Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in th...Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.展开更多
Inconel 718, a high temperature alloy, is extensive ly used in aircraft, gas engines and nuclear-power plants. It is generally known that the life of ceramic cutting tools in machining Inconel 718 is often restric ted...Inconel 718, a high temperature alloy, is extensive ly used in aircraft, gas engines and nuclear-power plants. It is generally known that the life of ceramic cutting tools in machining Inconel 718 is often restric ted by depth-of-cut (DOC) notch wear. In view of the number of various factors involved and the variety of tool materi als and cutting conditions available, the analysis of the DOC notch wear is very difficult. According to previous work concerning the DOC notch wear of ceramics tools, some Al 2O 3 - and Si 3N 4 -based ceramics tools have show n that the degree of tool notching depends on the thermal shock resistance of a tool material and thermal gradients (interrupted cutting, use of flood coolants) . Other observations suggest that there are chemical interactions between the to ol material and the work-piece. At the same time, an analytical technique based on thermodynamic properties for estimating cutting tool wear was proposed. Howe ver, so far, there is no concrete and convincing explanation for the DOC notch w ear. In all previous studies on the DOC notch wear, it is often assumed that notch we ar happened in the contacting region of the cutting tool and the work-piece, wh ile the exact position of notch wear is always neglected. In his article, He Ning measured the distance l n between tool nose and the center of DOC notch wear, and calculated the theoretical working length l d ― the ideal distance between the DOC notch center and the intersection of th e theoretical depth of cut line and the cutting edge. He found that l n is always greater than l d. It means that the position of the DOC notch is not at the depth of cut line, but out of the theoretical cutting area. He supposed that the saw-tooth shaped burrs and fin-shaped chip edges cause the DOC no tch wear, because only the saw-tooth shaped burrs and fin-shaped chip edges ha ve effect on the tools at the region of notch wear. Although He described the reason of notch wear and did some theoretical analysis of it, he has not done some experiments to verify it. In this paper, an experim ent was done to verify He’s assumption about DOC notch wear. In the present exp eriment, which has been done with the ceramic inserts (LT55), Working conditions at the region of DOC notch wear were analyzed. By using a KISTLER 9265B dyn amometer, the dynamic cutting force signals in three directions were pick up. By comparison between the theoretical frequency, with which the saw-shaped burr a nd fin-shaped chip edge impact on the region of notch wear, and the experimenta l results, it can be seen that the high frequency components of dynamic cutting forces mainly result from the impact effects of the saw-shaped burr and fin-sh aped chip edge. In high speed machining of nickel based alloys, DOC notch wear of ceramic tools is mainly because the impact effect of the burr and fin-shaped chip edge causes tools to be of fatigue damage, and the adherence between tool material and work piece material changes the direction of pressure stress and makes the micro-cra ck to appear and extend quickly.展开更多
The research and development of various classes of ceramic cutting tools in China are described,because manufacturing efficiency is fundamental to the growth of China's economy.
High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional ther...High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional thermal resistance and the ability to retain mechanical properties at elevated temperatures of service environment over 700 ℃. However, they are classified as difficult-to-cut materials due to their high shear strength, work hardening tendency, highly abrasive carbide particles in the microstructure, strong tendency to weld and form built-up edge and low thermal conductivity. They have a tendency to maintain their strength at high temperature that is generated during machining. The Inconel 718 workpiece material used in the experiment was in the hot forged and annealed condition. The commercially available inserts (all inserts were made by Kennametal Inc.) were selected for the tests, a PVD TiAlN coated carbide, a CVD/PVD TiN/TiCN/TiN coated carbide and a CVD Al 2O 3/TiC/TiCN coated carbide were used at the cutting speed range about 50～100 m/min. Three kinds Sialon grade inserts with various geometry and cutting angles were used at the cutting speed range from 100 m/min to 300 m/min. For evaluating the inserts machinability when high speed cutting Inconel 718, Taylor Formula within certain cutting speeds, an high speed cutting experiment of tool life was carried out to establish the models of tool life by means of rapid facing turning test. The conclusions drawn from the turning of Inconel 718 with silicon nitride based ceramic; PVD and CVD coated carbide inserts are as follows: Studies on tool wear in high speed machining. The thorough investigations and studies were made on the tool wear form, wear process and wear mechanism in high speed cutting of difficult-to-machine materials with ceramic tools and with coated carbides. The major wear mechanisms of nickel-based alloys are interactions of abrasive wear, adhesion wear, micro-breakout and chipping. Optimization analysis on the application of high speed machining. Based on the experimental results, the optimal cutting parameters were determined for machining of Inconel 718 at high speed. The recommendation of tool inserts for high speed cutting inconel 718 were ceramic inserts of KY2000 with negative rake angle and KY2100 with round type, the PVD coated carbide insert KC7310 was recommended for its lower price.展开更多
文摘Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.
文摘Inconel 718, a high temperature alloy, is extensive ly used in aircraft, gas engines and nuclear-power plants. It is generally known that the life of ceramic cutting tools in machining Inconel 718 is often restric ted by depth-of-cut (DOC) notch wear. In view of the number of various factors involved and the variety of tool materi als and cutting conditions available, the analysis of the DOC notch wear is very difficult. According to previous work concerning the DOC notch wear of ceramics tools, some Al 2O 3 - and Si 3N 4 -based ceramics tools have show n that the degree of tool notching depends on the thermal shock resistance of a tool material and thermal gradients (interrupted cutting, use of flood coolants) . Other observations suggest that there are chemical interactions between the to ol material and the work-piece. At the same time, an analytical technique based on thermodynamic properties for estimating cutting tool wear was proposed. Howe ver, so far, there is no concrete and convincing explanation for the DOC notch w ear. In all previous studies on the DOC notch wear, it is often assumed that notch we ar happened in the contacting region of the cutting tool and the work-piece, wh ile the exact position of notch wear is always neglected. In his article, He Ning measured the distance l n between tool nose and the center of DOC notch wear, and calculated the theoretical working length l d ― the ideal distance between the DOC notch center and the intersection of th e theoretical depth of cut line and the cutting edge. He found that l n is always greater than l d. It means that the position of the DOC notch is not at the depth of cut line, but out of the theoretical cutting area. He supposed that the saw-tooth shaped burrs and fin-shaped chip edges cause the DOC no tch wear, because only the saw-tooth shaped burrs and fin-shaped chip edges ha ve effect on the tools at the region of notch wear. Although He described the reason of notch wear and did some theoretical analysis of it, he has not done some experiments to verify it. In this paper, an experim ent was done to verify He’s assumption about DOC notch wear. In the present exp eriment, which has been done with the ceramic inserts (LT55), Working conditions at the region of DOC notch wear were analyzed. By using a KISTLER 9265B dyn amometer, the dynamic cutting force signals in three directions were pick up. By comparison between the theoretical frequency, with which the saw-shaped burr a nd fin-shaped chip edge impact on the region of notch wear, and the experimenta l results, it can be seen that the high frequency components of dynamic cutting forces mainly result from the impact effects of the saw-shaped burr and fin-sh aped chip edge. In high speed machining of nickel based alloys, DOC notch wear of ceramic tools is mainly because the impact effect of the burr and fin-shaped chip edge causes tools to be of fatigue damage, and the adherence between tool material and work piece material changes the direction of pressure stress and makes the micro-cra ck to appear and extend quickly.
文摘The research and development of various classes of ceramic cutting tools in China are described,because manufacturing efficiency is fundamental to the growth of China's economy.
文摘High speed machining (HSM) technology is one of important aspects of advanced manufacturing technology. Nickel-based superalloys have been widely used in the aircraft and nuclear industry due to their exceptional thermal resistance and the ability to retain mechanical properties at elevated temperatures of service environment over 700 ℃. However, they are classified as difficult-to-cut materials due to their high shear strength, work hardening tendency, highly abrasive carbide particles in the microstructure, strong tendency to weld and form built-up edge and low thermal conductivity. They have a tendency to maintain their strength at high temperature that is generated during machining. The Inconel 718 workpiece material used in the experiment was in the hot forged and annealed condition. The commercially available inserts (all inserts were made by Kennametal Inc.) were selected for the tests, a PVD TiAlN coated carbide, a CVD/PVD TiN/TiCN/TiN coated carbide and a CVD Al 2O 3/TiC/TiCN coated carbide were used at the cutting speed range about 50～100 m/min. Three kinds Sialon grade inserts with various geometry and cutting angles were used at the cutting speed range from 100 m/min to 300 m/min. For evaluating the inserts machinability when high speed cutting Inconel 718, Taylor Formula within certain cutting speeds, an high speed cutting experiment of tool life was carried out to establish the models of tool life by means of rapid facing turning test. The conclusions drawn from the turning of Inconel 718 with silicon nitride based ceramic; PVD and CVD coated carbide inserts are as follows: Studies on tool wear in high speed machining. The thorough investigations and studies were made on the tool wear form, wear process and wear mechanism in high speed cutting of difficult-to-machine materials with ceramic tools and with coated carbides. The major wear mechanisms of nickel-based alloys are interactions of abrasive wear, adhesion wear, micro-breakout and chipping. Optimization analysis on the application of high speed machining. Based on the experimental results, the optimal cutting parameters were determined for machining of Inconel 718 at high speed. The recommendation of tool inserts for high speed cutting inconel 718 were ceramic inserts of KY2000 with negative rake angle and KY2100 with round type, the PVD coated carbide insert KC7310 was recommended for its lower price.
