Chip Breaking Research Articles

Three-dimensional multi-physical modelling of the influence of the cutting fluid on the chip formation process

In today’s manufacturing, cutting fluid systems are widely used in modern machine tools to improve the process performance. The influence of cutting fluids on the specific cutting force components as well as the resulting heat distribution is a complicated physical phenomenon, which is difficult to experimentally investigate due to the restricted optical accessibility in the machining process. To better understand the working principle of the cutting fluid system, a three-dimensional fluid-structure interaction simulation approach for orthogonal cutting processes was developed in this work. The simulation approach overcomes the underestimation of the fluid velocity perpendicular to the cutting direction in conventional two-dimensional simulations and allows a more accurate resolution of the flow behavior in the cutting zone. This method provides a detailed investigation of the mechanical effect of the coolant jet on the chip formation process. To evaluate the simulation results, orthogonal cutting experiments were conducted on a lathe under both wet and dry conditions. The comparison of chip shapes between simulation and experiment shows that the three-dimensional model can accurately predict cutting fluid induced chip breakage. Furthermore, the simulative investigation showed that chip formation is strongly dependent on the orientation of the nozzle jet. This result provides first findings for improving chip removal by varying the coolant supply parameters.

Effect of cutting parameters and high-pressure coolant on forces, surface roughness and tool life in turning AISI 1045 steel

Abstract The machining industries constantly look for novel techniques to decrease the forces generated in metal cutting, enhance the tool life and improve the surface quality. High-pressure coolant delivery is one such technique that is believed to enhance the overall machining process with its superior cooling capabilities. Hence, an investigation was made to compare the behavior of a turning tool in machining AISI 1045 steel material under conventional coolant (CC) and high-pressure coolant (HPC) conditions. The influence of applying coolant at high pressure on forces and surface finish was measured at various cutting speeds and feeds, and tool life analysis was performed at a constant cutting parameter. The study reveals that a 12–23% reduction in cutting force, a 17–27% reduction in feed force, and a 14–33% reduction in surface roughness values can be obtained when a high-pressure coolant is used. Besides, around 40% improvement in tool life was also seen. The capability of the coolant in the effective removal of heat from the tool-chip interface zone, decrease in frictional forces between the tool and work material, and superior chip breaking capabilities at high-pressure conditions are attributed to the performance improvement.

Novel chip-breaking structure of step drill for drilling damage reduction on CFRP/Al stack

Abstract CFRP/Al stacks are popular for aerospace structures which require one-shot drilling thousands of stack holes within strict damage tolerance. However, CFRP is susceptible to cutting damages; the evacuation of Al chips through the upper CFRP may also cause unexpected damages even with a preferable step drill bit, of which second step faces the challenge of breaking chips due to its space and cutting angle limitations. This article proposes a novel structure on the second step of a step drill bit to effectively break the Al chips and reduce the chip-induced damage in one-shot drilling of CFRP/Al stack. The cutting chip generation/motion of the second step is analyzed, and it is found that adding a block surface beside the rake surface to restrain the side-curl of the chips could increase the surface strain of the chip and possibly break it. More importantly, the block surface is an additional structure beside the secondary cutting edge, which will neither affect its cutting angle nor be limited by space. Then a novel chip breaking structure based on the block surface is invented at the inner side on the rake surface of the secondary cutting edge. Comparative experiments are carried out for one-shot drilling of CFRP/Al, and the interactions between chips and CFRP/Al are revealed. With the novel structure, effective Al chip breaking and significant improvement of CFRP drilling quality are achieved.

Análise das superfícies de saída e de folga de ferramentas de corte empregadas no torneamento de ferro fundido cinzento perlítico com diferentes adições de nióbio

Cast iron corresponds to the second most used metallic material worldwide. However, its production has shown reductions, mainly due to the development of lighter materials. In this sense, metallurgical efforts have been made to add elements to obtain different solid solutions that would lead to the improvement and guarantee of the diversity of this alloy. However, modifications of any kind to the properties of a material have an impact on its machinability. Thus, this work aimed to evaluate the influence of the addition of niobium (0.21-0.24% by weight) in a pearlitic gray cast iron alloy (equivalent to the EN-GJL-250 class) on the wear of the tools of cemented carbide (class K20) during the turning. The wear on the rake and clearance surfaces was qualitatively evaluated via scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDS). Together, the chemical composition variation occurred with the chip breaker geometry: tools with chip breaker (GH) or without chip breaker (Flat Top). All these variations were indifferent in relation to the wear of the tools and their mechanisms. Regardless of the chemical composition, material of the machined part was found adhered to both the rake surface and the clearance of all cutting tools. In addition, grooves were found in the flank, suggesting the abrasion mechanism.

Enhancement of chip breakability of aluminium alloys by controlling the solidification during direct chill casting

Refinement and uniform dispersion of the free machining elements within the matrix is always desirable for aluminium billets produced by direct chill (DC) casting. The conventional grain refiner addition cannot ensure uniformity of microstructure and homogeneous distribution of insoluble or intermetallic phases. Melt conditioned direct-chill (MC-DC) casting is a key technology for producing uniform microstructure and refinement of secondary phases. This physical approach combines conventional vertical direct chill (DC) casting with a high shear device directly immersed in the sump for in situ microstructural control. Increased heat extraction rate due to forced convection, a larger temperature gradient at the solidification front and a shallower sump contribute to fine equiaxed dendritic grains with fine dendritic arm spacing that favor the fine and uniform distribution of second phase particles in the as-cast billet. This trend of the microstructural features was preserved even after thermomechanical downstream processing, giving rise to much improved machinability for the extruded solid bars.

Performance analysis of micro textured cutting insert design parameters on machining of Al-MMC in turning process

Turning operation is one of the primary machining operations and enhanced machining performance is obtained by its process parameters. In turning process, heat is generated and it must be removed from the machining zone. Now a days, hydrocarbon oil based cutting fluid is used and it generates environmental issues as well as operator health issues. Recently, textured cutting tool inserts are attempted towards sustainable machining. In this work, turning process is carried out on aluminium-metal matrix composite (Al-MMC) with micro hole textured cutting tool inserts. Micro hole texturing involves various parameters such as hole diameter, hole depth and pitch between the holes. The main aim of this work is to analyze the effect of micro hole design parameters on machining performance. The input parameters include diameter of the micro hole, pitch between hole and hole and depth. Process outcomes include surface roughness, tool wear and power consumption. The experiments are performed based on L9 Taguchi orthogonal array. The result revealed that micro hole textured tools with solid lubricant embedded cutting inserts and its design parameters influence machining performance. Texture with solid lubricant could act as alternative to hydrocarbon oil based cutting fluid and also chip breaker.

Influence of dynamic angles and cutting strain on chip morphology and cutting forces during titanium alloy Ti-6Al-4 V vibration-assisted drilling

Vibration-assisted machining (VAM) is implemented in titanium alloy processing to solve some challenges, such as difficulty in chip breaking, large cutting forces, and high cutting temperatures. Based on the multi-region dynamic angles and the double-side wedge angle deformation mechanism, this study improves the vibration-assisted drilling (VAD) cutting forces and chip breaking model. The dynamic kinematics angles, the behavior of parameter influence, and the cutting strain effect of intermittent VAM are analyzed. VAD and conventional drilling (CD) experiments are carried out for model validation and mechanism analysis. The experiments show that the maximum deviation of the drilling forces simulation value and the experimental value is 9.13 %. Compared with the CD, the cutting force of the VAD is decreased by 10.1 %–46.2 %. The dynamic feed angle causes multiple cutting angles fluctuations, which affects cutting performance. The adjustment of the VAD cutting parameter value could reduce the chip length by 26.6 %–43.9 %. Material cutting strain presents multi-region characteristic, which influences the chip morphology. This study provides a reference for VAM parameter optimization.

Influence of cryogenic cooling on milling hole exit of QFRP based on thermal–mechanical coupling

Quartz fiber–reinforced polyimide composites (QFRP) had heterogeneous and anisotropic properties. Because of the gradient change of cutting force at hole exit, some fibers could not be effectively chipping breaking and the defect of delamination burr was often inevitable. In this paper, a cutting force model of fiber fracture stripping considering thermal–mechanical coupling was constructed based on the mechanism of cutting force and thermal action. A series of milling hole tests at different temperatures (from 290 to 80 K) was carried out using liquid nitrogen inner-cooling equipment. Similarly, the hole exit morphology, milling force, and cutting temperature were investigated and the delamination factors were calculated in detail. The results show that the model can explain the reason of hole exit defect, which is attributed to the lack of tangential cutting force and the large gradient change of axial force considering the high cutting temperature. Meanwhile, cryogenic cooling can reduce the effect of cutting temperature for hole exit defect. Although the cutting force is increased, the gradient degree of axial force can be reduced, and the delamination factor can be decreased from 1.08 at low-speed dry cutting to 1.01 of high-speed cryogenic one. At the same time, the increase of tangential force and the decrease of fiber ductility improve the chip breaking ability and the processing efficiency. Conclusion: the spiral hole milling process with cryogenic medium intervention can inhibit the milling hole delamination defects.

Application of Environmentally-friendly Cooling/Lubrication Strategies for Turning Magnesium/SiC MMCs

The material having high strength to weight ratio is constantly in high demand for automotive industries to increase fuel efficiency. With this view, AZ91/5SiC (an Mg-based Particulate Metal Matrix Composites (PMMCs)) is fabricated using an in-house developed stir casting setup and characterized through Field Emission Scanning Electron Microscopy (FESEM) with Energy-Dispersive X-ray Spectroscopy (EDS) analysis. However, the machinability of PMMCs is found to be lower due to the existence of harder ceramic constituents and appropriate cutting fluid strategies are required to follow to combat this situation. But limited studies are available identifying the impact of recently developed sustainable cooling and lubrication techniques on machining performance when PMMCs is turned. To fill this bridge, customized setups of minimum quantity lubrication (MQL), cryogenic and CryoMQL machining with LN2 have been developed to provide eco-friendly cutting fluid approaches to turn AZ91/5SiC. The cutting force, energy consumption, surface roughness (Ra) and chip breakability index (Cin) have been analyzed for MQL, cryogenic and CryoMQL techniques with variation in process parameters. By considering the average value of all turning tests, 64.65% and 40.39%; and 11.49% and 7.13% higher value of cutting force and energy consumption is found correspondingly for cryogenic and CryoMQL machining respectively as compared to MQL technique respectively. Overall, 25.59% and 18.35% lower values of Ra have been observed for CryoMQL technique as compared with MQL and cryogenic machining respectively. The powder type chips with comparable higher values of Cin have been found in all three cooling and lubrication techniques.

Influence of longitudinal-torsional ultrasonic-assisted vibration on micro-hole drilling Ti-6Al-4V

As Ti-6Al-4V is a typical hard to machine material, especially in micro drilling aviation parts, chip breaking difficulty is of increasing interest to explore its further development. In this study, Longitudinal-Torsional Ultrasonic Assisted Drilling (LTUAD) was employed to machine Ti-6Al-4V, and its feasibility was evaluated by comparing with Conventional Drilling (CD). By combining periodical characteristics and vibration models (the separated or the unseparated ultrasonic elliptical vibration), the influence of ultrasonic frequency on the intersection characteristics of trajectories were analyzed. And the intersection characteristics were divided into four categories: even periodicity, odd periodicity, non-odd and even periodicity and composite periodicity, indicating different capability for chip breaking. By applying the longitudinal-torsional compound vibration horn, the micro-hole drilling experiment was carried out on machining center. The chip morphology, the thrust force, and the burr height were discussed. Experimental results showed that the morphology of chips presented as smaller and more fragmentary ones in LTUAD compared with continuous helical conical ones and fold-shaped ones in CD. Compared with CD, the average values of the thrust force in LTUAD reduced by 1.98% to 24.9%. According to the burr around the hole exit in both LTUAD and CD, the height of the latter was greatly affected by the drilling parameters. And the burr around the exit of the hole were distributed rather evenly with smaller extension in LTUAD. Consequently, the LTUAD employed in micro-hole drilling was effective.

A novel chip breaker structure of PCD tool for the reaming of 7050 aluminum alloy

The 7050 aluminum alloy is becoming more and more popular in aerospace industry, because it has good wear resistance, high strength, and high toughness while having low density. However, due to the small cutting allowance and good plastic, aluminum alloy chips are usually difficult to be broken naturally in high-speed reaming which induced the machined surface scratched. Both the tool structure and matching process parameters are the key ways to solve this problem. Different sizes of chip breaker have been analyzed by FEM simulation. Based on the FEM, three kinds of PCD reamers which have different chip breakers have been compared with the ability of chip breaking in different cutting parameters. It is found that when rotational speed is 288.8 m/min and feed rate per tooth is 0.04 mm/Z with 0.17 mm depth of chip breaker PCD reamer, the best surface quality and lowest cutting force were achieved. It is also found that the cutting force of shallow-breaker-tool (tool B) is the smallest when compared with non-breaker-tool (tool A) and deep-breaker-tool (tool C). The effect of chip breaker size on cutting force, chip curling, and surface roughness has been analyzed in both dry and wet cutting.

Chip Breaking During Automated Processing by Cutting Hard-to-Work Steels by Integrated Use of Chip Breaking Tools and High-Temperature Embrittlement

Purpose of research is to increase productivity when cutting hard-to-work steels by integrated use of chip breaking tool geometry and cutting modes, which reduce the viscous properties of the chips and the processed material. The article discusses the problems of mechanical processing of parts of oil production equipment at enterprises in Western Siberia. It is presented the main condition for ensuring chip crushing and revealed the problem of low efficiency of existing methods in modern industry, to one degree or another guiding, curling and chip-cutting method.Methods. Simulation modeling, calculation of chip direction and crushing were performed; effective methods for solving the problem of chip crushing during the machining of parts made of materials with corrosion-resistant, heat-resistant properties were identified; laboratory, persistent tests of the complex method were carried out.Results of studying the mechanism of chip formation during processing by cutting heat-resistant and corrosionresistant alloys are given here. To solve the problem, we have formulated two tasks that were solved using information taken from the theory of material resistance, tensile diagrams when testing samples of corrosionresistant, heat-resistant materials with high operational properties. A chip breaking exchangeable insert with a variable rake angle is designed and presented. The results and analysis of laboratory test data, in which a plate with chip breaking geometry of the front surface is used, are presented, the operating conditions of effective chip breaking are shown. The conclusions on the solution of the first problem are formulated, it is shown that the determining factor in chip breaking is the physical and mechanical characteristics of the processed material, which vary with different cutting conditions.Conclusion. The work shows that chip removal from the cutting zone prevents it from entering the cutting edge area, reducing impact loads on it and improving the quality of machining. It is possible to form stress concentrators in the chips, leading to chip self-destruction even when processing viscous heat-resistant alloys. The hypothesis is used that the temperature conditions for the maximum workability of heat-resistant and corrosion-resistant steels and alloys correspond to the conditions of high-temperature embrittlement, with the help of which it is possible to create conditions for effective chip crushing and conditions for maximum workability when cutting heat-resistant steels and alloys.

Reduction of Power Consumption by Chip Breakability Control in Ti6Al4V Titanium Alloy Turning.

The paper concerns the problem of energy savings in turning of titanium alloy Ti6Al4V. Since this alloy belongs to difficult to cut materials, there is a problem with chip forming and breaking. The turning process is often supported by implementing a high-pressure cooling (HPC) system. Based on the observations and the adopted chip classification method, the authors proved that it is not necessary to use this method in roughing operations, however it helps with the chips breaking process in finishing operations. A general algorithm for machining optimization due to the chip geometry is presented and described. In the presented case, it was shown that the acceptable chip geometry could be obtained with a reduced power consumption by approximately Pc = 0.5 kW. The authors concluded that it was not necessary to apply cutting data and a coolant system to achieve perfect chip geometry. An acceptable form was often sufficient, while requiring less energy. An additional factor resulting from the operation of systems supporting the cutting process, such as an HPC device, should be taken into account in the formula concerning the energy consumption (EC) of a computerized numerical control (CNC) machine tool.

Study on chip morphology and surface roughness in ultrasonically assisted drilling of 304 stainless steel

Difficulties in chip breaking and poor machined surface quality are usually considered as the main negative outcomes in conventional drilling (CD). Although researchers have attempted to solve these problems for many years by employing ultrasonic vibrations in the drilling process, studies containing both experimental and theoretical analyses are seldom reported. Based on an in-depth analysis of the kinematic characteristics of ultrasonically assisted drilling (UAD), the conditions for complete geometric chip breaking are derived. The results of the theoretical analysis are verified through a series of experiments, wherein good agreement is found between the experimental and theoretical results. The analyses reveal that UAD has obvious advantages over CD in breaking chips and improving the final surface quality. Additionally, the results show that a low feed rate and an appropriate rotational speed are favorable for chip breaking. The influences of the vibration amplitude, spindle speed, feed rate, and drill bit diameter on the surface roughness are analyzed, and the optimal processing parameters are investigated. The influences of the four factors on the surface roughness in descending order as obtained is amplitude, spindle speed, drill bit diameter, and feed rate. The optimum machining parameters are obtained as 15 μm of amplitude, 450 r/min of spindle speed, 4 mm of drill diameter and 0.08 mm/r of feed rate. Furthermore, a reliable prediction model of surface roughness is established through regression analysis. With this prediction model, the surface roughness under different processing parameters can be approximately predicted.

An Investigation on Turning of Hard Steel using Coated Carbide Inserts

Employing conventional machining operations in material removal type manufacturing processes for processing difficult-to-machine hard materials through some ways and means is the focus of research by machining research groups across the globe since long. This gives considerable advantages over the grinding process in terms of higher material removal rate, better surface integrity of the work surface, etc., although grinding is commonly used for material removal of quite hard materials along with their finishing. In this paper, machinability of hard AISI 4340 steel is explored employing groove-type chip breaking coated carbide inserts under various cutting velocity and feed at dry condition. Hardened AISI 4340 is considered to be a difficult-to-machine material, and hence, recommendable machining conditions need to be found out. Favourable flat continuous chip is acquired at a cutting velocity of 231 m/min and at a feed of 0.08 mm/rev. At 391 m/min cutting velocity, cutting edges are detected to have worn-out quite fast.

Assessment of Chip Breakability during Turning of Stainless Steels Based on Weight Distributions of Chips

Currently, the available evaluation methods for determining the chip breakability in the industry are mainly based on subjective visual assessment of the chip formation by an operator during machining or on chips that were collected after the tests. However, in many cases, these methods cannot give us accurate quantitative differences for evaluation of the chip breakability of similar steel grades and similar sets of machining parameters. Thus, more sensitive methods are required to obtain more detailed information. In this study, a new method for the objective assessment of chip breakability based on quantitative determination of the weight distribution of chips (WDC) was tested and applied during machining of stainless steels without Ca treatment (316L) and with Ca treatment (316L + Ca). The obtained results show great consistencies and the reliability of this method. By using the WDC method, significant quantitative differences were obtained by the evaluation of chips, which were collected during the machining process of these two similar grades of steel at various cutting parameters, while, visually, these chips look very similar. More specifically, it was found that the Ca treatment of steel can improve the chip breakability of 316L + Ca steel in 80% of cutting trials, since a fraction of small light chips (Type I) from this steel increased and a fraction of large heavy chips (Type III) decreased accordingly. Moreover, the WDCs that were obtained at different cutting parameters were determined and compared in this study. The obtained results can be used for the optimization of chip breakability of each steel at different cutting parameters. The positive effect of Ca treatment of stainless steel was discussed in this study based on consideration of the modification of different non-metallic inclusions and their effect on the chip breakability during machining.

Control and Mechanism Analysis of Serrated Chip Formation in High Speed Machining of Aluminum Alloy 7050-T7451

Aluminum alloy 7050-T7451 is widely used in aeronautical large structural parts, and high speed cutting is often used in machining. The serrated chip is a critical state for chip formation in high speed cutting, and its formation and control mechanism are of great significance for actual machining. To study the chip formation of high speed cutting aluminum alloy 7050-T7451, the chips at different cutting speeds are obtained by high speed cutting experiments. Combined with microscopic observation, the chip shape evolution, chip localization fracture process and mechanism of different cutting speeds are analyzed. The morphological evolution of chips and the mechanism of chip breaking during high speed cutting of aluminum alloy are revealed. According to the machined surface of the chip root and the angle of the chip, the formation mechanism of the curl radius formed by the chip is analyzed. The critical cutting speed of plastic-brittle transformation of aluminum alloy 7050-T7451 in high speed cutting is obtained by studying the critical condition for strip-to-serration transition of chip morphology.

Experimental Research on Turning of Superalloy GH4169 under High Pressure Cooling Condition

Superalloy GH4169 possesses excellent high temperature strength, thermal stability, and thermal fatigue, and is widely used in aerospace and other fields. However, it is a typical difficult-to-cut material owing to its poor thermal conductivity, high plastic toughness, severe workpiece hardening, and difficult chip breaking. In this study, high pressure cooling was used for GH4169 cutting test. The effects of high pressure cooling on the cutting force, chip morphology, and tool wear were analyzed, which can provide technical support to achieve high efficiency turning of GH4169.

3D FEM simulation of chip breakage in turning AISI1045 with complicate-grooved insert

In order to solve the problem of low efficiency and high cost in designing inserts with groove, finite element simulation (FEM) method has been employed to directly simulate the chip breaking condition. However, the current methods tend to involve a large number of cutting experiments and a user subroutine program used for secondary development, causing inconveniency in engineering application. Here, we propose a high-efficient three-dimensional (3D) FEM method to analyze the chip breakage properties of complicate-grooved insert. For the simulation, a three-dimensional cutting simulation model is established by Deform 3D FE package, and the Johnson-Cook (J-C) material constitutive model and Cockcroft-Latham (C-L) ductile fracture criterion are adopted. To verify the validity of the model, the simulations and corresponding turning experiments of AISI 1045 steel are performed with complicate-grooved insert at several combination groups of cutting depth and feed rate. The estimated chip morphology, chip breaking process, and cutting force from the simulation are in good consistency with those from the experiments. Additionally, the comparisons between the simulations and corresponding turning experiments with complicate-grooved insert and flat rake insert are conducted. The results show that the chip breaking groove can significantly change the chip flow angle and the chip geometry and that the complicate-grooved insert can more efficiently promote chip breakage than the flat rake insert. Therefore, the 3D FEM method proposed can be used to effectively investigate the chip formation mechanism and chip breakage properties and has promising application prospects in complicate-grooved insert design and cutting parameter optimization.

Removal Mechanism of Titanium Alloy Material in Ultrasound Vibration Drilling

In drilling the ultra-slim small diameter deep hole of titanium alloy, the problem of chip breaking and chip removal is common. When the drill is working normally, the ultrasonic vibration can be applied for the drill bit to cut the bit in the vibration to form a pulse. The cutting force waveform in drilling, should select the reasonable vibration frequency, amplitude, feed amount, workpiece rotation and other parameters to match, control the size and shape of the chip, get satisfactory chips, and avoid chip clogging. In this study, the ANSYS finite element simulation software was used to simulate the TC4 drilling process, and the difference between ultrasonic vibration drilling and ordinary drilling was analyzed. Drilling experiments were carried out. The experimental results show that compared with conventional drilling, ultrasonic vibration drilling has better surface quality, reduced tool wear and increased material removal rate.