Influence of cutting edge radius on cutting forces in machining titanium

The performance of machining titanium can be enhanced by using cutting tools with rounded cutting edges. In order to better understand the influence of rounded cutting edges and to improve the modelling of the machining process, their impact on active force components including ploughing forces and tool face friction is analysed. This paper presents experimental results of orthogonal turning tests conducted on Ti-6Al-4V with different cutting edge radii and changing cutting speeds and feeds. As an accurate characterisation method for the determination of the cutting edge radius is prerequisite for this analysis, a new algorithm is described which reduces uncertainties of existing methods.     

Characteristics of cutting forces and chip formation in machining of titanium alloys

Chip formation during dry turning of Ti6Al4V alloy has been examined in association with dynamic cutting force measurements under different cutting speeds, feed rates and depths of cut. Both continuous and segmented chip formation processes were observed in one cut under conditions of low cutting speed and large feed rate. The slipping angle in the segmented chip was 55°, which was higher than that in the continuous chip (38°). A cyclic force was produced during the formation of segmented chips and the force frequency was the same as the chip segmentation frequency. The peak of the cyclic force when producing segmented chips was 1.18 times that producing the continuous chip.The undeformed surface length in the segmented chip was found to increase linearly with the feed rate but was independent of cutting speed and depth of cut. The cyclic force frequency increased linearly with cutting speed and decreased inversely with feed rate. The cutting force increased with the feed rate and depth of cut at constant cutting speed due to the large volume of material being removed. The increase in cutting force with increasing cutting speed from 10 to 16 and 57 to 75 m/min was attributed to the strain rate hardening at low and high strain rates, respectively. The decrease in cutting force with increasing cutting speed outside these speed ranges was due to the thermal softening of the material. The amplitude variation of the high-frequency cyclic force associated with the segmented chip formation increased with increasing depth of cut and feed rate, and decreased with increasing cutting speed from 57 m/min except at the cutting speeds where harmonic vibration of the machine occurs.     

Prediction of cutting forces and chip geometry in oblique machining from flow stress properties and cutting conditions

An approximate theory of oblique machining is given in which the mean friction angle previously used to describe the frictional condition at the tool-chip interface is replaced by the shear strength of the chip material at the tool-chip interface. The shear strength is expressed as a function of strain-rate and temperature using a velocity-modified temperature. Good agreement is shown between theory and experiment.     

Three-dimensional cutting force analysis based on the lower boundary of the shear zone. Part 1: Single edge oblique cutting

Traditional models of cutting based on Merchant's shear plane idealization are incapable of predicting any of the cutting force components without a priori knowledge of chip-tool friction. However, Rubenstein's work on orthogonal cutting has shown that this limitation can be avoided by utilizing the stress distributions on the lower boundary of the shear zone. The present work aims to extend this approach to oblique cutting with. single and two edged tools. This paper focuses on single edge oblique cutting whereas Part 2 analyses two edge cutting. It is assumed that the progressive deformation of the work material into chip material occurs within the effective plane. The resulting stress distributions on the lower boundary are integrated to yield expressions for estimating cutting forces from given tool and chip geometries. This provides a mechanism for predicting the power and lateral components of the cutting force in single edge oblique cutting. The predictions are verified against new and previously published experimental data.     

Influence of cutting edge geometry and cutting edge radius on the stability of micromilling processes

The occurrence of tool vibrations in the micromilling process is undesirable because of its negative influence on the quality of microstructures. Due to the small dimensions of the undeformed chip parameter, the influence of the cutting edge on the chip formation and on the regenerative effect seems to be larger than in macrodimensions. Within this paper the results of an experimental investigation with micro end-milling cutters (d = 1 mm) are presented. Additionally, the influences of the cutting edge radius, the corner radius, and the feed per tooth on the tool vibration trajectories, the process forces, and chatter and its causes are discussed.     

Shear cutting of press hardened steel: influence of punch chamfer on process forces, tool stresses and sheared edge qualities

In order to cope with the difficulties of shearing operations of press hardened steels, this work attempted to optimize these processes. Herefore, it is necessary to reduce the press forces and stresses in tools, while still obtaining adequate sheared edge quality levels. To reach this goal, different punch chamfer angles (0°, 2°, 7° and 20°) and relative cutting clearances (5, 10 and 15?% of the sheet thickness) were tested in a cutting tool, which was adapted in a way that different active elements could be mounted. The tool was equipped with a measurement system, which allowed the determination of the process forces in three dimensions at each punch stroke. Basis was an AlSi coated 22MnB5 sheet with a thickness of 1.5?mm. In addition a finite element model was developed to predict the stress distribution in tools and the sheared edge qualities. According to the experimental results the application of a 20° chamfer angle succeeded to reduce the forces and stresses of tools, but the sheared parts had a poor quality. In contrast, the 7° chamfer angle gave lowest tool stresses and sufficient part qualities, but the forces were very high. The simulation results agreed with the experimental data, except for the prediction of the rollover zone. These deviations were attributed among others to the presence of the AlSi coating, which was not considered.     

Analytical modeling and experimental validation of micro end-milling cutting forces considering edge radius and material strengthening effects

This paper presents a novel micro end-milling cutting forces prediction methodology including the edge radius, material strengthening, varying sliding friction coefficient and run-out together. A new iterative algorithm is proposed to evaluate the effective rake angle, shear angle and friction angle, which takes into account the effects of edge radius as well as varying sliding friction coefficient. A modified Johnson–Cook constitutive model is introduced to estimate the shear flow stress. This model considers not only the strain-hardening, strain-rate and temperature but also the material strengthening. Furthermore, a generalized algorithm is presented to calculate uncut chip thickness considering run-out. The cutting forces model is calibrated and validated by NAK80 steel, and the relevant micro slot end-milling experiments are carried out on a 3-axis ultra-precision micro-milling machine. The comparison of the predicted and measured cutting forces shows that the proposed model can provide very accurate predicted results. Finally, the effects of material strengthening, edge radius and cutting speed on the cutting forces are investigated by the proposed model and some conclusions are given as follows: (1) the material strengthening behavior has significant effect on micro end-milling process at the micron level. (2) Cutting forces predicted increase with the increase of edge radius. (3) Considering varying sliding friction coefficient can enhance the sensitivity of the predicted cutting forces to cutting speed.     

Effects of micro-milling conditions on the cutting forces and process stability

Determining stable cutting conditions for corresponding cutting tools with specific geometries is essential for achieving precision micro-milling with high surface quality. Therefore, this paper investigates the influence of the tool rake angle, tool wear and workpiece preheating on the cutting forces and process stability. An advanced micro-milling cutting force model considering the tool wear is proposed. The micro-milling cutting forces are predicted and compared with experimentally obtained results for two cutting conditions and four edge radii measured at different stages of the tool wear. It is found that the cutting forces increase by increasing the edge radius. It is also observed that the cutting forces are higher at a rake angle of 0° compared with a rake angle of 8°. The increase of the cutting forces is mainly associated with the change of the friction conditions between the tool and workpiece contact. Stability lobes are obtained for different edge radii, rake angles of 0° and 8°, initial workpiece temperature and different measured static run-outs. The predicted stability lobes are compared with the micro-milling force signals transformed into the frequency domain. It is observed that the predicted stability limits result in good correlation with the experimentally obtained chatter free conditions. Also, the stability limits are higher at smaller edge radii, higher preheating workpiece temperature and positive rake angles.     

Three-dimensional cutting force analysis based on the lower boundary of the shear zone. Part 2: Two edge oblique cutting

The problem of partitioning the overall cutting force between the two active cutting edges in two edge oblique cutting, although of crucial importance in modelling the temperature and wear rates prevailing in form cutting, has so far eluded solution. This paper presents two solutions to the problem: one utilizing the Merchant shear plane (MSP) approach and the other utilizing the solution developed in Part 1 for single edge oblique cutting based on the lower boundary (LB) of the shear zone. Both approaches avoid the anomalies encountered in previous attempts at solving the partitioning problem. This was done through the simultaneous application of the principles of chip equilibrium, force-velocity collinearity and chip interaction. Arguments are presented to indicate that the LB approach is more reliable than that of the MSP approach. Further, the LB approach is able to predict the power component of the overall cutting force in two edge cutting just as in the case of single edge cutting.     

A three-dimensional model of clip flow, chip curl and chip breaking for oblique cutting

In recent years, many publications have appeared dealing with chip breaking in orthogonal cutting of metals. However, in industry, oblique cutting and not orthogonal cutting is encountered in almost all actual machining operations. This paper deals with a model of chip flow, chip curl and chip breaking for oblique cutting. To simplify the analysis, a set of equivalent parameters are introduced. The relationship between the machining parameters and their corresponding equivalent parameters is developed theoretically and experimentally. To assess the level of chip breaking, a criterion of chiplbreaking is suggested under the concept of these equivalent parameters. The agreement of the experimental results with the predictive data of the model verifies that the definition of these equivalent parameters is reasonable. The influences of various machining parameters are discussed, in relation to their corresponding parameters. One significant finding is that the effect of each of the machining parameters on chip breaking is not totally inpdependent of one another. This implies that careful attention must be paid to the relationship between various machining parameters in three-dimensional parameters.     

Basic geometric analysis of 3-D chip forms in metal cutting.: Part 1: determining up-curl and side-curl radii

The works of Nakayama et al. represent the prevailing view on how the geometry of 3-D helical chip relates to the radii of its up-curl and side-curl. The view is re-examined in this paper and it is shown that the corresponding definitions of the radii are ambiguous. Six sets of alternative hypothetical definitions of up-curl and side-curl radii, which are consistent and plausible when examined from the viewpoints of 2-D up-curl and side-curl, are identified and the respective expressions are derived from a geometric analysis of 3-D chip. The hypotheses are tested using six criteria. It is found that the expressions for the radii of up-curl and side-curl proposed by Nakayama et al. do not satisfy one of the criteria whereas a new solution satisfies all the criteria. Part 2 extends the 3-D geometric analysis and discovers a number of new implications.     

Investigation of wear behavior and chip formation for cutting tools with nano-multilayered TiAlCrN/NbN PVD coating

A comprehensive investigation of the wear progress and chip formation was performed on an ultra-fine-grained cemented carbide ball nose end mill coated with a novel nano-multilayered TiAlCrN/NbN coating, by dry machining-hardened steel AISI H13 (HRC 55–57) at a cutting speed of 300 m/min. Flank wear and cutting forces were measured as the wear progressed; chip temperatures were estimated. The surface morphology of the tools were studied by using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis techniques. Results showed that protective oxide films (Al–O, Cr–O and Nb–O) were formed during cutting. With the combination of the protective oxide films and the fine-grain tough substrate, the tool wear rate was greatly reduced compared to the other coatings tested. Continuous and saw-tooth chips were identified, corresponding to a new sharp tool and a worn tool, respectively. The mechanisms of saw-tooth chip formation were found to be a combination of “crack theory” and “adiabatic shear theory”. The characteristics of the chips were studied in detail with the results showing that during formation the chips underwent a combined effect of strain hardening and thermal softening, followed by a quenching phenomenon.     

Basic geometric analysis of 3-D chip forms in metal cutting.: Part 2: implications

The geometric analysis of 3-D chip forms developed in Part 1 is extended and several new implications are identified: (i) the geometric properties at every point on the tool–chip separation line are fully determined once those at any one point are known, (ii) all possible 3-D chip forms are confined to a relatively restricted parameter space defining the chip velocity direction and the orientation of the axis of the helical chip, (iii) 3-D helical chips are only approximately conical, and (iv) the radii of up-curl and side-curl can be determined from a set of simple measurements of the chip-in-hand. Unlike past analyses, the new analysis paves the way to the study of chip forms from empirical data obtained from practical 3-D chips.     

Influence of microstructure on surface integrity in turning—part II: the influence of a microstructure of the workpiece material on cutting forces

Analysis of cutting forces in fine turning is most frequently related to workpiece-material hardness and strength under different machining conditions. Material hardness and strength as well as material machinability, however, can be related to the material microstructure. Consequently, an additional influence exerted by the microstructure was included in the present study to find the relationship between the size of the soft phase described by intercept lengths and the magnitude of the cutting force measured during the fine-turning process. The magnitude of cutting force is usually treated in terms of its static and dynamic components. In our case, both the components are of importance. Because of different types of aluminium–silicon alloys, significant differences occur in the magnitude of the static and dynamic components of the cutting force mainly because of different types of microstructures. The latter can be described by the fraction and quantity of individual microstructure phases. The results obtained are represented by an average magnitude of static and dynamic components of the cutting force in relation to the intercept lengths of the soft phase.     

Some theories on the effects of atmospheric humidity on tool forces and chip formation in turning

A series of experiments were performed in which steel, aluminium and brass were turned on a lathe without using any lubricant or coolant and under various conditions of relative humidity. The results show that if other parameters are kept constant, all three (axial, radial and tangential) components of tool force in dry turning decrease quite significantly with increasing relative humidity. This paper puts forward some possible explanations for this phenomenon.     

Tool wear effect on cutting forces: In routing process of Aleppo pine wood

This paper uses the cutting forces in a routing process of Aleppo pine wood to estimate the tool wear effect. The aim is to obtain further information about the tool wear effect by monitoring the variation in the cutting forces. A Kistler 9257A 3 axes Dynamometer was positioned under the workpiece to measure the cutting forces at frequencies up to 10,000 Hz. The experiments were carried out on a CNC routing machine RECORD1 of SCM. A carbide tool was used and the cutting parameters were fixed. The cutting speed was approximately 25 m/s. Dasylab software was used to capture the data. The results show a correlation between the tool wear and the computed angle (θ), between the tangential and cutting forces. In fact, the variation of (θ) is unstable in the running period and stable in the linear wear zone, included in the interval [?1.11°; ?1.10°]. This study was performed as part of a development program for the Algerian wood industry, hence the selection Aleppo pine wood as the working material.     

New observations on tool life, cutting forces and chip morphology in cryogenic machining Ti-6Al-4V

The use of cryogenic coolant in metal cutting has received renewed recent attention because liquid nitrogen is a safe, clean, non-toxic coolant that requires no expensive disposal and can substantially improve tool life. This work investigates the effectiveness of cryogenic coolant during turning of Ti-6Al-4V at a constant speed and material removal rate (125 m/min, 48.5 cm³/min) with different combinations of feed rate and depth of cut. It is found that the greatest improvement in tool life using cryogenic coolant occurs for conditions of high feed rate and low depth of cut combinations. However, this combination of machining parameters produces much shorter tool life compared to low feed rate and high depth of cut combinations. It is found that preventing heat generation during cutting is far more advantageous towards extending tool life rather than attempting to remove the heat with cryogenic coolant. Although cryogenic coolant is effective in extracting heat from the cutting zone, it is proposed that cryogenic coolant may limit the frictional heat generated during cutting and limit heat transfer to the tool by reducing the tool-chip contact length. The effect of cryogenic coolant on cutting forces and chip morphology is also examined.     

An analytical evaluation of the cutting forces in self-piloting drilling using the model of shear zone with parallel boundaries. Part 1: Theory

The performance of a self-piloting tool is affected by its design and geometry parameters. These parameters constitute the tool-force system which directly defines quality of the machined holes, tool life and required power. This paper presents an analytical approach to describe the cutting forces in self-piloting drilling. The approach is useful at the level of tool and process design. The subject has been covered in two parts. Part one deals with the analysis of the cutting mechanics employing the shear-zone model with parallel boundaries. The analysis of the continuity condition results in better understanding of the traditional cutting model's characteristics, such as the chip compression ratio and velocity diagram. Based on this analysis and using the thermomechanical model of the work-material resistance to cutting, a cutting-force model is proposed and has been verified experimentally.     

Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass

The chip light emission and morphology, cutting forces, surface roughness, and tool wear in turning of Zr-based bulk metallic glass (BMG) material are investigated. Machining results are compared with those of aluminum 6061-T6 and AISI 304 stainless steel under the same cutting conditions. This study demonstrates that the high cutting speeds and tools with low thermal conductivity and rake angle activate the light emission and chip oxidation in BMG machining. For the BMG chip without light emission, serrated chip formation with adiabatic shear band and void formation is observed. The cutting force analysis further correlates the chip oxidation and specific cutting energy and shows the significant reduction of cutting forces for machining BMG at high cutting speeds. The machined surface of BMG has better surface roughness than that of the other two work materials. Some tool wear features, including the welding of chip to the tool tip and chipping of the polycrystalline cubic boron nitride (PCBN) tool edge, are reported for turning of BMG. This study concludes that BMG can be machined with good surface roughness using conventional cutting tools.     

Influence of punch geometries on the divided material flow in a double cup extrusion process

This paper provides an analysis of the deformation patterns in a backward can extrusion combined simultaneously with a forward can extrusion process, which is known as a double cup extrusion process. The main objective of this study is to examine the divided material flow characteristics in DCEP. Analyses were conducted in a numerical manner by employing a rigid-plastic finite element method. Among many process parameters, the major design factors chosen for analysis include the reduction in area (RAB), the wall thickness ratio (TR), the punch nose radius (R), and the friction condition. The simulation results were summarized in terms of relationships between the process parameters and the ratios of extruded length and volume, and between the process parameters and force requirements, respectively. Comparisons between a multi-stage forming process in sequential operations and one-stage combined operation were also made in terms of the forming load and pressure exerted on the tool. The force requirement and self-regulating characteristics were more greatly influenced by the wall thickness ratio among the selected major design factors. And more severe load to form the same shape is expected in sequential operations than in a combined extrusion process.