Yes, 12 mm (0.472 inches) Cadmium Copper rod can be butt welded. However safety must be considered with this material. OSHA regulations and cadmium's listing as a carcinogen have restricted the manufacture of this material in many parts of the world including North America.
In previous decades it was manufactured as rod and wire and was butt welded successfully. It was butt welded to make longer lengths in the various mills for drawing into wire coils. Any use of this material that could generate cadmium fumes in the work environment might need to be engineered properly to protect the personnel and the environment.
Butt welders are being used in industry to join copper alloy rods of this size in industry every day. Any butt welder manufacturer can develop a machine and process that would be suitable to butt weld this material provided that your OSHA/Safety laws permit its manufacture.
Flash and butt welding both use the work piece as the electrode. They both use a clamp to hold the parts and apply force. This clamp carries current so it must conduct current and dissipate heat. This makes copper alloys a first choice. In many cases the Group A copper alloys will be used for this application. If mechanical wear is an issue Class 3 might replace Class 2.
Flash and butt welds are tested much like other resistance welds. Quality criteria is established at the start of a production run. This criteria is used for subsequent evaluation during the manufacturing process. Tensile or destructive testing is the normal method of testing random samples during a production run.
Flash and butt welding both use the work piece as the electrode. They both use a clamp to hold the parts and apply force. The entire cross section of the work piece is welded. It is in the timing and application of force and current that they differ.
In butt welding the parts are clamped brought together under force and then current is applied. The parts heat due some arcing and to Joule H= I2rt heating. The joint gets hot upsets and after cooling the force is removed. The result is a strong butt joint.
Butt welding is more sensitive because the surface of the part coming together decides the current flow pattern and where the heating will occur.
Yes, two sheets of metal can be butted together and butt welded. Butt welding is a joining process used to join two parts together. The work acts as the electrode and the entire cross section is welded. The parts are clamped and brought together with force and a current is applied. The intention is to create heat using Joules Law H= I2rt at the joint surface with current flow. As the joint heats up the force upsets the joint and a bulged area is formed. The current is stopped. The weld area cools under force and then the force is removed and the butt weld is complete. The limit to part size is the power and ability to clamp the part.
So two sheets of metal can be butted together or one sheet as shown on the example below can be formed into a ring and brought together to form the joint. The limits are power and the ability to hold the product and deliver the force evenly. If the machine is large enough with sufficient power you are making product. The example below illustrates a good example of a long butt joint being formed in one operation of the machine.