CNC milling of threads

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CNC milling of threads

Source: China Bearing Network Time: 2018-03-08
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1. Introduction The traditional thread processing method is mainly to use thread turning tools to turn threads or taps, die technology tapping and buckles. Follow the development of CNC machining skills; especially the presentation of three-axis CNC machining system; make more advanced thread processing The CNC milling of the thread is completed. The thread milling process is compared with the traditional thread machining method; it has great advantages in machining accuracy and machining power; and it is not subject to thread layout and thread rotation when machining; for example, a thread milling cutter can be used. Processing a variety of different internal and external threading. Threads that do not allow the transition buckle or undercut layout; it is difficult to machine with traditional turning methods or taps and die; however, CNC milling is very simple. The durability of the thread milling cutter is more than ten times or even tens of times that of the tap; and in the process of CNC milling thread; the adjustment of the thread diameter scale is very convenient; this is difficult to select taps and die. Because of thread milling Many advantages; the current large-volume thread production in developed countries has been widely used in the milling process.
2, thread milling processing example Figure 1 shows the M6 ​​specification internal thread milling processing example. Workpiece data: aluminum alloy, tool: carbide thread drilling and milling cutter, thread depth: 10mm, milling cutter speed: 2,000r / min, Cutting speed: 314m/min, drilling feed: 0. 25mm/min, milling feed: 0. 06mm / tooth, processing time: 1. 8s per hole.
The processing station flow shown in Figure 1 is: 1 position; the thread drilling and milling cutter runs to the workpiece safety plane, 2 positions; the thread drilling and milling cutter is drilled to the hole depth scale, 3 positions; the thread drilling and milling cutter is rapidly increased to Thread depth scale, 4 positions; thread drilling and milling cutter cuts into the starting point of the thread with a circular arc, 5 positions; the thread drilling and milling cutter makes the X and Y direction interpolation motion around the thread axis; together, it moves in the +Z direction parallel to the axis; 360° per winding axis; one pitch in +Z direction; three-axis linkage running track is a spiral, 6 positions; thread drilling and milling cutter retracts from the starting point (also the finishing point) with arc, 7 positions; The thread drilling and milling cutter rushes back to the workpiece safety plane; the next hole is prepared for machining. The machining process includes drilling, chamfering, internal thread milling and thread clearing groove milling; one tool is used to complete the end; the machining power is extremely high. .
3. The primary type of thread milling cutter is in thread milling; three-axis CNC machine tools and thread milling tools are two essential elements. The following are some common types of thread milling cutters:
(1) Cylindrical thread milling cutter The cylindrical thread milling cutter has a shape similar to that of a cylindrical end mill and a thread tap (see Fig. 2; Fig. 2 is a taper thread milling cutter); but its thread cutting edge and The taps are not the same; there is no spiral lift on the tool; the spiral lift in machining is completed by the machine tool movement. Because of this special layout; the tool can process both right-handed threads and left-handed threads; but not for larger ones. Processing of pitch thread.
Commonly used cylindrical thread milling cutters can be divided into coarse thread and fine thread. For the consideration of machining power and durability; thread milling cutters are mostly made of hard alloy materials; and can be coated with various coatings. Customized processing requirements for special materials. Cylindrical thread milling cutters are suitable for medium and small diameter thread milling of steel, cast iron and non-ferrous metal materials; smooth cutting; high durability. Defects are high cost of tool making; messy layout; expensive.
(2) Machine clamp thread milling cutter and blade machine clamp thread milling cutter are suitable for thread processing of larger diameter (such as D>25mm). It is characterized by easy to manufacture blade; lower price; some threaded inserts can be cut on both sides; However, the impact resistance function is slightly worse than that of the whole thread milling cutter. Therefore, the tool is often recommended for processing aluminum alloy data. Figure 3 shows two types of machine clamp thread milling cutters and blades. Figure 3a shows the machine clamp single-blade thread milling cutter And triangular double-sided blade; Figure 3b is machine clamp double-edged thread milling cutter and rectangular double-sided blade.
(3) Combined multi-station special thread boring and milling cutter combined multi-station special thread boring and milling cutter features one-blade multi-blade; one-time multi-station processing; can save auxiliary time such as tool change; obviously improve yield. Figure 4 shows an example of a combined multi-station special thread boring cutter. The workpiece needs to be machined with internal threads, chamfers and channels d4. If single-station active tool change is used, the single-piece machining time is about 30s. Combined multi-station special thread boring and milling cutter processing; single piece processing time is only about 5s.
4, thread milling track thread milling motion track is a spiral; can be completed by the three-axis linkage of CNC machine tools. Figure 5 is a schematic diagram of the milling motion of left-handed and right-handed external threads.
It is the same as the CNC milling which is generally summarized; the 1/4 arc cutting or straight cutting can also be used when the thread milling starts. The milling cutter should use the milling cutter with the blade width larger than the length of the thread to be machined; thus; the milling cutter only needs to rotate 360° can complete the thread processing. The orbital analysis of the thread milling cutter is shown in Figure 6.
5, thread milling programming is now associated with M30 × 1. 5 right-hand internal thread milling processing examples to clarify the programming method of thread milling. Workpiece data: 42CrMo4, thread bottom hole diameter: Di = 28. 38mm, thread diameter: Do = 30mm, thread Length L = 20mm, pitch: P = 1. 5mm, machine clamp thread milling cutter diameter: D2 = 19mm, milling method: down milling.
(1) Parameter calculation spindle speed N is
N=1000V/(D2×p=1000×150/(19×3.14)=2512r/min
The number of teeth of the milling cutter is Z=1; the feed rate per tooth is f=0.1mm; the feed speed F1 at the cutting edge of the milling cutter is
F1=fz×N=0. 1×1×2512=251. 2mm/min
The intermediate feed speed F2 of the milling cutter is
F2=F1(D0-D2)/D0=251. 2×(30-19)/30=92. 1mm/min
Set the safety interval CL = 0.5mm, cut into the arc radius Re
Re=[(Ri-CL)2+R02]/(2R0)=[(14.19-0.5)2+152]/(2×15)=13.747mm
Cut into the arc view b
b=180°-arcsin[(Ri-CL)/Re]=180°-arcsin[(14.19-0.5)/13.747]=95.22°
For the convenience of accounting; the approximate value is 90°. The Z-axis displacement Zα when cutting into an arc is
Zα=Pα/360°=1. 5×90°/360°=0.375mm
The coordinates of the starting point of the cut arc are
(2) Thread milling program (Fanuc system)
%
N10 G90 G00 G57 X0. Y0.
N20 G43 H10 Z0. M3 S2512
N30 G91 G00 X0. Y0. Z-20.375
N40 G41 D60 X0. Y-13.690 Z0.
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