Impulse Forming

Impulse Forming

Definition

According to [LAN93] impulse forming or high velocity forming includes all processes converting stored energy in order to form workpieces in a very short time. In [Bru68] high velocity forming is defined more precisely as “any process which operates at forming speeds of more than 50 ft/s” (approx. 15 m/s). Typical strain rates during impulse forming are in the range of 10^2 to 10^4 and the mere forming duration is usually in the range of microseconds or milliseconds. To achieve such high velocities three typical energy sources are being used. These are:

  • Chemical energy (explosive forming, propellant forming)
  • Electrical energy (electrohydraulic forming, electromagnetic forming, vaporizing foil actuators), and
  • Mechanical energy (high rate mechanical presses, hydropunch process)

Electrohydraulic forming, the hydropunch process, propellant forming and some variants of explosive forming can be grouped as high rate hydroforming processes.

impulse-forming-process_principles

Advantages and Disadvantages of Impulse Forming

Due to the high strain rates compared to conventional forming technologies, the impulse forming technologies feature several advantages as e.g.

  • increased formability for several materials including aluminium alloys as e.g. EN AW-6061 and EN AW-7075, titanium alloys as e.g. Ti-6Al-4V, iron, steels as e.g. 42CrV6, copper, and some magnesium wrought alloys as e.g. AZ31 or ZEK100. This phenomenon is often called hyperplasticity and was investigated in several publications [ALT96, BAL92, BAL94A, BAL94B, ELM04, PSY06, WEI95].
  • reduced wrinkling and springback effects [NEU09],
  • the possibility to use inertia locking mechanisms in the tool design allowing to apply smaller and thus cheaper presses [Rup79],
  • the adiabatic character of the impulse forming technologies [ZEN44], which allows exploiting the forming heat more efficiently than in quasistatic forming operations.

On the other hand, typical disadvantages are

  • high acoustic emissions,
  • the necessity of evacuating the die volume before the forming operation, and
  • increased demands on the measurement technique.