Patent DE-102008028385-A1 (DE)
Title: Measuring property such as resistance of a material or a function of resistance of a material of a sheet metal, comprises placing sheet between two electrodes, driving a test current traversing the electrodes, and setting a resistance
Inventor: RUSCH HANS-JUERGEN
IPC: G01N27/04
Filed: 2008-06-13
Abstract: The process of measuring a property such as resistance (R 7) of a material or a function of resistance of a material of a sheet metal (7), comprises placing a sheet between two electrodes (3, 4), driving a test current traversing the electrodes through the sheet, and setting a resistance or a development of resistance through the simultaneous detection of the current and voltage. The amplitude of test current is approximately current amplitude of the welding process of prepared welding. A standardized test current is present between 6 kA and 12 kA. The process of measuring a property such as resistance (R 7) of a material or a function of resistance of a material of a sheet metal (7), comprises placing a sheet between two electrodes (3, 4), driving a test current traversing the electrodes through the sheet, and setting a resistance or a development of resistance through the simultaneous detection of the current and voltage. The amplitude of test current is approximately current amplitude of the welding process of prepared welding. A standardized test current is present between 6 kA and 12 kA for preparing a microwelding between 0.1 kA and 5 kA. The test current is preset by changing a set point, which has bounce and increases continuously. The resistance or change of resistance is determined by changing a set value for the test current. Parameters or additional changes such as a pressure force of electrodes, a depth of penetration of the electrodes in the surface of the concerned sheet metal and/or a temperature of the sheet metal, are monitored. The measured or monitored settings or changes are used to determine the properties of the sheet material and/or its surface. A sheet is subjected to a current having a preset change of evolution. A characteristic value for the classification of the sheet is set after the change of current. The change of current in wire has two current pulses. The characteristic value depending on the change of current, change in resistance and/or characteristic value comprise a coefficient of resistivity to characterize the resistivity of the sheet, an overall coefficient of resistivity for characterizing an average resistance of the sheet, a heating index to characterize the heating effect on the sheet in a preheated state during circulation of current, an index of heat level to characterize the effect of heating and cooling of the sheet, and a surface index to characterize a surface of the sheet metal. A second sheet is used in the same change of preset current and/or by preserving the other setting conditions, using the same electrode terminal ends and/or using the same pressure forces of electrodes against the sheets. Depending on the characteristic value or determined classification value, a parameter of welding and/or type of material is assigned to the sheet and/or the surface of the sheet is closed. One or more property such as a degree of wearout is determined. The terminal ends arranged on the electrodes are taken for the measurement. The adequacy of terminal ends are taken for use during determining the resistance of the material and/or to obtain a welding result having a level of quality and optionally carrying out a shifting of terminal ends first, before applying the current. The properties of ends are determined immediately after change of ends. Independent claims are included for: (1) a process for resistance welding two steel plates at single point; and (2) a device for resistance welding two steel plates at single point.