This guide to chemical etching looks at the key considerations design engineers must appreciate in order to get the most from the chemical etching process, and benchmarks etching against other metal machining technologies.
Chemical etching achieves exacting tolerances, is highly repeatable and in many instances is the only technology that can cost-effectively manufacture precision metal components with the accuracy necessary in demanding and often safety-critical applications.
Once design engineers select chemical etching as their preferred metalworking process, it is important that they fully appreciate not just its versatility, but also the specific aspects of the technology that can affect — and in many instances enhance — product design.
How does etching work?
Below is a basic overview of the chemical etching process.
- Sheet metal is cleaned (step 2) then laminated (step 3) with a light-sensitive photoresist.
- The photoresist is exposed with UV-light (step 4) to transfer the CAD image of the component.
- The areas of unexposed photoresist are developed (step 5).
- Etchant chemistry is sprayed onto the sheet (step 6) removing the unprotected metal.
- The remaining photoresist is removed (step 7) to reveal the final etched component.
Which metals can be etched?
Chemical etching can be applied to almost any metal.
Typical metal types include:
- Steel and stainless steels
- Nickel and nickel alloys
- Copper and copper alloys
- Other specialist metals, such as molybdenum
How accurate is chemical etching?
Tolerances are a key consideration in any design and with chemical etching varies dependent on the material thickness.
- For metals 0.01 mm to 0.25 mm thick the minimum standard etch tolerance is ±0.025 mm.
- For thicknesses above this (to a maximum of 1.5mm) the minimum standard etching tolerance is typically ±10% metal thickness.
In some instances, traditional metal machining technologies can achieve tighter tolerances, but there are limitations. For example, laser cutting can achieve accuracy to 5% o metal thickness but it is often limited to a minimum feature size of 0.2 mm.
Laser cutting is a “single point” machining process, which means it is usually more expensive to produce complex parts with lots of openings such as custom meshes. Also, laser cutting cannot achieve the depth or engraved features necessary for fluidic devices, such as bipolar fuel cell and heat exchanger plates, which are easily attained using depth etching.
Minimum feature sizes
Chemical etching can achieve a minimum standard feature size of 0.1 mm, but openings below 0.050mm are possible with development, as is accuracy to ±8% metal thickness.
Burr- and stress-free machining
When it comes to replicating the accuracy and minimum feature size capabilities of chemical etching, stamping probably gets the closest. The trade-off is the stress that is imparted in the metal and residual burrs that are a characteristic of stamping.
Stamped parts often need costly post-processing and as expensive steel tooling is used to produce the parts it is not viable for short runs. In addition, when processing hard metals, tool wear is an issue with expensive and time-consuming refurbishment often necessary.
Many spring designers specify chemical etching due to its burr- and stress-free nature, zero tool wear and speed of supply.
Unique features at no additional cost
Unique characteristics can be designed into products manufactured using chemical etching due to the inherent edge “cusp”.
Precision Micro can control etch cusp, and by doing so introduce a range of profiles allowing the manufacture of sharp cutting edges, such as those used in medical blades, or conical openings, such as those used to direct fluid flow in filtration meshes.
Low-cost set-up and design modifications
For designers looking for feature-rich, complex and precise metal parts and components, chemical etching is now the technology of choice. Etching not only copes well with difficult geometries, but it also allows enormous flexibility, facilitating the adjustment of designs right up to the point of manufacture.
One major factor that allows for this is the use of digital tooling, which is inexpensive to produce and therefore inexpensive to change even up to a few minutes before manufacturing commences.
Unlike stamping, the cost of digital tooling does not increase with part complexity which stimulates innovation as designers focus on optimised part functionality rather than cost.
For most sheet metalworking it is fair to say that increased part complexity equals increased cost, much of this being a product of costly and intricate tooling. Costs also escalate when traditional technologies have to cope with non-standard materials, thicknesses and grades, none of which have any effect on the cost of chemical etching.
Chemical etching does not use hard tools and distortion and stress are eliminated. Also, components produced are absolutely flat, with a clean surface and no burrs as the metal is dissolved away uniformly and evenly until the desired geometries are achieved.
With chemical etching, you pay by the sheet, not by the part, which means components with different geometries can be processed at the same time from a single tool. This ability to produce many part types in one production run is the key to the enormous cost savings inherent in the process.
Chemical etching can be applied to virtually any metal type, including those soft, hard or brittle. Aluminium is renowned for being difficult to stamp due to its soft nature, and laser cut due to its reflectively. Equally, titanium’s hardness can prove challenging.
Precision Micro has developed propriety processes for both of these specialist materials and is one of the few etching companies in the world with a dedicated, production titanium etching capability.
Add into the mix the fact that chemical etching is inherently speedy (for example, tooling typically takes a day to produce not 16 weeks!) the rationale behind the exponential growth in uptake of this technology in recent years is obvious.