Tap Chipping
Tapping is a relatively difficult machining process, because its cutting edge is basically in 100% contact with the workpiece, so various problems that may arise should be considered in advance, such as the performance of the workpiece, the selection of tools and machine tools, and the high cutting speed , Feed rate, etc.
The following editor will tell you about the selection of taps and how to tap them!
Selection of taps
Choice of Tap and Cutting Amount
First of all, five questions should be clarified before tapping:
1. What is the material of the processed workpiece?
2. What is the strength of the workpiece material?
3. Is the processed screw hole a through hole or a blind hole?
4. How deep is the screw hole (or what is the working thickness?
5. What is the type and size of the screw hole to be processed?
For materials with high hardness and high strength, the tap should choose an eccentric relief angle starting from the cutting edge.
Tapping speed reference table
Selection of chip removal flutes for taps
Appearance of straight groove type, spiral groove type and tip spiral groove type:
picture
Straight groove, balanced choice.
picture
Spiral Tap
Suitable for blind hole processing, the disadvantage is that the positive angle edge is too sharp,
Not durable and expensive.
picture
Tip spiral groove type
Conducive to chip evacuation Compared with the straight groove type, it is more durable and suitable for through holes,
The disadvantage is that the invalid filament at the tip is too long.
picture
Simple comparison relationship between straight flute, spiral flute and tip spiral flute taps:
Spiral Fluted Taps
Spiral flute taps are mainly used for threading blind holes. When processing workpiece materials with high hardness and strength, a tap with a smaller helix angle can be used to improve its structural strength.
picture
For machining 400 series stainless steel (15° helix angle)
picture
Used to process 300 series stainless steel (helix angle is 41°) Figure 3 Spiral flute tap
Spiral vs Spiral
The spiral shape is suitable for blind holes, and the iron filings are discharged to the outside of the hole. The apex is spiral-shaped, and the chips are discharged downward.
picture
Intuitive comparison between straight groove type and spiral shape
picture
Tapping of special workpiece materials
The machinability of the workpiece material is the key to the difficulty of tapping. According to the performance of the material, it is very important to change the geometry of the cutting part of the tap, especially its rake angle and the degree of depression in front of it.
picture
Rake angle and undercut
Machining of high-strength workpiece materials
For high-strength workpiece materials, the rake angle and undercut of the tap are usually smaller, increasing the strength of the cutting edge. Long chipping materials require larger rake angles and undercuts for chip curling and chip breaking. Machining harder workpiece materials requires larger relief angles to reduce friction and sufficiently cool the cutting edge.
Processing of materials with different degrees of softness and hardness
For materials with high hardness and high strength, the tap should choose an eccentric relief angle starting from the cutting edge.
For example, when processing stainless steel materials, a spiral groove with a small rotation angle will be selected to deal with the hard and sticky processing characteristics of stainless steel, so as to facilitate long-lasting cutting and chip removal for blind hole tapping.
picture
Tapping stainless steel material
Common problems in tap tapping process
picture
There are many reasons for the breakage of taps: machine tools, fixtures, workpieces, processes, chucks and tools, etc., may never find the real reason just by talking on paper. All of the above problems require operators to make judgments or give feedback to technicians.
