JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 30

low cost manufacturing

Holistic quality approach for autoclaveinjection composite manufacturing

By
Erik Kappel, Nico Liebers, Manuel
Buggisch, Philipp Hilmer, Markus
Kleineberg, Christian Hühne
Institute of Composite Structures
and Adaptive Systems, German
Aerospace Center (DLR)

he LOCOMACHS EU project (Low
Cost Manufacturing and Assembly
of Composite Hybrid Structures)
challenges today's manufacturing and assembly processes in order to smooth the
way for the impending ramp-up of nextgeneration aircraft. When manufacturing a
high-performance composite structure, the
term "quality" needs to be regarded from
diverse viewpoints since it covers various
laminate-specific parameters, such as fibre
volume content, porosity, homogeneity of
the degree of cure (DoC) and geometric
tolerance aspects. In the case of the ribs
for the LOCOMACHS Lean Assembly
Wing Box (LAWiB) shown in figure 1,
geometrical accuracy is as important as the
laminate quality itself. Therefore, a variety
of measures were implemented to monitor

Fig. 1: LOCOMACHS Lean Assembly Wing Box
(LAWiB)

High, reproducible CFRP product quality at a competitive
cost level as well as faster and more cost-efficient assembly processes are the enabler to high-rate production scenarios, which are essential to meet the increasing demand
for mobility in the future.

and actively tune all the relevant production
parameters.
The LOCOMACHS Lean Assembly
Wing Box (LAWiB) demonstrator is
derived from a previous Demonstrator
provided by Bombardier. This article focuses
on the CFRP ribs, which are manufactured
in an autoclave-supported, resin-injection
process. It outlines essential design, manufacturing, tool compensation, quality control
and overall cost aspects, which were considered within the project in order to allow
the manufacture of a competitive CFRP rib.
In particular, the cost assessment underlines
the holistic character of the approach.

Rib design, tool compensation
and manufacturing
In modern aircraft structures, part diversity
is immense since there are almost no common parts. Consequently, a specific mould
is necessary for each part variant, which is a
cost nightmare that directly suggests the aim
of reducing tooling expenditure by substituting cost-intensive state-of-the-art Invar
(Ni36) tools by cheaper aluminium tools.
Designing tools for CFRP components with
excellent dimensional fidelity is a challenging task in general, since the composite's
anisotropy and high-temperature processes
generate undesired process-induced distortions (PID) due to spring-in, warpage or

30 jec composites magazine / No96 April 2015

forced interaction [1]. The PID issue is even
exacerbated when low-cost tool materials are
used, since they typically show considerable
thermal expansion which can induce additional distortions. For the LOCOMACHS
ribs, these challenges were considered and
tackled. A weight-reduced, single-sided
aluminium tool was used which allowed for
the fabrication of a full set of two ribs in a
single shot. The autoclave injection process
was chosen because it combines economic
advantages, excellent part quality and considerable tuning capabilities. The nominal
tool shape of the aluminium tool was biased
based on PID predictions, derived with a
novel, efficient pheno-numerical simulation
strategy (p-approach) [2]. The approach
was extended within LOCOMACHS and
provided PID predictions of satisfying
accuracy while related modelling and parameter efforts were reduced to a minimum.
The preforming of the ribs, with NCF fibre
materials, was performed manually, while
the resin injection took place within the
autoclave. In-situ measurement data was
obtained with a novel ultrasound quality
control system which is briefly described
below. Real-time data was used to control
the parts' laminate thickness and, therefore,
its fibre-volume fraction by adjusting the
resin injection pressure during the process,
as shown in figure 2.

JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #96 - April 2015