Weld Nut Sensing

Location bolt with integrated sensor reliably identify and secure welding nuts and sleeves

To join sheet metal, the automobile industry frequently uses spacer sleeves. In order to ensure a smooth and zero-error production process, continuous monitoring is necessary to ensure the presence of these parts. With the new welding nut sensor, Turck is now offering an affordable and process reliable alternative to previously used and expensive optical detection methods that are prone to error or malfunction.
  • The new welding nut sensors are primarily used in chassis construction in the automotive industry

  • The magnetic field sensor forms the heart

  • A sheathed stainless steel centering and bushing secures the 1

  • After the operator has placed a welding nut on the location bolt, the sensor sends a signal to the PLC

  • After release by the PLC, the welding robots score the nuts and bushings on the sheet metal

Spacer sleeves and welding nuts are used to ensure that vehicle components such as frames, U-beams, car seats or tanks are assembled to meet the design requirements. If even one single nut or bushing is missing from its intended location, production comes to a standstill and the work goes into the scrap pile. One approach to solving the component inspection problem is the use of fiber optics which can sense the bolts laterally. However, because the weld spatter that builds up can impair the fiber optic functions and even disable them, this process is expensive and unsuitable.

Process reliable sensors

Because all optical systems are prone to malfunction, customer requests for an affordable and process reliable sensor became more and more frequent. This was incentive enough for Turck to develop a robust sensor for detecting welding nuts. An ingenious solution has been developed that not only detects metal, but also replaces the location bolt. The sensor is designed for damping caused by welding nuts and detects ferro-magnetic components such as bushings, nuts, and disks. It has a brass housing and meets the requirements for IP67 protection. LEDs reliably indicate the current switching status, including both the presence of the target as well as errors that have occurred.

Because the welding nut query takes place in a harsh environment and employees do not always work carefully, the sensor must be sufficiently protected mechanically. Protection is provided by a stainless steel centering bushing that is inserted onto the sensor and secured by the nut. Together, the sensor and the stainless steel bushing form the location bolt. The welding nut sensors can detect ferro-magnetic material through non-ferro-magnetic stainless steel bushings so that they emit a signal only in the case of magnetic metals. Because the welding nuts are made of steel, they represent an excellent target for sensors.

The new Turck sensor can be programmed to sense only the nut and not the sheet metal via pin 2 of the M12 x 1 plug-in connector and an additio­nal teach adapter (VB2-SP1). At the press of a button, the sensor “learns” both the status of just the sheet metal as well as the status of the sheet metal and welding nut so that it can reliably detect their pres­ence. Once the programing has been learned, it remains intact until a new teach process is initiated. The major temperature changes caused by the weld­ing process are intercepted by temperature compensation.

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