Holes are important surfaces on parts such as boxes, brackets, sleeves, rings, and disks, and are also surfaces often encountered in machining.
Under the same requirements for machining accuracy and surface roughness, machining holes is more difficult than machining cylindrical surfaces, resulting in low productivity and high cost.
Productivity is low and costs are high because:
▶The size of the tool used for hole machining is limited by the size of the hole to be processed. It has poor rigidity and is prone to bending deformation and vibration;
▶When using fixed-size tools to process holes, the size of the hole often directly depends on the corresponding size of the tool. The manufacturing error and wear of the tool will directly affect the machining accuracy of the hole;
▶When machining holes, the cutting zone is inside the workpiece, and chip removal and heat dissipation conditions are poor, making it difficult to control the machining accuracy and surface quality.
Hole processing methods include drilling, reaming, boring, drawing, grinding, finishing of holes, etc.
Below, we will introduce several hole processing techniques in detail to solve the hole processing problems.
Drilling is the first step in machining holes in solid materials, and the diameter of the hole is generally less than 80mm.
There are two ways of drilling: one is drill bit rotation; the other is workpiece rotation.
The errors produced by the above two drilling methods are different.
In the drilling method with drill bit rotation, when the drill bit is deflected due to the asymmetry of the cutting edge and insufficient drill bit rigidity, the center line of the hole to be processed will be deflected or It is not straight.
but the hole diameter is unchanged; on the contrary, in the drilling method where the workpiece rotates, the deviation of the drill bit will cause the hole diameter to change, but the hole centerline remains straight.
Reaming is one of the finishing methods of holes and is widely used in production.
For smaller holes, reaming is a more economical and practical processing method compared to internal grinding and fine boring.
Boring is a processing method that uses a cutting tool to enlarge a pre-made hole.
Boring work can be performed on a boring machine or a lathe.
Honing principal and honing head
Honing is a method of finishing holes using a honing head with a grinding bar (whetstone).
When honing, the workpiece is fixed and the honing head is driven by the machine tool spindle to rotate and make reciprocating linear motion.
During the honing process, the grinding bar acts on the surface of the workpiece with a certain pressure, and a very thin layer of material is removed from the surface of the workpiece, and its cutting trajectory is a cross pattern.
To prevent the movement trajectories of the abrasive grains from being repeated, the number of revolutions per minute of the honing head's rotary motion and the number of reciprocating strokes of the honing head per minute should be prime numbers to each other.
---EDITOR: Miya Ma/Cynthia Lee
---POST: Cynthia Lee