Chip Breaking Research Articles

Research on Deep Hole Machining Based on Aircraft Landing Gear

A landing gear is the main large bearing structural part of an aircraft. The change of material and structure makes the processing of the aircraft landing gear more difficult. Aiming at the structural characteristics of the aircraft landing gear deep cavity, the deep hole processing technique of a 300M steel workpiece was studied. A separated NC deep hole drilling and boring machine was adopted to process the workpiece. Cavity hole special cutting tools were introduced. Fixture and sealing mode were improved. NC programs were optimized. Thus, the processing problems of deflection, vibration, chip breaking and chip removal were solved. The workpiece with width to diameter ratio greater than 10 and surface roughness of hole is 3.2 μm was successfully machined by machining experiment, and the high efficiency machining of deep hole of ultra-high strength steel was realized. Thus the theoretical foundation is laid for the machining of complex cavity deep holes for cutting high-strength alloy materials.

Effect of Wear on Vibration Amplitude and Chip Shape Characteristics during Machining of Eco-Friendly and Leaded Brass Alloys

The dynamic stability of the machining set and the entire cutting process, together with the appropriate form of chips generated during machining under the given conditions, are the basic prerequisites for autonomous machining in accordance with the Industry 4.0 trend. The research, based on a newly designed method, aims to study the frequency response of the machining system to different values of tool wear and cutting speed, which cause the worsening of the machined parts’ quality and the instability of the whole cutting process. The new idea is based on the inverse principle, in which the wear with various values of VB was artificially prepared in advance before machining. Consequently, the effect of artificial wear and cutting speed on vibration and chip shape characteristics were studied. Three types of brass alloys were used within the experiments as the machined materials. Measured data were statistically processed and the desired dependencies were plotted. Chips were collected for each combination of machining conditions, while the article presents a database of the obtained chip shapes at individual cutting speeds so that they can be compared and classified. The results showed that brass alloys CW510L and CW614N exhibit an average of three times lower vibration damping compared to the CW724R alloy, while relatively good chip formation was noted in the evaluated machining conditions even without the use of a chip breaker. The problematic chip shape occurred only in some cases at the machining of CW510L and CW724R, which cannot be generalized.

Cutting performance and wear mechanism of zirconia toughened alumina ceramic cutting tools formed by vat photopolymerization-based 3D printing

Zirconia toughened alumina (ZTA) cutting tools are widely used for machining hard and wear-resistant materials. However, the processing of ZTA ceramic cutting tools with complex shapes using traditional methods is difficult and time-consuming. Until now, to the best of our knowledge, commercial ceramic cutting tools do not contain grooves because it is very difficult to process grooves on the ceramic cutting tool, resulting from the feature of high hardness and brittle attribute of ceramics. This study investigated high-performance, complex-shaped zirconia-toughened alumina (ZTA) ceramic cutting tools equipped with a chip breaker for the first time. The investigated samples were prepared using vat photopolymerization based 3D printing combined with a hot isostatic sintering process. The relative density of 99.34%, Vickers hardness of 17.98 ± 0.20 GPa, bending strength of 779 ± 47 MPa and fracture toughness of 5.41 ± 0.29 MPa m1/2 of the ZTA cutting tools were obtained. The effects of three cutting parameters, namely the cutting speed vc, feed rate f, and back cutting depth ap, on the cutting performances of the cutting tools were investigated, and the wear mechanisms of the cutting tools were examined. We believe that our study makes a significant contribution to the literature because this study provides an in-depth investigation of the properties and wear mechanisms of ZTA ceramic cutting tools with chip breaker grooves. The findings of this study provide insight into the preparation of high-performance, complex-shaped ZTA ceramic cutting tools. Further, the preparation methods investigated in this study and the evaluation of the properties of the fabricated specimens in comparison with a commercially available cutting tool illustrate the potential advantages that may be obtained via the further development of these materials.

The Chip Formation Process When Cutting High-Speed Steels and Ti3SiC2 Ceramics

The paper presents the microstructural characterization of the chip roots in high-speed steels and ceramic Ti3SiC2. The process of chip formation and the obtaining of adequate samples were carried out using the quick-stop method. The tests were carried out during the milling process; the “quick stop” method was carried out in order to obtain samples of the chip roots. This method was developed in-house by the authors. The chip roots were microscopically studied by means of a light microscope (LM) and a scanning electron microscope (SEM). Before the actual analysis, preparation was performed based on the standard metallographic technique. The analysis of the high-speed steels samples showed that, for the used cutting conditions, a discontinuous chip with a built-up edge (BUE) was formed. During the processing of the Ti3SiC2 ceramic, a significant difference was manifested in the chip formation process and a powder-like chip was produced. After utilizing a careful cutting process, a chip pattern was observed, from which it is evident that chip breakage during ceramic processing occurs without prior plastic deformation. In addition, the cutting force Fc was also measured during the milling process of the high-speed steels and the ceramic, and it was correlated with the cutting speed, feed per tooth and depth of cut.

Chip Morphology and Surface Integrity in Turning AZ31 Magnesium Alloy under Dry Machining and Submerged Convective Cooling

Magnesium alloys have broad applications, including medical implants and the aerospace sector owing to their great density and high strength-to-weight ratio. Dry cutting is a frequent technique for machining this material. However, it always leads to an excessive rise in temperature due to the absence of cooling at the cutting zone, which affects the machined surface integrity and chip morphology. In this study, chip morphology and surface integrity of the AZ31 magnesium alloy were investigated in the turning process using an internal cooling method called submerged convective cooling (SCC) to overcome the absence of cooling in dry cutting. This method can exploit the advantage of the high specific heat capacity of water as a cooling fluid without any reaction between water and magnesium to create a cooling element in the cutting zone. The chip morphologies and surface integrity were analyzed experimentally with varying cutting speeds under SCC and dry cutting. The experimental results revealed that SCC and dry cutting produced saw-tooth or serrated chip formation. The chips produced in dry cutting were continuous, while SCC was short and discontinuous as a result of a severe crack on the back surface of the chip. It was discovered that the grain refinement layer on the machined samples was thinner under SCC turning. SCC machining increased the microhardness of the AZ31 magnesium alloy by 60.5% from 55 HV to 88.3 HV, while dry turning exhibited a 49% increase in microhardness. The result revealed that surface roughness improved by 10.8%, 9.4% and 4.7% for cutting speeds (V) of 120, 180, and 240 m/min, respectively, under the SCC internal cooling. Based on the result obtained, SCC cutting outperformed dry cutting in terms of chip breakability, grain refinement, microhardness, and surface roughness.

Novel drill geometries for dry drilling of stainless steel

One completely new geometry and two modified chip breaker geometries were designed to increase the stability and reliability of the stainless steel dry drilling process. Experiments were performed and the results of individual tools were compared with a conventional solid carbide twist drill Gühring Ratio with a diameter of 5 mm. A matrix of three feed rates (0,03–0,07 mm/rev) and three cutting speeds (20–30 m/min) was designed for the cutting conditions. Precipitation-hardenable stainless steel 17-4 PH was chosen as a workpiece. During the experiment, the values of thrust force, spindle torque, temperature of the tool, surface roughness, chips morphology and chips division were recorded and compared with the reference tool.The results showed that compared to the reference tool A, the tool C - a multipoint drill with grooves through the cutting edge achieve approximately 4 % lower values of thrust force and 10–15 % lower values of spindle torque. Tool D with a step drill geometry achieve approximately 17 % lower values of thrust force and 10–15 % lower values of spindle torque and there is no chip clogging in the flute with C and D geometries. This effect is confirmed by the fact the spindle torque basically does not increase with the increasing depth of drilling. Tool B – new designed geometry achieve approximately 15 % lower values of thrust force and similar spindle torque values as the reference drill A. Tool temperature is a very important factor when dry drilling. Compared to the reference drill A, it was possible to achieve the tool temperature reduction of 20 % with the new geometry B, as well as with the multipoint drill C reduction by 26 % and with the step drill D reduction approximately by 30 %. All the modified drills also achieved a reduction in the surface roughness of the drilled holes. By 17 %, 35 % and 48 % lower surface roughness Ra was achieved with drills B, C and D. Chip morphology was significantly different for the tested drills. Conventional twist drills A and B generated helical short chips. While C and D twist drills with divided cutting edges generated ribbon snarled chips. Thanks to the reduction of cutting forces and temperature, it is possible to stably operate the drilling process with a higher cutting speed and feed rate, which leads to an increase in the efficiency and reliability of the machining process.

Study on the Mechanism of Burr Formation by Simulation and Experiment in Ultrasonic Vibration-Assisted Micromilling

Due to the strong plasticity of Inconel 718 and the significant size effect of micromachining, a large number of burrs will be produced in traditional processing. The addition of ultrasonic vibration during machining can reduce the burr problem. The mechanism of burr generation in traditional micromilling (TMM) and ultrasonic vibration-assisted micromilling (UVAMM) was analyzed by simulation, and verified by corresponding experiments. It is found that applying high-frequency ultrasonic vibration in the milling feed direction can reduce cutting temperature and cutting force, improve chip breaking ability, and reduce burr formation. When the cutting thickness will reach the minimum cutting thickness hmin, the chip will start to form. When A/ƒz > 1/2, the tracks of the two tool heads start to cut, and the chips are not continuous. Some of the best burr suppression effects were achieved under conditions of low cutting speed (Vc), feed per tooth (ƒz), and large amplitude (A). When A is 6 μm, the size and quantity of burr is the smallest. When ƒz reaches 6 μm, large continuous burrs appear at the top of the groove. The experimental results further confirm the accuracy of the simulation results and provide parameter reference.

Inhibition behavior of milling hole outlet defects inhibition on quartz fiber polyimide composite through LN2 inner cooling

The helical milling hole process of quartz fiber reinforced polyimide composites (QFRP) aimed to remove high-strength fiber and low-strength resin through thermodynamic interaction. But the defects, especially delamination at hole outlet, were difficult inhabited because of heterogeneous and anisotropic of composite. A mechanics model of milling hole force of QFRP was established by considering the shearing force of single fiber and temperature. A liquid nitrogen (LN2) inner-cooling machining equipment was employed for cryogenic milling hole testes. Compared with the conventional dry milling hole, the processed composite surface morphologies, cutting temperature, and milling force were investigated at hole outlet in detail. The study results show the predict values of the established model are compared and verified through the experimental measurement. And the cryogenic coolant processes can improve the composite mechanics properties, milling forces, and cutting heat. The composite can be completely chip breaking in cryogenic cooling, and the burr and delamination are effectively inhabited at hole outlet. Meanwhile, the rapid decline of cutting force and lower interlamination bonding force problems can be solved by the cryogenic cooling cutting. And the fiber avoidance can be improved through the increased tangential force, and the fiber can be efficiency chip breaking under the bigger tangential force. In addition, LN2 cooling can inhabit the cutting high temperature and increase the bonding force, the delamination defect of composite can be adequately improved in cryogenic.

Effect of Cryogenic Cooling on Mechanical Properties and Cutting Force of 6061 Aluminum Alloy

With the increasingly strict environmental protection requirements, cryogenic cutting technology as an environmentally friendly machining technology has received more and more attention. In this article, the affect of cryogenic cooling on the mechanical behaviors, cutting force and swarf shape of 6061 Aluminum Alloy were studied. Test result display that cryogenic increase strength of materials and reduces the plasticity of the material. Cryogenic cooling improves the cutting force and improves the chip breaking effect.

Study on tool wear mechanism under cryogenic CO2-assisted minimum quantity lubrication technology

Cryogenic CO2-assisted minimum quantity lubrication milling technology is a green processing technology with broad application prospects. Aiming at the problem of tool wear in the application of cryogenic CO2-assisted minimum quantity lubrication in difficult-to-machine materials and the influence of relevant parameters on tool wear, this study used coated cemented carbide tools to perform milling experiments under cryogenic CO2-assisted minimum quantity lubrication technology conditions. The micro-morphology of the tool and chip was observed, and the energy spectrum of the tool chip contact area was analyzed. The results show that reducing CO2 temperature and increasing the oil flow of minimum quantity lubrication can improve the tool wear. The tool wear mechanisms under cryogenic CO2-assisted minimum quantity lubrication are mainly abrasive wear, diffusion wear, and oxidation wear. The chip sawtooth degree of the optimal parameter group is more conducive to chip breaking than that of dry-cutting and wet-cutting groups. The temperature of the tool-chip contact area is an important factor affecting tool wear; the higher the temperature, the faster the tool wear. At the same time, it is verified that cryogenic CO2-assisted minimum quantity lubrication technology can replace cutting fluid in hard-to-machine materials under certain conditions.

Ultrasonic longitudinal torsion-assisted biotic bone drilling: An experimental study

Abstract State-of-the-art treatment of such orthopedic diseases as fracture and femoral head necrosis implies the installation of prosthesis or fixed equipment into patients’ injured parts using bone drilling. This study proposes an ultrasonic longitudinal torsion-assisted drilling (ULTAD) technique for biotic bone drilling. A comparative experiment was carried out between conventional drilling and ULTAD drilling in biotic bone, namely porcine femur. These tests proved that under the same drilling parameters, the ultrasonic component in bone drilling could reduce the drilling temperature and forces, improve the material removal by chip breaking, shorten the length of bone debris, and facilitate their discharge. Moreover, the proposed ULTAD technique reduced the number, length, and width of microcracks in the borehole wall, thus protecting the drilled biotic bone from internal damage.

Vat photopolymerization-based 3D printing of complex-shaped and high-performance Al2O3 ceramic tool with chip-breaking grooves: Cutting performance and wear mechanism

ABSTRACT Due to the processing of alumina ceramic cutting tools with complex shapes using traditional methods is difficult and time-consuming, vat-photopolymerization-based 3D printing was adopted to fabricate Al2O3 ceramic cutting tools with grooves for the first time. Subsequently, cutting performance evaluation and wear mechanism analysis were conducted. The relative density, Vickers hardness, and bending strength of the alumina cutting tools were determined. The effects of the cutting speed, feed rate, and cutting depth on the cutting performance and wear mechanism of the cutting tools were systematically investigated. In addition, two commercial cutting tools, namely cemented carbide and ceramic tools without grooves, were used for comparison. The cutting speed has the highest influence on the cutting performance, whereas the cutting depth has the least influence. The cutting performance of the prepared alumina cutting inserts with chip breaker grooves superior to that those without chip-breaking grooves and that of the cemented carbide tools. The wear mechanisms of the prepared alumina cutting tools and commercial tools were determined to be abrasive and adhesive wear, and those of the cemented carbide tools were adhesive wear and breakage. This work opens a new avenue for the future preparation of high-performance and complex-shaped ceramic cutting tools.

Comparison of penetrated MnS grains by steel matrix in variously loaded free-cutting steels with/without Pb as one of the workability parameters

The free-cutting steel is one of the essential structural steels in electrical appliance industry and automotive industry. Most of the steel contains Pb, as solid lubricant, chip breaker, tool edge stabilizer and tool life extender. MnS grains also play the same role of Pb. However, Pb is toxic so that it will be prohibited to add to the steel in near future. Steel industry has tried to replace Pb with other element(s) and/or compound(s). The trials are still going on. This study proposes a candidate of the workability parameters for free-cutting steels with/without Pb. Investigated steels were loaded quasi-statically (strain rate: 1×10-3 s-1) and dynamically (1×103 s-1) up to fracture. Half of the specimens were pre-fatigued to form easier slip situation in steel matrix. After fracture, thin steel matrix penetrated into plenty of MnS grains. For the steel with Pb, the ratios of the number of such penetrations to those of total grains maintained almost the same value for all loading conditions. The ratios were varied with the loading conditions for the steel without Pb. These facts meant that Pb was a key element for easier slip of steel matrix. Therefore, this ratio had a feasibility to be one of the workability parameters for the free-cutting steel.

Study on the mechanism affecting the quality of micro-hole in ultrasonic-assisted drilling of high-speed circuit boards

High-speed circuit boards are created to meet the high-speed signal transmission requirements of 5G communication technology, but the non-polar resins, flat glass fibers, and multiple and hard fillers used for this purpose have posed new challenges to their micro-hole processing. The quality of micro-hole has always been a decisive factor in board performance. Therefore, this paper aims at proposing a new processing method for improving the micro-hole drilling quality of high-speed circuit boards. By establishing an ultrasonic-assisted drilling tool motion model, analyzing the changes in drilling method, material deformation, chip breakage, and chip removal during ultrasonic-assisted drilling of printed circuit boards, the influence mechanism on micro-hole quality during ultrasound-assisted drilling is studied prudently. Besides, an experimental platform for ultrasonic-assisted drilling is designed and built, and single-factor experiments for verification of ultrasonic effects, optimization of drilling parameters, and orthogonal experiments for ultrasonic-assisted drilling of high-speed circuit boards are conducted on this platform. The experimental results show that the loading of ultrasonic vibration has made an obvious improvement on several machining defects including hole wall roughness, entrance burr, and nail head in micro-hole drilling of high-speed circuit boards. In addition, the influence order of each processing parameter and a better combination of them are discovered, which provides a theoretical research basis and instructions for the improvement of micro-hole quality of high-speed circuit boards.

Cutting mechanics and efficiency of forward and reverse multidirectional turning

In the manufacturing industry, many studies have been conducted on the features of cutting force, temperature and chip that are directly related to tool wear and cutting performance. However, most of the leading investigations have focused on unidirectional cutting and relatively few on multidirectional cutting. This study proposes a new approach to one of the most popular cutting operation of turning, in the form of forward-and-reverse multidirectional turning (MDT) to overcome deficiencies of tool wear, low processing efficiency and chip breakage using conventional turning. The mechanism and fundamentals of MDT are illustrated through dynamics analysis. A thermomechanical coupling simulation model is established in ABAQUS to analyze the mechanical properties of MDT. Three machining schemes are created with tool cutting edge angles as variables, and the optimal machining scheme is selected by analyzing features of cutting force, temperature, stress and chip morphology. Furthermore, the smaller-the-better characteristic of Taguchi's method and signal-to-noise ratio are used to analyze the effect of cutting parameters on the MDT performance. Finally, a case study illustrates practicability of the proposed approach is verified by the experimental studies.

Realization of complex-shaped and high-performance alumina ceramic cutting tools via Vat photopolymerization based 3D printing: A novel surface modification strategy through coupling agents aluminic acid ester and silane coupling agent

It is still a challenge to prepare high-performance ceramics due to the inherent problems of poor compatibility between ceramic powder and photosensitive resin in Vat photopolymerization. Herein, we used two types of coupling agents, aluminic acid ester and silane coupling agent, to modify Al2O3 ceramic powder based on transesterification reactions. In addition, after pressureless sintering, hot isostatic pressing sintering was followed to further improve the mechanical performance of the Al2O3 ceramic. Furthermore, Al2O3 ceramic cutting tools with chip breaker grooves were prepared based on vat photopolymerization and adopted for cutting for the first time. Simulation and experimental results showed that the as-prepared ceramic cutting tool with grooves has the best surface processing quality and the medium flank wear amount compared with that without grooves and even Kyocera commercial ceramic cutting tool. The results open a new avenue for the preparation of high-performance and complex-shaped ceramic cutting tools in the future.

Optimized design of structural parameters of Si3N4-based ceramic tools with variable cross-section

Through theoretical analysis and finite element simulation experiments, this paper proposes an optimal design method for the structural parameters of ceramic tools with variable cross-sections. On this basis, the tool angles of Si3N4-based ceramic tools for cutting inconel 718 high-temperature alloy are investigated, including rake angle γ0 = −5°, clearance angle α0 = 5°, cutting edge inclination λs = −2°, cutting edge angle Kr = 45°. By comparing the main cutting force, temperature and chip-breaking effect of flat face and three different groove ceramic tools, it is found that straight chip breaker has the most obvious optimization effect, main cutting force is 14.5% lower than that of the flat face, the temperature is reduced by 10.2%, and radius of chip curl curvature is the smallest, which is easy to break chips.

Improved chip control on PCD tools by positioning of brazed chip breakers

A brazed chip breaker capable of controlling the chip curling and flow is proposed on the rake face of a polycrystalline diamond (PCD) tool to obtain ideal chip shape of aluminum alloy materials. Two new position parameters, the breaker-point distance and the rotation angle of chip breaker, are proposed for positioning the chip breaker on the rake face of PCD turning tool. Influences of two position parameters of the chip breaker on the chip curling and chip flow direction are studied through finite element simulations and cutting experiments. The appropriate breaker-point distance can improve the up-curling and back-flow of the chip, and control the chips flow to the tool flank face to form a C-shaped chip. After setting the appropriate breaker-point distance, increasing the rotation angle of chip breaker can promote the trend of side-curling and side-flow of the chip, which is beneficial to the formation of short helical chip. Based on the chip-breaking criterion and the geometric relationship between the chip breaker and tool rake face, the equations of two position parameters of chip breaker are established, and effective chip breaking can be achieved within the reasonable range of chip breaker position parameters calculated by the established equations. The proposed chip breaker which position parameters are convenient to measure and install can be brazed on turning and drilling tools to obtain needed chip shape of aluminum alloy materials. • Proposed two position parameters of chip breaker for PCD turning tools. • Derived a set of equations to determine the effective range of the two position parameters. • Analyzed the influence of the position parameters on the chip curl, chip flow direction and chip shape.

Study on machining characteristics with variable distribution density micro-texture tools in turning superalloy GH4202

Micro texture tools (MTTs) with variable distribution density were proposed, and the novel MTTs can adapt to different friction states in the tool chip contact area and maintain good anti-friction and wear resistance. The novel MTTs were composed of two regions with different groove width and distribution density which were prepared on the rake face by femtosecond laser technology. The cutting processes were carried out in turning superalloy GH4202. According to the machining characteristics (rake wear, tool wear volume, workpiece material adhesion volume, and the chip morphology), the role of variable distribution density in turning was analyzed. The experimental results showed that the texture parameters of the texture region near and away from the edge have different effects and mechanisms on the machining characteristics. Compared with a non-textured tool and uniform textured tool, the proper design of texture parameters of variable distribution density texture can make the MTTs have better wear resistance and chip breaking ability when turning superalloy GH4202.

Surface feature and material removal in ultrasonic vibration-assisted slot-milling of Ti–6Al–4 V titanium alloy

The continuous optimization of processing technology and evaluation methods is an important way to achieve high processing quality and processing efficiency for difficult-to-process materials. To solve the problem of frequent defects in the slot, the ultrasonic vibration-assisted slot-milling (UVASM) technology was developed for processing titanium alloy. Simultaneously, comparative experiments were carried out between UVASM and conventional slot milling (CSM), in terms of surface features of slot bottom and slot sidewall, cutting force, tool trajectory, chip morphology, and micro-hardness. The results show that uniform vibration micro-texture could significantly improve surface topography of slot bottom in UVASM, while numerous tool feed trajectories and observable machining defects detract from the surface quality in CSM. The UVASM can greatly reduce material spalling and edge breakage, thereby maintaining a smooth and regular edge profile of the slot sidewall. The tool tip trajectories of the two machining methods are highly corresponding to the machining textures of the slot sidewall surface. There is a high-frequency and small-amplitude force fluctuation signal on the axial force waveform in UVASM, which can reduce the instantaneous maximum milling force and milling force in the stable stage by 8.7 and 12.2%, respectively. The UVASM has a better chip breaking effect and surface anti-scratch effect, and the UVASM can obtain higher surface micro-hardness and deeper plastic deformation layer than those CSM. In summary, the multi-dimensional evaluation of slot processing status has been completed, and the processing quality of the slot has been improved.