4th-axis CNC refers to X, Y, Z, and rotary axes. The fourth axis is used to rotate around other axes. Refers to the four-axis machining center.
Types of axis machine tools: cradle, vertical, horizontal, NC table + NC indexing head, NC table +90°B axis, NC table +45°B axis, NC table + general horizontal five Axis linkage CNC machine tool A axis °, two axis NC spindle, etc.
There are two ways of the rotary axis of the vertical five-axis machining center. One is the rotary axis of the worktable. The worktable set on the bed can rotate around the X axis, which is defined as the A axis. 120 degrees.
There is also a rotary table in the middle of the worktable, which rotates around the Z axis, which is defined as the C axis, and the C axis is 360 degree rotation. The advantage of this arrangement is that the structure of the spindle is relatively simple, the rigidity of the spindle is very good, and the manufacturing cost is relatively low.
But the general worktable cannot be designed too large, and the load bearing is also small, especially when the rotation of the A axis is greater than or equal to 90 degrees, the workpiece will bring a great load moment to the worktable during cutting.
4th axis structure
The structure of the fourth axis is: servo motor drive reducer type, servo motor direct drive type. The reducer is a relatively precise machine, and its purpose is to reduce the speed and increase the torque. The types of reducers generally used for four axes are divided into three types: worm gear type, roller cam type, harmonic reducer type.
- The main feature of the worm gear reducer is the reverse self-locking function, which can have a larger reduction ratio. The input shaft and the output shaft are not on the same axis or on the same plane. However, the volume is generally large, the transmission efficiency is not high, and the accuracy is not high.
- The harmonic drive of the harmonic reducer transmits motion and power using flexible deformation controlled by flexible components. The volume is small and the precision is high, but the disadvantage is that the flexible wheel has a limited life, is not resistant to impact, and is rigid and metal. In comparison, the input speed cannot be too high.
- The Roller Driver (cam roller) transmission application arc surface indexing principle is currently the most accurate motion control method. The work piece is composed of an input shaft (arc indexing cam) and a roller (output shaft). The surface of the cam groove on the input shaft is in line contact with the outer ring surface of the driven roller element on the roller to drive The runner (ie worktable) rotates. The driven roller element uses internal roller bearings to transmit torque during rotation. This working principle guarantees zero backlash, excellent working accuracy and working efficiency, and effectively avoids the loss of internal parts, providing a durable high-precision working state.
- Direct drive motor DD is the abbreviation of direct driver, including torque motor and linear motor, followed by the motor is called DD direct drive motor also called direct drive motor. Due to its large output torque, some companies directly refer to this product as torque servo. Unlike traditional motors, the high torque of this product allows it to be directly connected to the motion device, thus eliminating the need for connecting mechanisms such as reducers, gear boxes, and pulleys, so it will be called a direct drive motor. Since this type of motor is generally equipped with a high-resolution encoder, the product can achieve a level of accuracy higher than that of ordinary servos. And because of the direct connection, the positioning error due to the mechanical structure is reduced, so that the process accuracy can be guaranteed. The characteristics of the direct-drive fourth shaft, because there is no reducer to reduce the torque to increase the torque, so the rotational torque is small, usually in order to increase the torque, the motor coil is larger, so the price is more expensive. The advantage is that the servo-driven four-axis, no intermediate transmission components, no error accumulation, no backlash, so it can be processed at high speed and high precision.
Why to use 4th Axis
The general machine tool has only three axes, that is, copy, that is, the workpiece platform can move left and right (1 axis), back and forth (2 axes), and the spindle head (bai3 axis) is used to cut the workpiece. 360 degree rotating electric indexing head! In this way, bevel holes can be automatically indexed, bevel milling, etc. The advantage of adding a fourth axis to the CNC machining center is
- It can make the processing plane of the tool more extensive, and can reduce the repeated clamping of the workpiece, improve the overall machining accuracy of the workpiece, help simplify the process, and improve the production efficiency.
- It can make the plane of the tool processing more extensive, and can reduce the repeated clamping of the workpiece, improve the overall machining accuracy of the workpiece, help simplify the process, and improve the production efficiency. Specifically, the fourth axis refers to the CNC indexing head of the machining center. It can complete the tasks that the three-axis machining center cannot complete at one time. It can realize multi-face machining by rotating, which greatly improves the machining efficiency. Reduced the number of clampings.
- It can make the processing plane of the tool become wider, and can reduce the repeated clamping of the workpiece, improve the overall machining accuracy of the workpiece, help simplify the process, and improve the production efficiency. Shorten the production time, so many companies need to use a four-axis machining center. The three axes are XYZ three linear movement coordinates. The fourth axis is generally a rotary axis, which can cause an angular offset between the tool and the workpiece. The normal of the workpiece surface is at an angle to expand the processing range.
- When undertaking external processing tasks, in addition to the normal contour and hole processing on the CNC machine tool, sometimes curve and curved surface parts are also required, which is difficult to complete on the ordinary three-coordinate CNC machine tool At this time, the fourth axis can be installed on the CNC machine tool to expand the machine tool functions and greatly reduce the cost investment. Install the CNC indexing head as the fourth axis on the table of the three-axis CNC machining center. Through this transformation, not only can the processing that requires multiple processes on the CNC machine tool be concentrated in one installation, but also increase the freedom of the machine tool. , Expand its functions, and improve processing accuracy, quality and efficiency.
What is the difference between 4-axis CNC and 3-axis CNC? How to program?
Three-axis machining only has XYZ three axes, and four-axis machining has XYZA or XYZB programming which is relatively cumbersome
The three-axis vertical CNC machining center is three axes of linear movement in different directions, which are up and down, left and right, and front and back. The up and down direction is the main shaft, which can be rotated at high speed; the four-axis vertical machining center adds a new one The axis of rotation, that is, the horizontal plane can rotate 360 degrees, but not at high speed.
The range of use is different
The three-axis machining center is the most widely used. The three-axis machining center can perform simple planar processing, and can only process one side at a time. The three-axis machining center can process very well materials such as aluminum, wood, and lost foam.
The use of four-axis machining centers is less than that of three-axis machining centers. It can realize multi-face machining through rotation, which greatly improves the machining efficiency and reduces the number of clampings. Especially the processing of cylindrical parts is more convenient. And it can reduce the repeated clamping of the workpiece, improve the overall machining accuracy of the workpiece, help simplify the process and improve the production efficiency. Shorten production time.
The four-axis linkage center is divided into horizontal and vertical; if it is horizontal, then add a B axis to the Y axis. The programming method is the same as the 3 axis, but it can rotate 4 sides at a time, and has reached a higher position. Degrees and other precision requirements, when you need to use the fourth axis when programming, just enter B**! It should be noted that when setting up the workpiece coordinate system, care must be taken, each inner surface needs to establish a coordinate system (or sub-coordinate system) such as: G51.1, G51.2. . . . Wait, the vertical is the same as the horizontal capacity, the difference is that the vertical is the A axis, and the horizontal is the B axis.
Analysis of parts drawing
According to the drawing of the part, through the analysis of the material, shape, size and accuracy, surface quality, rough condition and heat treatment of the part, the processing content and requirements are clarified, and the appropriate CNC machine tool is selected.
This step includes:
1) Determine the type or machine tool where the part should be arranged for processing.
2) What kind of fixture or clamping method is used.
3) Determine which tool or how many tools are used for processing.
4) Determine the processing route, that is, select the tool setting point, the starting point of the program (also known as the starting point of the machining, the starting point of the processing often coincides with the setting point), the path of the cutting tool, and the end point of the program (the ending point of the program often coincides with the starting point of the program).
5) Determine cutting parameters such as cutting depth and width, feed speed, and spindle speed.
Determine the process
Based on the analysis of the part drawing, determine the part’s processing technology (such as determining the positioning method, selecting tooling fixtures, etc.) and processing route (such as determining the tool setting point, tooling route, etc.), and determine the cutting amount. The process treatment involves many contents, mainly including the following:
1) Determination of processing method and process route According to the principle of fully exerting the functions of CNC machine tools, reasonable processing method and process route are determined.
2) Design and selection of cutting tools and fixtures When determining CNC cutting tools, comprehensive consideration should be given to factors such as processing methods, cutting amounts, and workpiece materials to meet the requirements of convenient adjustment, good rigidity, high accuracy, and good durability. When designing and selecting CNC machining fixtures, it should be able to quickly complete the positioning and clamping process of the workpiece to reduce auxiliary time.
And try to use combined fixtures to shorten the production preparation cycle. In addition, the fixture used should be easy to install on the machine tool, and it is convenient to coordinate the dimensional relationship between the workpiece and the machine tool coordinate system.
3) Selection of tool setting point Tool setting point is the starting point of program execution. The selection should be based on the principles of simplified programming, easy alignment, easy inspection during processing, and reduction of processing errors.
The tool setting point can be set on the workpiece to be processed, or on the fixture or machine tool. In order to improve the machining accuracy of parts, the tool setting point should be set as much as possible on the design basis or process basis of the part.
4) Determination of the processing route When the processing route is determined, the requirements of the accuracy and surface roughness of the parts to be processed must be ensured; the cutting path should be shortened as much as possible, and the empty cutting stroke should be reduced; the amount.
5) Determination of cutting amount Cutting amount includes cutting depth, spindle speed and feed speed. The specific value of the cutting amount should be based on the provisions of the manual of the CNC machine tool, the material of the workpiece to be processed, the processing content and other process requirements, and be considered in combination with empirical data.
6) Determination of coolant Determine whether coolant needs to be provided during the machining process, whether the tool needs to be changed, and when to change the tool.
Because the parts are processed on the CNC machining center, the process is very concentrated. Under one clamping, it is often necessary to complete roughing, semi-finishing and finishing. When determining the technological process, it is necessary to arrange the processing sequence of each process carefully and reasonably to improve the processing accuracy and production efficiency.
Numerical calculation is to calculate the input data required for CNC machining according to the geometric dimensions of the parts and the determined processing route. The general CNC system has the functions of linear interpolation, circular interpolation and tool compensation. For the contour processing of parts with simple shapes (such as parts composed of straight lines and arcs), calculate the starting point and end point of geometric elements, the center of the arc, the coordinate values of the intersection or tangent point of the two elements, etc.
For parts with complex shapes (such as parts composed of non-circular curves and curved surfaces), straight line segments or arc segments are used to approach, and the node coordinate values are calculated from the accuracy requirements. In this case, you need to use a computer to calculate with relevant software.
Write processing program
After finishing the process processing and mathematics processing, according to the instructions, program segment format, technological process, numerical calculation results and auxiliary operation requirements of the CNC system of the machine tool used, write it in sections according to the program instructions and format requirements specified by the CNC Part processing program.
Before programming, programmers must understand the performance, functions and program instructions of CNC machine tools in order to write the correct CNC machining program.
Enter the written program into the CNC system. There are two common methods:
1) Manual input on the operation panel of the CNC milling machine;
2) Using the DNC (data transmission) function, the program is first entered into the computer, and then the dedicated CNC transmission software. The processing program is input into the CNC system. Then it is called out to execute. Or processing while transmitting.
The compiled program must be checked for program operation. Processing procedures should generally be verified and trial cut before they can be used for formal processing. It can be used to check the correctness of the trajectory and movement of the machine tool by means of empty walking and empty running drawing.
On the CNC machine tool with graphic display function and dynamic simulation function or in the CAD/CAM software, it is more convenient to use the method of graphic simulation tool to cut the workpiece for inspection. However, these methods can only check whether the trajectory is correct, and cannot check the machining accuracy of the processed parts
How to upgrade the four-axis engraving machine
Three-axis engraving machine can only process one plane. However, the four-axis engraving machine can process one surface and then process other surfaces at will. Upgrade from three-axis to four-axis, buy a separate cnc rotary 4th axis and a controller using four-axis linkage, it is recommended to use (4 axis offline cnc controller)