ME 251: Topic 14 - Nontraditional Machining

These are the advantages of EDM processes

- Applicable to all materials that are good electrical conductors - Hardness, toughness, or brittleness of the material imposes no limitations - Fragile and delicate parts can be made, as well as complex geometries

These are the advantages of using nontraditional machining processes, all of which stem from the fact that little to no mechanical force is used during these processes

- Capable of making complex, delicate, and very small (<<1mm) features - Tight tolerances - Often very good surface finish - Little or no burring or residual stress - Materials with high strength or hardness can be machined (since we are not relying on force to shape the material)

These are the advantages of chemical machining

- Induces no stress or cold working in the workpiece - Can be applied to almost any material - Large areas can be etched simultaneously - Can be applied to virtually unlimited shapes - Possible to make thin sections and very small (<1 micrometer) features

These are the disadvantages of electrochemical machining

- Initial tooling can be expensive (biggest problem) - Environmentally harmful byproducts - Control of electrolyte flow can be difficult - Current densities tend to concentrate at sharp edges or features (causing extra material removal near corners) - Workpiece material must be electrically conductive

These are the disadvantages of using nontraditional machining processes

- NTM processes are typically slower and often require more power consumption - Expensive

These are the disadvantages of chemical machining

- Requires the handling of dangerous chemicals - Disposal of potentially harmful byproducts - Material removal rate is slow compared to other traditional and NTM processes

These are the disadvantages of EDM processes

- Slow, expensive compared to conventional machining - Produces a hard recast surface (vaporized material re-solidifies) - Surface may contain fine cracks caused by thermal stress - Fumes can be toxic - Tool wear

These are the advantages of electrochemical machining

- Well suited for the machining of complex-two dimensional shapes - Delicate parts may be made - Poorly machinable materials may be processed (even very strong, brittle, or tough materials) - Little to no tool wear

Etchant

A caustic(corrosive)/acidic chemical that will dissolve the workpiece material

1. Cool the tool and workpiece 2. Flush away debris

Besides becoming locally ionized to help machine the workpiece, the dielectric used in EDM processes also serves to do these things

specificity

If an etchant has a high ___________, it will dissolve the workpiece much faster than it dissolves the masking material (this is what we want)

Metal removal rate

In EDM processes, this parameter measures the degree of sparking that occurs

1. High Hardness 2. Friability (ability for something to break or chip into smaller, sharp pieces; opposite of ductility)

These are desirable properties for an abrasive used in mechanical NTM to have

1. Chemical 2. Electrochemical 3. Thermal 4. Mechanical

These are the four basic groups of material removal that use NTM processes

Ceramics such as: - Aluminum Oxide - Diamond - Cubic Boron Nitride - Silicon Carbide

These are typical abrasives that are used

Nontraditional Machining Processes (NTM)

These processes remove material using something other than mechanical cutting/scraping

Sinker EDM

This EDM process can make 3-D geometry and involves submerging the tool and workpiece in a dielectric fluid; the tool would be made of a material that is easy to machine, while the workpiece would be made of a material that would be harder to machine using traditional processes

Wire EDM

This EDM process is usually limited to making 2-D geometry and involves reels that release and take-up the tool as needed

Chemical Machining Processes

This NTM process involves material being removed from a workpiece by exposing it to a chemical etchant; a chemical reaction occurs everywhere the etchant contacts the workpiece

Electrochemical Machining Process

This NTM process removes material by anodic dissolution with a rapidly flowing electrolyte; the tool is the cathode; the workpiece is the anode; the tool and workpiece are separated by an electrolyte, which helps sweep away by-products of the reaction

Thermal Machining: Electrical Discharge Machining (EDM)

This NTM process removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap; the gap is filled by a dielectric (material that is generally an electrical insulator) fluid which becomes locally ionized; we can control where the sparks are created to machine the metal by putting the tool and workpiece close together at desirable locations

Masking Material (Cut-and-Peel)

This chemical machining process involve covering the workpiece in a masking layer and then submerging it in the etchant so that only the exposed area of the workpiece gets dissolved away

Gel Milling

This chemical machining process involves using a gel-type etchant and placing it on the specific location where you want the workpiece to be machined

MRR = C*I/T where C is a constant, I is current, and T is the melting temperature

This equation governs the metal removal rate in an EDM process

Photopatterning

This is a type of masking material chemical machining process that can make masking layers with <1 micrometer size features (makes geometry for electrical circuits)

Thermal Deburring

This thermal machining process is used to remove burrs and fins by exposing the workpiece to hot corrosive gases for a short period of time; technically a "thermo-chemical" process; this process can remove burrs or fins from almost any material but is especially effective with materials of low thermal conductivity (limits thickness of affected area)

Ion Beam Machining (IBM) or Focused Ion Beam (FIB)

This thermal machining process uses a beam of charged ions (usually gallium)

Laser-Beam Machining (LBM)

This thermal machining process uses a beam of coherent light

Electron Beam Machining (EBM)

This thermal machining process uses a beam of high-energy electrons

Plasma Arc Cutting (PAC)

This thermal machining process uses a superheated stream of electrically ionized gas (plasma) to melt and remove material; it can be used on exotic materials at high machining rates; the material being cut must be electrically conductive

Thermal Machining

This type of NTM process uses focused, high-energy beams to melt, vaporize, or chemically ablate (remove) materials

Abrasive Waterjet Cutting (AWC)

This type of mechanical NTM involves abrasives being added to a waterjet to improve the efficiency

Abrasive Jet Cutting (AJC)

This type of mechanical NTM involves abrasives being mixed in a high velocity air stream at 1000 ft/s

Ultrasonic Machining (USM)

This type of mechanical NTM involves abrasives being mixed in a slurry and ultrasonic transducers providing mechanical agitation to remove the material; the tool and the workpiece never come into contact; this process is used for glass cutting and other brittle material cutting

Waterjet Cutting (WJC)

This type of mechanical NTM involves concentrated water at 60,000 psi and 3000 ft/s being used to erode a material; this process is limited to softer materials