CNC lathe programming basics

1. Metric (metric) and imperial programming

The unit of length used in CNC lathes is metric (metric) and English. The length unit dimension is set by a dedicated command code. For example, the FANUC-0TC system uses G20 to indicate the use of imperial units. G21 indicates the use of metric (metric) ) Unit Dimensions. After the system is powered on, the machine is automatically in metric size.

2. Diameter programming and radius programming

(1) Diameter programming: When using diameter programming, the coordinate value of the X axis in the NC program is the diameter value on the part drawing.

(2) Radius programming: With radius programming, the coordinate value of the X axis in the NC program is the radius value on the part drawing. Considering ease of use, diameter programming is generally used. The default programming method of the CNC system is diameter programming.

a) Diameter programming b) Radius programming

Figure 1 CNC Turning Programming Classification

a) A: (30.0, 80.0), B: (40.0, 60.0) b) A: (15.0, 80.0), B: (20.0, 60.0)

3. Lathe's front tool post and rear tool post

CNC lathe tool rack layout has two forms: as shown in Figure 2

Figure 2 Lathe's front tool post and rear tool post

(1) Front knife holder. The front tool rest is located in front of the Z axis. Like the layout of the traditional horizontal lathe tool holder, the tool guide rail is a horizontal guide rail, and a four-station electric tool rest is used;

(2) rear knife holder. The rear tool post is located behind the Z axis, and the guide rail position of the tool post is inclined with the positive plane. This structure form is convenient for observing the cutting process of the tool, easy removal of chips, and large rear space, and more tool posts can be designed. General multi-function CNC lathes are designed as rear cutters.

4. Tool nose radius compensation

In the numerical control turning programming, for the convenience of programming, the tool tip is regarded as a cusp. The trajectory of the tool in the numerical control program is the trajectory of the hypothetical cusp. (As shown in Figure 3)

Fig. 3 Imaginary nose and nose radius

The tool nose radius compensation is introduced in the CNC system: After the NC program is written, the known tool nose radius value is entered into the tool compensation table. When the program is running, the CNC system automatically performs the tool's actual movement path according to the corresponding tool nose radius value. make up.

In CNC machining, indexable inserts are generally used. The radius of the tip of each insert is fixed. The type of the insert is selected and the radius of the tip of the insert can be determined.

Tool tip arc radius compensation instruction:

Instruction Format G41(G42, G43)G01(G00)X(U)_Z(W)

Command function G41 is the left edge radius compensation of the tool nose;

G42 is the right radius compensation of the tip radius;

G40 cancels the tool nose arc radius compensation.

Instruction Explanation Following the direction of the tool movement, the tool is on the left side of the workpiece for the left edge radius compensation; the tool on the right side of the workpiece is the right edge radius compensation. The tool nose radius compensation can only be established and deactivated by the linear motion of the tool.

5. Initial state of CNC machine tools

Initial state: The status of the exponential control machine after it is powered on, also known as the default state of the CNC system. Normally, the absolute coordinate mode is programmed, the metric length unit dimension is used, the tool compensation is cancelled, the spindle and the cutting fluid pump stop working, etc. As the initial state of CNC machine tools.