## Definition of the axes of a CNC machine tool

To program and operate multi-axis machining, the definition of each axis of the CNC machine tool must first be understood and firmly grasped. The standard co-ordinate system is a right-handed Cartesian co-ordinate system. The basic axes of CNC machine tools are X, Y, Z three linear axes of motion, corresponding to each of the linear axes of motion of the rotary axes of motion are represented by the A, B and C axes.

Generally, the Z axis is parallel to the axis of the machine tool spindle for the transmission of cutting power, the positive direction of the Z axis is to increase the distance between the workpiece and the tool direction. x axis as a horizontal, parallel to the workpiece clamping plane axis, it is parallel to the main cutting direction, and this is the positive direction. y axis movement is based on the X and Z axis according to the right-hand rule to determine.

The axes of rotation around the X, Y and Z axes are named A, B and C. The positive direction of the A, B and C axes is accordingly determined in the positive direction of the X, Y and Z axes in accordance with the right-handed spiral.

Depending on requirements, the machine may also have additional axes in addition to the three linear axes X, Y and Z and the three rotary axes A, B and C. For linear motion, a second set of linear axes parallel to the X, Y and Z axes, respectively, are designated as the U, V and W axes, and the machine example is shown in Figure 1-2. If there is a third set of linear axes, these are designated as the P, Q and R axes respectively. For rotary axes, if the machine has a first set of rotary movements A, B and C and a second set of rotary movements parallel to A and B, designate the D and E axes.

## CNC machine tool movable axes and linked axes

The movable axes of a machine tool are the single axes that can achieve linear or rotary motion. When designing special machine tools and equipment, any number of movable axes can be configured according to the needs of the process. The linked axes of a CNC machine tool are the axes that can move simultaneously under the control of the CNC system. Therefore, the machine has the number of linked axes depends on the structure of the machine itself, but also with the CNC system has the ability to control these movable axes at the same time. For example, we say that a “nine axis five linkage” machine tool, is the number of movable axes of the machine tool has 9, and can be linked at the same time the number of axes for 5.

## Multi axis machining and its mode

General agreement, the number of axes of motion greater than 3 machine tools for multi-axis machining. Multi axis machining refers to the form of machining when the number of simultaneously combined axes of a multi-axis machine is greater than 3. The so-called 3 + 2 axis machining, refers to the five-axis CNC machine tools (typical machine tool motion axis configuration for the X, Y, Z axis and A, C axis), two rotary axis (such as A, C axis) fixed at an angle does not move, three linear axis (X, Y, Z axis) joint movement of a machining method. 3 + 2 axis machining is the most commonly used in the five-axis machining method, can complete most of the inverted hook structure machining. As shown in Figure 1-5 is an example of 3+2 axis machining with a double pendulum head 5-axis CNC machine tool tilting the tool axis. 4+1 axis machining is a form of machining in which one rotary axis is positioned at a fixed angle and the remaining three linear axes and one rotary axis move together at the same time on a 5-axis CNC machine tool. Figure 1-6 shows an example of a 5-axis CNC machine with the tool axes positioned horizontally for 4+1 axis finishing on a tapered surface. According to the number of simultaneous joint axes of motion, there are four main ways to achieve multi-axis machining.

- (1) Four-axis positioning machining: commonly known as 3+1 axis machining. It refers to the 3 axis CNC machining tools, the realization of three motion axes at the same time the joint movement, the other motion axis intermittent movement of a machining method. As shown in Figure 1-3, the machine tool after machining a square part of a side, rotate the fourth axis to position another machining surface, so as to achieve a clamping to complete four-sided machining.
- (2) Four-axis simultaneous machining: in the four-axis CNC machine tools (more common machine tool motion axis configuration is X, Y, Z and A four axes) on the four axes of motion at the same time a joint movement of the machining method. Four-axis simultaneous machining can be completed as shown in Figure 1-4 parts and similar parts of the machining.
- (3) Five-axis positioning machining: This machining method can be further subdivided into 3+2-axis machining and 4+1-axis machining.
- (4) Five-axis simultaneous machining: also known as continuous five-axis machining. Five-axis simultaneous machining refers to the five-axis CNC machine tools on the five axes of simultaneous joint movement of a machining method. Five-axis linkage machining can be processed such as the engine as a whole impeller, the overall model of a complex shape of the zero (part), such as Figure 1-7 shows a double swing head five-axis CNC machine tool using five-axis linkage machining method of machining the overall model of the lamp contour line example.