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Brief Discussion on Thread Milling

Release time:Apr 27, 2019 Visits:

The emergence of a three-axis linkage CNC machining system enables thread milling.


First, the seven contrasts with traditional tapping


First, the tap (screw) can only process fixed pitch, and the thread milling cutter can machine threads with different pitches. Second, when machining blind holes, the tap can only reach a certain depth. A thread milling cutter with a flat bottom actually has no "guide cone" and can process deeper complete threads. Third, thread milling cutters can machine threads with special fits, tolerances or positions, and standard taps cannot. Fourth, the thread milling cutter can machine a variety of internal and external threads with different directions of rotation (left-handed, right-handed). For threads that do not allow transitional or undercut structures, traditional turning methods or taps and dies are difficult to machine, but CNC milling is very easy to implement. Fifth, when machining the internal thread with a tap, it is necessary to ream the taper of 1 degree and 47 minutes after drilling, and then use a head tapping tap to open a guide. If it is a blind hole, the third tapping cone is also required. Milling does not require a reaming hole in most cases. Sixth, the continuous length of swarf generated by tapping on certain materials can be entangled in the hole or piled up at the bottom of the blind hole to cause the tap to break. Thread milling is an interrupted cut that produces short, shredded chips with sufficient space between the tool and the hole to allow the chips to be easily discharged without chipping. Seventh, when tapping, due to poor tap performance or difficult material processing, the processed thread is easily out of tolerance. Thread milling, especially for difficult-to-machine materials, does not have the problem of excessive thread size. The thread size is controlled by the machining cycle (program value) and the tool offset value, and the surface quality of the milled thread is also significantly better than tapping. By cutting a threaded hole and a tapped hole and observing the result under a magnifying glass, it is easy to see that the tapped hole appears to be a little flash because the cutting edge of the tap tends to be blocked and sometimes at the time of tapping. Biting the tap sometimes tears the thread, causing defects in the tooth shape; eighth, once the tap breaks in the threaded hole being machined, it is quite difficult to remove the broken tap from the threaded hole, especially for very expensive materials. It will cause great economic losses. This is not the case after the thread milling cutter has been broken.

Second, the type of thread milling cutter


1. Overall cylindrical thread milling cutter

Commonly used integral cylindrical thread milling cutters can be divided into two types: machining coarse thread and machining fine thread. Thread milling cutters are made of hard alloy and can be coated with various coatings (such as TiCN, TiAlCN, WC, etc.) to increase tool life. Suitable for milling small and medium diameter threads of steel, cast iron and non-metallic materials, with smooth cutting and long life. Table 1 shows the standard thread pitch P of common specifications.


2. Machine clamp thread milling cutter

Machine clamp thread milling cutters are suitable for threading of larger diameters (generally 25mm or more in diameter). The jaws are divided into two types from the tooth profile: single-toothed blades and multi-toothed blades. The tool path when milling threads is basically the same.

Third, the programming and processing of milling threads

The thread milling movement path is a spiral, which can be realized by the three-axis linkage of the CNC machine tool.

1. Single-thread thread milling cutter milling internal thread circulation (FANUC system)

O2345;

#1=;Thread nominal diameter

#2=;pitch

#3=[1.1*#2]/2; thread depth

#4=; Milling cutter diameter

#5=;Thread depth

#6=;feed speed

#7=[#1-#4]/2.+#3; Blade radius of gyration

#8= 0 ;variable

G54 G90 G21;

GOO Z5O.;

XO YO;

M03 S600;

G01 X#7 F#6;

WHILE[#8GT-#5]DO 1;

G00 Z#8;

#8=#8-#2

G02I-#7 Z#2; left-handed with G03

END 1;

G00 XO YO;

Z50.;

M30;


2. Single-blade thread milling cutter milling external thread circulation (FANUC system)

O3456;

#1=;Thread nominal diameter

#2=;pitch

#3=[1.1*#2]/2; thread depth

#4=; Milling cutter diameter

#5=;Thread depth

#6=;feed speed

#7=[#1+#4]/2.-#3 ;

#8= 0 ;variable

G54 G90 G21;

GOO Z5O.;

XO YO;

M03 S600;

G01 X#7 F#6;

WHILE[#8GT-#5]DO 1;

G00 Z#8;

#8=#8-#2

G02I-#7 Z#2; left-handed with G03

END 1;

G00 XO YO;

Z50.;

M30;


Thread milling also has limitations:

First, it is necessary to use a 3-axis CNC machine tool; second, it can only process 3 times the diameter of the thread; third, the thread milling cutter is more expensive than the tap; fourth, the programming of the thread milling is more troublesome.


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