What is Electroforming and where is it used?

The best way to describe electroforming is a metal forming process used to manufacture parts using electrolyte deposition onto a model. In the manufacturing industry this model is known as a mandrel. It is a highly specialized process which sounds fairly simple in theory but not so easy in practice. We will now take a look at the process in more details, when it is used and the advantages and disadvantages.                                         

The process of electroforming

The electroforming process involves the use of an electrolytic solution/bath. It is used to deposit nickel and other electro-formable metals onto a conductive pattern surface. This surface could be stainless steel, alloy steel, etc. The key is to build up the deposited material to the desired thickness at which point the master electroformed part is moved away from the substrate.

It is possible to use non-conductive materials such as glass, silicon and plastic for the mandrel. In this situation the mandrel would need to be covered with a conductive coating in order to encourage the electroforming process. When using non-conductive materials a conductive layer can be deposited chemically or using vacuum deposition techniques.

The electroforming process starts by passing high current through very clean water which produces ions from the anode. The water through which the current is passed needs to be extremely clean. It should not have more than about five parts per million organic contaminations. The active ions from the anode will find the missing electrons after contacting the mandrel surface. This creates an atom which will bind to its new donor surface.

Creating positively charged ions

During the electroforming process the positively charged metallic source material, the anode, is broken down (ionized) in the copper electrolyte solution. Due to the positive charge it is attracted to the negatively charged mandrel (model) the cathode. After the completion of the depositing process the mandrel needs to be removed. One of the best options is to remove the mandrel by chemical dissolution as it can be dissolved fairly easily.

Applications for electroforming

You will probably be surprised at the number of everyday items which are produced using electroforming. These include:-

1. The production of DVD_S and CD
2. This process is used to create molds to make interior parts/components for the automotive/aerospace industries
3. Coating the surface of the thrust chambers for rocket engines
4. The main combustion chamber for the space shuttle is electro fabricate with the nickel
5. Leading edges of blades and wings are coated by this method
6. Nickel stamper created on music album
7. The electronics industries uses electroforming to improve manufacturing/coating of components
8. Production of currency notes and postage stamps
9. To produce plastic optical lenses, holograms and mirrors
10. Creating tiny features and holes up to 2 microns in foils as thin as 5 microns
11. Adding nickel plating to medical instruments, screen printing, optical encoders, filtration and electric shaver foils

Materials

While there are many materials which can be used in the electroforming process, there are some restrictions. The materials more commonly used include:-

1. Mandrels are usually made of metallic materials like stainless steel and aluminium
2. A mandrel can also be made from a conductive plastic material
3. Materials which can be electroformed such as copper, chromium and nickel – sometimes with a variety of modifications
4. Expensive metals like gold and silver are also suitable for electroforming

Mechanical design guidelines

As with any process, there are specific mechanical design guidelines for electroforming which ensure that there is a uniform process across the board.

1. Products with a mass range of 1 Kg to 80 kg are suitable for electroforming
2. Section thickness for this product is limited to between 0.985 mm and 10 mm
3. A surface roughness of between 0.0157mm and 0.252mm is achievable via this process
4. The process has very tight tolerance limits of between 0.09 mm and 0.5 mm
5. The deposition rates is consider more effective in the range 12μm/h to 20μm/h
6. Able to create all types of complex solid and hollow bodies with flat and circular shapes
7. Tensile strength will reduce with increases in temperature above 50⁰C – in some cases the internal stresses decrease with increased solution temperature
8. Elongation is elevated slightly with the increased nickel content
9. When the PH of the electrolytic solution is increased the elongation of the product decreases
10. A brittleness property will be produced using this process
11. Material plated using electroforming is not suitable for welding

Advantages of electroforming

It is safe to say there are many advantages to electroforming over other metal forming processes such as:-

1. This process is very effective compared to other metal forming processes such as forging, casting, deep drawing, machining, fabricating and stamping
2. Within one micrometre of tolerance it can reproduce the external shape of a mandrel
3. The metal layering created using electroforming is extremely pure
4. Multiple layers of electroformed metal can be molecularly bonded together
5. A wide variety of shapes in different sizes can be made
6. Low production numbers can be made at relatively little cost
7. The metal crystallite structure created using electroforming is superior to other similar processes
8. There is excellent uniformity in the product shape because of uniform deposition

Disadvantages of electroforming

Unfortunately, there are always some drawbacks regarding specialist procedures and some of the disadvantages of electroforming include:-

1. More time is required for thick electroforming – some deposits may require a day or more
2. Electroforming can be expensive compared to other methods
3. The process is not suitable for deep or narrow recesses and sharp angles
4. Special attention and operating parameters are required for this process

Economics of process

Various elements of the electroforming process compare favourably to similar metal forming procedures but there are always some drawbacks. Comparing the pros and cons will dictate whether electroforming is the correct process for a specific product. Issues to take into consideration include:-

1. The fabrication of a product requiring only a single mandrel/pattern is easy to complete – therefore it is relatively cheap, compared to other metal forming processes, where only small volumes are required
2. The relative cost can be a little expensive for small production volumes of up to 100 units but the production cost is much more competitive above 500 units
3. Equipment cost is moderate compared to comparable processes
4. The tooling cost are low to moderate, depending up on the complexity of the design
5. Labour costs tend to be moderate – multiple skills are required for the job
6. There is a higher chemical cost compared to other electroplating procedures

References

1. Book of Nickel, cobalt and their alloys by joseph R. Davis by ASM international.
2. Super alloys by Matthew J. Donachie, Stephen j. Donachie