Structural Classification of Bending Machine Dies

Bending machine dies are auxiliary tools used in bending machines to form and process sheet metal. These dies are composed of various components, with the specific parts and configurations varying depending on the type of die. Primarily, they achieve changes in the external shape of materials—mainly metal sheets—by inducing physical-state transformations in the material under the pressure exerted by the bending machine, thereby producing the desired geometry. Let us now explore the structural classifications of bending machine dies.

Bending machine dies are structurally classified into two types: upper dies and lower dies. In most cases, the upper die is the active component (the upper die moves, which we refer to as the moving die), while the lower die is the passive component (the lower die remains stationary, which we refer to as the fixed die). However, there are also instances where the roles are reversed depending on the bending process configuration, though the overall die geometry remains unchanged.

Bending machine dies are generally classified into standard dies and special dies based on their application. Common upper-die cutting-edge angles include 30° (with an actual range of 26°–28°), 60°, and 78°–88°, while the lower-die V-groove angles typically range from 30° to 45°, 60°, and 80°–90°.

Bending machine dies can be classified by shape into pointed-die, arc-die, curved-die, and forming dies. Typically, cutting dies are manufactured in 30° and 60° angles, with occasional custom specifications such as 45° or 55°. Arc dies are primarily designed based on the radius and arc length of the desired curve; however, this alone is often insufficient. Bending dies are mainly used to produce “U”-shaped parts or multiple bends, while forming dies are the most complex, as they can be either integral or modular. In general, modular dies are designed and manufactured as matched upper and lower halves for coordinated use. From a production-cost perspective, integral forming dies tend to be relatively expensive to manufacture, especially for large-scale applications, and it is also challenging to maintain tight dimensional tolerances. By contrast, modular dies offer significant advantages when handling large molds and complex-shaped tooling.

Bending machine dies can be classified according to their function into single-function dies and multi-function dies. Single-function dies are capable of processing only one type of workpiece, whereas multi-function dies can handle various types of workpieces and, in some cases, can be disassembled and reassembled. These are also referred to as composite dies, such as step dies and forming dies.

Bending machine dies can be broadly classified according to the number of die slots into single-V, double-V, and multi-V types. As the names suggest, single-V and double-V dies have only one or two die slots on a single surface; these are commonly used in CNC bending machines and offer high precision due to their standardized design, which is why they are also referred to as concentric dies. They can be freely interchanged. On the other hand, multi-V lower dies are typically square-shaped, with several die slots of varying sizes cut into each of their four surfaces. With a larger number of die slots, they have the advantage of being able to handle sheet metal of various thicknesses for bending operations.

With the continuous advancement of modern society, the demands on products are steadily increasing, as are the requirements for bending processes and materials. Consequently, bending machine dies have also evolved significantly, with insert-type lower dies, non-impression lower dies, and adjustable-opening lower dies now widely adopted across various industries.

1. The insert-type lower die is primarily used to improve the utilization rate of die materials or to perform bending operations on special materials.

2. Types of non-imprinting lower dies include ball-type non-imprinting lower dies, flip-plate-type non-imprinting lower dies, and polyurethane rubber non-imprinting lower dies. Non-imprinting lower dies primarily eliminate surface scratches, abrasions, and indentations on the material.

3. Adjustable-opening lower dies are available in plug-in, counter-plug-in, wedge, and rack-and-pinion types. In addition to improving the utilization rate of die materials, open-type lower dies also significantly enhance work efficiency by reducing die-change time and labor intensity.

The appeal points out that, with the passage of time and the progress and development of society, bending-machine dies are continuously updated through the emergence of new materials and technologies, constantly evolving and advancing. As this refinement continues to advance, it will become easier and faster to obtain the desired products, thereby delivering greater social benefits.