Abstract
Alloys made of magnesium are valuable materials used in many different engineering
applications. Because of its high strength-to-weight ratio and low density, AZ31B magnesium
alloy is widely used in orthopaedic implants, aircraft fuselages, cell phone, and laptop cases,
speaker cones, notebook computer frames, digital cameras, PDAs, and other consumer
electronics products. Their tendency to chip and stick to the tool faces at high temperatures is
the main problem during machining. This calls for the use of high volumes of cutting fluids
and lubricants, optimized parameter machining, and the use of tools that have been coated or
treated in order to improve cutting ability. Many traditional methods are unsustainable and
have a negative impact on the environment. This forces scholars to look into sustainability.
This compels researchers to look into long-term solutions. Dry machining is one such
technique in which no lubrication is used, thus significantly reducing machining costs and
helping to keep the environment clean and green by emitting fewer emissions. However, dry
machining alone is insufficient to achieve the best machinability, necessitating the use of
other techniques to achieve machining success. The purpose of this research is to find
optimum turning variable parameters to perform the dry turning of AZ31B magnesium alloy
bars by manual lathe tool using the coated triangular-shaped tool without fire ignition.
Before experimentation, a thorough review by other investigators was carried out in
order to establish a foundational understanding of the effects of variable turning parameters
on the machining performance/responses for turning AZ31B magnesium alloy bars (AZ31BMACBs)
using a manual machine lathe tool. Most of the earlier studies concentrated on
variations in material removal rate, mean surface depth, tool wear (i.e. flank wear), and chip
morphology. Considering this review, it is clear that tool wear, surface roughness, and chip
morphology are the most important performance indicators for turning AZ31B-MACBs.
Certain works that have been reviewed concentrate on the dry hybrid machining of AZ31BMACBs
with cryogenic, coated, and textured tool inserts. Previous research revealed the use
of various optimization techniques to obtain the best turning combinations. The research gap
and the objectives of the current work are identified through this review of previous work.
Because it was observed that tool wear and surface finish have a major impact on the
machining of magnesium alloy, an investigation was conducted to determine the best turning
combination to improve the life of the tool and surface quality.
Experimentation is required for this purpose to thoroughly examine the impacts of
machining input variables on the machining performance indicators namely flank wear, mean
roughness depth, and material removal rate, to evaluate tool wear, surface finish, and
productivity while machining AZ31B magnesium alloy cylindrical bar. One-factor-at-time
approach and Box-Behnken Design (BBD) of the response surface methodology (RSM)
approach were employed to effectively conduct a set of experiments. Cutting speed ‘Vc’ (in
mm/min), feed rate ‘f’ (mm/rev), and depth of cut ‘ap’ (in mm) were selected as machining
input variables. Each machining input variable has three different levels and their impacts on
machining performance indicators were reported.
Pilot/Trial, main, and confirmation runs are three stages of experimentation for the
present research work. In stage 1, a total of fourteen experimental runs were carried out to
bracket the ranges of the three machining input variables. Turning length, and mean
roughness depth ‘Rz’ were considered as major machining performance indicators (i.e.
responses) to bracket the ranges of variable turning parameters (i.e. cutting speed ‘Vc’, feed
rate ‘f’, and depth of cut ‘ap’) of manual lathe tool. This bracketed range of variable turning
parameters of the manual lathe tool was then used for further investigation (i.e. stage 2) to
examine in detail the influence of machining input variables on selected performance
indicators namely flank wear ‘Fw’, mean roughness depth ‘Rz’, and material removal rate
‘MRR’ during turning AZ31B magnesium alloy cylindrical bars (AZ31B-MACBs). The
fifteen experiments were designed and conducted according to BBD-RSM and each
experimental run was repeated twice. Therefore, thirty experimental runs were conducted by
performing straight turning on AZ31B-MACB by manual lathe tool using a coated tool insert.
Multi-response optimization of input variables of manual lathe tool provided the best possible
set of turning parameters, improving tool life, surface quality, and productivity significantly.
The optimum results obtained from the optimization technique i.e. desirability function
analysis (DFA) were validated by carrying out two confirmation experiments. Subsequent to
validation tests, a thorough investigation of tool wear and chip morphology was carried out
for the surface of AZ31B-MACB turned at optimum turning parameters.
Keywords: Dry machining; Magnesium alloys; Tool wear; Material removal rate; Surface
roughness; Design of experiments; Optimization