• To classify the process, it can only be stated that "spraying processes" allow a higher production accuracy than pressing processes.
  • The classification of moulding material stiffness and hardness is unproblematic, as corresponding data are always available (moulding material manufacturers, databases). The classification of cross-border data is at the discretion of the user.
  • The classification of the expected calculation value of the processing shrinkage should be agreed with the manufacturer of the moulded part, if no own experience is available. A detailed compilation of guide values is available in the programme as a guide.
  • The assessment of the expected fluctuations in shrinkage may be problematic as a result of many influencing factors. This is where the moulded part manufacturer can be expected to provide the most effective help. In case of doubt, "only inaccurately possible" should be entered in order to consider further processing by means of a more precise tolerance series if necessary. ISO 20457/DIN 16742 specifies the following aids for classification:
    • Exactly possible: Calculated values of the VS are known, e.g. from experience, systematic measurements, computer simulations. Shrinkage anisotropy is insignificant or can be sufficiently accurately considered in the respective dimensional direction. Possible deviations from the calculated value are max. ± 10 %.
    • Accurately possible: Calculated values are known in ranges up to ± 20 %.
    • Only inaccurately possible: Calculated values of the VS are only known as rough guide value ranges. Shrinkage anisotropy cannot or only insufficiently be considered. Practical experience for estimating relevant calculation values is not available. Possible deviations from the calculated value are above ± 20 %.


In agreement with the users of rotational moulding of thermoplastics, the tolerance group TG9 was defined for this process.

For multicomponent parts, the tolerance group must be determined for each material and specified as a separate general tolerance (e.g. hard component according to TG5, soft component according to TG7). The more inaccurate material is the basis for defining tolerances for all material sizes.