Research On The Theoretical Model Of Straightness Error In Gun Drilling Of Small Diameter And Deep Hole

The processing of small-diameter deep holes(depth diameter ratio ≥ 20)occupies an increasingly important proportion.Deep hole processing is mainly reflected in the national key development industries such as weapons and equipment,aerospace,medical equipment,construction,and energy.Gun drilling is an ideal method for processing smalldiameter deep holes.The gun drill has a relatively complex structure and weak rigidity.So the gun drill is easy to bend and deform under force during drilling.Also,the current theoretical model of straightness deviation is inconsistent with the working condition of deep hole gun drilling,making the active control of hole straightness deviation still a difficult point in deep hole processing.At the same time,there are few reports on the influence of stiffness on straightness deviation and the relative importance of errorinfluencing factors.Therefore,we have carried out the basic theory and method research of the straightness deviation model,to solve the problem that the axis deviation of small diameter deep hole gun drilling is difficult to control.And we conducted experimental verification and active deviation control research.The main work contents are as follows:(1)Through the force analysis of gun drilling,we found out the mechanism of the drill pipe stiffness,drilling axial force,support stiffness,support clearance,and spacing on straightness deviation.This paper establishes the theoretical model of the straightness error of the middle four supports by using the Euler-Bernoulli beam theory and reveals the relationship between the bit deflection and the deviation of the hole axis.In addition,we use experiments to verify the reliability of the relevant theoretical models.(2)Based on the four supports straightness deviation prediction model,we analyzed the influence of support clearance,support spacing,feed rate,drilling axial force,and some uncertain factors on straightness deviation.In addition,the relevant error curve is drawn with the help of MATLAB.And the straightness deviation rate under a certain machining depth is calculated.(3)We extract the straightness deviation evaluation index through the straightness deviation theoretical model.Through analyzing the basic ideas of the analytic hierarchy process,entropy weight method,and gray correlation method,we elaborated the calculation and analysis of the weight of hole deviation factors.We further put forward a method to calculate the weight of the straightness deviation evaluation index by the combination of the AHP-entropy weight method and the AHP-grey correlation analysis method.And we used the Kappa coefficient method for correlation questioning.The application example shows that the combined weighting method of AHP and entropy weight can better evaluate the significance of the influencing factors of straightness deviation.(4)According to the straightness deviation mechanism,the active control of straightness deviation of the machined hole is realized by changing the feed rate,support spacing,support clearance size,and direction.With the help of MATLAB,the deviation curve of the relevant straightness deviation is drawn,and its reliability is further verified.The theoretical model of straightness deviation in deep hole gun drilling and the active deviation control method studied in this paper have important theoretical significance and engineering application value for the development of hole processing level.It can promote the development of parts processing technology in the manufacturing industry.