A new low-feed chip breaking tool and its effect on chip morphology

This paper investigates the influence of cutting conditions on the formation mechanism of chips using a Tungsten Carbide in–house lasered cutter (grooved chip breaker) and a benchmark commercial cutter during turning of AISI1040 medium carbon steel. Microstructure of the free surface and segment underside the chips are experimentally characterised via scanning electron microscopy (SEM) and white light interferometry. The mechanism of chip formation is classified into continuous, partially segmented, segmented and discontinuous. Chip breaking ability are achieved for all tested feed speeds at depth of cut above 1.2 mm, marking the transition from continuous to segmented chips. The chip breaker manufactured via a nanosecond laser, proves to enable for the first time breaking of the chip below a feed rate of 0.1 mm/rev outperforming the commercial cutter and showing viability for the production capabilities of lasers for mass manufacture. Lamellae-type chips are revealed from machining using the lasered tool; while brush-stroke chips are discovered and introduced for the first time from machining using the benchmark cutter. While the lamellae form from cleavage cracks due to strain incompatibility at inclusions caused by an excess in critical shear strain. The brush-stroke chips are caused by a localized increase of temperature at the tool/material interface which lead to thermal softening of the workpiece: the resulting surface experiences large areas of plastic deformation. For the in-house lasered tool, at higher cutting speed the shear strain hardening reduces the flow stress of the workpiece material in the shear zone

Effect of laser texturing on the performance of ultra-hard single-point cutting tools

This paper investigates the cutting performance and anti-adhesive properties of textured single point polycrystalline diamond (PCD) cutting tools in machining Aluminium 6082 alloys. The micro/nano textures were first milled using a fibre laser (1064 nm wavelength) at different power intensities, feed speeds and pulse durations, and finally characterised using scanning electron microscopy, white light interferometry and energy dispersive X-ray spectroscopy. The effect of different textures on the cutting performance was investigated in turning tests under dry cutting conditions. The test was stopped at regular lengths of cut to allow analysis of height of adhesion through 3D white light interferometry. The data processing of the cutting forces and the microscopical characterisation of the tested cutting tools enabled the evaluation of the effects of texture design, friction coefficient and adhesive properties. The results indicated that feed force in tools with grooves perpendicular to the chip flow direction (CFD) was more stable (20-40N) than the benchmark (6-41N). Similarly, the thrust force for tools with grooves parallel to CFD and grooves perpendicular to CFD showed a homogeneous trend fluctuating between 60N to 75N as compared to the benchmark (ranging between 73N to 90N). For texture depth in the order of 260 nm and post process roughness in the order of tens of nanometers a reduction of average friction coefficient (0.28±0.14) was reported when using lasered inserts with grooves parallel to the chip flow direction compared to the benchmark tools (0.34±0.26) corroborated by reduced stiction of workpiece material on the rake face. In machining via textured tools with grooves perpendicular to CFD, the cutting forces were reduced by 23%, and the surface quality of the machined workpiece was improved by 11.8%, making this geometry the preferred choice for finishing applications. Using grooves parallel to CFD reduced the cutting forces by 11.76%, adhesion by 59.36% and friction coefficient by 14.28%, however it increased the surface roughness of the machined workpiece, making this geometry suitable for roughing operations. For the first time, laser manufacturing is proposed as a flexible technique to functionalise the geometrical and wear properties of PCD cutting tools to the specific applications (i.e. roughing, finishing) as opposed to the standard industrial approach to use microstructurally different PCDs (i.e. grain size and binder%) based on the type of operation. </div

Multiscale numerical and experimental analysis of tribological performance of GO coating on steel substrates

Herein, nano-tribological behaviour of graphene oxide (GO) coatings is evaluated by a combination of nanoscale frictional performance and adhesion, as well as macroscale numerical modelling. A suite of characterisation techniques including atomic force microscopy (AFM) and optical interferometry are used to characterise the coatings at the asperity level. Numerical modelling is employed to consider the effectiveness of the coatings at the conjunction level. The macroscale numerical model reveals suitable deposition conditions for superior GO coatings, as confirmed by the lowest measured friction values. The proposed macroscale numerical model is developed considering both the surface shear strength of asperities of coatings obtained from AFM and the resultant morphology of the depositions obtained from surface measurements. Such a multi-scale approach, comprising numerical and experimental methods to investigate the tribological behaviour of GO tribological films has not been reported hitherto and can be applied to real-world macroscale applications such as the piston ring/cylinder liner conjunction within the modern internal combustion engine

An assessment of the wear characteristics of microcutting arrays produced from polycrystalline diamond and cubic boron nitride composites

The current methods for manufacturing super-abrasive elements result in a stochastic geometry of abrasives with random three-dimensional abrasive locations. This paper focuses on the evaluation of wear progression/failure characteristics of micro-abrasive arrays made of ultrahard composites (polycrystalline diamond—PCD; polycrystalline cubic boron nitride—PCBN) in cutting/wear tests against silicon dioxide workpiece. Pulsed laser ablation (Nd:YAG laser) has been used to manufacture repeatable patterns of micro-abrasive edges onto microstructurally different PCD/PCBN composites. Opposing to these highly engineered micro-abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives, respectively, have been chosen as benchmarks and tested under the same conditions. Contact profiling, optical microscopy, and environmental scanning electron microscopy have been employed for the characterization of the abrasive arrays and electroplated tools before/during/after the wear/cutting tests. For the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. In this respect, the micro-arrays made of PCD with mixed diamond grain sizes have shown slower wear progression when compared to the electroplated diamond pads confirming the combination of the high wear resistance typical of the fine grain and the good shock resistance typical of the coarse grain structures. The micro-arrays made of fine grained diamond abrasives have produced lower contact pressures with the workpiece shaft, confirming a possible application in polishing or grinding. As for the PCBN abrasive micro-arrays, the increase of metallic binder and the presence of metalloids in the medium content-CBN specimens have shown to produce higher contact pressure with the workpiece when compared to the electroplated specimen, causing fracturing as the main wear mechanism; while the PCBN micro-array with purely a metallic binder phase has shown slower wear and lower contact pressure in comparison to the electroplated CBN specimen. Among all of the tested arrays, the mixed grained PCD and the purely metallic binder phase PCBN micro-arrays have shown slower wear when benchmarked to the electroplated pads, giving a possible application of their use in the cutting tool industry

Supplementary information files for 'A new low-feed chip breaking tool and its effect on chip morphology'

Supplementary information files for 'A new low-feed chip breaking tool and its effect on chip morphology'Abstract:This paper investigates the influence of cutting conditions on the formation mechanism of chips using a Tungsten Carbide in–house lasered cutter (grooved chip breaker) and a benchmark commercial cutter during turning of AISI1040 medium carbon steel. Microstructure of the free surface and segment underside the chips are experimentally characterised via scanning electron microscopy (SEM) and white light interferometry. The mechanism of chip formation is classified into continuous, partially segmented, segmented and discontinuous. Chip breaking ability are achieved for all tested feed speeds at depth of cut above 1.2 mm, marking the transition from continuous to segmented chips. The chip breaker manufactured via a nanosecond laser, proves to enable for the first time breaking of the chip below a feed rate of 0.1 mm/rev outperforming the commercial cutter and showing viability for the production capabilities of lasers for mass manufacture. Lamellae-type chips are revealed from machining using the lasered tool; while brush-stroke chips are discovered and introduced for the first time from machining using the benchmark cutter. While the lamellae form from cleavage cracks due to strain incompatibility at inclusions caused by an excess in critical shear strain. The brush-stroke chips are caused by a localized increase of temperature at the tool/material interface which lead to thermal softening of the workpiece: the resulting surface experiences large areas of plastic deformation. For the in-house lasered tool, at higher cutting speed the shear strain hardening reduces the flow stress of the workpiece material in the shear zone.</div

Laser finishing of polycrystalline diamond as strengthening mechanism

Polycrystalline diamonds are widely used in the cutting tool industry for machining of aluminium alloy and metal matrix composites as they exhibit superior wear resistance. However, their wear characteristics are dependent on their microstructural features (i.e. percentage of binder phase and size of grains) which are defined during the sintering process. Low-energy fibre laser process of polycrystalline diamond composites with different grain dimensions is proposed to promote microstructural changes, enhance their hardness, and retain surface finish. Specimens were processed with a nanosecond pulsed fibre laser (ytterbium-doped) at a wavelength of 1064 nm. Samples treated at various fluences, beam speeds and pulse durations were characterised via 3D interferometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and microindentation hardness test. At a fluence below the composite’s ablation threshold (i.e. 20 J cm 2), the investigated finishing/polishing process for a coarse grain polycrystalline diamond resulted in a change of diamond grain size, a surface integrity of 140 nm and increased micro hardness (i.e. 240 GPa). The laser treatment caused plastic deformation of the grains, changing the intergranular boundaries area therefore impeding dislocation movements and enhancing hardness.</div

Effect of laser micro-texturing on the performance of a polycrystalline boron nitride [Powerpoint]

Polycrystalline boron nitride cutting tools are widely used for hard-part steel turning due to their high wear resistance and long durability, however the issue of adhesion of workpiece to the cutting tool significantly affects the cutting tool lifetime. Using a nanosecond fibre laser surface texturing of a polycrystalline boron nitride single point cutting tool is proposed to improve its wear properties and extend tool life in turning of continuous AISI L2 hardened steel components. The textures, with topographical features’ depths and pitch ranging from tens of nanometers to tens of micrometers, were first milled using a fibre laser (1064-nm wavelength) at different fluences, feed speeds and pulse durations, and finally characterised using a combination of optical microscopy and an Alicona 3D high resolution optical microscopy. The effect of different textures on the wear properties was investigated in turning tests under dry conditions and compared to a benchmark cutting tool made of the same material. The tests were stopped every 6 passes and the wear analysed. The online monitoring and postprocessing of the cutting forces and the microscopical characterisation of the tested cutting tools allowed the evaluation of the effects of texture design on the wear progression. For textures depths in the order of 1.7 μm and post process roughness in the order of tens of nanometers, a reduction of cutting force and a decreased flank wear were achieved in dry turning

Enhanced wear performance of laser machined tools in dry turning of hardened steels

Polycrystalline boron nitride cutting tools are currently used for precision machining of automotive components made of hardened steel due to their high wear resistance and long durability, however adhesion of workpiece to the cutting tool can reduce cutting tool lifetime. Laser surface engineering of polycrystalline boron nitride single point cutting tools using a nanosecond fibre laser is proposed to improve their wear properties and extend tool life in turning of continuous hardened steel components. The effect of different designs on the wear properties was investigated in turning tests under dry conditions and compared to benchmark cutting tools made of the same material. Condition monitoring of machining forces revealed a 20% reduction of cutting force and 30% reduction of feed force for tools with crosshatch design and grooves perpendicular to chip flow direction, when benchmarked to commercial cutting tools. The number of grooves in contact with the forming chip contributed to the creation of three distinguished interfacial secondary deformation areas. Texturing the chamfer proved to alter the dynamic of chip formation in the secondary deformation zone, while engineering the formation of laser-induced solid lubricant h-BN improved the heat dissipation rate in the secondary and tertiary deformation areas. To the best of authors’ knowledge, this paper reports for the first time the possibility of simultaneously engineer geometry and chemistry of PcBN cutting tools so to enhance their service life by up to 20%

Surface defect detection and prediction in carbide cutting tools treated by lasers

Laser surface engineering of cutting tools is used to improve the performance of cutting processes via altering the material interaction between the tool surface and workpiece. Laser processing applied to cemented carbide cutting tools can induce various thermal and mechanical surface defects including porosity, splatter, cracks, balling, spherical pores, voids, and dissociation. Those defects could be detrimental to the integrity of the tool, therefore parametric optimization is crucial to limit and control possible post-processing defects. This study aimed to identify and classify surface defects in post laser processed carbides to better understand the relationship between parameters and resultant surface integrity. A region convolutional neural network (R-CNN) was trained for identification and classification of these surface defects using scanning electron microscopy images (SEM) as inputs. The R-CNN provided a quantitative analysis of each defect with an average accuracy of 91%. Using the data from the R-CNN matched with the laser parameters, a back propagation neural network (BPNN) was trained to act as a predictive network. The network predicts the number and proportion of defects when the tool grain size, roughness and laser parameters are entered. The accuracy of this predictive network was 96.6%. The effect of individual laser parameters on the surface integrity is estimated by this method, enabling the optimization of laser processing in cutting tools. For the first time this can be used to predict tool performance based on tool’s surface integrity.</p

Crack identification in tungsten carbide using image processing techniques

Laser processing of cutting tool materials particularly cemented carbides can induce many surface defects including porosity, balling, and micro-cracks. When present in the microstructure of cutting tools, micro-cracks can lead to chipping and early failure. The detection and identification of cracks can be used to predict tool performance post laser processing. To develop a method for crack identification scanning electron microscopy (SEM) images were used. The manual review of SEM images is subjective and time consuming. This study presents a method to identify and quantify cracks from an SEM microstructure of tungsten carbide (WC) in MATLAB. Image processing algorithms were used to segment crack regions from other surface defects and the background microstructure; and subsequently to extract crack geometry and information. The results show successful segmentation of cracks from SEM images with an identification accuracy greater than 95 % across a range of different laser processing parameters