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CN-121979097-A - Method and system for positioning cutter of 5-axis numerical control machine tool for machining engine cylinder cover

CN121979097ACN 121979097 ACN121979097 ACN 121979097ACN-121979097-A

Abstract

The invention relates to the technical field of 5-axis numerical control machining, in particular to a method and a system for positioning a cutter of a 5-axis numerical control machine tool for machining an engine cylinder cover, wherein the method comprises the steps of determining a transitional machining area according to a machining model of a combustion chamber of the engine cylinder cover; generating a machining point sequence along a transitional machining area, respectively determining the axial direction of a valve seat, the local normal direction of the top wall of a combustion chamber and the constraint direction of the periphery boundary of a spark plug hole at each machining point, constructing a continuous transitional relation between the axial direction of the valve seat and the local normal direction of the top wall of the combustion chamber, determining the corresponding cutter shaft direction by combining the constraint direction of the periphery boundary of the spark plug hole, determining the position and the appearance of a cutter, constraining the variation of the cutter shaft and the variation of the rotating shaft of a 5-axis numerical control machine tool to obtain a continuous cutter position and appearance sequence, solving each motion shaft control parameter to obtain a cutter positioning sequence. The invention realizes continuous transition of the cutter shaft direction among different geometric references, and improves the smoothness and processing stability of the cutter pose sequence.

Inventors

  • LI SHIJUN
  • FENG JIE

Assignees

  • 重庆红亿机械有限公司

Dates

Publication Date
20260505
Application Date
20260407

Claims (8)

  1. 1. A method for positioning a 5-axis numerically-controlled machine tool cutter for machining an engine cylinder head, the method comprising: The method comprises the steps of obtaining a processing model of a combustion chamber of an engine cylinder cover, determining a transitional processing area according to the processing model of the combustion chamber of the engine cylinder cover, generating a processing point sequence along the transitional processing area, and respectively determining the corresponding axial direction of a valve seat, the local normal direction of the top wall of the combustion chamber and the peripheral boundary constraint direction of a spark plug hole at each processing point in the processing point sequence; According to the relative position parameters of the processing points in the transitional processing area, constructing a continuous transition relation between the axial direction of the valve seat and the local normal direction of the top wall of the combustion chamber, determining the cutter shaft direction corresponding to each processing point according to the continuous transition relation and the constraint direction of the peripheral boundary of the spark plug hole; Constraining the cutter shaft variable quantity and the 5-axis numerical control machine tool rotating shaft variable quantity according to the cutter pose corresponding to the adjacent processing points to obtain a continuous cutter pose sequence; and solving the control parameters of each motion axis of the 5-axis numerical control machine tool according to the continuous tool pose sequence and the 5-axis numerical control machine tool kinematic model to obtain a tool positioning sequence.
  2. 2. A method of positioning a tool of a 5-axis numerically controlled machine tool for machining an engine cylinder head according to claim 1, wherein said method of determining a transition machining region from said engine cylinder head combustion chamber machining model comprises: Extracting a valve seat throat boundary, a spark plug throat boundary and a curved surface of a top wall of a combustion chamber from a processing model of a combustion chamber of an engine cylinder cover, taking the valve seat throat boundary as an initial boundary, expanding a first preset width outwards according to the geodesic distance of the curved surface of the top wall of the combustion chamber to obtain a throat transition zone, expanding a second preset width outwards according to the geodesic distance of the curved surface of the top wall of the combustion chamber to obtain a spark plug transition zone by taking the spark plug orifice boundary as the initial boundary, extracting a communication curved surface subregion between the throat transition zone and the spark plug transition zone on the curved surface of the top wall of the combustion chamber to obtain a preliminary transition zone; And in the constrained transition region, eliminating curved surface units with normal change rate exceeding a preset normal change rate threshold or curvature change rate exceeding a preset curvature change rate threshold from the constrained transition region to obtain a screened transition region, and carrying out boundary bias shrinkage on the screened transition region according to cutter diameter parameters to obtain a transitional processing region.
  3. 3. The method for positioning a tool of a 5-axis numerically-controlled machine tool for machining an engine cylinder head according to claim 2, wherein the method for determining the corresponding valve seat axis direction, the combustion chamber top wall local normal direction, and the spark plug hole peripheral boundary constraint direction at each machining point in the sequence of machining points, respectively, comprises: For each processing point in the processing point sequence, calculating the space distance between the processing point and each valve seat hole axis, selecting the valve seat hole axis with the smallest space distance, and determining the valve seat axis direction corresponding to the processing point; the method comprises the steps of taking each processing point as a center, constructing a spherical neighborhood, extracting curved surface units of a curved surface of the top wall of the combustion chamber in the spherical neighborhood, calculating unit normal vectors of the curved surface units, carrying out weighted average and normalization on the unit normal vectors according to the distance between the curved surface units and the processing points, and obtaining initial local normal directions of the top wall of the combustion chamber corresponding to the processing points; Determining boundary points with the minimum distance from each processing point on the boundary of the spark plug hole, and constructing a direction vector of the boundary points to the processing points; And when the included angle variation is larger than a preset direction variation threshold, updating the direction corresponding to the processing point according to a weighted average result of the corresponding direction of the adjacent processing point to obtain the local normal direction of the top wall of the combustion chamber and the constraint direction of the periphery boundary of the spark plug hole.
  4. 4. A method of positioning a tool of a 5-axis numerically controlled machine tool for machining an engine cylinder head according to claim 3, wherein the method of constructing a continuous transition relationship between the valve seat axis direction and the combustion chamber top wall local normal direction based on the relative positional parameters of the machining point in the transition machining region comprises: Determining a transition path along a transition processing area, and calculating the geodetic path arc length of each processing point along the transition path in the transition processing area, wherein the ratio of the geodetic path arc length to the total arc length of the transition path is used as an initial position coefficient corresponding to each processing point; calculating curvature change rate of the local normal direction of the top wall of the combustion chamber at each processing point, taking a normalized value of the curvature change rate as a weight modulation factor, calculating a first weight coefficient of the axial direction of the valve seat according to the correction position coefficient and the weight modulation factor, determining a second weight coefficient of the local normal direction of the top wall of the combustion chamber according to the first weight coefficient, enabling the sum of the first weight coefficient and the second weight coefficient to be 1, and taking the first weight coefficient and the second weight coefficient as a continuous transition relation between the axial direction of the valve seat and the local normal direction of the top wall of the combustion chamber.
  5. 5. The method for positioning a tool of a 5-axis numerical control machine for machining an engine cylinder head according to claim 4, wherein the method for calculating a first weight coefficient in the valve seat axis direction based on the corrected position coefficient and the weight modulation factor comprises: the method comprises the steps of correcting a position coefficient, carrying out power function transformation on the corrected position coefficient to obtain a first position weight item, carrying out product operation on the weight modulation factor and the corrected position coefficient, carrying out power function transformation to obtain a second position weight item, constructing a normalized distribution relation according to the first position weight item and the second position weight item, and calculating to obtain the first weight coefficient in the axial direction of the valve seat.
  6. 6. The method for positioning a tool of a 5-axis numerically controlled machine tool for machining an engine cylinder head according to claim 5, wherein the method for determining the cutter axis direction corresponding to each machining point according to the continuous transition relation and the constraint direction of the peripheral boundary of the spark plug hole comprises: Calculating a minimum clearance between a cutter corresponding to the initial cutter shaft direction and a spark plug hole port boundary at each processing point according to the geometric parameters of the cutter and the spark plug hole port boundary, calculating an included angle between the constraint direction of the spark plug hole peripheral boundary and the initial cutter shaft direction in a tangential plane of the processing point when the minimum clearance is smaller than a preset safety clearance, and determining a corrected rotation shaft direction corresponding to the included angle; The method comprises the steps of determining a correction angle according to a difference value between the minimum clearance and a preset safety clearance, rotating the initial cutter shaft direction around a correction rotation shaft direction to obtain a candidate cutter shaft direction, carrying out update calculation on the minimum clearance corresponding to the candidate cutter shaft direction to obtain an updated minimum clearance, determining the candidate cutter shaft direction as the cutter shaft direction corresponding to a machining point when the updated minimum clearance is not smaller than the preset safety clearance, incrementally adjusting the correction angle and repeatedly rotating and checking the clearance when the updated minimum clearance is still smaller than the preset safety clearance until the minimum clearance is not smaller than the preset safety clearance or a preset convergence condition is met, and determining the final candidate cutter shaft direction as the cutter shaft direction corresponding to the machining point.
  7. 7. The method for positioning a tool of a 5-axis numerically-controlled machine tool for machining an engine cylinder head according to claim 6, wherein the method for constraining the variation of a cutter shaft and the variation of a rotation axis of the 5-axis numerically-controlled machine tool according to the tool positions corresponding to adjacent machining points to obtain a sequence of continuous tool positions comprises: the method comprises the steps of adding a tool pose corresponding to a first processing point in a processing point sequence into a continuous tool pose sequence as a starting pose, carrying out inverse kinematics solution on the corresponding tool pose according to a kinematics model of a 5-axis numerical control machine tool for each processing point in the processing point sequence to obtain a rotation axis angle solution set; calculating the cutter shaft included angle variation between the current cutter pose and the previous cutter pose and the rotation angle variation between corresponding rotation shaft angle solutions, and determining a smooth intensity coefficient according to the correction position coefficient of the current processing point in the transitional processing area when the cutter shaft included angle variation is larger than a preset cutter shaft included angle threshold or the rotation angle variation is larger than a preset rotation angle threshold; And when the constraint condition is not met, the smooth strength coefficient is increased, the cutter shaft direction adjustment and the constraint verification are repeated until the condition that the cutter shaft included angle variation and the corner variation are not larger than the corresponding threshold values is met, and the final candidate cutter pose is added into the continuous cutter pose sequence.
  8. 8. A 5-axis numerically-controlled machine tool cutter positioning system for machining an engine cylinder head, the system comprising: The device comprises a region definition module, a transition processing region generation module, a processing point sequence generation module, a gas valve seat axis direction determination module and a spark plug hole peripheral boundary constraint direction determination module, wherein the region definition module is used for acquiring an engine cylinder cover combustion chamber processing model; the cutter shaft generating module is used for constructing a continuous transition relation between the axial direction of the valve seat and the local normal direction of the top wall of the combustion chamber according to the relative position parameters of the processing points in the transition processing area, determining the cutter shaft direction corresponding to each processing point according to the continuous transition relation and the constraint direction of the peripheral boundary of the spark plug hole, and determining the corresponding cutter pose according to the cutter shaft direction and the space coordinates of each processing point in the processing point sequence; the motion smoothing module is used for restraining the cutter shaft variable quantity and the 5-axis numerical control machine tool rotating shaft variable quantity according to the cutter pose corresponding to the adjacent processing points to obtain a continuous cutter pose sequence; and the cutter positioning module is used for solving the control parameters of each motion axis of the 5-axis numerical control machine tool according to the continuous cutter pose sequence and the 5-axis numerical control machine tool kinematic model to obtain a cutter positioning sequence.

Description

Method and system for positioning cutter of 5-axis numerical control machine tool for machining engine cylinder cover Technical Field The invention relates to the technical field of 5-axis numerical control machining, in particular to a method and a system for positioning a cutter of a 5-axis numerical control machine tool for machining an engine cylinder cover. Background Numerical control finish machining of a combustion chamber of an engine cylinder cover relates to collaborative machining of a complex space curved surface and a porous structure, and tool gestures are usually required to be determined according to the normal direction of the curved surface or the direction of a hole axis. In the four-valve shed roof structure, the combustion chamber is formed by a valve seat throat area, a top wall curved surface and a central spark plug hole peripheral area, and the cutter needs to continuously move among different geometric features and finish posture adjustment in the processing process. In the existing processing method, a cutter shaft determination mode based on a local normal direction is generally adopted for a curved surface area, and a cutter shaft determination mode based on a hole axis direction is adopted for a hole system area. When the machining path spans different areas, the arbor direction needs to be switched between different references. However, because of the limited internal space of the combustion chamber and the short geometric transition area, there is a significant difference between the normal direction of the curved surface and the axial direction of the valve seat bore within the transition zone formed between the valve seat throat and the top wall of the combustion chamber and the spark plug bore, while the spark plug bore structure has a spatial constraint on the tool pose. Disclosure of Invention The invention aims to provide a method and a system for positioning a cutter of a 5-axis numerical control machine tool for processing an engine cylinder cover, which are used for solving the problems of abrupt change of cutter shaft postures and discontinuous positioning in a short transition area among a valve seat throat, a combustion chamber top wall and a spark plug hole. To achieve the above object, in one aspect, the present invention provides a method for positioning a tool of a 5-axis numerical control machine for machining a cylinder head of an engine, the method comprising: The method comprises the steps of obtaining a processing model of a combustion chamber of an engine cylinder cover, determining a transitional processing area according to the processing model of the combustion chamber of the engine cylinder cover, generating a processing point sequence along the transitional processing area, and respectively determining the corresponding axial direction of a valve seat, the local normal direction of the top wall of the combustion chamber and the peripheral boundary constraint direction of a spark plug hole at each processing point in the processing point sequence. The method comprises the steps of constructing a continuous transition relation between the axial direction of a valve seat and the local normal direction of the top wall of a combustion chamber according to relative position parameters of machining points in a transition machining area, determining the cutter shaft direction corresponding to each machining point according to the continuous transition relation and the constraint direction of the peripheral boundary of a spark plug hole, and determining the corresponding cutter pose according to the cutter shaft direction and the space coordinates of each machining point in a machining point sequence. And constraining the cutter shaft variable quantity and the 5-axis numerical control machine tool rotating shaft variable quantity according to the cutter pose corresponding to the adjacent processing points to obtain a continuous cutter pose sequence. And solving the control parameters of each motion axis of the 5-axis numerical control machine tool according to the continuous tool pose sequence and the 5-axis numerical control machine tool kinematic model to obtain a tool positioning sequence. Further, the method for determining the transitional processing area according to the engine cylinder cover combustion chamber processing model comprises the following steps: The method comprises the steps of extracting a valve seat throat boundary, a spark plug hole boundary and a curved surface of a top wall of a combustion chamber from a processing model of the combustion chamber of an engine cylinder cover, taking the valve seat throat boundary as an initial boundary, expanding a first preset width outwards according to the geodesic distance of the curved surface of the top wall of the combustion chamber to obtain a throat transition zone, expanding a second preset width outwards according to the geodesic distance of the curved surface of the top wall of the combus