Photochemical Machining

Basics

• A form of Industrial Etching
• It applies processes similar to Photolithography but for Sheet Metal Fabrication
• Due to the gentle nature of the process it can even work with Foil
• The main applications are:
  • Mesh
  • Features such as Grates etc, which are too small and/or too closely placed to be produced by other methods such as Waterjet Cutting or Laser Cutting
  • Although suboptimal compared to Stamping at larger scales, PCM can be of use for Complex yet Thin Metal Parts Such As:
    • Fuel Filters for Cubesats
    • Potentiometer "Wipers", Battery Connectors
    • Small Trays/Doors for Portable Electronics (Sim Card Slot Holder, Battery+Data Card Door on Cameras, etc)
    • Grills for Speakers/Microphones

Basic Process

• Acquire the Sheet Metal / Shim Stock / Foil
  • As per This Timecode of the Applied Science YouTube Video , even via small orders on Mcmaster Carr the price tends to not be that bad ($5-20 etc)
• Clean the Metal
• Apply Photoresist / Laminate on Photoresist Film
• Use a Photomask (Made via Transparency Film and an Inkjet Printer ) in the Applied Science video) to Create the Patterns that will be Exposed
• Expose the Photoresist
• Develop the Photoresist
• Etch the Parts
  • Applied Science (YouTube Channel) did this with an interesting (and m o d u l a r ) device they made
  • It used an Air Operated Double Diaphragm Pump to pump the Etchant (in their case Ferric Chloride ) into spray nozzles
  • The Mesh Bag Containing the Metal Plate to be Etched was moved through the spray in an up and down manner through the glass container via a magnetically coupled OpenBuilds axis
    • This would be easily adapted to a Universal Axis

Existing Open Source Designs

Applied Science (YouTube Channel)

• Utilized a Dry Photoresist Fil
  • In the YouTube Video's Description they provided this as the source they used:
    • 30cm×5m Portable PCB Photosensitive Dry Film ( ~15 USD as of This Edit )
• This was run over the cleaned metal sheets via a Laminator
• Given the Film is Multilayered, an thus "Uptake" Spool was needed for each side to peel off the protective layer
• A Photomask was then applied
• It was then Exposed via a Device Consisting of:
  • A Mostly Wood Frame
  • A Darkroom Timer
  • 2x (One for Each Side) 150 Watt 400-410nm Wavelength UV LED Lights
    • The Source Provided in the Description Was the KUKUPPO 150W Black Lights 2 Pack, UV Led Black Light ( ~140 USD As of This Edit )
• The Sheet was then Developed
  • The Developer they Used Was Tap Water + Sodium Carbonate
  • As shown at 16:04 in the Video they made a device for this step
    • It Consisted of a Clear Plastic Bin with two Spinning Tipjet Type Portable Irrigation Sprinklers , a Submersible Aquarium Heater , and an external Water Pump (Impeller Type?)
  • The Solution's Temp Should be ~28*C as per 16:15 in the Video
• The Sheet was then Rinsed
  • They mentioned a Rinse Tank was used, unsure if this was a device similar to the developer machine/the etching machine, or if it was merely a tub filled with water
• THe Sheet was then Etched
  • As shown at around 17:16 in the Video they made a device for this step
    • It consists of a holder for the mesh bag the sheet is in
      • The Holder is a Square Plastic Frame with Clips to Hold the Bag on the Inside of the Frame (It also is mentioned a handle could be added to the top to allow moving from device to device)
      • It has rollers, making it akin to the frame of a small cart
      • Via a magnet holding module attached to the square frame (in this case perpendicular to the overall frame) ,the Bag Holder and an external OpenBuilds cnc axis are magnetically coupled. This allows the bag to be moved in a reciprocating motion in and out of the spray nozzles, without the motors and other components being exposed to the Etchant
  • There are two Spray Nozzle Bars used to Speed up the Etching Time Drastically
    • They are powered by a Air Operated Double Diaphragm Pump
      • A device similar to a Water Hammer Arrestor is attached at the exhaust (need to double check if it is in fact the exhaust, device in question is shown at 19:04 in the Video ) of the pump to smooth out the airflow
• Finally the Photoresist is Removed
  • At 20:41 this process is mentioned
    • They used a Sodium Hydroxide Solution
    • Mentions that (at least with this Photoresist) it doesn't dissolve but rather "comes off in chunks"
    • They mention a "Flow Cell" where the solution would be flowed over the part, transporting any chunks with it out of the top of the bag (to aid in the automation of the overall process)
      • Didn't mention how successful it was, but either way mentioned that it has been disassembled pre-documentation and that the rest of the video will just leave the photoresist on

Internal Links

• Industrial Etching
• Engraving

External Links

• The Wikipedia Page On Photochemical Machining