Processing plan for parts drilling and tapping

When drilling, select a high-speed steel drill bit made of a special titanium alloy, and increase the rigidity by thickening the drill core and minimizing its length. During processing, the drill will withdraw after drilling 1-1.5mm, and then withdraw after drilling to improve heat dissipation and lubrication conditions and reduce elastic force. Do not allow the drill to spin in the hole without feeding, so as not to cause work hardening. In actual processing, the measured hole diameter is about 0.1mm smaller than the drill diameter. This is one of the characteristics of titanium alloy materials. Therefore, drills with a diameter of about 01mm larger than the standard diameter can be used for drilling. The center drill point hole tapping is required before drilling. During processing, the processing effect can be improved through the following two ways.

(1) The structure of the feed tap improves the rigidity of the tap and reduces the contact area with the processed material. The method is to thicken the cone core, reduce the friction between the chips and the rake surface, select the rake angle of the tap as 8-10 degrees, increase the tap clearance angle during processing, widen the chip flute, reduce the width of the edge, and use the skipping tap. Wait. In addition, the spiral groove can increase the sharpness of the tap and reduce the cutting force to avoid the breaking of the tap and improve the processing quality; it is good for chip removal, so that the titanium mesh can be discharged along the spiral groove to the outside of the workpiece, avoiding jamming of the tap, improving the processing conditions and making the coolant easier Enter the cutting area to improve tap cooling and lubricity. It was confirmed during processing that satisfactory results can be achieved when tapping threaded holes above M3 on the machining center using machine tapping taps with spiral grooves.

(2) Tolerance requirements for the design of the threaded bottom hole shall be required for the diameter tolerance of the threaded bottom hole. On the premise of meeting the requirements of thread accuracy, the threaded bottom hole should be processed to the upper difference of the small diameter of the thread as much as possible. If necessary, the hole can be drilled to meet the tolerance requirements. Titanium alloy material should be drilled with a diameter of about 0.1mm larger than the bottom hole. In order to offset the rebound amount, a sharp drill is required to drill the bottom hole to reduce the surface hardening layer of the threaded bottom hole. When tapping a threaded hole on a machining center, a floating tapping collet is required to offset the coordination error between the spindle and the feed, and the end of the bottom hole is chamfered before tapping to enhance the accuracy of tap entry. A slower speed can be selected when tapping to ensure smooth cutting

(3) The coolant used for wire and drilling is the same. It is not recommended to use chlorine coolant. Because in the cutting process, the cutting fluid decomposes at high temperature to release hydrogen gas, which causes hydrogen embrittlement after being absorbed by titanium. At the same time, chlorine may also cause high temperature stress corrosion cracking of titanium alloy. When drilling shallow holes, you can use electrolytic cutting fluid; when drilling deep holes, use N32 mechanical oil and kerosene, the ratio is 31.5, you can also use sulfurized cutting fluid. The cooling fluid for titanium alloy processing is properly formulated to extend the life of cutting tools; it is prohibited to use low melting point metals and their alloys (lead or zinc-based alloys, copper, tin and cadmium-based alloys for work, fixtures or temporary fasteners and The tools, fixtures or other devices in contact with the titanium alloy must be clean and free of dirt. Lead, zinc steel, tin and other low-melting metals are not allowed to remain on the surface of the titanium alloy after processing. If there is any residue, hydrogen acid and ferrous sulfate solution should be used Carefully clean. When loading and unloading cleaned titanium alloy workpieces, it is necessary to prevent grease and fingerprint contamination to avoid salt stress and bird corrosion, which may cause the titanium alloy workpiece to break