Achieving safety with hydraulics for hydroforming presses

Hydroforming processes have been established as efficient alternatives to conventional press forming for pressing – with the help of pressurized fluid – complex, single-component work pieces into shape. Correctly using a continuous forming process allows more finished product to be created from less raw material.

08/15/2008


Hydroforming processes have been established as efficient alternatives to conventional press forming for pressing %%MDASSML%% with the help of pressurized fluid %%MDASSML%% complex, single-component work pieces into shape. Correctly using a continuous forming process allows more finished product to be created from less raw material.

High-pressure forming can produce smaller and lighter components when compared to other manufacturing processes, and it features greater mechanical stability. However, a wide array of safety precautions must be followed when using hydroforming technology.

Existing safety standards

In several western regions, safety standards describe how to achieve safe control for hydraulic presses. For example, ANSI B11.2 Hydraulic Power Presses %%MDASSML%% Safety Requirements for Construction, Care and Use is the standard used in the U.S. Canada cites Z142-02 Code for Power Press Operation: Health, Safety and Guarding Requirements, and EN 693 Safety %%MDASSML%% Hydraulic Presses is used in Europe.

All of these standards have the same basic requirements for safe press control. While the ANSI standard only scratches the surface, the Canadian and European standards go more in depth. The Canadian standard was largely influenced by the European standards, which have more demanding requirements, and the European safety standards are more accepted worldwide as customary engineering practices as they comply with a broader range of regulations. The goal of all three standards is to avoid a dangerous closure of the press due to a fault.

All of the standards assume that the probability of two components failing from independent causes during a press cycle is very small. If a safety controller detects a single failure, the press slide will stop and a new cycle cannot begin. The probability that a second independent failure would occur after the press is stopped, allowing the press to stroke again before the first failure is detected, is also very low.

Standard EN 693 strives to accomplish a level of security within hydraulic controls. Some requirements include:

  • A minimum of two independently controlled components, arranged in series (redundancy)

  • When the components are in their neutral position, pressure must not be allowed to build up in the cylinder piston area, or the pressure in the annulus area (for a down-acting press) must not be allowed to decay

  • Control valve spool positions must be monitored with limit switches %%MDASSML%% or similar devices %%MDASSML%% for critical function valves

  • After each cycle, a safety control must determine whether the “safe” neutral positions were achieved; if not, a new cycle start must be prevented

  • Protection against pressure intensification in the annulus side of the cylinder must be designed into the circuit.