Flow drilling
Flow drilling is a drilling process in metalworking that forms bores without cutting by plasticizing the material. The displacement creates a bead in the sheet metal into which a thread can be cut and a screw can be fastened.
principle
The aim is to plasticize the material to be processed. This is achieved through axial force and high speed , which creates friction . This friction causes a local heat of approx. 600 ° C, and in connection with a high surface pressure the plasticization of the material is achieved.
Process flow
In the first step, the rotating flow drilling tool is positioned on the material to be machined and the required friction is generated by applying pressure. The material heats up and the flow drill forms the hole by plasticizing the material. Threads can be created afterwards without cutting using a thread former .
Tools
Flow drills are basically available in two variants. The standard type leaves a bead on the surface of the material when drilling, which is caused by the displacement of the material in the plasticized state. The flat type removes the bead by cutting and leaves a flat surface. Flow drills require a collet chuck for mounting in a corresponding machine. These collet chucks have ventilation spokes to dissipate the high levels of heat that may damage the machine.
Advantages and disadvantages
The advantage, or rather the actual purpose of flow drilling, results from the resulting bulge on the inside of the hole. This gives you enough material to cut a larger load-bearing thread into a thin sheet of metal. Example: A conventional drill drills a clean hole in a one-millimeter thick sheet metal. You cannot cut a resilient M6 thread in this hole, as only a load-bearing thread would be created. Due to the bead that is created during flow drilling, there are several threads and the thread is more resilient. With the same basic material thickness, complex and relatively expensive constructions with press nuts, weld nuts or rivet nuts can be replaced under certain circumstances.
Disadvantages include the high heat generation and the high costs for the drill, but it has a significantly longer service life, it wears less and does not need to be re-sharpened. The drive machine must provide a high level of power (for example approx. 500 W spindle power even with a 1.8 mm drill hole), generate high axial forces and enable relatively high speeds, especially with larger drilling diameters. Depending on the material, about 1000 to 1800 rpm are required for a hole for an M20 thread with a diameter of 18.7 mm. The required spindle power is then almost three kW. Because of the high level of heat generated, the material must not be too heat-sensitive and, as a rule, not coated, i.e. it must not (yet) be painted, galvanized, plastic-coated or galvanized. Also heat-treated material is critical. Drilling in solid material is not possible because the displaced material needs space to evade. The maximum material thickness corresponds approximately to half the drilling diameter.