Introduction to Micro Machining Processes

 

Micro Machining is an advanced manufacturing technique used to create small and precise features on materials. It is widely used in industries like electronics, biomedical, and aerospace for making micro-sized components. One such method is Electrochemical Micromachining (ECMM), which removes material using electrochemical reactions without generating heat or mechanical stress.

Overview of Electrochemical Machining (ECM)

ECM is a reverse electroplating process where the workpiece (anode) dissolves in an electrolyte solution while the tool (cathode) shapes the material. Unlike traditional machining, ECM does not involve physical contact, reducing tool wear and thermal damage.

Key Parameters:

• Voltage: Controls the material removal rate.
• Current Density: Affects surface finish and machining accuracy.
• Electrolyte Flow Rate: Ensures smooth machining by removing dissolved material.
• Inter-Electrode Gap (IEG): The distance between tool and workpiece affects precision.

Electrochemical Reactions in ECM:

At the anode (workpiece): $M \rightarrow M^{n+} + ne^-$
(Where M is the metal being machined, n is the oxidation state, and e⁻ are electrons.)

At the cathode (tool): $2H_2O + 2e^- \rightarrow H_2 + 2OH^-$

What is Electrochemical Micromachining (ECMM)?

ECMM is a specialized form of ECM used for micro-scale applications. It operates at lower voltages and currents, enabling high-precision machining with minimal side effects.

Differences between ECM & ECMM

Parameter	ECM	ECMM
Voltage	10-30V	<10V
Current	150-10000A	<1A
Electrolyte Flow	10-60 m/s	<3 m/s
Accuracy	0.1 mm	0.02-0.1 mm
Surface Finish	0.1-1.5 µm	0.05-0.4 µm

Types of Electrochemical Micromachining (ECMM)

1. Through-Mask ECMM: Uses a patterned mask to restrict material removal.
2. Maskless ECMM: Directly removes material without a mask.
3. Jet ECMM: Uses a high-speed electrolyte jet for localized machining.
4. Capillary Drilling: A precise method for micro-hole formation.
5. 3D ECMM: Creates complex 3D structures using specialized tools.

Key Factors Affecting ECMM

1. Power Supply: Pulsed DC voltage improves accuracy.
2. Inter-Electrode Gap (IEG): Small gaps ensure better precision.
3. Electrolyte Properties: Affects machining rate and surface finish.
4. Micro-Tool Feed: Controls machining depth and shape.

Fabrication of Micro-Tools

Micro-tools play a crucial role in ECMM and can be fabricated using:

• Wire Electro Discharge Grinding (WEDG)
• Electrochemical Etching
• Coatings (SiC, Si3N4) to reduce stray currents

Nano-Fabrication Using ECMM

Researchers are exploring nano-structuring with ECMM to create ultra-small features. Techniques like Solid Electrochemical Machining (SSEM) and Scanning Tunneling Microscope (STM) based ECMM have achieved nanometer precision.

Example of Nano-Scale Electrochemical Reactions:

For nickel machining: $Ni \rightarrow Ni^{2+} + 2e^-$

For titanium machining: $Ti + 2H_2O \rightarrow TiO_2 + 4H^+ + 4e^-$

Advantages of ECMM

• No heat generation, preventing thermal damage.
• High precision and surface finish.
• Can machine hard-to-cut materials like Titanium and Super Alloys.
• Ideal for biomedical implants, MEMS, and micro-electronics.

Challenges & Future Research

• Micro-Spark Formation: Can affect machining accuracy.
• Tool Wear & Sludge Formation: Needs better monitoring.
• Electrolyte Management: Reducing toxicity and disposal concerns.

Conclusion

Electrochemical Micromachining (ECMM) is a revolutionary technique for micro and nano-scale manufacturing. With ongoing research, ECMM will play a vital role in precision engineering, especially in medical devices, electronics, and aerospace applications.