Study On Micro-pool Self-lubricating Cutting Tools

Micro-pool self-lubricating tools were designed and developed based on micro-pool lubricating idea, excellent tribological properties of solid lubricating materials, the tribological behaviors and wear mechanisms of dry cutting tools. The lubricating mechanism of micro-pool lubricating tools were detailed studied as well as its preparation methods and design theory.The concept and design ideas of the micro-pool self-lubricating tool was proposed based on the analysis of solid lubricanting technology and cutting lubricanting mechanism. Micro-holes were made on the rake face or the flank face of tool inserts. Solid lubricants were embedded into the micro-holes to form micro-pool self-lubricating cutting tool. During cutting processes, the chip slides against the tool rake face at a high speed, and induces high cutting temperature. Under high cutting temperature and chip friction, the solid lubricants may be released from the micro-holes, smeared on the tool face. Then a thin lubricating film may create on the tool face which achieve the micro-pool lubricating and reduce the tool wear. The designed models of micro-pool self-lubricating cutting tool were established under the analysis of tribological behaviors and wear mechanisms of dry cutting tools.The Finite Element Analysis (FEA) modeling for analysis of cutting temperature and cutting forces distribution of micro-pool self-lubricating tool were established and used to analyze the theory of cutting temperature and cutting forces of micro-pool self-lubricating cutting tool. Analysis results indicated that three cutting force components and cutting temperature are both proportional to the average shear strengthτc and the tool-chip contact length If. A reduction of average shear strengthτc or the tool-chip contact length If will both result in the reduced cutting forces and cutting temperature during cutting processes. The micro-holes structure of the micro-pool self-lubricating tools were studied. The effect of micro-holes on stress distribution of the cutting tools were analyzed and the appropriate micro-holes structural parameters were put forward:the micro-holes are circular; the number of micro-holes is 4; the diameter of micro-holes is 0.15±0.02 mm; the distance L1 is about 0.3mm; the distance L2 is about 0.3mm; the distance L36 is about 00.3 mm; the depth H is 0.30 mm; the axis distance L4 is 0.05 mm.Micro-EDM method was choosed to prepare micro-holes of the micro-pool self-lubricating tools after analysis of micro-holes preparing methods. The appropriate process parameters of EDM was determined:the machining voltage is 125 V, the processing capacitance is 4.45 nF. The influence of processing paremeters on processing quality was analyzed.In order to investigate tribological behaviors of the micro-pool self-lubricating tool, friction and wear tests were conducted on the micro-pool self-lubricating tool samples with the same micro-holes structures as the micro-pool self-lubricating tool. The influence of micro-holes structure and the solid lubricants embedded in the micro-holes on the wear behaviors were studied. Results indicated that friction coefficient and wear rate of the micro-pool self-lubricating tools sample MP-MS are both lower than those of the traditinal sample YT14, the friction coefficient can be decreased about 55%-65% and the wear rate can be reduced about 40%-50%. The best antifriction lubricating properties appeared when the ratio of pool depth and pool spacing was 0.4 to 0.5 and the pools were filled with solid lubricant MoS2. The tribological mechanism of micro-pool self-lubricating tool filled with solid lubricant was put forward:the solid lubricant was squeezed out or smeared on the interface during sliding process, a lubricating film is formed to lead to reduce the friction coefficient between the contact interface, and the friction and wear behaviors of micro-pool self-lubricating tool samples were improved.Cutting tests on 45# steel were carried out with cutting tool MPR-4MS, cutting tool MPR-4MH, MPF-4MS, cutting tool MPF-4MH and traditional tool YT14. The results showed that, compared with the traditional cutting tool YT14, cutting with cutting tool MPR-4MS and cutting tool MPR-4MH could result in obviously reduced cutting forces, cutting temperature and average friction coefficient on the rake face. The cutting tool MPR-4MS had the best rake wear resistance and the cutting tool MPF-4MS had the best flank wear resistance.Micro-hole structure of micro-pool self-lubricating tool affects the cutting performance. Based on cutting tests with micro-pool self-lubricating cutting tool MPR-4MS, the micro-holes filled with MoS2 near the tool tip and the main cutting edge have larger effect on cutting performance than other holes for the MPR-4MS tools. The cutting performance of micro-pool self-lubricating cutting tool vary with the different solid lubricant additives, and are affected by cutting speed obviously. when the cutting speed is less than 100 m/min, the cutting performance of the MPR-4MS cutting tool is best; the cutting performance of the MPR-4CF cutting tool significantly slows down when the cutting speed is higher than 100 m/min; the MPR-4C cutting tool has steady cutting performance, which is affected lightly by the cutting speed. Micro-pool self-lubricating cutting tools will not be able to achieve self-lubricating when the cutting speed is higher than 220 m/min, for severe chip adhesives on the micro-holes. Therefore, the micro-pool self-lubricating cutting tools are fit to cutting whthin cutting speed of 200 m/min.The self-lubricating mechanism of micro-pool self-lubricating cutting tool is put forward. on the one hand, during cutting processes, the chip slides against the tool rake face at a high speed, and induces high cutting temperature. Under high cutting temperature and chip friction, the solid lubricants may be released from the micro-holes, smeared on the tool face. Then a thin lubricating film may create on the tool face, which results in reduced average shear stressτc and coefficient of friction on the rake face, increasd shear angle, reduced cutting forces, the cutting heat and the cutting temperature; on the other hand, the reduced contact length lf at the tool-chip interface results in a reduction in cutting forces and cutting temperature, which is contributed to the decrease of tool wear. The former factor is primary.