Resistance welding is a reliable, low-cost, and effective method of permanently joining two or more pieces of metal together. While resistance welding is a real welding process, no filler metal, no welding gas. There is no excess metal to remove after welding. This method is suitable for mass production. The welds are solid and barely noticeable.

Historically, resistance welding has been effectively used to join high resistance metals such as iron and nickel alloys. The higher electrical and thermal conductivity of copper alloys makes welding more complex, but conventional welding equipment often has the ability to make these The alloy has a good quality full weld. With proper resistance welding techniques, beryllium copper can be welded to itself, to other copper alloys, and to steel. Copper alloys less than 1.00mm thick are generally easier to weld.

Resistance welding processes commonly used for welding beryllium copper components, spot welding and projection welding. The thickness of the workpiece, the alloy material, the equipment used and the surface condition required determine the appropriateness for the respective process. Other commonly used resistance welding techniques, such as flame welding, butt welding, seam welding, etc., are not commonly used for copper alloys and will not be discussed. Copper alloys are easy to braze.

The keys in resistance welding are current, pressure and time. The design of electrodes and the selection of electrode materials are very important to the assurance of welding quality. Since there is a lot of literature on resistance welding of steel, the several requirements for welding beryllium copper presented here refer to the same thickness. Resistance welding is hardly an accurate science, and welding equipment and procedures have a great impact on welding quality. Therefore, presented here as a guide only, a series of welding tests can be used to determine the optimum welding conditions for each application.

Because most workpiece surface contaminants have high electrical resistance, the surface should be cleaned routinely. Contaminated surfaces can increase the operating temperature of the electrode, reduce the life of the electrode tip, render the surface unusable, and cause the metal to deviate from the weld area. cause false welding or residue. A very thin oil film or preservative is attached to the surface, which generally has no problems with resistance welding, and beryllium copper electroplated on the surface has the least problems in welding.

Beryllium copper with excess non-greasy or flushing or stamping lubricants can be solvent cleaned. If the surface is severely rusted or the surface is oxidized by light heat treatment, it needs to be washed to remove the oxide. Unlike the highly visible reddish-brown copper oxide, the transparent beryllium oxide on the strip surface (produced by heat treatment in an inert or reducing gas) is difficult to detect, but must also be removed before welding.

Beryllium Copper Alloy

There are two types of beryllium copper alloys. High strength beryllium copper alloys (Alloys 165, 15, 190, 290) have higher strength than any copper alloy and are widely used in electrical connectors, switches and springs. The electrical and thermal conductivity of this high-strength alloy is about 20% of that of pure copper; high-conductivity beryllium copper alloys (alloys 3.10 and 174) have lower strength, and their electrical conductivity is about 50% of that of pure copper, used for power connectors and relays. High strength beryllium copper alloys are easier to resistance weld due to their lower electrical conductivity (or higher resistivity).

Beryllium copper obtains its high strength after heat treatment, and both beryllium copper alloys can be supplied in pre-heated or heat-treated state. Welding operations should generally be supplied in a heat-treated condition. The welding operation should generally be carried out after heat treatment. In resistance welding of beryllium copper, the heat affected zone is usually very small, and it is not required to have a beryllium copper workpiece for heat treatment after welding. Alloy M25 is a free-cutting beryllium copper rod product. Since this alloy contains lead, it is not suitable for resistance welding.

Resistance spot welding

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 too low pressures.

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 of beryllium copper and steel, or other high resistance alloys, better thermal balance can be obtained by using electrodes with smaller contact surfaces on one side of beryllium copper. The electrode material in contact with beryllium copper should have higher conductivity than the workpiece, a RWMA2 group 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 the beryllium copper and the high resistivity alloy is greater than 5, projection welding should be used due to the lack of practical 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. The power must be momentarily energized 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.

Safe Handling of Beryllium Copper

Like many industrial materials, beryllium copper is only a health hazard when handled improperly. Beryllium copper is completely safe in its usual solid form, in finished parts, and in most manufacturing operations. However, in a small percentage of individuals, inhalation of fine particles may lead to poorer lung conditions. Using simple engineering controls, such as venting operations that generate fine dust, can minimize the hazard.

Because the welding melt is very small and not open, there is no special danger when the beryllium copper resistance welding process is controlled. If a mechanical cleaning process is required after soldering, it must be done by exposing the work to a fine particle environment.