| Carbon fiber composites(CFRP)are often used as large structural parts in aircrafts due to their advantages such as light weight and high strength.The connection between them and conventional metal parts(mainly titanium alloys)is usually riveting and screwing after drilling,by which CFRP/Ti laminate structures are formed.In order to ensure connection accuracy and processing efficiency,these structures are usually drilled integratedly.Since the joints are subjected to large and complex loads,it is necessary to ensure drilling quality to improve the reliability of laminates.There are two main problems in CFRP/Ti laminated drilling.One is that high drilling temperature is easy to cause damage to composites,thus the temperature field needs to be predicted reasonably.The second is that Ti chips' outflow will cause damage to drilled composite holes,so the influence of the chips needs to be further analyzed and suppressed.In this paper,these two problems are analyzed separately.The temperature field model of laminated drilling is obtained.The influence of titanium alloy chips on composite materials and the suppression methods are discussed,which provides a reference for high-quality drilling processing of laminated materials.For drilling temperature,a temperature field model is established by the principle of thermodynamics.The drilling process is analyzed to make the necessary assumptions,and the numerical calculation method is used to solve the characteristics of material removal in laminated drilling.The iterative schemes of various nodes under different boundary conditions are discussed.,and a program is written to solve the temperature field problem,which realizes the prediction of the laminated drilling temperature.The heat source is simplified.For there is material removal in laminated drilling,numerical calculation method is used to discretize the heat transfer equation.The iterative equations of various nodes under different boundary conditions are classified and conditions for obtaining a stable solution are analyzed.To verify the model,a laminate drilling experiment is performed and interface temperature at several points are measured.Use laser to obtain shallow grooves on the surface of composites,and then fine thermocouples are placed in there and fixed.Next the position of drilling center is determined by a specific fixture.Finally,drilling experiments were carried out after fixing with Ti alloy.Substituting data such as cutting force and torque measured in the experiment into the temperature field model to correct the efficiency coefficient.Comparing the calculated value with the experimental one,and the result is found to be highly accurate.The model can be used for lamination under other processing parameters.Drilling temperature field calculation.As for the influence of titanium alloy chip,the relationship between chip types and process parameters is analyzed,and the effects of different chips on the quality of composite hole are obtained through experiments.The chip type is mainly determined by the feed per revolution.a folded strip of chip will form under a small feed and extruded chips will form under a large feed.Titanium alloy chips cause hole enlargement and pit shape damage to the scrape wall of the composites.When drilling to the underlying titanium alloy,a small feed should be selected to avoid the formation of extruded chips to reduce the impact on the composite hole.On the basis of selecting good machining parameters and chip types for composite holes,drilling process and low frequency vibration assisted drilling are selected to further improve chip breakage.Through the experimental comparison,it is found that the chip breaking is realized,which avoids the ring scratch at the entrance of the composite hole caused by long chip winding knife,and the damage of the pit on the wall of the compound hole is alleviated.At the same time,the aperture and roughness of the compound hole are better improved. |
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