Heavy Threads whirlwind milling

Processing mainly uses the traditional thread thread thread or use the Turning tap, die, and sets of hand-tapping and other methods of deduction. With CNC screw machine technology, in particular, three-axis NC machining technologies, so more advanced processing methods thread - The NC milling can be achieved. CNC Thread Milling mainly hit, milling machine or machining center.

For small diameter internal thread (≤ 20mm) used tapping, set deduction and other methods to process; for materials, high hardness, a large number of holes greater precision non-standard internal thread processing, traditional processing methods with these more difficult. Ingersoll thread within the NC-120 whirlwind milling method is a good solution to be difficult using traditional methods for processing large-scale precision processing problems within the thread. It can be strictly controlled in the diameter tolerance, reducing or eliminating the cutting tool on the tooth type of interference, which greatly improved the precision of screw thread to be processed, and processing efficiency. This paper describes the processing technology of whirlwind milling and programming.

2 machining principle and processing methods

Processing principles and trajectories

NC Milling machine tool large internal thread, can be used whirlwind milling, the machining principle is: high-speed rotating cutter shape, its tip turning circle diameter is always inscribed within a thread state, at the same time, tool axis of the workpiece around the hole for screw motion, then 60 ° forming knife tip interference with the metal removal, hole in the workpiece to cut the thread groove wall. Spiral movement of the spiral from the CNC interpolation function to achieve. To prevent the processing to the hole bottom, chip and tool interference resistance extrusion and machining parts were covered chips, whirlwind milling out the bottom holes are used for processing from the cutting direction.

Tools and accompanied

Thread Whirling, including when to use NC-120 device on the blade, cutter and arbor, its agencies shown in Figure 1. And the design and manufacture of a special access bar, in front of connection NC-120 and the cutter arbor, the back of the taper shank and spindle connection (Figure 1). The blade is indexable, not re-grinding carbide blade, the angle of its size and high accuracy can be installed on the milling cutter, to put in 4 to 6 blades to form multi-edge milling cutter. By centering the tail cutter and arbor columns and threaded coupling, but also through the arbor of short tail cone, keys and screws, fastening holes in the cone can be mounted on a special arbor. The tools are also involved in multi-blade cutting, high precision and good wear resistance. As the tool spindle directly connected, in the choice of cutter, the main processing of pitch is to consider the size and depth of screw, screw diameter is not a major consideration. Thread milling tool can be used to design, but its manufacturing accuracy to meet the job requirements. Tooth profile to ensure dimensional accuracy and surface roughness, as a multi-edge structure.

Calculation of the parameters of thread

Thread of tooth size and knife point type shown in Figure 2. Thread standard set forth in the tooth type is an isosceles triangle with the peak slashing the H / 8 high, and to here as the thread nominal diameter. Figure 2 reflect the thread with the clearance requirements. CNC milling, for the tip shown in Figure 2 A and tooth type size of the point B coincide, we must calculate the maximum screw diameter D1. The calculation is as follows: D1 = d +2 × H / 8 = d + H / 4 type in, H = 0. 866P, P is pitch, the diameter tolerance of the value of its tolerance of 1 / 3 considered, the D1 diameter will also increase: D1 = d + H / 4 + e / 3 type in, e is the diameter tolerance value.

3 Programming

Siemens 8 system as an example to introduce the NC program preparation. Subroutine written in the form. Replace the statement with the R parameter value in the digital and can be applied to different diameters, different pitch, different depths of thread processing, and has some versatility. Procedures prepared by tool center path, so you do not use knife offset compensation. Program can be stored machine tools, used by the main program calls and gives cutting, the initial parameter assignment, while positioning the tool center top bottom has been processed.

The initial assignment process definition and trajectory parameters

Figure 3 is the internal thread milling process cyclone trajectory and parameters defined: RO1-processing thread nominal diameter; R03-special milling cutter tip diameter (SK);
R05-processing thread depth; R06-thread in the path of tolerance value; R08-thread milling tool path velocity; R09-pitch; R11-tool axis number (X axis, 111 = 1; Y axis, 111 = 2; Z axis , R11 = 3). XY plane within the thread milling the block diagram in XY plane inside the thread milling on the block diagram shown in Figure 4:

Figure 4 process flow chart

XY plane within the thread milling process

For CNC boring, milling machine tools (machining centers), the thread milling process of the preparation of the main use of G02, GO3 circular interpolation instruction, the formation of helical interpolation movement. Here is a subroutine Siemens 8M system uses a single: N1 R1O 0. 8S6 R12 4 R50 0; R52 2 R53 R02 0R54 0N2 R30 RO9 R00 0 R30/R32; N3 R01 R30 R00 0 R06/R51; N4 R01 R06 R00 0 R01 -R01; N5 R01/R52 R00 0 R02 R01;
N6 R02/R52 R00 0 R54 R01; N7 R54 × R51 R00 0 R05 R54; N8 G64 G91 G01 Z-R05 FR08 M03; cutting tool into the hole bottom N9 G03 X-R01 Y0 PR2; arc to cut into the largest diameter N10 G03 X0 Y0 IR01 J0 ZR9; helical interpolation milling a deduction N11 R50 R09; has been processed to increase the length of a pitch N12 @ 02-10 R5 R50; judge R05> R50, the first paragraph jump N10 N13 G00 XR01 M05; R05 ≤ R50, the Hole Cutter retreat center N14 G90 G60 M17; subroutine end.

Program is based on the design of internal thread processing right hand, but also can be prepared the same way a common thread within the parameters of L subroutine.

4 Conclusion

Whirlwind milling method used to process large-scale precision within the thread, can strictly control the diameter tolerance, good precision and high efficiency. As a result of routine technical, programming is more convenient. And for different types of thread, just modify the parameters of the program can be, the program can be stored in the CNC system, the processing time to time out, suitable for mass production.

Our model for the XK713 CNC machine tools milling M200 uses a large cyclone within the thread, the results show that the method processing, production efficiency than the traditional method of processing increased by 40%, and easy to control the machining accuracy.

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