Metal Etching

View A Video on Metal Etching - A Quick Introduction

Traditionally, etching was performed by hand; hand engraving was implemented by using a fine tipped tool such as a burin to etch metal according to a desired pattern. This results in a unique and almost unrepeatable image being created although it is a time-consuming process. Today however, more commonly used techniques include chemical etching, photo etching or photofabrication and other processes such as stamping, laser engraving and water-jet cutting which are faster and more accurate than hand engraving. Laser etching is able to create very fine, clean lines in surfaces with little need for secondary finishing. Electro discharge machining, or EDM, is another method of metal etching which is able to achieve close tolerances. During the process, the metal part is exposed to streams of corrosive electromagnetic discharge. Any resulting imperfections, burrs or marks may be smoothed and polished away after the metal has been etched. It is a very versatile procedure and almost all metals can be processed using chemical milling, photo engraving or mechanical etching including: aluminum, brass, copper, nickel and stainless steel.

A popular method for metal etching is the use of chemicals, acids and bases as a reagent on surface of the metal part or plate. Using the process of masking and corrosive chemical exposure to create grooves, images, lines and holed surfaces, acid etching is able to achieve precise lines and specific depths. First, the metal sheet to be etched must be stripped of all oils and chemicals. Cleansers such as alkaline cleaners are used to strip organic materials, followed by an acid cleaner to remove chemical residue; neither of these cleansers can be too strong, or the polished surface of the metal will be scratched. Next, a masking is applied to the entire surface. Masking types are often tapes or paints, elastomers (rubber) or plastics. A pattern is cut into the masking in the same shape the metal is to be cut, then the cut masking is removed from the areas to be etched, and the chemical, or "reagent", is applied. After the acid has achieved its desired etch, both the reagent and the remaining photoresist are stripped from the metal part to reveal the final design. The length of time a chemical is allowed to react with a metal part depends on the desired depth of the grooves, and the strength of the acid. An understanding of chemicals and their corresponding characteristics is necessary to successfully implement chemical etching.

Mechanical milling, a common method used for metal etching, uses a lathe or CNC machine with fine tips which are able to process a range of materials and dimensions, including straight or curved surfaces. The computer of these machines controls the laser's or cutter's direction, pressure and speed resulting in a precise image or design with clean, fine lines. This method achieves precise and consistent results, but the initial tooling costs are high, and maintenance of the machines requires qualified personnel. Milling and grinding machines are also used to achieve certain etching finishes on metals, especially on larger sheeting used for architectural decorative or furniture purposes. A wide range of manufacturing options are available with these methods which are precise, accurate and repeatable. For some smaller processes and more intricate, decorative purposes, hand engraving is still used however it is restricted to a few narrow fields, but is still seen in jewelry, firearms, small decorative pieces and some musical instruments. Engraving or etching by machine and mechanical tools is more common. Widely available engraving machines are fairly simple to use and are able to engrave a number of surfaces such as metal, glass or plastic. Diamonds are typically used as the stylus, especially for machines required to engrave on harder materials and metals. Engraving equipment consists of three parts: a stylus or marking tool, a controller, and a surface

A variety of industries use methods of metal etching or acid etching for different purposes. Decorative uses include jewelry, firearm and musical instrument decoration, plaques, trophies and awards, as well as larger decorative purposes for architecture and furniture especially using stainless steel etching. For decorative etching, the surfaces are sometimes smoked so that the lines will be more visible. Industrial uses include stencils, printing plates, foil-stamping dies and more. Other industries requiring precision parts, such as the medical field, also use metal etching and chemical machining in order to achieve the desired fine finish on parts and components such as stents, cathodes and implants. Metal etching can also be used to help a metal part meet restrictive weight demands by removing a surface layer of a part through chemical or mechanical means. Metal etching services also create longer lasting stencils for the woodworking and art fields, printed circuit boards for the aerospace and electronics industries, and engraved or reduced missile skin panels and jet frames for defense.

Image Provided by VACCO Industries	Image Provided by KEMAC Technology, Inc.

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Metal Etching Types

• Abrasive etching is the process of using controlled, high-pressure compressed air to direct an abrasive, such as sand or aluminum oxide, at the surface of a material to create the etched effect.
  
• Acid etching uses acid to engrave the surface of sheet metal.
• Aluminum etching is used to create aluminum industrial parts that require many small grooves or holes, or a decorative finish.
  
• Brass etching is used to create brass industrial parts that require many small grooves or holes, or a decorative finish.
• Chemical etching uses acids, bases, and other chemicals to etch into the surface of metal.
• Chemical machining is used in many metal manufacturing industries to etch, cut or engrave metal plates in a number of capacities as it provides delicate and precise design capabilities.
• Chemical milling is a chemical process used by many industrial metal parts manufacturers to etch, cut, or engrave extremely delicate or precise lines into metal.
• Copper etching is used to create copper industrial parts that require many small grooves or holes, or a decorative finish.
  
• Dry etching refers to any etching process that does not employ the use of chemicals.
  
• Electroetching is an etching process that involves the use of chemicals, along with the employment of direct electric current.
• Laser etching employs the use of a laser for the removal of a specified pattern on a metal piece. Laser etching is often used in the jewelry industry.
  
• Metal engravers are metal tools used to carve designs into metal surfaces.
• Metal engraving is the process by which metal tools are employed to carve a design into metal.
• Photo engraving uses photosensitive material that is resistant to acid and applies it to the surface of a metal sheet. Acid is then applied, creating an image by burning through the areas where the acid-resistant material is missing.
• Photo etching, the most common metal etching process and otherwise referred to as "metal chemical etching," "chemical milling," "photochemical etching," "chemical etching" or "photochemical machining," is the process in which a desired image is etched on the surface of the metal part via a photosensitive template. The piece is then exposed to an appropriate acid (or etchant) that removes a layer of metal in areas left unprotected by the template, after which the piece is cleaned and the photoresist template removed.
  
• Photofabrication combines photographic processes and materials with chemical machining to etch, cut or engrave metal parts for a variety of industries. 
  
• Reactive Ion Etching (REI), also known as "plasma etching," is a dry etching technique. REI involves the use of electrical circuits and high-energy gas made up of ionized particles containing fluorine or chlorine.
• Sputter etching is a type of REI etching but without the employment of ions.
• Stainless steel etching is used to create stainless steel industrial parts that require many small grooves or holes, or a decorative finish.
• Vapor phase etching is a dry etch technique that uses reactive gases to achieve the desired etching pattern.

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Metal Etching Terms

Acid - A substance that, when dissolved in water, forms a solution with a pH of less than seven.

Bend Lines - Lines that are partially etched into the surface of the metal, which aid in the bending of the part in a subsequent operation.

Burn-In - The process of heating a developed photoresist image until the resist coating becomes chemically resistant.
 
Chemical Blanking - A term originally used to refer to the process of photo chemical machining (PCM).
 
Chlorine Regeneration - A process in which ferric chloride acid is regenerated to maintain high quality acid for the etching process.
 
Coating - The dipping, rolling, spraying, laminating, spinning, printing or flowing of the substrate surface layer of a photoresist material in order to cover it with a resist.
 
Contact Printing - A photographic process in which an image is transferred from one substrate to another.
 
Conversion Coating - The subjection of a substrate surface to high temperatures or the pickling process in order to improve photoresistant adhesion.
 
Dry Film Resist - Photoresist in the form of rolled sheet laminate.
 
Etch Band Design - Designing artwork for parts to be photochemically machined so that all shapes are outlined with a controlled line to be etched.
 
Etchant - An acid used to dissolve a layer of metal to form the component.
 
Fret - A series of etched parts that are tagged into a frame. Blanks usually have several frets etched into them.
 
Halogen - Non-metallic elements fluorine, chlorine, bromine and iodine.
 
Intaglio - An image etched/sunk into the surface of a piece.
 
Ion - An electrically charged atom or group of atoms, the electrical charge of which results from a neutral atom or group of atoms losing or gaining one or more electrons.
 
Liquid Resist - A photoresist applied to the substrate by dipping, roller coating or spraying.
 
Photodiode - A device that receives optical power and changes it into an electrical signal.
 
Photoresist - A material that, when applied to any of a variety of substances, becomes sensitive to portions of the electromagnetic spectrum and, when properly exposed and developed, masks a portion of the material.
 
Spectral Sensitivity - The rate of response of a photographic material to a particular range of the electromagnetic spectrum.
 
Substrate - A structure that underlies and supports or forms base material on which coatings are applied.
 
Ultraviolet (UV) - Invisible electromagnetic radiation.

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