What is part marking for CNC machining? Practical tips for laser engraving, silk screening and more

Part marking, also known as direct part marking (DPM), is a secondary manufacturing process for adding logos, lettering or other customized designs to your custom CNC-machined parts. Two of the most common methods for part marking are laser engraving and silk screening. 

Typically, part marking is a required step in manufacturing full-scale production parts (if you have a lot of parts, you’re probably adding serial numbers or some other identifiers). Of course, you’re likely to find this customization across the full spectrum of CNC projects, especially with the relative ease and cost-effectiveness of most part marking processes. 

This article covers common ways to mark parts and also provides practical tips on how to get the most out of part marking techniques. For more in-depth knowledge on CNC machining, head to our comprehensive guide, perfect for new engineers and seasoned ones looking for a handy refresher.

What is laser engraving? Adding logos, serialization and part numbers

Laser engraving is one of the most common methods of part marking. With laser engraving, a laser vaporizes a thin layer of material to create a tracking code, by sending a highly localized laser pulse onto your part. 

Instead of adding a raised micro-surface on the material of your part, laser engraving digs into the material. In general, laser engraving can reach a depth of 500 microns. Common applications for laser engraving include steel and aluminum parts.

What is screen printing? Also known as silk screening 

Screen printing uses a mesh to transfer ink onto a substrate. The process meets many Mil-Spec requirements for industrial marking methods. 

Screen printing machines move a squeegee glade across a screen mesh to fill the open mesh and graphic areas with ink. The screen mesh uses a blocking stencil or emulsion outfitted with an image. After this, a similar print stroke is used, which causes the screen to touch the substrate quickly, pushing ink through the mesh openings and transferring the image onto the substrate. 

This method is most commonly seen on parts that have already gone through several metal post-processing rounds. It’s more versatile than traditional printing methods, such as lithography or etching, as it doesn’t require printing under pressure. You can use a variety of different inks to silk screen almost any material or object. Silk screening works well on many plastic and metal materials. 

What is dot peen marking? Also known as pin marking or impression marking

Dot peen marking lets manufacturers make permanent impressions in an impressive range of materials. This is generally for identification and traceability purposes. Dot peening machines use a vibrating tool to produce a series of evenly spaced, small indentations in the surface of a part. 

With dot peening, the material of your part is pushed back into a recess and not burned or milled, so you’re not left with excess material shavings.

What is pad printing?

Pad printing uses a silicone pad to transfer a 2D image onto a 3D object. The silicone pad is able to pick up the image from a flat surface and transfer it to a variety of surfaces including flat spherical, cylindrical, textured, concave and convex surfaces. 

This process achieves a similar result to silk screening, so we often opt for the latter.

What is laser etching?

Laser etching creates black and white marks on a part and is the most efficient process to permanently add logos and other customized designs to most materials. Etching is faster than engraving because it requires less energy from the laser beam, though the result is pretty similar. 

To etch a part, you use a laser to heat and distort the micro surface of the material you’re marking. This expands and creates a texture on the etched surface. Laser etching works with virtually any metal material, apart from SS. 

What is laser annealing?

A less common part marking technique, laser annealing is the only solution for marking stainless steel and chrome-plated components. This is because it’s the only process that creates permanent markings while maintaining the part’s natural resistance to corrosion. 

Laser annealing heats metal instead of engraving it, chemically modifying the steel located under the initial chromium oxide layer. 

To do this, laser annealing heats the surface until it temporarily melts. In this short time span (we’re talking milliseconds), oxygen travels below the surface, creating a controlled form of oxidation beneath this top layer. When the surface cools down and solidifies, oxidation has modified the color of the part’s surface. The result is permanent, chromatic and cosmetic.

Most importantly, laser annealing doesn’t remove any material from the surface of the part, as opposed to laser engraving, which ablates material. This means that any protective layers remain unaffected. 

The difference between annealing and etching is that annealing is a chemical reaction and that it does not melt the material’s surface. The difference is subtle to the eye. Common applications include SS and chrome-plated metals.

What is ink stamping?

A relatively simple process for customizing parts, ink stamping consists of pressing an inked stamp onto the surface of a part. It’s the automated version of hand stamping and works well for a variety of plastic and metal materials.