扭转超声辅助切削CFRP材料微观去除机理研究

Microscopic Removal Mechanism of Torsional Ultrasonic Assisted Cutting CFRP Materials

目的研究加工过程中碳纤维增强复合材料(CFRP)的破坏形式,提高CFRP的表面质量。方法对扭转超声辅助切削CFRP的切削行为进行分解,建立扭转超声辅助切削CFRP理论模型,进行扭转超声辅助切削CFRP圆盘实验。实验后对切削力、表面粗糙度、表面凹坑特征等参数进行分析评定,并用超景深显微镜与SEM扫描电子显微镜对加工表面质量进行观察。结果纤维切削力与表面粗糙度呈负相关关系,在粗糙度较大的凹坑区域,其径向力和切向力均相对较低。超声的附加使切削力数值高于该时刻平均水平,同时伴随着更大的能量,使纤维几乎来不及发生弯曲变形就被高能量的切削力瞬间剪断,与传统加工相比,纤维的断裂点和脱粘点之间的距离更小。在传统加工方式下,表面凹坑的平均宽度在50°附近达到最大值(652μm),表面凹坑的平均深度最高超过30μm,严重影响了装配精度;在超声加工方式下,凹坑的特征宽度和特征深度明显减小且波动幅度较小。结论树脂-纤维的脱粘深度决定了表面凹坑的深度和宽度,在扭转超声振动加工方式下,纤维弯曲变形较小,可以有效抑制脱粘情况,纤维断裂形式以剪切断裂为主,而且纤维方向性也得到了抑制,有利于提升表面质量。为了避免CFRP加工中的损伤,可以从复合材料结合强度、CFRP铺层布局与加工工艺等方面着手。

The work aims to study the failure mode of carbon fiber reinforced composite(CFRP)during processing,and improve the surface quality of CFRP after processing.The cutting behavior of torsional ultrasonic assisted cutting CFRP was decomposed,the theoretical model of torsional ultrasonic assisted cutting CFRP was established and the experiment of ultrasonic assisted cutting CFRP disc was carried out.After the experiment,the cutting force,surface roughness,surface pit characteristics and other parameters were analyzed and evaluated and the quality of the machined surface was observed by super depth of field microscope and SEM scanning electron microscope.There was a negative correlation between fiber cutting force and surface roughness.In the concave region with larger roughness,the radial and tangential forces were relatively low.Due to the effect of ultrasonic impact force,the cutting force in ultrasonic machining added a periodic spike,which was significantly higher than the average level at that time and the higher impact cutting force was accompanied by the greater energy,so that the fiber was almost cut off by the high-energy cutting force without bending deformation in time and the distance between the breaking point and the debonding point of the fiber was smaller than that of traditional processing.The average width of the surface pit under the conventional processing method firstly showed an increasing trend with the increase of the fiber angle,reaching a maximum value of 652μm near 50°and then decreased rapidly in a straight line and the average depth of surface pit was more than 30μm,which seriously affected the assembly depth.The average width and average depth of surface pit were significantly reduced during torsional ultrasonic assisted machining,the appearance range of pits was between 20°and 80°,and the damage range was relatively small,the width and depth of the pit also increased firstly and then decreased with the increase of the fiber direction angle,and showed a stable state between 40°and 50°and the directionality of the fibers was also inhibited.The surface morphology of the processed fiber with cutting angleθ=50°was observed.Under the traditional machining,there were many regular pit damages on the processed surface,and most fibers had bending fracture.Under torsional ultrasonic assisted machining,the fiber was mainly subject to shear fracture,and the machined surface was relatively smooth and flat.The depth of the resin fiber debonding determines the depth and width of the surface pits.Under the torsional ultrasonic vibration machining mode,the fiber bending deformation is small,which can effectively suppress the debonding situation and shear fracture is the main form of fiber fracture,and the fiber directionality is also inhibited,which is beneficial to improving the surface quality.Damage can be avoided during CFRP processing in the following ways:firstly,the bonding strength of the fiber resin interface of the material is improved to inhibit the debonding of the fiber resin and the expansion of the debonding;secondly,starting from the layout of CFRP plies,the fiber cutting angle can be changed to reasonably avoid the cutting angle in the high incidence area of pits;finally,the fracture form of the fiber can be changed by the processing technology to inhibit the damage,so as to improve the quality of the machined surface.