SHAPING OF EXPANDING CHANNEL FOR PRODUCING PLANAR DETONATIONS AT OPEN END

Abstract

In [1], the innovative technology is proposed for pulsed detonation stamping of thin sheet parts. The technology consists in periodically exposing a workpiece to detonation waves and hot gaseous detonation products. The distinctive feature of the technology is the absence of a punch (the mating part of a pro¦led matrix). Compared to the detonation of condensed explosives, the use of gaseous detonation for stamping allows multiple periodic gasdynamic and thermal impact on a workpiece and simpli¦es the execution of technical supervision requirements. Due to the combined gasdynamic and thermal e¨ects of gas detonation on the workpiece, the new technology makes it possible to stamp workpieces made from brittle heat-resistant alloys without the use of expensive hot stamping technologies. A laboratory setup (Fig. 1) for pulsed detonation stamping has been created. The main part of the installation is a thick-walled expanding §at vertical channel with a volume of 30 l. In the lower narrow part of the channel, there is a prechamber with a mixing device and spark plugs. In the upper wide part of the channel, there is a §at §ange with a pro- ¦led matrix and fastening for a workpiece. The setup allows heating the workpiece and matrix with gas burners and operates as follows. Firstly, the channel is ¦lled through the prechamber with a stoichiometric methane oxygen mixture. Secondly, the mixture is ignited by spark plugs, and the arising §ame is transitioned to detonation. Finally, once a detonation wave is formed, it propagates along the channel and re§ects from the heated workpiece exerting a mechanical and thermal e¨ect on it. By changing the degree of channel ¦ll with an explosive mixture and cycle frequency, one can vary the intensity of the impact on the workpiece as well as the temperature of the workpiece and matrix. The duty cycle of the pulses can vary from 10 to 30 s. The shape of the expanding §at vertical channel must ensure that the workpiece is subjected to a planar detonation wave to avoid nonuniform deformation. For estimating the §ow pattern ahead of the workpiece and the parameters of the incident detonation wave, multivariate three-dimensional numerical simulations were performed. Calculations provided pressure and temperature ¦eld evolution ahead of the workpiece for di¨erent shapes of the expanding channel and allowed choosing the optimal channel shape. The characteristic time of mechanical and thermal action of a detonation wave on the workpiece was estimated at 0.1 and 10 ms, respectively. Experiments showed that the developed technology made it possible to stamp thin sheet parts of complex shape made from various materials, including brittle heat-resistant alloys. As an example, Fig. 2 shows a photograph of the stamping product.