tool wear and a self-sharpening effect on the cutting edge. Thus, the reduction in the effective rake of the drill used in LFVAD is obviously smaller than the reduction in conventional drilling. The reduction in the effective clearance angle of the drill used in the LFVAD is also less than the reduction in conventional drilling, while this difference is attenuated as the cutting radius increases. The edge radius of the cutting edge is found to be much smaller than CD. In summary, the difference in the cutting edge geometry between LFVAD and CD is the root cause of the tool used in LFVAD to avoid severe edge chipping.

Analytical Modeling of Process Damping in Machining

The machining process induced damping caused by the indentation of the cutting edge into the wavy cut surface greatly affects the process stability in low-speed machining of thermally resistant alloys and hardened steel, which have high-frequency vibration marks packed with short wavelengths. This paper presents an analytical model to predict the process damping forces and chatter stability in low-speed machining operations. The indentation boundaries are evaluated using the cutting edge geometry and the undulated surface waveform. Contact pressure due to the interference of the rounded and straight sections of the rigid cutting edge with the elastic-plastic work material is analytically estimated at discrete positions along the wavy surface. The overall contact pressure is obtained as a function of the cutting edge geometry, vibration frequency and amplitude, and the material properties of the workpiece. The resulting specific indentation force is evaluated by integrating the overall pressure along the contact length. Then, the process damping force is linearized by an equivalent specific viscous damping, which is used in the frequency domain chatter stability analysis. The newly proposed analytical process damping model is experimentally validated by predicting the chatter stability in orthogonal turning, end milling, and five-axis milling of flexible blades. It is shown that the proposed model can replace currently used empirical models, which require extensive experimental calibration approach or computationally prohibitive finite elements based numerical simulation methods.

Innovative method for cutting edge preparation with flexible diamond tools

The micro geometry of the cutting edge is of central importance for the performance of cutting tools. It influences all essential parameters in the machining process: chip formation, thermal and mechanical load on the tool and the workpiece, tool wear and the resulting workpiece quality. The effect depends on the size and shape of the cutting edge rounding. Depending on the machining process, asymmetrical roundings often show the greatest potential. In addition to increasing tool life, the quality of the surfaces produced can be improved by a specifically designed asymmetrical rounding. For edge preparation, blasting, brushing and drag finishing are used in industrial applications. However, an economic production of asymmetrical cutting edge geometries on cutting tools with complicated cutting edge geometry, such as solid carbide tools with helical cutting edge, cannot be achieved with these methods. Therefore, a novel method for preparation of the cutting edge rounding using flexible bond diamond polishing tools is introduced. Hence, the conducted research in this study analyzes the basic mechanisms and influencing factors using the new preparation method. For this purpose, polishing tests are carried out on carbide indexable inserts. The results show that the polishing tools can be used to create both asymmetrical and symmetrical roundings in an industrially relevant dimension.

The evolution of cutting forces during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composites

Cutting forces generated during traditional machining of fiber reinforced polymer composites play an important role in determining machined surface quality. The cutting force signals also provide a live indicator of the dynamic behavior of the chip formation process. Cutting forces in machining FRPs are dependent primarily on the instantaneous fiber cutting angle, chip thickness, cutting edge geometry and the current state of cutting edge wear. In this study, effects of the cutting edge rake angle and tool wear on cutting force evolution during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composite was investigated. The cutting forces were measured in the feed and normal directions and then transformed to the tangential and radial directions of the tool path. A simplified cutting force model consisting of a shearing region and a pressing was used to determine the shearing and friction force components. This allowed determination of the friction coefficient on the clearance face of the tool. It was found that the friction coefficient varied significantly with rake angle and fiber cutting angle. The effect of rake angle on cutting forces is more discernable in the shearing region with positive rake angle tool providing the most efficient cutting. Furthermore, correlations were found between machining damage and the magnitude and orientation of the resultant shearing force.

Ultrasonic assisted peripheral milling of fiber reinforced plastics in consideration of clamping and cutting edge geometry

In the field of machining fiber reinforced plastics (FRP) with defined cutting edges, there is still a high demand for research and development, especially, when various fiber types are embedded. Thus, when machining glass fiber reinforced plastics, the application of uncoated tools from tungsten carbide is often state of the art. This material is subject to excessive wear during machining FRP, which negatively affects the process performance and makes a regular tool change necessary. This is caused by a high abrasiveness of the fibers and by vibrations of the FRP components, which affects the cutting edge. One approach to reduce the process forces and therefore reduce tool wear is to superimpose the tool movement with a longitudinal high-frequency movement in ultrasonic range. Many studies showed that this technology is able to generate advantages in drilling and face milling processes. Primarily it reduces tool wear and improves machining quality. This study shows that positive effects also occur during peripheral milling of FRP, especially when using an unstable clamping. In this case, ultrasonic assistance can reduce the machining forces significantly. Additionally, it is shown that the shape and the state of wear of the cutting edge affects the impact of ultrasonic assistance in this application case.

Scanning and modeling for non-standard edge geometry endmills

This paper describes a reverse engineering solution for modeling the behavior of non-standard edge geometry endmills. Structured light scanning is used to produce a solid model of the endmill and spatial coordinates for the points that define the cutting edges are extracted. These points are used to determine the cutting edge radius and angle at equally spaced points along the tool’s axis. This cutting edge geometry is then incorporated in a time domain simulation that predicts cutting force and tool/workpiece deflection for user-selected operating parameters. Good agreement between predicted and measured cutting forces is first demonstrated. Second, the results of stability tests are compared to simulation predictions for multiple spindle speed-axial depth of cut combinations. The time records are analyzed by periodically sampling the measured and predicted displacement and velocity.

Dynamic effects on cutting forces with highly positive versus highly negative cutting edge geometries

Understanding the influence of the cutting edge geometry on the development of cutting forces during the milling process is of high importance in order to predict the mechanical loads on the cutting edge as well as the dynamic behavior on the milling tool. The work conducted in this study involves the force development over the entire engagement of a flute in milling, from peak force during the entry phase until the exit phase. The results show a significant difference in the behavior of the cutting process for a highly positive versus a highly negative cutting edge geometry. The negative edge geometry gives rise to larger force magnitudes and very similar developments of the tangential and radial cutting force. The positive cutting edge geometry produces considerably different developments of the tangential and radial cutting force. In case of positive cutting edge geometry, the radial cutting force increases while the uncut chip thickness decreases directly after the entry phase; reaching the peak value after a certain delay. The radial force fluctuation is significantly higher for the positive cutting edge geometry. The understanding of such behavior is important for modelling of the milling process, the design of the cutting edge and the interactive design of digital applications for the selection of the cutting parameters.

Ball End Mill with Curved Cutting Edge and Constant Cutting Geometry

A design method is proposed for a ball end mill with constant inclination of the cutting edge to the spherical section. The tooth profile specified in the normal cross section is the generatrix, while the curved cutting edge at the sphere in the form of a loxodrome is the directrix.

Numerical Investigation on Effect of Rounded Cutting-Edge Radius and Machining Parameters in End Milling of AISI H13 Tool Steel

Rounded cutting-edge radius is commonly applied to finish and semi-finish cutting, precision machining and micro-machining. The optimum effect is closely related to the work and tool material as well as machining parameters. However, for numerous cutting process, the optimal radius of rounded cutting-edge radius and machining parameters applied in the AISI H13 of end-milling is yet unknown Therefore, in improving tool life and cutting tool performance, a suitable design of cutting edge geometry regarding cutting edge-radius and machining parameters need to be examined and properly selected. In this regard, the paper deals to examine the effect of cutting edge-radius in rounded form and machining parameters of cutting force, cutting temperature and chip formation through the end-milling process of AISI H13 using uncoated cemented carbide cutting tool through finite element simulation of Thirdwave AdvantEdge 7.2 software. The machining parameters applied in the simulation setup were 200 and 240m/min of cutting speed, 0.03 and 0.06mm/tooth of feed-rate and axial depth of cut of 0.1 and 0.2mm while width of cut in radial direction was kept constant at 6.0mm. The cutting geometries includes the cutting-edge radius of 0.03 and 0.05mm and 10° of rake angle. The obtained results revealed that cutting forces and cutting temperature is increase as depth of cut in axial direction and cutting-edge radius increases while increasing value of speed and feed-rate of cutting resulted in decreasing cutting forces but increasing cutting temperature. The maximum cutting temperature is 674.91℃. The value obtained is lesser than the AISI H13 austenitizing temperature, therefore a layer known as white layer is supposedly hard to be created based on the cutting geometry and machining parameters applied.

Experimental analysis of cutting edge effects on vibrations in end milling

The ability to minimize vibrations in milling by the selection of cutting edge geometry and appropriate cutting conditions is an important asset in the optimization of the cutting process. This paper presents a measurement method and a signal processing technique to characterize and quantify the magnitude of the vibrations in an end milling application. Developed methods are then used to investigate the effects of various cutting edge geometries on vibrations in end milling. The experiments are carried out with five cutting edge geometries that are frequently used in machining industry for a wide range of milling applications. The results show that a modest protection chamfer combined with a relatively high rake angle has, for the most of cutting conditions, a reducing effect on vibration magnitudes. Furthermore, dynamics of a highly positive versus a highly negative cutting geometry is explored in time domain and its dependency on cutting conditions is presented. The results give concrete indications about the most optimal cutting edge geometry and cutting conditions in terms of dynamic behavior of the tool.

Design and models of helical needle geometries for core biopsies

Biopsy needles are standard medical devices for extracting biological tissue with the purpose of diagnosing a specific anomaly such as cancerous masses, or lumps. The outcome of these procedures greatly relies on the quality of the samples which, in turn, depends on the forces acting on the needle during its insertion. In this scenario, the design of the needle tip plays a fundamental role in determining the cutting forces. Yet, since the dawn of modern medicine, only a few studies have proposed novel needle tip configurations. In this study, the geometry of biopsy needles is investigated, and helical cutting edges characterized by a three-dimensional (3D) profile are conceived. Mathematical models were formulated to compute the cutting angles and the tissue fracture forces. The proposed methodology is general and can be applied to any 3D needle cutting edge geometry. The utility of the helical geometry was demonstrated on a 14-gauge hollow needle which is generally used during breast biopsies. Experimental insertions were performed at different cutting speeds on phantom tissue. The results show that helical needles generate lower cutting forces than commercial needles and recommendations are formulated for the selection of their cutting parameters. The outcome of this investigation is applicable to biopsy examinations in which a hollow needle is adopted to acquire soft tissue samples.

Analytical Model of Progression of Flank Wear Land Width in Drilling

In multipoint operations like drilling, cutting velocities and cutting-edge geometries vary along cutting lips so is the rate of progression of flank wear. Analytical evaluation of flank wear land width in the case of complex tools has received a limited attention so far. This work evaluates progression of flank wear in orthogonal machining and adopts it to drilling. An abrasive flank wear has been modeled, wherein, cutting speed determines the rate of abrasion, and the feed rate determines the chip load. The model considers stress distribution along rake surfaces, and temperature-dependent properties of tool and work materials. Assuming that the flank wear follows a typical wear progression as in a pin-on-disk test, the model evaluates cutting forces and the consequent abrasive wear rate for an orthogonal cutting. To adopt it to drilling, variation in cutting velocity and dynamic variation in rake, shear, and friction angles along the length of the cutting lips have been considered. Knowing the wear rate, the length of the worn-out flank (vb) has been evaluated. The model captures progression of flank wear in zones (i), (ii), and (iii) of a typical tool-life plot. It marginally underestimates the wear in the rapid wear region and marginally overestimates it in the steady-state region.

Influences of Cutting Edge Microgeometry on Durability when Milling ISO S Material

This article investigated the influences of the cutting edge microgeometry on durability. Combination of cutting edge geometry, cutting conditions and the properties of the machining material all influences the cutting process. It is necessary to modify the cutting edge to increase of cutting tool life and cutting process efficiency when machining materials, which are difficult to machine, such as Inconel 718 nickel alloy. Increasing the cutting tool durability and resistance are the main goals with difficult to machine materials. The cutting edge radius is the main parameter, which is modified during the experiment described in this article. After modification of the cutting edge radius, the cutting tools are tested when milling Inconel 718. Twelve cutting tools are tested. The radii of the cutting edge of these cutting tools are 15 μm, 20 μm and 25 μm. Drag finishing and abrasive water jet are used to modify the cutting edge. The cutting tool durability was evaluated by wear measurement on the clearance surface on the cutting tool. The critical cutting tool wear was 150 μm. Linear type of wear (VBB) was measured on a Multicheck optical microscope.

Mechanistic modelling for predicting cutting forces in machining considering effect of tool nose radius on chip formation and tool wear land

Tool wear during machining has been seen to result in changes in tool geometry, which adversely affect the performance characteristic of the process. Various force models have been proposed to compensate for the tool wear and thus enhance the process performance. The study undertaken proposes a mechanistic model to predict the cutting forces based on three-dimensional cutting operations. The model has been developed for predicting forces due to chip formation and due to worn-out cutting tool including cutting tool nose radius. The force that has been predicted due to chip formation is a function of chip flow angle and equivalent cutting edge geometry. The prediction of force due to worn-out cutting tool is based on the actual chip-tool contact area and the rubbing force. The total force estimated has been further optimised to get accuracy in the model. Optimisation process is achieved by using a technique of order preference by similarity to the ideal solution. Results of the proposed force model have been experimentally validated as well as found to be in good agreement with the results of the force models proposed by Huang and Liang [39] and Chinchanikar and Choudhury [21]. Further, a regression equation has been developed in order to check the adequacy of the proposed model. The modelling approach proposed may be readily extended to other machining operations such as drilling and milling.

Development and experimental validation of a mechanistic model of cutting forces in micro- ball end milling of full slots

ABSTRACTIn the present work, a mechanistic model of cutting forces is developed with a novel approach to arrive at the cutting edge geometry as well as the cutting mechanics. The geometry of cutting elements derived and verified using a virtual tool generated in CAD environment is considered. The cutting and edge force coefficients at every discrete point on the cutting edge of micro-ball end mill are established in a novel way from the basic metal cutting principles and fundamental properties of materials, considering edge radius and material strengthening effects. Further, measured edge radius is used in the model. Full slot micro-ball end milling experiments are conducted on a high-precision high-speed machining center using a 0.4 mm diameter tungsten carbide tool and cutting forces are measured using a high-sensitive piezo-electric dynamometer. It is established that the predicted as well as experimental cutting forces are higher at very low uncut chip thickness in comparison with the cutting edge radius in micro-ball end milling also. Amplitudes of cutting forces and instantaneous values with incremental rotation of the tool are compared with predicted values over two revolutions for validation of proposed model.

Comparison of the discrete element and finite element methods to model the interaction of soil and tool cutting edge

Soil tillage is an energy intensive operation and design improvements that reduce forces have been pursued for many different tools. Due to the high cost of prototyping and testing, computer modelling has been adopted to design tillage equipment. In order to model soil-tool interaction two methods namely; finite element method (FEM) and discrete element method (DEM) have been used. Fielke (1994 and 1996) found that for shallow working low rake angle tools the cutting edge geometry of a tillage tool has a major effect on tillage forces and soil movement. FEM modelling of the tests was also carried out in Fielke (1999) . In this paper the experimental work of Fielke (1994) was simulated using DEM techniques and the results were compared to both the measured data and FEM predicted results. The results of the study showed that better vertical force prediction was obtained using DEM whereas forward soil movements below the tillage depth were simulated more accurately using FEM. This can be attributed to the larger size of particles used in DEM simulation than needed to pass around the cutting edge. It was also shown that DEM can be used to accurately predict soil failure planes.

Bias voltage effect on the mechanical properties, adhesion and milling performance of PVD films on cemented carbide inserts

The potential of coated cutting inserts to withstand effectively cutting loads depends among others on the coating's mechanical properties and adhesion. These data are strongly affected by the applied PVD process parameters, even if the coatings comprise the same chemical composition. Hereupon, one significant parameter is the bias voltage during the film deposition. For detecting its effect on the occurring film mechanical properties, adhesion and wear behavior, PVD TiAlN coatings were deposited on cemented carbide inserts at diverse bias voltages. The properties of the manufactured coatings were determined via FEM-supported results evaluation of nanoindentations, perpendicular and inclined impact tests. Coatings produced at elevated bias voltage possess comparably increased mechanical properties and fatigue endurance. However, their adhesion deteriorates, thus reducing the coated inserts cutting performance especially when a good adhesion during a material removal process as in milling hardened steel is required. Relevant FEM calculations of this process were employed to explain the wear evolution on the flank and rake of the used coated tools considering their cutting edge geometry and their actual film's mechanical properties and adhesion dependent upon the applied bias voltage during the coating deposition.