In the aircraft industry to obtain the necessary form of long panels and sheaths the shot peen forming is successfully used. Due to impact of shot on the processed surface, the specific microgeometry is formed, the characteristic feature of this microgeometry are the numerous dimples of shot with different diameters and depths. At the same time, the depth of the dimples significantly exceeds the valleys of the surface microroughnesses formed as a result of the previous treatment. The presence of these dimples leads to an increase in surface roughness. Therefore, after shot peening the mandatory requirement is implementation of surface grinding with flap wheels for partial removal of the shot dimples. During grinding with flap wheels, depending on the value of allowance for grinding on the treated surface, a new microrelief is formed in the form of a combination of the traces of abrasive grains of flap wheels during grinding and the remains of the dimples from shot peen forming. Since the dimples have a spherical shape with a much larger radius of curvature than their depth, they have a specific effect on the degree of coverage of dimples, roughness and removal of material of treated surface. The paper presents an analytical description about the change process of the area covered with current dimples and roughness during grinding with flap wheels around the surface pre-treated with shot peening depending on the set value of allowance. Based on the results of the research, mathematical models were built to determine the current area of coverage with dimples, the average value of the depth and degree of coverage of the remaining dimples, the amount of material removed from the treated surface and roughness during grinding with flap wheels, and a numerical method for determining the allowance for obtaining the permissible degree of coverage and the required values of roughness. Keywordsshot peening; grinding with flap wheels; dimple; degree of coverage; surface roughness during shot peening; surface roughness during grinding with flap wheels; volume of material after shot peening; volume of material after grinding; allowance.
To obtain the desired shape of long panels and sheaths in the aircraft industry, the technology of shot peen forming with subsequent grinding with flap wheels is successfully used. To implement this technology, a special UDF-4 (shot peen forming equipment of the 4th version of modernization) device was designed and manufactured. The last version of this device is equipped with a CNC system and a revolver head with the 4-flap wheels for optimizing the grinding operation. The ability to select the desired flap wheel during the grinding process, depending on the curvature and width of panels or sheaths, has significantly expanded the technological capabilities of this equipment. During grinding with flap wheels of a rectilinear profile, to ensure uniform removal along the cross-section of the part’s curvilinear contour, it is necessary to carry out processing with overlapping previous passages. The need for overlapping passages significantly increases the processing time. At the same time, the calculation of the overlapping width during the changing curvature of the part’s profile is quite a difficult task. This paper presents analytical studies of the use of profiled flap wheels for grinding the part’s surface with a variable radius of transverse curvature, and also proposed the mathematical models for selecting the necessary profiled flap wheels depending on the curvature of the part’s processing surface.
The study was performed to develop a method for selecting a rational profile of a profiled flap wheel for a turret stripping head for cleaning parts with different radius of the transverse curvature. Researchers from the Irkutsk National Research Technical University and Irkutsk Aviation Plant designed and fabricated a special PFS-4 (peen forming setup) unit to implement manufacturing technology of large-scale contour-forming components. The unit is equipped with a CNC system, two movable operating elements, a shot blaster and a turret stripping head with four flap wheels. The paper offers methods and criteria for selecting the profiled flap wheel for stripping the contour-forming surfaces of the components, depending on the curvature radius of the latter. A flap wheel with an optimal curvature radius of 40 m was chosen for analysis, which allows a sufficiently large range of profile curvature of the processed components (from 8 to 40 m) to be covered. Profiled flap wheels 100 and 200 m wide with a flap profile radius of 40 m provided uniform material removal when cleaning the surface with a curvature radius from 8 to 40 m without further overlapping with a finished strip. It was shown that wider profiled flap wheels are necessary to increase stripping efficiency. In this case, a 300 mm wide flap wheel can be used for a component surface area with a transverse curvature radius over 14 m and a 400 mm wheel for surface areas with a curvature radius of over 20 m. Thus, comparing the stripping process of a curved surface by the straight flap wheel revealed that profiled flap wheels significantly expand the workability of the PFS-4 unit turret stripping head.
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