Classification of Electrochemical Machining

Electrolytic processing

A method of forming a metal material by an electrochemical reaction in which an anode is dissolved.

When the tool cathode is continuously propelled to the workpiece, the current density is the highest, and the anode of the workpiece dissolves the fastest at the point where the gap is the smallest, because the gap between the two surfaces is not equal.

Therefore, the metal material is continuously dissolved in the shape of the cathode profile of the tool.

At the same time, the electrolysis product is washed away by the electrolyte until the surface of the workpiece forms a shape approximately opposite to that of the cathode profile, at which point the desired surface of the part is machined.

Electrolytic processing uses a low-voltage DC power supply (6 ~ 24 volts), a large operating current.

In order to maintain a continuous and smooth supply of electrolyte to the electrolysis zone with sufficient flow rate and suitable temperature , the processing is generally carried out in a sealing device.

Conductive grinding

Also known as electrolytic grinding.

It is a combination of electrolysis and mechanical grinding.

In the case of conductive grinding, the workpiece is connected to the anode of the DC power supply, and the conductive grinding wheel is connected to the cathode.

Both maintain a certain contact pressure and introduce electrolyte into the processing zone.

When the power is turned on, the metal surface of the workpiece is anodic dissolved and a very thin oxide film is formed.

Its hardness is much lower than that of the workpiece, and it is easily scraped off by the grinding wheel of the high-speed rotating wheel.

A new oxide film is formed and is polished by a grinding wheel.

This is done until the processing requirements are met.

Electrochemical polishing

Also known as electrolytic polishing.

The mechanically processed parts are directly processed by electrochemical reaction using anodic dissolution to improve the surface finish of the workpiece.

Electropolishing is more efficient than mechanical polishing, high precision, and is not affected by the hardness and toughness of the material, and has gradually replaced the trend of mechanical polishing.

The basic principle of electropolishing is the same as electrolytic machining, but the electrolytically polished cathode is fixed, the distance between the poles is large (1.5 to 200 mm), and the amount of metal removed is small.

When electropolishing, it is necessary to control the appropriate current density.

When the current density is too small, the metal surface will be corroded and the production efficiency is low;

When the current density is too large, a discharge phenomenon of hydroxide ions or oxygen-containing anions occurs, and gaseous oxygen is precipitated, thereby reducing current efficiency.

Electroplating

The metal is deposited on the surface of a conductor (such as metal) or a non-conductor (such as plastic, ceramic, fiberglass, etc.) by electrolysis to improve its wear resistance, increase its electrical conductivity, and provide corrosion protection and decorative functions.

For the surface of a non-conductor article, electroplating can only be carried out after proper treatment (using graphite, conductive paint, electroless plating, or vapor phase coating) to form a conductive layer.

During electroplating, the plated article is attached to the cathode and the metal to be plated is attached to the anode.

The electrolyte is a solution containing the same ions as the anode metal.

After energization, the anode gradually dissolves into metal cations, and an equal number of metal ions in the solution obtain electrons on the cathode and then precipitate on the surface of the article to be plated to form a metal plating layer.

For example, nickel plating is performed on a copper plate, and an aqueous solution containing nickel sulfate is used as a plating solution.

After energization, the nickel on the anode gradually dissolves into positive ions, and nickel is continuously deposited on the surface of the copper plate of the cathode.

Electroetching

Also known as electrolytic etching.

The desired pattern or text is etched on the metal surface using the principle of electrochemical anodic dissolution.

The basic processing principle is the same as electrolytic machining.

Since the amount of metal removed by electroetching is small, there is no need to use a high-speed flowing electrolyte to wash away the product dissolved from the workpiece.

The cathode is fixed during processing.

Electroetching has the following four processing methods.

① According to the pattern or text to be engraved, the punch is processed as a cathode with a metal material, and the metal workpiece to be processed is used as an anode, and the two are placed together in an electrolyte.

When the power is turned on, the surface of the workpiece will dissolve the same pattern or text as the punch.

② Cut the conductive paper (or metal foil) or use the knife to engrave the pattern or text to be processed, and then paste it on the insulating sheet, and try to connect the unconnected lines in the pattern with the wires on the back of the insulating board as the cathode.

Suitable for workpieces with simple graphics and low precision requirements.

③ For the complex workpieces, the technology of making printed circuit boards can be used.

That is, a positive pattern of the desired processing is formed on one side of the double-sided copper clad plate, and each isolated line in the pattern is managed to be connected to the other side of the copper clad plate as a cathode.

Not suitable for processing fine and unconnected graphics.

④ Apply a layer of photoresist on the surface of the metal to be processed, and then make a negative photographic film on the photosensitive adhesive, or use a photolithography technique to expose the portion to be engraved.

At this time, the anode is still a workpiece to be processed, and the cathode can be made of a metal plate.

Electrolytic smelting

Refining and refining colored and rare metals using the principle of electrolysis.

It is divided into two types: aqueous electrolytic smelting and baking salt electrolytic smelting.

Aqueous electrolytic smelting is widely used in the metallurgical industry to extract and refine metals such as copper, zinc, lead and nickel.

For example, electrolytic purification of copper: crude copper (99% copper) is preliminarily made into a thick plate as an anode, pure copper is used as a thin plate as a cathode, and a mixed solution of sulfuric acid (H2SO4) and copper sulfate (CuSO4) is used as an electrolyte.

After electrification, copper dissolves from the anode into copper ions (Cu2+) and moves toward the cathode. After reaching the cathode, electrons are obtained and pure copper (also called electrolytic copper) is precipitated at the cathode.

Impurities in blister copper, such as iron and zinc, which are more active than copper, dissolve as ions (Zn2+ and Fe2+) with copper.

Since these ions are less likely to precipitate than copper ions, it is possible to prevent these ions from being deposited on the anode by appropriately adjusting the potential difference during electrolysis.

Impurities such as gold and silver, which are inactive than copper, are deposited at the bottom of the electrolytic cell.

Baked salt electrolytic smelting is used to extract and refine active metals (such as sodium, magnesium, calcium, aluminum, etc.).

For example, industrially extracting aluminum: purifying ore containing alumina (Al2O3), and placing the obtained alumina into molten cryolite (Na3AlF6) to make it into a molten electrolytic body, using carbon rod as an electrode , the electrochemical reaction of the two poles is

4Al3++6O2-+3C─→4Al+3CO