Shop Floor Background
During a recent production test, we were asked to create M10 threaded connections on stainless steel square tubes without using welded nuts. The tubes were intended for load-bearing industrial frames where both strength and surface appearance were important.
Material used was SUS304 stainless steel square tube, 50×50 mm, with a wall thickness of 3 mm.
Issues with Traditional Methods
When conventional drilling and tapping were used, the effective thread depth was limited by the tube wall thickness. Welding nuts solved the strength issue but added extra labor, heat distortion, and post-weld surface finishing.
The customer wanted a cleaner and more efficient solution.
Thermal Friction Drilling Setup
To address this, a thermal friction drilling and tapping process was tested on our CNC tapping machine.
- Thermal drill diameter: 8.5 mm
- Spindle speed: approx. 2,800 RPM
- Feed: CNC-controlled linear feed
- Cooling: dry, no cutting fluid
The friction heat softened the stainless steel and formed a bushing approximately 9–10 mm long.
Tapping and Results
After forming, M10 threads were tapped directly in the same setup.
- Thread engagement: full-length
- Deformation: none observed on tube surface
- Cycle time per hole: ~5 seconds
- Strength: passed torque testing for structural use
Practical Limitations
This method works well for stainless steel tubes above 2.5 mm thickness. For thinner materials, thread strength may not meet M10 load requirements without reinforcement.
Application Notes
This process is suitable for industrial frames, fitness equipment structures, and heavy-duty furniture systems where welding needs to be avoided.
