Machining Processes Part III

• This lecture covers Machining Processes Part III
• Presented by Dr. Rita Palabeyekian and Dr. Amira Eladly

Classification of Negative Manufacturing Processes

• Negative manufacturing processes are classified as conventional, nonconventional, and advanced
• Conventional processes include:
  • Turning
  • Drilling
  • Milling
  • Grinding
• Nonconventional processes include:
  • Ultrasonic M/c
  • Dry Ice Blasting
  • Laser Beam Machining
• Advanced processes include:
  • CNC M/C
  • Robotics

What is Nonconventional Machining?

• Refers to processes that remove excess material without a sharp cutting tool
• Utilizes nontraditional means such as mechanical, electrical, thermal, or chemical energy (or a combination)

Nonconventional Machining Types

• Mechanical processes include:
  • Ultrasonic Machining (USM)
  • Water Jet Machining (WJM)
  • Abrasive Water Jet Machining (AWJM)
  • Abrasive Jet Machining (IJM)
• Electrical processes include:
  • Electrochemical Machining (ECM)
  • Electron Beam Machining (EBM)
• Thermal processes include:
  • Electrical Discharge Machining (EDM)
  • Electron Beam Machining (EBM)
  • Laser Beam Machining (LBM)
  • Ion Beam Machining (IBM)
  • Plasma Beam Machining (PBM)
• Chemical processes include:
  • Chemical Machining (CHM)
  • Photochemical Machining (PCM)

Classification of Nonconventional Machining Processes by Type of Energy Used

• Machining Processes:
  • Ultrasonic Machining (USM)
  • Laser Beam Machining (LBM)
  • Chemical Machining (CHM)
  • Abrasive Water Jet Machining (AWJM)
  • Water Jet Machining (WJM)
• Electrical Processes:
  • Electro-Chemical Machining (ECM)
  • Electro-Chemical Grinding (ECG)
  • Electro Jet Drilling (EJD)
• Thermal Processes:
  • Electric Discharge Machining (EDM)
  • Laser Jet Machining (LJM)
  • Electron Beam Machining (EBM)
  • Electric Discharge Machining (EDM)
  • Laser Jet Machining (LJM)
• Chemical Processes:
  • Chemical Milling (CHM)
  • Photochemical Milling (PCM)

Conventional versus Nonconventional Machining Processes

• Conventional:
  • The cutting tool and workpiece are always in physical contact
  • Results in a relative motion against each other
  • Results in friction and tool wear
  • Material removal rate is limited by the mechanical properties of the work
• Nonconventional:
  • There is no physical contact between the tool and the workpiece
  • Easily deals with difficult-to-cut materials like ceramics, fiber-reinforced materials, carbides, and titanium-based alloys

Why Nonconventional Machining?

• Used when conventional machining processes are not possible, unsatisfactory, or uneconomical
• This includes situations where:
  • The workpiece material is too hard
  • The workpiece shape is complex
  • A high surface finish is required
  • Temperature rise is unacceptable

Nonconventional Machining Using Mechanical Energy

Ultrasonic Machining (USM):

• Erosion of workpiece material by a high velocity stream of abrasives or fluid (or both)
• The workpiece is held in a tank full of slurry that contains abrasive particles
• The slurry is injected into the space between a vibrating tool and stationary workpiece
• Material is abraded away until a mirror image of the tool is cut into the workpiece

The Principle of USM

• A metal tool is given a high frequency, low amplitude oscillation perpendicular to the workpiece
• This transmits a high velocity to fine abrasive particles between the tool and the workpiece
• Particles strike the workpiece, chipping away small particles
• The tool is gradually fed into the workpiece
• "Chips" are carried away from the workpiece by a constant flow of cooled slurry
• The workpiece is abraded into a mirror image of the tool

Applications of USM

• Hard, brittle work materials such as ceramics, glass, and carbides
• Certain metals like stainless steel and titanium
• Used for shapes including non-round holes and holes along a curved axis
• Used for "Coining operations" where the pattern on the tool is imparted to a flat work surface.

Water Jet Machining (WJM)

• Erosion of workpiece material by a high velocity stream of abrasives or fluid (or both)
• WJM is a precision cutting process
• Employs a high-velocity stream of water to erode materials
• When mixed with abrasive particles, it is called Abrasive Water Jet Machining (AWJM)
• It is an environmentally friendly non-conventional machining process used to cut, shape, and machine various materials with high precision

Applications of WJM

• WJM is preferred for cutting soft and easily machinable materials such as thin sheets, foils, wood, non-ferrous metallic alloys, textiles, plastics, polymers, leathers, and even frozen substances
• AWJM is well-suited for machining hard-to-machine materials like thick steel and aluminum plates, reinforced plastics, metal matrix and ceramic matrix composites, layered composites, stones, glass, and others
• High-pressure water jets are used for paint removal, surgery, and cleaning
• AWJM can also perform drilling, pocket milling, turning, and reaming operations

Advantages and Disadvantages of WJM/AWJM

• Advantages:
  • No crushing or burning of work surface
  • No environmental pollution
  • Ease of automation
  • Enables complex cuts in various materials
  • High precision
• Disadvantages:
  • Not suitable for machining extremely thick materials
  • High initial cost of WJM

Nonconventional Machining Using Electrical Energy

• Electrical energy is used in combination with chemical reactions to remove material
• It is a reverse of electroplating
• Work material must be a conductor
• Processes include:
  • Electrochemical Machining (ECM)
  • Electrochemical Deburring (ECD)
  • Electrochemical Grinding (ECG)

Electrochemical Machining (ECM)

• In the ECM process, a negatively-charged (cathode) cutting tool is advanced into a positively-charged (anode) workpiece
• Pressurized electrolyte is injected at a set temperature into the area being cut

Applications of ECM

• Die sinking for irregular shapes and contours for forging dies, plastic molds, and other tools
• Multiple hole drilling, as many holes can be drilled simultaneously with ECM
• For holes that are not round (no rotating drill)
• Deburring to remove burrs and round sharp corners on holes in metal parts produced by conventional drilling

Nonconventional Machining Using Thermal Energy

• Involves very high local temperatures
• Material is removed by fusion or vaporization
• Involves Physical and metallurgical damage to the new work surface
• In some cases, the resulting finish is so poor that subsequent processing is required
• Thermal Energy Processes include:
  • Electric Discharge Machining (EDM)
  • Electric Discharge Wire Cutting (EDWC)
  • Electron Beam Machining (EBM)
  • Laser Beam Machining (LBM)
  • Plasma Arc Machining (PAM)

Electric Discharge Machining (EDM)

• Involves Metal removal by a series of discrete electrical discharges (sparks) causing localized temperatures high enough to melt or vaporize the metal.
• Can be used only on electrically conducting work materials

Applications of EDM

• Tooling for many mechanical processes: molds for plastic injection molding, extrusion dies, wire drawing dies, forging dies, and sheet metal stamping dies
• Production parts:
  • Delicate parts not rigid enough to withstand conventional cutting forces
  • Machining of hard metals

Laser Beam Machining (LBM)

• The source of energy is a laser that generates a highly focused, high-density energy beam

Chemical Machining (CHM)

• Material removal through contact with a strong chemical etchant
• Processes include chemical milling and chemical blanking