Photochemical Etching and Machining
Precision Photochemical Machining provides an alternative to conventional stamping and machining methods for the generation of prototypes and production quantities. Alloys used for this process come in stock with thicknesses from 0.0003" to 0.063". Metals commonly used in this process are aluminum, copper, beryllium copper, brass, phosphor bronze, molybdenum, stainless steel, nickel alloys, kovar, mu metal and alloy 42.
The first step in the photochemical machining process is to generate artwork. A computer with Computer-Aided Design (CAD) software and a laser photo plotter are normally used to generate the artwork. It is produced from a fully dimensioned print or a DXF file. If a DXF file is provided, a print with at least the critical dimensions and tolerances should also be provided. Tolerances, type and thickness of metal, and quantity of parts need to be considered at this point. After the artwork is generated, a contact is made which is pin registered with the original. These two pieces of film make up the tooling from which parts are made.
The process then moves to the production department where the metal is cut, cleaned and coated with photochemical resist. The coated metal is sandwiched between the two pieces of tooling. During the printing process, images on the tooling are transferred to the resist, then developed, leaving the protective resist over the material which will become the part.
After etching, the parts are stripped of the remaining resist coating, dried and moved to the inspection station. Some companies provide secondary processes including forming, heat treating and plating. Parts should be inspected after the secondary operations have been completed.
General guidelines for photochemical machining are:
- Hole diameter in thinner materials can approach material thickness, but can never be smaller than material thickness unless reamed in a secondary operation.
- The smallest inside corner radius is directly proportional to the thickness of the metal.
- Outside radiuses are considered to be at least 0.66" of metal thickness. If requirements for a radius smaller than material thickness are necessary, other specific conditions are achievable.
- Type of metal, depth of etchdown, yield in relation to prototype, short runs, and production runs affect the acceptable tolerances.
Applications include shielding, screens, brackets, contacts, covers, lids, shims, spacers, coater wheels, lead frames, laminates, springs and heat sinks for aerospace, aviation, automotive, computer, electronics, dental, defense, medical, optical and telecommunications industries.
Advantages of photochemical machining are low-cost tooling, no burrs and no tool wear. Also, mechanical properties of metals are unaffected and there is no limitation on the complexity of the design.
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