JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition - 67

into account in mass production of automotive components.
Moreover, the cost of the finished part that is directly linked to
the material and process cost will determine the selling price of
the vehicle and thus is a parameter of the highest importance.
Finally, considering vehicles life cycle and recent regulations,
recyclability cannot be neglected.
To summarize, the use of composite material for structural
parts in automotive mass production is subject to the following
constrains:
- Production time cycle
- Process automation
- Cost of the finished part
- Recyclability
- Performances (no regression allowed versus metallic parts)
The need for process automation and the production time cycle
requirements (thousands of parts per day) eliminates manual
lay-ups (textile or prepregs) as well as tape or yarn laying or
filament winding processes widely used in aeronautic industry.
Processes based on non-continuous fibers (short or long
fibers) as Sheet Molding Compound (SMC), Bulk Molding
Compound (BMC), Glass fiber Mat reinforced Thermoplastics (GMT) and Long Fiber reinforced Thermoplastics (LFT)
are complying with time cycle constraints but are secondary options because of the usual decreased mechanical performances
compared to continuous fibers processes. Finally, prepregs and
particularly thermosets that are quite expensive with costly
storage conditions and short life duration are not adapted to the
industry challenges.
Thus a "natural" selection of adapted manufacturing processes
for mass production of structural components can be done. It
leads to the two main following processes:
- Thermoplastic pre-pregs thermoforming (thermoplastics
remain quite expensive however they offer non-neglectable
recyclability possibilities and do not require costly storage
conditions). A schematic of the manufacturing chain is represented in figure 1.

Fig. 1: Thermoplastic prepregs manufacturing chain

Fig. 2: Dry textile/thermoset manufacturing chain

Both manufacturing chains generate stresses in the part that
will make it distort after demolding. In order to reach shape
tolerance requirements, most of the time the geometry of the
tool must be compensated.
For simple parts (simple in terms of complexity of the geometry and/or material layup) geometrical distortion can be
minimized by respecting recommendations on manufacturing
process parameters as well as product design rules coming
from either empirical approach, experience or rules of thumb.
However these approaches will not be sufficient when dealing
with more complex parts and besides the respect of product/
process rules, warping and/or spring-in will still be observed
after demolding. It then usually takes lots of testing modifying
process parameters and cycles compensating mold geometry
to obtain a part within desired geometrical tolerances and
respecting all minimum quality criteria for acceptance. These
trials are time consuming and very costly. Performing these
trials through simulation is of the highest interest because of the
consequent development time and cost reduction it represents.
Through the use of simulation, virtual trials can be multiplied
for a better understanding of the influencing parameters and
thus an optimized solution to the geometrical distortions.
However, industrial adoption of simulation for geometrical distortion prediction and correction is only possible when trusting
the simulation tool. A secondary criterion of acceptance is the
ease of use of the application that should not complicate the
task of the engineers. Whereas Finite Element Analysis (FEA)
is already well adopted in the industry for spring-back prediction and correction of metallic parts and besides several solutions already available in the market for composites application,
full industrial adoption (meaning replacement of physical trials
by numerical trials as what we can observe with metals) has not
been achieved.
This observation led ESI as a specialist in the physics of the
materials and leader in the simulation of the manufacturing
No88 April 2014 /

jec composites magazine 67

JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #88 - April 2014 - Special JEC Americas Spring Edition