Chip Formation Mechanism Research Articles

Chip Formation and Orthogonal Cutting Optimisation of Unidirectional Carbon Fibre Composites.

This study presents a thorough experimental investigation utilising the design of experiments and analysis of variance (ANOVA) to examine the impact of machining process parameters on chip formation mechanisms, machining forces, workpiece surface integrity, and damage resulting from the orthogonal cutting of unidirectional CFRP. The study identified the mechanisms behind chip formation and found it to significantly impact the workpiece orientation of fibre and the tool's cutting angle, resulting in increased fibre bounceback at larger fibre orientation angles and when using smaller rake angle tools. Increasing the depth of cut and fibre orientation angle results in an increased damage depth, while using higher rake angles reduces it. An analytical model based on response surface analysis for predicting machining forces, damage, surface roughness, and bounceback was also developed. The ANOVA results indicate that fibre orientation is the most significant factor in machining CFRP, while cutting speed is insignificant. Increasing fibre orientation angle and depth leads to deeper damage, while larger tool rake angles reduce damage. Machining workpieces with 0° fibre orientation angle results in the least subsurface damage, and surface roughness is unaffected by the tool rake angle for fibre orientations between 0° to 90° but worsens for angles greater than 90°. Optimisation of cutting parameters was subsequently carried out to improve machined workpiece surface quality and reduce forces. The experimental results showed that negative rake angle and cutting at moderately low speeds (366 mm/min) are the optimal conditions for machining laminates with a fibre angle of θ = 45°. On the other hand, for composite materials with fibre angles of θ = 90° and θ = 135°, it is recommended to use a high positive rake angle and cutting speeds.

Serrated chip characteristics and formation mechanism in high-speed machining of selective laser melted Ti6Al4V alloys

Serrated chip characteristics and formation mechanism in high-speed machining of selective laser melted Ti6Al4V alloys

Study on nanometer cutting mechanism of single crystal silicon at different temperatures

Thermal-assisted single point diamond turning technology is currently one of the most important methods for realizing nano-scale machining. However, the nano-chip formation mechanism as the core of the nano-cutting mechanism is still unclear, which limits the development of this advanced technology. In this study, based on the molecular dynamics simulations, the nano cutting behaviour of single crystal silicon at different temperatures were studied. The cutting force, crystal structure, particle motion characteristics, stress-strain distribution and temperature distribution during chip formation process were systematically analyzed. The underlying mechanism of nano-chip formation in single crystal silicon was summarized. The results showed that the chip formation mechanism can be divided into two types: crack and shear. At low temperatures, chips are formed by crack propagation. The concentrated distribution of high stress triaxiality and local high temperatures at the crack tip are the main causes of crack propagation. With an increase in temperature, the chip formation mode gradually changed from crack to shear. The highly resolved shear stress distributed along the slip plane is the main reason for the expansion of the amorphous bands. In addition, it's found that higher quality machined surfaces can be obtained through chip formation process by shear than by crack.

An experimental and numerical study on the wear mechanism of cutters on workover bits under thermo-mechanical coupling

The workover bit is the core tool for removing mental junk in the wellbore and determining construction efficiency. In order to solve technical bottlenecks of slow footage and fast wear, a thermo-mechanical coupling analytical model of cutter on workover bit was proposed based on the principle of the heat source method, which clarified the quantitative relationship between temperature, structure, and physical parameters. Also, a thermo-mechanical coupling 3D numerical model of cutter was proposed by the penetration contact algorithm of temperature-displacement coupling, which revealed the chip formation mechanism and distribution characteristics of high-temperature areas. Besides, as the severe conditions of insufficient cooling of workover bits, the non-cooling milling experiment of the workover bit with single cutter was carried out. Then the wear morphology characteristics and wear mechanism under the action of thermo-mechanical coupling were explored. The results show that the temperature error of the thermo-mechanical coupling numerical model of cutter is within 13.0%, which meets the accuracy requirements of basic engineering analysis. Under the action of thermo-mechanical coupling, the workover bit produces roll-shaped chips with a curvature radius of 2.03 mm. The high-temperature area of cutter is distributed on the outside of the cutting edge. In the meanwhile, the temperature on the rake face of cutters has the fastest increase and the highest temperature, and the highest temperature can reach 541.6 °C. The wear mechanism of cutter can be divided into four stages: gradual indentation stage, mechanical wear stage, bond wear stage, and high-temperature oxidation stage. When milling continuously for 5 min, the wear volume of the cutter reaches 0.51 mm3, and controlling temperature is the key to reducing the wear of the cutter. This research can provide theoretical guidance and a scientific basis for revealing the wear mechanism and prolonging the service life of workover bits.

Frictional Damage Mechanism for Matrix Failure in Cutting Unidirectional CFRP

Abstract In machining carbon fiber–reinforced polymer (CFRP) materials of different fiber orientations, the uncut material fracture occurs at different chip formation angles owing to either the fiber-dominated failure or matrix failure. For the matrix failure mode, it is found that the cracks in the damaged material can still affect the chip formation by providing additional Coulomb friction on the closed crack surfaces. To investigate the effect of the damage state of the matrix on the chip formation mechanism, this paper proposes a new cutting mechanics model for CFRP, by attributing the increase of the matrix shear strength to the Coulomb friction on the closed fracture surface. The frictional damage of matrix material, including damage initiation, propagation, and complete failure, is considered to provide a physical explanation for the increase of matrix shear strength and prove that the damaged matrix still influences the chip formation after complete failure. The proposed model determines the transition of chip formation mode, the variation of chip formation angle, and the cutting forces with the fiber orientation, considering the friction in the damaged area and the elastic stress in the undamaged area. According to the comparison with the models which do not consider the material damage state and attribute the increase of shear strength to the “internal friction” without a physical explanation, it is found that the proposed frictional damage model is able to capture the matrix failure in chip formation in the fiber orientation of [0deg,66deg] and [90deg,180deg] and explains the change of chip formation mechanism from matrix compression failure to fiber tension failure in the fiber orientation range of [67deg,89deg]. The necessity of considering the friction on the fractured surfaces in the machining process of CFRP is experimentally validated by cutting experiments at various fiber orientations.

Influence of Size Effect in Milling of a Single-Crystal Nickel-Based Superalloy

This paper details an experimental investigation on the influence of the size effect when slot-milling a CMSX-4 single-crystal nickel-based superalloy using 1 mm- and 4 mm-diameter TiAlN-coated tungsten carbide (WC) end-mills. With all tools having similar cutting-edge radii (re) of ~6 µm, the feed rate was varied between 25-250 mm/min while the cutting speed and axial depth of cut were kept constant at 126 m/min and 100 µm, respectively. Tests involving the Ø 4 mm end-mills exhibited a considerable elevation in specific cutting forces exceeding 500 GPa, as well as irregular chip morphology and a significant increase in burr size, when operating at the lowest feed rate of 25 mm/min. Correspondingly for the Ø 1 mm micro-end-mills, high levels of specific cutting forces up to ~1000 GPa together with severe material ploughing and grooving at the base of the machined slots were observed. This suggests the prevalence of the size effect in the chip formation mechanism as feed per tooth/uncut chip thickness decreases. The minimum uncut chip thickness (hmin) when micromilling was subsequently estimated to be less than 0.10 re, while this increased to between 0.10-0.42 re when machining with the larger Ø 4 mm tools.

The effects of cryogenic cooling on tool wear and chip morphology in turning of tantalum-tungsten alloys Ta-2.5W

Tantalum‑tungsten alloy is particularly difficult to cut due to its high plasticity. Environmentally friendly liquid nitrogen cooling and hybrid minimum quantity of lubricant-low temperature CO2 (MQL + CO2) technology can improve the machinability of ductile materials. In this paper, the experimental and numerical turning of tantalum‑tungsten alloy Ta-2.5W were carried out under cryogenic cooling conditions. The effects of liquid nitrogen cooling and MQL + CO2 cooling on the wear mechanism of cutting tools and the formation mechanism of chips were studied. The Rehbinder effect induced by the surfactant in MQL + CO2 system was analyzed. The results show that the cutting tool life can be effectively improved by 50 % in turning of Ta-2.5W under both cryogenic cooling conditions. Different from the flank wear dominated by adhesive wear under water-based emulsified cutting fluid, the tool failure was mainly caused by the notch wear under cryogenic cooling conditions. The chips in turning of high plastic Ta-2.5W showed a “pomelo-meat shaped” morphology with non-uniformed and non-periodic folds. Rehbinder effect was induced by the surfactant in MQL + CO2 system, which transformed the “pomelo-meat shaped” chips into “layered-rock shaped” chips. Under this effect, the machinability of tantalum‑tungsten alloy was effectively improved with a reduction of chip thickness and increment of the tool life.

Towards understanding the mechanism of vibration-assisted cutting of monocrystalline silicon by cyclic nanoindentation

Ultrasonic vibration cutting (UVC) is a promising technology that can promote the processing of hard-brittle materials in ductile mode. The feature of intermittent cutting in UVC is considered to promote the ductile responses of brittle materials. However, the effect of cyclic loading/impact on microscopic deformation behavior of the workpiece material in UVC is not clearly understood. This study used cyclic nanoindentation to reveal the UVC mechanism in monocrystalline silicon (Si). The surface morphology and subsurface microstructure of the residual indents were characterized and compared with those of the UVC-machined grooves. This work attempted to correlate the tool-workpiece contacts for cyclic nanoindentation and vibration cutting. Cyclic nanoindentation results show that cyclic loading promotes the extent of silicon amorphization and decreases the threshold for transitioning the β–Sn phase to the bc8 and r8 phases. As the number of indentation cycles increases, the subsurface microstructure changes from the amorphous phase to the bc8 and r8 phases. In UVC, both the critical cutting depth for brittle-to-ductile transition and the degree of amorphization in cutting chips increase in comparison to conventional cutting, which matches the trend of cyclic nanoindentation results. The findings inform the chip formation and subsurface deformation mechanisms of brittle materials during UVC.

A real-time cutting temperature monitoring of tool in peripheral milling based on wireless transmission

In the milling process, the milling heat generated by the interaction between the tool, the workpiece, and the chips has a significant impact on the chip formation mechanism, tool wear mechanism, tool life, surface quality and so on. Therefore, it is of great significance to explore the heat and temperature distribution in milling. In the method of measuring temperature distribution, continuous measurement of transient temperature is the main method to study the temperature change during the rotation of the tool. During the rotation of the tool, the conventional temperature measurement method will cause stranding due to the linkage of the tool and the worktable, and cannot achieve continuous temperature measurement during the rotation. Therefore, the continuous measurement technology of tool transient temperature based on wireless transmission has been widely used, such as Bluetooth, wifi, radio frequency and so on. However, the current continuous measurement technology of tool transient temperature based on wireless transmission usually cannot provide sufficient bandwidth (low sampling rate). In order to narrow this gap, a high sampling rate continuous tool transient temperature measurement platform is needed to develop. Therefore, the milling temperature of the peripheral milling tool is studied from two aspects: theoretical research and experimental verification. The specific research process is: take the milling tool (insert) as the research object, and elaborate on the milling temperature from several aspects such as temperature field modeling and transient temperature continuous measurement key technology, experimental research, and influencing factors. Manual thermocouple and wireless transmission technology continuously measure the transient temperature of tool peripheral milling with high sampling rate. A real-time temperature monitoring of tool in peripheral milling based on wireless transmission is verified in the paper.

Tough-brittle transition mechanism and specific cutting energy analysis during cryogenic machining of Ti–6Al–4V alloy

Reducing the cutting energy consumption in machining is important to improve the sustainability of cryogenic machining. Currently, the analysis of cutting energy for cryogenic machining mostly relies on equipment testing, while less research has been conducted on energy analysis based on material removal mechanisms. In this paper, the chip formation mechanism of cryogenic machining is studied on the basis of liquid nitrogen orthogonal milling experiments with Ti–6Al–4V alloy, and the corresponding specific cutting energy model is established. First, the effects of cooling conditions and process parameters on chip microscopic morphology were analyzed based on orthogonal milling experiments. Next, a specific cutting energy model was established according to the chip formation mechanism. Finally, the reliability of the model was verified by cutting forces. The results show that in cryogenic machining, when the cutting speed is less than 200 m/min, adiabatic shear dominates the formation of serrated chips, and the cutting energy consumption is higher than that of dry cutting. As the cutting speed exceeds 200 m/min, adiabatic shear and periodic fracture together dominate the formation of serrated chips, and the energy consumption of cutting is significantly reduced at this time. This research provides a reference and guidance for the sustainable development of cryogenic machining.

Formation Mechanism of Novel Chips and Application Research in Biochemistry

It is crucial to systematically study the interaction between samples and components at different concentrations in biochemical analysis. Microfluidic chip technology can complete precise liquid control in micron-scale channels and has been widely used in the biochemical analysis in recent years. The microfluidic concentration gradient chip is a tool that can rapidly construct a stable biochemical concentration gradient, which can be combined with most cell culture, chemical analysis, and other technologies to provide a new platform for traditional biochemical analysis. This paper reviews the formation mechanism of microfluidic concentration gradient chips and their applications in biochemistry and other fields and provides new ideas for broadening the application research of concentration gradients.

Experimental study and smoothed particle hydrodynamics simulation of synthetic diamond grit scratching on steel

Superabrasives like synthetic diamonds are indispensable in today’s construction industry, particularly for core drilling applications in reinforced concrete. The increase of the cutting efficiency of such core bits strongly depends on the material removal behavior of single diamond grains placed in a diamond segment acting as cutting elements. Therefore, this paper presents a newly developed experimental setup for a 3-mm single diamond grain scratch test, as well as the application of a Smoothed Particle Hydrodynamics (SPH) method to model single diamond grains scratching a rebar base material at operational parameters. Diamonds in two main different crystallographic and geometric orientations are tested and investigated with respect to their forces and temperatures at the cutting edge. Furthermore, the chip formation and different material removal mechanisms are analyzed for each orientation and compared with the model output. Validation tests and sensitivity analyses are performed in 3D and high resolution, thanks to the runtime acceleration of SPH through parallel computing on the graphics card. The results indicate: 1) A significantly different material removal behavior as a result of changing the diamond orientation; 2) The capability and high efficiency of SPH for modeling single grain scratch tests.

Experiment and numerical study of chip formation mechanism during cryogenic machining of Ti-6Al-4V alloy

The chip formation mechanism is a key factor in determining cutting stability and machined surface integrity. At present, the research on chip formation mechanism is mainly focused on conventional machining, while there is less research related to liquid nitrogen cooling conditions. In this paper, the chip formation mechanism of cryogenic machining is investigated based on the combination of liquid nitrogen external cooling milling experiments and cutting simulation with Ti-6Al-4V alloy as the research object. Firstly, the effect of cooling conditions and cutting speed on the degree of chip serration and chip micromorphology was analyzed based on orthogonal milling experiments. Next, the temperature and strain rate during chip formation were calculated and analyzed by simulation modeling. Finally, the formation of serrated chips under liquid nitrogen cooling conditions was modeled. The results show that the degree of chip serration increases under liquid nitrogen cooling conditions, and adiabatic shear and brittle cracking jointly dominate the formation of serrated chips. This research provides a reference and guidance for chip control in cryogenic machining processes.

Investigations on chip formation mechanism and surface integrity analysis in LAM of 45%SiCp/Al composites

Investigations on chip formation mechanism and surface integrity analysis in LAM of 45%SiCp/Al composites

Study on mechanism of chip formation of grinding plasma-sprayed alumina ceramic coating

The mechanisms of ductile–brittle transition and surface/subsurface crack damage during the grinding of plasma–sprayed alumina ceramic coatings were investigated in an experiment and simulation on single diamond abrasive grain cutting. We observed that the brittle damage modes of alumina ceramic include boundary cracks, median cracks and lateral fractures. The normal force of the abrasive grain results in the initiation of median cracks, whereas the tangential force of the abrasive grain results in the propagation of median cracks in the direction of the abrasive grain cutting. Some cracks propagate downward to form machined surface cracks, whereas others propagate to the unmachined surface of the workpiece to produce brittle removal. Owing to the alternating tensile and compressive stresses, the material in contact with the top of the abrasive grain fractures continuously, forming the main morphology of the machined surface. The geometry and cutting depth of the abrasive grain have a significant influence on the ductile–brittle transition, whereas the cutting speed of the abrasive grain have no significant influence. On one hand, the stress concentration at the pore defects result in crack propagation to the deep layer; on the other hand, it reduces the local strength of the surface material, produces brittle fracturing, and interrupts crack propagation. The pores exposed on the machined surface and the broken morphology around them are important factors for reducing the surface roughness. Experimental observations show that the machined surface morphology of the alumina ceramic coating is composed of brittle fracturing, ductile cutting and plowing, cracks, original pores, and unmelted particles.

Predictive model of chip segmentation in machining of high-strength metallic alloys

Chip segmentation is the dominant chip formation mechanism during the machining of high-strength metallic alloys which directly affects the machining productivity and the final product’s quality. This paper investigates the mechanism of shear band formation and its contact with the cutting tool for different titanium and nickel alloys. First, we reveal that the shear bands are in direct contact with the cutting tool due to rolling on its rake face, although the contact mechanism is different for titanium and nickel alloys. In addition, the effect of the stored energy at the tool-chip interface, which is believed to be the reason for chip segmentation in some studies, is investigated theoretically. We found that the stored energy at the tool-chip interface affects the strain rate temporarily and has minimal impact on the chip segmentation. Moreover, we provide a theoretical prediction of the workpiece material’s displacement, its distribution, and degree of segmentation for the first time without any post-mortem analysis of the produced shear bands. To this end, the rolling process must be taken into account for accurate prediction. We show that the segmented chip’s displacement can be accurately predicted without any fracture criterion since the shear band itself is a type of ductile material failure. It is shown that the shear bands can accommodate large strains (for example, around 45 when cutting Ti-6Al-4V at 60 m min−1 cutting speed) without fracture presumption.

Chip profile studies on SiC reinforced mono and SiC and graphite reinforced hybrid ZA43 MMCs

ABSTRACT This paper depicts an experimental model for investigating the mechanism and nature of chip formation during the machining of Zinc-Aluminium alloy-based SiC reinforced mono and SIC and graphite reinforced hybrid metal matrix composites. The stir casting process is followed for the fabrication of both categories of composites. The morphology of the fabricated specimen tells the uniform distribution of reinforcing particles. Machining trials are done on mono and hybrid composites using coated carbide tool. The chips produced during the machining process are carefully collected and examined for their nature and shape. It is concluded that mono composite materials show lengthier chips than hybrid composite materials. The machining parameters and material composition influence the chip formation process. Due to retained ductility in the mono composites, lengthier chips are produced and hybrid composite being more brittle than mono composite material produces short segmental chips.

The effect of interstitial fluid on the machining behaviour of cortical bone

Bone machining research is usually conducted ex-vivo with standard laboratory equipment, implying mostly that the cutting process takes place in dry state. While these studies are useful for understanding the bone cutting process, they cannot represent the real clinical cutting condition due to the disregard of internal irrigation (i.e., interstitial fluid and blood within the tissue’s vascular porosities). As bone possesses ca. 20 % water, internal irrigation can influence the bone’s properties (e.g., shear strength, friction coefficient) and alter the cutting mechanism and surface deformation (e.g., crack formation, smearing). Hence, to study the ex-vivo bone cutting process in an internally irrigated state, a novel machining and pumping setup is proposed here, which enables a scenario closer to a surgical condition than the traditional dry machining method. Cutting tests demonstrated that portions of bone near the fluid-filled porosities possess shear strength and friction coefficient gradients due to the bone’s permeability. This resulted in machining forces and necrosis up to 52 % and 55 % lower than in dry bone, respectively. A cutting forces model was developed considering the internal irrigation condition and the randomness and anisotropy of the tissue. Moreover, it was found that internal irrigation can change the chip formation mechanism and induce minimised surface morphological damage due to the minimised friction between the tool and the cutting surface in near-porosity sites. This research highlights the importance of conducting bone machining research with the consideration of internal irrigation, an imperative aspect to more realistically mimic surgical scenarios in a laboratory environment.

Numerical modeling of Ti-6Al-4V alloy orthogonal cutting considering microstructure dependent work hardening and energy density-based failure behaviors

Numerical modeling of the cutting process provides an effective method to obtain the micro-scale and instantaneous process information which is difficult to be measured by experiments. A new microstructure (grain size) dependent work hardening plastic (JCM-ms) model was developed to characterize the effect of grain refinement on the cutting process. An energy density-based failure law was applied to control the chip formation and material removal mechanisms ahead of the cutting edge. Orthogonal cutting experiments with different edge radii and uncut chip thickness values for Ti-6Al-4V alloy were carried out to validate the finite element (FE) simulation results. The simulation results were thoroughly validated by the measured principal and thrust forces, segmented chip morphology, and the grain refinement within the machined surface layer. The distribution of grain refinement of the chips and machined surface agreed well with the experimental results. The positions of stagnation points with different edge radii and uncut chip thickness values were measured by the FE simulation results. The variation of surface morphology along the speed direction with larger edge radius is related to the variation of the stagnation points, which will affect the ratio of material being compressed to the machined surface by the tool, during the formation of the adiabatic shear band. The degree of the subsurface shear deformation determines the final distribution of the micro-hardness. Larger shear displacement at the top surface will lead to thicker layer of grain refinement. Residual stresses along the depth from machined surface are mainly related to the displacement normal to the machined surface. The height of the stagnation point is in proportion to the peak compressive stresses induced by the material flow ahead of cutting edge for different conditions. This work provides an effective method to characterize the forces, grain refinement and surface integrity for the orthogonal cutting of Ti-6Al-4V alloy.

A study investigating the cutting mechanism of compacted graphite iron based on a novel microstructure of finite element model

Compacted graphite iron is internationally recognized as a material that has the potential to be applied for preparing high performance engine components. However, difficulties during machinability seriously limit the mass production of these. A novel method based on MATLAB image recognition and python programing was used to establish a microstructural model that included graphite and pearlite particles. The thermal conductivity and specific heat capacity at different temperatures was measured and the results were used to validate the model. Using this novel model, the chip morphology and formation mechanism, cutting surface morphology and formation mechanism and cutting temperature distribution were studied. The simulation results show that crack formation on the chip surface and generation of graphite fragments occurs during the cutting process. The crack opening angle during this is approximately 33°. Significant graphite cavities also appeared on the cutting surface. The stress concentration at the boundary of graphite and pearlite during cutting process was analyzed, and demonstrated to be the primary reason for these phenomena. The temperature of both the rake face and flank face are simulated with the highest cutting temperature concentrated in the secondary deformation zone reaching approximately 322 °C. Furthermore, the simulation results are consistent with the experimental results.