The machining steps and methods of multi head thread CNC lathe are super practical!

In modern industrial production, using CNC lathes to process threads can greatly improve production efficiency, ensure thread processing accuracy, and reduce the labor intensity of operators. However, there is a common phenomenon in the training and teaching of CNC lathes in vocational colleges, where some teachers and the vast majority of students find thread processing difficult, especially when processing multi head threads, and are even more at a loss. Below, through the actual machining analysis of threaded parts, the machining steps and methods of multi head threads will be explained.
1, Basic characteristics of threads
In mechanical manufacturing, threaded connections are widely used, such as the connection between the spindle and chuck of CNC lathes, the firmness of screws on square tool holders for cutting tools, and the transmission of lead screws and nuts. It is a continuous protrusion and groove with a specified tooth shape formed along a spiral line on a cylindrical or conical surface, and there are two types of threads: external thread and internal thread. According to the different shapes of thread profiles, there are mainly four types: triangular threads, trapezoidal threads, serrated threads, and rectangular threads. According to the different number of threads, they can be divided into single thread and multi thread. In various machinery, the main functions of threaded parts are as follows: firstly, they are used for connecting and fastening; Secondly, it is used to transmit power and change the form of motion. Triangle threads are commonly used for connection and durability; Trapezoidal and rectangular threads are commonly used to transmit power and change the form of motion. Due to different uses, their technical requirements and processing methods also vary.
2, Processing methods
The processing of threads, with the development of science and technology, often uses CNC machine tools in addition to ordinary machine tools. This can not only reduce the difficulty of processing threads, but also improve work efficiency, and ensure the quality of thread processing. CNC machine tools commonly use G32, G92, and G76 commands for thread machining. The instruction G32 is used for machining single thread threads, with heavy programming tasks and complex programs; By using the instruction G92, a simple thread cutting cycle can be achieved, greatly simplifying program editing, but requiring the workpiece blank to undergo rough machining in advance. Instruction G76 overcomes the shortcomings of instruction G92 and allows for the one-time processing of the workpiece from the blank to the finished thread. And the program is simple and can save programming time.
Turning multiple threads on a regular lathe has always been a machining difficulty: after the first thread is turned, it is necessary to manually feed the small tool holder and calibrate it with a dial gauge to accurately move the tool tip along the axis by one pitch before machining the second thread; Alternatively, open the gear box, adjust the gear meshing phase, and then sequentially process the remaining threads on each end. Due to various factors such as the pitch error of the ordinary lathe screw, the transmission error of the hanging wheel box, and the movement error of the small drag plate, it is difficult to achieve high accuracy in the lead and pitch of multi head threads. Moreover, throughout the entire machining process, there are inevitably issues such as tool wear and even cutting. Once the tool is changed, the new tool must be accurately positioned on the unfinished thread line. All of this requires the operator to have rich experience and superb skills. However, in mass production, relying solely on the operator's personal experience and skills cannot guarantee production efficiency and product quality. In today's modernized manufacturing industry, the application of high-precision CNC machine tools and high-performance CNC systems has made it easy to achieve precision that is difficult to control in many ordinary machine tools and traditional processes, and production efficiency and product quality have also been greatly guaranteed.
3, Example analysis
We are currently using the GSK980T lathe of FANUC system to process M30 threads × Taking 3/2-5g6g as an example, illustrate the CNC machining process of multi head threads:
Workpiece requirements: Thread length is 25mm, with a chamfer of 2 on both ends × A thread with a surface roughness of Ra3.2 and a 45 ° angle. The material used is 45 # round steel billet.
1. Preparation work. By analyzing the processed parts and using the lathe manual to search for M30 × Basic parameters of 3/2-5g6g: The workpiece is a double threaded screw with a lead of 3mm and a pitch of 1.5 (this parameter is an important basis for table lookup); The major diameter is 30 and the tolerance zone is 6g. It was found that the upper deviation of the size is -0.032, the lower deviation is -0.268, and the tolerance is 0.236, indicating a relatively loose tolerance requirement; The pitch diameter is 29.026 and the tolerance zone is 5 g. It was found that the upper and lower deviations of the dimensions are -0.032 and -0.150 respectively, with a tolerance of 0.118. The tolerance requirement is relatively tight; The minor diameter is determined by subtracting the turning depth from the major diameter. The relationship between the total back cutting amount ap of the thread and the pitch is close to the empirical formula ap ≈ 0.65P, and the back cutting amount for each step is determined based on the initial precision machining and material. The major diameter is the programming basis for turning the outer circle of thread burrs, the medium diameter is the standard for thread size detection and the basis for debugging thread programs, and the minor diameter is the basis for programming thread machining programs. Leave a certain size of tool retraction groove on both sides.
2. Choose the correct machining tool. There are many types and materials of thread turning tools, and the selection should be reasonable based on the type of material being processed. The material grade should be determined according to different processing stages. For 45 # round steel material, it is advisable to use YT15 hard alloy turning tool. This tool material is suitable for both rough machining and precision machining, with strong universality, and is suitable for CNC lathe thread processing. In addition, it is necessary to consider the shape error of the thread and the angle and symmetry of the ground thread turning tool. Turning 45 steel threads, the blade inclination angle is 10 °, the main back angle is 6 °, the secondary back angle is 4 °, the blade tip angle is 59 ° 16 ', the left and right edges are straight, and the radius of the blade tip arc is determined by the formula R=0.144P (where P is the pitch). The blade tip fillet radius is very small, so special attention should be paid when grinding.
4, Method and Program Design for Multi head Thread Processing
The programming method for multi head threads is similar to that for single head threads, which is achieved by changing the initial position or angle of the cutting thread. Assuming that the blank has been processed as required and the thread turning tool is T0303, the following two methods are used for programming processing.
1. Use the G92 instruction to machine cylindrical multi head threads. The G92 instruction is a simple thread cutting cycle instruction. We can use it to first machine a single thread, and then move a pitch in the Z-axis direction according to the structural characteristics of the multi head thread, in order to achieve the machining of the multi head thread. Program editing is shown in the figure. (The origin of the workpiece is set at the center of the right end face)
2. Use the G33 instruction to machine cylindrical multi head threads. When programming with the G33 instruction, in addition to considering the thread lead (F value), the number of threads (P value) should also be considered to illustrate the indexing angle of the thread axis.
In the formula: X, Z - The coordinates of the thread end point for absolute size programming (using diameter programming).
U. W - Thread endpoint coordinates for incremental dimension programming (using diameter programming)
F - Lead of thread
P - Number of threads
3. Control factors for multi head thread machining. Special attention should be paid to controlling the following issues when using programs to process multiple heads:
(1) Determination of spindle speed S280. Due to the fact that CNC lathe machining threads relies on spindle encoders, the spindle encoder has a limit recognition requirement for the spindle speed of threads with different lead lengths during machining. The empirical formula S 1200/P-80 should be used to determine (where P is the lead length of the thread), and S cannot exceed 320r/min, so S280 r/min.
(2) Surface roughness requirements. The final cutting of thread machining is basically achieved through repeated cutting, which can obtain a smoother tooth surface and meet the requirements of Ra3.2.
(3) Batch processing process control. Before running the cutting program on the test piece, in addition to the normal requirement of tool alignment, the tool wear value should be set between 0.3 and 0.6 in the FANUC CNC system. After the first machining, precision measurement should be carried out using a thread micrometer and data should be recorded. The wear value should be reduced by 0.2 and the second automatic machining should be carried out. The measurement data should be recorded. In the future, the decrease in wear compensation value should be reduced and the relationship between its decrease and the decrease in pitch diameter should be observed. Repeat the process, Until the pitch diameter dimension is adjusted to the center of the tolerance zone. In future batch processing, changes in dimensions can be inspected using thread ring gauges, and compensated by changing the X data in the program or adjusting the tool wear value.