Study On DTH Hammer Virtual Prototype And Its Transient Impact While Rock Drilling

DTH (Down-The-Hole) hammer drilling, with high efficient rock drilling, shortconstruction period and significant economic benefits, is a rotary percussive drillingtechnique widely used in mining, exploration, water-well drilling, road construction,and other drilling operations around the world. The DTH hammer is the keyequipment in the drilling system，be given priority to with experience design. Itstransient impact is still a "bottleneck" of the flexible multi-body dynamics problemsin the current study.This paper is funded by National Natural Science Foundation of China (No.50475056). The DTH hammer as the main part in the drilling system is studied and itsvirtual prototype is established. The effect of the system’s and structural parameterson the main performance (impact energy and impact frequency) of the DTH hammeris researched. The transient impact response of piston-drill-rock is numericallyanalyzed. On the basis of prior research, the NSFC project (No.51275493) had benapplied and gets approved. The general theory of flexible contact/impact response,yielding and critical impact speed is mainly researched. The specific contents are asfollows:(1) The DTH hammer and gas source are acted as one system. Based onquasi-stable state method, gas state mathematical model of air chambers is establishedwith the flow equation, state equation and isentropic equation, in order to set upnonlinear gas-solid coupling dynamic model for the gas-drive-piston. DTH hammervirtual prototype is successfully built in ADAMS. It is easy to modify defects indynamic and structural design of the DTH hammer with virtual prototype instead ofphysical prototype, which will shorten the development cycle and improve thereliability of DTH Design. It is demonstrated that it is suitable to develop the virtueprototype of DTH hammer.(2) Due to its high nonlinearity, large deformation and damage behaviors whilerock drilling, taking H-J-C model as brittle materials (concrete, granite and sandstone),the explicit time integration nonlinear finite element code LS-DYNA3D was innovatively employed to analyze the Piston-Bit-Rock impact response in the drillingsystem. The propagation process of stress wave was reappeared in the complexflexible body while the DTH hammer impacting rock.(3) The discrete techniques of modal analysis and modal truncation are creativelyadopted in order to settle down the modeling theory of the plane contact/impact in theDTH hammer system. The governing equation of the two flexible plane-impactingrods, end of which is supported by a spring, is initially built up. General solution ofthe partial differential equation will be solved by means of separation of variables. Bysolving characteristic equation, the regular effect of system parameters, boundary andinitial conditions, such as supporting stiffness and length ratio, on flexiblepiston-bit-rock is researched with mathematical mechanics method.(4) The impact velocity effects on the impact force between piston and drill, butthe rock properties not obviously on the impact force; both the impact velocity and therock properties have obviously effect on the impact force and impact time when thebit insert impacting the rock.(5) The Hertz transient contact/impact dynamic response is systematicallystudied with the combination of the theory and numerical analysis. The characteristicof the closed yielding zone of the Hertz contact/impact is revealed. In thecircumstance contact pressure increases, the boundary of the yield zone exceeds thatof the contact zone, and the significant plastic deformation reduces the intensity ofcontact pressure pulse. The critical yielding criterion of the flexible or local flexibleHertz contact/impact is constructed, and the equations of the critical impact velocitywith wave effect and quasi-static Hertz contact/impact is rebuilt up.Based on the application of engineering equipment and tools, the contact/impacttheory and modeling of the flexible multi-body are established, which willcontribute to the promotion of flexible multi-body contact/impact dynamic theoreticaldevelopment, and lay a solid theoretical foundation for the innovative design of thekey components of engineering machinery with the contact/impact.