Page 15 - MetalForming April 2020

Cam driver
Cam
Fig. 2—Force vectors in a cam operation.
besides the one illustrated for cutting. Force vectors are present during right- angle bending, nonsymmetrical form- ing and drawing operations. Using cams also generates large side thrusts. Cams with 45-deg. driving angles (Fig. 2) produce horizontal forces equal to the vertical force acting on them.
The press also applies horizontal forces, especially when the ram is not parallel to the bed or guided properly
in its gibs. In this case, side thrusts of very high magni- tude act on die components and the die assembly. Dies that are somewhat self-align- ing—draw dies, for example— will attempt to overcome this situation. Sometimes, larger guide pins and additional heel blocks are employed to move the ram into a parallel posi- tion. Unfortunately, the forces required to shift or guide the press ram into proper align- ment likely are much greater
than can be handled by the die-align- ment components, causing deflection of these components.
A well-constructed, symmetrical blanking die, with no shear and a well- aligned press ram, will result in the minimum horizontal loads.
Significant side loads in dies often have multiple causes, including poor alignment of die components during die construction; misalignment result-
ing from a mis-hit or die crash; angular contact between surfaces, such as angular form steels; nonsymmetrical forms or draws where the punch and die are loaded off-center at initial con- tact; the use of shear or angular cutting faces to reduce cutting forces; or cutoff, trim, bending and flange dies where forces act on only one side of the die steel.
Historically, dies have been con- structed based on experience, intuition and rules of thumb. Various compo- nents in dies are designed and used without a real understanding of their function or the forces acting on them. A better understanding of the purpose and function of each die component from an engineering perspective (e.g., loads, deflections, vector angles, bend- ing moments, etc.), is required to improve die life and accuracy of the stamping, and to reduce die mainte- nance cost. Otherwise, it could cost more to maintain the die than it did
Tooling by Design
to build it.
MF
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MetalForming/April 2020 13
INNOVATION FOR 3 GENERATIONS
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