Requirements in tube bending

The three principal requirements in tube bending are simply: machine, operator and tooling.

All three factors must be especially good to work with thin wall tubing on tight radii. Too many facilities still depend on the operators genius to compensate for near useless tooling. Poor tooling results in longer set-up time, scrapping of expensive tubing, poorly bent tubes and fail to produce an acceptable pipe bender. Highly competitive custom tube bending companies realize cheap and inferior tooling is the most expensive they can buy. Interlock tooling represents the ultimate in tube bending tooling. Complete interlock tooling, although developed and successful for numerical control tube benders, has proven advantageous for conventional machines. Each tool of the matching set is laterally locked in alignment. The clamp die is keyed and locked to the bend die, the wiper die located and locked to the pressure die, and the pressure die in turn is locked in alignment to the bend die.

Field reports have confirmed several advantages of interlock tooling. The clamp die, with all the hydraulic pressure available to it, will not crush or even mark the tube, thereby providing vastly improved gripping properties. Bend die and pressure die marks on the top and bottom of the tube are completely eliminated. In 23 instances tested, set up averaged one-third the time allotted for conventional tooling. A 32% reduction of scrap was recorded over previous runs using conventional tooling.

The five pieces of tooling (bend die, pressure die, wiper die, mandrel and clamp die) must all be close-tolerance excellent tooling. The bend die should have a maximum run out at the bottom of the bend groove of not more than . To help prevent tooling marks on the top and bottom of the tube bending machines, the bend groove should be deeper than half the tube diameter. The bend groove should be dead round and the diameter should measure 10% timeís wall thickness over tube diameter. The clamping area, unless cleated or with other provision such as flaring, beading, etc., should be three to six times tube diameter with a sandblasted or rough finish. The diameter of a clamp area should not be undersize more than 10% of wall thickness. Grip or pinch clearance should be held to a minimum. To permit the bend die to be used on right and left hand machines, the counter bore and keyway often are machined on both sides of the die. Centerline height must be maintained for both sides.