How do you guys calculate tonnage for a new job? I've been using the basic formula but I feel like I'm always adding a bigger safety margin than I should need.
We published a comprehensive tonnage calculation guide covering blanking, drawing, bending, and forming. But tonnage calculation in practice is messier than any formula suggests.
The biggest mistake I see engineers make: calculating tonnage for a single operation and sizing the press to that number with a 10-15% safety margin. Then they run a progressive die with 8 stations and wonder why the press is overloaded. You need to sum all simultaneous forces, account for stripping force (often 5-10% of cutting force per station), and add snap-through shock loads. I've seen real-world totals come in 40-60% higher than naive single-station calculations.
Another gotcha: material properties vary. The tensile strength on the mill cert is a nominal value. Hot-rolled steel can vary ?10% within the same coil. If you're running close to press capacity, that variance matters.
Some questions for the community:
- What safety factor do you use? I typically go 20-25% for blanking, 30% for drawing. Anyone go higher?
- How do you handle tonnage calculations for progressive dies with varying station loads?
- Has anyone had a press overload incident? What was the root cause?
Share your calculation methods, spreadsheets, or war stories. Real numbers from real shops are worth more than textbook formulas.