In order to accurately obtain the dynamic characteristics of the cutting mechanism of the mining longitudinal roadheader,combined with the working principle of the mining longitudinal roadheader,the theoretical analys...In order to accurately obtain the dynamic characteristics of the cutting mechanism of the mining longitudinal roadheader,combined with the working principle of the mining longitudinal roadheader,the theoretical analysis and derivation are carried out in detail.By using ADAMS to simulate,the resistance curve and torque curve of the cutting mechanism in different directions are obtained.The results show that ADAMS can effectively predict the excavation resistance and torque of the cutting mechanism of mining longitudinal roadheader,which has certain reference value for future optimization design.展开更多
This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force （FC） values with theoreti- cally estima...This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force （FC） values with theoreti- cally estimated ones. First, a review on theoretical rock cutting models proposed for both chisel and conical picks was presented in detail. Experimental study consists of both chisel and conical pick cutting tests in unrelieved （single-pick） cutting mode with varying cutting depths. FC＇ values were determined from experimental results, and theoretical models were utilized to compute FC for all cutting conditions. Computed and experimentally determined F（ data were then compared for a referenced cutting depth. It is shown that the theoretical models might overestimate or underestimate FC＇ and cannot give reliable results. Finally, explanations for these mismatches were presented.展开更多
To research the loading charactefistc of rocks with different structures cut by helical cutting mechanism （HCM）, three different structures of rock （hard-soft-hard rock, soft-hard rock and soft-hard-soft rock） wer...To research the loading charactefistc of rocks with different structures cut by helical cutting mechanism （HCM）, three different structures of rock （hard-soft-hard rock, soft-hard rock and soft-hard-soft rock） were built. And each type model was further divided into three types when the experiments were carried out. To reduce the errors of cutting load caused by manually configured rock in each test, the cutting load of soft rock was taken as a benchmark, and the differences of the cutting load of the different structures of rocks and the soft rock were used to reflect the cutting load change rules of the HCM. The results indicate that, the cutting load of only the HCM top cutting hard rock is larger than that of only the HCM bottom cutting hard rock for dextral HCM, and the cutting load fluctuation is larger, too. However, when the top and the bottom of the HCM cutting hard rock simultaneously, its cutting load is the largest, but the cutting load fluctuation is the least. And the HCM cutting load increment is increased linearly with the increase of rock compressive strength. The HCM cutting load increment is increased exponentially with the increase of hard rock cutting thickness.展开更多
There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plast...There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.展开更多
The research of rare earth elements (RE), added into cemented carbide tools, is one of the recent developments of new types of tool materials in China. Systematic experiments about RE carbides YG8R. (K30), YT14R (P20)...The research of rare earth elements (RE), added into cemented carbide tools, is one of the recent developments of new types of tool materials in China. Systematic experiments about RE carbides YG8R. (K30), YT14R (P20) and, YW1R (M10) were made to study on the cutting performance in comparison with non-RE carbides YG8, YT14 and YW1. The cutting experiments were as follows: tool life, cutting force, tool-chip friction coefficient and interrupted machining. The action of RE on the carbide materials and the cutting mechanism of the RE carbide tools in the cutting process were verified with the aid of SEM and energy spectrum analysis. Experimental results show that the RE carbide tools have a good overall performance.展开更多
An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and f...An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC （LZ） ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.展开更多
An experimental study on cutting amorphous alloy at nanometer scale is conducted by applying the principle and technology of scanning probe microscope(SPM) It is revealed from the experiments that cutting inside SPM...An experimental study on cutting amorphous alloy at nanometer scale is conducted by applying the principle and technology of scanning probe microscope(SPM) It is revealed from the experiments that cutting inside SPM is an excellent and direct way to research the material removal process at small size Based on the experimental results,the chip formation mechanism for the cutting of amorphous alloy is discussed It is found that the deformation along the direction of chip flow occurs ahead of the appearance of localized shear,and a simplified geometrical model is proposed to illustrate the deformation.展开更多
The deposit scale in the coal mine shaft usually causes serious accidents, such as making rope broken, cage seized or dropped. To solve this kind of problems, the re-search of the cutting scale mechanism was made, and...The deposit scale in the coal mine shaft usually causes serious accidents, such as making rope broken, cage seized or dropped. To solve this kind of problems, the re-search of the cutting scale mechanism was made, and a new type of removal scale equipment was made with using imported hard alloy material. The cutting experiment and actual cutting show that it can adapt to abominable condition in the shaft, such as narrow space, wet and excessive shaft crevice water and so on, and can work safely and reliably, and has high cutting scale efficiency. It can also cut out the deposit scale in the circular section of shaft.展开更多
The transverse cutting mechanism of the checkerboard paving robot, which directly affects the robot＇s operation, is regarded as the most important part in a transverse pavement system This research aims at designing ...The transverse cutting mechanism of the checkerboard paving robot, which directly affects the robot＇s operation, is regarded as the most important part in a transverse pavement system This research aims at designing a new system which is appropriate for desert wofidng en- vironments and finishing cutting the rope of straw. In this paper, computer emulating technology is applied, and with three-dimensional modeling by Pro/ENGINEER software, can observe whether or not interference exists. Also, the speed and displacement parameters of the main parts of the cutting system are given by the dynamic emulation by Automatic Dynamic Analysis of Mechanical System （ADAMS）, which theoretically assures the feasibility and appropriateness of the cutting mechanisrn~ Finally, results of the experinaent shows that the cutting mechanism can cut the straw strand as designed.展开更多
The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal mat...The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.展开更多
The technique of cutting slabstone with stone-sawi ng machine is analyzed completely. A new kind of cutting movement trajectory is gi ven whose actual cutting efficiency is near to 100%. It can reduce the energy w ear...The technique of cutting slabstone with stone-sawi ng machine is analyzed completely. A new kind of cutting movement trajectory is gi ven whose actual cutting efficiency is near to 100%. It can reduce the energy w earing greatly, and the surface quality of the product is improved to the utmost extent. The design mechanism of the optimal cutting movement trajectory system structure is analyzed incisively. At the same time, the principle of the complex movement of horizontal movement and swing is researched. The optimal design scheme of th e cutting movement trajectory system structure is set up. The choice method to g et the superior value of the movement system structure is found. The mathematics function formula is established which exhibits the relationship between the par ameter of the complex movement structure and that of the system movement structu re. By the formula, the precision value of the offset can be figured out. The r ule is adapted to different types of energy-saving stone-sawing machines. The complex movement structure of horizontal movement and swing is designed to f ulfill the cutting movement. It can make the saw frame move up with the hanging pod deviating from the vertical direction. At the same time, the saw frame have a down-movement. Then the sum of the two movements is near to zero, and the saw blade and the stone can keep in touch during the whole horizontal cutting. The result is that the actual cutting efficiency is 100%. Also, when the hanging pod moves to the limited position, the saw frame can keep the original inertia, and continue to swing up. It makes the back-cutting have high energy-storing. The optimal design of the eccentricity balance wheel is done. The mathematics fo rmula for expressing the movement system structure is deduced. The calculation m ethod and formula is set up which is used to get the value of important componen ts such as offset. The choice method and formula of elasticity distortion coeffi cient is set up when the saw frame moves smoothly. It is concluded that the offs et is the key dimension to actualize the optimal cutting movement trajectory. The resolving of the technical problems discussed above offers a theoretic and technical basis for optimal design of energy-saving stone-sawing machines.展开更多
This work investigates the machining temperatures of ultra-fine-grained titanium(UFG Ti),prepared by equal channel angular extrusion,through analytical modeling.UFG Ti has great usefulness in biomedical applications b...This work investigates the machining temperatures of ultra-fine-grained titanium(UFG Ti),prepared by equal channel angular extrusion,through analytical modeling.UFG Ti has great usefulness in biomedical applications because of its high mechanical strength,sufficient manufacturability,and high biocompatibility.The temperatures were predicted using a physics-based predictive model based on material constitutive relation and mechanics of the orthogonal cutting process.The minimization between the stress calculated using Johnson–Cook constitutive model and the same stress calculated using mechanics model yields the estimation of machining temperatures at two deformation zones.Good agreements are observed upon validation to the values reported in the literature.The machinability of UFG Ti is investigated by comparing its machining temperature to that of Ti–6Al–4V alloy under the same cutting conditions.Significantly lower temperatures are observed in machining UFG Ti.The computational efficiency of the presented model is investigated by comparing its average computational time(~0.5 s)to that of a widely used modified chip formation model(8900 s)with comparable prediction accuracy.This work extends the applicability of the presented temperature model to a broader class of materials,specifically ultra-fine-grained metals.The high computational efficiency allows the in situ temperature prediction and optimization of temperature condition with process parameters planning.展开更多
A total of 219 embryonic-germ-cell-like （EG-like） clumps were derived from 15 selected goat fetuses. Isolation of primordial germ cells （PGCs） based on co-culture with primary goat embryonic fibroblast showed no d...A total of 219 embryonic-germ-cell-like （EG-like） clumps were derived from 15 selected goat fetuses. Isolation of primordial germ cells （PGCs） based on co-culture with primary goat embryonic fibroblast showed no difference from traditional feeder layer-based culture method used in mouse and human. The putative primary EG colonies were multilayer clumps of compact cells with unclear cell-cell boundaries. Three subculture methods of goat EG-like colony, traditional enzymatic digestion, mechanical cutting and combination of the both, were compared in this study. As a result, EG-like colonies traditionally disassociated with collagenase 1V could be subcultured for up to 4 passages. And the mechanically disaggregated EG-like colonies were successfully maintained 9-12 passages with or without enzymatic treatment. The pluripotency of the EG-like colonies was identified by their specific marker staining, spontaneous differentiation and embryoid bodies （EBs） formation in vitro. Most goat EG-like colonies （〉 80%） were AKP positive and immunocytochemically characterized with positive SSEA-1, Oct-4 and c-kit staining but SSEA-4. Under the condition of delaying passage, goat EG-like cells could differentiate into fibroblast-like, epithelium-like, and neuron-like cells. In addition, EBs could be obtained successfully in routine hanging drop culture. The serum free culture system （feeder layer-based） used in this study was suitable for keeping PGCs and EG-like cells in their undifferentiated condition, but failed to converse them to immortal cells. These results indicated that mechanical cutting is an effective method for passaging goat EG cell colonies. However, the microenvironment of conversing EG cells to immortal cells is still unclear.展开更多
A no-tillage planter of narrow row spacing was designed according to the agronomic requirements of wide/narrow row farming mode in the black soil region of Northeast China.Due to the narrow spacing of the seeder unit,...A no-tillage planter of narrow row spacing was designed according to the agronomic requirements of wide/narrow row farming mode in the black soil region of Northeast China.Due to the narrow spacing of the seeder unit,a gear-tooth stalk cutting mechanism was designed in order to prevent residues from blocking the planter.The basic parameters,number and edge curve of the stalk cutting blade were designed and optimized.Three-factor and three-level combined orthogonal experiments were conducted using the factors of working speed(1.12 m/s,1.57 m/s and 2.02 m/s),tillage depth(75 mm,90 mm and 105 mm)and cutter spacing(15 mm,30 mm and 45 mm),which significantly affected stalk cutting rate and soil disturbance rate.The optimal combination is the working speed of 1.62 m/s,tillage depth of 92 mm and cutter spacing of 35 mm.Under this condition,the stalk cutting rate is more than 90%and soil disturbance rate is 7.5%-12.0%.The performance of the new no-tillage planter was tested by using the above parameters.The results showed that the no-tillage planter of narrow row spacing came up to the relevant national standards in China.展开更多
The ever-increasing requirements for the scalable manufacturing of atomic-scale devices emphasize the significance of developing atomic-scale manufacturing technology. The mechanism of a single atomic layer removal in...The ever-increasing requirements for the scalable manufacturing of atomic-scale devices emphasize the significance of developing atomic-scale manufacturing technology. The mechanism of a single atomic layer removal in cutting is the key basic theoretical foundation for atomic-scale mechanical cutting. Material anisotropy is among the key decisive factors that could not be neglected in cutting at such a scale. In the present study, the crystallographic orientation effect on the cutting-based single atomic layer removal of monocrystalline copper is investigated by molecular dynamics simulation. When undeformed chip thickness is in the atomic scale, two kinds of single atomic layer removal mechanisms exist in cutting-based single atomic layer removal, namely, dislocation motion and extrusion, due to the differing atomic structures on different crystallographic planes. On close-packed crystallographic plane, the material removal is dominated by the shear stress-driven dislocation motion, whereas on non-close packed crystallographic planes, extrusion-dominated material removal dominates. To obtain an atomic, defect-free processed surface, the cutting needs to be conducted on the close-packed crystallographic planes of monocrystalline copper.展开更多
Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness...Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness ofγ-TiAl is still a critical obstacle to its large-scale applications.In this context,researchers have made many attempts to study the machinability ofγ-TiAl.At present,existing relevant reviews have mostly discussed the processing methods ofγ-TiAl.Hence,there is still a lack of a perspective on material properties to analyze the cutting mechanism.Herein,this paper provides the systematic review of such perspectives.Above all,the developmental process,phase transformation,and microstructural evolution ofγ-TiAl are discussed,as well as its deformation mechanism at quasi-static.These topics can provide a materials science foundation for the machining ofγ-TiAl.And then,the review focuses on the cutting mechanism and surface integrity ofγ-TiAl.Moreover,special attention is paid to the microscope deformation mechanism and surface defects evolution ofγ-TiAl during cutting.Finally,the review indicates that the highperformance machining technology ofγ-TiAl faces challenges and proposes potential future research directions.Solving the difficulties during machiningγ-TiAl aero-engine components will accelerate the development of new aero-engines.展开更多
Direct milling of sand molds is an important development in rapid manufacturing of sand molds. Direct milling is an effective method for manufacturing single or small batches of cast parts. This paper describes experi...Direct milling of sand molds is an important development in rapid manufacturing of sand molds. Direct milling is an effective method for manufacturing single or small batches of cast parts. This paper describes experimental investigations to find sand blocks with the appropriate strength, to describe wear patterns of different tools (high-speed steel (HSS), carbide, and polycrystalline diamond (PCD) tools), and to analyze sand mold cutting mechanisms. The results show that the PCD tool outperformes the other tools in terms of tool life. Average flank wear and micro-tipping are the dominant tool failure modes in the sand mold milling process. With a flank wear limit of 0.3 mm, the PCD tool works continuously for about 70 h under the experimental conditions. The experimental results show that the cutting mechanism for direct milling sand molds differs from metal cutting.展开更多
文摘In order to accurately obtain the dynamic characteristics of the cutting mechanism of the mining longitudinal roadheader,combined with the working principle of the mining longitudinal roadheader,the theoretical analysis and derivation are carried out in detail.By using ADAMS to simulate,the resistance curve and torque curve of the cutting mechanism in different directions are obtained.The results show that ADAMS can effectively predict the excavation resistance and torque of the cutting mechanism of mining longitudinal roadheader,which has certain reference value for future optimization design.
文摘This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force （FC） values with theoreti- cally estimated ones. First, a review on theoretical rock cutting models proposed for both chisel and conical picks was presented in detail. Experimental study consists of both chisel and conical pick cutting tests in unrelieved （single-pick） cutting mode with varying cutting depths. FC＇ values were determined from experimental results, and theoretical models were utilized to compute FC for all cutting conditions. Computed and experimentally determined F（ data were then compared for a referenced cutting depth. It is shown that the theoretical models might overestimate or underestimate FC＇ and cannot give reliable results. Finally, explanations for these mismatches were presented.
基金Project(51005232) supported by the National Natural Science Foundation of ChinaProject(20100481176) supported by the China Postdoctoral Science Foundation
文摘To research the loading charactefistc of rocks with different structures cut by helical cutting mechanism （HCM）, three different structures of rock （hard-soft-hard rock, soft-hard rock and soft-hard-soft rock） were built. And each type model was further divided into three types when the experiments were carried out. To reduce the errors of cutting load caused by manually configured rock in each test, the cutting load of soft rock was taken as a benchmark, and the differences of the cutting load of the different structures of rocks and the soft rock were used to reflect the cutting load change rules of the HCM. The results indicate that, the cutting load of only the HCM top cutting hard rock is larger than that of only the HCM bottom cutting hard rock for dextral HCM, and the cutting load fluctuation is larger, too. However, when the top and the bottom of the HCM cutting hard rock simultaneously, its cutting load is the largest, but the cutting load fluctuation is the least. And the HCM cutting load increment is increased linearly with the increase of rock compressive strength. The HCM cutting load increment is increased exponentially with the increase of hard rock cutting thickness.
基金the Research Committee of The Hong Kong Polytechnic University and the Innovation Technology Commission of The Hong Kong SAR Government for their financial support of the Hong Kong Partner State Key Laboratory of Ultra-Precision Machining Technology
文摘There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.
文摘The research of rare earth elements (RE), added into cemented carbide tools, is one of the recent developments of new types of tool materials in China. Systematic experiments about RE carbides YG8R. (K30), YT14R (P20) and, YW1R (M10) were made to study on the cutting performance in comparison with non-RE carbides YG8, YT14 and YW1. The cutting experiments were as follows: tool life, cutting force, tool-chip friction coefficient and interrupted machining. The action of RE on the carbide materials and the cutting mechanism of the RE carbide tools in the cutting process were verified with the aid of SEM and energy spectrum analysis. Experimental results show that the RE carbide tools have a good overall performance.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50275086)the University of New South Wales Visiting Professorship Scheme,Australia.
文摘An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC （LZ） ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.
基金This project is supported by Foundation of National Education Ministry for Returned Overseas Chinese Scholars(No.2000367) an
文摘An experimental study on cutting amorphous alloy at nanometer scale is conducted by applying the principle and technology of scanning probe microscope(SPM) It is revealed from the experiments that cutting inside SPM is an excellent and direct way to research the material removal process at small size Based on the experimental results,the chip formation mechanism for the cutting of amorphous alloy is discussed It is found that the deformation along the direction of chip flow occurs ahead of the appearance of localized shear,and a simplified geometrical model is proposed to illustrate the deformation.
文摘The deposit scale in the coal mine shaft usually causes serious accidents, such as making rope broken, cage seized or dropped. To solve this kind of problems, the re-search of the cutting scale mechanism was made, and a new type of removal scale equipment was made with using imported hard alloy material. The cutting experiment and actual cutting show that it can adapt to abominable condition in the shaft, such as narrow space, wet and excessive shaft crevice water and so on, and can work safely and reliably, and has high cutting scale efficiency. It can also cut out the deposit scale in the circular section of shaft.
基金supported by National High Technology Research and Development Program 863(Grant No.2002AA422170)the grant of Educational Commission of Heilongjiang Province of China(Grant No.10541042)
文摘The transverse cutting mechanism of the checkerboard paving robot, which directly affects the robot＇s operation, is regarded as the most important part in a transverse pavement system This research aims at designing a new system which is appropriate for desert wofidng en- vironments and finishing cutting the rope of straw. In this paper, computer emulating technology is applied, and with three-dimensional modeling by Pro/ENGINEER software, can observe whether or not interference exists. Also, the speed and displacement parameters of the main parts of the cutting system are given by the dynamic emulation by Automatic Dynamic Analysis of Mechanical System （ADAMS）, which theoretically assures the feasibility and appropriateness of the cutting mechanisrn~ Finally, results of the experinaent shows that the cutting mechanism can cut the straw strand as designed.
基金the National Natural Science Foundation of China(No.U2037601)。
文摘The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.
文摘The technique of cutting slabstone with stone-sawi ng machine is analyzed completely. A new kind of cutting movement trajectory is gi ven whose actual cutting efficiency is near to 100%. It can reduce the energy w earing greatly, and the surface quality of the product is improved to the utmost extent. The design mechanism of the optimal cutting movement trajectory system structure is analyzed incisively. At the same time, the principle of the complex movement of horizontal movement and swing is researched. The optimal design scheme of th e cutting movement trajectory system structure is set up. The choice method to g et the superior value of the movement system structure is found. The mathematics function formula is established which exhibits the relationship between the par ameter of the complex movement structure and that of the system movement structu re. By the formula, the precision value of the offset can be figured out. The r ule is adapted to different types of energy-saving stone-sawing machines. The complex movement structure of horizontal movement and swing is designed to f ulfill the cutting movement. It can make the saw frame move up with the hanging pod deviating from the vertical direction. At the same time, the saw frame have a down-movement. Then the sum of the two movements is near to zero, and the saw blade and the stone can keep in touch during the whole horizontal cutting. The result is that the actual cutting efficiency is 100%. Also, when the hanging pod moves to the limited position, the saw frame can keep the original inertia, and continue to swing up. It makes the back-cutting have high energy-storing. The optimal design of the eccentricity balance wheel is done. The mathematics fo rmula for expressing the movement system structure is deduced. The calculation m ethod and formula is set up which is used to get the value of important componen ts such as offset. The choice method and formula of elasticity distortion coeffi cient is set up when the saw frame moves smoothly. It is concluded that the offs et is the key dimension to actualize the optimal cutting movement trajectory. The resolving of the technical problems discussed above offers a theoretic and technical basis for optimal design of energy-saving stone-sawing machines.
文摘This work investigates the machining temperatures of ultra-fine-grained titanium(UFG Ti),prepared by equal channel angular extrusion,through analytical modeling.UFG Ti has great usefulness in biomedical applications because of its high mechanical strength,sufficient manufacturability,and high biocompatibility.The temperatures were predicted using a physics-based predictive model based on material constitutive relation and mechanics of the orthogonal cutting process.The minimization between the stress calculated using Johnson–Cook constitutive model and the same stress calculated using mechanics model yields the estimation of machining temperatures at two deformation zones.Good agreements are observed upon validation to the values reported in the literature.The machinability of UFG Ti is investigated by comparing its machining temperature to that of Ti–6Al–4V alloy under the same cutting conditions.Significantly lower temperatures are observed in machining UFG Ti.The computational efficiency of the presented model is investigated by comparing its average computational time(~0.5 s)to that of a widely used modified chip formation model(8900 s)with comparable prediction accuracy.This work extends the applicability of the presented temperature model to a broader class of materials,specifically ultra-fine-grained metals.The high computational efficiency allows the in situ temperature prediction and optimization of temperature condition with process parameters planning.
基金supported by the National Programs for High Technology Research and Development of China(2005AA219050)the National Natural Science Foundation of China(30200137).
文摘A total of 219 embryonic-germ-cell-like （EG-like） clumps were derived from 15 selected goat fetuses. Isolation of primordial germ cells （PGCs） based on co-culture with primary goat embryonic fibroblast showed no difference from traditional feeder layer-based culture method used in mouse and human. The putative primary EG colonies were multilayer clumps of compact cells with unclear cell-cell boundaries. Three subculture methods of goat EG-like colony, traditional enzymatic digestion, mechanical cutting and combination of the both, were compared in this study. As a result, EG-like colonies traditionally disassociated with collagenase 1V could be subcultured for up to 4 passages. And the mechanically disaggregated EG-like colonies were successfully maintained 9-12 passages with or without enzymatic treatment. The pluripotency of the EG-like colonies was identified by their specific marker staining, spontaneous differentiation and embryoid bodies （EBs） formation in vitro. Most goat EG-like colonies （〉 80%） were AKP positive and immunocytochemically characterized with positive SSEA-1, Oct-4 and c-kit staining but SSEA-4. Under the condition of delaying passage, goat EG-like cells could differentiate into fibroblast-like, epithelium-like, and neuron-like cells. In addition, EBs could be obtained successfully in routine hanging drop culture. The serum free culture system （feeder layer-based） used in this study was suitable for keeping PGCs and EG-like cells in their undifferentiated condition, but failed to converse them to immortal cells. These results indicated that mechanical cutting is an effective method for passaging goat EG cell colonies. However, the microenvironment of conversing EG cells to immortal cells is still unclear.
基金the National Science and Technology Support Project of China(No.2016YFD070030201)Jilin Province Science and Technology Development Plan Project(No.20160441004SC)。
文摘A no-tillage planter of narrow row spacing was designed according to the agronomic requirements of wide/narrow row farming mode in the black soil region of Northeast China.Due to the narrow spacing of the seeder unit,a gear-tooth stalk cutting mechanism was designed in order to prevent residues from blocking the planter.The basic parameters,number and edge curve of the stalk cutting blade were designed and optimized.Three-factor and three-level combined orthogonal experiments were conducted using the factors of working speed(1.12 m/s,1.57 m/s and 2.02 m/s),tillage depth(75 mm,90 mm and 105 mm)and cutter spacing(15 mm,30 mm and 45 mm),which significantly affected stalk cutting rate and soil disturbance rate.The optimal combination is the working speed of 1.62 m/s,tillage depth of 92 mm and cutter spacing of 35 mm.Under this condition,the stalk cutting rate is more than 90%and soil disturbance rate is 7.5%-12.0%.The performance of the new no-tillage planter was tested by using the above parameters.The results showed that the no-tillage planter of narrow row spacing came up to the relevant national standards in China.
基金The authors would like to thank the finical support from the Science Foundation Ireland(Grant No.15/RP/B3208)the‘111’Project by the State Administration of Foreign Experts Affairs and the Ministry of Education of China(Grant No.B07014).
文摘The ever-increasing requirements for the scalable manufacturing of atomic-scale devices emphasize the significance of developing atomic-scale manufacturing technology. The mechanism of a single atomic layer removal in cutting is the key basic theoretical foundation for atomic-scale mechanical cutting. Material anisotropy is among the key decisive factors that could not be neglected in cutting at such a scale. In the present study, the crystallographic orientation effect on the cutting-based single atomic layer removal of monocrystalline copper is investigated by molecular dynamics simulation. When undeformed chip thickness is in the atomic scale, two kinds of single atomic layer removal mechanisms exist in cutting-based single atomic layer removal, namely, dislocation motion and extrusion, due to the differing atomic structures on different crystallographic planes. On close-packed crystallographic plane, the material removal is dominated by the shear stress-driven dislocation motion, whereas on non-close packed crystallographic planes, extrusion-dominated material removal dominates. To obtain an atomic, defect-free processed surface, the cutting needs to be conducted on the close-packed crystallographic planes of monocrystalline copper.
基金co-supported by the Science Center for Gas Turbine Project,China(No.P2022-A-IV-001-002)the National Natural Science Foundation of China(Nos.51875473 and 91960203).
文摘Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness ofγ-TiAl is still a critical obstacle to its large-scale applications.In this context,researchers have made many attempts to study the machinability ofγ-TiAl.At present,existing relevant reviews have mostly discussed the processing methods ofγ-TiAl.Hence,there is still a lack of a perspective on material properties to analyze the cutting mechanism.Herein,this paper provides the systematic review of such perspectives.Above all,the developmental process,phase transformation,and microstructural evolution ofγ-TiAl are discussed,as well as its deformation mechanism at quasi-static.These topics can provide a materials science foundation for the machining ofγ-TiAl.And then,the review focuses on the cutting mechanism and surface integrity ofγ-TiAl.Moreover,special attention is paid to the microscope deformation mechanism and surface defects evolution ofγ-TiAl during cutting.Finally,the review indicates that the highperformance machining technology ofγ-TiAl faces challenges and proposes potential future research directions.Solving the difficulties during machiningγ-TiAl aero-engine components will accelerate the development of new aero-engines.
基金Supported by the National Natural Science Foundation of China(No. 50775092)the China International Science and Technology Cooperation Project (No. 2008DF71250)
文摘Direct milling of sand molds is an important development in rapid manufacturing of sand molds. Direct milling is an effective method for manufacturing single or small batches of cast parts. This paper describes experimental investigations to find sand blocks with the appropriate strength, to describe wear patterns of different tools (high-speed steel (HSS), carbide, and polycrystalline diamond (PCD) tools), and to analyze sand mold cutting mechanisms. The results show that the PCD tool outperformes the other tools in terms of tool life. Average flank wear and micro-tipping are the dominant tool failure modes in the sand mold milling process. With a flank wear limit of 0.3 mm, the PCD tool works continuously for about 70 h under the experimental conditions. The experimental results show that the cutting mechanism for direct milling sand molds differs from metal cutting.
