Deep micro-hole drilling for hadfield steel by electro-discharge machining (EDM)

Abstract

In this study, a new system for drilling deep micro-holes was designed for Hadfield steel (which is difficult to process with classical methods) with the electro-discharge-machining method (EDM) and the system was experimentally examined. The tests were carried out at three different discharge currents (6, 12 and 24) A, three different electrode-tool rotational speeds (200, 400 and 600) r/min, three different dielectric spray pressures (40, 80 and 120) bar, a constant pulse duration (12 μs) and a constant pulse interval (3 μs). After the tests the effects of the processing parameters on the basic performance outputs (the material removal rate -MRR), the electrode wear rate (EWR) and the relative wear (RW)) were investigated. Additionally, an analysis of variance (ANOVA) was also applied to identify the most significant factor. Optimum operating parameters were determined using the desirability-function analysis through the response surface methodology (RSM). It was found that the most effective variable affecting the MRR, EWR and RW was the discharge current. The discharge current was found to be the most significant control factor influencing the performance of the machining process. Keywords: deep micro-EDM, hole drilling, Hadfield steel, multi-response optimization, ANOVA V tej {tudiji je bil postavljen nov sistem za vrtanje globokih mikrolukenj v jeklo Hadfield (ki se te`ko obdeluje z navadnimi metodami) z metodo elektroerozije (EDM) in bil tudi eksperimentalno preizku{en. Poskusi so bili izvedeni s tremi razli~nimi tokovi (6, 12 in 24) A, pri treh razli~nih hitrostih vrtenja orodja (200, 400 in 600) r/min, pri treh razli~nih dielektri~nih tlakih razpr{evanja (40, 80 in 120) bar, pri konstantnem trajanju impulza (12 μs) in konstantnem intervalu impulza (3 μs). Preiskovani so bili u~inki procesnih parametrov na zmogljivost (hitrost odvzema materiala (MRR), stopnja obrabe elektrode (EWR) in relativna obraba (RW)). Dodatno je bila uporabljena analiza variance (ANOVA) za ugotovitev najpomembnej{ega faktorja. Optimalni obratovalni parametri so bili dolo~eni z analizo funkcije odziva na metodologijo odziva povr{ine (RSM). Ugotovljeno je bilo, da je razelektritveni tok najpomembnej{i kontrolni faktor, ki vpliva na zmogljivost procesa obdelave.

Investigation of hole profiles in deep micro-hole drilling of AISI 420 stainless steel using powder-mixed dielectric fluids

“…As the spark is spread on the workpiece, crater depth is reduced, resulting in shallower craters. 2,7,10,18,30 As R a values are directly related to the presence of craters on the workpiece, craters with less depth mean improved (lower) R a values.…”

“…Controlling the spark discharge is very important to obtain the desired R a values. [1][2][3]19,20,31 A spark gap region cluttered with debris also impedes the plunging action of the electrode, causing larger craters to be formed when the electrode's movement is obstructed; increasing the dielectric fluid spray pressure curtails this problem.…”

“…With faster flushing of the spark gap, the molten debris is better removed from the region, which leads to uninterrupted spark discharges. 1,2,7,16,32 With uninterrupted spark discharges, continuous arcing between the electrode lateral surfaces and cavity walls increases ARO values (depicted in Figure 10).…”

“…[1][2][3]33,34 In this study, fluctuations in the hole profile were prevented by the use of electrode rotation and dielectric fluid spray through the electrode itself. Through the selection of machining parameters, the creation of large depressions in the cavity were prevented; however, a certain increase in ARO values could not be avoided.…”

“…In EDM, there is no direct contact between the drilling tool and the workpiece, a significant benefit which eliminates the problems associated with physical contact. [1][2][3][4][5][6][7][8] The EDM method is based on principles of thermal and electrical conductivity whereby small regions on the workpiece surface are removed by melting and vaporization. EDM systems allow the drilling of specific diameter holes provided that the material is electrically conductive.…”