manufacturing course

1. 4. NONTRADITIONAL MACHINING
PROCESSES
By: Kasahun N.
1

2. NONTRADITIONAL MACHINING AND
THERMAL CUTTING PROCESSES
I. Mechanical Energy Processes
II. Electrochemical Machining Processes
III. Thermal Energy Processes
IV. Chemical Machining
2

3. Nontraditional Processes Defined
 A group of processes that remove excess material by various
techniques involving mechanical, thermal, electrical, or
chemical energy (or combinations of these energies) but do
not use a sharp cutting tool in the conventional sense
3

4. Why Nontraditional Processes are Important
 Need to machine newly developed metals and non-metals
with special properties that make them difficult or
impossible to machine by conventional methods
 Need for unusual and/or complex part geometries that
cannot easily be accomplished by conventional machining
 Need to avoid surface damage that often accompanies
conventional machining
4

5. Classification of Nontraditional Processes by
Type of Energy Used
 Mechanical - erosion of work material by a high velocity
stream of abrasives or fluid (or both) is the typical form of
mechanical action
 Electrical - electrochemical energy to remove material
(reverse of electroplating)
 Thermal – thermal energy usually applied to small portion of
work surface, causing that portion to be removed by fusion
and/or vaporization
 Chemical – chemical etchants selectively remove material
from portions of work part, while other portions are
protected by a mask 5

6. I. Mechanical Energy Processes
 Ultrasonic machining
 Water jet cutting
 Abrasive water jet cutting
 Abrasive jet machining
6

7. Ultrasonic Machining (USM)
 Abrasives contained in a slurry are driven at high velocity
against work by a tool vibrating at low amplitude and high
frequency
 Tool oscillation is perpendicular to work surface
 Tool is fed slowly into work
 Shape of tool is formed in part
7

8. Working Principle
 In ultrasonic machining, a tool of desired shape vibrates at
an ultrasonic frequency (19 ~ 25 kHz) with an amplitude of
around 15 – 50 μm over the workpiece.
 Generally the tool is pressed downward with a feed force,
F. Between the tool and workpiece, the machining zone is
flooded with hard abrasive particles generally in the form of a
water based slurry.
 As the tool vibrates over the workpiece, the abrasive
particles act as the indenters and indent both the work
material and the tool.
8

9.  The abrasive particles, as they indent, the work material,
would remove the same, particularly if the work material is
brittle, due to crack initiation, propagation and brittle fracture
of the material.
 Hence, USM is mainly used for machining brittle
materials {which are poor conductors of electricity and thus
cannot be processed by Electrochemical and Electro-
discharge machining
 ch 4USM.mp4
9

10. Advantage of USM
 USM process is a non-thermal, non-chemical, creates no
changes in the microstructures, chemical or physical
properties of the workpiece and offers virtually stress free
machined surfaces.
 The main advantages are;
◦ Any materials can be machined regardless of their
electrical conductivity Especially suitable for machining of
brittle materials
◦ Machined parts by USM possess better surface finish
and higher structural integrity.
◦ USM does not produce thermal, electrical and chemical
abnormal surface 10

11. Some disadvantages of USM
 USM has higher power consumption and lower material-
removal rates than traditional fabrication processes.
 Tool wears fast in USM.
 Machining area and depth is restraint in USM.
11

12. USM Applications
 Hard, brittle work materials such as ceramics, glass, and
carbides
 Also successful on certain metals, such as stainless steel and
titanium
 Shapes include non-round holes, holes along a curved
axis
 “Coining operations” - pattern on tool is imparted to a flat
work surface
12

13. Water Jet Cutting/Machining (WJC/M)
 Uses a fine, high pressure, high velocity stream of water
directed at work surface for cutting
13

14. Working Principle
 Water is pumped at a sufficiently high pressure, 200-400
MPa (2000-4000 bar) using intensifier technology.
 An intensifier works on the simple principle of pressure
amplification using hydraulic cylinders of different cross-
sections.
 When water at such pressure is issued through a suitable
orifice (generally of 0.2- 0.4 mm dia), the potential energy of
water is converted into kinetic energy, yielding a high
velocity jet (1000 m/s).
14

15. WJC/M Applications
 Usually automated by CNC or industrial robots to
manipulate nozzle along desired trajectory
 Used to cut narrow slits in flat stock such as plastic, textiles,
composites, floor tile, carpet, leather, and cardboard
 Not suitable for brittle materials (e.g., glass)
 WJC advantages: no crushing or burning of work surface,
minimum material loss, no environmental pollution, and ease
of automation
15

16. Abrasive Water Jet Cutting/Machining
(AWJC/M)
 When WJC/M is used on metals, abrasive particles must be
added to jet stream usually
 Additional process parameters: abrasive type, grit size,
and flow rate
◦ Abrasives: aluminum oxide, silicon dioxide, and garnet (a
silicate mineral)
◦ Grit sizes range between 60 and 120
◦ Grits added to water stream at about 0.25 kg/min (0.5
lb/min) after it exits nozzle
16

17.  WJC/M and AWJC/M have certain advantageous
characteristics, which helped to achieve significant
penetration into manufacturing industries.
◦ Extremely fast set-up and programming
◦ Very little fixturing for most parts
◦ Machine virtually any 2D shape on any material
◦ Very low side forces during the machining
◦ Almost no heat generated on the part
◦ Machine thick plates
ch 4Fast Extreme Water Jet Cutter Machine Working,
Modern Technology Waterjet Cutting Compilation -
YouTube.mp4
17

18. Abrasive Jet Machining (AJM)
 High velocity stream of gas containing small abrasive
particles
18

19. Working Principle
 In Abrasive Jet Machining (AJM), abrasive particles are
made to impinge on the work material at a high velocity.
 The jet of abrasive particles is carried by carrier gas or air.
 The high velocity stream of abrasive is generated by
converting the pressure energy of the carrier gas or air to
its kinetic energy and hence high velocity jet.
 The nozzle directs the abrasive jet in a controlled manner
onto the work material, so that the distance between the
nozzle and the work piece and the impingement angle
can be set desirably.
19

20.  The high velocity abrasive particles remove the material
by micro-cutting action as well as brittle fracture of the work
material.
 In AJM, generally, the abrasive particles of around 50 μm grit
size would impinge on the work material at velocity of 200
m/s from a nozzle of I.D. of 0.5 mm with a stand off distance
of around 2 mm.
Limitations:
 MRR is rather low (around ~ 15 mm3/min for machining
glass)
 Abrasive particles tend to get embedded particularly if the
work material is ductile
 Tapering occurs due to flaring of the jet 20

21. AJM Application Notes
 Usually performed manually by operator who directs nozzle
 Normally used as a finishing process rather than cutting
process
 Applications: deburring, trimming and deflashing, cleaning,
and polishing
 Work materials: thin flat stock of hard, brittle materials (e.g.,
glass, silicon, mica, ceramics)
21

22. II. Electrochemical Machining Processes
 Electrical energy used in combination with chemical
reactions to remove material
 Reverse of electroplating
 Work material must be a conductor
 Processes:
◦ Electrochemical machining (ECM)
◦ Electrochemical deburring (ECD)
◦ Electrochemical grinding (ECG)
22

23. Electrochemical Machining (ECM)
 Material removal by anodic dissolution, using electrode
(tool) in close proximity to the work but separated by a
rapidly flowing electrolyte
23

24. Electrochemical Deburring (ECD)
 Adaptation of ECM to remove burrs or round sharp
corners on holes in metal parts produced by conventional
through-hole drilling
24

25. Electrochemical Grinding (ECG)
 Special form of ECM in which a grinding wheel with
conductive bond material is used to augment anodic
dissolution of metal part surface
25

26. Working Principle
 During ECM, there will be reactions occurring at the
electrodes i.e. at the anode or workpiece and at the cathode
or the tool along with within the electrolyte.
 Let us take an example of machining of low carbon steel
which is primarily a ferrous alloy mainly containing iron.
 For electrochemical machining of steel, generally a neutral
salt solution of sodium chloride (NaCl) is taken as the
electrolyte.
 The electrolyte and water undergoes ionic dissociation
as shown below as potential difference is applied.
26

27.  As the potential difference is applied between the work piece
(anode) and the tool (cathode), the positive ions move
towards the tool and negative ions move towards the
workpiece.
 Thus the hydrogen ions will take away electrons from the
cathode (tool) and form hydrogen gas as:
 Similarly, the iron atoms will come out of the anode (work
piece) as:
 Within the electrolyte iron ions would combine with
chloride ions to form iron chloride and similarly sodium
ions would combine with hydroxyl ions to form sodium
27

28.  In practice, would form and get precipitated
in the form of sludge.
 In this manner it can be noted that the work piece gets
gradually machined and gets precipitated as the sludge.
 Moreover there is not coating on the tool, only hydrogen gas
evolves at the tool or cathode.
 As the material removal takes place due to atomic level
dissociation, the machined surface is of excellent surface
finish and stress free.
28

29. Schematic diagram of an electrochemical drilling unit
29

30. Advantages of ECM
 The components are not subject to either thermal or
mechanical stress.
 No tool wear during ECM process.
 Fragile parts can be machined easily as there is no stress
involved.
 ECM deburring can debur difficult to access areas of
parts.
 High surface finish (up to 25 μm in) can be achieved by
ECM process.
 Complex geometrical shapes in high-strength materials
particularly in the aerospace industry for the mass production
of turbine blades, jet-engine parts and nozzles can be
30

31.  Deep holes can be made by this process.
Limitations of ECM
 ECM is not suitable to produce sharp square corners or
flat bottoms because of the tendency for the electrolyte to
erode away sharp profiles.
 ECM can be applied to most metals but, due to the high
equipment costs, is usually used primarily for highly
specialised applications.
31

32. III. Thermal Energy Processes
 Very high local temperatures
◦ Material is removed by fusion or vaporization
 Physical and metallurgical damage to the new work
surface
 In some cases, resulting finish is so poor that subsequent
processing is required
32

33. Thermal Energy Processes
 Electric discharge machining
 Electric discharge wire cutting
 Electron beam machining
 Laser beam machining
 Plasma arc machining
33

34. Electric Discharge Processes
 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
 Two main processes:
1. Electric discharge machining
2. Wire electric discharge machining
34

35. Electric discharge machining (EDM): (a) overall setup, and (b)
close-up view of gap, showing discharge and metal removal
ch 4EDM.mp4
Electric Discharge Machining (EDM)
35

36. Working Principle
 The EDM system consists of a shaped tool or wire
electrode, and the part. The part is connected to a power
supply to create a potential difference between the
workpiece and the tool.
 When the potential difference is sufficiently high, a
transient spark discharges through the fluid, removing a
very small amount of metal from the workpiece.
 The dielectric fluid:
1. acts as an insulator until the
potential is sufficiently high,
II. Acts as a flushing medium,
36

37. Process basics
37

38. EDM Applications
 Tooling for many mechanical processes: molds for plastic
injection molding, extrusion dies, wire drawing dies, forging
and heading dies, and sheet metal stamping dies
 Production parts: delicate parts not rigid enough to
withstand conventional cutting forces, hole drilling where hole
axis is at an acute angle to surface, and machining of hard
and exotic metals
38

39. Advantages of EDM
 By this process, materials of any hardness can be
machined;
 No burrs are left in machined surface;
 One of the main advantages of this process is that thin and
fragile/brittle components can be machined without
distortion;
 Complex internal shapes can be machined
39

40. Limitations of EDM
 This process can only be employed in electrically
conductive materials;
 Material removal rate is low and the process overall is
slow compared to conventional machining processes;
 Unwanted erosion and over cutting of material can occur;
 Rough surface finish when at high rates of material
removal.
 Produces slightly tapered holes, specially if blind.
40

41. Wire EDM
 Special form of EDM that uses small diameter wire as
electrode to cut a narrow kerf in work
Electric discharge wire cutting (EDWC), also called wire EDM
41

42. Electron-Beam Machining (EBM)
Working Principle
 A stream of electrons is started by a voltage differential
at the cathode.
 The concave shape of the cathode grid concentrates the
stream through the anode.
42

43.  The anode applies a potential field that accelerates the
electrons.
 The electron stream is then forced through a valve in the
electron beam machine.
 The beam is focused onto the surface of the work
material, heating, melting, and vaporizing the material.
 The entire process occurs in a vacuum chamber because
a collision between an electron and an air molecule causes
the electrons to veer off course.
43

44. Laser Beam Machining (LBM)
 Uses the light energy from a laser to remove material by
vaporization and ablation
44

45.  Laser Concept
◦ Add energy to make electrons “jump” to higher energy
orbit
◦ Electron “relaxes” and moves to equilibrium at ground-
state energy level
◦ Emits a photon in this process (key laser component)
Photon
Emission
Model
45

46. ◦ Two mirrors reflect the photons back and forth and
“excite” more electrons
◦ One mirror is partially reflective to allow some light to
pass through: creates narrow laser beam.
 Laser Beam Machining
◦ Its more precise
◦ Useful with a variety of materials: metals, composites,
plastics, and ceramics
◦ Smooth, clean cuts
◦ Faster process
◦ Decreased heat affected zone
ch 4LBC.mp4
46

47. Advantage of laser cutting
 No limit to cutting path as the laser point can move any
path.
 The process is stress less allowing very fragile materials to
be laser cut without any support.
 Very hard and abrasive material can be cut.
 Sticky materials are also can be cut by this process.
 It is a cost effective and flexible process.
 High accuracy parts can be machined.
 No cutting lubricants required
 No tool wear
 Narrow heat effected zone
47

48. Limitations of laser cutting
 Uneconomic on high volumes compared to stamping
 Limitations on thickness due to taper
 High capital cost
 High maintenance cost
 Assist or cover gas required
48

49. Plasma Arc Cutting (PAC)
 Uses a plasma stream operating at very high temperatures
to cut metal by melting
 Plasma is a state of matter where the gas phase is
energized until atomic electrons are no longer associated
with any particular atomic nucleus.
49

50.  Plasmas are made up of positively charged ions and
unbound electrons.
 Plasma may be produced by either heating a gas until it
ionized or by subjecting it to a strong electromagnetic
field.
 This process is suitable for a wide range of metal
materials, including structural steel, alloy steel, aluminum,
and copper, and can cut through material thicknesses
ranging between 0.5 mm to 180 mm
ch 4PAC.mp4
50

51. IV. Chemical Machining (CHM)
Material removal through contact with a strong chemical
etchant
 Processes include:
◦ Chemical milling
◦ Chemical blanking
◦ Chemical engraving
◦ Photochemical machining
 All utilize the same mechanism of material removal
51

52.  Chemical machining, basically an etching process, is the
oldest nontraditional machining process.
 Material is removed from a surface by chemical dissolution
using chemical reagents, or etchants, such as acids and
alkaline solutions.
 A maskant is applied over areas you don’t want to
machine
◦ Photochemical methods
◦ Apply maskant to entire surface and use laser to cut
 Place the entire part in a chemical bath (acid or alkali
depending upon the metal)
 Control temperature and time of exposure to control
material removal 52