Beryllium copper has lower resistivity, higher thermal conductivity and coefficient of expansion than steel. Overall, beryllium copper has the same or higher strength than steel. When using resistance spot welding (RSW) beryllium copper itself or beryllium copper and other alloys, use higher welding current, (15%), lower voltage (75%) and shorter welding time (50%) . Beryllium copper withstands higher welding pressures than other copper alloys, but problems can also be caused by pressures that are too low.
To obtain consistent results in copper alloys, welding equipment must be able to precisely control time and current, and AC welding equipment is preferred due to its lower electrode temperature and low cost. Welding times of 4-8 cycles produced better results. When welding metals with similar expansion coefficients, tilt welding and overcurrent welding can control the expansion of the metal to limit the hidden danger of welding cracks. Beryllium copper and other copper alloys are welded without tilting and overcurrent welding. If inclined welding and overcurrent welding are used, the number of times depends on the thickness of the workpiece.
In resistance spot welding beryllium copper and steel, or other high resistance alloys, better thermal balance can be obtained by using electrodes with smaller contact surfaces on the beryllium copper side. The electrode material in contact with beryllium copper should have a higher conductivity than the workpiece, a RWMA2 group grade electrode is suitable. Refractory metal electrodes (tungsten and molybdenum) have very high melting points. There is no tendency to stick to beryllium copper. 13 and 14 pole electrodes are also available. The advantage of refractory metals is their long service life. However, due to the hardness of such alloys, surface damage may be possible. Water-cooled electrodes will help control tip temperature and prolong electrode life. However, when welding very thin sections of beryllium copper, the use of water-cooled electrodes can result in quenching of the metal.
If the thickness difference between beryllium copper and the high resistivity alloy is greater than 5, projection welding should be used due to the difficulty of practicable thermal balance.
Resistance projection welding
Many of the problems of beryllium copper in resistance spot welding can be solved with resistance projection welding (RPW). Due to its small heat affected zone, multiple operations can be performed. Different metals of different thicknesses are easy to weld. Wider cross-section electrodes and various electrode shapes are used in resistance projection welding to reduce deformation and sticking. Electrode conductivity is less of a problem than in resistance spot welding. Commonly used are 2, 3, and 4 pole electrodes; the harder the electrode, the longer the life.
Softer copper alloys do not undergo resistance projection welding, beryllium copper is strong enough to prevent premature bump cracking and provide a very complete weld. Beryllium copper can also be projection welded at thicknesses below 0.25mm. As with resistance spot welding, AC equipment is usually used.
When soldering dissimilar metals, the bumps are located in higher conductive alloys. Beryllium copper is malleable enough to punch or extrude almost any convex shape. Including very sharp shapes. The beryllium copper workpiece should be formed before heat treatment to avoid cracking.
Like resistance spot welding, beryllium copper resistance projection welding processes routinely require higher amperage. Power must be applied instantaneously and high enough to cause the protrusion to melt before it cracks. Welding pressure and time are adjusted to control bump breakage. Welding pressure and time also depend on bump geometry. The burst pressure will reduce weld defects before and after welding.