Common Arc Machining Techniques in CNC Turning

Compared with ordinary lathes, CNC lathes have the characteristics of strong adaptability, high processing precision, high production efficiency, and ability to complete the processing of complex surfaces. With the development of new products, its shape is more and more complex and the accuracy requirements are getting higher and higher. Undoubtedly, we must give full play to the advantages of CNC lathes. Arc machining embodies the advantages of CNC lathes. However, in the actual processing of large circular arcs, due to improper selection of the processing technology or lack of auxiliary calculation tools, programming difficulties often occur, and abnormal processing errors occur in severe cases. This attracted my attention. Through long-term trial experiments, it was proved that the following method is simple in arc programming and the precision of machined parts is high. Below I discuss with several common parts for example.

A circular arc cutting method

1) The arc start point and end point do not change, only change the radius R

As shown in Fig. 1, a convex arc is formed on the part, and the smaller the radius is, the larger the curvature is, based on the two points made of arcs. Therefore, when cutting the convex arc, the starting point and the ending point can be fixed to gradually decrease the radius R from small to large. Increase to the specified size. However, it should be noted that the radius of the arc must not be less than half of the finished arc chord length.

figure 1

N10 G01 X40 Z-5 F0.3;
N20 G03 X40 Z-25 R10.2 F0.2;
N30 G00 X53;
N40 Z-5;
N50 G01 X40 F0.3;
N60 G03 X40 Z-25 R12 F0.2;
N70 G00 X53;
N80 Z-5;
N90 G01 X40 F0.3;
N100 G03 X40 Z-25 R16 F0.1 :

2) The starting point of the arc, the coordinates of the end point change, the radius R is unchanged

As shown in Fig. 2, a concave arc is machined on the part. In order to reasonably distribute the amount of knife and ensure the processing quality, it adopts the progressive cutting of equal radius arc, and the programming idea is simple.

figure 2

N10 G01 X54 Z-30 F0 .3;
N20 G02 X60 Z-33 R10 F0 .2;
N30 G00 X54 Z-30;
N40 G01 X48 F0.3 ;
N50 G02 X60 Z-36 R10 F0.2;
N60 G00 X48 Z-30;
N70 G01 X42 F0.3 ;
N80 G02 X60 Z-39 R10 F0.2;
N90 G00 X42 Z-30;
N100 G01 X40 F0.3;
N110 G02 X60 Z-40 R10 F0.1;

3) The starting point of the arc, the coordinates of the end point, and the radius R are all changed

As shown in Figure 3, a hemisphere is machined at one end of the part. In this case, the radius R of the trajectory is equal to the difference between the radius R of the previous pass and the change in the Z (or X) direction ∆Z(∆X). .

image 3

N10 G01 X0 Z10 F0.3;
N20 G03 X60 Z-20 R30 F0.2 ;
N30 G00 Z6;
N40 X0;
N50 G03 X60 Z-20 R26 F0.2;
N60 G00 Z2;
N70 X0;
N80 G03 X60 Z-20 R22 F0.2 ,
N90 G00 Z0;
N100 X0;
N110 G03 X60 Z-20 R20 F0.1;

Second, the first cone after the arc method

The method is to cut off the excess cutting allowance by the method of the vehicle cone first, and the final tool takes the circular arc cutting arc shaping, as shown in FIG. 4 .

Figure 4

N10 G01 X102 Z-30 F0.3;
N20 G90 X100 Z-50 I-5 F0.2;
N30 I-10;
N40 I-15;
N50 I-20;
N60 G01 X60 Z-30 F0.3;
N70 G02 X100 Z-50 R20 F0.1;

When it is a convex arc, the length of the ab section can be calculated based on the geometry knowledge, then the car cone, and finally the car arc, as shown in FIG. 5 .

Figure 5

Db=1.414R+R=0.414R
Ab=1.414*db=0.585R

Take a part of the finishing allowance, ab takes 0.5R,

Ab=bc

According to the method in 1 to process the cone first, then finish the arc.

Third, the conclusion

In the numerical control processing, often the machine tool operator is also the preparation of the part cutting program, which requires the preparation of the program process is simple, easy adjustment, high processing accuracy. In the operation site without CAD drawing software, computer and other auxiliary calculation tools, using the above method to program the cutting arc can greatly reduce the calculation. The idea is simple, the process is appropriate, the service life of the tool is prolonged, the precision of the machined parts is high, and it is convenient for the processing of the arc parts.

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