What Are the Most Commonly Used Thread Machining Methods in CNC Machining Center

Thread machining is one of the very important applications of CNC machining center. The machining quality and efficiency of thread will directly affect the machining quality of parts and the production efficiency of machining center.With the improvement of the performance of CNC machining center and the improvement of cutting tools, the method of thread machining is also improving, and the accuracy and efficiency of thread machining are also gradually improving. In order to enable technicians to reasonably select thread processing methods in processing, improve production efficiency and avoid quality accidents, several thread processing methods commonly used in CNC machining center are summarized as follows:1. Tap processing method

1.1 classification and characteristics of tap processingUsing tap to process threaded hole is the most commonly used processing method. It is mainly applicable to threaded holes with small diameter (d30) and low requirements for hole position accuracy.

In the 1980s, the flexible tapping method was adopted for threaded holes, that is, the flexible tapping collet was used to clamp the tap. The tapping collet can be used for axial compensation to compensate the feed error caused by the non synchronization between the axial feed of the machine tool and the spindle speed, so as to ensure the correct pitch. The flexible tapping collet has complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC machining center Gradually, the rigid tapping function has become the basic configuration of CNC machining center.

Therefore, rigid tapping has become the main method of thread machining.That is, the tap is clamped with a rigid spring collet, and the feed of the spindle is consistent with the spindle speed controlled by the machine tool.Compared with the flexible tapping chuck, the spring chuck has the advantages of simple structure, low price and wide application. In addition to holding the tap, it can also hold the end milling cutter, drill bit and other tools, which can reduce the tool cost. At the same time, the rigid tapping can be used for high-speed cutting, improve the use efficiency of the processing center and reduce the manufacturing cost.

1.2 determination of threaded bottom hole before tappingThe processing of threaded bottom hole has a great impact on the life of tap and the quality of thread processing. Generally, the diameter of threaded bottom hole drill is close to the upper limit of the diameter tolerance of threaded bottom hole,For example, the bottom hole diameter of M8 threaded hole is 6.7 0.27mm, select the drill bit diameter as 6.9mm. In this way, the machining allowance of tap can be reduced, the load of tap can be reduced, and the service life of tap can be improved.

1.3 selection of tapWhen selecting taps, first of all, the corresponding taps must be selected according to the processed materials. The tool company produces different types of taps according to different processing materials, and special attention should be paid to the selection.

Because the tap is very sensitive to the processed materials compared with the milling cutter and boring cutter. For example, using the tap for processing cast iron to process aluminum parts is easy to cause thread dropping, disorderly threading and even tap breaking, resulting in workpiece scrapping. Secondly, pay attention to the difference between the through-hole tap and the blind hole tap. The front-end guide of the through-hole tap is long, and the chip removal is the front-end chip. The front-end guide of the blind hole is short, and the chip removal is the front-end It is the back chip. Machining the blind hole with a through-hole tap cannot guarantee the thread machining depth. Moreover, if a flexible tapping collet is used, it should also be noted that the diameter of the tap handle and the width of the four sides should be the same as that of the tapping collet; the diameter of the tap handle for rigid tapping should be the same as that of the spring jacket. In short, only a reasonable selection of the tap can ensure the smooth machining.

1.4 NC programming of tap machiningThe programming of tap machining is relatively simple. Now the machining center generally solidifies the tapping subroutine and only needs to assign values to various parameters. However, it should be noted that the meaning of some parameters is different due to different NC systems and different subroutine formats.For example, the programming format of Siemens 840C control system is g84 x_y_r2_r3_r4_r5_r6_r7_r8_r9_r10_r13_. Only these 12 parameters need to be assigned during programming.

2. Thread milling method2.1 characteristics of thread millingThread milling adopts thread milling tool and three-axis linkage of machining center, that is, x-axis and y-axis arc interpolation and z-axis linear feed.

Thread milling is mainly used to process large hole threads and threaded holes of difficult to process materials. It mainly has the following characteristics:(1) high processing speed, high efficiency and high processing precision. The tool material is generally cemented carbide, with fast tool walking speed. The manufacturing precision of the tool is high, so the milling thread precision is high.(2) the milling tool has a wide range of application. As long as the pitch is the same, whether it is left-hand thread or right-hand thread, one tool can be used, which is conducive to reducing the tool cost.

(3) milling is easy to remove chips and cool, and the cutting condition is better than that of tap. It is especially suitable for thread processing of difficult to process materials such as aluminum, copper and stainless steel, especially for thread processing of large parts and components of precious materials, which can ensure the thread processing quality and workpiece safety.(4) because there is no tool front-end guide, it is suitable for machining blind holes with short thread bottom holes and holes without tool return grooves.2.2 classification of thread milling tools

Thread milling tools can be divided into two types, one is the machine clamp cemented carbide blade milling cutter, and the other is the integral cemented carbide milling cutter. The machine clamp cutter has a wide range of applications. It can process holes with thread depth less than the blade length or holes with thread depth greater than the blade length. The integral cemented carbide milling cutter is generally used to process holes with thread depth less than the tool length.2.3 NC programming of thread millingThe programming of thread milling tool is different from that of other tools. If the processing program is wrong, it is easy to cause tool damage or thread processing error. The following points should be paid attention to during programming:

(1) firstly, the threaded bottom hole shall be processed well, the small diameter hole shall be processed with a drill, and the larger hole shall be bored to ensure the accuracy of the threaded bottom hole.(2) when cutting in and cutting out the tool, the arc path shall be adopted, usually 1 / 2 turn, and 1 / 2 pitch shall be traveled in the z-axis direction to ensure the thread shape. The tool radius compensation value shall be brought in at this time.(3) the x-axis and y-axis circular arc shall be interpolated for one week, and the main shaft shall travel a pitch along the z-axis direction, otherwise the threads will be buckled disorderly.

(4) specific example program: the diameter of thread milling cutter is 16. The threaded hole is M48 1.5, the depth of threaded hole is 14.The processing procedure is as follows:(the procedure of threaded bottom hole is omitted, and the bottom hole shall be bored) G0 G90 g54 x0 y0g0 Z10 m3 s1400 m8g0 z-14.75 feed to the deepest thread G01 G41 x-16 Y0 F2000 move to the feed position, add radius compensation G03 x24 Y0 z-14 I20 J0 f500 cut in with 1 / 2 circle of arc G03 x24 Y0 Z0 I-24 J0 F400 cut the whole thread G03 x-16 Y0 z0.75 I-20 J0 f500 cut out with 1 / 2 circle of arc G01 G40 x0 Y0 return to the center and cancel radius compensation G0 Z100M30

3. Snap method3.1 characteristics of snap methodLarge threaded holes can sometimes be encountered on box parts. In the absence of tap and thread milling cutter, the method similar to lathe pick-up can be adopted.

Install the thread turning tool on the boring bar to bore the thread.The company once processed a batch of parts with m52x1.5 thread and 0.1mm positional degree (see Figure 1). Because of the high positional requirements and large thread hole, it is impossible to process with tap and there is no thread milling cutter. After the test, the thread picking method is adopted to ensure the processing requirements.3.2 precautions for buckle picking method

(1) after the spindle is started, there shall be a delay time to ensure that the spindle reaches the rated speed.(2) during tool retraction, if it is a hand ground thread tool, because the tool cannot be grinded symmetrically, reverse tool retraction cannot be adopted. The spindle orientation must be adopted, the tool moves radially, and then the tool retraction.(3) the manufacturing of the cutter bar must be accurate, especially the position of the cutter slot must be consistent. If it is inconsistent, multiple cutter bars cannot be used for processing, otherwise it will cause disorderly buckle.

(4) even if it is a very fine buckle, it cannot be picked with one knife, otherwise it will cause tooth loss and poor surface roughness. At least two knives shall be divided.(5) the processing efficiency is low, which is only applicable to single piece, small batch, special pitch thread and no corresponding tool.3.3 specific procedures

N5 G90 G54 G0 X0 Y0N10 Z15N15 S100 M3 M8

N20 G04 X5 delay to make the spindle reach the rated speedN25 G33 z-50 K1.5 turnbuckleN30 M19 spindle orientation

N35 G0 X-2 cutterN40 G0 z15 tool retractionEditing: JQ