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Abdelhak Nafi
Abstract
Evaluation and optimization of plastics injection moulds obtained by Stratoconception® process
Abdelhak Nafi - 23 march 2005
This research is a contribution to the study of the behaviour of
brazed assemblies, intended for the realization of
thermoplastics injection moulds, obtained by the
Stratoconception® process. This rapid-tooling process is
characterized by the stacking of elementary steel sheets,
machined then brazed together. For deep cavities, it represents
an attractive alternative to bulk machining, bringing a
significant profit in cost and delivery time of moulds.
During the injection process, the mould undergoes significant
stresses due to the closure forces on the mould and due to the
flow of the injected polymer. Assessing the mechanical strength
of the mould to these stresses requires a fine study of the
behaviour of the brazed assembly. The prediction of the working
conditions of a brazed assembly constitutes the objective of
this study.
In a preliminary stage, tensile tests have been carried out on
laminated specimens, brazed with three grades of silver-copper
braze alloy, in order to determine the most favourable operating
conditions.
In a second stage, mechanical (tensile, compression, shearing,
and fatigue) tests have been carried out, in order to
characterize the brazed assembly under the configuration
regarded as favourable. An elastoplastic behaviour with
isotropic work hardening of the braze material was identified
using a least-squares method, based on experimental results and
on finite-elements calculations. The 3D elastic behaviour within
the brazing joint was studied, under various loading conditions,
so as to predict the conditions for plastification of the joint.
Last, a numerical study of the geometrical parameters of a
brazed assembly was carried out to evaluate the stress
distribution within the brazing joint (under pure shear and
traction loadings, respectively). One of the most important
results of this research provides the coefficients of stress
concentration applicable to an injection mould built via the
Stratoconception® process.
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