Tube Bending is a metalworking process used to permanently form stock tubing in to the shape of a die. Straight tube stock can be formed using a bending machine to create a variety of single or multiple bends and to shape the piece into the desired form. This process can be used to form complex shapes out of different types of ductile metal tubing..
Process
The process of Tube Bending involves using mechanical force to push stock material pipe or tubing against a die, forcing the pipe or tube to conform to the shape of the die. Often, stock tubing is held firmly in place while the end is rotated and rolled around the die. Other forms of processing including pushing stock through rollers that bend it into a simple curve. For some tube bending processing, a mandrel is placed inside the tube to prevent collapsing. The tube is also held in tension by a wiper die to prevent any creasing during stress. A wiper die is usually made of a softer alloy i.e. aluminum, brass to avoid scratching or damaging the material being bent.
Tubing Geometry
A straight cylindrical tube can be transformed into a vast variety of shapes depending upon the needed application. A tube can be bent in multiple directions and angles. Although a single die can produce various shapes, it cannot shape other tube sizes and make different bend radii. Common simple bends consist of elbow (2-90 degrees), and U-bends. Complex bends include helical and coiled (more than one wrapping revolution), complex two-dimensional, and complex three dimensional bends as well. One side effect on the workpiece as a result of this process is the deformation of the wall thickness. The wall along the inner radius of the tube becomes thicker and the outer wall becomes thinner, depending on the tension in the tubing, the workpiece material, and the radius of the bend.
Tubing Specifications
Tube diameter can vary from 1/4" - 8" or approximately 6.3 mm - 203 mm. The cross section generally consists of a thin-wall with wall thickness varying from 0.031" - 0.375" or approximately 0.79 mm - 9.5 mm.
Mandrel Style
In production of a product where the bend is not critical a plug mandrel can be used. A form type tapers the end of the mandrel to provide more support in the bend of the tube. When precise bending is needed a ball mandrel (or ball mandrel with steel cable) should be used. The conjoined ball-like disks are inserted into the tubing to allow for bending while maintaining the same diameter throughout. Other styles include using sand, cerrobend, or frozen water 2 . These allow for a somewhat constant diameter while providing an inexpensive alternative to the aforementioned styles.
Process Results
There are several factors that effect the process results:
- Workpiece material - Stainless steel, mild steel, copper, brass, aluminum, titanium, etc.
- Bend geometry
- Lubrication - type and quality
- Sturdiness of workholding methods
- Rigidity of actual bending equipment
- Surface finish of holding toolsTool Materials
Much of the tooling is made of hardened steel or tooled steel to maintain and prolong the tools life. However wherever there is a concern of scratching or gouging the work piece, a softer material such as aluminum or bronze is utilized. For example, the clamping block, rotating form block and pressure die are often formed from the hardened steel because the tubing is not moving past these parts of the machine. On the other hand, the pressure die and the wiping die are formed from aluminum or bronze to maintain the shape and surface of the workpiece as it slides by.
Power Requirements
The power required to bend the tubing is directly dependent on the tubing's material,diameter, and wall thickness. For a wall thickness of 0.035 inches and a tubing material of aluminum the typical power requirements range from 4 to 80 foot-pounds. While steel tubing from of the same thickness typically requires power in the range between 12 and 245 foot-pounds.
Calculations
To calculate the speed at which a particular bend can be made in the workpiece, one must utilize the following formula where α is the angle of the bend (in degrees) and R is the rate of the bend (in degrees per second).
Speed = α/RReferences
Notes
- ^ Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes Reference Guide (1st ed.), Industrial Press Inc., ISBN 0-8311-3049-0 .
- ^ Pipe Bending Methods , http://www.ttb.com/process.htm , retrieved 2009-02-01 .
see also http://sciencehack.com/videos/category/8
Bibliography
- Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Process Reference Guide (1st ed.), Industrial Press Inc., ISBN 0-8311-3049-0
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