19-06-2014, 03:11 PM
UN-CONVENTIONAL MACHINING PROCESSES
[attachment=65070]
INTRODUCTION
Machining process in which the tool does not makes the contact with the workpiece is known as Unconventional Machining process. It mainly consists following types of machining process.
Electrochemical Machining.
Electric discharge Machining.
Laser beam machining.
Electric beam machining.
Water jet & Abrasive jet machining.
Ultrasonic machining.
THE REQUIREMENTS THAT LEAD TO THE DEVELOPMENT OF UNCONVENTIONAL MACHINING
Very high hardness and strength of the material. (above 400 HB.)
The work piece is tool flexible to support the cutting or grinding forces.
The shape of the part is complex, such as internal and external profiles, or small diameter holes.
Surface finish or tolerance better than those obtainable by conventional process.
Temperature rise or residual stress in the work piece are undesirable.
WATER JET MACHINING (WJM)
Water jet acts like a saw and cuts a narrow groove in the material.
Pressure level of the jet is about 400MPa.
Advantages
No heat produced
Cut can be started anywhere without the need for predrilled holes
Burr produced is minimum
Environmentally safe and friendly manufacturing.
Application – used for cutting composites, plastics, fabrics, rubber, wood products etc. Also used in food processing industry.
ABRASIVE JET MACHINING (AJM)
In AJM a high velocity jet of dry air, nitrogen or CO2 containing abrasive particles is aimed at the work piece.
The impact of the particles produce sufficient force to cut small hole or slots, trimming and removing oxides and other surface films.
ELECTRICAL DISCHARGE MACHINING (EDM)
Based on erosion of metals by spark discharges.
EDM system consist of a tool (electrode) and work piece, connected to a dc power supply and placed in a dielectric fluid.
When potential difference between tool and work piece is high, a transient spark discharges through the fluid, removing a small amount of metal from the work piece surface.
This process is repeated with capacitor discharge rates of 50-500 kHz.
Dielectric fluid – mineral oils, kerosene, distilled and deionized water etc.
ULTRASONIC MACHINING (UM)
In UM the tip of the tool vibrates at low amplitude and at high frequency. This vibration transmits a high velocity to fine abrasive grains between tool and the surface of the work piece.
Material removed by erosion with abrasive particles.
The abrasive grains are usually boron carbides.
This technique is used to cut hard and brittle materials like ceramics, carbides, glass, precious stones and hardened steel.
ELECTRO CHEMICAL MACHINING
Reverse of electroplating.
An electrolyte acts as a current carrier and high electrolyte movement in the tool-work-piece gap washes metal ions away from the work piece (anode) before they have a chance to plate on to the tool (cathode).
Tool – generally made of bronze, copper, brass or stainless steel.
Electrolyte – salt solutions like sodium chloride or sodium nitrate mixed in water.
Power – DC supply of 5-25 V.
ELCTRON BEAM MACHINING (EBM)
Similar to LBM except laser beam is replaced by high velocity electrons.
When electron beam strikes the work piece surface, heat is produced and metal is vaporized.
Surface finish achieved is better than LBM.
Used for very accurate cutting of a wide variety of metals.
LASER BEAM MACHINING (LBM)
In LBM laser is focused and the work piece which melts and evaporates portions of the work piece.
Low reflectivity and thermal conductivity of the work piece surface, and low specific heat and latent heat of melting and evaporation – increases process efficiency.
Application - holes with depth-to-diameter ratios of 50 to 1 can be drilled. e.g. bleeder holes for fuel-pump covers, lubrication holes in transmission hubs
ADVANTAGES
A good surface finish can be eaisly obtained.
Complex shapes are produced easily that would be difficult to produce with conventional tool.
Extremely hard material to very close tolerence.
Very fine holes can be easily drilled.
DISADVANTAGES
The slow rate of material removal.
Additional time and cost requires.
Over cut is formed.
Excessive tool wear occures.
APPLICATIONS
Used for the machining of comlex workpieces.
Used for the flexible workpieces.
Used to produce very fine holes .
To produce the product of very high tolerence.
[attachment=65070]
INTRODUCTION
Machining process in which the tool does not makes the contact with the workpiece is known as Unconventional Machining process. It mainly consists following types of machining process.
Electrochemical Machining.
Electric discharge Machining.
Laser beam machining.
Electric beam machining.
Water jet & Abrasive jet machining.
Ultrasonic machining.
THE REQUIREMENTS THAT LEAD TO THE DEVELOPMENT OF UNCONVENTIONAL MACHINING
Very high hardness and strength of the material. (above 400 HB.)
The work piece is tool flexible to support the cutting or grinding forces.
The shape of the part is complex, such as internal and external profiles, or small diameter holes.
Surface finish or tolerance better than those obtainable by conventional process.
Temperature rise or residual stress in the work piece are undesirable.
WATER JET MACHINING (WJM)
Water jet acts like a saw and cuts a narrow groove in the material.
Pressure level of the jet is about 400MPa.
Advantages
No heat produced
Cut can be started anywhere without the need for predrilled holes
Burr produced is minimum
Environmentally safe and friendly manufacturing.
Application – used for cutting composites, plastics, fabrics, rubber, wood products etc. Also used in food processing industry.
ABRASIVE JET MACHINING (AJM)
In AJM a high velocity jet of dry air, nitrogen or CO2 containing abrasive particles is aimed at the work piece.
The impact of the particles produce sufficient force to cut small hole or slots, trimming and removing oxides and other surface films.
ELECTRICAL DISCHARGE MACHINING (EDM)
Based on erosion of metals by spark discharges.
EDM system consist of a tool (electrode) and work piece, connected to a dc power supply and placed in a dielectric fluid.
When potential difference between tool and work piece is high, a transient spark discharges through the fluid, removing a small amount of metal from the work piece surface.
This process is repeated with capacitor discharge rates of 50-500 kHz.
Dielectric fluid – mineral oils, kerosene, distilled and deionized water etc.
ULTRASONIC MACHINING (UM)
In UM the tip of the tool vibrates at low amplitude and at high frequency. This vibration transmits a high velocity to fine abrasive grains between tool and the surface of the work piece.
Material removed by erosion with abrasive particles.
The abrasive grains are usually boron carbides.
This technique is used to cut hard and brittle materials like ceramics, carbides, glass, precious stones and hardened steel.
ELECTRO CHEMICAL MACHINING
Reverse of electroplating.
An electrolyte acts as a current carrier and high electrolyte movement in the tool-work-piece gap washes metal ions away from the work piece (anode) before they have a chance to plate on to the tool (cathode).
Tool – generally made of bronze, copper, brass or stainless steel.
Electrolyte – salt solutions like sodium chloride or sodium nitrate mixed in water.
Power – DC supply of 5-25 V.
ELCTRON BEAM MACHINING (EBM)
Similar to LBM except laser beam is replaced by high velocity electrons.
When electron beam strikes the work piece surface, heat is produced and metal is vaporized.
Surface finish achieved is better than LBM.
Used for very accurate cutting of a wide variety of metals.
LASER BEAM MACHINING (LBM)
In LBM laser is focused and the work piece which melts and evaporates portions of the work piece.
Low reflectivity and thermal conductivity of the work piece surface, and low specific heat and latent heat of melting and evaporation – increases process efficiency.
Application - holes with depth-to-diameter ratios of 50 to 1 can be drilled. e.g. bleeder holes for fuel-pump covers, lubrication holes in transmission hubs
ADVANTAGES
A good surface finish can be eaisly obtained.
Complex shapes are produced easily that would be difficult to produce with conventional tool.
Extremely hard material to very close tolerence.
Very fine holes can be easily drilled.
DISADVANTAGES
The slow rate of material removal.
Additional time and cost requires.
Over cut is formed.
Excessive tool wear occures.
APPLICATIONS
Used for the machining of comlex workpieces.
Used for the flexible workpieces.
Used to produce very fine holes .
To produce the product of very high tolerence.