What is CNC machining boring? CNC boring refers to expanding or refining the original hole on the workpiece. The boring feature of CNC machining is to correct the eccentricity of the lower hole, obtain accurate hole position, and obtain high-precision roundness, cylindricity and surface finish. Therefore, boring is often used in the final process.
Boring by CNC is a kind of difficult machining compared with other machining. It only needs to adjust a blade (or blade holder) to process micron sized holes like H7 and H6.
What are the characteristics of CNC boring?
1. Tool rotation
CNC machining is different from lathe machining. Because of the tool rotation during machining, it is impossible to timely grasp the situation of the tool tip during machining to adjust the feed rate. It is also impossible to change the machining diameter just by adjusting the numerical control button, like the numerical control lathe. This has become a big obstacle to fully automated processing. It is precisely because the machining center does not have the function of automatic machining diameter adjustment (except for those with U-axis function), it requires that the boring tool must have a fine adjustment mechanism or automatic compensation function, especially when fine boring, it must be adjusted at the micron level according to the tolerance requirements.
In addition, because the chip flow direction is constantly changing when boring the machining center, it is much more difficult to cool the tool tip, workpiece and discharge the chip than it is when machining the lathe. Especially when the vertical machining center is used for rough boring of steel blind holes, this problem has not been completely solved so far.
2. Flick knife
The most common and troublesome problem in boring is tool spring. The main reasons for tool spring on the machining center are as follows
① Rigidity of tool system: including the rigidity of tool handle, boring bar, boring head and intermediate connecting parts. Because it is cantilever machining, especially when machining small holes, deep holes and hard workpieces, the rigidity of the tool is particularly important.
② Dynamic balance of the tool system: if the tool itself has an unbalanced mass relative to the rotation axis of the tool system, it will cause chatter due to the unbalanced centrifugal force during rotation. Especially in high-speed machining, the dynamic balance of tools has a great impact.
③ Fixing rigidity of the workpiece itself or the workpiece: for example, some smaller and thinner parts cannot be fully fixed with a reasonable fixture due to their insufficient rigidity or the shape of the workpiece.
④ The shape of the blade tip: the cutting resistance varies with the front angle, escape angle, tip radius and chip breaking groove shape of the blade.
