Guest contributor: Dave Bird, Balluff
Roughly four sensing-related processes occur in a welding cell with regards to parts that are to be joined by MIG, TIG and resistance welding by specialized robotic /automated equipment:
- Nesting…usually, inductive proximity sensors with special Weld Field Resistance properties and hopefully, heavy duty mechanical properties (coatings to resist weld debris accumulation, hardened faces to resist parts loading impact and well-guarded cabling) are used to validate the presence of properly seated or “nested” metal components to ensure perfectly assembled products for end customers.
- Poke-Yoke Sensing (Feature Validation)…tabs, holes, flanges and other essential details are generally confirmed by photoelectric, inductive proximity or electromechanical sensing devices.
- Pneumatic and Hydraulic cylinder clamping indication is vital for proper positioning before the welding occurs. Improper clamping before welding can lead to finished goods that are out of tolerance and ultimately leads to scrap, a costly item in an already profit-tight, volume dependent business.
- Connectivity…all peripheral sensing devices mentioned above are ultimately wired back to the controls architecture of the welding apparatus, by means of junction boxes, passive MIB’s (multiport interface boxes) or bus networked systems. It is important to mention that all of these components and more (valve banks, manifolds, etc.) and must be protected to ensure optimum performance against the extremely hostile rigors of the weld process.
Magnetoresistive (MR), and Giant Magnetoresistive (GMR) sensing technologies provide some very positive attributes in welding cell environments in that they provide exceptionally accurate switching points, have form factors that adapt to all popular “C” slot, “T” slot, band mount, tie rod, trapezoid and cylindrical pneumatic cylinder body shapes regardless of manufacturer. One model family combines two separate sensing elements tied to a common connector, eliminating one wire back to the host control. One or two separate cylinders can be controlled from one set if only one sensor is required for position sensing.
Unlike reed switches that are very inexpensive (up front purchase price; these generally come from cylinder manufacturers attached to their products) but are prone to premature failure. Hall Effect switches are solid state, yet generally have their own set of weaknesses such as a tendency to drift over time and are generally not short circuit protected or reverse polarity protected, something to consider when a performance-oriented cylinder sensing device is desired. VERY GOOD MR and GMR cylinder position sensors are guaranteed for lifetime performance, something of significance as well when unparalleled performance is expected in high production welding operations.
But!!!!! Yes, there is indeed a caveat in that aluminum bodied cylinders (they must be aluminum in order for its piston-attached magnet must permit magnetic gauss to pass through the non-ferrous cylinder body in order to be detected by the sensor to recognize position) are prone to weld hostility as well. And connection wires on ALL of these devices are prone to welding hostilities such as weld spatter (especially MIG or Resistance welding), heat, over flex, cable cuts made by sharp metal components and impact from direct parts impact. Some inexpensive, effective, off-the-shelf protective silicone cable cover tubing, self-fusing Weld Repel Wrap and silicone sheet material cut to fit particular protective needs go far in protecting all of these components and guarantees positive sensor performance, machine up-time and significantly reduces nuisance maintenance issues.
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