Tube Fabrication

Tube cutting, tube bending, tube flaring and tube swaging are highly specialized processes which require specific equipment, such as hydraulic tube benders, CNC mandrel bending and swaging machines, as well as skilled engineers, operators and a range of other facility capabilities to ensure that the integrity of the tube structure is maintained and minimal material wastage occurs. Tubing is formed from many types of common metals such as aluminum, brass, bronze, copper or other alloys, and can range greatly in diameter and length. Material choice will depend on intended use and location of the tubing as it can vary greatly in terms of durability, density and hardness. Many consumer products, as well as automotive, aerospace and industrial parts are fabricated by precision tube fabrication, including commonly used items such as steel handrails, bicycle frames and other exercise equipment, tent frames, point of purchase displays (POP), plant hangers and outdoor patio furniture. Industrial and manufacturing industries use fabricated tubing and mandrel bent tubing extensively in hydraulic pipe applications such as automotive fuel lines, exhaust pipes, hydraulic cylinders, shell and tube heat exchangers. Selecting the appropriate tube fabrication service requires an analysis of both the physical properties of the tubing and the production capabilities of the manufacturer.

The processes of tube forming require specialized equipment and skill in order to form metal tubes in a number of ways. Tube cutting may involve notching, punching or drilling; for precision applications, these processes are often done by CNC machining to ensure accuracy and a secure fit between the tube ends. Most tube cutting is done by the blade making a full rotation around the circumference of the tube, either interior or exterior. As tube cutting can result in surface imperfections, sanding or polishing may be required for secondary finishing. Tube flaring and swaging are both typically cold forming processes which expand the diameter of a certain length of tube or pipe using high pressure. A tube end forming process, flaring is applied only to the end of a tube, usually to make the end of the tube capable of connecting tightly with another tube for hydraulic applications. Swaging is a more involved process which expands the diameter of an indefinite length of tube, creating sections of thin wall tubing without compromising the integrity of the material. Precision swaging can be critical for certain applications, particularly in telescoping tube applications when one tube must slide within another tube. The swage, or the diameter by which a tube is expanded, must be precise in order for one tube to slide snugly inside another tube or tube end. Telescoping tubes are common in consumer and business applications such as stands, tripods and adjustable furniture, and automotive manufacturers and specialty body shops use swaging to control vehicle exhaust fumes.

Pipe bending can be performed manually using a hand-held mandrel, but most tube fabrication facilities have semi-automated and automated equipment which is faster and more precise. A length of tubing is clamped down and forced to take on the shape of a die, or fed through rollers to create a simple curve. CNC tube bending machines, which are often powered hydraulically for extreme torque power, are capable of forming complex tubing shapes such as coils and zigzags with extreme precision and short processing times, although all these processes may still be performed manually on traditional tube benders with longer process times. Tube bending performed without a mandrel forms wrinkles in the inside of the tube's curve which can affect the flow capacity of a pipe, and by distorting the interior structure of the pipe create potential weak spots. Another tube fabricating process, tube rolling is the process of producing tubular parts through heat curing materials that have been wrapped around a circular mold and then removing the mold to reveal the tube.

Although wrinkled tube bends are acceptable for some low-performance and non-aesthetic applications, high performance mufflers, hydraulic piping and decorative handrails require smooth, unobstructed tube bends. Pipe elbows, commonly used in flow and hydraulic applications such as plumbing, require both mandrel bending and flaring or swaging. For these types of applications, mandrels are placed inside the tube in the area being bent, or the tubes are packed with sand before the bending process. Mandrels are typically a rounded-tip steel rod, linked ball bearings or unlinked steel balls; the straight mandrel, called a plug mandrel, is used on normal bends, while ball mandrels with linked or unlinked ball bearings are used to form critical precision bends. Mandrels and sand are essential parts of the tube fabrication process as they preserve the interior shape of the pipes around the curve.

Tube Fabrication and Tubing Image Provided by Stam, Inc.	Tube Fabrication and Tubing Image Provided by Woolf Aircraft Products, Inc.

Tube Fabrication Types

• CNC tube bending bends tubes and pipes using computer-controlled machines that ensure the quality and efficiency of a product. Today's modern CNC technology has made it possible to produce high volume, close tolerance, tubular metal parts quickly and economically.
  
• Hydro-forming is a metal fabrication method of forming tubular metal parts within a die cavity. This high-pressure method forces fluids inside the die so that the part expands into its final shape.
• Mandrel bending, also known as mandrel tooling, is a sub-process of tube bending.
• Pipe bending is a process that uses computerized machines to bend pipes.
• Pipe fabrication are processes that involve the shaping, cutting, bending or size alteration of pipes formed from various materials for wide-ranging applications.
• Roll forming metal is the tube fabrication process that is most common, although it is not used for thicker metal tubing. It involves rolling a strip of sheet metal and curing it.
  
• Rotary draw bending employs mandrels and various dies to manage and control metal flow during the bending process. In this process, a precision mandrel is positioned inside the tube, while a pressure die, wiper die, bend die and clamp dies surround the outside of the tube.
• Thin wall tubing is tubing with very little wall thickness, typically ranging from .001 in. (.0254 mm) to about .065 in. (1.65 mm).
• Tube bending uses computerized machines to bend tubes.
• Tube cutting is a process that uses computerized machines to cut pipes and tubes.
• Tube end forming refers to various processes that are used to shape, cut, bend or enlarge the inside or outside ends of tubing.
• Tube fabricating employs a variety of techniques to shape, bend, enlarge and cut tubes of all sizes and metals into parts and products.
• Tube flaring is a process used to form an extremely tight seal at the end of a tube.
• Tube forming can refer to several processes that are used to form raw metal materials into tubes. 
• Tube rolling is the process of producing tubular parts through heat curing materials that have been wrapped around a circular mold, then removing the mold.
• Tube swaging uses high pressure to shape tubes.

Tube Fabrication Terms

Alloy Steel - Steel that is alloyed with moderate amounts of chromium and other elements, such as molybdenum. Alloy steel is distinguished from stainless steel by good hardening characteristics and from tool steel by possessing better "toughness" after hardening.

Annealing - The heating and cooling of steel to remove stresses, alter physical, mechanical and metallurgical properties, increase corrosion resistance and thermally treat steel prior to age hardening.

Arc - The curved section of bent tubing.

As-Welded - Tubing that is not given heat treatment after the initial welding.

Austenitic - A family of chromium nickel stainless steels that have good corrosion resistance and good formability, but can only be hardened by cold working.

Bend Die - Less commonly known as the "bend form" or the "radius die," it is the primary tool on a rotary-draw tube-bending machine. The bend die is the form against which the tube is clamped and then drawn around to produce a bend.

Bright Annealing - The process of annealing in a controlled atmosphere so that dark, adherent oxides do not form on the metal.

Burst Pressure - The amount of pressure that will make tubing fail or burst by exceeding the tensile strength of the material from which the tubing is made.

Camber - A measure of warp in tubing material or the deviation from straightness.

Cold Drawing - The normal method of rotary-draw tube-bending, which is done without heating the tubing material.

Ductility - A measure of a tube's ability to deform without fracturing.

Elongation - The amount of permanent extension of the material before it fractures.

Full-Finished - A term that refers to the state of the tube after the weld has been processed to produce uniform strength and dimensions and the tube has been annealed for corrosion resistance.

Manipulation Tests - Tests used to evaluate the quality of finished products, such as crush, flare, bend, flange, flatten, reverse flatten, reverse bend and expanding.

Ovality - The deformation of round tubing into an elliptical shape or a symmetrical flattening of a round tube. Ovality is the measure of the difference between the maximum and minimum outside diameters of a round tube.

Passivation - A protective layer made of oxides, which is on the outside of tubing, that resists corrosion.

Pickling - The chemical removal of oxides on the surface of metals.

Pressure Tubing - Tubing specified for the containment of liquids and gasses, as opposed to structural or mechanical purposes.

Tangent - The unbent section of a bent tube.