Analysis And Control Of Machining Defects During Abrasive Cutting Of Unidirectional CFRP Laminates

As one of the earliest and most widely used advanced composites in the field of national defense and aerospace industry, carbon fiber reinforced plasitcs(CFRP) possess many advantages such as high specific strength, specific modulus, high fatigue resistance, high corrosion resistance and so on. However, the anisotropy and heterogeneity of CFRP may result in poor finished surface integrity and rapid tool wear. Also many machining defects such as delamination, burrs, chipping and resin smearing are often unavoidable.In present investigation, this paper focuses on various kinds of defects during trimming of CFRP laminates Also the influences of machining parameters and structures of CFRP laminates on cutting forces, finished surface integrity and machining defects during trimming of CFRP laminates with various workpiece inclined angles were studied. The control strategy of different types of defects and evaluation method of finished surface integrity were discussed based on the abrasive machining processes. A computing method and model for different types of delaminations, burrs and chipping was introduced which may explain mechanism and regularity of various kinds of machining defects. The results obtained could contribute to control the defects and improve machining process performance during trimming of CFRP laminates.The main work is summarized as follows:(1) Based on the machining defects during trimming CFRP laminates, four kinds of delaminations were classified systematacially. The bending/fracture models for carbon fiber bundles was introduced to explain mechanism and regularity of machining defects.(2) CFRP laminates with various workpiece inclined angles were trimmed by the milling cutter. The influences of workpiece inclined angles, fiber direction and machining parameters on milling forces, surface integrity and machining defects were analyzed. The milling forces in machine coordinate system also keep constant, while the milling forces in workpiece coordinate system along the direction of workpiece thickness increase with the increase of workpiece inclined angle. The defects of workpiece profile and finished surface get severe with the increase of workpiece inclined angle. The fiber bundles will bend instead of rupture and crack grows into the workpiece along the fiber direction. The numbers of damaged plies also increase with the increase of workpiece inclined angle. At the same time, the surface morphology was analyzed by considering the relationships among fibre directions, feed and surface integrity.(3) Four kinds of stacking sequences of CFRP laminates with various workpiece inclined angles were trimmed by the single-layer brazed diamond grinding points. The influences of machining parameters(including spindle speed, feed speed and workpiece inclined angle), stacking sequence and fiber direction on grinding forces, surface integrity and machining defects were studied. The advantages and disadvantages between the milling precess and abrasive machining processes were discussed. To solve the problem of machining defects such as burrs during machining of CFRP, a computing method of the length of carbon fiber cut by per tooth was proposed based on fiber cutting angle. This method explained the mechanism and regularity of burrs.