Comparison with other technologies
Tolerances
Borings
Threads
Uniform cross-sections
Injection
The injection point (gate) is usually positioned so as to belong to the die line. The effects of gate location must be considered as far as possible at the design phase and must be accounted for when considering the feasibility, balance of weights, functionality and aesthetics of the part.
The gate, just like the parting line, leaves a thin line of flash which can normally be estimated at:
- Parting line flash: maximum excursion 0.04mm, with average excursion 0.018mm and 70% of values below 0.02mm.
- Gate flash: maximum excursion 0.2mm, with average excursion 0.14mm.
The gate is generally positioned at the maximum cross-section of the part, to enable the material to flow from the larger towards the narrower section, for obvious reasons of fluid dynamics; indeed the material, as it fills out the shape, tends to cool down and thus lose much of its fluidity (due to the increased viscosity of the lower boundary temperature). It is thus evident that the boundary should be used for filling small, narrow spaces, and that sudden increases in section, which tend to obstruct even further the flow of the material, should be avoided, as they create areas of lower density.
Only when the part is narrow relative to its length (ba••>6l where l indicates the length and a and b are the lateral dimensions) is it advisable, to promote rectilinearity, to position the gate at the narrower section rather than the widest one, although special injection parameters must be used to optimise the injection process.
Surface finish
Assembly of green parts
Materials
Mechanical characteristics