electroforming

Electroforming Basics at Opti-Forms, Inc.

The Electroforming Process

Specialized Shapes

What is a Mandrel?

The Electroforming Process

The electroforming manufacturing method generates an exact copy via replication in metal (typically nickel or copper) of a master mandrel. Specific benefits of electroforming are low unit costs, exact atomic scale repeatability and excellent process control for quality.  Often times the design engineer will find electroforming is preferred for many applications requiring a complex true geometric shape form factor, thin walls, and high repeatability.

The process is additive in that the geometry of the desired part is accomplished by deposition of metal instead of removal of material as in typical machine tooling.  This mandrel is often three-dimensional, as in the case of a reflector (parabola, ellipse, conic etc.) or other complex shapes.

The mandrel is placed into a special electroforming tank where nickel is electrodeposited over it under very tightly controlled conditions.  Over a period of time (minutes to hours) the amount of nickel will increase in thickness, however the original mating surface against the mandrel remains perfect.  This addition gives the product appropriate structural integrity.

During the process, pure nickel is deposited onto a stainless steel mandrel.  This mandrel is precision machined, ground and polished in a precise negative of the desired form geometry.  Other materials can be used for a master (high grade plastics, glass, aluminum, etc.) with special preparation, but due to their high attrition rate, they are not suited for high-volume, long production runs.  Since the master is directly responsible for the electroformed mirror's geometry as well as for its surface specularity, the finished mirror is an extremely accurate replication of the master's surface.

When the electroforming process is finished, and the pre-determined thickness achieved, the mandrel is removed from the plating solution and the electroformed part is carefully separated from the mandrel.  The mandrel is cleaned and prepared to make yet another cost effective exacting replica.  The nickel replica is processed to remove any sharp edges and becomes a solid freestanding, exact replica of the mandrel surface.  The replica is now ready to be coated with a spectral enhancement for its specific use.

Opti-forms has developed specialized fabrication techniques for the production of these masters as well as testing methods to insure the highest possible surface accuracies. Typically, our master geometry will not deviate from the specified theoretical geometry by more than +/- 2 arc minutes of surface slope. The final surface specularity of the polished master is typically 80-50 scratch and dig per Mil-O-13830A.  Another advantage of stainless steel masters is their capability, in most cases to produce thousands of electroforms with only minimal interval polishing to preserve the original surface quality.

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Quality Control

Our extremely accurate electroforms are a result of careful and precise control of all the vitally important plating parameters which can adversely affect the internal stress of plated deposits during the electroforming cycle.

More on our Quality Control

Specialized Shapes

The unique process of electroforming affords the production of exotic, complicated shapes at substantial cost savings over conventional manufacturing methods such as grinding and polishing glass, diamond or other single point machining etc.   Aspheric shapes such as paraboloids, ellipsoids, hyperboloids, as well as off-axis segments can be produced in volume at a fraction of the cost of these conventional optical fabrication techniques.  Since electroforming is a process of replication, each electroform will exhibit equal physical and optical characteristics as the previous one for a uniform consistency in product quality.

OFI has the capability of producing a variety of these specialized shapes including laser pumping cavities, parabolic and elliptical 2-axis linear troughs, ophthalmic molds, multi-faceted integrating mirrors, as well as full aperture, stress-free, off axis mirror segments. These “segments” along with custom-cut geometric configurations and access holes are precision cut with our electrical discharge machine (EDM). This unique and extremely accurate process eliminates optical distortions and dimensional deviations usually induced by conventional machining methods.

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What is a Mandrel?

A mandrel is the original from which a replica is electroformed. Most mandrels are made from stainless steel.

Mandrels are either expendable or reusable. Reusable, or permanent, mandrels are often made of stainless and expendable mandrels of softer, easily machined materials like aluminum.

The expendable mandrel is destroyed in the separation process.  They are commonly used when the mandrel has features preventing it from being mechanically separated from the electroform. Coldshields, by design, contain reentrant angles and must be electroformed on expendable aluminum mandrels that are chemically dissolved after electroforming as there is no other way to disassociate the two.

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