LIST OF FIGUTES 3
LIST OF TABLES 3
1. ELECTRO DISCHARGE MACHINING – EDM 4
1.1 Introduction 4
1.2 History of Electro Discharge Machining Process 5
1.3 Detailed Explanation of how the process works 6
1.4 Uses/applications of the Electro Discharge Machining Process 8
1.4.1 Prototype production 8
1.4.2 Coinage die making 8
1.4.3 Small hole drilling 8
1.4.4 Metal disintegration machining 9
1.5 Examples of products produced by Electro Discharge Machining Process 9
1.6 Advantages of Electro Discharge Machining Process 9
1.7 Limitations of Electro Discharge Machining Process 10
2. 3D PRINTING 10
2.1 Introduction and Definition of 3D Printing 10
2.2 History of 3D printers 11
2.3 Detailed Explanation of how the process works 11
2.4 Methods and technologies of 3D Printing 12
2.4.1 Selective laser sintering (SLS) 13
2.4.2 Fused deposition modelling (FDM) 13
2.4.3 Stereolithography (SLA) 13
2.4.4 PolyJet photopolymer 13
2.4.5 Syringe Extrusion 14
2.5 Applications of 3D printing 14
2.5 1 Medical applications 14
2.5 2 Automobile Industry 14
2.5 3 Applications in Education 14
2.5.4 Rapid prototyping 15
2.5.5 Apparel 15
2.6 Advantages of 3D Printing 15
2.7 Drawbacks of 3D Printing 15
3. ELECTROCHEMICAL MACHINING PROCESSES 16
3.1 Introduction 16
3.2 History of the electrochemical machining processes 16
3.3 The process of electrochemical machining processes 17
3.5 Applications of the electrochemical machining processes 18
3.5 Advantages of electrochemical machining processes 19
3.6 Limitations of electrochemical machining processes 19
REFERENCES 20
LIST OF FIGUTES
Figure 1: Configuration of electro-discharge machining process 4
Figure 2: EDM Machine 5
Figure 3: Spark propagation in EDM machining process 6
Figure 4: detailed representation of EDM process, (Elman, 2001) 7
Figure 5: Schematic diagram of the EDM process with a di-electric tanl 7
Figure 6: Material removal after machining 8
Figure 7: Food printer, (Barnatt , 2013). 11
Figure 8: Technologies for 3D manufacturing 12
Figure 9: Three dimensional human spines 14
Figure 10: Electrochemical machining (ECM) 18
LIST OF TABLES
Electric discharge machining (EDM) is an industrial process in which the required shape is made on a work piece using electrical sparks. The original material is removed from the work piece when the electrode is brought near it through a series of fast and repeated current discharges that occur between two electrodes. The electrode which advances to the work-piece is called the tool electrode while the work-piece end is called the work-piece electrode. The electrodes are connected to a voltage and have a di-electric material between them to regulate the spark (Chandrasekar, 2005).
Figure 1: Configuration of electro-discharge machining process
The intensity of the arc produced depends on a number of factors like the amount of electric voltage, the di-electric material and the separation distance between the two electrodes. The intensity of the electric field of the sparks during electro-discharge machining becomes greater with reduction in the separation distance between the electrodes. When the separation distance between the two electrodes is reduced, the force exerted by the electric field becomes higher than that exerted by the strength of the di-electric material allowing the flow of current between the electrodes (Chandrasekar, 2005).
The process occurs as in the breakdown of a capacitor whereby the material is removed from both electrodes. On stoppage of the flow of current, new di-electric material is allowed to flow into the arc region in order to convey all the debris away from the machined area. This cleans up the area and restores the insulating properties of the di-electric.
Electrical discharge machining (EDM) process is broadly used in the machining of work-pieces with complex geometries and hard materials. The most suitable candidate work-pieces for EDM are work-pieces which cannot be machined using other conventional machining processes.
1.2 History of Electro Discharge Machining Process
The abbreviation EDM stands for Electrical Discharge Machining process. The process was first observed by Joseph Preistly in 1770 when he realized that electrical sparks remove material from the other electrodes during the course of his experiments. He called the phenomenon electro-discharge erosion. It was not until 1940's when the two Russian scientists, Lazarenkos’, learnt how to control the process and enhanced the process for industrial use for machining purposes (Patel & Rathod, 2012).
Figure 2: EDM Machine
The EDM machine tool was first manufactured in 1980 after further enhancements. The diagram of the EDM machine tool is shown in figure 2. The discovery of the tool made it easier to machine complex parts as it was better than traditional machining practices. In the modern world scenario, EDM has become so complicated that it is possible to machine even the hardest materials within the required precision and tolerances.
There are two types of EDM machining operations, sinker EDM and wire-EDM. The Sinker EDM is made up of an electrode and a work-piece both submerged in the cloistering liquid, and both are connected to a power supply. Examples of insulating liquids used include kerosene, oils and other di-electrics. The power supply supplies the potential difference between the two electrodes and a spark is created as the electrode approaches the work-piece leading to the formation of a plasma channel. In wire electrical-discharge machining (WEDM) process, a small wire is provided by the work-piece that remains submerged in a tank of de-ionized water di-electric. It is typically meant for complicated work pieces and it is normally computer-guided.
1.3 Detailed Explanation of how the process works
The principle of operation of EDM is not complicated. The EDM machine tool, as explained above, has a work-piece end, the di-electric material, the electrode end and a connection to the voltage. Following a specified pattern, an electric spark is created when the electrode advances towards the work-piece. The spark visibly re[resents flow of electricity between the two electrodes. The spark reaches high temperatures in the range of 8000 to 12000 degrees Celsius which melts the work-piece material. Controlling the spark leads to formation of the desired shapes. The debris formed are carried away by the di-electric material, leaving a claen machined part (Chandrasekar, 2005).
Figure 3: Spark propagation in EDM machining process
Figure 4: detailed representation of EDM process, (Elman, 2001)
It should be noted that the EDM process of machining occurs without the electrodes coming into contact with each other.
Figure 5: Schematic diagram of the EDM process with a di-electric tanl
Material removal mechanism of EDM process is by the movement of the di-electric material as shown in figure 7.
Figure 6: Material removal after machining
1.4 Uses/applications of the Electro Discharge Machining Process
1.4.1 Prototype production
EDM is widely used in the manufacture of prototypes especially in the mould-making and die industry. It is used in making prototypes in the automobile and aircraft industry and sometimes in the electronics industry where numbers for production are low.
1.4.2 Coinage die making
EDM is broadly applied in the production of dies and for making coins. Negative dies are made through the process and they are stamped on work-pieces for mass production of the desired shapes.
1.4.3 Small hole drilling
Wire EDM is used in making small through holes in the surfaces of work-pieces. For example, the techniques are used in making holes in the leading and trailing ends of turbine blades as one of the design specifications. Small hole EDM processes are used in the production of microscopic orifices in fuel systems.
1.4.4 Metal disintegration machining
Metal disintegrating machining- MDM is used in removing broken tools from the surfaces of work-pieces. This machining operation enables users to remove targeted parts only without affecting the rest of the work-piece. Some of the parts that can break in other work-pieces include studs, bolts, taps and drill bits.
1.5 Examples of products produced by Electro Discharge Machining Process
- The process can successfully machine complex shapes that could otherwise not be machined by conventional methods
- It can machine parts that are extremely hard to high tolerance and precision levels
- It can machine very small work-pieces in which other cutting methods can damage the work-pieces due to extra pressure.
- The work-piece and the electrode do not come into direct contact, which can therefore ensure machining of delicate parts without damage or distortion.
- Excellent surface finishes are achieved
- Very small holes can be drilled
1.7 Limitations of Electro Discharge Machining Process
- The process involves slow material removal rates
- There are high chances of fire hazards as a result of oily di-electrics used
- It takes additional time in creating dies
- Electrode wear hinders the production of sharp corners
- The process consumes a lot of power for each specific activity
- More "overcut" may be formed than not
- The sparks lead to excessive tool wear
- It is not easy to machine insulators without proper re-designing of the EDM tool (Patel & Rathod, 2012).
2. 3D PRINTING
2.1 Introduction and Definition of 3D Printing
3D printing is a machining process in which three dimensional objects of any shape are made with the help of computer aided design software models. This process is achieved through a manufacturing process technique called Additive Manufacturing (AM). Additive Manufacturing is a digital three dimensional design process in which a component or a part is constructed in layers by adding and depositing the desired materials on top of each other vertically until the final form of the work is reached (Barnatt , 2013).
Three dimensional printing can produce prints from materials such as plastics, nylons, metallic materials and other materials which meet the design specifications of the desired product. Other movable three dimensional objects can also be printed by 3D manufacturing process.
Figure 7: Food printer, (Barnatt , 2013).
2.2 History of 3D printers
Additive manufacturing, also called 3D printing is not a novel discovery since it has been in use for some time. However, it took a lot of time since its inception to commercialization and some people do not even know of its existence. The most important dates in the discovery of 3D printing are provided in this section. In 1986, Charles Hull established 3D systems. It is recorded that he designed and developed the first ever 3D printer called the Stereolithography Apparatus. Later in 1988, Scott Crump discovered the Deposition Modelling (FDM) process. After three years, in 1991, Helisys, a manufacturing company, sold the first Laminated Object Manufacturing (LOM) and later in 1992 the first Selective Laser Sintering (SLS) system found its way to the market from DTM manufacturers. Since its inception, 3D printing has revolutionized the process of rapid production of prototypes and further enhancements have hit the modern market (Barnatt , 2013).
2.3 Detailed Explanation of how the process works
The process starts with a virtual design of the object that is needed to be printed in three dimensions. The virtual design is drawn using computer aided design (CAD) file with the help of a 3D modelling program. This program helps in generation of the 3D digital design of the desired object and inputs it in the modelling program ready for printing. Before printing is done, the modelling program helps in dividing the design model into many small horizontal layers for additive manufacturing through addition of the materials (Dougherty, 2012).
On uploading the ready file to the 3D printer, the printer prints the final form of the desired product through building it layer by layer until it is completed. Although the object is made layer by layer, the printer is designed in such a way that it achieves its work without showing any layers.
This manufacturing technology is like building a brick house in which all the bricks are assembled and the house is built layer by layer until it is completed. The main difference with the actual construction of brick houses is that the layers generated in 3D printing are so small for accuracy purposes (Dougherty, 2012). The technology is mostly employed in almost all fields of life, for example in jewellery, automobiles, beauty among others.
Figure 8: Technologies for 3D manufacturing
2.4 Methods and technologies of 3D Printing
Since its inception, 3D printing has grown into many technologies. Some methods employ the melting and softening of the raw materials before it is used in printing of layers while others use liquid materials. There are three main technologies used in 3D printing namely; Selective laser sintering (SLS), fused deposition modeling (FDM), PolyJet photopolymer, Syringe Extrusion and stereolithography (SLA).
2.4.1 Selective laser sintering (SLS)
This technology makes use of high power laser to coalesce small plastic, metallic, glass or ceramic powders into the required three dimensional shapes. The laser does this through selective fusion of materials through scanning of the layers that have been generated by the 3D modelling program. After scanning of the cross-section, the layer then lowers the powder bed and applies a layer of the material according to the design. This process is continued until the desired product is built. All the remaining powder is converted to the support framework of the product.
2.4.2 Fused deposition modelling (FDM)
The Fused Deposition Modelling technology uses a plastic filament that conveys the material to a controlled extrusion nozzle. The material is melted by heating the nozzle and the heated material can be moved in any direction using numerically controlled instruments that are regulated by a computer-aided manufacturing program. The desired product is produced through extrusion of the molten material from the nozzle through formation of small layers.
2.4.3 Stereolithography (SLA)
This technique makes use of a container of molten ultraviolet curable photopolymer resin. It makes use of a laser beam to construct one layer of the form at a time. When the layer is exposed to the ultraviolet laser light, it cures and coagulates the pattern made by the layer, ready for building the next later until all the product is completed.
2.4.4 PolyJet photopolymer
This technology was developed by Objet and it functions just like an inkjet printer. The liquid material is sprayed out in layers and cured by exposure to the ultraviolet light. More layers are formed until the final form is obtained. This technology is very flexible to alow mixing of colours for production of beautiful products.
2.4.5 Syringe Extrusion
Syringe Extrusion uses materials with creamy viscosity in 3D printing. The syringe may need heating in some cases depending on the material being used. Materials like clay, silicone, chocolate and cheese can be used in this process.
2.5 Applications of 3D printing
2.5 1 Medical applications
It is now possible for doctors to print some parts of the human body using 3D printing. The artificial parts are printed using highly specialised laser 3D printers using pre-determined materials. For example, 3D spines have been produced to support patients with spinal injuries.
Figure 9: Three dimensional human spines
2.5 2 Automobile Industry
It is now possible to print automotive spare parts on demand using 3D automobile printing technologies.
2.5 3 Applications in Education
Three dimensional printed works can be used in class demonstrations. It is possible for a teacher to illustrate three dimensions by just printing an object in class.
2.5.4 Rapid prototyping
Rapid prototyping is now even faster with 3D printing. It is possible to generate a prototype of a large machine using 3D printing within a shorter time period.
2.5.5 Apparel
3D printing is now used in making clothe and shoes. Commercial production of three dimensional apparels is ongoing and it has revolutionized the world of attires (Valenti, 2001).
2.6 Advantages of 3D Printing
- The modern 3D printers can handle a variety of materials including plastics, metals, glass and ceramics
- It is possible to print in many colours depending on the customer tastes and for aesthetic purposes.
- 3D printing saves costs since it avoids repeated designs and the associated costs
- It is now possible to design something elsewhere and send it online for printing in another place
- It is possible to have portable manufacturing plants that can move from place to place for printing on demand
2.7 Drawbacks of 3D Printing
- There are many designers online some of which may be substandard.
- Currently, the three dimensional printers take a considerable amount of time in completing a small product.
- The technology does not allow mass manufacturing as each product has to be completed before the next is started.
- The initial cost of setting up 3D printers is currently high (Valenti, 2001).
3. ELECTROCHEMICAL MACHINING PROCESSES
3.1 Introduction
Electrochemical machining (ECM) is a manufacturing technology in which metal surfaces are removed by electrochemical processes. The technology is employed in mass production of products that are hard and very difficult to machine using the existing conventional manufacturing techniques. However, electrochemical machining is limited to conductors. The technique can be used in making small intricate patterns on hard metals. Examples of hard metals machined by ECM method include titanium aluminides, nickel, cobalt and Waspaloy. With this technology, both the internal and external parts of a work-piece can be machined.
The main difference between electrochemical machining and 3d printing discussed in the previous pages is its subtractive property. Instead of adding materials to the work-piece, just like Electro Discharge Machining, it subtracts. It is often called reverse electroplating technique for that reason. The process is similar to Electro Discharge Machining since in both cases, a high current is passed between the electrodes. For electrochemical machining, the electrolyte has a negative charge, the work-piece has a positive charge and a conductive electrolyte is employed. In ECM, there is no tool wear. The cutting tool is directed to the desired path without coming in contact with the work-piece. There are no sparks formed in the cutting process although there are high rates of metal removal with no passage of stresses from the cutting tool to the work-piece (Hocheng, 2013).
3.2 History of the electrochemical machining processes
The use of ECM can be tracked way back to 1929 when W.Gussef performed the first experiment based on the technology. However Anocut Engineering Company only started commercial processes using ECM in 1959. The two Russian scientists B.R. and J.I. Lazarenko also hypothesized the use of electrolysis in removal of metal from work-pieces. The main work in the development of electrochemical machining process was done between 1960 and 1970 especially in development of the gas turbines. However, the progress of ECm was hindered by profound interest in EDM since ECM had lots of dimensional inaccuracies and pollutants.
Today, electrochemical machining is broadly used in production of complicated products such as blades of turbines with a smooth surface finish in hard metals. It is also applied in deburring process whereby it removes projecting metal forms left after complete machining operations have taken place. In essence, it provides smooth curves by eating away metal projections. Deburring using ECM is faster than any other known deburring technique.
3.3 The process of electrochemical machining processes
The term Electro-Chemical Machining is an umbrella word for a variety of electro-chemical processes used in machining. In this method, the materials of work-pieces are eaten away by electrochemical means leading to formation of the required products. This process is used in many fields for the manufacture of parts like in the aviation industry, automotive, manufacture of power systems and medical apparatus. All types of metals can be electrochemically machined. Tool wear does not occur since the tool does not come in contact with the work-piece and there are no mechanical stresses, heat transfers and oxidation of work-piece surfaces.
The electro-chemical machining process works on the basis of electrolysis. The tool acts as the cathode and it is moved towards the anode, that is, the work-piece. The electrolyte is pressurized and injected to the cut areas. The gap can be varied between 80 and 800 micrometres.
Figure 10: Electrochemical machining (ECM)
The work-piece, in this process, represents the anode. The material that is removed is separated from the rest of the electrolyte as the metal hydroxide. Whether the material is hard or soft, machining can be accomplished without interfering with its microstructure (Hocheng, 2013).
3.5 Applications of the electrochemical machining processes
Aerospace Alloys: The process is used in processing alloys since all constituents are cut at the same time regardless of hardness.
High Accuracy & Repeatability: The process is used in the manufacture of intricate products at high accuracies. It is possible to make more than 50, 000 copies of the same product at same tolerances since there is no tool wear.
Surface Quality: ECM produces smooth surface finishes. There is no need for surface inspections
The process is basically applied in:
- Production of die-sinks
- Production of jet engine blades
- Drilling of multiple holes
- Machining of turbine blades
- Machining of jet engine parts
3.5 Advantages of electrochemical machining processes
- Since the tool and the work-piece do not come in contact, there is no need of having a tool with expensive strong and tough alloys. Therefore, cheap tools are used
- The tool wears to a lesser extent as compared to other machining operations.
- Any material of the work-piece can be machined, whether hard, soft or brittle
- It has high accuracies with removal of only the targeted materials
- There is no mechanical stresses or pressures on the cutting tool and the work-piece
- Finishing is accomplished in one pass
- It can be used in deburring of rough edges; therefore machined parts do not need deburring
- It is a fast process with high productivity rates (Groover, 2013).
3.6 Limitations of electrochemical machining processes
- The acidic or alkaline tool may corrode parts of the work-piece or the cutting tool; therefore it is necessary to make wise choices
- The process can only be used for electrically conductive materials
REFERENCES
Barnatt Christopher, 2013. 3D printing: the next industrial revolution .Explaining theFuture.com
Chandrasekar, S. (2005). High-speed micro-electro-discharge machining. Washington, D.C.: United States. Dept. of Energy
Davim, J. (2012). Machining of complex sculptured surfaces. London: Springer.
Dougherty Dale, 2012. MAKE: Ultimate guide to 3D printing, O'Reilly Media
Elman C. Jameson, 2001. Electrical Discharge Machining, Society of Manufacturing Engineers
Groover, Mikell P., 2013. Fundamentals of modern manufacturing: materials, processes, and systems, John Wiley & Sons, Inc.
Hocheng, H., 2013. Advanced analysis of non-traditional machining, Springer
Patel, B., & Rathod, K. (2012). Application of response surface methodology Electro discharge Machining (1. Aufl. ed.). Saarbrücken: LAP LAMBERT Academic Publishing.
Valenti, Michael, 2001. Making the Cut. Mechanical Engineering, American Society of Mechanical Engineers
