Friction drilling is a method of making holes in metal in which the material is pushed out of the way with the aid of heat from friction. The process is also called thermal drilling, flow drilling, form drilling, or friction stir drilling. Friction drilling is commonly used on

bicycle frame A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangl ...

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

s, and to create holes for mounting bearings.

History

In 1923, the Frenchman Jean Claude de Valière tried making a tool that could make holes in metal by friction heat, instead of by machining. It was only a moderate success, because at that time the right materials were not yet available. Moreover, he hadn't yet discovered the right shape for this kind of tool. It was not until the 1980s that a useful tool could be produced.

Principle

Friction 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 Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc. The symbol fo ...

and high pressure. That way, there is a high local production of heat which softens the object, making it

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

. The tool then "sinks" through the object, making a hole in it. Lubricants help prevent work-material from adhering to the bit. Unlike drilling, material that is flowed is not lost but it forms a sleeve around the hole. The length of that sleeve is up to 3 times the original thickness of the material. The presence of this metal lip around hole edges makes connections stronger. Several options are available with this technology. Bits may include a cutting device that removes the typical "collar" of plastified material that flows upwards, so that an even top surface is the result. Drilled starter holes may be used to reduce the required axial force and to leave a smooth finish in the bushing’s lower edge. Internal screw threads may be cut with taps or rolled with dies.

Advantages

* Very quick process (2 to 6 seconds) * The process reshapes all material so that no material is lost. The excess material forms a sleeve that is about 3 times longer than the original thickness of the target material, which makes it possible to make very strong bolt joints in thin material. * It is a clean process because no litter (particles) is produced. * No access needed to back of workpiece, as with press-in or self-clinching hardware. * More reliable and faster than

rivet nut A rivet nut, also known as a blind rivet nut, or rivnut, is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. It is a kind of threaded insert. There are two types: one is designed to for ...

s (an alternative that also does not require access to back of workpiece). * Works in almost all kinds of metal.

Disadvantages

* Friction drilling is not possible in massive material since displaced metal must be able to flow somewhere. Maximum material thickness is typically half of the hole diameter with bit manufacturers providing specific guidance. * The target material must be able to withstand the added heat. Materials that have been painted, plastic coated,

galvanized Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged ...

, or heat treated are often unsuitable for this process. * Requires higher motor capacity and rotational speed than conventional drills.

References

{{reflist

External links

Video of the flow drill process
Hole making