Study On Rock-breaking Mechanism Of Combined Cutter Bit Under Percussive Load

Rotary percussion drilling is one of the important means to improve the drilling speed.The combination of the two bits has great development potential.However,it is not clear what characteristics the percussive load generated by the speed-up equipment of percussive drilling should have and what kind of drilling parameter matching should be adopted in order to give full play to the advantages of the combination cutter bit.It is very difficult to observe the rockbreaking process of the combination cutter bit under the percussive load by using the experimental method.In order to improve the understanding of the rock-breaking mechanism of the combination cutter bit under the condition of rotary percussion drilling,the rock-breaking mechanism of the combination cutter bit under the percussive load is studied by using the method of numerical simulation and experimental verification.In this paper,the finite element method is used to establish the rock-breaking numerical analysis models of single cutting cutter,double cutting cutter combination and full-scale combination cutter bits.The rock-breaking characteristics of plane cutter,cone cutter and ax cutter under percussive load are compared and analyzed,and the rock-breaking mechanism of different combination cutters under percussive load is studied.At the same time,the influence law of percussive load amplitude,waveform and vibration frequency on rock-breaking effect of combined cutter bit is also studied.It provides a reference for the combination of rotary percussion drilling technology and combined cutter bit and bit design.The results show that the rock-breaking effect of different cutter shapes is different under the percussive load.All kinds of cutter shapes have their own suitable rock types.The axe cutter and cone cutter are more suitable for breaking hard rock,and the plane cutter is more suitable for breaking soft rock.The results show that the rock-breaking effect of different cutter combinations is quite different.The combination of ax shaped cutters and cone shaped cutters has higher stress peak value and larger stress response range,and has better rock-breaking effect on hard formation.In the process of rock-breaking by the combined cutter bit under percussive load,the propagation of stress wave makes the internal tensile stress and compressive stress of rock appear alternately,cracks are easier to produce and expand,the specific work of rockbreaking is reduced,and the rock-breaking efficiency is greatly improved.The characteristic parameters of percussive load have obvious influence on the rock-breaking efficiency of the combined cutter bit.When the average load is equal,the optimal amplitude of the percussive load can maximize the rock-breaking efficiency,and the optimal vibration frequency can maximize the rock-breaking efficiency of the combined cutter bit.