Machine measurement

Aspects of the power system and the re-setting unit are not considered here.

The electrical system of a capacitor discharge machine (CD machine) influences the welding behaviour. Whilst the operator is only able to affect the welding process via the charging voltage of the capacitors, and therefore via the energy fed to the joining process, it is ultimately the resistance and inductance of the machine, as well as the capacitance of the capacitor bank – the basic variables – that determine the current progression. Whilst the capacitance is installed in the machine as a compact module, the overall resistance and inductance comprise multiple main components. As the following figure shows, the transformer variables and the inductance of the secondary circuit have the greatest influence.

Shares of the assemblies in the overall inductance and resistance of a CD machine with: L.o1, L‘.o2 as leakage inductances and R.w1, R‘.w2 as winding resistances of the transformer; R.pri, L.pri as variables of the primary circuit and R‘.sec, L‘.sec of the secondary circuit and R‘.last the load resistance.
According to a widely-held opinion, welding parameters cannot be transferred from one CD machine to another. This drawback arises due to the unknown basic variables of the machines and heavily simplified designated welding parameters, which are limited almost exclusively to the specification of energy E and peak current IP. According to this, the two curves in the following figure show identical parameters with E = 8.45 kWs and IP = 105 kA, although they depict strongly deviating welding behaviour.

Current characteristic curves of two machines with different basic variables but identical welding parameters.

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