The purpose of using a mandrel when bending tube is to prevent the tube from flattening and to prevent wrinkles and kinks. To achieve this, the mandrel is held in a fixed position, and the tube is pulled over it. The tube stretching process is localized on the outer radius of the bend, and the material is work-hardened to retain its shape and not flatten. The material stretching is done on the forward tip of the mandrel. This force, acting on the mandrel tip, supports the inner radius of the bend, holding it firmly into the bend die groove.
The mandrel, or mandrel assembly, consists of a mandrel body, mandrel nose insert, a mandrel link or insert link, mandrel screw, and (if needed) a ball subassembly. The mandrel is the part of the rotary-draw tube-bending process to maintain the shape of the tube as it sets into the arc of the bend.
The mandrel is the tooling component that provides support to the inside of the tube. Its primary function is to prevent the tube from buckling and necking. Many different variations of mandrels exist. The required style and material depend on the outside diameter (OD) and wall thickness (WT) of the tube being bent. The simplest design style is the plug mandrel, and the most complex design style is the ball mandrel. The ball mandrel is designed to internally support the tube beyond tangent and depending on the number of ball segments, throughout the entire bend.
The bend die is the primary tool forming the tube to produce the desired bend radius. This is the form against which the tube is clamped and then drawn around to produce the bend. The essential specifications of a bend die are the outside diameter and the bend radius of the tube to be bent.
The wiper die keeps the tube from wrinkling during the bending process. A wiper die is required when the tube’s resistance to compression is high.
A clamp die clamps the tubing material against the bend die as it rotates to form the bend. There are two specifications of primary importance in a clamp die; Length and cavity texture, which are related to each other. The shorter the clamp, the rougher the cavity surface must be to maintain the force of the grip on the tube. Serrations, knurling, and carbide impregnation roughen the cavity surface which improves the clamp die’s grip upon the tube.
A pressure die holds the tube against the bend die under constant pressure at a tangent and follows the tube through the bend. The follower type of pressure travels forward during the bending process, and almost all modern rotary draw bending machines are equipped with this type of pressure.
On most bending machines, two settings control the operation of the pressure die: direct pressure and assist pressure. To reduce drag on the point of bend, direct pressure must be kept to the minimum necessary to hold the tube without it separating from the bend die cavity.
|Tube OD Range (In)||Link Size||Mandrel Rod Thread||Standard Shank Length (in.)|
|00.219 - 00.279||1/2||#6-32 TPI||1.50|
|00.280 - 00.373||1||#8-32 TPI||1.50|
|00.374 - 00.498||2||#10-24 TPI||1.50|
|00.499 - 00.623||3||1/4-20 TPI||3.00|
|00.624 - 00.748||4||5/16-18 TPI||3.00|
|00.749 - 00.935||5||3/8-16 TPI||3.00|
|00.936 - 01.185||6||5/8-11 TPI||5.00|
|01.186 - 01.498||7||5/8-11 TPI||5.00|
|01.499 - 01.748||8||1.000-8 TPI||8.00|
|01.749 - 02.123||9||1.000-8 TPI||8.00|
|02.124 - 02.623||10||1.000-8 TPI||8.00|
|02.624 - 03.373||11||1.000-8 TPI||10.00|
|03.374 - 04.623||12||1-3/4-10 TPI||12.00|
|04.624 - 06.010||13||1-3/4-10 TPI||14.00|
*Close Pitch specifications: One link smaller, than Standard Pitch
**Ultra-Close Pitch Specification: Two link sizes smaller, than Standard Pitch
(click image to enlarge)
|Item||Tube Dia.||“A”Wiper Reach||“B”Wiper Height||“C”Wiper Length|
|-01||.062 to .559||1.00||.72||6.00|
|-02||.560 to .684||1.00||.80||6.00|
|-03||.685 to .934||1.00||1.20||6.00|
|-04||.935 to 1.309||1.20||1.50||6.00|
|-05||1.310 to 1.434||1.50||1.70||6.00|
|-06||1.435 to 1.558||1.50||1.70||8.00|
|-07||1.559 to 1.809||1.50||2.40||8.00|
|-08||1.810 to 1.934||1.50||2.80||8.00|
|-09||1.935 to 2.434||2.00||2.80||10.00|
|-10||2.435 to 2.809||2.38||3.20||10.00|
|-11||2.810 to 3.059||2.38||3.40||10.00|
|-12||3.060 to 4.000||4.00||4.70||14.00|