Albert Tsang, technical manager, Precision Micro
This article analyses the use of photo etching as a preferred route to the manufacture of meshes and filters. Through the use of case studies, it is shown that in a variety of applications, not only can photo etching be the most cost-effective and accurate machining technology for intricate meshes and filters but actually assist in the stimulation of product designs impossible to manufacture using conventional technologies.
Manufacturing complex, intricate and feature-dense metal products has proved a challenge for decades. The majority of sheet metalworking technologies have drawbacks, be it in material degradation under processing regimes, long and costly lead-times, high tooling costs or indeed a mixture of the aforementioned. The precision necessary when manufacturing customised intricate meshes and filters highlights machining issues particularly well, and today a growing number of manufacturers are turning to photo etching as the process of choice for such products.
A best kept secret? This may be overstating the situation somewhat, but it is fair to say that many in industry have failed to recognise the true potential of photo etching and often categorise it as a prototyping technology rather than recognising its usefulness and adaptability as a mass manufacturing process.
The photo etching process
Photo etching employs chemical etching through a photoresist stencil as a method of material removal over selected areas. The use of photoresists allows for the manufacture of high-resolution parts with complex geometries or with large arrays of variable aperture profiles in thin, flat metal sheet.
As a manufacturing process, photo etching has a key attribute when it comes to part integrity, and this is that during the production process, it does not affect or degrade material properties. It is in this area that many metal processing technologies fail to deliver. For example, punching, stamping and laser and water cutting all cause significant stresses and degradation of the metal being worked, and when the metal becomes thinner, heat distortion and material shredding are common issues.
The burrs and rough cuts that are associated with more traditional metal processing technologies are eliminated when using photo etching, which is also agnostic when it comes to shapes and unusual features in products to be manufactured. The nature of the process means that feature complexity is not an issue, and in many instances, photo etching is the only manufacturing process that can accommodate certain part geometries.
In addition, while photo etching can be used on a variety of metal thicknesses, it can also work on ultra-thin sheet metal, even as low as 10 micron foil.
Beyond the positive attributes of the process in terms of the resultant metal parts post-processing, photo etching is also characterised by its cost-effectiveness and versatility at the tooling stage. Tooling for photo etching is digital and therefore substantially less expensive than the tooling for alternative metal manufacturing technologies. This means that multiple design iterations and the consequent tooling changes to ensure manufactured part integrity are not a significant issue.
Photo etching of meshes and filters
When applied specifically to the manufacture of customised meshes and filters, photo etching affords a number of process advantages.
Lead times are reduced dramatically, as are contingent costs, owing to the tooling setup and iterations (which are often necessary) being quick and relatively simple. As it is digital, the tooling for photo etching can be manipulated on screen with ease and takes a matter of hours rather than the days or weeks that would be expected with traditional processes.
Furthermore, and of particular interest to mesh manufacturers, special features and various aperture shapes can be incorporated in a single mesh without any cost penalty. Varying bar sizes and open area ratios can be incorporated to control flow rates across the mesh, and something that appeals to design engineers across industry is that the photo etching process allows for far greater open areas than is possible using alternative processing technologies due to its ability to produce tiny and intricate wire sizes.
Compared with meshes that are woven, the single-part meshes and grids that are produced via photo etching are characterised by their consistent cross-sectional thickness and accuracy of aperture shapes and sizes. Also, as they are manufactured from a single piece of metal, they are slimmer, have greater integrity, are robust when being handled and exhibit better electrical properties with no risk of poor contact at the weave intersect. Custom borders can also be added for additional strength.
Finally, as chemical etching uses fluid to remove metal, it does not produce straight or orthogonal walls and edge profiles. Instead, the process produces a rounding effect that, coupled with the ability to tightly control the etched profiles, can allow for the creation of special features and functionality in meshes that alternative processes cannot achieve. (Figure 1)
Figure 1: Different edge profiles achieved through photo etching
Applications
Precision Micro possesses considerable expertise in the photo etching of meshes and filters for a variety of OEM applications as demonstrated in the following case studies.
Shower head
A shower manufacturer required a shower head for which the edge profiles of the holes were critical to functionality. A rough etch rather than a completely smooth etch was necessary to achieve a high-quality spray.
The shower head featured a simple flip action for switching between four different sprays referred to as rain, storm, cloud and burst. Its spray plate was designed with 900 0.148 mm precision apertures with a tolerance of +/-0.02 mm. Water was required to pass through these apertures smoothly, and it was soon determined that the geometry and shape of each aperture was critical to the spray pattern achieved.
Alternative technologies, and indeed conventional photo etching, struggled to produce a high enough spray quality, so Precision Micro developed a process for consistent apertures that generated incredibly fine, even spray patterns with little to no directional bias. (Figure 2)
Figure 2: Showerhead with 900 0.148 mm precision apertures with a tolerance of +/-0.02 mm
The showerhead is now being mass manufactured using the same photo etching technology that was used during product development to produce the initial prototypes.
Blood filtration product
A medical OEM approached Precision Micro having become frustrated by attempts to produce a micro filter for a blood filtration product. The company had made the filter using a hugely expensive, time-consuming and—due to the occurrence of burrs on the underside of the component —inefficient and ineffective laser process.
Precision Micro was required to pierce a 78 mm diameter, 50 micron-thick stainless steel disc with over 130,000 apertures, each being 100 microns in diameter, on a staggered pitch of 200 microns with a maximum allowable tolerance of +/-10 microns against a standard tolerance for photo etching of +/-25 microns.
As the photo etching process —unlike the previously used laser process—allowed for the etching of all 130,000 holes simultaneously, not only was Precision Micro able to provide burr- and stress-free filters, but they were produced in a fraction of the time, thus affording the OEM a cost-effective route to mass production.
Smoke detector
A manufacturer of industrial fire detection products required a mesh to prevent insects getting inside a smoke detector and triggering false alarms. As well as keeping insects out, it was vital that the mesh did not prohibit the free movement of air.
Initially the manufacturer had used expanding meshes, but these were found to be too course to prevent insects from entering the unit, and there were issues seating the component in the plastic moulding, which had multiple locating pillars.
Precision Micro worked on the development of a mesh made from 0.125 mm stainless steel with thousands of square holes separated by 0.125 mm wide bars that encouraged maximum airflow. The perimeter holes that fitted over the pillars were serrated to allow the filter to bite into the plastic and thus hold it in place securely. (Figure 3)
Figure 3: A mesh to stop insects entering a smoke detector made from 0.125 mm stainless steel with thousands of square holes separated by 0.125 mm wide bars that encouraged maximum airflow.
Automotive speaker grilles
Precision Micro has worked with numerous manufacturers of automotive speaker grilles to replace those traditionally made from pre-perforated sheet materials.
The company was able to produce a series of complex designs, mesh patterns and company logos and indents simultaneously in a single machining operation, something that would be cost-prohibitive if, for example, stamped press tools caused damage to such cosmetic parts, leaving scuffs. Burr-free grilles were produced with micron tolerances and high-definition surface engravings. The ability to change grille patterns with minimal tooling costs, and quickly, was also extremely advantageous in these applications. (Figure 4)
Figure 4: Complex designs, mesh patterns and company logos produced simultaneously in a single machining operation.
Such versatility allows OEMs to look at ways of mass customisation when providing automotive interiors, giving the impression of personalisation and uniqueness model to model and even within a single model range.
Conclusion
The variety of aforementioned applications show that the use of photo etching not only provides a route to manufacture when other technologies struggle but also actually stimulates new product designs. When it comes to the production of cost-effective and reliable meshes and filters, it is difficult, if not impossible, for alternate machining technologies to compete.
With the ability to produce complex, feature-rich designs, and with the added opportunities to vary edge profiles to cater for the demands of specific applications, design engineers have the freedom to design products that were previously impossible to manufacture reliably and cost-effectively, and this enhances product aesthetics and functionality across all key industry sectors.
Precision Micro