Design Of Gundrill Chip Breaker Groove And Its Application In Deep-hole Drilling Of 42CrMo And RuT450

Gundrills have been in use for a long time in automobile and mold manufacturing.They are extensively used as a useful means of deep and precision-hole drilling.The effective surface finish can be achieved with an accuracy of surface roughness and straightness.Recently,there is much work needed to be done for the chip control when drilling the components with the difficult-to-machine materials and the holes with an excessive depth-to-diameter ratio.These problems become serious,extremely to lead the drills to be broken,when drilling gear shaft of alloy steel 42CrMo for Great Wall Automobile Company and cylinder head block of vermicular cast iron RuT450 for Wuxi Diesel Engine Company.In this paper,a chip breaker groove has been developed for gundrill.The on-line tests demonstrate that performance of the novel gundrill increases in comparison with that of a conventional drill point.When drilling slant oil holes on crankshafts of alloy steel 42CrMo,problems of long chip often become hazardous to the operator,as well as the surface finish of the part produced.The reason of this cutting phenomenon is that plasticity and hardness of alloy steel 42CrMo is higher than those of the common carbon steel.In the recommended cutting speed from64m/min to 112m/min and the cutting feed from 0.02mm/r to 0.03mm/r,chips produced with these ductile materials have an average length more than 80mm.A typical chip breaker groove is designed in this paper.Its geometry is defined by five parameters,which includes slot width L_Bn,oblique angle?,axial inclination angle?,radial inclination angle?and nose radius R.The mathematical model is described by the vectors and the matrix of coordinates transformation.It can be ground on the planar rake face of gundrill by a grinder,when the configuration of the grinding wheel position is accurately determined.As a result,the rake angles distribution along the cutting edge in the breaker groove gundrill are bigger than those of conventional gundrill.It means that breaker groove will sharp the cutter and improve the drilling performance without reduction strength of the cutting edge.In addition,when deep-hole drilling on guide oil holes on cylinder head block of vermicular cast iron RuT450,problems of severe wear in drill flank become intensified,due to the higher thermo resistant fatigue strength of this material.In the condition of cutting speed 58m/min and the cutting feed 0.08mm/r,the tool life to drill RuT450 descends to be only half of that to drill HT250.The optimal geometric parameters of chip breaker groove have been investigated in RuT450 deep drilling and the gundrill wear is reduced significantly.A mass of tests have been compared the cutting performance of a conventional gundrill with a newly gundrill with the chip breaker groove.It is summarized as follows:?1?Under different cutting conditions,the optimal cutting speed 96m/min and cutting feed 0.025mm/r are explored to drill 42CrMo with a suitable axial cutting force and torque.Similarly,the cutting speed 1800r/min and cutting feed 0.08mm/r is the optimum values when drilling RuT450.?2?The Survey of the chip morphology shows that the chip breaking widely take place when the axial inclination angle?is designed to be 14°for the chip breaker groove.In this condition,a large number of small chips like polliwog are evacuated.This indicates that on the planar rake face in the conventional gundrill,the chip slide over the surface and does not have a chance to break.However,if a groove is made on the surface,then the chip will curl and then will broken by the extra curl when colliding on the wall of parts or tool surfaces.This will increase the chip breaking steadily.?3?In above processes,the surface roughness,roundness and hole diameter error of the material are analyzed.Among them,the surface roughness of drilling 42CrMo decreased by23.5%,the roundness error decreased by 16.4%,the hole diameter error decreased by 17.3%,the surface roughness of processed RuT450 decreased by 11.6%,the roundness error decreased by 6.6%,and the hole diameter error was basically the same.The test results show that the newly designed gundrill with axial inclination angle?with the recommended values from 14°to 12°.It has good chip texture,machined hole surface integrity and low drill flank wear under this condition.The drilling axial force and torque inspected by the newly gundrill is less than that of a conventional drill when drilling both42CrMo and RuT450 materials.This application of gundrill with chip breaker groove provides the parameters and successful case to deep-hole drilling.Model modification and performance amendment are always needful,in the advanced machining,such as efficient and high-speed drilling process.In the following study,predetermination of the cutting performance would be developed by the dynamics of plasticity and FEM to investigate the mechanism of chip breaking.