Papers by Author: Cheng Yong Wang

Abstract: Sawing concrete with diamond saw blade is a complex process with alternating loading. However, due to the poor working conditions of the thin circular blade made of high manganese steel core, and the lack of research on its failure mechanism, a large number of used blade are abandoned every year in China and all over the world without steel core reused. Therefore, exploring the failure mechanism of diamond saw blade can improve the cutting quality and efficiency, and extend the service life of the saw blade. In this paper, the failure mechanism of diamond saw blade sawing concrete was analyzed through segment wear experiment and microstructure observation of segments and steel core of failed sawblade. The results showed that the stress concentration exited at the bottom of slot, where it became the most dangerous section. The crack at the bottom of the cooling hole caused the saw blade to deviate violently and bear unevenly. The microstructure is great different along the outer to the center of the steel core. The closer to the teeth of the saw blade, the more obvious the microstructure change, while the central core still retains the original structure. Under the same sawing area of 0.01m², the stable dust adhesion of plain concrete is less than that of the steel fiber concrete. However, when the dust adhesion increases to more than the stable adhesion, the phenomenon of blockage will occur. Therefore, deflection, crack, wear and burn were the main failure reasons of diamond saw blade when sawing concrete.

Abstract: In order to obtain better surface quality after high speed milling high hardness mold steel, and reduce tool wear in cutting process, prolong the service life of cutting tools, obtain superior levels and optimal combination of cutting parameters in the test range. Through the design of orthogonal experiment, the use of Taguchi method, and noise ratio analysis and variance analysis of dry cutting high hardness mould steel PM60 under different cutting parameters; and finally, the optimal cutting parameters of surface roughness and cutting force value were predicted and verified. Research showed that: the worst cutting parameters influenced the surface roughness R_a was radial depth of cut a_e, its influence was highly significant, followed by spindle speed n and depth of axial cut a_p; the most serious impact cutting parameter of cutting force F was the feed speed v_f, followed by the spindle speed n and radial depth of cut a_e; verification test showed that the optimal cutting parameters combination were reasonable and the calculation errors of the predicted values and experimental values were very small, indicating that Taguchi method in cutting parameters optimization of cutting mould steel PM60 was valid.

Abstract: Dental ceramics has become dominant materials used in dental restorations. Dental ceramics have several advantages, such as stable performance, good bio-compatibility, little possibility to attach plaque, and similarity to the color of permanent tooth. However complex surface characteristics and hard and brittle properties of dental ceramic materials caused difficulties in the processing and subsequent grinding. The complicated craft and high failure rate of dental ceramics greatly limit its wide application in clinical. Thus, fully understanding the special cutting tools grinding performance and researching the material damage process caused by grinding temperature and grinding force are of great significance. Research on dental ceramic grinding was reviewed in this paper. The removal mechanism of dental ceramic materials and the influence of parameters settings on the grinding force, grinding temperature, and the surface quality have been studied. Besides the existing problems in dental ceramic grinding technology were pointed out.

Abstract: In this paper, the chip morphologies and sizes of hardened PM steel S790 (68 HRC) using four types coated end mills (TiAlN TiCrAlN TiSiN and TiAlSiN) under different cutting parameters in dry milling condition were studied. During the process of high speed milling hardened steel S790, the chip morphologies change from continuous strip to sawtooth with the increase of cutting speeds. When cutting speed reaches 100 m/min, obvious shear slip occoured on the top surface of the chips, which are formed by multilayer metal unit piled by shear slip plane segmentation. The bottom of the chips, which squeeze and slid with rake face of end mills, show shiny smooth surface. TiAlSiN and TiSiN coatings are more suitable for high speed milling than TiAlN and TiCrAlN coatings. With the increase of cutting parameters such as cutting speed, feed rate and axial cutting depth, the chips morphology of S790 change from continuous strips to trapezoidal and triangle sawtooth, and the chips trend easy separation.

Abstract: Due to the weak rigidity of micro-drills and impulse effects, the micro-drill breakage is a common problem in printed circuit board micro-drilling. Traditional micro-drill breakage detection methods and principles, including vacuum-type, laser-type, and contact-type detection, were reviewed in this paper. The comparison of three detection methods showed that the contact-type detection can more satisfy the performance of CNC drilling machine. Three effective contact-detection circuits, including no transformer and rectifier circuit pulse-type, active-type, and trigger-type detection circuit, were introduced. And as a conclusion, differences of these detection methods were compared. Based on the characteristic of three effective micro-drill breakage contact detection circuits, the development trends and designs of innovative detection circuit were proposed to meet the challenges in micro-drill breakage measurement during PCB drilling.

Abstract: There are four kinds of ultra-precision lapping machine bed were developed: with/without reinforcing rib, with/without a pair of closed sides. The finite element analysis was used to find the optimal design of the machine bed. The 3D model of the ultra-precision lapping machine bed was built by SolidWorks, and ANSYS software was used for static analysis and modal analysis. The results suggest that when reinforcing rib and a pair of closed sides were owned, the machine bed had some better static and dynamic characteristics. The mix-deformation of this machine bed was 1.911μm, and the first-order inherent frequency was 101.74Hz.

Abstract: Graphite chip formation is important for the understanding of high speed milling of brittle graphite. This paper is aimed to reveal the influence of cutting conditions on the graphite chip formation in high speed milling. The relationship between the maximum undeformed chip thickness and cutting parameters was analyzed, and the influence of cutting parameters, tool geometry and milling patterns on the chip formation of brittle graphite was studied. It is concluded that the transitions of graphite chip formations were highly dependent on the undeformed chip thickness which is decided by the combination setting of feed per tooth and radial depth of cut. Big fractured block chip occurs more easily in up milling than down milling. Tool rake angle influences the chip formation according to the maximum undeformed chip thickness.

Abstract: An ultra-precision lapping machine is developed, with precision turning technology to condition lapping plate in situ, pressurizating by cylinder pressure, and cooling frictional heat with inner cooling system, the lapping machine is used for ultra-precision lapping of brittle materials. The design concept and the structure of the key components of the utra-precision sngle-plane lpping mchine are discussed. After precision turning, the flatness of lapping plate is down to 0.002 mm/400 mm, and experimental results show that the flatness of circular grating glass has been greatly improved after ultra-precison lapping.

Abstract: This paper introduces the micro-abrasive suspension jet polishing technology in precision machining technology. In order to understand the micro-abrasive suspension jet erosion morphology and material removal mechanism, the erosion experiments of micro-abrasive suspension jet on 40CrMnMo7 special steel work-piece were taken. We found that when the incident angles are 90°, 60°, 30°, the polishing area is respectively annular shape, horseshoe shape and blade shape. During the erosion process, as the incident angle becomes smaller, most amounts of abrasive particles impact angles will also be small, and these cause more material removal. When the particles impact the work-piece with small angles, most particles play shearing action on the work-piece and leave the work-piece nanoscale scratches; while the particles impact the work-piece at large angles, extrusion and blow are formed by the majority of the particles on the work-piece, leaving different small size pits.

Abstract: The surface quality of graphite cannot be completely evaluated only by the roughness value Ra measured by profilometer. The surface damage ratio Sc is presented to give quantitative description of surface quality of graphite, which was calculated as the ratio of the projection area of fracture craters to the overall area of free surface. The machined surface was observed and taken photo by use of the stereo microscope with CCD image acquisition system. Matlab image processing tool was used to convert the color photo to binary image, in which fracture craters were shown as black pixels and the other surfaces as white pixels. The surface damage ratio is the result of the sum of black pixels divided by the overall pixels. Under the same conditions of high speed machining experiments for verification, the surface damage ratio was calculated in comparison with the Ra values measured by profilometer. The variation tendency of surface damage ratios exhibited good coherence to the measured roughness.