Understanding Laser Marking And Laser Etching Systems

Writen by Jim Morin

Laser marking and laser etching are becoming more and more important in a growing number of industries. The basic reasons to laser marking or laser etch your products include:

• The mark is extremely durable, permanent and in most cases cannot be removed without destroying the product itself, this is true for laser marking, laser etching, or laser annealing.

• The laser marking process is accurate, 100% repeatable, fast, with very clear sharp results.

• The laser mark or laser etch can quickly and easily be changed without any machine change over, and, without replacing any tools. The changing of a laser marking or laser etch is a simple drag and click computer operation.

• The laser requires no consumables and no additional purchases of added materials or supplies. Therefore the operating and maintenance costs of owning and running the laser marking or laser etching system are virtually non existent.

Laser Basics

The word laser is an acronym for light amplification by simulated emission of radiation. The laser beam is formed in a sealed tube with an electrode set, laser gas, and electrical discharge. The beam is emitted into a telescope which expands the laser beam from a size of approximately 2mm as the beam exits the laser tube up to 7mm to 14 mm for most laser marking or laser etching operations. The expanded beam is directed into a laser head containing two mirrors located on high speed galvo motors. The laser beam is directed off the mirrors though a single element flat field lens to the product being laser marked or etched.

Typically the laser marking or laser etching fields created range in size from 65mm x 65mm [2.5" x 2.5"] at the smallest size to 356mm x 356mm [14.0" x14.0"] square at the largest. The next consideration is the laser beam spot size. This is the size of the focused laser light energy at the laser marking or laser etching point on the product and can vary from approximately 200 micron [micrometers] or .0078" at the smallest to approximately 540 microns or .021" for Co2 lasers. The laser beam spot size ranges from approximately 20 microns or .0007" at the smallest to approximately 70 microns or .0027" at the largest for Nd:YAG lasers. These small spot sizes and highly focused laser light energy create the detailed, clear, permanent marking that is typical of the laser marking or laser etching process.

Controlling Lasers and Laser Marking Options

Laser markers and laser etchers are controlled via software. Several variables need to be controlled:

1. Laser power as measured in watts

2. Frequency, meaning the pulse frequency of the laser beam

3. Inches per second, meaning the speed that the beam steering mirrors are moving

Determining the correct setting for the laser is the single most important and critical element in the success or failure of the laser marking process. Once the proper settings have been determined and demonstrated a 100% repeatable laser mark can be achieved.

Laser controller software is accessed via a PCI interface card. This sends the digital signals of the computer based marking or etching files to the motors and directs the laser beam to the product being laser marked or laser etched.

There are several different types of laser marking and laser etching and several different considerations in terms of visual results for the laser mark or laser etch.

1. Laser etching produces a visible etching or depression into the material. Laser etching replaces traditional process like mechanical press or pin scribing. Laser etching can be done with either a Co2 or YAG laser on virtually any material surface and to any depth from very light etching to very deep etching. For example, laser etching is used to engrave serial numbers into metal gun frames. Generally speaking with laser etching the material being laser etched is vaporized at the laser etching point due to the typically high power densities of the laser beam at the point of laser etching.

2. Laser marking produces a surface mark with very little engraving and very little disruption of the material surface. This is especially useful in certain industries such as discrete electric components, semi-conductor, electrical fuse, and ceramics where laser etching can actually damage part or change the conductive qualities of the part. Generally in order to produce the laser mark without deep engraving a high speed per inch setting for the galvo head is used.

3. Laser etching and laser marking generally do not produce any color changes and create a colorless impression. There are exceptions as certain plastics will sometimes react to and change color under either Co2 or YAG laser light. Also, in some cases, additives can be incorporate into the materials being laser marked or laser etched in order to produce a color change. Another exception occurs when the wavelength of either the Co2 or YAG laser is changed from those typically used in laser etching and laser marking. This can produce a color change after laser etching on some materials.

4. Laser annealing is another popular form of laser marking. This type of laser marking is generally undertaken with a YAG laser on metal surfaces using lower power, high frequency and slow writing speeds to produce heat on the surface of the product. Laser annealing can be used to replace electro chemical etching and ink marking as the laser annealing process creates a black mark with no etching. Care must be used, as the heat generated can cause iron in some metals to be pulled to the surface, and rust can result if the parts are subjected to sterilization after laser annealing. This can be an especially difficult issue for medical devices

5. Laser ablation is also a popular use for laser marking systems. In this case the laser is used to remove a layer of paint, anodized or some other material covering the surface of the part. For example this process is used to create bear metal contact points on a painted part, to allow battery connection as in cell phones, or to remove paint for identification of parts and manufacturer details.

Jim Morin writes for Worldwide Laser a company that specializes in Co2 and YAG marking systems used in a wide range of applications. For more information visit http://www.wlsc.com