The removal of material from a workpiece is referred to as machining. The following are the machining categories.
- Cutting involves the use of single-point or multipoint cutting instruments, each having a distinct geometry.
- Grinding is an example of an abrasive process.
- Nontraditional machining that makes use of electrical, chemical, and optical energy sources.
Traditional vs. Nontraditional
- The primary source of energy :- Traditional: mechanical, and Nontraditional: electrical, chemical, optical
- Primary method of material removal :- Traditional: shearing, and Nontraditional: does not use shearing
Why Nontraditional Machining?
Situations in which standard machining methods are inadequate or cost-effective.
- The workpiece material is very hard, robust, or tough.
- The workpiece is either too flexible to withstand cutting forces or is too difficult to clamp.
- The part form is quite complicated, with internal or exterior profiles as well as tiny perforations.
- Surface polish and tolerance requirements are quite stringent.
- Temperature increases and residual strains are both undesirable or unacceptable.
Ultrasonic Machining (USM)
The tool, which is the negative of the workpiece, vibrates in an abrasive grit slurry at the workpiece surface at low amplitude (0.013 to 0.08 mm) and high frequency (approximately 20 kHz).
The slurry also removes debris from the cutting area. The tool is gradually pushed down, with a constant gap of around 0.1 mm between the tool and the workpiece surface.
Hard, brittle materials such as ceramics, carbides, glass, precious stones, and hardened steels are ideally suited for USM.
Tolerances of 0.0125 mm or greater can be achieved using fine abrasives. Ra ranges from 0.2 to 1.6 μm.
Pros & Cons
Pros:- precision cutting of fragile materials; produces small holes (0.3 mm); does not cause electric, thermal, or chemical damage since the material is removed mechanically.
Cons:- Low material removal rate (usually 0.8 cm3/min); fast tool wear; restricted cutting area and depth.
Water-Jet Machining (WJM)
WJM is a type of micro-erosive process. It operates by pushing a huge amount of water through a tiny hole in the nozzle.
The accelerated water particles’ tremendous pressure hits a tiny region of the workpiece and operates like a saw, cutting a narrow groove in the material.
Pros and Cons
Pros:- There is no need for predrilled holes, there is no heat, there is no workpiece bending (thus it is ideal for flexible materials), there is a little burr, and it is ecologically benign.
Cons:- Material with naturally existing tiny fractures or softer material is restricted.
- Typically used to cut low-strength materials including wood, plastics, rubber, paper, leather, composites, and so forth.
- Preparation of food.
- For materials that cannot resist the high temperatures of other techniques due to stress deformation or metallurgical causes, this approach is ideal.
Abrasive Water-Jet Machining (AWJM)
The water jet contains abrasive particles like silicon carbide, which raises MRR. Metallic materials are able to be sliced. Especially suited to heat-sensitive materials.
Under regulated circumstances, a high-velocity jet of dry air, nitrogen, or carbon dioxide containing abrasive particles is directed towards the workpiece surface.
The gas supply pressure is around 850 kPa (125 psi), and the jet velocity, which is regulated by a valve, may reach 300 m/s.
Material removal:- Cutting speeds vary between 25 -125 mm/min.
Dimensional Tolerances:- Typical range ±2 – ±5 μm.
Surface Finish:- Typical Ra values vary from 0.3 – 2.3 μm
AJM Applications & Limitations
Applications:- Can cut traditionally difficult-to-cut materials such as composites, ceramics, and glass. For materials that cannot withstand high temperatures.
Limitations:- The procedure is costly. Flaring can grow to be quite big. Because of the high maintenance needs, it is not suited for mass manufacturing.
Chemical Machining (CM)
The earliest unconventional machining method is chemical machining, which is essentially an etching procedure. Chemical dissolution removes material off a surface by employing chemical reagents, or etchants, such as acids and alkaline solutions. The workpiece is submerged in an etchant-containing bath. Masking tapes, paints, or polymeric materials are used to mask areas that do not need to be etched. Shallow cavities are created on plates, sheets, forgings, and extrusions during chemical milling to reduce overall weight (e.g., in the aerospace industry). Removal depths of up to 12 mm are possible.
Burr-free etching of printed circuit boards (PCB), ornamental panels, thin sheet-metal stampings, and the fabrication of complicated or tiny forms are all examples of chemical blanking.
Chemical milling: reducing the weight of space launch vehicles.
Pros: minimal setup, maintenance, and tooling costs; tiny, delicate components may be machined; appropriate for limited production runs on complicated designs.
Cons: sluggish (0.025-0.1 mm/min); surface flaws; chemicals might be hazardous to one’s health.
Electrochemical Machining (ECM)
A dc voltage (10-25 v) is supplied across space between an anode workpiece and a pre-shaped cathode tool in ECM. An electrochemical response to the form of the tool dissolves the workpiece. To disperse heat and wash away the dissolved metal, the electrolyte flows at high speeds (10-60 m/s) via the gap (0.1-0.6 mm).
Pros: great form complexity is feasible, as is high MRR, high strength materials, and mirror surface quality.
Cons: workpiece must be electrically conductive; expensive tooling (specialized) and equipment; high power consumption.
Application: Complex cavities in high-strength materials, particularly in the aerospace sector for mass manufacturing of turbine blades.
Electrical Discharge Machining (EDM)
EDM is a thermal erosion technique in which material is melted and evaporated from an electrically conductive workpiece submerged in a liquid dielectric using a power supply to generate a sequence of spark discharges between the tool electrode and the workpiece.
EDM is a high-precision, low-cost manufacturing method.
The EDM system is made up of a shaped tool or a wire electrode, as well as a component. To establish a potential difference between the workpiece and the tool, the component is linked to a power source. When the potential difference is large enough, a transitory spark discharges through the fluid, removing just a tiny quantity of metal off the workpiece.
The dielectric fluid serves as an insulator until the potential is sufficiently high, a flushing medium, and a cooling medium.
MRR:- The flow rate ranges from 2 to 400 mm3/min. High rates result in a rough finish, a melted and recast structure, poor surface integrity, and poor fatigue characteristics.
Dimensional Tolerances:- The function of the material being processed is typically between ±0.005 – ±0.125 mm.
Surface Finish:- Ra varies from 0.05 – 12.5 μm.
In aerospace, mold building, and die casting, it is often utilized to make die cavities, small deep holes, narrow slots, turbine blades, and complex forms.
In certain circumstances, a hard skin or recast layer is formed, which may be undesirable. A heat-affected zone exists underneath the recast layer, which may be softer than the original material.
At low MRR, finishing cuts are required. Produces somewhat tapered holes, particularly when blind.
Laser-Beam Machining (LBM)
Increase the energy to cause electrons to “jump” to a higher energy orbit. The electron “relaxes” and approaches equilibrium at the ground-state energy level. In this process, a photon is emitted (key laser component). The photons are reflected back and forth by two mirrors, which “excite” additional electrons. One mirror is partly reflecting, allowing some light to get through and resulting in a narrow laser beam.
MRR:- The cutting speed can reach 4 m/min. The typical rate of material removal is 5 mm3/min.
Dimensional Tolerance:- Typical ranges from ±0.015 – ±0.125 mm.
Surface Finish:- Ra varies between 0.4 – 6.3 μm.
Applications:- Multiple holes in materials that are both thin and thick. Unusually shaped holes and slots Parts. for prototyping. Hard material trimming, scribing, and engraving Lubrication holes with a small diameter.
Limitations:- Thermal strains, heat impacted zones, recast layer, and thermal dispersion in thin components are all examples of localized thermal stresses. The difficulty of material processing is determined by how close the boiling and melting points of the materials are. The geometry of the hole wall might be uneven. In most cases, inert gas is used to aid in the cutting of combustible materials.