Optimization of Hardness Strength in Tungsten Inert Gas Mild Steel Weld Using Response Surface Methodology

Abstract

During welding operation, excessive heat input or limited heat
input can compromise the quality of welded joint which affect the
hardness strength. This study was carried out to optimize the
factors responsible for achieving maximum hardness strength
using Tungsten Inert Gas (TIG) welding. An experimental matrix
was developed with the design expert software, which resulted in
central composite design.100 pieces of Mild steel plate was cut into
dimension 27.5mm in length,10mm diameter and 10mm thick for
the Experiment. Thereafter hardness test was carried out for all the
weld samples, the experimental results obtained was used as data
for the Analysis. The Response Surface Methodology (RSM), was
applied to optimize the responses from input parameters which
includes current, voltage and gas flow rate. The experimental
results showed that the minimum value for current is 120 Ampere,
voltage 20 volts, gas flow rate 12 Lit/min and the maximum value
are 170 Amperes, 25 volts, 14 Lit/mm. The RSM model selected the
quadratic model as the suitable model for the test because it has a
P – value less than 0.05. The goodness of fit statistics gave R2,
value of 86.07%. From the optimization results it was observed
that a current of 120 amperes, voltage of 20 volts, and gas flow
rate of 12.00 Lit/min will produce Hardness of 299.269N/mm2.