The design of a tubular steel part is much more important than the actual bending of the metal. The bending machine and its operator merely follow the instructions determined by the engineer who designs the part. The engineer is responsible for making the design efficient & affordable to manufacture, as well as ensuring that the part will meet tolerances after bending.
Engineering a part for manufacturing is tougher than it looks. The designer has to understand the effect of tube bending and fabrication on the physical and chemical makeup of the part. A poorly designed part will be weak and defective right off the line.
Further, designing requires knowledge of how to keep a component simple. Even if they fit manufacturing requirements, complex parts create unnecessary limitations and costs for both the client and the manufacturer.
Want to produce a viable, affordable part right from the get-go? Here are some tube bending tips from expert manufacturing engineers.
Here are our top six tube bending design guidelines for designing with tubular steel:
Your material must have enough ductility to bend without fracturing. It must also be strong enough for its intended use after bending. If you're not familiar with which materials are best for which applications, here are a few helpful articles:
You can also have your manufacturer assist you in materials selection.
For an overview of standard tube sizes and shapes, check out this quick reference guide.
With the exception of those projects that absolutely require non-standard shapes, there are many advantages to choosing a standard shape over non-standard.
The more bends you add to your tubular steel product, the more your costs and production times creep upward. More bends require more equipment and tooling, especially if there are multiple bend angles or radii, or you have a non-standard bent tube shape.
Unnecessary bends should be eliminated from a design to increase efficiency. If you're not sure how to optimize your design, a good manufacturing engineer should be able to help.
The bend radii in your design, whether they're small, large, or a mix of both, should be simple and follow these basic design principles.
In general, a standard draw bend radius is 2x the diameter of the tube. A tube with a diameter of 1" performs best with a 2" bend radius, though you can go down to .5 x D with mandrels. Larger bend radii are only limited by the tooling and machinery you use.
Extremely small radii bends are best done on a rotary draw bender with mandrels. They're difficult to make aesthetically pleasing without mandrel support.
Extremely large radii are best created on a push or roll bender. These large radius benders require a bend radius of at least 7 x D for best results.
Multiple radii bends require either multiple machines/tooling, a multistack machine, or a CNC machine with combined capabilities. It's best if you can design your bends to be the same radius so your manufacturer only has to use one machine for your bends. If you absolutely require multiple bend radii, speak to your manufacturer about best practices for your specific radius combination.
Bends that are designed too close together cause problems for both the machinery and the final product. Most bending machines require a certain length of straight tubing between bends for gripping. This allows the machine to use lower pressures to bend, and decreases the likelihood of the part slipping during bending.
A good rule to follow is: for less severe bends, allow at least 3 x OD distance between bends. For more severe bends, allow at least 4 x OD.
If you absolutely require bend locations that are close together, be aware you may sacrifice part quality and aesthetics. You may also find more part defects, which can majorly increase your manufacturing costs.
As you may know, tooling can be one of the most expensive parts of manufacturing. However, there are a few ways you can design your tubular product to decrease tooling costs.
Following these three practices can cut down on (or eliminate) the need for mandrels, special dies, lubricants, and additional costly tooling features.
All engineers have their specialties, but not all know the tricks of the trade for designing parts for manufacturing. That's OK -- that's why we have engineers who specialize in tube bending services.
If you want to optimize your part, or simply cut manufacturing costs, talk to your manufacturer about your design. Oftentimes, manufacturers are happy to offer this service -- all you have to do is ask!
(This article was originally published in May 2016 and was recently updated.)