June 24, 2011
There are a few popular ways to affix the clamp die and pressure die to a rotary draw bending machine. All aim to accomplish the same thing: provide precise vertical alignment to the mating bend die and provide rigid support for the respective die during the bending process so it resists the associated forces and stays in place. This article discusses two ways of holding a clamp die.
For a single-stack bender, the clamp die can be supported in part by a round key (see Figure 1).
When a tube is being bent, the round key, attached to the clamp die holder, transmits a portion of the forces from the clamp die to the clamp die holder. Depending on the design of the round key, the clamp die may transmit a portion of the side load directly to the clamp die holder itself.
One of the functions of the clamp die hanger is to prevent the clamp die from separating from the clamp die holder when the clamp die retracts. Adding a set screw to the clamp hanger provides a means to adjust the clamp die vertically for precise alignment with a mating bend die. This is most important with reverse interlocked tooling.
Note that a round key allows fast tool changeovers.
The function of a dovetail-type key is similar to that of a round key: It provides for alignment and is critical in transmitting forces from the clamp die to the clamp die holder. However, unlike the round key style, the dovetail style can be adapted to multistack benders (see Figure 2).
This method does not use hangers. The dies are machined to a very close tolerance, which allows stacking the dies on top of one another.
Some dovetail designs use a set screw for vertical die adjustment. This screw, usually found below the bottom-most clamp die, is adjusted to position the bottom die relative to the mating bend die. Then it is left to the precision of the individual clamp dies to ensure the distance from tube groove to tube groove.
A drawback to the dovetail design is that it costs more to manufacture than the round key style. This is offset by an advantage. The dovetail key's geometry eliminates the need for hangers, which allows stacking the dies.
This approach also allows for fast tool changeovers.
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