Boring processing on CNC machining center

The so-called boring processing refers to expanding or refining the original holes in the workpiece. It is characterized by correcting the eccentricity of the lower hole, obtaining accurate hole position, and obtaining high-precision roundness, cylindricity and surface finish. Therefore, boring processing is often used in the final process as a high-precision processing method. For example, the processing of bearing holes of various machines and the casing and cover of various engines.

Compared with other mechanical processing, boring processing is a more difficult processing. It only needs to adjust a blade / (or blade holder /) to process micron-level holes like H7 and H6. With the popularization of machining center / (Machining center /), the current boring process only needs programming, button operation, etc. Because of this, simpler, more convenient and more precise tools are needed to ensure the quality of products. Here, the boring process of the machining center is mainly analyzed from the perspective of tool technology.

2. Features of boring processing of machining center

2.1 Tool rotation

Different from lathe machining, because the tool rotates during machining in the machining center, it is impossible to grasp the situation of the tool tip in time to adjust the amount of feed. It is also impossible to change the machining diameter only by adjusting the NC button like a CNC lathe. This becomes a big obstacle for fully automated processing. It is also because the machining center does not have automatic machining diameter adjustment function / (except for the U-axis function /), it requires that the boring tool must have a fine adjustment mechanism or automatic compensation function, especially when fine boring according to tolerance requirements sometimes must be in the micron Level adjustment.

In addition, since the outflow direction of the chips is constantly changing during boring in the machining center, it is much more difficult to cool the tool tip, the workpiece and discharge the chips than when turning the lathe. Especially when the longitudinal blind machining center is used for rough boring of steel blind holes, this problem has not yet been completely solved.

2.2 Chatter / (Chatter /)

The most common and most troublesome problem in boring processing is chattering. The main reasons for chattering on the machining center are as follows:

  • ①Rigidity of tool system / (Rigidity /): Including the rigidity of tool shank, boring bar, boring head and intermediate connecting part. Because it is cantilever machining / (Stub Boring /), especially when processing small holes, deep holes and hard workpieces, the rigidity of the tool system is particularly important.
  • ②Dynamic balance of the tool system / (Balance /): Compared to the rotation axis of the tool system, the tool itself has an unbalanced mass, and the flutter occurs due to the effect of unbalanced centrifugal force during rotation. Especially in high-speed machining, the dynamic balance of the tool has a great influence.
  • ③Clamping rigidity of the workpiece itself or the workpiece / (Clamping Rigidity /): Like some small and thin parts, due to insufficient rigidity of their own, or because of the shape of the workpiece, it is impossible to use a reasonable fixture to adequately fix.
  • ④ Geometry of Edge / of the blade: The cutting resistance caused by the difference of the rake angle, escape angle, blade radius, and chip breaker shape of the blade is also different.