What is friction “flow” drilling?
Friction drilling (aka “flow drilling”) uses a conical bit made of very heat-resistant material such as cemented carbide. This device is pressed against a target material with both high rotational speed and high pressure. That way, there is a high local production of heat which softens the material, making it soft enough to flow. The tool then “sinks” through the object, making a hole in it. Lubricants can be used to help prevent work-material from adhering to the bit, extending the life of the tooling.
Unlike drilling, material that is flowed is not removed. The material forms a sleeve around the hole. The length of that sleeve is up to three times the original thickness of the material. The presence of this metal lip around hole edges makes connections stronger. Internal threads can be cut with a tap or rolled with a die.
Several options are available with this technology. Bits may include a cutting device that removes the collar of material that flows upwards out of the hole. This creates an even top surface that is level with the drilled material. Drilled starter holes can be used to reduce the required axial force, and with leave a smooth finish in the flowed material lower edge.