April 26, 2010
While most fabricators could probably name three methods for notching tube, they actually have six choices. Understanding the advantages and disadvantages of each is the first step in selecting one.
Fabricators use notching for applications as varied as bicycle frames, automobile components, aerospace parts, and household piping systems. Notching takes many forms and shapes. The equipment and process needed depend on the notch shape, the raw material, and manufacturing considerations such as tolerance and production rate.
Tube notching is most often performed before joining tubes together to make a T or similar joint. Either one or both tubes may be notched before being welded together. End notching is the process of forming a cut on the end of a tube to create a shape that will mate to an existing tube. Side notching (offset notching) is the process of cutting an opening into the side of a tube to create a V notch for bending or a V notch for a T joint.
Six processes are used for making notches.
A hole saw (see Figure 1) is simple, inexpensive, and portable, so it is suitable for job site work. In some cases a hole saw requires just a simple jig to obtain the required shape. Disadvantages include inconsistent repeatability, rough finish, limited size range, and the inability to notch shapes other than a circle.
The drum sander and abrasive-belt notcher are inexpensive notching tools. Because these use a sanding process, they generate dust, sparks, and heat. They are labor-intensive processes, limiting their suitability for high-volume production. The abrasive-belt life depends on the finish and part material. The part may need to be cleaned to remove the abrasives before welding.
End milling can be an inexpensive notching process if a CNC mill is already available. This process produces an accurate, tight-tolerance notch and the machine can be programmed to create nearly any shape imaginable. It does not produce dust or sparks. A main drawback is that the process likely will leave some chips in the tube, requiring cleaning before welding. Depending on the shape and size of the notch, cycle time can be a disadvantage.
A notching die combines low cost with good accuracy and repeatability (see Figure 2). In addition, it provides short cycle times for high-volume production runs. However, it does have some drawbacks. A die makes just one hole size and shape, so fabricators need dedicated tooling for each application. This process also tends to distort the tube.
Like the notching die, a hydraulic press is a common choice for high-volume production runs because of its accuracy and short cycle times (see Figure 3). Another advantage is the ability to re-round or size the tube while trimming or notching. Drawbacks include the cost of the machinery and the dedicated tooling required for each application parameter—tube size and notch size and shape.
Laser notching is an emerging technology that is efficient, accurate, clean, quiet, and flexible (see Figure 4). The shapes and sizes obtainable are virtually unlimited. The main drawback to this method is the cost of the machine.
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