intensification of laser radiation

IFOST 2008

106

978-1-4244-2320-0/08/$25.00 ©2008 IEEE

Possible Ways for Intensification of Dimensional

Electrochemical Machining (DECM)

Rakhimyanov H.M. Gaar N.P.

Novosibirsk State Technical University, Novosibirsk, Russia

Abstract – Several methods for intensification of dimensional electrochemical machining are considered. A new method of the process activation through intensification of laser radiation is offered. I . I NTRODUCTION The dimensional electrochemical machining of metals (DECM), based on anodic dissolution of metals and alloys in electrolyte, has been successfully used for several decades. It is constantly being developed and improved, new advantages and potentials being revealed. DECM is widely used for processing parts made of hard-to-machine materials such as heatproof and hard metal alloys as well as alloys based on titanium, aluminum and other metals. This method of machining is also applied to producing formed components and processing of delicate materials. DECM is considered to be preferable due to the lack of surface cold working and temper in the surface coating of the material machined. However, this kind of machining materials can not be called highly productive.

II . MAIN BODY Low productivity of DECM can be explained by a number of reasons. It is known that electrochemical machining is based on anodic dissolution. The process occurred at the “solid body-solution” inter-phase boundary is known as heterogeneous and consists of several stages. According to chemical kinetics [1], the rate of a complex reaction depends on the rate of the slowest stage. This stage can differ from material to material. So, the awareness of the reason for low productivity, that is the limiting stage of the process, makes it possible to increase the rate of dissolving the machined material by means of changing this stage which will result in raising productivity. There are following methods of DECM intensification: fluid, thermal, reverse polarity, etc.

As electrochemical theory treats, the diffusion layer thickness as well as reaction product venting and anion supply from the depth of solution influence the rate of material removal and consequently productivity of the process [1]. The increase of solution pumping through workpiece-to-electrode spacing positively influences most

stages of the process of electrochemical stripping. What is more, the given method makes it easier to remove adsorbed films when their joint with the surfaced machined is not sufficient enough. However, the increase in solution flowing rate in the workpiece-to-electrode spacing does not influence such stage of the process as chemical conversion. Also, the instability of fluid dynamics parameters increases surface undulation which decreases working accuracy [2]. It is because of this reason the method in question is not widely used The rise in solution’s temperature makes the DECM

productivity 3-5 times higher due to increasing current

efficiency resulting from enabling solution anions to react

faster. It fosters the activation of electrochemical change and diffusion process in DECM. Moreover, the rise in solution’s temperature decreases its specific resistance while water solubility of anodic process increases. But, if solution temperature exceeds its specific value, chemical activity of solution anion decreases [4] and results in lowing down the process productivity. Another essential disadvantage of the activation method under consideration is the substantial solution evaporation and gas emission at high temperatures which requires personal protection of

people involved and installation of exhaust ventilation.

The latter is of great importance because, without it, it is impossible to apply the thermal method of DECM

activation on industrial scale. As a rule, the intensification of electrochemical

stripping by means of reversed polarity method is used

when sparingly soluble films appear on the surface [5]. The application of activation method means that the anode is recurrently exposed to the current of direct and reversed polarity. When current of direct polarity is applied, anode material dissolves, while application of reversed polarity current reduces the atomic oxygen and the film tears off the anode surface. Although the method does increase the process productivity (by factor of 1.6-1.8), it is not widely used due to the fact that its application results in substantial run out of electrochemical machining electrode when current of reversed polarity is applied. The above mentioned analysis of the methods of electrochemical machining intensification (EMI) shows that there is no method to meet the requirements of EMI

with regards to productivity, quality of machining, manufacturing capability, simplicity of implementation due to the limitation of purposeful influence at a specific stage of DECM. There is a need for method of electrochemical machining intensification allowing to arbitrary influence any stage of anode dissolution.

From the theoretical point of view the most promising seems to be the method of anode dissolution by means of laser emission. The assumption that it universally influences DECM materials is based on the specificity of laser emission itself, such as high degree of monochromatism and coherence, extremely low beam divergence and power density, focused radiation