Study On The Drilled Disfigure Of Carbon Fiber Reinforced Plastics And Its Countermeasures

Carbon fiber reinforced plastics (CFRP) are characterized with light weight, superior strength-to-weight and stiffness-to-weigh ratios, low thermal expansion coefficient, high fatigue strength corrosion resistance, good thermal shock resistance and vibration absorption. It has been widely used in military field such as airplanes and spaceships, and civil field such as automobile, electronic communication and high speed machinery, etc. It is extremely difficult to process CFRP because of its anisotropy, high strength and low thermal conductivity. Due to its low strength between two layers, it's easy to produce delamination and avulsion under the cutting force while machining, and the condition is worse when drilling.The paper was supported by the Basic Research Foundation of the Ministry of Education of China and Natural Science Foundation of Liaoning Province. By focusing on some problems during drilling like burr, delamination and avulsion, tool abrasion and blockage, drilling force and its effect on the defects, etc., this study focuses on the following points:(1) In this paper, common drilling defects of carbon fiber reinforced plastics at exit of the hole are observed and classified, and a comprehensive exit defects model is established. Exit drilling burrs are classified into type I and type II. For the evaluation of the defects of torn and delamination, an area factor method is developed.(2) A single-blade scratch test of the unidirectional carbon fiber reinforced plastics is carried out to study the cutting mechanism of the material and the defect forming mechanism. Unidirectional carbon fiber reinforced plastics material is simplified as the dual cutting model to analyze the materials deformation and the chip formation in the process of cutting. The effect of cutting angle on the cutting mechanism and defects is studied by experimental and theoretical method.(3) The drilling force to CFRP is measured under different cutting parameters; meanwhile the effects of different parameters on the drilling force are analyzed. A mechanical model on drilling force is constructed according to the theoretical analysis. Considering the drill diameter, spindle speed, feed rate and other factors, an empirical formula of drilling force for CERP is built using multiple linear regression analysis. By analyzing the relationship between drilling force and defect characteristics, cutting parameter and defect factor, the technical parameter range for CERP drilling is predicted.(4) In view of the electroplated diamond drill blocked by the cuttings block of the carbon fiber plastics, a new step-core drill is designed. By comparing the new step-core drill to the carbide twist drill and the electroplated diamond drill from the different views such as the form of the process of drilling, drilling force, boring quality, material removal way and chip shape, etc., it is concluded that step-core drills with "boring - reaming integration method" for drilling carbon fiber reinforced plastics are better than the traditional method of drilling process.