Internal hole turning is also called boring. It uses turning to enlarge the inner hole of the workpiece or process the inner surface of the hollow workpiece. It can be processed by most cylindrical turning techniques. Today we will discuss common troubles in internal hole turning and provide you with some practical solutions to teach you how to deal with them easily and make internal hole processing more comfortable.
01
Problems with internal hole turning
1) Vibrating knife
Long overhangs are a major cause of blade deflection and vibration problems. The inner hole turning tool is subjected to radial force and axial force at the same time, which will cause the tool tip to deviate from the predetermined position, causing the tool holder to deform. The longer the tool holder, the more obvious the deformation will be, and the more obvious the vibration will be.
picture
picture
2) Poor surface quality
Poor chip removal may lead to poor surface quality of the workpiece. If the iron chips cannot be removed from the inner hole as planned, they will squeeze and rub the inner wall of the workpiece, causing the inner hole turning process to fail.
picture
3) The blade breaks easily
Vibration and poor chip evacuation can cause the blade to break. The blade is prone to chipping during vibration and iron chip extrusion.
picture
02
Solutions to internal hole turning problems
1) Basic principles
The general rule for internal hole machining is to minimize tool overhang and choose the largest possible tool size for maximum machining accuracy and stability.
2) Factors that improve the quality of inner hole processing from the perspective of tool application
Selection of insert geometry:
The insert geometry has a decisive influence on the cutting process. For internal hole machining, a positive rake angle insert with sharp cutting edge and high edge strength is generally used.
picture
picture
Selection of tool main declination angle:
When selecting the main declination angle, it is recommended to choose a main declination angle as close as possible to 90° and not less than 75°. Otherwise, the radial cutting force will increase sharply.
picture
Selection of tool nose radius:
In internal hole turning operations, small tool nose radii should be preferred. Increasing the tool nose radius will increase radial and tangential cutting forces, and will also increase the risk of vibration trends. At the same time, using the maximum nose radius results in a stronger cutting edge, better surface texture and more even pressure distribution on the cutting edge while ensuring a minimum radial cutter.
picture
3) Effective discharge of chips
In internal hole turning, chip removal is also very important for the processing effect and safety performance, especially when processing deep holes and blind holes.
picture
Shorter spiral chips are ideal chips for internal hole turning. This type of chips is easier to discharge and will not put a lot of pressure on the cutting edge when the chips break.
picture
If the chips are too short during processing and the chip breaking effect is too strong, higher machine tool power will be consumed and there will be a tendency to increase vibration.
picture
If the chips are too long, it will be more difficult to remove the chips. The centrifugal force will press the chips towards the hole wall, and the remaining chips will be squeezed onto the surface of the processed workpiece, which will cause the risk of chip blockage and damage to the tool.
picture
Therefore, when performing internal hole turning, it is recommended to use tools with internal coolant. In this way, the cutting fluid will effectively expel the chips out of the hole.
picture
4) Selection of tool clamping method
The clamping stability of the tool and the stability of the workpiece are also very important in inner hole processing. It determines the magnitude of vibration during processing and determines whether this vibration will increase. It is very important that the clamping unit of the tool holder meets the recommended length, surface roughness and hardness.
picture
The overall support is better than the tool bar directly clamped by screws. It is more suitable to clamp the tool bar on the V-shaped block with screws. However, it is not recommended to use screws to directly clamp the cylindrical handle tool bar because the screw will be damaged if it acts directly on the tool bar. Toolbar.
picture
5) Use a special tool bar to reduce vibration and increase the effective removal of iron chips
Damping arbor
This type of tool holder generally uses solid carbide as the tool body, which can effectively reduce the vibration of the tool in the field of small holes.
Features of damping tool holder:
picture
Anti-vibration tool holder
This type of tool holder generally has an anti-seismic unit inside the tool holder, which can effectively reduce vibration caused by excessive overhang.
However, this kind of anti-seismic means starting from cutting tools is often expensive and has harsh application scenarios.
