Why there should be no chips in roll tapping
Roll tapping does not remove material: the tap plastically deforms the material of the hole, generating the thread through compression. For this reason, the presence of chips is always an abnormal sign and indicates that the material is not flowing correctly along the tap profile.
The defect can compromise thread quality, reduce the mechanical strength of the joint and cause assembly problems.
Signs that indicate the presence of chips in the thread
- thread with small metal fragments trapped between the thread flanks;
- thread surface is irregular or compressed;
- screw enters with difficulty or locks in the first turns;
- metal residues on the tap after a few cycles;
- abnormal noises during tapping;
- tap requires more torque than normal.
Technical causes of chips in roll tapping
The main causes are related to pre-hole quality and material flow during deformation. The most common include:
- Rough pre-hole: a non-smooth internal surface generates micro-removal during deformation.
- Ovalized pre-hole or out of tolerance, which forces the tap to deform more material than expected.
- Material too hard or not ductile enough, which does not flow correctly.
- Insufficient lubrication, which increases friction and micro-tearing.
- Tap geometry unsuitable for the material or type of hole.
UFS solutions to eliminate the problem
To obtain clean threading with no residues, it is essential to work on the pre-hole, lubrication and tool. The most effective UFS solutions include:
- Check pre-hole quality: it must be smooth, cylindrical and free from excessive roughness.
- Check the wear of the drill or drill used to produce the tap-drill hole, replacing them when necessary.
- Use fluteless forming taps or with geometries optimized for plastic deformation.
- Prefer taps with internal lubrication (FOR/FORY versions) to improve material flow.
- Optimize lubrication with fluids with high friction-reducing capacity.
Best practices to prevent residues in the thread
- use high-quality drills to obtain smooth and regular pre-holes;
- avoid ovalized or out-of-tolerance pre-holes;
- ensure constant and adequate lubrication;
- choose taps specifically designed for roll tapping;
- monitor tapping torque as an indicator of smooth material flow;
- regularly check the surface of the thread produced.