1 tool rotation
Different from lathe processing, because of tool rotation in machining center, it is impossible to master the situation of tool tip in time to adjust the feed rate. It is impossible to change the machining diameter just by adjusting the NC button like the NC lathe. This has become a big obstacle to fully automated processing. Because the machining center does not have the function of automatic diameter adjustment (except for those with U-axis function), the boring cutter must be equipped with fine adjustment mechanism or automatic compensation function, especially in fine boring, sometimes it must be adjusted at micron level according to tolerance requirements.
When machining center boring, because the direction of chip outflow is constantly changing, it is much more difficult to cool the tool tip, workpiece and chip discharge than when machining with a lathe. Especially when the longitudinal machining center is used for rough boring of steel blind hole, this problem has not been completely solved.
2 chatter
Chatter is the most common and headache problem in boring. The main causes of chatter on machining center are as follows:
① Rigidity of tool system: including the rigidity of toolholder, boring bar, boring head and intermediate connecting part. CNC machining is a kind of cantilever machining, so the rigidity of tool system is very important, especially when machining small holes, deep holes and hard workpieces.
② Balance of tool system: relative to the rotating axis of the tool system, if there is an unbalanced mass of the tool itself, the chatter will occur due to the action of unbalanced centrifugal force during rotation. Especially in high speed machining, the dynamic balance of the tool has a great influence.
③ Clamping rigidity of workpiece itself or workpiece: for example, some small and thin parts cannot be fully fixed with reasonable fixture due to insufficient rigidity or workpiece shape.
④ Geometry of edge: different rake angle, escape angle, nose radius and chip breaking groove shape have different cutting resistance.
What we call boring in CNC machining center is to enlarge or refine the original hole on the workpiece. The feature of CNC machining is to correct the eccentricity of the lower hole, obtain the accurate position of the hole, and obtain high-precision roundness, cylindricity and surface finish. Therefore, boring as a high-precision machining method is often used in the final process. For example, the bearing holes of various machines and the processing of boxes and covers of various engines.
Compared with other machining, boring is a difficult process. It only needs to adjust one blade (or blade holder) to process micron sized holes such as H7 and H6. With the popularization of machining center, the boring process only needs programming and button operation. Because of this, it is necessary to have simpler, more convenient and more precise cutting tools to ensure the quality of products.
