three hybrid machining process- ECG, USMEC, ECDG

2. INTRODUCTION

3. WHAT IS HYBRID MANUFACTURING
A hybrid manufacturing process combines two or
more established non-traditional manufacturing
processes into a new combined set-up . The reason
for such a combination and the development of a
hybrid machining process is mainly to make use
of the combined advantages and to avoid or
reduce some adverse effects the constituent
processes produce when they are individually
applied.

4. FLOW DIAGRAM OF HYBRID MACHINING

5. ELECTROCHEMICAL GRINDING
The electrochemical grinding process combines traditional
electrochemical machining and grinding processes to remove
material from a workpiece. A grinding wheel is used as a cutting
tool as a cathode and the workpiece is an anode. During the
process, electrolytic fluid, typically sodium nitrate, is pumped into
the space between the workpiece and the grinding wheel. Other
electrolytes used include sodium hydroxide, sodium carbonate, and
sodium chloride. This electrolytic fluid will cause electrochemical
reactions to occur at the workpiece surface which oxidize the
surface, thereby removing material. As a consequence of the
oxidation which occurs, layers of oxide films will form on the
workpiece surface, and these need to be removed by the grinding
wheel.

6. CONTINUED….

7. ACCURACY AND SURFACE QUALITY
-Traditional grinding removes metal by abrasion, leaving tolerances of
about ±0.003 mm and creating heat and stresses that make grinding thin
stock very difficult. In ECG however a production tolerance of ±0.025 mm
is easily obtainable. Under special circumstances a tolerance of ±0.008 mm
can be achieved. The ability to hold closer tolerances depends upon the
current, electrolyte flow, feed rate, and metallurgy of the workpiece itself.
Accuracies achieved are usually about ±0.125
mm.
-The surface finish produced varies from 0.2 to 0.3 μm depending on the
metal being machined, abrasive grit size and wheel speed and feed rate. For
better surface quality a finish pass at a low voltage of 3 to 5 V and relatively
high speed (250–500 mm/min) is recommended.

8. PROCESS PARAMETERS
1. interelectrode gap-0.025 mm or less.
2. The wheel rotates at a surface speed of 20 to 35 m/s.
3. current ratings are from 50 to 300 A.
4. A gap voltage of 4 to 40 V is applied between the cathodic
grinding wheel and the anodic workpiece.
5. current density of about 120 to 240 A/cm2 is created.
6. The volumetric removal rate (VRR) is typically 1600
mm3/min.

9. ADVANTAGES AND DISADVANTAGES
-One of the key advantages of electrochemical grinding is the
minimal wear that the grinding wheel tool experiences.
- It can be used to machine hard materials
-Higher mrr than ecm and good surface quality
- Both the workpiece and the grinding wheel must be
conductive.
-The electrolytic fluid can cause corrosion at the workpiece
and grinding wheel surfaces.
-Require more experienced personnel to operate the
machinery, which will lead to higher production cost.

10. APPLICATIONS
1. Machining parts made from difficult-to-cut materials, such as
sintered carbides, creep-resisting (Inconel, Nimonic) alloys,
titanium alloys, and metallic composites.
2. Production of tungsten carbide cutting tools, fragile parts, and
thin walled tubes.
3. Producing specimens for metal fatigue and tensile tests.
4. Machining of carbides and a variety of high-strength alloys.
5. Removal of fatigue cracks from steel structures under
seawater.

11. ULTRASONIC-ASSISTED ECM
Ultrasonic machining (USM) produces parts having
better surface quality. However, the material removal
rate and hence the machining productivity is low. On the
other hand ECM has the advantage of achieving high
machining rates as well as better surface quality. ECM is
only effective for machining conductive materials, while
USM is suitable for hard and brittle materials such as
ceramics. However, these two processes are not effective
when machining composite materials that contain a
mixture of metallic and nonmetallic phases.

12. WORKING PRINCIPLE
1. A voltage of 3 to 15 V dc is
normally used
2. current densities between 5 and
30 A/cm2.
3. ultrasonic frequency of 20 kHz
and an amplitude of 8
to 30 μm.

13. ADVANTAGES AND DISADVANTAGES
-HIGH MRR AS COMPARED TO USM AND ECM
-USED TO MACHINING COMPOSITE TYPE OF MATERIAL
CONSISTING OF BOTH METALAND NONMETAL
-LESS WEAR OF TOOL
-HIGH PRECISION AND ACCURACY
-HIGH INITIAL COST

14. ELECTROCHEMICAL DISCHARGE
GRINDING
Electrochemical discharge grinding (ECDG) combines the
electrodischarge erosion (EDE), ECD, and the MA of the
grinding process. In the schematic diagram of ECDG, the
grinding wheel is connected to the negative terminal while the
workpiece is connected to the positive polarity of a pulsed power
supply. The electrolyte flows into the interelectrode gap. The
rotating wheel is set at a depth of cut, while the workpiece is fed
at a constant rate. Surplus material is removed from the
workpiece surface by the anodic dissolution ECD phase, the MA
action of abrasives or diamond grains, and the erosion phase
due to the spark discharges.

15. WORKING PRINCIPLE

16. PROCESS PARAMETERS
1. Power requirements: Generally pulsating d-c is used, frequency is 120 Hz; voltage ranges between 4 and 12 V (8 V is
optimum for most applications); and amperage range between 200 and 1000A. Alternating-current power requirements are
usually: frequency is 60 Hz; voltage ranges between 8 and 12V; and amperage ranges between 200 and 500A.
2. Current density: Typically current density of 0.93 A/mm2 is practical. Current density is a function of gap thickness, which
is dependent upon the force applied to the workpiece against the grinding wheel. Operating gaps typically range between 0.013-
0.038 mm. The pressure between the wheel and the work is usually between 35 and 138 kPa.
3. Wheel speed: Wheel rotation (usually 20-30 m/s) is necessary in ECDG to introduce clean electrolyte through the gap and
reduce the possibility of gap-spark formation. Rotation also increases electrolyte pressure at the gap and helps to avoid
electrolyte boiling. When carbide is surface ground at 2.5 mm depth of cut, it is typically cut at a feed rate of about 3.8
mm/min; steel is ground under the same conditions at about 12.7 mm/min.
4. Material removal rate: When machining is done at 200 A and a 12.5 mm depth of cut, approximately 6.0 cm3 of carbide, or
about 14.7 cm3 of steel, can be removed in an hour.
5. Tolerances: Production tolerances for ECDG operations are typically ± 0.03 mm, but with close attention, tolerances as tight
as ± 0.013 mm can be held.
6. Electrolytes: In ECDG operations, electrolytes of various types are used, including solutions of NaCl, NaNO3, at
concentrations of between 180-240 g/L. Usually, electrolyte temperature is maintained between 25-40 °C.
7. Surface finish: Carbide workpiece are usually machined to 0.13-0.38 mm Ra; steel workpieces typically exhibit somewhat
rougher finish as 0.38-0.76 mm Ra.

17. ADVANTAGES AND DISADVANTAGES
-ECDG produces a high surface finish free from microsize
cracks and burrs.
-High MRR
-One of the key advantages of electrochemical grinding is the
minimal wear that the grinding wheel tool experiences.
-High precision and accuracy
-very high initial cost

18. APPLICATIONS
-For high precision and accuracy jobs
-For machining harder materials like tungsten carbide,
silicon carbide, aluminium oxide
-Current successful applications of the process include
grinding and sharpening of carbide inserts, generation of
delicate profiles using form grinding, grinding of
honeycomb material, and grinding of carbide thread
chasers.

19. FUTURE DEVELOPMENTS
Aviation, aerospace, medical and military industry demand advanced materials like
ceramics, sintered carbides, titanium alloys, nickel alloys etc. These materials are
difficult to shape and difficult to reach satisfactory efficiency and proper part surface
quality that would be acceptable for practical applications. In finishing operations
satisfactory results can be obtained by application of EDG and ECG. Smaller values of
surface roughness can be reached by application of electrochemical grinding.
Combination of allowance removal by electrical discharge or electrochemical
dissolution and abrasive grinding enables:
1. increasing of machining efficiency in relation to classical EDM and mechanical
grinding.
2. reaching satisfactory properties of surface layer and geometrical structure of
surface.
3. decreasing abrasive grain wear and increasing of the grinding wheel lifetime.
4. grinding wheel self-sharpening phenomena.

20. GREETINGS….
THANK YOU