Chengyong Wang

Study on the fuzzy ranking of granite sawability

The ranking system of granite sawability is very important for selecting the optimum machining parameters and suitable tools to obtain high tool life and production rate. On account of the complicated relation between the mineral composition and mechanical properties with the sawability of granite, a new method by fuzzy mathematics was developed to establish the dependence function and fuzzy relationship between the quartz content, quartz grain size, hardness, compressive strength, and abrasiveness of granite with sawing force as well as tool wear. The sawability of several types of granite was evaluated and classified by this method. With the fuzzy ranking system established and the sawability classification, it is very convenient to evaluate the sawability and select a suitable saw blade and the proper sawing parameters for a new granite type by only the petrographic analysis and mechanical properties testing.

Drilling force and temperature of bone under dry and physiological drilling conditions

Many researches on drilling force and temperature have been done with the aim to reduce the labour intensiveness of surgery, avoid unnecessary damage and improve drilling quality. However, there has not been a systematic study of mid- and high-speed drilling under dry and physiological conditions(injection of saline). Furthermore, there is no consensus on optimal drilling parameters. To study these parameters under dry and physiological drilling conditions, pig humerus bones are drilled with medical twist drills operated using a wide range of drilling speeds and feed rates. Drilling force and temperature are measured using a YDZ-II01W dynamometer and a NEC TVS-500EX thermal infrared imager, respectively, to evaluate internal bone damage. To evaluate drilling quality, bone debris and hole morphology are observed by SEM(scanning electron microscopy). Changes in drilling force and temperature give similar results during drilling such that the value of each parameter peaks just before the drill penetrates through the osteon of the compact bone into the trabeculae of the spongy bone. Drilling temperatures under physiological conditions are much lower than those observed under dry conditions, while a larger drilling force occurs under physiological conditions than dry conditions. Drilling speed and feed rate have a significant influence on drilling force, temperature, bone debris and hole morphology. The investigation of the effect of drilling force and temperature on internal bone damage reveals that a drilling speed of 4500 r/min and a feed rate of 50 mm/min are recommended for bone drilling under physiological conditions. Drilling quality peaks under these optimal parameter conditions. This paper proposes the optimal drilling parameters under mid- and high-speed surgical drilling, considering internal bone damage and drilling quality, which can be looked as a reference for surgeons performing orthopedic operations.

DYNAMIC ANALYSIS OF THE LENGTHENED SHRINK-FIT HOLDER AND CUTTING TOOL SYSTEM IN HIGH-SPEED MILLING

A finite element model of the matching of lengthened shrink-fit holder (LSFH) and cutting tool is established and the Rayleigh viscous damping model is used to calculate the reasonable structural damping of this model. A milling force model is developed to predict the transient milling force using back propagation neural network (BPNN). The dynamic characteristic of matching of LSFH and cutting tool is analyzed by means of the universal commercial software ANSYS10.0. The results of numerical simulation are obtained and verified against the practical measurements that show that they are consistent. This study is important to optimum design of LSFH, and to rationally choose the matching of LSFH and cutting tool, deformation analysis, error compensation and parameters optimization in high-speed milling.

Radial grip rigidity of the matching of lengthened shrink-fit holder and cutter in high-speed milling

Though the lengthened shrink-fit holder (LSFH) is widely applied in high speed milling of the parts characterized by deep cavities at present, its design and selection mainly depends on the experience and lacks a correct theoretical guidance. In this paper, attention is focus on the radial grip rigidity of the matching of LSFH and cutter in high speed milling. Based on the experiment modal analysis (EMA) technique, an accurate finite element model of the matching of LSFH and cutter is established firstly. Subsequently, the influence of different interference, grip length and spindle speed on the grip rigidity of LSFH are analyzed. The analysis results show that there is a reasonable interference and grip length between the LSFH and cutter so that to have a steepless grip and have a good radial grip rigidity and at the same time to avoid the strength of LSFH to exceed it’s yield limit which will reduce the precision and service life of LSFH, besides when spindle speed reach a extension the weakening influence of the centrifugal force on the radial grip rigidity of the matching of LSFH and cutter should been taken into account. Finally, the finite element analysis results are verified based on the construction of measurement method of the grip rigidity and the results fit very well. The studies provide a theoretical basis for the design, selection and the serialization and standardization of the matching of LSFH and cutter.

Constitutive equation for hardened SKD11 steel at high temperature and high strain rate using the SHPB technique

In this present work, dynamic tests have been performed on hardened SKD11 steel (62 Rockwell C hardness) specimens by means of a high temperature split Hopkinson pressure bar (SHPB) test system. Effects of temperature as well as those of strain and strain rate for the hardened steel are taken into account by using two ellipsoidal radiant heating reflectors with two halogen lamps and magnetic valve. The result obtained at high stain rates were compared with those at low strain rates under the different temperature. It was seen that the flow stress curves are found to include a work hardening region and a work softening region and the mechanical behavior of the hardened steel is highly sensitive to both the strain rate and the temperature. To determine the true flow stress- true strain, temperature relationship, specimens are tested from room temperature to 1073K at a strain rate form 0.01 s-1 to 104 s-1: The parameters for a Johnson-Cook constitutive equation and a modified Johnson-Cook constitutive equation are determined from the test results by fitting the data from both quasi-static compression and high temperature-dynamic compression tests. The modified Johnson-Cook constitutive equation is more suitable for expressing the dynamic behavior of the hardened SKD11 steel above the vicinity of the recrystallization temperature.

The entry drilling process of flexible printed circuit board and its influence on hole quality

Purpose – The purpose of this study is to present the entry drilling process of flexible printed circuit board (FPCs) and its influence on hole quality, especially hole location accuracy. Compared with the traditional PCB drilling process, the technology of drilling FPCs is facing more problems, such as hole location accuracy, smear on the hole wall surface, burned hole wall surface, etc. Moreover, the materials of FPCs are quite different from the rigid printed circuit boards (RPCs). FPCs no longer contain glass fiber cloths to reinforce resin, resulting in flexibility. Micro-hole quality is the most important issue in FPC drilling. Suggestions were given to obtain higher hole qualities and higher FPC reliability. Design/methodology/approach – The entry drilling process of FPC with different kind of entry boards was observed by a high-speed camera. The hole qualities of FPC micro-drilling, especially hole location accuracy and hole entrance quality, were measured. The relationship between entry boards an...

Drilling characteristics of entry board and the influence on PCB micro drilling process

In this paper, the drilling characteristics of aluminum (Al) entry boards, resin coated Al entry boards, and phenolic resin entry boards were investigated. The chip removal, chip morphology, thrust force, and drilling temperature were measured and analyzed. The cutting characteristics among those materials were compared. In addition, the influence of alloy materials on thrust force of entry boards was analyzed. The results demonstrated four efficacy of entry boards, including chip removal, heat dissipation, buffering, and location. The function of location and buffering were mainly reflected in the beginning of drilling. Effect of chip removal and heat dissipation were related to material of entry board. The resin coated Al entry board performed better than aluminum entry board in buffer and chip removal. Moreover the influence of coating resin and its thickness on drilling process of entry board was obvious. Chips of aluminum entry board were easy to wrapping the drill bit than that of resin coated Al entry board. Thermal deformation of coating resin can increase the curl of aluminum chip, thus contributing to the chip removal. The effect of alloy material on thrust force was significant. The increase of coating resin thickness can enhance the buffer effect on thrust force in some degree. The heat dissipation of MVC resin coated Al entry board in PCB drilling was the best.

The tool-wear characteristics of flexible printed circuit board micro-drilling and its influence on micro-hole quality

Purpose Micro-holes are drilled and plated in flexible printed circuit boards (FPCs) for connecting circuits from different layers. More holes, with diameters smaller than 0.3 mm, are required to be drilled in smaller areas with flexible circuits’ miniaturization. The micro-hole quality of micro-drilling is one of the biggest issues of the flexible circuit manufacturers’ production. However, it is not easy to control the quality of micro-holes. The purpose of this study was to conduct research on the tool wear characteristics of FPC drilling process and its influence on micro-hole quality to improve the micro-hole quality of FPC. Design/methodology/approach The tool-wear characteristics of micro-drills after FPC drilling were observed. The influence of spindle speed, feed rate, number of drilled holes and entry board materials on tool-wear was analyzed. The hole qualities of FPC micro-drilling were measured and observed. The relationship between tool-wear and hole quality was analyzed. Findings The result showed that the tool-wear characteristics of FPC micro-drilling was similar to the tool-wear characteristics of rigid printed circuit board (RPC) micro-drilling. Abrasive wear occurred on both the main cutting edges and the chisel edges of micro-drills, even though there was no glass fiber reinforcing the cloth inside FPC. Resin adhesion was observed on the chisel edge. The influence of feed and number of drilled holes on tool-wear was significant. Tool-wear significantly influences the hole quality of FPC. Tool-wear will largely decrease the hole position accuracy of FPC micro-holes. Tool-wear will increase the thickness of PI nail heads and the height of exit burrs. Fracture was the main difference between tool wear of FPC and RPC micro-drilling. Resin adhesion of RPC was much more severe than FPC micro-drilling. Increasing the spindle speed properly may improve tool life and hole quality. Originality/value The technology and manufacturing of FPC has been little investigated. Research on micro-drilling FPC and research data is lacking so far. The micro-hole quality directly affects the reliability of FPC. Thus, improving the micro-hole quality of FPC is very important.