1, structural analysis
The high-speed steel twist drill bit is connected with the common plain steel shank. It is the welding of dissimilar materials. The main difficulty is the chemical composition of the two materials, the mechanical properties are different, and the crack is easy to occur in the weld zone. After the test, some necessary measures are taken. Welding can be successful.
2, processing groove
(1) Carefully remove the oil, rust, oxides, etc. from the weld and the surrounding area until the pure base metal is exposed.
(2) Grind the joint with a grinding wheel into a 60-70 degree X-shaped symmetrical groove, leaving a blunt edge of 2-3 mm and a gap of 1.5-2 mm.
3, the selection of welding rod
The electrode is selected as J506 or J422, dried at 200 degrees, and kept for 1-2 hours.
4, preheating before welding
Depending on the situation, consider pre-weld preheating as appropriate, and the end of the drill can be heated to 450-500 degrees with an oxyacetylene flame.
5, welding process
(1) In the high-speed steel twist drill part, except for the welding place, all the asbestos is wrapped and immersed in the oil oil basin. It can be placed vertically or obliquely. The oil basin should be covered with iron plate to prevent the droplets from splashing into the oil. Grease splash.
(2) It can be reversed by DC power supply or AC welding power supply. ã€Metal Processing Onlineã€‘
(3) Using a thin electrode, a small current, a thin layer is deposited at the end of the drill bit as a transition layer, and the angle of the transport bar should be as small as possible to prevent the base metal from being excessively melted into the weld.
(4) Fix the drilled layer of the transition layer and the carbon steel weldment with the clamp, straighten, and then carry out the positioning welding every 90 degrees along the circumference. The arc is biased toward the carbon steel side, and the side of the high speed steel is minimized. Melt deep.
(5) Apply symmetrical and short weld bead welding. Note that in the case of penetration, the weld bead should be thinner, with small diameter welding rod and small current welding. Generally speaking, the diameter of the welding rod is 3.2 mm and the welding current is 80-100A. The electrode diameter is 2.5 mm at 60-80A.
(6) The angle of the transport bar should be appropriate. The arc should be directed to the side of the carbon steel, with an angle of 25-35 degrees from the axis of the drill bit and an angle of 35-40 degrees from the circumferential tangent. ã€Metal Processing Onlineã€‘
(7) Apply welding at low heat and average temperature to control the melting temperature of the joint. During welding, the welding rod should move smoothly and evenly. When the arc is closed, it should be returned to fill the crater and weld the weld. The total arc heat should be better than the welding. Carbon steel is about 1/3 lower.
(8) After the welding, the red hot state, quickly mount the workpiece on the machine tool, and slowly drill into the steel pipe with the size of the drill bit fixed in advance on the workbench for straightening. The temperature during the straightening process should be higher than 400 degrees.
6, post-weld treatment
(1) During the welding process, if the cutting edge of the drill reaches the annealing temperature, the heat treatment shall be carried out according to the heat treatment specification of the twist drill.
(2) For the workpiece whose cutting edge is not affected by heat, it is immersed in the oil after the welding, and the joint part is covered with asbestos for heat preservation and slow cooling treatment. ã€Metal Processing Onlineã€‘
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