Effects of Electrode Polarity on SKD61 Steel Surface Properties in Powder Mixed Electrical Discharge Machining

I n t e r n a t io n a l J o u r n a l o f S c ie n c e a n d R e s e a r c h (I J S R )

ISSN (Online): 2319-7064

Index Copernicus V alue (2013): 6.14 I Im pact Factor (2013): 4.438

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Effects of Electrode Polarity on SKD61 Steel Surface

Properties in Powder Mixed Electrical Discharge

Machining

B.T. Long', N. Cuong2, N. H. Phan3

'H a n o i U n iv e r s ity o f S c ie n c e and T e c h n o lo g y , H a n o i, V ie tn a m

2' 3T e c h n ic a l-e c o n o m ic sc o l!e g e , T h ai N g u y e n U n iv e r sity , V ie tn a m

Abstract: MetaI powder oralloy powder is suspended in a suitable dielectric fluid during electrical machining dischagre (EDM)is veiy

effective in improving the productivity anti quality o f the machined surface. Thus, the researches in this area have been very interesting. This

paper introduces the investigated results influencing the electrode polarityon theqnality o f the machined surface after EDM with powder

mixed in dielectric flu id (PMEDM). Titanium powder, SKD61hot die steelandcopper and graphite electrodeswere used fo r the research.

These parameters were selected to evaluate the quality o f the machined surface such asand thickness o f the heat-affected layer, chemical

composition, topography and microhardness.The results showed that the electrode polarity in EDM with titanium powder mixed in oil

dielectric fluid can significantly affect th equality o f the machined surface.

K eyw ords: E D M , P M E D M , H e a t-a ffe c te d la y er. C h e m ica l c o m p o s itio n , T o p o g ra p h y , M icro h a rd n ess

1. Introduction

Using the traditional processing methods for forming surface

moulds is often difficult due to machined surface complex

shapes and high mechanical properties o f materials. EDM -is

comm only used to shape the m ould surface. This method can

be the machined surfaces; w ith complex shapes and materials

o f any hardness. However, the surface layer o f dies after EDM

hasthe topography andmetallurgical and physicochemical

of the Inconel 718 steel surface layer affected by the heat pulse

[3], The results showed thatalum inum powder gave the

smallest affected heat and the highest M RR.Theeffects o f

electrical parameters onMaterial Removal Rate (M RR), Tool

W ear Rate (TW R) and surface roughness (SR) were

investigated in machining nickel alloy with aluminum pow der

mixed in dielectric fluid and reverse electrode polarity [4]. The

effect o f copperelectrode polarityon the quality o f SKD61 steel

surface after EDM with alum inum powder was mixed in

properties changed significantly and the special machined dielectric fluid was shown [5], SR has received optimal value

r. i i i i • 1 : '¡V iÄ j o i-ee* n ^ lo f ih r T lii» in fln p n r ’p r\ r ttap» n n n /n p r surface showsa white layer with more microcracks and low

toughness. The change o f the surface layer that reduces the

ability o f the working dies is necessary to improve the surface

quality o f the work product o f this type. In practice, the

machined surfaceby EDM often requiresfine machining, such

as grinding, polishing, etc. to rem ovelayer defect.

''V i *

The research results showed that, PM EDM is the effective

method to eliminate the limitations o f EDM. PM EDM can

improve the productivity and machining quality o f EDM.

However, the working principle o f PM EDM processis very

complex, so it is affected by many technological parameters.

Beside the influence o f the parameters, such as current, pulse

on time, pulse o f time, concentration o f powder, powder

materials, the electrode polarity alsohas significantimpact on

the quality o f the machined surface. The negative polarity of

copper(<l>l mm) electrode on SKD61 steel machining by EDM

with titanium powder mixed in dielectric fluid created the

coating hardness o f 2000 HV on the surface o f the workpeice

[1]. W hentungsten powder was mixed in dielectric fluid in

EDM with negative polarity copperelectrode also created a

surface layer o f the steel mould (OHNS, D2 and HI 3), which

increased the microhardnessby 2 times [2].'The negative

polarity o f tungsten (<t>l mm) electrode was used to evaluate

the influence ofaluminum and silicon powder on the thickness

Paper ID: SUB153385

with reverse electrode polarity. The influence o f the powder

Al, Cr, Cu, SiC on S K D ll steel surface in EDM with reverse

electrode polaritywas introduced [6]. The results showed that

Al powder gaveSR and thickness affected by the minimum

heat pulse with positive electrodeand then increased

respectively in thfe materials pow der Cr, SiC and Cu. The

positive electrode polarity o f copper was used to research the

effect o f Si powder to M RR in AIST D2 steel machining [7].

The results showed that current intensity and powder

concentration werethe two param eters having thegreatest

impact on MRR. The pow der Al, Cr and Al + Cr mixed in

dielectric fluid affected the surface quality o f steel SKD61

after EDM withCu reverse electrode polarity[8]. The powder

o f Al, Cr and Al + Cr increased the hardness and strength

erosion o f the SKD61 steel surface. The smaller particle size

leads to smaller surface roughness. The copper

electrodepolarityhave little effect on the TW R in EDM with

graphite powder mixed in dielectric fluid. The reverse

electrode polarity gavesm aller TW R [9]. The influence o f the

concentration and size o f Al pow der andelectrode polarityon

the MRR, WR and SR in m achining 718 stainless steel by

EDM was introduced [10]. The results showed that the reverse

polarity hadstrong influence on M RR and the negative polarity

hadgood impact on WR and SR. The influence o f the electrode

polarityon MRR, TW R in EDM , Dry-EDM and PMEDM was

investigated [11]. The results indicated that the diameter o f the

Volume 4 Issue 4, April 2015

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