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INTRODUCTION
Dry machining processes are much better for environment than classical machining processes using
coolant. On removing coolant, we need to develop the new technologies needed. The productivity of
these technologies is now very good and is equivalent to the classical productivity rates. The main
question is to know if these new emerging technologies are fundamentally better for the environment.
The new technology developed is said to be dry technology, here splitting of the chip in deep drilling
can be obtained by vibrating the drill axially. The studies conducted on self-vibratory drilling (SVD)
has led to the design of a drilling head compatible with the existing tools and machines, and that does
not require additional energy. The aim of this paper is to demonstrate that the environmental impacts
generated by SVD over an industrial production are significantly less than those of TD and to quantify
them. For that purpose here we are comparing both traditional and SVD with the help of graphs. The
graph comparing the relative weight of environmental impacts of the two processes according to the 10
indicators like abiotic depletion, acidification, eutrophication, global warming, ozone layer, human
toxicity, fresh water aquatic ecotox, marine aquatic ecotoxicity, terrestrial ecotoxicity, photochemical
oxidation. The negative impact created by dry machining is that it produces high temperature during
the friction between the tool and the work piece, somehow this can be counteract by providing a
interrupted machining environment. Dry machining also helps in the reduction of thermal shocks.
1.1. LITERATURE SURVEY
Sreejith PS, Ngoi BKA were the first to conduct study on Dry Machining: They introduced this kind of
machining as it reduced the use of coolant to its maximum, thereby it seems to be the machining of the
Future. Then it was Tichkiewitch S, Moraru G, Brun-Picard D, Gouskov A who conducted experiments
later and provided with the idea of Self-Excited Vibration in Drilling Models in order to remove chips
during machining. Hauschild M, Jeswiet J, Alting L studied on ‘From Life Cycle Assessment to
Sustainable Production’.Canter NM ,Onder O, Paris H, Rech J, Grenier L also studied on Self-Vibratory
Drilling: An Answer for Sustainable Manufacturing.
1.2. OBJECTIVES
To demonstrate that the environmental impacts generated by SVD over an industrial
production are significantly less than those of TD
To know, after the coolant is removed, what the main contributors to the environment
are to optimize the machining process.
To discuss different approaches of manufacturing processes using Life Cycle Analysis
NEED FOR A COOLANT IN MACHINING
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat
produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal
capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor promoting
corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.
While the term coolant is commonly used in automotive, residential and commercial temperaturecontrol
applications, in industrial processing, heat transfer fluid is one technical term more often used,
in high temperature as well as low temperature manufacturing applications. A coolant can be any phases
like gases, liquids, molten metals and salts and solids.
The purpose of the application of the cutting fluids in metal cutting was stated as reducing cutting
temperature by cooling and friction between the tool, chip and work piece by lubrication. Chip
formation and curl, which affects the size of the crater wear and the strength of the cutting tool edge, is
also affected when coolant is carried out during machining. Generally, a reduction in temperature results
in a decrease in wear rate and an increase in tool life. However, a reduction in the temperature of the
work piece can increase its shear stress, so that the cutting force may be increased and this can lead
Water soluble fluids were defined suitable for operations where cutting speeds were very high and
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pressures on the tool were relatively low. Neat cutting oils are straight mineral oils, or mineral oils with
additives. Coolant is very much useful in machining for removal of heat generated due to friction. Under
high pressure, coolant is essential to split and evacuate the chip in deep drilling. It also provides the tool
with better life and surface finish. This is achieved by the coolant by safely removing the chips produced
during drilling and removing excess heat developed during machining process. During drilling there
may be also having the possibility of edge formation, these are also removed by the use of coolant.
Every conceivable method of applying cutting fluid can be used, with the best choice depending on the
application and the equipment available .For many machining applications the ideal has long been high
pressure, high volume pumping to a force stream of liquid directly in to the tool chip interface, with
walls around the machine to contain this splatter and the sump to catch, filter, and recirculate the fluid.
This type of system is commonly employed, especially in manufacturing. It is often not a practical
option for MRO or hobbyist metal cutting, where smaller, simpler machine tools are used. Fortunately
it is also not necessary in those applications where heavy cuts aggressive speeds and feeds and constant all day cutting are not vital.
DRY MACHINING TECHNOLOGY
It is an ecologically desirable process by which the environmental impacts created by usage of coolants
can be reduced. The splitting of the chip in deep drilling can be obtained by vibrating the drill axially.
The studies conducted on self-vibratory drilling (SVD) has led to the design of a drilling head
compatible with the existing tools and machines, and that does not require additional energy. This
technology is candidate to automotive industry and should be environmentally qualified and optimized
in practical working conditions. During SVD, the axial vibrations that cause the splitting of the chip are
obtained by the instability of the cut. The cutting parameters selected in SVD maintains or improves
productivity by referring to a drilling operation using a twist drill. A special drill holder called selfvibrating
drilling head (SVDH) was developed .The SVD is composed of three main elements; the drill
holder called sliding body, with a mass m, fixes the twist drill and enables axial vibrations. The vibrating
device body connects the device to the spindle and the leaf spring, with a stiffness k, is a dynamic
cutting fixture enabling a magnitude and an adapted frequency. The cutting parameters are chosen to
be in the area of unstable cutting. The chip is then naturally evacuated without coolant.16-20% of
manufacturing costs lowered. Hence it is much cheaper to involve this technology. The main pecularity
of using dry machining is that it causes less pollution when compared with traditional drilling. Waste
materials that are disposal is very much less and it does not cause pollution to atmosphere and water.
The health problems caused by this technology is less when compared with traditional drilling. Many
metal cutting processes have been developed and improved based on the availability of coolants. It is
well known that coolants improve tool life and tool performance to a great extent .In dry machining
there will be more friction and adhesion between the tool and the workpiece, since they will be subjected
to high temperatures. This will result in increased tool wear and hence reduction in tool life. Dry
machining has some positive effects such as reduction in thermal shock and hence improved tool life in
an interrupted-machining environment. Research in dry machining has led to the following
achievements such as an under cooling system, an internal cooling by a vapourisation system, cryogenic
systems, thermo cooling systems. Another approach is to improve the properties of tool material by
making them more refractory or generate less heat during machining. There has been a continuous
development in the field of cutting tool materials starting with HSS, cobalt alloys, cemented tungsten
carbide, coated carbides and coated HSS, cubic boron nitride and diamond. The need for machining
with increasingly higher cutting speeds and also to machine difficult to machine materials are imposing
pressure for the development of new tool materials. As a result newer tool materials such as ceramics
and also different types of coatings on the tool materials will address the problems in dry machining to some extent.
Here the chips are naturally fragmented to small pieces implying that there is no need to perform the
stripping operations classically used to split up chips. The friction of chip on the manufactured hole
surface is limited which leads to improved hole quality. The drill is made of cemented tungsten carbide
drill of 5 mm diameter with a split point grinding. The hole produced by this drill is about a length of
90 mm. Cemented tungsten carbide is used because of its ease to machine hard materials such as carbon
steel or stainless steel, whereas at these tough conditions other tools would easily wear away such as
high quantity production runs. These carbide tools also provides better surface finish and allow faster
machining. Carbide tools can also withstand higher temperature than standard high speed steel tools
which are used as drill material. Three main elements; the drill holder called sliding body, with a mass
M, fixes the twist drill and enables axial vibrations; vibrating device body, a leaf spring of stiffness k.
Axial vibrations remove metal chip. Another approach consists in using the cutting energy to create the
axial vibrations necessary to split the chips. The objective is then to set up the cutting conditions in
order to create drill axial chatters. The axial vibrations at low frequency have amplitude bigger than the
feed rate allowing the chip to be split and easily removed by the cutting fluid.
DYNAMIC MODEL OF SVDH
The machining of deep holes is limited due to inadequate chip evacuation, which induces tool breakage.
An alternate response is the use of dry vibratory drilling. A specific tool holder induces axial selfmaintained
vibration of the drill which enables the chip to be split. The chips are thus of smaller size
and can be evacuated. Elements constituting the machining system (machine tool, work piece, fixture
and cutting tool) have a stiffness higher than the axial stiffness of the SVDH. The spring of the SVDH
has a very big rigidity in twisting and low rigidity in compression. The dynamic behaviour of the
machining system was modified as a second order system characterized by a mass (m), stiffness (k) and
damping ©.For a hole diameter of 5 mm, a mass m of 3.2 kg, a stiffness k of 380 N/mm, the range of
the rotation speed is between 7000 and 14,000 rpm. The surface generated by a lip of the drill is the
result of the axial feed of the drill and of the spindle speed. The cutting force in drilling are modified
by a thrust force and a torque around the drill, with the hypothesis that the sharpening of the tool and
that the lips of the drill work in the same way, the lateral force being on every lip counterbalance.
The cutting forces in drilling are modelled by a thrust force and a torque around the drill, with the
hypothesis that the sharpening of the tool is perfect and that the lips of the drill work in the same way,
the lateral force being on every lip counterbalance. Juhchin proposed a cutting thrust force model where
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this force was proportional at the uncut chip section. This model does not take into account the nonlinear
behaviour generated by the indentation force on the chisel edge. Indeed, this zone of the drill has
a geometry that does not facilitate the cutting. Furthermore in this small region around the center of the
chisel edge, the tool did not cut but instead extruded the material.
EXPERIMENT
The goal of this study is to prove that the environmental impacts of SVD are significantly less than
those of TD and to quantify them. The study was based on an (LCA) life cycle analysis of the two
processes and illustrated on the machining of industrial crankshaft lubrication holes. The holes diameter
is 5 mm and the depth is 100 mm. The crankshaft is made of steel 35MnV7. The other manufacturing
steps of the crankshaft are not taken into account. The assessment and comparison of the environmental
impacts of the two processes are based on the machining of crankshaft lubrication holes over 5 years of
production. The manufacturing system is working 22 h per day, 47 weeks per years, and produces 6026
crankshaft per week. The machining time of the holes is the same regardless of the process so the two
processes will produce the same number of crankshafts, with holes of the same quality. The study is
conducted over three main life cycle phases:-production, use and end-oflife (EOL) phases. The system
includes all elements necessary to drill the crankshafts: the milling machine, the lubricant system and
all the machines to process it before, when and after the drilling operation, the drill and the drill head,
the chip system and all the machines to treat them until recycling. The production phase deals with the
processes to obtain every element of the system. It includes the obtaining of the raw materials, the
energy consumed to process them and the transportation needed to produce the 5 axes milling machine,
the drilling heads, the twist drills and the coolant. The transportation of each element from the
manufacturer to the crankshaft production site is also included. The use phase includes the energy
consumption of the milling machine when processing and the energy consumed by the additional
machines that are necessary for the treatment of the soiled chips: chip crusher, spinner, centrifuge and
washing machine. The EOL phase addresses the transport of waste (chips, twist drills, drill heads and
coolant) from the production site to their recycling sites. LCA is made using SimaPro software. Each
element included in the boundaries of the study has been decomposed in subsystems, and each
subsystem in components. For each component, the weight (or volume) of material has been associated
from the database of the software, as well as the manufacturing processes that are required.
RESULTS
The comparison carried out between TD and SVD, using SimaPro, of the relative weight of the
environmental impacts of these two processes, according to 10 indicators:- Abiotic depletion,
Acidification, Eutrophication, global warming, Ozone layer, Human toxicity, Fresh water aquatic
ecotox, Marine aquatic eco-toxicity, Terrestrial eco-toxicity, photochemical oxidation. The results
shows that the environmental impacts created by SVD is much lesser than that of TD.TD uses more
energy for the treatment of soiled chips, whereas SVD the energy consumption in the use phase is the
major consumer of energy. Comparing these two graphs we can find that the major contributors of
environmental impacts are the coolants used during traditional drilling. They contribute to about 85%
of the environmental impacts. Abiotic depletion refers to the degradation of the non-living chemical
and physical factors in the environment. Abiotic factors can be classified as light, water, atmospheric
gases and soil. Acidification is caused due to excess protons present which will affect the pH of either
the soil or oceanic environment. Eutrophication is the ecosystems response to the addition of artificial
or natural substances such as nitrates and phosphates. The waste produced from a machining process
could also include that kind of waste, these waste when in contact with lakes or rivers leads to
eutrophication. Global warming is the rise in the average temperature of earth’s atmosphere and oceans
mainly due to the presence of increased concentration of greenhouse gases. Ozone layer depletion is
also caused due to presence of CFCs and other contributory substances referred to as ozone depleting
substances mainly UV light. Human toxicity refers to the contents which causes harmful effects to
humans, the harmful waste materials and dusts produced during machining processes also contains
wastes that are harmful to humans. Fresh water ecotox refers to the harmful effects created to the fresh
water aquatic environment due to the dumping of waste produced during machining affecting that
ecosystem. Terrestrial ecotox means the harmful effects created in the terrestrial eco system due to the
waste formed during machining. Photo chemical oxidation is the oxidisation process to produce harmful
elements that are harmful to environment when the ultra violet rays react to that substrate.
5.1 Environmental impacts of td during its life cycle
The figure shows the relative weight of the contributors to the environmental impacts, on a scale of
100%. It can be seen that the main contributors are the energy required for the treatment of soiled chips
(red part) and the use of consumables (grey part). The other minor contributors are the energy
consumption during the use phase (yellow part) and the production of the milling machine (blue part).
Furthermore, among the consumables parts, it was noted that it is the production and EO-L of the
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coolant that generate at least 85% of the environmental impacts (the production and E-O-L of the twist
drills and drill heads generating the remaining impacts)
CONCLUSIONS
The use of coolant in TD generates at least 90% of the environmental impacts during the drilling
operation. The environmental impacts of Self Vibratory Drilling are significantly less than those of
Traditional Drilling. The studies conducted on self-vibratory drilling (SVD) has led to the design of a
drilling head compatible with the existing tools and machines, and that does not require additional
energy. It is feasible in a very near future to increase the lifespan of twist drills, by optimizing the
geometry and the material of the tools. Research in dry machining has led to the following achievements
such as an under cooling system, an internal cooling by a vapourisation system, cryogenic systems,
thermo cooling systems. Another approach is to improve the properties of tool material by making them
more refractory or generate less heat during machining. There has been a continuous development in
the field of cutting tool materials starting with HSS, cobalt alloys, cemented tungsten carbide, coated
carbides and coated HSS, cubic boron nitride and diamond. The need for machining with increasingly
higher cutting speeds and also to machine difficult to machine materials are imposing pressure for the
development of new tool materials. As a result newer tool materials such as ceramics and also different
types of coatings on the tool materials will address the problems in dry machining to some extent.