The Etching Process
Also known as 'Chemical Milling', 'Acid Etching', or 'Photo Etching', the etching process provides a versatile and cost effective manufacturing process for 2D metal components that apply to a range of applications.
Unlike alternative methods such as Stamping or Punching the Etching process requires no traditional 'hard tooling' which results in lower costs, other benefits of the Etching process include:
There are 8 separate steps between the receipt of the customer design and the final etched component, these are:
- Artwork Editing & Phototool Production
- Metal Selection & Cleaning
- UV Exposure
Artwork Editing & Phototool Production
The first step in the process involves the receipt of our customer artwork, our CAD & Sales Technicians will check and edit the file to create a 'phototool' ready artwork. This is arguably the most important step as ultimately the quality of the original artwork will determine the quality of the finished etched component, this is the reason why we request vector files as opposed to rastor type files.
Once complete the digital file is printed on photographic film, usually there is 'front' and 'back' tool which is joined to create an 'envelope', the registration is checked to ensure a high level of accuracy between the front and back image.
Metal Selection & Cleaning
Step 2 involves the metal selection and cleaning to remove amy oils/residue that may be present on the coils/sheet.
The cleaning of the metal can involve both a chemical and a mechanical cleaning process depending on the type and thickness of the metal.
Once the metal is cleaned and free from residue, a UV sensitive 'resist' is applied by a lamination process, this is applied to both sides of the sheet.
The laminated sheet is cut to size specific to the customer design, unlike other etching companies PPD Ltd. do not have a 'standard' sheet size, we process sheets as small as 300mm x 100mm up to large format sheet at 1500mm x 300mm or 600mm x 1200mm depending on the metal type and thickness, this ensures that the order is cost effective for both small hobbyists and also larger companies who are at the prototype stage of their project.
The laminated sheet is inserted into the phototool, a UV Exposure light creates a vaccum to ensure that the contact between the laminated sheet and the phototool is as high as possible.
The sheet is exposed to the UV light for a predetermined time, areas which are clear on the phototool are exposed to the light and are 'hardened', the black detail on the phototool remain unexposed and 'unhardened'. Areas that are 'unhardened' on both sides of the sheet in same position will ultimately result in a hole through the metal when etched, black detail on only one side of the phototool side result in an etch from one side only - normally referred to as a 'surface etch' or 'halfetch'.
The exposed sheet is passed through a conveyor 'Developing' machine where an alkaline solution 'washes' away the unhardened resist, leaving the hardened resist areas behind on the sheet. In the right hand image below you can see the bare stainless steel that ultimately will be etched during the etching stage.
Once developed our Metal Prep. Technicians carry out an inspection of both sides of each sheet prior to the etching stage.
The sheets are passed to our Etching Techncians who feed the sheets into the etching machines, the sheets travel on rollers between a series of top and bottom spray nozzles, these nozzles spray an acid etchant onto both sides of the sheet as the sheet travels through the machine.
The areas of the sheet that are protected by the resist remain unetched, bare metal is gradually etched away by the acid, parts that have bare metal in the same position on both sides result in a hole through metal, at the same time parts that have bare metal on one side only results in a 'surface' or 'half' etched detail.
You can see in the images below a sheet that in partially etched, the Etching Technician refeeds the sheets into etching machine until completion of the etch.
As the acid etches down into the metal it also etches into the sides of the metal, this results in a 'v' shape cusp on all etched through holes and around the cut perimeter, this is referred to as the 'undercut'. This results on all metals and thicknesses that are etched, on thinner metals it is not as prominant however on thicker metals it is visible and depending on the application may need to be removed and/or considered when drawing a part to be etched.
The pdf file below describes the etching process in schematic form and shows how the undercut is created.
Once the etching process is complete, the blue resist film must be removed, this part of the process involves using an alkaline solution that dissolves the resist leaving the sheets clean and ready for inspection
Each sheet is inspected and dimensional checks carried out to check for non-conformities, each sheet is then wrapped in tissue and packed for shipping.