Tapping stainless steel is much more difficult than tapping regular steel. Often, due to the large torque, the screw tap is “bitten” into the screw hole, collapses or breaks, and the thread surface is not light. The groove has a groove, the size is out of tolerance, and the chaos and taps are badly worn. Therefore, corresponding technical measures must be taken to solve the problem of machining stainless steel threads.
1. When tapping a stainless steel thread.
The phenomenon of “tooth enlargement” is more serious, and the tap is “easy to bite” into the hole, so the hole at the bottom of the thread must be properly enlarged. In general, the diameter of the bottom hole of a screw with a pitch less than 1 mm is equal to the nominal diameter minus the pitch. If the pitch is greater than 1 mm, the diameter of the hole at the bottom of the thread is equal to the nominal diameter minus 1.1 times the pitch.
2. Choosing the right tap and the right amount of cut is the key to tap quality.
The tap material should be selected from cobalt or aluminum carbide high speed steel. The main deviation angle is related to the pitch and the number of tap handles. Head cone Kr = 5-7, 2nd and 3rd cone Kr = 10-20. Calibration parts are typically 3-4 thread lengths and are 0.05-0.1 mm / 100 mm inverted cones. Generally, the direction of the tip holder is b = 8 to 15, which allows you to control the direction of the tip flow. For straight groove taps, the front edge of the tap can be ground into a spiral shape.The rake angle of the tap is generally gp = 15 ° to 20 ° and the back angle is 8 ° to 12 °.
3. You can tap stainless steel using tapless tap.
See Figure 7. The diameter of the bottom hole before extruding with a slotless tap is as follows.
d0 = dw-(0.5-0.6) P
Here, dw——work screw outer diameter, mm.
4. When tapping stainless steel, make sure you have enough cooling lubricant.
Sulfate oil is usually selected from + 15% to 20% CCl4. White lead oil + engine oil or other mineral oil; kerosene is diluted with chlorinated paraffins.
5. If the tap is damaged during tapping, the workpiece can be soaked in nitric acid solution to corrode, and the high speed steel wire cone can corrode quickly without discarding the workpiece.
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