Micro Resistance Welding

Welding today comes in many forms. One sector of the welding industry that is growing today as electronics and other devices shrink in size is the process of micro resistance welding. This is a thermal process where two parts to be joined are heated to the melting point and melted together, thus forming one body when the weld point cools. This process is similar to other types of thermal welding, but with several differences. The first of these differences is of course the size of the parts and components involved. Micro resistance welders are small units consisting of the welder itself which is a box with the electronics and controls for controlling the process, and the weld head which holds the micro electrodes and brings them into contact with the parts to be welded. The micro electrodes themselves are very small, often having tips, or contact points, as small as .010 of an inch square. The welders have very precision electrical current control and the heads have very precise force control to avoid breaking the fragile electrodes.

The three opposing electrode types of micro resistance welding include a straight-through, seam and projection welds. In a straight-through the electrodes are opposite each other on either side of the materials to be welded, and electrical current passes through the materials heating them at the intersection point, forming a weld. A seam weld is actually the same as the straight-through weld except that either the electrodes or the work-pieces are moved along to form a continuous series of overlapping spots. A projection weld derives its name from the fact that projections extend from one of the two surfaces. This technique is used for a number of reasons, such as decreasing the amount of energy required to make a weld, improving the heat balance when a thin piece is welded to a large piece, and to allow several welds to be made with one welding pulse.

The next two forms of micro resistance welding fall under the general heading of parallel gap welding. With this type of weld both electrodes approach the work-piece from the same direction. These techniques are especially useful where the opposite side of one of the pieces being welded has an insulated layer. The electrode arrangement in a series configuration allows weld current to flow down one electrode, through both materials and up the other electrode. With the step weld, one electrode touches each material and the current all flows across the material interface.

The first step to perform a micro resistance weld is to place the two parts on top of each other above a copper electrode. Then the weld head brings a top electrode down onto the point of weld, compression the two pieces together. With the two pieces squeezed together, electrical current is passed through the electrodes and the part at the point of intersection. The material heats rapidly, melting both pieces where they contact between the two electrodes. When the current is turned off, the molten zone cools and solidifies, forming a weld between the two pieces.

Micro resistance welding has many applications spanning nearly all areas of manufacturing, including automotive systems, aerospace, medical devices, and electronics. Micro resistance is used extensively in the electronics industry for welding small wires to other parts such as PCB pads. This type of welding is used in producing sensors, lights, battery packs, solar cells and smoke detectors, to name a few. In the automotive field micro resistance welding is used for lighting assemblies, airbag systems, electronic sensors, and ignition controls.

In conclusion, micro resistance is a popular option for joining small parts. It is low cost, clean, safe, and fast. These advantages make micro resistance welding a growing industry today.