As the ordinary lathe does not have the same programming function as the CNC lathe, it cannot realize the automatic control of the tool head travel, so it cannot directly process the spherical surface. The inner spherical surface processed by CNC machining center has accurate size and high precision. However, for a small number of workpieces with large inner sphere diameter, it is too expensive to use a large CNC vertical lathe, and there will be some errors. So how to eliminate the errors in NC machining of spherical surfaces? Now let's introduce it in detail.
1、 Causes of Errors in NC Machining of Spherical Surfaces
When machining spherical surfaces, especially quadrants of balls and curved surfaces, due to improper adjustment, it is easy to produce shoulder, backhoe, etc. The main reasons are:
1. System clearance
In the transmission pair of the equipment, there is a certain gap between the lead screw and the nut. As the equipment is put into operation for a long time, the gap gradually increases due to wear. Therefore, the corresponding gap compensation during reverse movement is the main factor to overcome the shoulder on the machined surface. The clearance is usually measured with a dial gauge, and the error is controlled within 0.01~0.02mm. It should be pointed out here that the meter base and the meter rod should not be extended too far, because the meter base is easy to move under force due to the long cantilever during measurement, which will lead to inaccurate counting and untrue compensation value.
2. Uneven machining allowance of workpiece
Before realizing the design surface of the part, whether the machining allowance of the surface to be machined is uniform is also an important reason for whether the formed surface can meet the design requirements, because the uneven machining allowance is easy to cause "reflection" error. Therefore, for parts with high surface shape requirements, the machining allowance shall be as uniform as possible before forming, or the design requirements shall be met by machining one more profile.
3. Improper tool selection
The cutting tool removes the material through the main cutting edge during cutting. However, after the arc passes the quadrant, and the arc is tangent to the cutting edge of the tool pair (the intersection line between the back of the pair and the base plane), then the sub cutting edge may participate in the cutting (that is, the backhoe). Therefore, the wedge angle of the tool must be considered when selecting or grinding the tool.
2、 The Method of Eliminating Errors Caused by NC Machining Spherical Surface
When machining a sphere, the sphere may be large in the middle and small at both ends, or small in the middle and large at both ends. In this case, the radius of the sphere should be adjusted to control. If it is large in the middle and small at both ends, increase the radius slightly. If it is small in the middle and large at both ends, the radius value will be reduced. After adjustment, the roundness error of the ball can be less than 0.05mm.