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Engineering Intricate Metal Parts

Fri, 12/14/2012 - 10:16am
Hassan Nojoumi, President, Shimifrez Inc., Toronto, Ont., Canada

Photochemical machining and electroforming offer alternative, non-mechanical prototyping methods for precision parts.

Microetched parts include gimbals, pinholes, optical grids and meshes, electrical probes, and flat springs. All image: Shimfrez Inc.Industries that require precision metal parts often turn to conventional mechanical processes such as pressing, stamping, and laser cutting. While these methods offer advantages, photochemical milling/machining (PCM), also known as chemical blanking, is a complementary process that can produce intricate metal components that are burr-free, stress-free, and ready to be quickly and economically heat-treated.

PCM processes are widely used to manufacture complex geometries and precision metal parts for aerospace, microelectronics, medical devices, automotive, and consumer industries. Each day, millions of chemically milled components are produced to within ± 10 to 15% of the metal thickness down to a thickness of 0.0005 inches. An overall tolerance of ±0.001 inches can be maintained and even closer tolerances can be achieved.

The PCM manufacturing process begins by cleaning the metal and coating it with a light-sensitive resist. The coated sheet is then exposed to ultraviolet light through the photo tool from both sides, hardening the photo resist where exposure takes place. The unexposed areas are developed away, removing the resist and leaving the metal bare where etching will occur. Etching solution is sprayed under pressure onto the top and bottom surfaces, accurately producing the component by removing the unwanted metal. The resist is then removed to leave burr- and stress-free precision components.

Microcontacts/pinhole contacts for microelectronics devices.One benefit of precision photoetching is the quick and inexpensive prototyping cycle. The photo tools used in photochemical machining replace conventional steel tools and dies and can be generated in hours from a supplied computer-aided design (CAD) drawing. Prototyping cycles can be reduced from weeks to days, compared to hard tooling. Furthermore, as the tooling does not wear out, it only requires replacement when design changes are made. The stop-and-repeat printing of masters ensures maximum material usage and significantly reduces individual component cycle time. From initial tooling to finished parts, the entire photoetching cycle can be completed in days.

The photo tool, which acts like a stencil, is the foundation of accuracy. Its only working exposure is to light; so there is no tool wear that needs to be monitored. Dimensional tolerances are a function of the thickness of the material. Typically, dimensions can be held to ± 10% of the thickness of the material.

Another benefit of photoetching prototypes is that material properties are unaltered. PCM imparts no mechanical stresses on metal substrates. Where stamping, punching, and die-cutting impart shearing deformation and laser and water-jet cutting can leave ablative deformation, photochemical machining simply dissolves the unneeded metal, leaving a flat and burr-free part.

Virtually all materials can be etched, although some are etched more easily than others. Etching is basically rapid, controlled corrosion; corrosion-resistant materials—titanium, tantalum, and gold—are difficult to etch and require extremely corrosive etchants. However, materials such as stainless steels, beryllium copper, copper-cladded materials, bi- and tri-metals, and nickel and brass alloys can be etched readily by using aqueous solutions with ferric chloride or cupric chloride.

Precision products
PCM has proven effective for producing thin (less than 0.040 inches thick), complex, precision parts at an economic price. Examples include sieves and meshes, shims, washers, optical encoder discs, metal filters, EMI/RFI shielding enclosures (board level shielding), hybrid circuit pack lids, sensor components, atomization applications (pin holes), beam aperture nozzles and flow orifices, evaporation masks, and fuel cell plates. In addition, the process has been used to fabricate components used in microelectromechanical systems (MEMS), medical diagnostic equipment, and biomedical engineering applications, such as body implants.

IC lead frame/heat sinks for integrated circuits applications.PCM can be used for 3D applications
Etched bend channels allow the sidewalls of a design from a 2D flat part to be folded into a 3D-finished shape quickly and precisely. The etched bend channels, which are typically intended to create 90 degree right angle bends, also can be used to create acute angle bends between 0 and 90 degrees. Since the shielding enclosure can be formed without the need for any traditional forming tooling, a user can cut tooling costs and delivery lead time for prototype and production needs. In addition, the etched bend channels exhibit a zero inside radii when formed.

Electroforming
Electroforming is a specialized process that produces precision metal parts that are four to five times more accurate in getting to tight tolerances than chemical etching. This metal forming process grows metal through the electroplating process. The process creates an electroform piece through electro-deposition of a mandrel in a plating bath (nickel, gold, or copper) onto a conductive patterned surface. The electroformed part can be stripped off the mandrel, once the material is plated in the desired thickness. The electroforming process allows extremely precise duplication of the mandrel. This results in perfect process control, high-quality production, and high repeatability. This makes electroforming suitable for low-cost production and high volumes. The high resolution of the conductive patterned substrate allows advanced geometries, tighter tolerances, and higher edge definition. When requirements call for extreme tolerances, electroforming is very effective.

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