Research On Surface Wettability Of Textured Cutting Tools

Cutting fluid is widely used in cutting,which can improve the lubrication of the tool-chip contact area,reduce cutting force,cutting temperature,and reduce tool wear.However,it is difficult for the cutting fluid to penetrate into the tool-chip contact area and play its due lubricating and friction-reducing effects in cutting with traditional tools,resulting in severe friction and adhesion between the tool-chip interface,and causing tool wear and shortening tool life.Aiming at this problem,this topic proposes a method that combines surface microtexturing technology and solid surface wettability.The influence of microtexture on the penetration process of cutting fluid was analyzed.The influence mechanism of cutting fluid penetration of micro-textured tools on tool-chip interface friction,cutting force and cutting temperature was revealed.The wettability of different textured surfaces was studied,and the influence of different textured surfaces on the wettability was clarified.A variety of textured surfaces with different wettability were designed and fabricated,and the influence of textured surface wettability on cutting performance and friction and wear characteristics of tools was obtained.The effect mechanism of textured surface wettability on tool friction reduction and lubrication is revealed.First,the penetration mechanism of cutting fluid in the cutting process is analyzed,and the penetration process of cutting fluid in traditional tools and micro-textured tools is compared.The analysis shows that the microtexture can make the cutting fluid enter the capillary of the tool-chip contact interface directly through the gas phase filling,without the liquid phase infiltration and droplet evaporation stages,which greatly reduces the time for the cutting fluid to penetrate into the capillary.Therefore,the shear strength of the boundary lubrication layer is reduced,and the cutting force and cutting temperature during the cutting process are effectively reduced.Through the penetration test of cutting fluid on the micro-textured surface and the cutting test of the micro-textured tool,the effectiveness of the micro-texture in promoting the penetration and lubrication of the cutting fluid is verified:the cutting fluid can realize the gas phase and liquid phase on the micro-textured surface.The cutting fluid can directly enter the capillary of the tool-chip interface in the form of gas phase through the micro-texture filling,reducing the shear strength of the tool-chip interface and improving the friction characteristics of the tool surface.Secondly,two types of microtextures are designed according to the penetrating lubrication characteristics of cutting fluids:linear microtexture and grid microtexture.Linear microtextures with width,depth and spacing of 30-50 μm,5-18 μm and 200-500μm were processed on the surface of the sample by nanosecond infrared laser,respectively.Grid-like microtextures with the width,depth and spacing of microgrooves of 17-23 μm,4-7 μm and 100-250 μm were processed on the surface of the sample by nanosecond ultraviolet laser.The wettability of different textured surfaces was measured,and the results showed that microtexturing can effectively reduce the contact angle of cutting fluid on the surface of the sample,increase the spreading area and spreading rate.At the same time,the wettability of the grid-like micro-textured surface is better than that of the linear micro-textured surface.The mechanism of microtexture enhancing the wettability of the surface of the sample was studied:the surface tension of the liquid will affect the wettability of the liquid,the smaller the surface tension of the liquid,the smaller the gravitational force of the surface molecules,the smaller the movement resistance,and the stronger the wettability.Microtexturing increases the surface area and surface roughness of the sample,increasing the actual contact area of the droplet with the sample.The laser processing microtexture produces polar components such as ether group(C-O),carbonyl group(C=O)and carboxyl group(O=C-O)on the surface of the sample,and these highly polar functional groups are hydrophilic.Then,the effect of textured surface wettability on the friction and wear characteristics was systematically investigated through friction and wear tests.The results show that under the same experimental conditions,the average friction coefficient of the textured surface with enhanced wettability is significantly lower than that of the untextured sample surface(UTS),and the average friction coefficient decreases with the enhancement of wettability.Compared with the UTS specimen,the friction coefficient of the mesh-textured specimen CPTS-3 when lubricated by oil-based cutting fluid and water-based cutting fluid is reduced by 68.9%and 62.7%,respectively.Meanwhile,the adhesive wear on the sample CPTS-3 surface is the lightest.This is mainly due to the decrease of the contact angle,which causes the lubricating fluid in the friction area to generate additional traction tension at the boundary,which increases the area of the absorbing lubricating film area in boundary lubrication and improves the lubrication state of the contact interface of the friction pair.The lubricating effect of the textured surface wettability on friction is more significant with the increase of sliding speed and load,which is mainly due to the increase of the spreading rate of the lubricating fluid on the surface of the textured sample,which makes it relative to the friction surface of the grinding ball.The hysteresis is reduced,and the frictional resistance between the fluid layers is also reduced.The enhanced surface wettability of the microtexture makes it easier for the friction interface to form a continuous lubricating film,especially under the condition of high sliding speed and high load,the boundary lubrication state of the friction zone can be partially transformed into a mixed lubrication state,thereby realizing the antifriction effect.Finally,textured cutting tools with different wettability were designed and fabricated,and the effect of surface wettability of textured cutting tools on cutting performance was studied through turning experiments.The results show that the textured tools(STS-3 and CPTS-3)with enhanced surface wettability can effectively reduce the cutting force,cutting temperature and the average friction coefficient between tool and chip compared with the conventional tool(UTS).The mesh textured tool CPTS-3 with the best wetting performance had the most significant decrease.By analyzing the wear morphology of different tools,it is found that the wear degree of the textured tools STS-3 and CPTS-3 is improved compared with the untextured tool UTS.The main mechanism of microtexture enhancing the surface wettability and improving the cutting performance of the tool is as follows:the microtexture improves the contact state of the tool-chip interface,and turns part of the dry friction into boundary friction and mixed friction.The microtexture reduces the time for the cutting fluid to penetrate into the capillary of the tool-chip interface,increases the area of the lubricating layer,improves the stress distribution of the cutter-chip interface,reduces the shear strength of the cutter-chip interface,and thus reduces the tool-chip contact Surface friction coefficient,cutting force and cutting temperature.