Pre
	Typical etchant diffusion
	Pre-breakout profile
	Finished

CHEMICAL ETCHING NON CONTACT FINE BLANKING
THE 2nd DIMENSION

Process Advantages

Prototype and production volumes
Non contact blanking process
Virtually any metal (see applications page click here.)
Stress free manufacture
Burr free products
Metal thickness from 0.013mm to 1.5mm
Blind hole etching
Surface etching
Multi level (Step) etching
Product part marking
Controlled and rapid profiling of multiple component parts simultaneously.

Component Manufacture

One of the key strengths of the etching process is that the chemistry is unaware of the hardness (or type) of material that it is etching through. This is due to the way that etchant chemistry breaks down the materials grain structure, which only changes slightly with temper. The component etching process was originally developed in the 1940s to manufacture parts from materials too hard to stamp or machine.
Etching also has no detrimental effect on the properties of the material surrounding the etched areas. Concerns of localised annealing or embrittlement do not occur during the process. This gives etching the advantage of being able to create component shapes in any hardness of material from annealed to spring hard.

Equipment

The modern spray-etching machine is almost universally used in production photo chemical machining. The workpiece, or sheet, travels along a horizontal conveyor consisting of rubber wheels on GRP rods which carries it through a rigid PVC chamber, where it is vigorously sprayed with hot etchant from batteries of nozzles above and below the track. The most productive etch rate is achieved when the etchant is sprayed perpendicular to the workpiece. This ensures that as the cut moves through the workpiece the main pressure is directed to the base of the cut, therefore only attacking the side walls by diffusion.

Etch Factor

The ratio of etch depth to undercut is called etch factor and is determined by the process chemistry and the spray pressure and direction of its application. The differential etch rates at the floor and sides of the spray etch cavity are responsible for the characteristic profile of the finished edge. The profile develops as if an ellipse of increasing size were sinking into the metal surface. As etchant is applied under pressure then the point that receives the greatest impact of that pressure will etch quicker. This is always intended to be the base of the cut, therefore the cut will travel down (and up) through the material quicker than along the horizontal

The cutting action of the chemicals does create a characteristic edge profile referred to as a bi-cuspic edge. This is the result of simultaneous etching from both sides leaving a witness at the point of breakthrough. As the etching proceeds the bicuspid edge retreats at a decreasing rate. The nearer to the horizontal the surface the faster it etches, therefore the protruding cusp is reduced faster than the nearly vertical sidewalls.

As etching continues the bicuspid edge becomes progressively straighter and almost vertical. Further etchback would result in overetching and a concave edge protruding into the materials section by as much as 1/5th of the materials thickness. The phototool will have been sized to achieve nominal dimension at straight wall. The rate of etch slows as the edge profile becomes vertical. Consequently if the product comes to size midway through a machine pass it will not be overetched.