CNC Knowledge: How to deal with the bottom hole of the extrusion valve

The extrusion tap is an advanced chip-free thread processing tool with high thread accuracy after processing. It is widely used in precision engineering industries such as automobile, aviation and electronics. Since there is no chip interference in extrusion molding, the thread processing precision can reach 4H, and the thread surface roughness can reach about Ra0.3.

The metal fibers of cutting wires are discontinuous, while the metal fibers of extrusion wires are continuous. Therefore, the strength of extrusion wires can be increased by about 30% compared to cutting wires. In addition, due to the cold hardening phenomenon caused by extrusion, the hardness of the thread surface can be increased by 40-50% compared with the core, and the wear resistance of the thread surface has also been considerably improved.

1. The main processing characteristics of extrusion taps are:

① Since the thread is extruded, the torque during the tapping process is large, which causes the processed thread to work harden, thereby improving the strength of the thread;

② No chips will be produced during the tapping process, which avoids tap breakage due to chip blocking;

③Processed internal threaded holes have high precision;

④Suitable for processing non-ferrous metals, alloys and materials with good plasticity and toughness, long service life, etc.

Compared with cutting taps, extrusion taps tend to generate larger torque during the tapping process due to different processing principles, resulting in heavier cutting loads. It is easy to cause a series of problems such as poor roughness of the threaded hole to be processed, tapping chipping, severe wear and fracture, etc., seriously affecting the service life. In order to effectively improve and solve the above problems, it is especially necessary to increase the service life of extrusion taps.

2. The need for the precision of the extrusion tap bottom hole and bottom hole diameter:

Extrusion taps process threads through plastic processing, so the size of the bottom hole will have a great impact on the shape of the thread, so high precision handling of the bottom hole is necessary.

3. Precautions for processing the bottom hole of the extrusion valve:

To process high-precision downholes, the main thing is to use carbide drills (smooth-edged drills with rollers, etc.) which are more precise than traditional high-speed steel drills.

For small diameter holes with strict hole size requirements, it is recommended to use high precision drill bits with drill diameters accurate to hundredths.

To achieve stable high-precision hole machining, it is very effective to use an end mill to carry out contouring and reaming after using a drill to carry out downhole processing.

4. Pay special attention to the following points when selecting extrusion taps:

Material

Generally, these are materials with greater plasticity, such as aluminum alloy, low carbon steel and ordinary stainless steel.

bottom hole

Extrusion taps have strict requirements for the size of the bottom hole of the tap. The bottom hole is too small, the extrusion thread is too full, and the tapping torque is too large, resulting in poor tap life. The bottom hole is too large, the formed wires are not full enough, and the resistance is reduced. Therefore, a suitable tapping bottom hole is particularly important for extrusion taps.

lubricant

Under permitted conditions, improve lubrication performance as much as possible. This is not only to reduce torque and improve the life of the tap, but above all to improve the quality of the thread surface.

In addition, when tapping with an extrusion tap, the threaded hole should not be too deep, and the effective depth of the thread should be controlled within 1.5 times the diameter. Tapping deep holes requires an extrusion tap with a lubrication groove. As shown below:

5. Causes, manifestations and methods of improving broken faucets