Contrinex’s new low-cost weld-immune inductives prove their value to a valve manufacturer

A valve manufacturer which uses spot welders in their manufacturing process trusts Contrinex’s new lower-cost 600 series Weld-Immune Inductive Sensors to provide reliable detection and switching. The sensors are used to prevent misalignment during the welding assembly process and need to withstand the exceptionally high currents used to weld aluminium parts and the strong magnetic fields generated by the spot welders.

Contrinex’s 600 Series Weld-Immune inductive sensors, available from PLUS Automation, are immune to electromagnetic interference with can cause unprotected sensors to malfunction or fail. The new, cost-effective, highly reliable and robust sensor range provides best-in-class performance including equal sensing of steel and aluminium targets ‘Factor 1’.

Customer application

Resistance welding, which is widely utilised by automotive, aerospace, electronics and white goods manufacturers, can kill inductive sensors. The strong magnetic fields generated by spot-welding processes cause unprotected sensors to malfunction or fail, resulting in costly downtime and high maintenance costs.

Inductive proximity sensors are heavily relied on for detection and positioning in automated assembly equipment. Industrial designers need devices that can withstand the harsh environment of a high-speed welding cell. In this particular application, the sensors are located near 50 Hz AC-welding equipment, where field strengths can read up to 40 mT or in medium-frequency (MF) resistance welding cells, where currents can be as high as 15kA. Therefore to ensure system reliability, sensors with strong weld-immunity performance are essential.

The industrial valve manufacturer, who uses MF resistance welding to join two aluminium parts, faces an especially demanding challenge. Aluminium’s lower electrical resistance means it requires welding currents two to three times higher than steel of equivalent thickness. Inductive sensors that monitor the position of the components before welding, therefore, require proven immunity to high-strength weld-field interference.

Customer Solution

Designers specify Contrinex Weld-Immune inductive sensors for positions directly exposed to electromagnetic fields. Sensing aluminium targets during an automated medium-frequency resistance-welding process is the application for inductive sensors from the new 600 Series weld-immune sensor family. The sensor features Contrinex’s ground-breaking weld-immune technology as well as true ‘Factor 1’ sensing where targets in steel and aluminium are detected equally effectively with no reduction in sensing distance.

In the welding cell, a high-speed robot gripper loads a valve body to the assembly jig, where a small pneumatic cylinder locates it longitudinally. The M8-diameter inductive sensor, located alongside the lower welding electrode, confirms that the body is correctly positioned and initiates the welding sequence, during which a current of around 15 kA flows through the components being welded. After welding, the assembly is ejected and the process repeats.

The low-cost 600 Series weld-immune sensors do not have the long sensing distance or extreme robustness of their infamous 700 Series sisters, but they are still rugged with a metal housing and a temperature-resistant sensing face in a high-strength PEEK polymer. The strong magnetic field from the welding equipment does not affect the sensor’s performance and its 2 mm sensing distance from an M8 sensor is more than adequate for the application. As a true ‘Factor 1’ sensor, no correction factor is required for the aluminium target, reducing the chance of an accidental collision during assembly.

To help protect sensors exposed to high-levels of weld-spatter, an ACTIVSTONE coating is available on both the 600 and 700 Series weld-immune sensors. The high-performance ceramic layer protects all external surfaces of the sensor, including the fixing nuts preventing spatter accumulation. ACTIVSTONE coated mounting brackets and spatter-resistant shroudings to prevent cable damage are also available.

The best-in-class service life provided by the Contrinex sensors, especially in tough conditions, is ideal for automated welding cells with high-strength magnetic fields due to their robustness and low maintenance requirements.

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