| Alumina（Al2O3）ceramics are widely used in industry because of their excellent mechanical and physical properties.However,cracks,holes,and high surface roughness（Sa）problems on the surface of Al2O3 ceramic parts produced in conventional industrial or additive manufacturing can seriously affect the mechanical properties of the part and limit the application of the part for high performance.Moreover,Al2O3 ceramic parts are not just flat shapes,the complex free-form shape of ceramic parts has been a difficult problem for further application of laser for polishing ceramic parts.It has also been very important to study how to apply the research methods on the plane to the actual industrial production of the parts.This paper presents a ultrafast laser ablation fracture polishing（ULAFP）method for Al2O3ceramic parts to improve the surface quality and enhance the mechanical properties of the polished surface.Based on the"filling"effect,the method first uses the remelted layer produced by laser remelt polishing to"fill"and eliminate surface hole defects.Then a combination of laser ablation and laser thermal stress-induced crack extension effect is used to remove the remelted layer to obtain a surface free of crack defects.Finally,precision polishing is performed using femtosecond laser ablation to obtain a smooth surface with submicron surface roughness.This method can reduce the original surface roughness Sa5.25μm polished to 0.80μm for Al2O3ceramics,while controlling the total ablation depth of the polishing process to less than 93.5μm,maintaining the dimensional accuracy of the parts and greatly improving the mechanical properties of the polished surface.Compared with the original surface,the polished surface hardness and elastic modulus increased by104.6%and 63.9%,respectively.In order to better meet the actual industrial needs and solve the practical engineering challenges of polishing Al2O3 ceramic parts.In this paper,two laser 3D machining methods suitable for free-form parts,laser partition processing and five-axis simultaneous laser processing,are investigated to eliminate or reduce the limitations of laser processing area size（LPAS）,laser incidence angle（LIA）and focal offset distance（FOD）in conventional laser 3D machining,and both are successfully applied to polish Al2O3 ceramic parts.Among them,laser partition polishing can reduce the limitation of laser 3D processing by LPAS and FOD,and reduce the number of partition division（5partitions）by considering only the limitation of LIA to achieve higher processing efficiency.Five-axis simultaneous laser polishing is an integrated process that is not limited by the LPAS,FOD and LIA,ensuring the quality,integrity,and aesthetics of the polished surface of the part. |
