When metals chemically corrode or disintegrate, the substance is removed by tiny electrochemical cell action. Even though the material removal penetration rates might only be 0.0025–0.1 mm/min, this controlled chemical dissolution will simultaneously etch all exposed surfaces. Etched metals can create larger objects, such as coins and plaques, but they are usually thin, like sheet metal or foil. Chemical milling is a specialized process that can help manufacturers save both time and money when carried out by qualified professionals.

Procedure for Chemical Milling

A chemical etchant is the cornerstone of how chemical machining works. Etchant is a term used to describe a mixture of strong acids that react with metal. When immersed, the etchant reacts with the workpiece and dissolves the metal at a predictable rate.

The workpiece is coated with an elemental material resistant to the chemical agent “maskant” prior to machining to produce the desired shape or structure. To achieve localized machining, which makes the machining area visible for the necessary metal removal, one must apply a suitable mask to all the places where they don’t want the etchant to react. 

When deciding how long to leave the reagent in situ, several factors are considered, including temperature, agitation, acid concentration, and the desired depth of the cut or etch. After achieving the desired result, the chemical is finally removed from the part and polished. Here is the step-by-step chemical milling process:

Cleanup of the Surface

Cleaning is the initial step to ensure the workpiece’s surface is free of contaminants, corrosion, and foreign objects. It usually uses diluted HCl, high-pressure water jets, and alcoholic beverages—unsatisfactory cleaning results in erroneous final measurements, unsatisfactory maskant adherence, and poor metal dissolving. 

After washing, the workpiece is dried using hot air blowers, and modern CNC machinery is always used to clean it.

Masking 

The process of masking entails applying a maskant to the workpiece’s surface. A coating of polymer or rubber is applied to the workpiece first. When this happens, masking prevents the etching process from occurring in a location that doesn’t require machining. The workpiece is completely covered in masking, excluding the areas that will be machined.

Etching 

The method used to remove the necessary metal is called etching. After a specified masking job, the workpiece is dipped into the chemical reagent tank with the warmth and stirrer turned on. Once the workpiece is dipped, the etchant reacts with the exposed areas. The outcome is that the very concentrated acid reacts with the workpiece, altering its chemical properties. 

Through this reaction, the predefined parts melt and separate off the workpiece, layer by layer. In this method, the cut’s depth and the dip’s length on the workpiece are perfectly aligned. The length of time the workpiece spends in the etchant, therefore, increases as more metal is removed from it.

Demasking 

Demasking is the process of removing the maskant following the etching procedure. Once the maskant has been eliminated, the workpiece is carried once more for cleaning, where any etchant that is still present is eliminated using high-pressure cold water. The piece of art is readied for delivery after drying.

The takeaway

Choosing the right chemical milling company ensures the most favorable outcome.