Identification of cutter offset in end milling without a prior knowledge of cutting coefficients

This paper presents a method for the identification of cutter offset through milling force without requiring the specific cutting coefficients to be known as priori. The total milling force in the presence of cutter offset is first obtained on the basis of dual cutting mechanisms, where the local force is comprised of a constant plowing force and a linear shearing force proportional to the chip load under the cutter offset. The total milling force is synthesized through convolution and is shown to be the sum of three force components: the nominal chip shearing force component, the plowing force components and the offset related shearing force component. Fourier analysis of these force components reveals the effects of offset geometry and yields formulas for the identification of offset geometry. The identification process requires only two cutting tests and the evaluation of two algebraic expressions; the shearing constants are found from the average forces of cutting tests and the offset geometry is identified from the force component at the spindle frequency. Through numerical simulation and experimental results, the efficacy of the identification method is demonstrated; the effects of feed per tooth and cutting depths on the accuracy of the model are investigated and criteria for the appropriate selection of these parameters are suggested.     

An analytical model to predict specific shear energy in high-speed turning of Inconel 718

Machining of Inconel 718 at higher cutting speeds is expected to provide some relief from the machining difficulties. Therefore, to understand the material behavior at higher cutting speeds, this paper presents an analytical model that predicts specific shearing energy of the work material in shear zone. It considers formation of shear bands that occur at higher cutting speeds during machining, along with the elaborate evaluation of the effect of strain, strain rate, and temperature dependence of the shear flow stress using Johnson–Cook equation. The model also considers the ‘size-effect’ in machining in terms of occurrence of ‘ploughing forces’ during machining. The theoretical results show that the shear band spacing in chip formation increases linearly with an increase in the feedrate and is of the order of 0.2–0.9 mm depending upon the processing conditions. The model shows excellent agreement with the experimental values with an error between 0.5% and 7% for various parametric conditions.     

A study on the cutting mechanism of microcutting using molecular Dynamics

Ultraprecision metal cutting (UPMC) technology, which makes possible submicrometre form accuracy and nanometre roughness, is developed to reach the 1 nm nominal (undeformed) thickness of cut. At this thickness level, the finite element method (FEM) cannot be used to solve the problem. Molecular Dynamics can be applied to this small cutting depth.In this paper using molecular dynamics simulation, microcutting with a subnanometre chip thickness, the cutting mechanism for the microcutting condition, i.e. tool edge configuration, cut material and cutting speed, are evaluated.As the result, the simulation of the cutting mechanism at subnanometre depth of cut is evaluated.     

Cutting and ploughing forces for small clearance angles of hexa-octahedron shaped diamond grains

Investigations on the cutting behaviour of hexa-octahedron diamonds outlined an enormous influence of the grains’ clearance angle on the material removal process. Small negative clearance angles lead to increased specific cutting forces, decreased cutting force ratios and micro-structural changes. This is caused by additional ploughing of the material. This paper presents a kinematic-phenomenological model predicting the specific forces that are caused by the ploughed material. Therefore, the theoretical value of the specific ploughed volume is introduced as characteristic parameter. Results are subsequently compared for different grain cutting situations to experimental data allowing a validation of the proposed model.     

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.     

Characterization of the transition from ploughing to cutting in micro machining and evaluation of the minimum thickness of cut

When the machining process is miniaturized two process mechanisms, ploughing and chip formation, are essential and a critical cutting thickness needs to be exceeded so that not only ploughing will occur but chips will also be formed. The ploughing effect thereby influences the chip formation process, workpiece surface roughness, burr formation and residual stress state after processing and is therefore of great interest. In order to optimize the machining process a better understanding of the minimum thickness of cut is crucial.The changes in surface topography along the cutting track occurring during machining with a constant feed rate of the cutting tool were analyzed. The influence of the built-up edge phenomena on the micro machining process was investigated for normalized AISI 1045 using confocal white light microscopy and scanning electron microscopy. Furthermore the sin²ψ-method was applied in order to study the residual stress state in the workpiece surface induced by the machining process. Both surface layer properties investigated, surface roughness and residual stresses, show a characteristic transition indicating a change in the dominating process mechanisms. Based on these results a model is developed to determine the minimum thickness of cut. The minimum thickness of cut is found to significantly decrease with higher cutting velocities and to moderately increase with higher cutting edge radii. In addition a propagation of error for the values obtained with the model was performed, proving the quality of the model developed.     

A model to calibrate and predict forces in machining with honed cutting tools or inserts

This paper describes a mechanistic approach towards modeling the effects on machining forces of the edge hone commonly ground on machining tools and tool inserts. This approach proposes that the ratio of the shearing to ploughing forces would remain identical for tools with different honed radii, machining under identical conditions of chip thickness to edge hone radius ratios and cutting velocity. This concept allows a very simple and new calibration technique toward separating out the effects of tool and machining parameters that influence the force coefficients in machining without a need for any additional parameters. The model has been presently developed for orthogonal cutting and its validation using a tube turning process on gray cast iron with straight edged inserts has shown very promising results. Continued research is being performed to evaluate the applicability of the model for more complex machining operations.     

Modelling of specific energy requirement during high-efficiency deep grinding

Grinding is a multi-point cutting operation. The specific energy or the energy expended for unit material removal in grinding is very high, typically one or two orders higher than the machining specific energy. Such high specific energy required in grinding can be attributed to the irregular and random geometry of the abrasive grits, which induce a lot of rubbing and ploughing actions along with the chip formation by shearing process. Also the effective angle in grinding is highly negative which is again responsible for such high-specific energy requirement in grinding. In grinding, a number of notable phenomena occur during the chip formation process, which actually consumes a significant percentage of energy. Such main energy consumers in grinding are:

• Chip formation due to shearing

• Primary rubbing

• Secondary rubbing

• Ploughing

• Wear flat rubbing

• Friction between the loaded chip and workpiece

• Friction between bond and workpiece, etc.

The present paper tries to analytically predict the specific energy consumed during high-efficiency deep grinding (HEDG) of bearing steel by monolayer cBN wheel. During the HEDG process, energy is spent mostly for shearing, rubbing and ploughing processes. The other energy consumers have insignificant role in such high-speed grinding process. So, models which take into account the processes of shearing, primary rubbing, secondary rubbing and ploughing process can reasonably be used to predict the energy requirement in such HEDG process. The total specific energy value obtained from the model has been validated with those experimentally observed values. A good trend matching of the modelled and experimental values have been observed and the root mean square error values have been found to vary between 7% and 11%.     

Effect of Erodent Particle Hardness on Velocity Exponent in Erosion of Steels and Cast Irons

This article reports the effect of hardness of erodent particles on velocity exponent of some weld deposited alloys. Three steels and two alloy cast irons were selected for the present investigation. The bulk hardness of the alloys was in the range of 300 to 800 HV, whereas erodnet particles were having hardness in the range of 400 to 1875 HV. Erosion tests were conducted with 125-150 µm cement clinker, 125-150 µm blast furnace sinter, 100-150 µm silica sand, and 125-150 µm alumina particles and at impingement angles of 30° and 90° and with impingement velocities in the range of 25 to 120 m sec^-1. The erosion rate showed power-law dependence on impingement velocity, E = kVⁿ, where kis a constant and nis the velocity exponent. The velocity exponents obtained in the present work were in the range of 1.91 to 2.52. The velocity exponent showed an increasing trend with increasing hardness of the alloys irrespective of the hardness of the erodent particles and the impingement angle. The velocity exponent increased with increasing hardness of erodent particles, irrespective of the impingement angle and hardness of the alloys. The velocity exponents obtained in the present work were rationalized with respect to erodent particle properties, material properties and erosion mechanisms.     

Wear behaviour of AE42+20% saffil Mg-MMC

The wear behaviour of AE42 magnesium alloy and AE42+20% saffil short fibre composite is investigated in dry sliding condition using a pin-on-disc set-up in the load range of 5–40 N with sliding speeds of 0.838, 1.676 and 2.513 m/s for a constant sliding distance of 2.5 km. In case of both the alloy and the composite wear rate increases with increasing loads and the wear rate of the composite is lower at lower loads. At all sliding speeds, a crossover in wear rate is observed with the increase in load, i.e., above a certain load the wear rate of the composite becomes greater than that of the alloy, and the crossover shifts to lower loads with increase in the sliding speed. Severe sub-surface plastic deformation and fibre breakage are found to be the dominant mechanism for the unreinforced alloy and the composite, respectively.