According to DIN8589 [DIN78a] abrasive blast cutting is to be classified with the group machining with geometrically undefined cutting edges. In contrast to other methods in that category such as grinding, honing and lapping, it is used for a targeted influence of the surface layer. From this angle, it has gained considerable significance and prevalence in many areas of application. It has indeed become invaluable in various production areas.
9.1.1 Operating Principle, Initial Process Parameters and Blast Parameters
According to DIN 8589, abrasive blast cutting entails a chip formation with the help of abrasives that are blasted on the surface to be treated by the energy source with a pressure or centrifugal method. This method is therefore based upon an energy-bound operating principle. Abrasive blast cutting serves to deburr, to improve the surface or to prepare for a subsequent surface treatment method. In abrasive blast cutting, we differentiate according to the energy source, the purpose of blasting and the blasting abrasive.
The mode of action of abrasive blast cutting is based on the fact that bodies strike the surface of the workpiece to be machined with high speed and are there slowed down substantially. In this way, chip removal and/or deformation of small subsections of the treated surface can occur. Simultaneously, part of the kinetic energy is converted to heat. The finished surface is then the result of the superimposition of the multitudinous impact locations of the individual grains. If the grits strike a ductile material, a surface covered with small craters results. Crater formation is associated with plastic flow processes that entail a solidification of the surface. A residual compressive stress condition which thereby develops can also remain after processing in the workpiece layers close to the surface. If the workpiece surface is brittle however, entire areas of the surface flake from contact with the cutting edges. On the whole, the condition of the workpiece is determined by the following initial parameters:
• abrasive blast material composition (the description of the abrasive blast material composition is determined by its type and chemical composition, state, grain size and morphology as well as by the grain hardness. Typical blasting abrasives are corundum, silicon carbide or quartz.),
• abrasive blast speed,
• abrasive blast flow rate,
• abrasive blast grain mass (this indicates the amount of blasting abrasive — for solid blasting abrasives in conjunction with an indication of the grain number -, which comes into contact with the surface to be treated per time and area unit.)
• blast angle (the angle between the blast direction and the tangent plane of the blasted surface),
• blast working time and
• blast target hardness (the surface hardness of the blasted workpiece).
DIN 8200 [DIN66] names the following blast parameters:
• the specific blast time (blast working time required in order to machine a determined surface section in a particular location such that the desired effect is achieved),
• blast time (duration of time in which the workpiece remains in the working
zone),
• blast removal rate (removed workpiece material per area and time unit) and
• the blast intensity (a measure for the hammering effect of the blasting abrasive on the surface of the workpiece).