Once the profile of a particular mould tool has been completed, post polishing can be completed to achieve a more consistent or higher specification of surface finish. For certain parts polishing is also used as a way of improving the moulding process by reducing surface friction while demoulding. In general, most moving sides of a tool require a line of draw finish to aid the ejection of the plastic part off the mould.
The level of polishing on moulds is defined by the SPI scale. There are 12 grades of mould finish ranging from mirror perfect to dull with SPI-A1 being the highest specification.
PolyGlobal’s core options:
A1 – requires tooling to be produced in high grade stainless steel but produces a flawless finish
A3 – accepted as a more general good quality and gloss finish
B1 – low polish finish where all polishing grains will be removed but surface finish will generally appear duller than higher grades
B3 – removal of machining lines to produce consistent finish but polishing grain will be visible
D1-3 – shot blast for a textured/rough finish. Will vary depending on the suitability of shot material/size which is part and mould material dependent
Unpolished – machine marks from mould cutting visible on the moulded parts
In general, the higher the surface finish required, the greater the polishing time involved and therefore cost in tool production. Some polishing standards require the moulds to be manufactured from certain grades due to their reaction to polishing materials. Unless requested, PolyGlobal tooling quotes are unpolished by default.
As well as varying levels of gloss finish, there are a number of graining preparation options for parts that require a textured finish. This is usually a very specific request linked to the application of the parts or to replicate a more traditional material such as leather.
Due to the variance between materials, some moulded parts will appear slightly different to others even though the surface finish of the mould is polished to the same specification. For example, polypropylene components will appear glossier than TPE parts from the same highly polished mould. Where matching an existing finish or reaching a certain specification is critical, samples can be provided in advance of finalising tooling options.