Edge Effect And Suppression Strategies In Extrusion Abrasive Flow Machining With Viscous Abrasive Media

The key of the manufacture of high-end equipment is the manufacture of its high performance parts with the technological requirements of complex surface structure,difficult-to-cut materials,extreme working conditions and high surface quality,for instance,aero-engine blade and screw element in large screw extruder.However,after the near-net-shape manufacturing by using NC milling or precision casting,only appropriate finishing process is adopted will the blade surface quality increase and meet its service requirements.Low machining efficiency and reachability,and high cost are the crucial insufficients exhibited in the manual finishing,vibratory finishing and CNC belt grinding technology.Thus,it is the important basis to cut down the development time and prolong the service life of these high performance parts by using efficient,high quality and low cost finishing technologies.Abrasive flow machining?AFM?is a non-traditional finishing technology with abrasive media extruded to-and-fro across complex surface.Due to the high machining reachability of abrasive media,this technology has great potential application in the finishing process of complex surface structure.In this paper,the researches were focused on the efficient and high-quality finishing process for the complex surface of high performance parts.For the decrease of surface quality caused by edge effect in AFM,the simulation mechanics model of abrasive media in constrained channel was established with the complement of power law constitutive model of abrasive media.The reasons of edge effect in AFM was revealed,likewise,the blocking control principle and stragety for the uniform finishing process of the whole surface were studied based the reverse design of constrained surface of mold and structure of guild blocks,the technological approach can achive precision grinding and finishing was explored.Finally,the application verification of these technologies was carried out taking blade and screw element as research objects.The main research contents and results are as follows:?1?The store modulus and loss modulus of abrasive media with different components and utility time were measured with frequency scanning method,the steady shear viscosities of abrasive media were obtained by Cox-Merz rule,and the steady shear viscosity of abrasive media FC024045M was predicted.The power-law constitutive model for abrasive media was established based on the above tested results,which will provide the relation between stress and shear rate for the simulation mechanics model of AFM.?2?By combining the theory of non-Newtonian fluid and the above power-law constitutive model,the simulation mechanics model of abrasive media in constrained channel was established based on continuum mechanics.Pressure testing system for near-wall _s^pp^r_pir_r^ee^s_mos^s_vus^u_elu^r_adr^e_{t i} i e_{t oh}v^w_naa a^a_til _n^su_{t h}e_A^bs_e^{u i}_F i_s^ln^t_iM,_m.i^an_ul_lⁿe_a^dt_t/_i^ao_oⁿu_nt^a l ^le_m^yt^s _e^ea_c^sn_h d_a^w _nc_i^ee_c^ren_s t ^cr_ma^olⁿ _oa_d^dr_e^ue_l^c a^t s_h^e,_a^d _sb ^b o_a^yt h_{f a}^cv_v^oa_o^ml_ru_a^bie_bⁿs_{l e}ⁱⁿh ^ga_a v_p^te_p^h _l^et_i h_c^se_aⁱ _b^ms_ia_li^ulm^a_tye^{t i} t_t^or_oⁿe n^a_thd_eⁿ,^d a_fln_o^md^e _w^ai t^{s u}_fiw_el^rea_d^dsà?3?Material removal function of multiple abrasive drove by flow filed was established,the computing method of near wall p vdistribution was provided.On this basis,the forecasting method of material removal distribution of the whole surface finished by AFM was proposed.The reasons why the edge effect in AFM were revealed and the influence of processing parameters on the edge effect were discussed in detail.?4?According to the distribution of edge effect in AFM,the blocking control strategy was proposed to reduce the edge effect based on the adjustment of constrained surface of mold and structure of guild blocks.The control strategy method for the improvement of blade finishing uniformity of blisk was discussed,and the blade surface roughness reduces from R_a0.51?m to R_a0.14?m,and the roughness uniformity improves from 0.098 to 0.029,particularly,the finishing texture on the whole surface is the same.In addition,an efficient selection method for abrasive media is proposed based the multi-scale characteristics of surface texture to reduce of processing time for the further elimination of edge effect.?5?The measurements of blade profiles were carried out using the contour measurement,the constrained surface of mold and structure of guild blocks were designed based on the flow field simulation and the forecasting method of surface topography.A manufacture method for the preferable mold using the mixture of epoxy resin and solid particle was proposed.Processing parameters for the AFM of blade with high efficient and high quality was determined based on the analysis of multi-scale characteristics of surface texture,the blade surface roughness reduces from R_a0.81?m to R_a0.17?m,roughness uniformity improves from 0.062 to 0.021.With the control of flow field in constrained channel,the maximum material removal of blade basin,blade back,leading edge and trailing edge reduce from 0.068mm,0.098 mm,0.12 mm and 0.29 mm to 0.010 mm,0.017 mm,0.062 mm and 0.11 mm,respectively,that is,the uniformity of blade profile is improved significantly;?6?Taking the feed screw element of the large granulator as research objects,over-finishing and under-finishing were found and explained based on the flow field analysis.From this,a special mold with guild blocks and local enhanced constraint was designed and used to finishing the screw elements.The finished surface roughness of feed screw reduces from R_a10.5?m to R_a0.45?m,and the roughness uniformity improves from 1.057 to 0.014,the uniformity of minium diameter is better than initial part.In addition,the finishing efficiency is higher than manual abrasive belt grinding.The control theory and implementation method of the edge effect can be direct used to the efficient and high-quality finishing of complex surface of blade and screw element,particularly,provide a new technical approach for the finishing process of similar high-performance and complex parts.