CNC machine parts, how to choose milling and reverse?

CNC machine parts, how to choose milling and reverse?

How do I define both forward and reverse milling?

The cutting speed of cutting tool and the movement direction of the workpiece is the same as the clockwise milling, cutting speed and the direction of the workpiece is the reverse milling.

The features of milling forward and back

1. Influence on cutting force

The vertical cutting force acting on the workpiece is always upward during reverse milling, which tends to lift the workpiece, easily causing vibration and affecting the clamping of the workpiece.

The vertical cutting force acting on the workpiece during milling is always pressed down on the workpiece, which is beneficial to the clamping of the workpiece.

2. Influence on the elastic deformation of cutter

When the end milling cutter is used to cut the profile of the workpiece, the reaction force of the workpiece to the cutter is pointed in the direction of the cutter.

When an end milling cutter is used to cut the profile of the workpiece, the reverse force of the workpiece on the cutter is pointed into the profile, and the elastic deformation of the cutter produces the phenomenon of "nibbling" (overcutting). The smaller the diameter of the cutter and the longer the extension of the pole, the more obvious the phenomenon of "let the knife" and "chew the knife".

Therefore, rough machining with milling, can leave less finishing allowance. When using reverse milling, must leave more finishing allowance, in case "nibbling" produce workpiece scrap.

3. Influence on tool wear

The vertical milling force of down milling can press the workpiece to the working table, and the sliding of cutter teeth and the processed surface and the friction phenomenon are small, which is beneficial to reduce the wear of cutter teeth, reduce the hardening phenomenon and reduce the surface roughness.

In addition, the cutting thickness of cutter teeth during milling is from the maximum to zero, which makes the impact force when cutting into the workpiece.

But the distance of the cutter tooth passing on the workpiece is shorter and the average cutting thickness is larger. Therefore, under the same cutting conditions, when using reverse milling, the tool is easy to wear, more cutting power consumption.

So how do you choose between milling forward and reverse?

1. Selection principle

When using the down milling, the first requirement is that the machine has a gap elimination mechanism, which can reliably eliminate the gap between the feed screw and nut of the worktable, so as to prevent vibration during the milling process.

Working table is driven by hydraulic pressure is the most ideal. Secondly, it is required that the surface of workpiece blank is not hard, and the process system should be rigid enough. If the above conditions can be met, milling should be used as far as possible, especially for the difficult material milling, using milling can reduce cutting deformation, cutting force and cutting power.

When the parts are rough machining, the cutting method of reverse milling is usually adopted. When finishing, in order to prevent "nibbling", the processing method of milling is usually adopted.

2. Relationship with tool radius compensation

The tool radius compensation is often used to program and process the profile milling on the nc machine tool. The tool radius compensation can be divided into the left tool radius compensation and the right tool radius compensation.

The discriminant method for the left compensation of cutter radius is: the cutter is turning forward (clockwise rotation), along the direction of the cutter, the cutter is located at the left side of the machining profile. On the contrary, the cutter is located on the right side of the profile.

Therefore, no matter the internal contour or the external contour machining, the processing method of the left compensation programming milling of cutter radius is forward milling, while the processing method of the right compensation programming milling of cutter radius is reverse milling.

When the disc milling cutter is used to process the plane profile, and when the cutting width of the cutter is greater than 50% of the cutter diameter, the cutting process is both forward milling and reverse milling.

3. Selection of CNC milling machine for both forward and reverse milling

Numerical control machine tools generally have gap elimination function, the reverse clearance of transmission mechanism is small, and numerical control machine tools mostly carry on the parts finishing. Therefore, in nc milling, the processing mode of milling is usually used, that is, in contour machining, programming and machining by using the left compensation of tool radius.