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One of the biggest manufacturing headaches of today for multi-curvature components in the tube and pipe sector is finding a suitable process to successfully produce them. During the bending of tube with multiple radii and multiple planes, the component’s inner-radius surface develops wrinkles, which in turn leads to substantial levels of scrap and re-work in any facility manufacturing them. Wrinkles to the inside wall of the tube do not just damage the quality of the component but they may also compromise how it’s used, which fortunately means there is the appropriate tool available; Free Bending Forming (FBF).
Understanding the Mechanics of Wrinkling in Multi-Curvature Bends
Wrinkling of the inner tube wall due to too high compress stress during bending arises from tubes being “pushed” over a stationary bending die in the usual way. Since the material gets “pinched” by the bending dies at the inner surfaces there will occur some wrinkling. That applies especially for tubes being made multi bends in different radii/orientations, leading to very complicated stress states when the tube being pulled through successive deformations. It has been found out experimentally that, when forming of tubes without constraints by forming process like free bending, wrinkles most likely occur in the stable arc part of the bent tube as well at transition lines where the bending angle reaches a definite level, a geometrical imperfection in the material, in extreme cases will increase wrinkling to a significant extent.
The Free Bending Advantage: Continuous Adjustment and Stress Control
Free bending forming has several advantages over conventional bending, particularly: ability to use different angles, radius, and directions - with free bending all of these are possible from a combined controlled multi-axis movement of the bending die, fed with feed movement. With conventional bending the tooling is a significant consideration for radius bends; as there are many types of dies, as the radius changes. However, free bending producing radius bends use single machine and doesn't require retooling. By careful controlling the movement of the bending die, there is equal stress on all of the deform area to achieve this without the formation of compressive stress.
Optimizing Process Parameters to Prevent Wrinkling
Attention to various parameters is required to get a wrinkle free bend with the free bending technique. Experiments showed that wrinkle Amount can be varied with feed speed, gap between die and tube, length of deformation zone, and bending radius. For example, High Feed speed increase wrinkling due to increase strain in deformation zone for a unit length, due to poor material availability. High Clearance between tube and die reduce wrinkling, and our large experience allows Baorui to find suitable parameters to reach optimal bending quality for different types of material and tube specifications. All machines are equipped with CNC controls that make it easy to tune parameters in real time during the bending, cancelling the factors which cause wrinkling.
Practical Solutions for Multi-Curvature Applications
With free bending a ready answer to their wrinkling problems, manufacturers using this technology no longer suffer the consequences of flawed welded joints associated with segmented bending, but they can use the same set of tooling to bend their multi-curvature tubes creating a considerable reduction in setup time. Therefore this technique offers great advantages for a variety of applications in many industries like kitchen and bathroom equipment manufacturers and those supplying the auto industry, where the quality and good looks of bent tubes and pipes are very important. The clever algorithms which control the movement of the bending die will always produce Wrinkle-free tubes that maintain consistent quality and perfection with every single bend, so you are looking for the ultimate quality multi-curve tubes and the last 20 years, we’ve delivered this. Our quality CNC hydraulic pipe bending machine use the proven method of free bending.