Duramax Diesels Forum Truck of the Week
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Old 12-29-2008, 06:03 AM
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Default How Mandrel Benders Work

Mandrel bending is a widely misunderstood bending term. Many customers and even some bending companies refer to the bending dies as mandrels or shoes. Technically the mandrel is a part of the tooling set but does not exist in most bending applications.

The mandrel actually goes inside the tube and is held by a mandrel rod to support the tube at the tangent point of the bend. The mandrel is then extracted after the bend is complete or within the last few degrees of bending. This requires a machine with a bed longer than the tube being bent and strong enough to support the forces against the mandrel.

Common mandrels configurations include the plug, ball, disc or multi-ball or disc design. The type of mandrel required varies depending on the wall thickness of the tube, radius required, and type of material being bent.

Mandrel bending can create a bend much tighter than empty bending as well as improve the appearance of bend. Radii as tight as one times the diameter of the tube (1D) are possible, whereas with empty bending (bends without an internal mandrel) acceptable radii are usually two to three times the diameter (2-3D). This is especially useful for automotive exhaust applications or when a fluid or gas is being flowed through a tube. Most chassis or frame tube bending applications do not require a mandrel and even though the bend may appear stronger the outer wall of the tube is actually stretched thinner by the mandrel bending process. For more questions regarding bending applications please call or email the bending experts at Van Sant Enterprises.
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Old 12-29-2008, 06:05 AM
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Default

For top performance and efficiency, your car's engine needs to “breathe” well. And, a big part of that is an efficient and unrestricted path to allow exhaust gasses to escape.
Typical factory-made and even some “performance” aftermarket systems use “crush-bent” pipes in the exhaust system. And, crush bending machines such as the Huth are the staple of local muffler shops everywhere. This manufacturing technique bends the pipe efficiently but unfortunately it allows the pipe to “crinkle” in the bend which decreases the inside diameter and causes restriction which robs your engine of both power and economy. Think of bending a drinking straw or even kinking a garden hose: It's exactly the same problem.
The alternative to “crush-bent” is mandrel bent pipes. Both processes use heavy concave dies outside to hold and form the pipe as it is bent. They both use hydraulic pressure to bend the pipe around the dies. But, mandrel bending adds an additional step, a die (the mandrel) that supports the pipe from the inside as it is bent and prevents the crinkling and collapsing. This inside die is mounted on a long shaft and it is articulated, meaning that it moves during the bending process. It has three, four or even five “donuts” that are ever so slightly smaller than the inside diameter of the pipe and are held to the tool by a ball and socket and spring arrangement. These donuts swivel and pivot as the pipe passes over them. White grease is injected through the mandrel to the inside of the pipe during the bending process.
The results are smooth, uniform, constant-diameter bends that greatly reduce restriction and improve both the performance and efficiency of your engine. One of the most immediately noticeable advantages of a mandrel bent aftermarket exhaust system is the deeper and more aggressive rumble and “growl” of your exhaust.

Crinkle Bend


Crush Bend

Mandrel Bend
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