Electroforming of hard nickel has been associated with the plastics industry for over 100 years. UK-based specialist of precision electoforming and mould making Rotoplas has been involved with this process for 50 years and, although conventional machining has vastly improved in recent times, there are still areas where the company’s process still rules.
The deposition of hard nickel on to male forms, or masters as they refer to them, is the basis of the process and comes into its own where accuracy and surface finish is of main importance. Take for example the reflex reflector part of the rear lens unit of any motor vehicle. It takes the sides of 3 hexagonal pins with precision ground forms on the end of each, mounted together to form a prism to allow the subsequent moulded reflector to do the job it was designed for. Rotoplas pioneered the process of producing solid one piece electroformed inserts, thereby eliminating the need to mount the pins themselves in the mould which could never be secured tightly enough that the plastic would not flow between them or, worse still, adhere themselves to the moulding on ejection.
Fresnel inserts are another good application because the required masters can be diamond turned in brass which allows an extremely accurate, highly polished surface finish to be achieved and can then be converted readily into electroformed tooling.
Helical gears, worms and threads are another superb application where to make the masters is a relatively straightforward gear cutting or thread grinding operation but with the bonus of knowing that whatever accuracy is achieved, the electroforming process will reproduce exactly. There is no need for EDM spark gap allowances nor worry over heat treatment movement normally associated with conventional machining techniques.
As well as injection mould inserts, Rotoplas supply electroformed components particularly allied to the medical industry. Known as melt or tip forming moulds, these are thin walled “shells” used for shaping the ends of extruded medical tubing. The average wall thickness is a nominal 0.5 mm and can be heated and cooled quickly to speed up cycle times. Because components are made from nickel, they will not corrode, thus allowing simple water cooling techniques.
Rotational casting moulds, particularly for PVC, is another area where electroforming comes into its own, especially where one piece moulds are required. Typical applications include moulds for prosthetic arms and legs, teaching aids, dolls and mannequin hands.
