| Aramid Fiber Reinforced Polymer Composites(AFRP)have been widely used in the manufacture of key parts of equipment such as aircraft,rockets and tank armor due to its high specific modulus,high toughness and excellent impact resistance.In the process of connection and assembly of AFRP parts,a large number of holes are often made.However,the material composition of AFRP has the characteristics of lamination,the interlaminar bonding force is weak and easy to crack,and the aramid fiber is tough and hard to cut.This results in flanging damage at the entrance of hole and burr and delamination damage at the exit of hole when the original drilling tool is used to make holes for AFRP.Drilling damage with AFRP can significantly reduce the strength of the connection between parts,seriously endangering the safety and reliability of equipment.Aiming at the problem that it is difficult to achieve low damage drilling AFRP,this paper started from analyzing the cutting effect of tool on entrance and exit materials when drilling AFRP,studied the influence law of key geometric parameters of tool on entrance and exit damage of AFRP drilling,and then designed tool structures that realize low damage drilling AFRP,and the cutting parameters were matched,AFRP drilling with low damage was preliminarily realized.The relevant research contents mainly include the following three aspects:(1)The contact form between the main cutting edge of the tool and the entrance surface material when drilling into AFRP was analyzed.It is found that the positive rake angle of the main cutting edge causes the rake face to exert upward force on the entrance surface material,while the negative angle of cutting edge inclination causes serious deformation of the entrance surface material.The combined effect of these two factors is the cause of flanging damage at the drilling entrance.Based on the above analysis,the entrance damage suppression mode was proposed to change the positive rake angle of the main cutting edge into negative rake angle,and the negative angle of cutting edge inclination into positive angle.Then,a drilling tool with tilting blade slot structures was designed,which could realize both negative rake angle and positive angle of cutting edge inclination.Experimental results showed that the drilling tool with tilting blade slot structures can suppress the damage of the drilling entrance of AFRP.(2)The contact form between the main cutting edge of the tool and the exit surface material when drilling out AFRP was analyzed.It is found that the tip angle has great influence on the damage of drilling exit.By changing the angle of the tip angle,the thrust compression of the surface fiber at the exit is changed into thrust tension,so as to reduce the deformation degree of the surface fiber at the exit under the action of the drilling tool,and then reduce the damage at the exit.Based on the above analysis and combined with the outstanding advantages of step drill,a three-point step drill with special tip angle structure and step structure was designed.Through the experiment of dynamic drilling process observation,it is found that the three-point step drill can effectively cut off the surface fiber at the exit,and the three-point step drill can reduce the thrust force of drilling,and achieve the simultaneous suppression of burr and delamination damage at the exit.(3)The combined drilling tool which can suppress the damage of entrance and exit at the same time was designed by combining the tilting blade slot structures with the three-pointed step drill,and optimizing the step diameter ratio of the drilling tool.The cutting parameters of the combined drilling tool were matched by a double factor five horizontal drilling experiment about spindle speed and feed speed.The experimental results showed that the combined drilling tool can suppress the damage at the entrance and exit of AFRP drilling at the same time under the appropriate spindle speed and feed speed. |
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