Recent trends in manufacturing. Dry Machining

DRY MACHINING

Jadhav Swapnil Rajan

Department Of Mechanical Engineering

Lokmanya Tilak College of engineering

Navi Mumbai, India

Abstract:

Machining process is a metal cutting operation by which finished surface of desired shape and dimensions is obtained by separating a layer from the parent work piece by pressing a wedge shape device called cutting tool to the work piece. Manufacturers all over the world are trying to discover new methods to eliminate the use ofcutting fluids. According to studies carried out the cost of the production is spent in purchase, storage, handling, utilizing and safe disposal of the fluid.

In recent years large amount of research has taken place to improve productivity in machining. The cost of using coolant in machining industry world-wide is very high. Through a literature survey, it costs multi-billion Dollars for coolant acquisition and disposition in industrialized countries. Furthermore, chemical substances contained in coolant are very harmful to environment and machine shop workers. Dry machining is inevitably the future trend in machining industry. In order to help dry machining methods be smoothly adapted by the industry, this paper provides an information model for cost and process of dry machining.

Key Words

Safe Disposal Of the fluid, Formal Wet Machining, Formal Wet Machining, Dry machining Challenge, Technologies

Introduction of Wet Machining:

Formal wet machining process involves use of cutting fluid.

The Function of wet machining as follows:

- To dissipate the heat generated due to plastic deformation of the metal during machining.
- To cool the tool for increasing the tool life.
- To cool the work for preventing thermal distortion of the work.
- To lubricate and reduce friction and so on

But, the use of metalworking fluids in manufacturing processes is viewed as undesirable for both economic and environmental reasons.

Environmental & Financial Effects of Machining:

Nowadays, coolant has to be used in machining some metals which are without coolant; they are extremely difficult to be machined. Costs of coolant usage and disposal are significant and keep increasing as environmental the number and extensiveness of protection laws and regulations increase .The coolant used by wet machining cause’s serious health problems to machine shop workers. Especially, the extreme pressure agent in coolant usually contains chlorinated paraffin, which is transformed into dioxin by the heat and high temperature generated by the cutting process. Furthermore, many workers in industrialized countries are being exposed to harmful coolant.

Disadvantages of cutting fluid:

Environmental reasons:

They may also create a mist or smoke those results in an unsafe work environment for the machine operator, particularly when machines have inadequate shielding or when shops have poor ventilation systems. They are usually limited to low temperature, low-speed operations. The oily film left on the work piece makes cleaning more difficult, often requiring the use of cleaning solvents. A number of health and safety concerns, such as misting and dermatitis, also exist with the use of synthetics in the shop.

Economical Reasons:

The cost of using coolant in machining industry world-wide is very high. Through a literature survey, it costs multi-billion Dollars for coolant acquisition and disposition in industrialized countries.

Concept of Dry Machining:

Dry Machining is also a process of metal removal but it does not involve the use of wet cutting fluids that are hazardous to environment and also cost sufficiently high. The reason for this seemingly counterintuitive trend is that the machining zone becomes very hot, often more than 1,000°C, especially when cutting at high speed s and in hard materials.

Both ordinary tools and coated tools are used in dry machining research and development activities. Ordinary high speed steel tools, aluminum ceramic tools, Cubic Boron Nitride (CBN), and ceramic can be used in machining various kinds of materials without coolant presence. Coating tools usually have longer tool life than non coated tools if coating is done properly to be effective. Coating provides insulation and lubrication in cutting. Materials used for coating cutting tools include TiAlN (Titanium Aluminum Nitride), TiN, and diamond.

Diamond coated tools generally outperform other coated tools. Recently, multilayered coating tools have also been demonstrated to provide multiple functions. One layer is several nanometers thick. Each layer provides a specific function, e.g., heat insulation, anti wear, or lubrication. These three functions are the major functions provided by coated materials Dry machining processes have been applied to cut several types of materials, from soft to hard, with different tools. CBN and ceramic tools can cut cast iron dry, coated tools (TiN coated) should be used for dry cutting steel to avoid flutes jammed by chips, especially in the case of drilling. In general, it is difficult to cut super alloys and titanium without coolant. High speed, low cutting depth, cryogenic machining is the trend for cutting hard metals

Because of the complexity nature of dry machining, it is necessary to develop new software tools to help manufacturing engineers plan the dry machining process based on product design. Information modeling of the process is the first step towards software and databases development.

The Dry-Machining Challenge:

Metalworking is composed of a number of different machining operations that place different requirements on the lubricant. Other parameters that must be considered are the alloy of metal being machined, the machine tool and the cutting tool used in the process.

“Open-faced operations such as milling and boring can be effectively run dry.” The resulting chips can be easily moved away from the tool/work piece interface. In these cases, there is not as great a need for lubricity, and the heat generated can be managed. In contrast, closed-face machining operations such as drilling and tapping cannot be efficiently run dry because the metal chip remains in close proximity to the tool/work piece interface. This possibility increases the prospects of chips damaging the tool and the work piece surface because there is no mechanism in place for their removal.

Techniques to improve dry machining:

- Tool Material
- Tool Coating
- Chip removal using air spindle

Tool Material:

Abbildung in dieser Leseprobe nicht enthalten

In the context ofmachining, acutting tool is any tool that is used to remove material from the work piece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, planning and similar operations, and remove material by means of one cutting edge. Milling and

Drilling tools are often multipoint tools. Grinding tools are also multipoint tools. Each grain of abrasive functions as a microscopic single-point cutting edge, and shears a tiny chip.

Cutting tools must be made of a materialharderthan the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the work piece without the rest of the tool dragging on the work piece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life, all of the above must be optimized, plus the speedsat which the tool is run.

Tool Coating:

Abbildung in dieser Leseprobe nicht enthalten

As rates of metal removal have increased, so has the need for heat resistant Cutting tools. The result has been a progression from high-speed steels to Carbide, and on to ceramics and other super hard materials.

Developed around 1900, high-speed steels cut four times faster than the carbon Steels they replaced. There are over 30 grades of high-speed steel, in three Main categories: tungsten, molybdenum, and molybdenum-cobalt based grades. Since The 1960s the development of powdered metal high-speed steel has allowed the Production of near-net shaped cutting tools, such as drills, milling cutters and Form tools.

The use of coatings, particularly titanium nitride, allows high-speed steel tools to cut faster and last longer.

Titanium nitride provides a High surface hardness resists corrosion, and it minimizes friction.

In industry today, carbide tools have replaced high-speed steels in most Applications. These carbide and coated carbide tools cut about 3 to 5 times Faster than high-speed steels. Cemented carbide is a powder metal product consisting of fine carbide particles cemented together with a binder of cobalt.

The major categories of hard carbide include tungsten carbide, titanium carbide, Tantalum carbide and niobium carbide. Each type of carbide affects the cutting Tool’s characteristics differently. For example, higher tungsten content Increases wear resistance, but reduce tool strength. A higher percentage of Cobalt binder increases strength, but lowers the wear resistance.

Chip removal using Air spindle:

Abbildung in dieser Leseprobe nicht enthalten

As the Machine Spindle Turns, the blades deploy to provide high volume air cleaning power.

- In-process cleaning without stopping production.
- Saves expensive compressed air.
- No more dripping coolant and flying chips from conventional air hose blasts.
- Less spindle downtimefor cleaning results inincreased profits.
- A quieter workplace environment.

Technologies in Dry Machining:

1.Removal of heat
2.Chip handling in dry machining
3.Lubrication in dry machining

Advantages of dry machining:

- Complete elimination of harmful cutting fluid.
- It Eliminates Cost involved in purchase, storage, handling, utilizing and safe disposal of the fluid.
- High cutting speeds can be achieved with improved surface finish.
- Reduction in overall production time and improved working condition.

Limitations of Dry Machining:

While the technology to carry out dry machining has improved, metalworking fluid is needed to ensure that higher speeds and feeds can be used and to ensure that the surface finish of work pieces meets expectations. Hun sicker revealed that Caterpillar has tried dry machining in a number of machining operations during the past 20 years. The new tool coatings have been helpful but still the problem exists that machining cannot be done dry at the rate needed to achieve the productivity found with using metalworking fluids.

In Dry machining there might be chances of carrying away of chips which might be cause harm to operators. For avoiding this telescoping covers, enclosure, seals, and dust collectors are also required to protect the operator from any dust that might get in air. This causes in increased cost.

Dry Machining Future:

While dry and near-dry machining will not, in the near future, replace wet machining, these two techniques will provide cost-effective alternatives in niche applications. One large OEM has been developing techniques to effectively dry machine and is close to moving this technology from R&D onto the shop floor. The function of the metalworking fluid when used with coated tooling may also change, as was described by Hun sicker. Traditional thinking dictates that heavy-duty soluble oil formulated with extreme pressure additives be used in a high-speed turning application. However, when the operation was conducted, Hun sicker found that the soluble oil stripped the coating from the cutting tool. Caterpillar determined that use of a synthetic metalworking fluid produced superior performance. The main role of the metalworking Fluid in this case was to efficiently remove the heat generated.

Conclusion:

In this a brief review of dry machining is presented. Dry Machining is defined as the machining without the use of cutting fluid.

Sometimes, the dry machining can be employed without any additional arrangement of cooling such as in high speed machining. While sometimes additional arrangement for cooling the tool is employed. The additional arrangement does not pose any environmental hazard.

Some self-lubricating tools are being used in dry machining. For better chip disposal in dry machining, the cutting tool and machine tool require some modification. This is essential for getting the optimum performance from dry machining.

References:

1 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5824980/

2 Machining and Machine Tools by A. B. Chattopadhyay (Wiley).

3 Manufacturing Process for Engineering Materials by S. Kalpakjain and S. Schmid (Pearson Education India).

4 DeGarmo’s Materials and Processes in Manufacturing by J. T. Black and R. A. Kohser (Wiley).

5 http://www.difference.minaprem.com/machining/difference-between-dry-machining-and-wet-machining/

6 https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=821121

7 https://www.theengineer.co.uk/the-benefits-of-dry-machining/

8 https://www.theengineer.co.uk/the-benefits-of-dry-machining/

[...]