1、 Causes of errors in CNC machining of spherical surfaces
When machining spherical surfaces, especially those with quadrants, due to improper adjustment, it is easy to produce shoulder, shovel back and so on. The main reasons are:
1. Caused by system gap
In the transmission pair of the equipment, there is a certain gap between the lead screw and the nut. With the increase of the operation time of the equipment, the gap gradually increases due to wear. Therefore, the corresponding gap compensation during the reverse movement is the main factor to overcome the shoulder on the machined surface. The clearance measurement is usually carried out 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 extend too high or too long, because the cantilever is long during measurement, the meter base is easy to move under force, resulting in inaccurate counting and untrue compensation value.
2. Caused by uneven machining allowance of workpiece
Before realizing the design surface of parts, 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 uneven machining allowance is easy to cause "reflection" error. Therefore, for parts with high surface shape requirements, the machining allowance should be as uniform as possible before forming, or the design requirements should be achieved by machining one more surface.
3. Caused by improper tool selection
The tool removes material through the main cutting edge in cutting. However, after the arc passes through the quadrant and the arc is tangent to the auxiliary cutting edge of the tool (the intersection line between the rear of the auxiliary cutting edge and the base surface), the auxiliary cutting edge may participate in cutting (that is, shovel back). Therefore, when selecting or grinding tools, we must consider the wedge angle of tools.
2、 Elimination method of errors in CNC machining spherical surface
When machining a sphere, the sphere may be larger in the middle and smaller at both ends, or smaller in the middle and larger at both ends. At this time, it should be controlled by adjusting the radius value of the sphere. If it is large in the middle and small at both ends, increase the radius value slightly. If it is small in the middle and big at both ends, reduce the radius value. After adjustment, the roundness error of the ball can reach less than 0.05mm.