Analysis of CNC Machining Technology for Small Screw Holes

1 Small screw hole machining problem

In the process of CNC machining, there are often many problems in the machining of small screw holes on thin-walled deep cavity parts. After careful research, we have obtained several reasons that may cause the problem. First of all, when machining small screw holes on thin-walled and deep-cavity parts, because the inner wall of the cavity is very thin, it is easy to generate vibration during the tapping process, especially when high-speed tapping, this vibration phenomenon will become more Obviously, this makes the load on the tap in the air unstable when tapping. In addition, during the clamping of thin-walled deep cavity parts, if excessive force is applied, the clamping inside the cavity will be deformed. If the clamping is not firm, it is easier to process the entire cavity of the screw hole. Vibration occurs. Secondly, the manufacturing materials for thin-walled and deep-cavity parts are generally hot-rolled sheets, and there are often some relatively hard particles. And when tapping, because the cutting conditions inside the hole are not very good, it is often difficult to provide cutting fluid in time. In addition, the current drill chuck has poor coaxiality with the spindle when tapping. When tapping on a CNC machining center, the spindle speed may also be unreasonable. Through the above-mentioned phenomena, we can know that due to the effects of vibration, variable load, etc., it is easy to cause taper breakage to occur when CNC tapping is performed on a thin-walled deep cavity.

2Small screw hole machining plan

Reasonable determination of the process plan for the small screw hole of the CNC machining center is a key element for the machining of the screw hole. As we have analyzed some of the reasons in the machining process above, we have proposed the following machining plan for the CNC machining of small screw holes on this basis. 1) When machining screw holes on thin-walled deep cavity parts, perform two clampings. Among them, the milling cavity is generally clamped once, and its cutting force is large, and the clamping force is also large. The machining and clamping of the screw hole is generally the second clamping, and the cutting force is weakened at this time, and the clamping force used is therefore reduced. And this can effectively reduce the deformation caused by the first clamping. 2) When machining screw holes on thin-walled deep cavity parts, support fixtures can be used for clamping for larger cavities, which can effectively reduce the vibration generated by cutting. In this process, it is necessary to design the supporting milling fixture of the cavity to effectively reduce the vibration generated during machining. 3) When machining screw holes on thin-walled deep cavity parts, the tapping speed should also be appropriately reduced, which can effectively reduce the cutting force and reduce vibration during machining. 4) When machining screw holes on thin-walled deep cavity parts, spring clamp sets should be used to clamp the taps, so that the coaxiality between the taps and the spindle is improved. 5) Extrusion taps can be used for tapping, which not only improves the strength of the taps, but also has a great effect on the improvement of tapping speed and efficiency. 6) If the deep-cavity thin-walled parts have a box body and a box cover, since the cover and the box body are often connected by countersunk screws, it is necessary to ensure that the threaded hole and the counterbore remain coaxial, and the position tolerance is general It is about ±0305mm. Therefore, after machining the small screw hole on the box body, when machining the counterbore on the box cover, a milling jig is required to ensure the position of the small screw hole on the box body.
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