CNC lathe thread cutting method - Solutions - Huaqiang Electronic Network

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In the current CNC lathe, thread cutting generally has two processing methods: G32 straight cutting method and G76 oblique cutting method. Due to different cutting methods and different programming methods, the machining error is also different. We must carefully analyze the operation and use, and strive to process parts with high precision.

Programming instructions for two processing methods

G32 X(U)_Z(W)_ F_;

Description: X, Z are used for absolute programming; U, W are used for relative programming; F is pitch;

The G32 programming depth of cut is generally a constant value, double-edged cutting, and each depth of cut is generally programmed by the programmer.

G76P(m)(r)(a) Q(Δdmin)R(d);

G76X (U)Z(w)R(i)P(k)Q(Δd)F(l);

Description:

m: number of finishing repeats;

r: chamfer width;

a: the angle of the tip;

△dmin: minimum cutting depth, when the depth of cut (Δd·n1⁄2-Δd·(n-1)1⁄2) is less than Δdmin, the cutting depth is limited to this value;

d: finishing allowance;

i: the difference in the radius of the threaded part, if i=0, it is the straight thread cutting mode;

k: thread height;

Δd: the depth of cut of the first cut;

l: pitch.

The G76 programming depth of cut is generally decremented, the cutting is a single-edge cutting, and the depth of cut is calculated by the control system.

Processing error analysis and use

G32 straight cutting method, because the two sides of the blade work at the same time, the cutting force is large, and the cutting is difficult, so the two cutting edges are easy to wear during cutting. When the thread with a large pitch is cut, the cutting edge wears faster due to the large cutting depth, which causes an error in the diameter of the thread; however, the precision of the processed tooth shape is high, so it is generally used for small pitch thread processing. Since the cutting of the tool is performed by programming, the machining program is long; since the blade is easy to wear, it is necessary to perform the measurement in the machining.

G76 oblique cutting method, because of the single-side cutting, the machining blade is easy to damage and wear, so that the thread surface of the machining is not straight, the cutting edge angle changes, and the tooth shape accuracy is poor. However, due to its single-sided blade operation, the tool load is small, the chip removal is easy, and the cutting depth is decreasing. Therefore, this processing method is generally suitable for large pitch thread processing. Since the processing method is easy to remove chips, the blade processing condition is good, and the processing method is more convenient when the thread precision is not high. When machining high-precision threads, it can be completed by two-knife. The G76 machining method is used for roughing, and then the G32 machining method is used for finishing. However, it should be noted that the starting point of the tool should be accurate, otherwise it will be easy to buckle and cause the parts to be scrapped.

Cutting fluid use

When turning the thread, the proper use of the cutting fluid improves productivity and part quality. The main functions of the cutting fluid are as follows:

It can reduce the heat generated during cutting and reduce the machining error caused by temperature rise.

It can form a film on the metal surface, reduce the friction between the tool and the workpiece, and wash away the iron filings, thereby reducing the surface roughness of the workpiece and reducing tool wear.

The cutting fluid enters the metal gap and helps the tool to cut smoothly.

Based on the above functions, our company has adopted the “micro-emulsified cutting fluid CCF-10” produced by “Talente Chemical Co., Ltd.” after many experiments. This cutting fluid is a new generation of water-based cutting fluid after emulsion and synthetic cutting fluid. It overcomes the defects of easy deterioration of emulsion, poor cleaning performance and erosion of machine tool paint surface and poor lubrication performance. Good lubrication, cooling, cleaning and rust prevention. Compared with other cutting fluids, it has the effects of improving machining efficiency, reducing power consumption, extending tool life and improving surface finish of the machine.

Programming example

For example, the thread of M36X1.5 is machined, as shown in Figure 3, programmed with G32 straight cutting (each cutting depth is 0.2mm):

N10 G00 Z234

N2O G00 X35.6

N30 G32 Z269 F1.5

N40 G00 X38

N50 G00 Z234

N60 G00 X35.2

N70 G32 Z269 F1.5

N80 G00 X38

N90 G00 Z234

N100 G00 X34.8

N110 G32 Z269 F1.5

N120 G00 X38

N130 G00 Z234

N140 G00 X34.38

N150 G32 Z269 F1.5

N160 G00 X300

N170 G0

0 Z300

G76 oblique cutting programming:

G76 P010160 Q200 R0.05

G76 X34.38 Z269 P812 Q200 F1.5

Description:

The minimum depth of cut is 0.02mm.

The first cutting depth was 0.02 mm.

The thread height is 0.812mm.

It is obvious from the above example that the difference between G32 programming and G76 programming is determined by the accuracy of the workpiece required in the work.