DIN 16742:2013 Plastic Moulded parts–Tolerances and acceptance conditions-1
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Plastics moulded parts – Tolerances and acceptance conditions;
DIN 16742-2013A
In comparison to metal materials, significantly larger deviations in respect to dimension, form and location are usually to be expected when applying and manufacturing the moulded parts. Based on particular properties of the plastics (e. g. high deformability, low stiffness), the functional accuracy requirements are much lower than for metals in order to economically manufacture moulded parts with sufficient dimensional accuracy.
The properties profile is completely different from that of the metals owing to the special structure of the plastics and their material modification options. Properties of the plastics relevant to dimensional accuracy in the moulding application and during processing by the original mould method (injection moulding, compression moulding, rotational moulding) therefore require a much different evaluation and quantification of geometrical tolerances in comparison to the metal materials. The tolerance standards applicable for metal parts therefore cannot be adopted for plastic structures, or can only be done so to a very limited extent. That makes this standard necessary for production tolerances in respect to plastic moulded parts.
The special properties profile of the plastics means that three different dimensional reference levels defined in Annex A and characterised in respect to the main influential factors have to be taken into consideration.
Foreword
This standard was prepared by the Working Committee NA 054-05-13 AA "Tolerances for plastics moulded parts" of the Plastics Standards Committee (FNK).
The German version of the DIN 16742 shall be taken as authoritative. No guarantee can be given with respect to the English translation. A comma is used as the decimal marker. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights.
DIN [and/or DKE] shall not be held responsible for identifying any or all such patent rights.
Amendments
The following changes have been made in respect to standard DIN 16901:1982-11 withdrawn in 2009-10:
a) establishment of an extensive compatibility with international tolerance and fitting system according to ISO 1, ISO 286-1, ISO 286-2, ISO 1101, ISO 1660, ISO 5458, ISO 5459, ISO 8015, ISO 10135, ISO 14253-1, ISO 14405-1, ISO 14405-2, ISO 14406, ISO 17450-1 and ISO 17450-2;
b) replacement of a moulding compound list to be continuously updated by a type assignment based on accuracy-relevant properties;
c) classification of the mobilised production expense (process stability, quality assurance) for the required accuracy level from a realistic analysis of the capacity of the moulded part manufacturer in tolerances series (expense series).
Previous editions
DIN 7710: 1941-08, 1943-09, 1951-03
DIN 7710-1: 1959-05, 1965-04, 1974-01
DIN 7710-2: 1959-05, 1966-12, 1974-01
DIN 16901: 1973-07, 1982-11
The following logical processing sequence shall be complied with for the cooperation relations between moulded part development, moulded part production and tool making:
a) The moulded part designer decides on the functionally required tolerances resulting from the application conditions and the assembly with consideration of the moulded part requirements.
b) The moulded part manufacturer confirms, for compliance with the relation "functionally required tolerance ≥ tolerance possible by manufacturing technology", the tolerances possible with the manufacturing technology for the acceptance conditions of the moulded part production, whereby economic agreements (e. g. price surcharges) may have to be incorporated. The functionally required tolerances shall always be defined in the design documentation. In this way, absurdly accurate and uneconomical "fear and habitual tolerances" are avoided.
c) The material of the moulded part is bindingly defined by the moulded part designer upon order placement. He therefore establishes the basis for determining the moulding shrinkage. After order placement, calculated values in respect to the moulding shrinkage shall be agreed between the moulded part manufacturer and toolmaker or tool designer, whereby external experience (e. g. moulded part compound manufacturer) may have to be utilised.
Depending on the moulded part compound specification, moulded part design and tool layout, the processing of the plastics has a significant effect on the dimensional stability of the moulded parts. The processing machines of the primary shaping method are complex thermodynamic-rheological compound systems, which are still processed and optimised empirically despite highly developed manufacturing technology.
Dimensionally-relevant properties of the plastics include the extreme range of the type-dependent stiffness or hardness as well as the moulding shrinkage. Unsteady and inhomogeneous tool and moulding temperatures in conjunction with orientations of microstructures and additional tolerances due to flow systems lead to property anisotropies, which cause a greater or lesser deformation (warpage, distortion, contortion) of the moulded parts. Furthermore, wall thickness differences or mass concentrations / material concentrations can be possible causes for deformation. Form, location and angle deviations are therefore connected in highly complex ways, which make standardisation much more difficult in comparison to metals.
Unavoidable process-induced deviations are therefore to be expected for the moulded part. The procedure to be followed in the case of deviations depends on the function of the moulded part and is subject to mandatory agreement:
Eliminate deviation by design measures (strengthening ribs, material thickening, form changes etc.);
correct deviation by specified retention in the tool;
retain deviation and document it by limiting sample agreement or drawing correction;
leave deviation and document by "production deviation".
NOTE Process-induced deviations can be reduced both by effective design of the moulded part and by optimisation of the production process.
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