Fdrilling process in thin walled materials
Screw unions on thin walled materials require complex additional operations like e.g. the welding on of a nut. The so called fdrilling process can form the thread directly in the arising passage, thereby making this additional operation unnecessary.
SUHNER and Fdrill are collaborating in this field of specialised technology. Thermal fdrilling uses a Fdrill-tool to produce passages several times the thickness of the thin walled material.
Example of a typical application – After flow drilling with the machining unit BEM20, the thread is formed with the GEM20 unit.
Core drilled holes formed with this method are essentially more precise than threads formed with conventional means. Moreover, this process, by forming the existing workpiece, saves time and material.
Fdrilling is based on a combination of axial force and relatively high speed that generates local heat through friction. This friction heat and high surface pressure cause the material to undergo plastic deformation. The special geometry of the tool and its special hard metal allow it to pass through the material in one operation.
The fdrilling process
1. Starting phase
● Crater shaped indentation around the tool tip
● Axial force raised to the maximum
● Material displaced counter to the feed direction
2. Material flow phase
● Wart shaped bulging on the bottom side
● Axial force reduced
● Torque raised to the maximum
3. Forming phase
● Forming of the bush
● Collar shaped according to the tool type. Either as an edge in the form of an
O ring or as a plane surface.
This bush made without chips in seconds can be used as a bearing, as a load bearing soldered or welded connection, or of course as a core hole sleeve for screw unions. In contrast to other processes, fdrilling induces material hardening for high tightening torques in threads and large load bearing capacities in bearing bushes. Flow drilling tools are available for diameters of 1.5–46.0 mm.
SUHNER can offer for this work a range of drilling units with various feeding systems. The classical flow drilling units are the BEM 12 and the BEM 20, each with pneumohydraulic feed, i.e. a pneumatic feed regulated with a hydraulic cushioning cylinder.
The following series of operations are implemented in practice.
1. The spindle moves the rotating flow drill in rapid traverse directly in front of the workpiece.
2. Now under regulated, but still rapid feed, the tool tip contacts the workpiece.
3. Under the action of friction, the material glows and starts to flow.
4. The feed movement, first obstructed by the contact, now continues, i.e. the spindle presses the flow drill through the material. The characteristic collar is formed.
The material flowing upwards is formed into a collar.
With this method, the flow process defines the spindle's feed movement.
Owing to the displacement the material is forced to flow.
This gives rise to a compressed thread profile.
When the threads are formed, their highest points are pressed into the material. The material is deformed and flows into the gaps between the thread former's teeth.
There are no chips.
As a comparison:
The structures of a closed and formed thread
Advantages of thread forming at a glance
● No chips
● Thread depths up to 4 x D possible
● Essentially lower roughness height in the thread flanks than with thread cutting
● Approx 20 % greater pullout strength under static load
● More than double the fatigue limit under dynamic load
● Thread formers not liable to break, so maximised machining reliability
● Considerably higher service life than taps, particularly whenthread pitches ≤ 1.5 mm
● Approx 65 % of all industrial machined materials can be formed: steel up to 1200 N/mm², stainless and acid resistant steel, copper and copper alloys, aluminium and aluminium alloys.
Some applications:
