| Carbon Fiber Reinforced Plastics(CFRP)is widely used in aerospace and other high-end manufacturing fields due to its high specific strength,high specific modulus,corrosion resistance,and high designability.In the machining of large composite components,the robot drilling system has the characteristics of strong flexibility,high efficiency and high precision,which makes its application in the field of digital assembly of aviation manufacturing industry become a trend.However,due to the characteristics of high hardness and low interlayer strength,CFRP is easy to produce damage during processing,which is a typical difficult material.Especially,CFRP is sensitive to cutting force during drilling,and is prone to produce delamination,burr,tear and other damages,which limits the application of robot in composite material processing.In this paper,the CFRP drilling process suitable for robot drilling system is studied based on the actual demand of enterprises for robot drilling system.In this paper,a tapered Angle diamond tool is developed independently.At the same time,the multi-functional end-effector of the robot drilling system was developed and the processing scheme was developed.The feasibility of the end-effector structure design and the processing scheme was verified through on-site processing.The main research contents and relevant achievements of this paper are as follows:Firstly,a simplified flexible joint model of the robot was established to carry out static analysis on the robot,the influence of flexible joint deformation on tool position under the action of axial force is analyzed.The analysis shows that when the axial force decreases from100 N to 60 N,the tool radial offset decreases from 90μm to 50μm.Therefore,reducing the axial force during cutting can improve the accuracy of drilling.Secondly,the multi-edge cutting principle of diamond tool and the cutting principle of traditional cemented carbide tool are compared and analyzed.The analysis shows that a single abrasive diamond tool has smaller cutting zone and smaller cutting force.In addition,the tapered diamond tool shows a smooth transition characteristic in the process of cutting into and out of the material surface,which can effectively restrain the machining damage and repair the damage to a certain extent.Thirdly,T800 CFRP helical milling experiments were carried out with taper Angle diamond tools.The results show that the feed speed has the greatest effect on cutting force,the screw pitch is the second,and the spindle speed has the least effect.The axial force decreases with the increase of the tool cone Angle.From 0° to 60°,the axial force decreases by 20.3%.In addition,the defects of tapered diamond abrasive tools are significantly reduced compared with those of flat head tools.The test results are basically consistent with the analysis of helical milling processing principle of tapered diamond tools mentioned above.The suitable tool structure and the range of process parameters are obtained: the diamond tool with 60° cone Angle is selected,the spindle speed is in the range of 6000～8000rpm,the feed speed is in the range of 150～200mm/min,and the pitch is in the range of 0.4～0.6mm/r.At this time,the processing quality is better under the premise of ensuring the processing efficiency.Finally,the multi-functional end-effector of robotic drilling system is developed in this paper,including mechanical spindle parts,indexing coaxial measuring system,auxiliary pressing system,tool detection system,follow-up dust collecting system,etc.Combined with helical milling process,it can realize high quality,high efficiency and drilling processing for large thin-wall CFRP. |
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