Frictional heat and feed pressure produce the material deformation and displacement. The frictional heat is generated through the rotational speed, the corresponding axial force (contact pressure) and feed rate. This means that, independently of the core hole size, the drill unit to be used must be capable of a speed of up to 500 rpm, a machine output of up to 5 KW, and a feed rate of up to 1000 mm/min. The right combination of feed rate and speed depends on the type (stainless steels, steel, or non-ferrous metals) and thickness of the material. For optimized results, the material must retain the correct temperature during forming and must not cool down too rapidly. Data listed later in this document are intended as reference values only and can vary significantly for different material grades and thicknesses.
The required axial force at the start of the flow drilling process is very high and decreases towards the end of the process when the core hole is fully formed. When processing thin materials, relining may be necessary to prevent deflection.
Rotational speed RPM
The normal speed for small core hole diameters is relatively high, at approx. 3000 rpm, and can be as high as 4500 rpm for non-ferrous metals. For larger core hole diameters such as M20, the necessary speed is only approx. 1000 rpm. Stainless steel, with a lower thermal conductivity, can be processed at speeds up to 20% lower.
Machine output kW
To generate the required axial force and torque, a machine with sufficient kilowatt output is indispensable. For small core hole diameters a lower axial force and kilowatt output is required than for larger diameters. The machine output determines the optimum process speed. Speedy machining of the metal is a determining factor for the quality of the core hole and especially for the life of the flow punch former.