Fabrication Guidelines for Galvanized Steel Tubing
- There are many ways to cut. The methods described in this manual are generally accepted as the primary methods used to cut steel tubing.
- Die cutting is the fastest way to cut tubing. The term "die-cut" refers to a die block, with appropriate inserts, to cut a particular size (OD) tubing. Additional equipment from a manual press to a mechanical/hydraulic press to a dedicated system is necessary to complete the process. The die block is designed for a specific OD range and gauge combination. The inserts in the die block can be used with one tube diameter. If several different tube sizes are being cut, a separate set of inserts will be needed for each tube OD. Die blocks are interchangeable in ten minutes to accommodate various tube sizes, wall thickness, and shapes. The die-cut process lends itself to a clean, burr-free end condition. If a two-blade cutoff is used (one blade scarfs the top of the tube and the second vertical blade comes down and cuts the tube) a burr-free, dimple-free end cut will result.
- Saw cutting is the slowest method of cutting tubing. The advantages of this method proportionately increase with the size of tube being cut (OD), the wall thickness (gauge), and the carbon content of the steel. There are two common methods of saw cutting, cold saw and band saw.
- Cold saw cutting equipment can be the most economical dedicated cutting system available. A cold saw is a self-contained system requiring a minimum of set-up and operator expertise, utilizing a spinning blade to cut a clamped tube. The quality of a cold saw cut is dimple-free and usually burr-free. The length of the cut can be controlled to ˝ .010".
- Band saw cutting utilizes a continuous ribbon blade in either a horizontal or vertical plane to cut a clamped tube or tubes. This method of cutting provides the ability to cut multiple pieces of tubing of the same or different diameters to the same length at the same time. For example, a bundle of tubing can be cut to a pre-determined length without breaking the bundle and cutting each piece individually. This is a self-contained dedicated cutting system requiring minimum operator skill. Length tolerances are dependent on the number of tubes being cut simultaneously. Generally, band saws can meet a length tolerance of ˝ 1/16".
- Lathe cutting is slower than die cutting but faster than saw cutting. The lathe method utilizes a stationary blade (tool bit) while spinning the tube to perform the cutting process. Only round tubing can be cut on a lathe. As a self-contained, dedicated system, the initial investment for lathe cutting equipment is high. A fairly skilled operator is required for optimum set-up and maintenance. The lathe cut is very clean and square. Cut ends can be chamfered on both the OD and the ID of the tube, and tolerances of ˝ .010" can easily be held.
- Piercing a tube is the fastest conventional method to perforate (put a hole in) a tube. There are four different types of perforations: Single Dimple, Double Dimple, Clean hole one end and Clean hole two walls. Different shapes and sizes of perforations can be punched into a tube depending on the design of the perforator. Some examples are elongated holes, square, diamond, rectangular, and star-shaped. Punching units can be used in an arbor press, punch press, press brake, air or hydraulic press, or in a self-contained system.
TUBE END FORMING & END FINISHING
- The terms end forming and end finishing can mean many different things, depending of the point of view of the interpreter. It is safe to assume that these terms are often overlapping and easily misinterpreted. In this guide, we will consider swaging, expanding, flaring, doming (closing), and beading (external or internal) as end forming operations. All other operations will be considered end finishing.
- Swaging is reducing the OD dimension at the end of a tube. The length of the swage and the final OD depends on the method used and the characteristics of the material being swaged. Swages can be round to round, round to square, round to oval, oval to round, etc. Swaging equipment is dedicated but existing presses can be utilized for short lengths. Expanding is increasing the OD dimension at the end of a tube. Like swaging, many options are available. The length, shape, and final OD depend upon the method, capacity, tooling, and tube characteristics.
- Flaring is an operation that forms the tube end at a specific angle, OD, and depth to meet application demand. This method can be achieved by band (thin wall tubing), punch press (short lengths), and primarily a dedicated end finishing machine. Beading means to expand the tube, internally or externally, a specific radius or diameter. A punch press and die assembly is required for each OD. Short lengths can be formed on a punch press, but long lengths require a dedicated end-forming machine. Doming is simply closing the end of a tube. The tube end is rolled or pressed to the application requirements. This operation is typically performed with a dedicated end-forming machine, but short lengths can be formed on a press.
- Compression bending. In compression bending, the work piece is clamped to a bend die (or radius block). A wipe shoe (or slide block) is then brought into contact with the work piece. As the wipe shoe rotates around the static bend die, it forces the work piece to assume the radius of the bend die. This type of bending represents certain advantages for bending of open extrusions and shapes Press bending. A ram die with the desired radius of bend is fitted to the press arm. The arm forces the tubing down against the opposing two wing dies. The wing dies, with resisting pressure, pivot up, forcing the tube to bend around the ram. Press bending is very fast and may bend more miles of tubing than any other method. Since the tubing cannot be internally supported, considerable distortion can occur. Rotary draw bending. Rotary draw bending may be the most versatile, precision system of bending. It certainly produces high quality bends on the tightest radius within thin wall tubes. With a heavy walled tube on a generous radius, only a three-piece family of tools is required. The work piece is locked to the bend die by the clamp die. As the bend die rotates the follower type pressure die advances with the tube. As the wall of the tube becomes thinner and/or the radius of bend is reduced, a mandrel and a wiper are required.
Contact one of our Sonco Tube professionals at 888-766-2613 for your galvanized steel tubing needs.