How Sensors Stand Up to Challenging Welding Conditions

  • July 01, 2010
  • Feature
Ensuring each product is properly assembled before all components are welded together is at the heart of an error-proofing system for welding applications. Sensors assist in this process by providing accurate, high-speed detection. For instance, sensors can be used to confirm proper placement of metal car parts before they are fused together. Additionally, sensors can detect a robotic arm’s position to determine if the welding mechanism is in the correct position for the current application. Error proofing reduces rejects, as well as the downtime and costs associated with rejected parts.The type and quantity of sensors used varies by the application from a handful to several hundred, but the conditions these sensors must endure in welding environments remain consistently harsh: temperatures in excess of 1,200 degrees Fahrenheit, currents ranging from 15,000 to 35,000 Amps, and frequent weld flash occurrences. The combination can cause some sensors to fail as often as three of four times a day under severe conditions. Even a sensor designed for weld resistance may no longer function after 5,000 weld flashes—and if that sensor is placed within ten inches of a weld tip, it can easily experience 1,000 to 2,000 flashes per day.As these sensors fail due to the harsh welding conditions, productivity suffers and manufacturers are forced to foot significant replacement and reinstallation costs. To combat these challenges, sensors have been designed with durable housings, encapsulated electronics and other construction features to help them deliver reliable, long-lasting operation in welding environments. These new sensors have allowed manufacturers to reliably error-proof production lines, without excessive downtime or high replacement costs.Error-proofing the assembly lineOn an automated production line, if metallic components are placed in the wrong order or orientation, the robotic welding arm may fuse these parts together incorrectly. Conversely, if a robotic clamp is positioned at the wrong angle while holding metal car parts waiting to be welded, it could result in a rejected automotive component. Examining a single component—such as a sheet of metal—is just as crucial, as if it does not contain all the nuts, bushings or spacer sleeves needed in order to complete the assembly process, it will not be welded properly.Proximity sensors can prevent rejects by detecting whether or not the correct components are in their proper places as the metal parts are transferred down the manufacturing line. Then, the sensors send a pass/fail output to initiate the welding process. In robotic clamping applications, a similar solution is used, but proximity sensors are also employed to detect whether the jaws or grippers are in the proper position (open or closed). Delivering increased reliability and data collection capabilities, weld-resistant sensors feature rugged construction that allows them to be placed close to the cylinder on the robotic arm mechanism. The sensors can be configured to detect the piston’s movement within the cylinder, which corresponds to the angle the jaws/grippers open, and signal the gripper to open to the precise position required. Meanwhile, another sensor—placed into a groove within the actual jaw/gripper—confirms the held component is moved to the proper location. This custom embedding serves the dual purpose of protecting the sensor from environmental conditions and providing complementary error proofing for part-in-place applications.Some magnetic-inductive sensors can be used to identify smaller components such as weld nuts or bushings on sheet metal, as the sensors can be programmed to differentiate between the nut or bushing and the sheet metal on which it is placed. These sensors offer simplified installation—they are mounted through holes in the sheet metal—and when a weld nut is present, the sensor produces an output that signals the welding process to begin. With simple “go/no go” operation and IP67 housings optimized for welding environments, these sensors can deliver a more robust and cost-effective solution than optical or vision-based systems. Long operational life in harsh conditionsSensors require varying levels of weld resistance depending upon their proximity to the welding mechanism. Ideally, a sensor positioned within inches of weld tips should withstand 10,000 to 20,000 flashes without failure—a performance level that is hard to reach due to the strong electromagnetic fields weld flashes produce. These weld flashes can cause a proximity sensor to falsely trigger, while weld slag or spatter in the application environment simultaneously accumulates and eventually causes the sensor to malfunction. Withstanding these environmental elements requires a combination of specialized construction and numerous protection techniques.Sensors featuring temperature compensation offer weld resistance by providing reliable operation in high temperature welding environments. To resist mechanical damage, sensors can be constructed with a stainless steel front cap design and copper housing. Some manufacturers may employ proprietary weld resistant material on the sensor body to ensure the sensor face, which is most often directly exposed to weld flash, withstands slag and spatter and that the housing resists the electromagnetic field.By incorporating fitted steel covers into the sensor housing prior to sealing the sensor, manufacturers can make the sensor impervious to physical damage from the side and weld damage from the front when combined with weld resistant front caps or coatings. Also, users can employ stainless steel sleeves to cover the sensor and help protect it from mechanical damage in welding areas.Benefits of factor 1 sensing in welding applications To further minimize sensor replacement costs, factor 1 sensors provide universal usability—they are easily applied in multiple applications, saving costs over purchasing specialized sensors only applicable in certain production areas—and combine it with exceptional EMI resistance.Factor 1 sensors can detect aluminum, stainless steel, mild steel, copper, lead, brass and other metals at the same rated distance, eliminating the need to reposition the sensor for each new material. Standard proximity sensors detect ferrous and non-ferrous metals at different distances—and this adjustment (known as the correction factor) requires additional labor and downtime for reinstallation. This is of higher consequence in welding applications. If the sensor must be moved closer to the welding mechanism to provide proper detection, it is consequently more susceptible to weld flash and at higher risk of physical damage. By using separate, independent sender and receiver coils on a PCB, rather than a single coil like standard proximity sensors, factor 1 sensors can detect ferrous and non-ferrous metals at the same range without adjustment and provide a longer overall sensing range. As they can be used with a broad range of metals in a wider variety of applications, factor 1 sensors additionally reduce sensor inventories.The majority of factor 1 sensors are designed without a ferrite core, making them inherently immune to magnetic field interference. These sensors are therefore especially suited for electric welding operations, lifts and electronic furnaces, and the design allows factor 1 sensors to operate at a higher switching frequency.The coil technology used in factor 1 sensors contributes to their mounting flexibility by allowing or limited or fully recessed mounting—with no or only a slight decrease in sensing range—further reducing the risk of physical damage. Many standard proximity sensors are non-embeddable and thus more susceptible to mechanical damage from the application environment. Because factor 1 sensors can be incorporated into multiple housing styles, they are also easier to use in areas where space is at a premium, such as under a conveyor belt.Design features ranging from weld resistance to factor 1 technology allows many sensors to provide reliable, long-lasting operation in even the most challenging welding applications. By reducing downtime and replacement costs while error-proofing operations, these sensor solutions optimize production right on the plant floor—despite harsh conditions. Learn More

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