The invention relates to a manufacturing method of a casing, the casing is a liquid accumulator casing for a compressor, a muffler casing for an air conditioner, a gas-liquid separator casing or an oil-gas separator casing for a central air conditioner, the casing is The shell is formed by socket welding of at least two parts, which is characterized in that: the at least two parts are welded by argon arc welding, plasma welding, quasi-ion welding, laser welding or high-frequency welding, and the heat distribution relationship is the sleeve The outer layer of the interface distributes higher heat, and the inner layer of the socket distributes lower heat, so that the outer and inner metals at the socket are welded by self-fluxing. When the invention is welded, the heat of each part is stable and controllable, and both the inner layer and the outer layer can reach the melting temperature, so as to realize good fusion, improve the welding quality, the welding joint is smooth and bright, and the welding strength is high, and the welding seam strength is 10 times higher than that of butt welding times, the production efficiency is high, and it will not cause pinching on the surface of the pipe section, and the equipment cost is only 1 / 3‑1 / 5 of flash welding.