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Durmapress specializes in designing, manufacturing, and selling various metal processing equipment, including bending machines, shears, punches, and laser cutting machines. The company was founded in 2014, with years of experience and technology accumulation. DurmaPress has become one of the well-known brands in China's metal processing machinery industry.
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1.What Is a Press Brake and How Does It Work?
A press brake is a machine tool designed to bend sheet metal by clamping it between a punch (upper tool) and a die (lower tool). When the ram descends, the punch forces the sheet into the die cavity, causing the metal to deform plastically and hold the bent shape.
The basic principle hasn't changed in decades — what has changed is control precision. Early mechanical press brakes relied on a flywheel and clutch system, which gave limited control over stroke position. Modern prensa hidráulica e electric press brake machines use closed-loop servo systems that control ram position to within 0.01mm, which is what makes repeatable CNC bending possible.
Three things determine what angle you get out of a bend:
- Stroke depth — how far the punch travels into the die
- Die opening width — the V-gap in the lower tool
- Material properties — thickness, tensile strength, and how much it springs back after the punch lifts
Understanding these three variables is the foundation of press brake operation. Everything else — tooling selection, tonnage calculation, springback compensation — connects back to them.
2.Types of Press Brake Machines
| Type | Drive System | Precisão | Tonnage Range | Best For |
|---|---|---|---|---|
| Hydraulic press brake | Oil cylinder | ±0.1mm | Up to 1000t+ | Thick plate, long bend length, heavy fabrication |
| Electric press brake | Servo motor | ±0.005mm | Up to 150t | Precision parts, high-mix low-volume, energy-sensitive shops |
| Prensa dobradeira CNC | Hydraulic or electric + CNC control | ±0.01mm | Varies | Automated multi-step bending, repeat production |
| Mechanical press brake | Flywheel + clutch | Limited | Low–medium | Basic bending, low-budget setups |
| Pneumatic press brake | Air pressure | Low | Low | Light sheet, simple profiles |
3.Pre-Operation Setup
3.1 Tooling Selection — Punch and Die
The tooling combination determines the bend angle, bend radius, and whether the part comes out right on the first hit.
For most standard sheet metal bending, a straight punch paired with a V-die handles the majority of jobs. The key variable is V-die opening width — a common rule of thumb is 6–10× the material thickness. Thinner sheet (1–2mm) typically uses a narrower opening; heavier plate (6mm+) needs a wider die to keep tonnage requirements manageable.
If you're working on parts with deep flanges or return bends, a gooseneck punch lets you clear the workpiece without collision. Acute-angle punches come into play when the drawing calls for angles below 30°.
3.2 Tonnage and Parameter Settings
Before the first bend, you need to confirm the machine has enough force — but not so much that you're overloading the tooling or the frame.
A simplified field formula for air bending:
Tonnage (kN/m) = (Material Tensile Strength × Thickness²) / (V-die Opening)
Most Prensa dobradeira CNC machines have built-in tonnage calculators — enter the material type, thickness, and die opening and it calculates automatically. For manual machines, operators typically reference a tonnage chart posted at the machine.
Back gauge position sets where the sheet stops before each bend. On multi-bend parts, verify the back gauge steps match the sequence on the drawing — incorrect sequence is one of the most common causes of scrap on complex parts.
4.Bending Methods — Choosing the Right One
Air bending is the default for most shops — it's forgiving, requires less force, and lets you adjust the angle by changing stroke depth rather than swapping dies. The tradeoff is springback, which must be accounted for in the program.
Bottoming is worth the extra tonnage when you need consistent angles across a large batch. Coining is rarely justified outside of aerospace or precision enclosure work.
| Method | How It Works | Precisão | Tonnage | Best For |
|---|---|---|---|---|
| Air Bending | Sheet touches punch tip and die edges only | ±0.5–1° | Low | General fabrication, flexible angle adjustment |
| Bottoming | Sheet fully contacts die at bottom of stroke | ±0.25° | 3–5× air bending | Consistent angles on repeat production |
| Coining | Extreme force, material fully conforms to tooling | ±0.1° | 5–8× air bending | High-precision, low-volume work |
5.Step-by-Step: Running the Press Brake
Step 1 — Position the material Slide the sheet against the back gauge fingers. For long parts, use a support stand on the front side to prevent the sheet from sagging under its own weight — a drooping workpiece produces a curved flange, not a straight one.
Step 2 — Load or enter the CNC programOn a CNC press brake machine, call up the part program and verify the first bend parameters on screen before cycling. On a manual machine, confirm stroke depth and back gauge position by measurement, not by memory.
Step 3 — Trial bend on a scrap piece Never start production bending without a trial piece, especially on a new setup. Run one part, measure the angle with a protractor or angle gauge, and compare to the drawing.
Step 4 — Compensate for springback If the measured angle is 2° open (e.g., you got 92° when you needed 90°), increase the stroke depth slightly and re-test. Most CNC systems let you enter a springback offset directly. Don't skip this step — springback varies by material batch.
Step 5 — Production run Once the trial part passes inspection, run the batch. On long runs, re-check angle every 20–30 parts, as tooling wear and thermal effects can cause gradual drift.
6.Understanding Springback — and How to Compensate
Step 1 — Position the material Slide the sheet against the back gauge fingers. For long parts, use a support stand on the front side to prevent the sheet from sagging under its own weight — a drooping workpiece produces a curved flange, not a straight one.
Step 2 — Load or enter the CNC programOn a CNC press brake machine, call up the part program and verify the first bend parameters on screen before cycling. On a manual machine, confirm stroke depth and back gauge position by measurement, not by memory.
Step 3 — Trial bend on a scrap piece Never start production bending without a trial piece, especially on a new setup. Run one part, measure the angle with a protractor or angle gauge, and compare to the drawing.
Step 4 — Compensate for springback If the measured angle is 2° open (e.g., you got 92° when you needed 90°), increase the stroke depth slightly and re-test. Most CNC systems let you enter a springback offset directly. Don't skip this step — springback varies by material batch.
Step 5 — Production run Once the trial part passes inspection, run the batch. On long runs, re-check angle every 20–30 parts, as tooling wear and thermal effects can cause gradual drift.
7.Safety During Operation
- Keep hands clear of the bending zone during any stroke — the light curtain protects the front, but side entry is not always guarded
- Never bypass the safety light curtain, even temporarily
- When loading heavy plate, use a crane or sheet lifter — manual handling under a loaded ram is a common injury scenario
- Inspect punch and die clamping before each new setup; loose tooling can eject under load
- If you hear an unusual sound during bending (cracking or a sharp pop), stop immediately and inspect — it may indicate tooling failure or a material defect
8.Common Problems and How to Fix Them
8.1 Angle Inconsistency Along the Bend Length
Usually caused by machine deflection — the ram bends slightly in the middle under load, creating a convex bow in the part. The fix is coroamento: most prensa hidráulica machines have an automatic crowning system that adjusts the bed to compensate. If the machine has no auto-crowning, manual shim plates under the die can partially correct this.
8.2 Material Cracking at the Bend
The bend radius is too tight for the material. Increase the inner radius by switching to a punch with a larger tip radius or a wider die. For stainless and high-strength alloys, a minimum bend radius of 1–1.5× material thickness is a practical starting point — check the material spec sheet for the actual minimum.
8.3 Surface Marks on the Workpiece
Worn or dirty tooling, or a die with too sharp an edge radius. Clean the tooling surface first. If marks persist, polish the die shoulder radius or replace the tooling. For cosmetic parts, nylon or polyurethane die inserts prevent marks entirely.
8.4 Part Not Repeating Correctly Between Setups
Back gauge reference has shifted, or the tooling isn't fully seated in the clamp. Always re-run a trial bend when restarting a job after any tooling change — even if the program is unchanged.
9.FAQ
Q1: How do you calculate tonnage for press brake operation?
Tonnage is calculated using: (Tensile Strength × Thickness²) / V-opening, or obtained directly from CNC press brake machine auto-calculation or tonnage charts.
Q2: What causes springback and how do you compensate for it?
Springback is material elastic recovery after bending; it is compensated by slight overbending, typically 1–3° for mild steel and 5–7° for stainless steel.
Q3: What is the difference between air bending and bottoming?
Air bending forms the angle without full die contact and needs less tonnage, while bottoming fully presses the material into the die for higher accuracy but requires more force.
Q4: How often should press brake tooling be inspected?
Tooling should be checked at the start of each shift and immediately after any abnormal noise or visible wear.
Q5: Can a press brake bend stainless steel and aluminum?
Yes. Stainless steel needs higher tonnage and more springback control, while aluminum is softer but more prone to surface marking.
10.Conclusion
Good press brake operation starts before the machine moves — tooling selection, parameter setup, and a proper trial bend prevent the majority of scrap and rework. Once those fundamentals are in place, the machine does the rest.
For equipment selection, visit our prensa hidráulica e electric press brake product pages to compare specifications by tonnage and application. If you're unsure which machine suits your production requirements, contactar-nos directly — our engineering team can recommend the right configuration based on your material, thickness range, and bend length.
