Over the past several decades, the photochemical etching process has proven to be a versatile and cost effective method of fabricating thin-gauge metal parts in many alloys.
One of the lightest metals, aluminum, is one of the more challenging alloys for metal etching. Aluminum is a very active and reactive metal. It oxidizes readily and actually becomes fuel for the reaction, much as it does when it is a component of solid rocket fuel.
For conventional fabricating processes like stamping and punching, aluminum is just another metal alloy. For the so-called nonconventional processes like plasma cutting, laser cutting and wire EDM, working with aluminum can be both challenging and hazardous.
Aluminum’s sensitivity to heat and its reflective surface mean that exposure to high temperatures from plasma, laser or electrical discharge can alter material properties. The Heat Affected Zone (HAZ) forms in metals when the temperature rises above the critical transformation point, making the metal brittle, and vulnerable to cracking during bending or stress. Thermal distortion can occur as a result of the sudden rise in temperature of the material near the cutting zone, and also to the rapid solidification of material remaining on the sides of the cut, known as a re-cast layer.
The hazards involved with heat-intensive fabrication processes such as plasma or laser cutting are not easily avoided. For example, dry cutting aluminum produces fumes and airborne particluates that could explode and must be evacuated.
For these reasons, manufacturers will try to plasma cut materials on a water table. While submerging the work under water removes the hazards associated with dust and heat, it poses other hazards.
As ESAB noted, when aluminum is submerged under water, it reacts with the water producing hydrogen gas. If hydrogen should become trapped under a workpiece, there is a potential for explosion.
Etching aluminum is the foundation of Conard’s business. In the early 1960’s, Richard Huttinger, a metallurgist for Pratt and Whitney, was trying to find a better way to finish the surfaces of forged aluminum propeller hubs. Huttinger believed that it could be done with a chemical machining process and developed the methodology that we continue to use.
Conard’s General Manager, Art Long, has worked in this industry for more than 30 years and is well familiar with the challenges of etching aluminum. “The biggest problem is edge consistency, sometimes the edge would look smooth and other times it would appear very rough. It was difficult to control the quality of the etchant from one bath to the next and from one alloy to the next,” said Long. “When I joined Conard in 2003, I noticed that the aluminum etching capabilities were head and shoulders above the previous companies I had worked for. The product had consistently smooth sidewalls and was precise in a wide range of different aluminum alloys and thickness.”
From the beginning, Conard has maintained equipment specifically for etching aluminum. Huttinger’s formulas and process metrics have been the basis for more than 40 years of continuous improvement. As Conard’s business expanded to encompass a broad range of ferrous, cuprous and specialty metals, the basic principles developed by the founder for maintaining consistent performance in photo etching many metal alloys are still employed every day.