Part Design

Once the product evaluation is complete (see previous tab), you can start thinking of designing the part geometry for welding/brazing/soldering; part design has to be done in conjunction with material selection and process selection. To start with, you will have to choose a type of welded connection, either lap, butt, or fillet joint.  A lap weld can be self-aligning, as with a tube to tube connection with smaller tube slipping into the bigger one.  The gap tolerance will be determined by the process selected; for most welding processes a tight fit is preferred, whereas for soldering/brazing applications, a defined gap is required for the filer alloy to be accommodated.  One of the downsides of lap welding is the need for higher power required to make a weld across the interface since the weld energy has to penetrate the entire thickness of the outer component before going across to the inner component.  Greater energy can produce more distortion and often more defects.  The other option is to go with a butt weld configuration which requires the least amount of energy to make a weld of similar weld area across the interface. Challenges with butt welding include precise edge preparation and alignment between weld energy and weld interface.  A fillet weld provides a compromise between lap and butt weld.

The above reasoning works well for laser, electron beam, and autogenous TIG processes.  For MIG and other arc welding processes that add filler wire, the logic has to be slightly modified and part geometry is often restricted to butt and fillet welds.  Resistance welding adds another complication where both sides of the weld have to be accessible to the welding electrodes.  In some situations where thin foils are to be welded, it is possible to bring both electrodes from the same side, as in welding nickel tabs to make battery packs.  Similar constraints are present in ultrasonic metal welding.

Soldering and brazing require a completely different way of thinking in terms of providing heat, adding filler and flux, controlling melt flow, and then providing a means of cleaning flux residue and visual identification of a good fillet.  Of the all the joining processes, soldering/brazing tend to be the most complex to setup but are the easiest for inspection since a good fillet is often an indication of a properly controlled process.

There are many variations and exceptions to each of the statements above.  If you have any specific questions, please do not hesitate to contact us.