Chemical Basics

How does chemical machining remove material?

By a strong chemical reaction that attacks exposed portions of a workpiece.

What are the four main CHM steps?

Cleaning, masking, etching, and demasking.

Why is cleaning required before chemical machining?

To ensure uniform material removal.

What is a maskant?

A chemically resistant protective coating applied where material should not be removed.

What happens during etching?

The part is exposed to an etchant that attacks unmasked regions.

How is the etching reaction stopped?

The part is removed from the etchant and washed.

What happens during demasking?

The maskant is removed from the part.

What are the three masking methods?

Cut and peel, photoresist, and screen resist.

What material is often used as a maskant?

A polymer such as polyvinyl chloride.

What factors affect etchant selection?

Work material, required depth, removal rate, surface finish, and compatibility with the maskant.

What is undercut?

Sideways etching underneath the maskant.

How is undercut related to depth of cut?

For a given material, undercut increases as depth of cut increases.

What is etch factor?

The ratio of depth of cut to undercut.