Photoetching and electroforming are processes to fabricate metal parts. Electropolishing is a process for improving the surface of metal parts using anodic dissolution rather than mechanical polishing.
In electropolishing, the workpiece is connected to the positive output of a DC power supply and submerged in an electrolytic solution. The negative output of the power supply is connected to a sacrificial cathode. The application of DC current causes oxidation at the surface of the workpiece, and especially on burrs and sharp edges where the current density is greatest. The oxidized particles are drawn to the cathode. Electropolishing is often described as the reverse of electroplating.
The only common ground is that all three processes use chemistry to affect metal.
Subtractive vs. Additive
The biggest difference is that photo etching starts with sheets of metal and dissolves metal with acid to make parts. Electroforming starts with a plating bath that contains metal already dissolved in solution and uses electric current to precipitate the metal out of solution onto a conductive pattern or mandrel.
Etching is like carving a sculpture from a block of stone and electroforming is like building a sculpture from Lego blocks.
Electroforming can be done with a narrow selection of metals including gold, nickel, copper, palladium, platinum, rhodium and specialized nickel-cobalt and nickel-iron alloys. Electroforming works at the molecular level, and very tiny structures can be created. Meshes and screens with grids as small as .0004 (four ten-thousandths) in width can be produced. Electroforming can also produce parts up to .025 thick.
To produce flat parts, electroforming can use a photoresist like photo etching does to create a deposition pattern on a conductive substrate.
Electroforming can also produce complex 3-dimensional parts. Mandrels, often machined from aluminum, are used to replicate complex miniature structures such as nozzles and bellows. After electro forming, the aluminum mandrels are dissolved in a caustic solution that does not affect the deposited metal.
Despite growing applications for nano-scale devices, electroforming is another rarity in the fabricating industries. There are fewer than 90 companies in the US that perform this unusual process.
Photo chemical etching is applicable to a much wider range of alloys including carbon and stainless steels, aluminum, molybdenum, silver, and most of the widely used alloys of copper and nickel. Thicker materials, including up to .040 in steel, .065 in copper and .080 in aluminum can be chemically etched.
For flat parts in metal thicknesses from .001 and up, photo etching is a fast and cost effective option for making dozens to tens of thousands of parts. Chemical etching is especially effective for parts with complex geometries or lots of holes (screens, grids, filters.) In the photo etching process, all features of the part emerge simultaneously. So, it doesnt make any difference in time, cost or tooling if the part is as simple as a disk, or riddled with holes like a screen.
Photo etching can make parts as small as .020 diameter and as large as 24 x 60. Its all the same process and all the same equipment.
Although photo etching competes in a spectrum of metal processes that include stamping, punching, laser and water jet cutting, and wire EDM, the etching process is little known and not well understood. This 2 minute video is a compact and accessible illustration of the process from end to end: Photo Etching Video
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