Page 69 - MetalForming August 2014

Tooling by Design
Table 2—Shift Loads 1.5 in. to Right
Station No.
Tonnage
Distance from Center, in.
Moment, in.-tons
1
3
-9.0
-27
2
30
-6.0
-180
3
10
-3.0
-30
4
10
-0.0
0
5
12
3.0
36
6
6
6.0
36
7
6
9.0
54
8
10
12.0
120
Total Moment
9
Table 3—Add Metal-Thickness Shear to Punch at Station 2
Station No.
Tonnage
Distance from Center, in.
Moment, in.-tons
1
3
-10.5
-31.5
2
15
-7.5
-112.5
3
10
-4.5
-45
4
10
-1.5
-15
5
12
1.5
18
6
6
4.5
27
7
6
7.5
45
8
10
10.5
105
Total Moment
-9
to the cutting punch in that station. The resulting reduction in force at that position (Table 3) balances the loads across the press slide.
It is not necessary to perfectly balance all of the forces across the slide. The press structure and die-guiding systems can handle some off-loading conditions. It also may be impos- sible to balance loads for many processes, especially in pro- gressive dies. Even under ideal conditions where the sum of all moments equals zero, there still can be some slide tipping because all of the forces are not generated at the same time or at the same slide position. This is because the forces generat- ed by forming processes may occur 1⁄2 in. or more above the bot-
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tom of the press stroke, while the forces generated by punch- ing and blanking occur near the bottom of the press stroke.
Correcting slide-tipping problems with an existing pro- gressive die is possible. One could shift the die in the press or introduce a dummy load somewhere in the die. A dummy load may consist of an added pressure system at one end of the die to counter the tipping moment, or adding a coining station in an area that eventually ends up in the scrap. When the die can- not be shifted in the press due to a lack of room on the press bed, adding a dummy load often is the only recourse.
A better solution: Address the problem during strip layout.
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MetalForming/August 2014 67