Stainless steel pipe fittings are produced using a combination of forming, forging, and machining techniques, depending on the fitting type, size, wall thickness, and required tolerances. The most common manufacturing processes are as follows:
1. Investment Casting (Lost-Wax Casting) Many complex-shaped fittings - such as tees, elbows, and valve bodies - are made by investment casting. A wax pattern is coated with ceramic slurry, the wax is melted out, and molten stainless steel is poured into the mold cavity. This process produces near-net-shape parts with good dimensional accuracy, which are then finished by machining and polishing.
2. Forging Forging uses compressive force (often with a forging hammer or press) to shape stainless steel billets into fitting preforms. It refines the grain structure of the metal, resulting in higher strength and better mechanical properties than cast fittings. It is commonly used for high-pressure and high-temperature fittings.
3. Hot Forming / Push Bending Elbows and bends are often made by pushing a heated pipe through a die (push bending) or by induction bending. The pipe is heated locally and conformed to the desired radius, producing smooth, uniform bends suitable for large-diameter and thick-walled applications.
4. Hydroforming (Bulging) Tees and certain complex shapes are produced by hydroforming. High-pressure fluid is applied inside a sealed pipe blank, expanding it into a die cavity. A simpler variant uses a rubber plug compressed by a punch to achieve the same bulging effect. This method is widely used for equal and reducing tees.
5. Roll Forming / Rolling Roll forming uses a set of rollers to progressively bend or round a pipe section. It is typically used for thin-walled tubes and for forming concentric shapes without an internal mandrel.
6. CNC Machining and Finishing After the forming step, almost every fitting goes through CNC machining to achieve precise end dimensions, thread forms, and flange faces, followed by grinding, polishing, or pickling to reach the required surface finish and dimensional tolerance.
