1. Introduction

In recent years, attention has made on achieving comprehensive strategy over sustainable manufacturing due to increased emission of CO2 in environment and waste. This ultimately will improve industry's economy [1]. Machining technology is referring to implement the sustainability, which has potential to improve environmental performance and save money. The problem in implementing sustainability in production companies is due to short-term financial planning. However, long-term strategy is necessary for sustainable manufacturing.

The initiatives for the sustainable development are established at different levels, e.g., UN, OECD and National level, and are well positioned on macro level of production [2] but are lacking in implementation at shop-floor level.

Conventional machining processes using mineral-based cutting fluids tend to increase environmental problems. Attempts are in focus to attain sustainable products and processes that will eliminate the bad effects of mineral-based cutting fluids. Alternative technique of cooling by using liquid nitrogen is in focus to eliminate the adverse effects of mineral oils. The cost of machining is a major element of a mechanical industry. Cutting tools having long tool life are preferred over those with short tool life in order to reduce overall machining cost and increase productivity.

In aerospace industry, the components are usually made from superalloys. These alloys can withstand the high operating temperatures and extreme physical stresses. Out of these alloys, titanium is the most commonly used alloy. Ti-6Al-4V shows good results in application where high strength-to-weight ratio along with excellent corrosion resistance is required. This alloy is used in aircraft turbine engine components, structural parts of aircrafts, aerospace fasteners, high-performance automotive parts, marine applications, medical devices and sports equipment.

Milling is one of the mostly used machining operations in manufacturing industry. The situation becomes very difficult to handle when hard materials are required to go through milling process. The probability of tool wearing and damaging of surface roughness increases when high cutting forces and high temperatures are involved at interface of cutting tool and work material.

2. Sustainable manufacturing

Sustainable Machining for Titanium Alloy Ti-6Al-4V DOI: http://dx.doi.org/10.5772/intechopen.82344

Figure 1.

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Sustainability basic dimensions.

Sustainability is defined as the ability to preserve, to keep or to maintain something. When something is sustainable it means that it is able to be kept and continued [4]. The three dimensions of sustainability (Figure 1) are environmental, social and economic, sometimes adding technology as the fourth one [5]. Initially sustain-

Manufacturing contributes by about 22% of Europe's GDP, while 70% of jobs in Europe are directly related with manufacturing [7]. Energy consumption is a major factor in manufacturing industry which is based on electrical energy and oil. According to the action plan for energy efficiency, industrial production is respon-

Sustainable manufacturing is important for the manufacturing industry as it helps to cope with the increasing environmental regulations, meeting the customer requirements for better environmental performance, lowering the material and energy costs resulting to greener products. Sustainable manufacturing is the creation of products using such processes that minimize the environmental impacts, conserving natural resources and energy, are safe for the communities, employees and customers and are economically sound. It has become a business imperative as companies across the world are facing increased costs of energy and materials coupled with higher expectations of customers, communities and investors.

In sustainable manufacturing, the things are created in such a way (Figure 2) that is economically, environmentally, socially and safety wise feasible for both the manufacturer and user. Greater emphasis is over the environmental issue followed

able development defined by Brundtland is reported in 1987 as 'the way for improving the well-being and quality of life for the present and future generation'.

More precisely it was defined as 'to meet the needs of the present without compromising the ability of future generations to meet their own needs' [6].

sible for about 18% of the total energy consumption of Europe [8].

Much energy is utilized in a machining operation along with the wastage of chips in material removal process. Operational safety and environmental friendliness of any machining process play a vital role in sustainability of process. It is estimated that machining process contributes to the gross domestic product (GDP) of developed countries by about 5% of total the GDP [3].

The present trend is to create new and smaller products of higher quality in a shorter time and at a lower cost. There are many materials, which can be classified as 'difficult-to-machine'. Machining of such materials requires special cutting tools. Cutting parameters affect directly on the surface roughness, tool wear and machining time.

The world has now become energy conscious, and every industry is going to follow the health and safety requirements at all levels. The concept of sustainable manufacturing has now become the key focus, which deals with the economic, social, safety and environmental issues. Proper selection of cutting tool, coolant and process type is important for efficient and economic machining. Alternative solutions of dissipating the heat generated at chip-tool interface and cutting tool materials is in exploration since the last few years. Titanium alloys and other materials used in aerospace industry need special attention for their machining as these are difficult-to-machine materials.

Experimental data shows that cryogenic cooling is more sustainable than dry and conventional cooling process, and it gives the best results for tool life, surface finish of machined part, productivity with least impact on the environment, least energy cost and machining cost.

#### 1.1 Problem related with conventional machining

Difficult-to-machine materials are heat resistant; therefore, in machining of such materials, huge amount of cutting tools and coolants is used. The cost of a machined part mainly involves the cost of tools used, electrical energy and coolant cost.

In conventional methodology, the parts are machined using mineral-based coolants. These coolants have disadvantages in worker's health and environment where it is disposed of. Titanium alloys and other nickel-based alloys are difficult-tomachine, and therefore a number of cutting tools are wasted in their machining increasing the overall cost of the product. Conventionally used coolants have many problems associated with the health of workers and environmental impact.

The problem becomes more critical when machining the difficult-to-machine materials where high temperatures are built at the tool-chip interface. Using of conventional mineral-based coolant to reduce the temperatures and frictions is creating other environmental problems because disposition of these lubricants is not only harmful for human life but also creating issues for aquatic organisms. Social impact of conventional lubricant and coolants is increasing health and safety problems of workers due to exposure to toxic chemicals. The working environments are being polluted increasing both the mist and noise levels. Industrial setups are required to adopt the sustainability principles in order to avoid increasing cost and environmental and safety issues. Alternative coolants are in exploration phase to replace with the conventional mineral-based coolants.
