1. Chapter 28: Nontraditional Manufacturing Processes
DeGarmo’s Materials and Processes in Manufacturing

2. 28.1 Introduction
Non-traditional machining (NTM) processes have several advantages
Complex geometries are possible
Extreme surface finish
Tight tolerances
Delicate components
Little or no burring or residual stresses
Brittle materials with high hardness can be machined
Microelectronic or integrated circuits are possible to mass produce

3. NTM Processes
Four basic groups of material removal using NTM processes
Chemical
Electrochemical
Thermal
Mechanical

5. Disadvantages of Machining Processes
Machining processes that involve chip formation have a number of limitations
Large amounts of energy
Unwanted distortion
Residual stresses
Burrs
Delicate or complex geometries may be difficult or impossible

6. Conventional End Milling vs. NTM
Typical machining parameters
Feed rate
Surface finish
Dimensional accuracy
Workpiece/feature size
NTM processes typically have lower feed rates and require more power consumption
The feed rate in NTM is independent of the material being processed

7. 28.2 Chemical Machining Processes
Typically involves metals, but ceramics and glasses may be etched
Material is removed from a workpiece by selectively exposing it to a chemical reagant or etchant
Gel milling- gel is applied to the workpiece
Maskant- selected areas are covered and the remaining surfaces are exposed to the etchant

8. Masking Several different methods
Cut-and-peel
Scribe-and-peel
Screen printing
Etch rates are slow in comparison to other NTM processes
Figure 28-1 Steps required to produce a stepped contour by chemical machining.

9. Defects in Etching If baths are not agitated properly, defects result
Figure 28-2 Typical chemical milling defects: (a) overhang: deep cuts with improper agitation; (b) islands: isolated high spots from dirt, residual maskant, or work material inhomogeneity; (c) dishing: thinning in center due to improper agitation or stacking of parts in tank.
If baths are not agitated properly, defects result

10. Advantages and Disadvantages of Chemical Machining
Process is relatively simple
Does not require highly skilled labor
Induces no stress or cold working in the metal
Can be applied to almost any metal
Large areas
Virtually unlimited shape
Thin sections
Disadvantages
Requires the handling of dangerous chemicals
Disposal of potentially harmful byproducts
Metal removal rate is slow

11. Photochemical Machining
Figure 28-4 Basic steps in photochemical machining (PCM).

12. Design Factors in Chemical Machining
If artwork is used, dimensional variations can occur through size changes in the artwork of phototool film due to temperature and humidity changes
Etch factor (E)- describes the undercutting of the maskant
Areas that are exposed longer will have more metal removed from them
E=U/d
d- depth
U- undercutting
Anisotropy (A)- directionality of the cut, A=d/U

13. Etch Rates

14. 28.3 Electrochemical Machining Process
Electrochemical machining (ECM) removes material by anodic dissolution with a rapidly flowing electrolyte
The tool is the cathode and the workpiece is the electrolyte
Figure 28-6 Schematic diagram of electrochemical machining process (ECM).

16. Electrochemical Processing
Pulsed-current ECM (PECM)
Pulsed on and off for durations of approximately 1ms
Pulsed currents are also used in electrochemical machining (EMM)
Electrochemical polishing is a modification of the ECM process
Much slower penetration rate

17. Other Electrochemical Processing
Electrochemical hole machining
Used to drill small holes with high aspect ratios
Electrostream drilling
High velocity stream of charged acidic, electrolyte
Shaped-tube elecrolytic machining (STEM)
Capable of drilling small holes in difficult to machine materials
Electrochemical grinding (ECG)
Low voltage, high-current variant of ECM

18. Figure 28-8 The shaped-tube electrolytic machining (STEM) cell process is a specialized ECM technique for drilling small holes using a metal tube electrode or metal tube electrode with dielectric coating.

20. Figure 28-9 Equipment setup and electrical circuit for electrochemical grinding.

22. Other Electrochemical Processes
Electrochemical deburring
Electrolysis is accelerated in areas with small interelectrode gaps and prevented in areas with insulation between electrodes
Design factors in electrochemical machining
Current densities tend to concentrate at sharp edges or features
Control of electrolyte flow can be difficult
Parts may have lower fatigue resistance

23. Advantages and Disadvantages of Electrochemical Machining
ECM is well suited for the machining of complex two-dimensional shapes
Delicate parts may be made
Difficult-to machine geometries
Poorly machinable materials may be processed
Little or no tool wear
Disadvantages
Initial tooling can be timely and costly
Environmentally harmful by-products

24. 28.4 Electrical Discharge Machining
Electrical discharge machining (EDM) removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap
The gap is filled by a dielectric fluid, which becomes locally ionized
Two different types of EDM exist based on the shape of the tool electrode
Ram EDM/ sinker EDM
Wire EDM

25. Figure EDM or spark erosion machining of metal, using high-frequency spark discharges in a dielectric, between the shaped tool (cathode) and the work (anode). The table can make X-Y movements.

26. EDM Processes Slow compared to conventional machining
Produce a matte surface
Complex geometries are possible
Often used in tool and die making
Figure Schematic diagram of equipment for wire EDM using a moving wire electrode.

27. EDM Processes
Figure (left) Examples of wire EDM workpieces made on NC machine (Hatachi).
Figure (above) SEM micrograph of EDM surface (right) on top of a ground surface in steel. The spherical nature of debris on the surface is in evidence around the craters (300 x).

29. Figure 28-14 The principles of metal removal for EDM.

30. Considerations for EDM
Graphite is the most widely used tool electrode
The choice of electrode material depends on its machinability and coast as well as the desired MRR, surface finish, and tool wear
The dielectric fluid has four main functions
Electrical insulation
Spark conductor
Flushing medium
Coolant

31. Advantages and Disadvantages of EDM
Applicable to all materials that are fairly good electrical conductors
Hardness, toughness, or brittleness of the material imposes no limitations
Fragile and delicate parts
Disadvantages
Produces a hard recast surface
Surface may contain fine cracks caused by thermal stress
Fumes can be toxic

32. Electron and Ion Machining
Electron beam machining (EBM) is a thermal process that uses a beam of high-energy electrons focused on the workpiece to melt and vaporize a metal
Ion beam machining (IBM) is a nano-scale machining technology used in the microelectronics industry to cleave defective wafers for characterization and failure analysis
Figure Electron-beam machining uses a high-energy electron beam (109 W/in.2)

33. Laser-Beam Machining
Laser-beam machining (LBM) uses an intensely focused coherent stream of light to vaporize or chemically ablate materials
Figure Schematic diagram of a laser-beam machine, a thermal NTM process that can micromachine any material.

35. Plasma Arc Cutting (PAC)
Uses a superheated stream of electrically ionized gas to melt and remove material
The process can be used on almost any conductive material
PAC can be used on exotic materials at high rates
Figure Plasma arc machining or cutting.

36. Thermal Deburring
Used to remove burrs and fins by exposing the workpiece to hot corrosive gases for a short period of time
Thermal deburring can remove burrs or fins from almost any material but is especially effective with materials of low thermal conductivity
Figure Thermochemical machining process for the removal of burrs and fins.