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ASME B5.55M-1994 (2013) — Specification and Performance Standard, Power Press Brakes
🔨 ASME B5.55M-1994 (REAFFIRMED 2013) is the first American National Standard for power press brakes, developed by Technical Committee 31 (Press Brakes and Shears) of the ASME B5 Committee starting in February 1990 and approved on August 18, 1994. The Standard defines and describes press brake size, capacity, and performance, and requires that any press brake referred to as an American National Standard Press Brake comply with all its requirements. Its ten sections cover scope, purpose, and application; definitions and terminology; units of dimension and capacity; machine characteristics; interface specifications; ergonomics; acceptance conditions; provision for information and instruction; manufacturer declaration of compliance; and reference standards.
💡 Forming force (tonnage) and working length are the two core indicators of a press brake. B5.55M is the first standard to define them unambiguously, making a “nominal 100-ton” machine comparable and acceptance-testable across manufacturers.
1. Scope and Exclusions 🔧
The Standard applies to power-operated press brakes used to form metal by bending. It explicitly excludes several machine types:
- Hand brakes (leaf brakes)
- Folding brakes and tangent benders
- Apron brakes (box and pan)
- Swivel bending brakes
The Standard also states that it does not cover safety: safety requirements for the construction, care, and use of power press brakes are established by the latest edition of the American National Standard B11.3. Any procurement that cites B5.55M must also satisfy B11.3 safety requirements.
⚠️ B5.55M covers only power-operated press brakes, not hand or simple machines, and contains no safety clauses. Treating B5.55M as a complete purchase specification without adding B11.3 safety requirements is a common engineering oversight.
2. Machine Characteristics and Forming Force Calculation 📐
The Standard gives a unified formula for the forming force required for air bending. For air bending, the required forming force F is:
F = 1.33 × S × W × t² / (D − 1.41R) (English)
F = 1.33 × 10⁶ × S × W × t² / (D − 1.41R) (Metric)
where F is the forming force, S is the material tensile strength, t is the sheet thickness, W is the bending width, D is the die opening, and R is the bottom die radius or the related radius. The Standard also provides Standard Size numbers and Standard Length designations, e.g., forming capacities from about 175 kN (20 tons) to 1,665 kN (about 187 tons) and beyond, with lengths selected by standard designations; machines may also be built to lengths not listed.
The Standard also standardizes the length designations: a press brake of a given Standard Size may be built to a Standard Length designation or to other lengths when required, but the machine designation should include both the forming capacity and the working length — for example “B5.55M 175 kN × 3 m,” which expresses both capacity and bed length at once. This naming rule avoids the classic selection mistake of looking only at tonnage while ignoring length.
3. Interface Specifications and Ergonomics 🔩
The Standard addresses the key tool-to-machine interfaces that determine interchangeability:
| Item | Content | Purpose |
|---|---|---|
| Upper tool interface | Mounting of the upper tool (punch) to the ram | Quick mounting and accurate locating of the punch |
| Lower tool interface | Locating and clamping of the die to the bed | Consistent location along the bending width |
| Accessory slots | Standard accessory slot dimensions on bed/ram | Mounting back stops, pressure bars, and accessories |
| Ergonomics | Operating position, pedal/button layout, visibility | Fit to human scale and operating habits |
All units of dimension and capacity follow ANSI B5.51M-1979 in SI units, with equivalent English units shown in parentheses, plus a metric/English conversion table in an appendix.
4. Acceptance Conditions and Performance Tests 📏
The Standard specifies delivery acceptance performance tests to verify that a machine reaches its stated capacity:
- Ram repeatability test: verifies repeatable positioning of the ram at bottom dead center.
- Squareness test: checks squareness between ram and bed.
- Flatness test: flatness of the working faces of bed and ram.
- Ram and bed deflection test: deflection under full load.
- Side frame deflection test: lateral rigidity of the frame.
In addition, the Standard specifies nameplate location, data plate content, and the manufacturer’s declaration of compliance, providing a basis for quality traceability.
✅ Acceptance essentials: run the repeatability, squareness, flatness, and deflection tests with the prescribed gauges and loading, and record results into the information required by the data plate so the machine carries a traceable factory acceptance record.
5. Engineering Practice Essentials 🛠️
- 🔍 Formula first: estimate required tonnage with the air-bending formula, then check bed length against sheet thickness and length, to avoid “enough tonnage but not enough length” or the reverse.
- 🔧 Tooling matching: match die opening D to sheet thickness (typically about 8–10 times the thickness); too small an opening requires more tonnage. Buy upper/lower tooling to the Standard for interchangeability.
- 📊 Safety linkage: purchase and operation must also comply with the B11.3 safety standard — light curtains, two-hand operation, and anti-pinch devices.
- 📋 Acceptance records: run the five acceptance tests and keep the data plate information as the basis for later capability assessment and dispute resolution.
6. Frequently Asked Questions ❓
❓ Q: What does the “M” in B5.55M mean?
A: The M suffix denotes a metric (SI) edition. This Standard follows ANSI B5.51M-1979 units in SI, with equivalent English units given in parentheses.
A: The M suffix denotes a metric (SI) edition. This Standard follows ANSI B5.51M-1979 units in SI, with equivalent English units given in parentheses.
❓ Q: Where does the 1.33 factor in the forming force formula come from?
A: It combines empirical factors for the air-bending condition so that the calculated tonnage matches engineering practice; the metric form uses the 10⁶ scaling to keep units consistent.
A: It combines empirical factors for the air-bending condition so that the calculated tonnage matches engineering practice; the metric form uses the 10⁶ scaling to keep units consistent.
🔍 Q: Are CNC press brakes within the scope of this Standard?
A: Yes. Any power-operated press brake used for bending forming is in scope; CNC or manual control does not change scope classification, though back-gauge and angle compensation behavior are covered by other arrangements of the machine specification.
A: Yes. Any power-operated press brake used for bending forming is in scope; CNC or manual control does not change scope classification, though back-gauge and angle compensation behavior are covered by other arrangements of the machine specification.
❓ Q: Why does the Standard require full compliance for the “American National Standard Press Brake” name?
A: To prevent “nominal compliance”: only if all clauses are satisfied may a machine be sold under that name with its compliance declaration, guaranteeing consistent quality and performance to users.
A: To prevent “nominal compliance”: only if all clauses are satisfied may a machine be sold under that name with its compliance declaration, guaranteeing consistent quality and performance to users.
