February 2017 Archives

(1)What is photo electroforming

"Photo electroforming" is an electroforming method developed by applying the photomechanical technology. This method has enabled ultra-fine processing at ultrahigh precision. Compared to the other processing methods, photo electroforming can reproduce a number of same images on a broader area at high precision. Owing to this superior feature, photo electroforming has been developed as a processing method for precision electronic components.

The photoresist technology has been applied to the production of CD and DVD discs. They are produced by applying photoresist on the glass master disc, followed by perforation using physical energy to record data and nickel electroforming. This processing method is frequently used for manufacturing plates with precise perforation.

The other method of using photoresists besides photo electroforming is called photo etching, which uses chemical reactions to dissolve and corrode the surface. This method is applied for precise processing of thin plates and films. Yet, photo electroforming is a better choice for fine processing of complex-shaped objects at higher precision.

Photo electroforming is similar to photo etching and chemical milling processes. The difference is that electroforming electronically deposits a metal layer on an area not covered by protective films (photoresist) whereas the latter uses etching (corrosive liquid) to dissolve the surface chemically.

Photo-electroforming can be used for more complex processing by integrating another precision processing method called photo etching.

Photo electroforming produces higher precision than the etching method, but it uses the plating technology to electroform thin metal plates into a desired shape. For this reason, this method can be used for certain types of metals, such as nickel, copper, gold, silver, nickel-copper lamination layer, nickel alloy and so on. The difference from the conventional electroforming is the process of creating an original plate and forming a photoresist layer.

Stamping (metal pressing) requires high precision molds. The mold production is not only time-consuming but also expensive, less accurate, and prone to processing strains or burrs. Compared to this, the photo electroforming method is less expensive, resistant to processing strains, and highly accurate. Although it requires an original plate that takes days to complete, you can create precise and sharp objects that you were not able to produce using stamping or electro-discharge machining.

The electroforming method is applied for production of electronic components and precision machinery parts for its excellent precision. However, the longer electrolysis time is not suitable for mass production, which makes this method less appropriate than etching. The electrodeposited layer must have at least 4 µm. Otherwise, it will fracture or crack when you separate the layer from the base material.

Electroforming has been utilized for producing precise copies of metal objects by accurately replicating surface conditions and dimensional accuracy even for complex-shaped objects that are difficult to work with or not compatible with machining. In recent years, electroforming has been developed for more applications in a wide range of fields. However, due to many disadvantages of electroforming introduced in the previous volume, it is frequently used for products that their quality and accuracy outweigh the cost performance. Electroforming is utilized in the following fields:

1) Production of replicas

Master copy of music records, compact discs, laser discs, and optical discs.
Marking board used for reproducing wood-grain, crocodile, and woven patterns on plastics, leather, or cardboards.
Press plates for printing, printing rolls, standard specimen for surface roughness, spray masks for painting, clock face, etc.

2) Production of molds

Production of plastic injection molds in complex shape/design, compression molding dies, continuous casting molds for steel, heat-resistant molds for glass, aluminum, and zinc die cast, molds for printing letters, etc.

3) Electrosizing

Repair, reclamation, or calibration of mechanical components, including molds, rolls, shafts, bearings, and gauges, to compensate the lack of dimensional accuracy or overlaying worn-out areas.

4) Electroassembly

Assembly of pitot tubes and waveguides, production of cutting tools with abrasives (diamonds/silicon carbide) attached, and production of various composite materials, etc.

5) Electrocladding

Nickel coating for steel plates, jewelry and rare metal decorations, coatings for plastic processing, photo film/print rolls, etc. Apply metal coating over wooden or plastic products to add mechanical strength and metallic appearance.

6) Production of foils, laminates, sheets, and hollow products

Production of seamless pipes, hollow containers, copper float, containers, foils, sheets, screens, wire meshes, sieves, outer blades of electric razors, etc.

7) Others

Production of parts requiring precise dimensions or surface conditions that cannot be produced by any other methods. The examples are radar waveguides, caps for fountain pens, reflecting mirrors, Venturi tubes, meandering tubes, bellows, mechanical parts including cams, horns (musical instrument), precision electronic components, jet engine parts, space development fields, etc.

Copper used to be the main material used as electroforming bath for its stability. However, the functional requirements for its physical metallurgy are becoming more important alongside the spread of electroforming.

Nickel has superior physical and mechanical strength with the enhanced resistance to corrosion and abrasion. A new technology established has allowed us to adjust physical and mechanical characteristics such as hardness, stress in electrodeposits, and flexibility of electroformed nickel in a broader range.

In addition, nickel aminosulfonate enabled electroforming while minimizing stress in electrodeposits at high current density. The physical and mechanical characteristics have been improved not only under normal temperature but also at high temperature by the alloying techniques of using cobalt or various metals, as well as the composite method where fine particles made of hard materials as fine ceramics are dispersed for causing a eutectoid reaction. Owing to this improvement, electroforming is now applied in a wide range of fields including accessories, fine arts and crafts, electronic and ultraprecise components.

The following measures must be implemented in order to meet the required characteristics:

(1)The material must be strong and durable enough for the designated purposes since electroformed objects are used as metal products.
(2)In order to prevent stress corrosion, metal fatigue, product warpages or cracks, the stress in electrodeposits must be zero or extremely small.
(3)In many cases, the electrodeposited layers tend to be thick. To reduce the electrolysis time, electrodeposition must take place at high speed using high current density. This will increase the electrical charges flown into the electroforming bath, but the solution must be stable under this condition.
(4)To make the additional processing of electroformed products easier or to obtain homogeneous strength, the thickness and metallic structure of the electrodeposited layer must be consistent.

[Table 1] summarizes the points of concern for adopting the electroforming technology.

[Table 1] Characteristics of electroforming

A surface treatment technique called "electroforming" is an applied technology of electroplating. According to the JIS terminology, "electroforming" is defined as a production, repair, or duplication method for metal products by electroplating. In English, "electroforming" is the most common terminology, but "electrotyping" and "electrocasting" are also used to refer to the same process.
A general electroforming process starts with depositing a metal layer of a certain thickness on a model (known as master mold or mandrel) by electrolysis of metallic salt solution (such as plating solution). Then, separate this electrodeposited layer from the master mold to form an object in reverse (negative) of the master mold. This electroformed object can be used as-is, but you can also form a positive object, which is a perfect replica of the master mold as well. In order to do this, first perform the resist separation treatment (pretreatment that prepares electrodeposited metal to be easily removed from the mold). Then, separate the mold after electrodepositing a metal layer of a certain thickness.
By repeating the same process using the inverted object, you can produce a number of objects replicating the master mold in the same dimensions.
In addition to separating a copied object from the mandrel, electroforming can be also applied by electrodepositing a metal layer directly over the substrate metal. This method is useful when you repair worn-out molds or shafts by overlaying their surfaces.

Electroforming can be classified into mold-release and plating-up methods.

1) Electroforming by mold release

In this method, products are manufactured by electronically depositing a metal layer over the master mold and separating it from the mold. Products manufactured in this way can be an extremely thin object like a mesh or a product as thick as several millimeters, such as an injection mold for plastics.

2) Electroforming by plating-up

This method is performed for repairing mechanical components or overlaying the worn-out surfaces by directly electrodepositing a thick layer on the substrate metal. This method is not designed for mass production. In most cases, all it takes is a single application of electroforming. The technology is applied for other techniques including electrosizing, electrocladding, and electroassembly.

Electroforming by plating-up is a method that deposits a thick layer by applying general electroplating for a long period. Electroforming by mold release has the following subcategories:

a) Transfer method (separating an electrodeposited layer by the resist separation treatment applied on the master mold);
b) Impression technique (replicating an original item using plastics, varnish, or cements when only one of those is available; such items include fine arts and crafts or items made of wood, leather, or textile);
c) Material removal by melting (creating an original mold with low-melting-point alloy or wax to make an electroformed shell after removing the mold material)

Electroforming is utilized for a wide range of applications, including fine arts and crafts, production of electronic and precision components, etc. Without electroforming, you cannot manufacture some of the complex-shaped items that are not compatible with machining. When the electroforming technology first became available, copper was the main material because of the stable characteristics of its solution suitable for electrodeposition. Today, nickel or its alloy material has been adopted for their superior mechanical strength. In addition, nickel aminosulfonate solution has speeded up the electroforming process.