Method and apparatus for machining the wall of a cylindrical tube by milling a groove therein

A method of machining a hollow part by milling along a line of cut which is predetermined relative to a theoretical surface of said part, said milling being performed by means of a cutter mounted at the end of a drive shaft which is carried by a moving support, said support being displaceable with at least two degrees of freedom in tilting and with at least one degree of freedom in translation, the quantity of material to be removed at any point of said line being determined by a reference difference between the end face of the cutter and a real reference surface, which real reference surface may be the inside surface or the outside surface of said part, said method comprising the following:

• a first stage of reconnaissance of the outside surface of the part, said stage consisting in causing the cutter to follow a first trajectory at a constant distance from the theoretical surface of the part, said distance being chosen in such a manner as to ensure that the cutter never comes into contact with the part and in performing the following operations at sample points along said line of cut:
• measuring the distance between the end face of the cutter and the real outside surface of the part on the axis of the cutter by means of a sensor integrated in the cutter, storing said measured distance, and determining the relative error at each sample point between the real surface and the theoretical surface;
• and
• determining and storing the direction of the normal to the real outside surface at each sample point, said determination being based on the error measured at each point and on the errors measured at the points adjacent thereto;
• a machining stage consisting in causing the cutter to follow said predetermined trajectory a subsequent time, with the position and the orientation of the cutter being controlled in such a manner that, at each sample point, the axis of the cutter is at a constant angle relative to the normal to the real surface and to the tangential direction to said line of cut at said point, and the distance between the end face of the cutter and the reference surface of the part is made equal to the reference difference for said point.