When Conventional Processes Don’t Fit The Bill…
Photo chemical machining (PCM), also known as photo etching or chemical etching, is a powerful subtractive manufacturing process ideal for producing intricate metal parts with tight tolerances and complex geometries. It offers several advantages—such as stress-free processing, no burrs, and the ability to handle high-precision, thin-gauge materials—that make it particularly attractive for industries like aerospace, electronics, medical devices, and automotive. However, to fully leverage the benefits of PCM, engineers and designers must understand its unique design considerations.
Material Selection Options for Photo Etching
PCM is compatible with a wide range of metals, including stainless, carbon and electrical steels, copper alloys, aluminum, nickel, silver, molybdenum, and range of specialty alloys. Material thickness typically ranges from 0.001″ to 0.080″, though optimal thickness is usually below 0.040″ for the best precision and cost-effectiveness. It’s critical to consider how the chemical etchants interact with your chosen metal. For instance, stainless steel and copper are very etch-friendly, whereas materials like silver and molybdenum require special etchants. A non-exhaustive list of alloys is here.
Feature Size and Tolerance
One of PCM’s major advantages is its ability to produce features as small as 0.004″ with tolerances as tight as ±0.001″, depending on material thickness and feature geometry. A useful rule of thumb is that the minimum feature size (hole diameter, slot width, etc.) should be no less than 110% of the metal thickness. For example, if you’re using 0.010″ thick material, the smallest practical hole size is about 0.011″.
Designers should note that tolerances are generally tighter on features that run parallel to the sheet surface (X-Y plane) than those involving depth (Z-axis), due to the isotropic nature of chemical etching. PCM is not a suitable method for parts requiring sharp internal corners or deeply etched pockets with vertical sidewalls.
Chemical Etch Compensation and Undercutting
Chemical etching removes material uniformly from both sides of the metal sheet. This means features will slightly undercut the mask dimensions due to lateral etching. To account for this, designers must include etch compensation: a minor increase in the size of features in the phototool to achieve the desired final dimension. The amount of compensation depends on the material and thickness but is typically in the range of 10–20% of the material thickness.
Rounded internal corners are another natural outcome of the process. While this may not be suitable for all designs, it’s often acceptable or even beneficial in applications where sharp corners could cause stress concentrations.
Part Nesting and Material Utilization
PCM lends itself well to cost-efficient production through sheet nesting—placing multiple parts on a single metal sheet. Designers should aim to maximize material usage while maintaining minimum web spacing between parts (often around 0.020″ to 0.050″) to avoid sheet distortion during processing.
Tabs or micro-joints are commonly used to keep individual parts attached to the parent sheet during etching, which simplifies handling and post-processing. These tabs are typically very small and can be easily broken or laser-cut after etching.
Marking, Bending, and Secondary Operations
Chemical etching allows for fine surface texturing or part numbering during the same process as the part formation. This can include logos, part numbers, or orientation marks—without adding cost or time. If parts will undergo forming or bending after etching, this should be accounted for in the design stage. Radiused corners and proper bend allowances are necessary to avoid cracking or distortion.
Secondary operations like plating, passivation, or forming may follow PCM, so designs should be compatible with these processes. Engineers should communicate these post-processing requirements early to ensure dimensional stability and performance throughout the manufacturing lifecycle.
RFQ Form
Conclusion
Designing for photo chemical machining requires a shift in mindset from traditional mechanical fabrication methods. By embracing PCM’s strengths—fine detail, no mechanical stress, and efficient prototyping—designers can unlock new levels of precision and flexibility in metal part manufacturing. By carefully considering material properties, feature tolerances, etch behaviors, and downstream operations, engineers can create designs optimized for quality, performance, and cost-efficiency.