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
A new method of ultrasonic vibration electrical discharge machining(UEDM) in gas is proposed in this paper. In UEDM in gas, the gap between tool electrode and workpiece is small(about 0.01mm), and the voltage between ...A new method of ultrasonic vibration electrical discharge machining(UEDM) in gas is proposed in this paper. In UEDM in gas, the gap between tool electrode and workpiece is small(about 0.01mm), and the voltage between them is higher than EDM in liquid, so short circuit is easy to take place. It is very important for improving the MRR to avoid short circuit. Therefore, some measures have been taken, a rotation and a planetary motion are superimposed upon the tool electrode. During UEDM in gas, workpiece is vibrating with ultrasonic frequency, which can have the molten workpiece material ejected out from base body of workpiece without being reattached to it again, it is very useful to increase MRR. The electrode is formed to be thin-walled pipe, the high pressure gas is supplied through the internal hole and flow over the machining gap with a high velocity. It can enhance the removal of molten and evaporated workpiece material. The gas with a high velocity also cools and solidifies the removed material and prevents them from adhering onto the surface of the tool electrode. Furthermore, during the pulse interval, the gas with a high velocity blows off the plasma formed by the previous discharge and decreases the temperatures of the discharge spots on the tool electrode and the workpiece due to heat transfer, thus guaranteeing the recovery of the dielectric strength of the gap. The experiments were performed on an electrical discharge small hole machine DK730(made in China, modified by author). The worktable of the machine was especially designed to accept an ultrasonic vibration unit, and the clamp of the machine was designed to accept high pressure gas when it turning. 45# steel and copper were selected as workpiece and tool electrode respectively. Air and oxygen gas were selected as gas mediums. Five sets of experiments were carried out to show the effects of open voltage, pulse duration, wall thickness of pipe electrode, amplitude of ultrasonic vibration and gas medium on the MRR. Some observations of the roughnes展开更多
The tool flank begins to wear out as soon as cutting process proceeds. Cutting parameters such as cutting forces and cutting temperature will vary with increasing degree of flank wear. In order to reveal the relations...The tool flank begins to wear out as soon as cutting process proceeds. Cutting parameters such as cutting forces and cutting temperature will vary with increasing degree of flank wear. In order to reveal the relationship between them, the theoretical situations of cutting process were analyzed considering the tool flank wear effect. The variation rules of cutting force, residual stress and temperature distributions along with the tool flank wear were analyzed comparing with the sharp tool tip. Through FEM simulation method, affections of the tool flank wear value VB on cutting forces, residual stress and temperature distributions were analyzed. A special result in this simulation is that the thrust force is more sensitive to tool flank wear, which can be used as a recognition method of tool condition monitoring. The FEM simulation analysis result agrees well with the experimental measuring data in public literatures and some experiments made also by the authors.展开更多
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.
文摘A new method of ultrasonic vibration electrical discharge machining(UEDM) in gas is proposed in this paper. In UEDM in gas, the gap between tool electrode and workpiece is small(about 0.01mm), and the voltage between them is higher than EDM in liquid, so short circuit is easy to take place. It is very important for improving the MRR to avoid short circuit. Therefore, some measures have been taken, a rotation and a planetary motion are superimposed upon the tool electrode. During UEDM in gas, workpiece is vibrating with ultrasonic frequency, which can have the molten workpiece material ejected out from base body of workpiece without being reattached to it again, it is very useful to increase MRR. The electrode is formed to be thin-walled pipe, the high pressure gas is supplied through the internal hole and flow over the machining gap with a high velocity. It can enhance the removal of molten and evaporated workpiece material. The gas with a high velocity also cools and solidifies the removed material and prevents them from adhering onto the surface of the tool electrode. Furthermore, during the pulse interval, the gas with a high velocity blows off the plasma formed by the previous discharge and decreases the temperatures of the discharge spots on the tool electrode and the workpiece due to heat transfer, thus guaranteeing the recovery of the dielectric strength of the gap. The experiments were performed on an electrical discharge small hole machine DK730(made in China, modified by author). The worktable of the machine was especially designed to accept an ultrasonic vibration unit, and the clamp of the machine was designed to accept high pressure gas when it turning. 45# steel and copper were selected as workpiece and tool electrode respectively. Air and oxygen gas were selected as gas mediums. Five sets of experiments were carried out to show the effects of open voltage, pulse duration, wall thickness of pipe electrode, amplitude of ultrasonic vibration and gas medium on the MRR. Some observations of the roughnes
基金Project(50435020) supported by the National Natural Science Foundation of China
文摘The tool flank begins to wear out as soon as cutting process proceeds. Cutting parameters such as cutting forces and cutting temperature will vary with increasing degree of flank wear. In order to reveal the relationship between them, the theoretical situations of cutting process were analyzed considering the tool flank wear effect. The variation rules of cutting force, residual stress and temperature distributions along with the tool flank wear were analyzed comparing with the sharp tool tip. Through FEM simulation method, affections of the tool flank wear value VB on cutting forces, residual stress and temperature distributions were analyzed. A special result in this simulation is that the thrust force is more sensitive to tool flank wear, which can be used as a recognition method of tool condition monitoring. The FEM simulation analysis result agrees well with the experimental measuring data in public literatures and some experiments made also by the authors.
