“Peel cutting” – A new cutting method for difficult-to-cut workpieces with hard oxide surfaces

A new cutting method named “peel cutting” is proposed in this research to suppress notch wear in machining of metals with hard oxide surfaces. In general, metals are produced by hot deformation processes like rolling, forging, and extrusion, which cause hard oxide surfaces called scales on their surfaces. These hard scales need to be removed first in machining of precision parts. However, the machining causes the severe notch wear at the depth-of-cut position, where the tool contacts the hard scale. To solve this problem, the proposed peel cutting avoids this direct contact between the tool and the scale by inclining the end cutting edge at an extremely large inclination (oblique) angle. This extremely oblique cutting changes the material flow and generates a “burr-like chip”. In the proposed cutting method, the tool contacts only soft non-oxide metal under the scale during cutting. Cutting of titanium alloy Ti–6Al–4V is conducted by modifying commercial tools to provide extremely large inclination angles, and it is clarified that an inclination angle of 70 deg or greater is required to realize the proposed cutting. Tool wear in the proposed cutting of the alloy with a hard scale is also observed in comparison with the ordinary cutting, and the result verifies that the notch wear can be suppressed successfully by the proposed peel cutting.     

Cutting force prediction for ball nose milling of inclined surface

Ball nose milling of complex surfaces is common in the die/mould and aerospace industries. A significant influential factor in complex surface machining by ball nose milling for part accuracy and tool life is the cutting force. There has been little research on cutting force model for ball nose milling on inclined planes. Using such a model ,and by considering the inclination of the tangential plane at the point of contact of the ball nose model, it is possible to predict the cutting force at the particular cutting contact point of the ball nose cutter on a sculptured surface. Hence, this paper presents a cutting force model for ball nose milling on inclined planes for given cutting conditions assuming a fresh or sharp cutter. The development of the cutting force model involves the determination of two associated coefficients: cutting and edge coefficients for a given tool and workpiece combination. A method is proposed for the determination of the coefficients using the inclined plane milling data. The geometry for chip thickness is considered based on inclined surface machining with overlapping of previous pass. The average and maximum cutting forces are considered. These two forces have been observed to be more dominating force-based parameters or features with high correlation with tool wear. The developed cutting force model is verified for various cutting conditions.     

Parametric tool wear estimation solution of HSC appropriate machining

New strategies are used in manufacturing enterprises due to global competition. High-speed cutting offers a very appropriate opportunity to reduce run times since the high cutting speeds and feed rates involved permit the reduction of production times and minimise rework. There are, however, difficulties in judging tool wear [1]. This paper analyses the formation mechanism of tool wear and presents a complete solution to calculate wear using a ball end cutter for high-speed cutting. Chip geometry generated to calculate tool wear is affected by machining conditions such as turning speed, cutting depth and geometries of tool and work piece which in turn determine the key parameters of chip sections such as length of cut and mean chip thickness. An improved algorithm and a knowledge-based decision model developed to calculate effective tool contact are also discussed to help reduce calculation time and improve calculation efficiency. The calculation results include output form and a 3D wear model showing wear data distributed on the tool contour.     

Extraction of flank wear growth models that correlates cutting edge integrity of ball nose end mills while machining titanium

The application of titanium alloys are increasingly seen at aerospace, marine, bio-medical and precision engineering due to its high strength to weight ratio and high temperature properties. However, while machining the titanium alloys using solid carbide tools, even with jet infusion of coolant lower tool life was vividly seen. The high temperatures generated at the tool?Cwork interface causes adhesion of work-material on the cutting edges; hence, shorter tool life was reported. To reduce the high tool?Cwork interface temperature positive rake angle, higher primary relief and higher secondary relief were configured on the ball nose end-mill cutting edges. However, after an initial working period, the growth of flank wear facilitates higher cutting forces followed by work-material adhesion on the cutting edges. Therefore, it is important to blend the strength, sharpness and surface integrity on the cutting edges so that the ball nose end mill would demonstrate an extended tool-life. Presently, validation of tool geometry is very tedious as it requires extensive machining experiments. This paper illustrates a new feature-based ball-nose-end-mill?Cwork interface model with correlations to the material removal mechanisms by which the tool geometry optimization becomes easier. The data are further deployed to develop a multi-sensory feature extraction/correlation model to predict the performance using wavelet analysis and Wagner Ville distribution. Conclusively, this method enables to evaluate the different ball nose end mill geometry and reduces the product development cycle time.     

Experimental investigations while hard machining of DIEVAR tool steel (50 HRC)

This paper describes hard machining which offers many potential benefits over traditional manufacturing techniques. In this work, investigations were carried out on end milling of hardened tool steel DIEVAR (hardness 50 HRC), a newly developed tool steel material used by tool- and die-making industries. The objective of the present investigation was to study the performance characteristics of machining parameters such as cutting speed, feed, depth of cut and width of cut with due consideration to multiple responses, i.e. volume of material removed, tool wear, tool life and surface finish. Performance evaluation of physical vapour deposition-coated carbide inserts, ball end mill cutter and polycrystalline cubic boron nitride inserts (PCBN) was done for rough and finish machining on the basis of flank wear, tool life, volume of material removed, surface roughness and chip formation. It has been observed from investigations that chipping, diffusion and adhesion were active tool wear mechanisms and saw-toothed chips were formed whilst machining DIEVAR hard steel. PCBN inserts give an excellent performance in terms of tool life and surface finish in comparison with carbide-coated inserts. End milling technique using PCBN inserts could be a viable alternative to grinding in comparison to ball end mill cutter in terms of surface finish and tool life.     

Blend of sharpness and strength on a ball nose endmill geometry for high speed machining of Ti6Al4V

The applications of titanium alloys are increasingly common at marine, aerospace, bio-medical and precision engineering due to its high strength to weight ratio and high temperature-withstanding properties. However, whilst machining the titanium alloys using the solid carbide tools, even with application of high pressure coolant, reduced tool life was widely reported. The generation of high temperatures at the tool–work interface causes adhesion of work material on the cutting edges, and hence, shorter tool life was reported. In order to reduce the high tool–work interface temperature-positive rake angle, higher primary relief and higher secondary relief were configured on the ball nose endmill cutting edges. Despite of careful consideration of tool geometry, after an initial working period, the growth of flank wear accelerates the high cutting forces followed by work material adhesion on the cutting edges. Hence, it is important to blend the strength, sharpness, geometry and surface integrity on the cutting edges so that the ball nose endmill would exhibit an extended tool life. This paper illustrates the effect of ball nose endmill geometry on high speed machining of Ti6Al4V. Three different ball nose endmill geometries were configured, and high speed machining experiments were conducted to study the influence of cutting tool geometry on the metal cutting mechanism of Ti-6Al-4V alloy. The high speed machining results predominantly emphasize the significance of cutting edge features such as K-land, rake angle and cutting edge radius. The ball nose endmills featured with a short negative rake angle of value ?5° for 0.05～0.06 mm, i.e. K-land followed by positive rake angle of value 8°, has produced lower cutting forces signatures for Ti-6Al-4V alloy.     

An empirical survey on the influence of machining parameters on tool wear in diamond turning of large single-crystal silicon optics

We conducted a series of screening experiments to survey the influence of machining parameters on tool wear during ductile regime diamond turning of large single-crystal silicon optics. The machining parameters under investigation were depth-of-cut, feed rate, surface cutting speed, tool radius, tool rake angle and side rake angle, and cutting fluid. Using an experimental design technique, we selected twenty-two screening experiments. For each experiment we measured tool wear by tracing the tool edge with an air bearing linear variable differential transformer before and after cutting and recording the amount of tool edge recession. Using statistical tools, we determined the significance of each cutting parameter within the parameter space investigated. We found that track length, chip size, tool rake angle and surface cutting speed significantly affect tool wear, while cutting fluid and side rake angle do not significantly affect tool wear within the ranges tested. The track length, or machining distance, is the single most influential characteristic that causes tool wear. For a fixed part area, a decrease in track length corresponds to an increase in feed rate. Less tool wear occurred on experiments with negative rake angle tools, larger chip sizes and higher surface velocities. The next step in this research is to perform more experiments in this region to develop a predictive model that can be used to select cutting parameters that minimize tool wear.     

Micromechanical machining of soda lime glass

Micromechanical machining, which is the mechanical removal of materials using miniature cutting tools, is one of the fabrication methods in the microrealm that has recently attracted a great deal of attention because it has the advantage of being able to machine complex shapes from brittle materials. The most challenging problem in the mechanical machining of brittle material is the fabrication of fracture-free surfaces. To avoid brittle fractures, a thorough investigation is required to find the machining parameters in the ductile cutting regime, which is characterized by plastic deformation of the material when the chip thickness is smaller than the critical value. In this study, cutting forces and surface characteristics of soda lime glass are examined in detail. Conical scratch tests are performed to identify the critical chip thickness, and the cutting forces in the ductile regime are modeled. In addition, coated ball end mill cutters were used to perform machining on inclined soda lime glass to investigate the feed rate effects, up and down milling, and depth of cuts on the surface finish and to examine tool wear.     

Prediction of cutting forces and machining error in ball end milling of curved surfaces -I theoretical analysis

This paper presents a theoretical model by which cutting forces and machining error in ball end milling of curved surfaces can be predicted. The actual trochoidal paths of the cutting edges are considered in the evaluation of the chip geometry. The cutting forces are evaluated based on the theory of oblique cutting. The machining errors resulting from force induced tool deflections are calculated at various parts of the machined surface. The influences of various cutting conditions, cutting styles and cutting modes on cutting forces and machining error are investigated. The results of this study show that in contouring, the cutting force component which influences the machining error decreases with increase in milling position angle; while in ramping, the two force components which influence machining error are hardly affected by the milling position angle. It is further seen that in contouring, down cross-feed yields higher accuracy than up cross-feed, while in ramping, right cross-feed yields higher accuracy than left cross-feed. The machining error generally decreases with increase in milling position angle.     

Influence of the process variables on the temperature distribution in orthogonal machining using the finite element method

The temperature distributions in the workpiece, tool and chip during orthogonal machining are obtained numerically using the Galerkin approach of the finite element method for various cutting conditions. The effect of a number of process variables such as speed, feed, coolant, rake angle, tool flank wear and tool material on the temperatures has been investigated.     

An explicit finite element model to study the influence of rake angle and friction during orthogonal metal cutting

A fundamental understanding of the tribology aspects of machining processes is essential for increasing the dimensional accuracy and surface integrity of finished products. To this end, the present investigation simulates an orthogonal metal cutting using an explicit finite element code, LS-DYNA. In the simulations, a rigid cutting tool of variable rake angle was moved at different velocities against an aluminum workpiece. A damage material model was utilized for the workpiece to capture the chip separation behavior and the simultaneous breakage of the chip into multiple fragments. The friction factor at the cutting tool–workpiece interface was varied through a contact model to predict cutting forces and dynamic chip formation. Overall, the results showed that the explicit finite element is a powerful tool for simulating metal cutting and discontinuous chip formation. The separation of the chip from the workpiece was accurately predicted. Numerical results found that rake angle and friction factor have a significantly influence on the discontinuous chip formation process, chip morphology, chip size, and cutting forces when compared to the cutting velocity during metal cutting. The model was validated against the experimental and numerical results obtained in the literature, and a good agreement with the current numerical results was found.     

高速铣削淬硬钢时切削载荷平稳化研究

和传统的铣削加工相比,高速铣削淬硬钢更需要稳定的切削载荷,以尽可能减少刀具碎裂和过度磨损。本研究借助三向压电石英测力仪,使用TiAlN涂层球形端铣刀,在13500 r/min的转速下,对淬火45#钢(47HRC~48HRC)进行了高速铣削试验,建立了高速铣削下的多项式切削力试验模型,模拟了以恒定切削力为目标、优化进给率的加工实例。结果显示,稳定的切削载荷能有效地提高加工效率,避免刀具剧烈磨损。     

Efficient Chip Breaker Design by Predicting the Chip Breaking Performance

As machining technology develops toward the unmanned and automated system, the need for chip control is considered increasingly important, especially in continuous machining such as in the turning operation. In this study, a systematic chip breaking prediction method is proposed using a 3D cutting model with the equivalent parameter concept. To verify the model, four inserts with different chip breaker parameters were tested and their chip breaking areas were compared with those obtained from the model. Finally, a new type insert (MF1) for medium-finish operations with variable parameters was designed by modifying the commercial one. The chip breaking region predicted by using the modified 3D cutting model for the above insert agrees with the one obtained experimentally. The newly designed insert showed better chip breaking ability than the base model, and other performance tests such as surface roughness, cutting force and tool wear also showed good results.     

Effect of tool stiffness upon tool wear in high spindle speed milling using small ball end mill

Longer tool life can be tentatively achieved at a higher feed rate using a small ball end mill in high spindle speed milling (over several tens of thousands of revolutions per minute), although the mechanism by which tool life is improved has not yet been clarified. In the present paper, the mechanism of tool wear is investigated with respect to the deviation in cutting force and the deflection of a ball end mill with two cutting edges. The vector loci of the cutting forces are shown to correlate strongly with wear on both cutting edges of ball end mills having various tool stiffnesses related to the tool length. The results clarified that tool life can be prolonged by reducing tool stiffness, because the cutting forces are balanced, resulting in even tool wear on both cutting edges as tool stiffness is lowered to almost the breakage limit of the end mill. A ball end mill with an optimal tool length showed significant improvement in tool life in the milling of forging die models.     

CHIP MORPHOLOGY CHARACTERIZATION AND MODELING IN MACHINING HARDENED 52100 STEELS

Hard machining is attracting more and more attention as an alternative to grinding in finish machining some hardened steels. The saw-toothed chips formed in hard machining have their own unique characteristics. The saw-toothed chip morphology is of great interest since the understanding of the saw-toothed chip morphology and its evolution in machining helps unveil hard machining chip formation mechanisms as well as facilitate hard machining implementation into industry. In this study, the effect of tool wear and cutting conditions on the saw-toothed chip morphology was examined in machining 52100 hardened 52100 bearing steel. It was found that the chip dimensional values and segmentation frequency were affected by tool wear and cutting conditions while the chip segmentation angles were approximately constant under different tool wear and cutting conditions. The shear band spacing has also been predicted at the same order of magnitude as the measurement, and improved spacing modeling accuracy is expected if the cutting process information can be better predicted first.     

The study of chip characteristics and tool wear in milling of SKD61 mold steel

In recent years, many machining applications have used dry cutting for high-speed cutting, for which, tool life prediction and research are important issues. In this study, a tungsten carbide tool cutting steel SKD61 was used, and the actual value of the chip shooting and the wear of the flank were determined using an industrial camera. The chip type and chip color are also discussed. After color calibration and chromaticity conversion, the model was trained through the neural network and the results were predicted. The tool wear curve and the theoretical curve were found to be closely related, and the chip color changed regularly. In the CIE XY chromaticity coordinate value, when the initial cutting was observed, the chip chromaticity coordinate point range was small, but as the wear amount increased, the chip chromaticity coordinate point range expanded gradually. The tool wear prediction established in this study was determined from the experimental results. The maximum errors of the test and verification were 0.031 mm and 0.022 mm. After calculation, the mean absolute percentage error (MAPE) was within 3 % and the accuracy level is MAPE is less than 10 %, so it has a high accurate prediction ability. Established tool wear predictions are also provided.

     

A comparative study of the tool–chip contact length in turning of two engineering alloys for a wide range of cutting speeds

Tool chip contact length is an important parameter in machining, as it provides an indication of the size of area of interaction between the hot chip and the tool surface and hence the interface heat transfer zone. Heat transfer and thermally activated wear modes usually dominate tool wear in the high speed machining of steels and machining of titanium alloys at most cutting speeds. In this study, existing models for the prediction of tool–chip contact length are reviewed and examined for their suitability in high speed machining of two widely used engineering alloys. Orthogonal turning tests for AISI 1045 steel and Ti6Al4V titanium alloy are conducted for a range of cutting speeds from conventional to high speeds. New contact length models are presented for both materials covering a wide range of cutting speeds. More significantly, these contact length models are appropriate for high speed machining where thermal loads significantly influence process performance. Additionally, the work discusses how the machinability of engineering materials influences the ability to predict contact length.     

CHIP MORPHOLOGY CHARACTERIZATION AND MODELING IN MACHINING HARDENED 52100 STEELS

Hard machining is attracting more and more attention as an alternative to grinding in finish machining some hardened steels. The saw-toothed chips formed in hard machining have their own unique characteristics. The saw-toothed chip morphology is of great interest since the understanding of the saw-toothed chip morphology and its evolution in machining helps unveil hard machining chip formation mechanisms as well as facilitate hard machining implementation into industry. In this study, the effect of tool wear and cutting conditions on the saw-toothed chip morphology was examined in machining 52100 hardened 52100 bearing steel. It was found that the chip dimensional values and segmentation frequency were affected by tool wear and cutting conditions while the chip segmentation angles were approximately constant under different tool wear and cutting conditions. The shear band spacing has also been predicted at the same order of magnitude as the measurement, and improved spacing modeling accuracy is expected if the cutting process information can be better predicted first.     

TOOL PERFORMANCE AND CHIP CONTROL WHEN MACHINING Ti6A14V AND INCONEL 901 USING HIGH PRESSURE COOLANT SUPPLY

Single point continuous turning tests were carried out on Ti6A14V and Inconel 901 using various geometries of straight grade (K20) cemented carbide inserts using a high pressure coolant jet directed at the tip of the tool where the chip is formed. Trials were also carried out using a conventional coolant supply for comparison. The test results show that improved tool life can be achieved when machining the titanium-base alloy under the high pressure coolant jet while shorter tool life was obtained when machining the nickel-base alloy. The use of high pressure coolant supply during machining generally maintains constant cutting forces and reduces the chip-tool contact length, thus increasing stresses at the tool edge. This behavior tends to accelerate notching that is predominant when machining the Inconel 901 alloy, resulting in shorter tool life. This effect is not obvious when machining Ti6Ai4V where the tools failed mainly due to excessive flank wear. Effective chip control was achieved when machining both materials because of the cyclic fragmentation mechanism of the newly generated chip.     

Comparative evaluations of machining performance during turning of 17-4 PH stainless steel under cryogenic and wet machining conditions

Productivity in machining of 17-4 PH stainless steel is adversely affected by the premature failure of tool and poor surface finish as a consequence of high cutting temperatures. Conventional cutting fluids not only create environmental and health problems but also fail to overcome the high cutting temperatures during machining. Cryogenic cooling is an environmentally clean cooling technology for attractive management of machining zone temperatures. The present study investigates the effect of cryogenic liquid nitrogen (LN₂ at ?196°C) on cutting temperatures, cutting forces (main cutting force, feed force), surface roughness, tool flank wear and chip morphology in turning of 17-4 PH stainless steel with AlTiN PVD-coated tungsten-coated carbide inserts and results were compared to wet machining. In overall, cryogenic machining reduces the cutting temperature, cutting forces, surface roughness and tool flank wear to a maximum of 73.4, 17.62, 44.29 and 55.55%, respectively. Improved chip breakability was found in cryogenic machining.