Dec 9, 2021
is a tolerance specification and is found on engineering drawings to describe the position of the center of a bore or surface.
The toleranced straight line or plane must lie between two planes that are perpendicular to the reference with the set distance.
For bore centers, the axis of a bore must be inside a cylinder of the given diameter.
The cylinder axis must therefore coincide with the location of the bore axes to the given reference planes.
There are special cases where a point can be set as a toleranced element (e.g. center of a sphere).
Quality assurance: Example for specifying a position
tolerance
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Dec 9, 2021
or also called line profile, is a form tolerance and describes a tolerance zone which is limited by two curves (envelope lines or envelope curves).
This tolerance defines how the curvature of a part must be designed.
The measured profile line must lie at every point across the thickness of the molded part between the envelope lines running at the given distance.
The distance between the two equidistant enveloping lines is formed by circles with the specified diameter.
The centers of the circles lie on the shape specified as geometrically ideal.
Quality assurance: Profile shape line
tolerance with enveloping lines at the distance of a circle diameter of 0.09mm
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Dec 14, 2021
This term refers to a tolerance zone which is bounded by two curves.
The area tolerated as the profile forming area must lie between two equidistant enveloping surfaces.
The spacing of these enveloping surfaces is formed by imaginary spheres with the diameter of the specified value, encompassing the entire specified curvature.
Quality assurance: Tolerated surface profile with representation of the enveloping surfaces
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Jan 17, 2019
The definition of quality according to DIN 55 350/T11 is “the nature of a unit as its suitability to meet specified and required needs”.
Different factors are used to evaluate the quality of plastic parts.
The easiest is the optical evaluation.
Visible surfaces should not contain streaks, burn marks, sink marks and/ or air traps.
The dimensional examination is used to control the functionality of the part.
Shrinkage and Warpage are main quality criteria.
The technical drawing shows the necessary tolerances of the part for an acceptable quality.
Mechanical testings are necessary to check the different applied forces on the part dependent on its usage.
Fiber orientation, weld lines, voids and wall thickness may lead to this quality failure.
The choice of the material and the processing, both influence the mentioned quality factors decisively.
Injection molding simulation and additional structure analysis help to check the quality of a part in advance.
May 31, 2019
Most of the resin used in injection molding are hygroscopic (water attracting).
After drying the plastic resin, a defined residual moisture content shall be ensured within the material.
This needs to be checked according to the specifications of the material supplier.
If the residual moisture is too high, there is an increased risk of air traps, void and other defects.
In addition to that, the mechanical properties of the part will be reduced, too.
Considering this, it is vital to measure the residual moisture content of plastic material before drying and before using it in injection molding.
Quality: Portable residual moisture meter.
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
