Mandrel Tube Bender

Overview

A mandrel tube bender makes tight, smooth bends in tube and pipe by supporting the wall from the inside with a mandrel while the tube is drawn around a bend die. The mandrel keeps the bore from collapsing and the outer wall from wrinkling, so the tube holds its round shape and its cross-section stays nearly constant through the bend. This is the method used wherever a tube must bend on a tight radius without flattening, such as exhaust systems, roll cages, hydraulic lines, and handrails.

The machine is built on a long Machine Bed with a rotary Bend Head at one end and a Feed Carriage that feeds the tube. The bend is shaped by the Clamp and Bend Dies tooling and supported inside by the Mandrel Assembly. A Hydraulic Power Pack supplies clamping force, the CNC Control runs the program, and the Guarding protects the operator.

How it works

This is rotary draw bending. The tube is clamped against the Bend Die by the Clamp Die, and the Bend Arm rotates the bend die through the programmed angle. Because the tube is clamped to the die, it is drawn around the die radius rather than pushed, which gives a controlled, repeatable bend. The Bend Die radius sets the centerline radius of the bend, so a different radius means a different die.

Three dies support the tube during the draw. The Pressure Die backs the outside of the tube and slides forward with it, reacting the outward force. The Wiper Die, a thin pointed tool set just behind the bend tangent on the inside radius, wipes out the wrinkles that would otherwise form where the inner wall is compressed. Inside the tube the mandrel holds the wall against collapse, which is what lets the machine bend on a radius as tight as one tube diameter.

The mandrel

The Mandrel Assembly is what names the machine. A Mandrel Nose plug sized to the tube bore sits exactly at the bend tangent, and behind it a chain of Mandrel Ball segments joined by Ball Link pins flexes around the bend while still pressing the wall outward. The balls let the support follow the curve where a solid plug could not. A Mandrel Rod holds the mandrel at the tangent and takes the heavy pull of the bending tube. After the bend the tube is sprung back slightly and the Mandrel Extractor withdraws the mandrel. Mandrel placement is precise: too far forward and the outer wall thins or splits, too far back and the bend wrinkles or flattens.

Feed and multi-bend work

The Feed Carriage turns the machine from a single-bend tool into a parts machine. Its Tube Collet grips the tube and a Ball Screw driven by the Feed Servo Motor feeds it forward to set the straight length between bends. The Rotation Servo Motor then rotates the collet to set the plane of the next bend. Together with the bend arm these give three CNC axes: feed distance, rotation angle, and bend angle, often written as the DRA values for each bend. A Carriage Encoder confirms each move. With these three axes the machine can bend a complex exhaust or frame from a single straight tube without the operator touching it between bends.

Hydraulics and control

The Hydraulic Power Pack supplies clamping. Its Hydraulic Pump feeds the clamp, pressure die, and extractor cylinders through a Valve Manifold that sequences them, with Pressure Sensor feedback. The CNC Control runs everything: a CNC Unit executes the part program while one Servo Drive per axis closes its loop, and the Bend Encoder and carriage encoders report position. The operator works through an LCD Panel. The control also adds spring-back compensation, over-bending each bend slightly so it relaxes to the right angle. Relay outputs switch heavier loads and signals run over a Wire Bundle and Connector set.

Materials and use

Mandrel bending suits steel, stainless, aluminium, and titanium tube, and is chosen whenever flow, appearance, or fit demands a clean cross-section through the bend. An automotive exhaust bent on a mandrel keeps its full bore so it does not choke gas flow, where a press bend would flatten and restrict it. Roll cages, aircraft tubing, hydraulic and fuel lines, furniture frames, and architectural rails all use it for the same reason. The tooling is dedicated: each tube size and bend radius needs its own die set and mandrel, so the machine is set up for a tube family and run in volume, while the CNC axes let one setup produce many different bent shapes by program alone.