Analysis Of Formation Mechanisms And Restraining Methods Of GF/PP Composites Drilling Damage

Thermoplastic composites not only have high specific strength,but they are also easy to repair and environmental friendly compared with thermosetting composites.Thermoplastic composites has a great potential for application in high-end industrial equipment and common civilian products,which have been developed gradually in recent years.Machining processes are inevitable for thermoplastic composites,such as drilling and milling,because of assembly process.However,it is very easy to appear burr,tearing and other damage during machining,due to its anisotropy as well as thermoplastic matrix,which causes mechanical properties decline.Therefore,its promotion and application in automobile and other fields are restricted,which need to be solved urgently.In order to reveal the drilling damage formation mechanism of thermoplastic composites,continuous glass fiber reinforced polypropylene composite(GF/PP)was used as an object,and a high-speed photography experimental platform with function of measuring thrust force and outlet temperature synchronously was built.Mechanism of GF/PP composites orthogonal cutting and drilling damage formation were studied and drilling damage were reduced by optimization of process parameters and tool structure improvement.The main research contents and conclusions are as follows:(1)Mechanism of GF/PP composites cutting was studied by orthogonal cutting experiments.Workpiece surface topography and chip shapes with various fiber cutting angles are analyzed.The results show that cutting quality is best with 45° fiber cutting angles and continuous chip is formed except 135 ° fiber cutting angle.Based on three deformation regions hypothesis,GF/PP composites orthogonal cutting force near 45° fiber cutting force is studied by theoretical analysis and the forecasting precision of formula for orthogonal cutting force variation coefficient is satisfactory.(2)In order to observe the drilling process,a high-speed photography experimental platform was built.Based on this platform,mechanism of drilling damage formation of thermoplastic composites is studied.Outlet tearing is mainly outlet damage,which is caused by the impact between large burrs and cutting edges.Cutting dead zone increasing can induce inlet tearing,because cutting force increasing can lead to interface crack.The results show that the outlet drilling temperature is high at low feed rate and is relatively steady at high feed rate.Improvement of spindle speed increases the outlet drilling temperature,while it has no effect on thrust force.Outlet tearing is serious with a higher or lower feed rate.0° burr is serious at low feed rate.Inlet tearing is serious at high feed rate.(3)An experimental study was conducted,and the tearing factors are reduced to 1.06~1.08 with appropriate parameters.Based on the thought of reducing the force during cutting inlet fibers,outer corner grooves were used to improve inlet drilling quality and sawtooth structure was used to reduce outlet burrs.A new general-purpose large hole tool was designed for application requirements and high quality holes was obtained.The author explores mechanism of GF/PP composites orthogonal cutting,and then analyzes the drilling damage formation mechanism in various positions,and finally improve the hole quality by choosing appropriate parameters and tool structures improvements.The results help to guide researches on tool development and practice production.