Plastics News Europe - June 2019 - 9

automotive plastics

He said that the "dog-house" structure with 30% rib-to-wall ratio needed on the under-surface of compact
parts to avoid sink marks requires high
pressure moulding with steel tools.
But "changing the way we design
plastic parts for foam moulding" allows a simpler rib structure with 90%
rib-to-wall ratio and therefore lower
pressure in less expensive aluminium
tools, due to lower milling costs.
Part costs are then lower on account of faster cycle times through
aluminium having five times higher
heat conductivity than steel. This also
helps, together with avoiding thick
wall sections, in avoiding post blowing with micro foam bubbles expanding in hot spots after demoulding,
which can otherwise only be avoided
with longer cooling time in steel
tools. One supplier gave up hopes of
using foaming moulding on this account alone, Prince said.
On tool life, Prince told Plastics
News Europe "Cars will not need high
volumes in future. Ideally, the tool
should just collapse when the required
production numbers have been
reached, but we can do one million
parts in aluminium, without steel tool
corrosion problems".
Prince favours Trexel's MuCell microcellular foam moulding technology for little or no moulded surface
swirling effects, in aluminium moulds

Audi A6 Infotainment carrier,
produced by a one-shot forming
and overmoulding process

with Cera Shibo liquid nano-ceramic
mould coating, developed by Eschmann Textures. The single-layer ceramic grain structure replicates better
than chemical etching or laser structuring and costs the same as graining
by spark erosion, Price said.
"Polypropylene is key", Prince
said, "the best, friendliest material,
used a lot in vehicles and it works well
with ceramic mould coating, with
which the plastic melt is more fluid
and flows better. So there are no
weld lines with sequential gating, enabling thin large parts to be easily
moulded".
For painted foam mouldings, "You
have to wait 3-4 days for nitrogen diffusion", Prince said. His company is
seeking a paint supplier for a solution
here. He was not sure whether release agents are still needed with the
ceramic coating when decorating surfaces with polyurethane in-mould
coating in e.g. in the KraussMaffei
Colorform process: "We haven't tested it, but should and will look at it".
Although talc filled PP and unfilled/
unreinforced ABS have low wear on
the ceramic coating, Prince admits GFABS has high wear, "But although I
am hoping to use more softer wood
fibre reinforced material in future, we
are nevertheless working on glass fibre
reinforced plastics wear".
Dr Wolfgang Meyer, head of central functions & innovation at the
Volkswagen pre-production development centre, spoke about "additive
manufacturing [AM] for agile product
development", which becomes more
important as car model availability in
the market reduces - from 9 years for
the relative simple Golf I in 19741983, to 4 years for the more complex
Golf V in 2008-2012, with corresponding lower sales, down from
6.72m to 2.85m cars.
The Volkswagen 3D printing centre produced 23,000 parts/year in
2017 on 12 machines in five processes: for plastics, EOS and 3D Systems
selective laser printing polyamide 12
(SLS: 13,981 parts), Stratasys Polyjet
Connex ink-jet ABS-like (3,012 parts),
Stratasys fused deposition modelling

Evonik
celebrates
40 years
of PEBA
june 2019

Ceramic-coated aluminium mould halves
developed by Prince-Weiss

ABS (FDM: 2,805 parts), 3D Systems
epoxide photopolymer stereography
(SLA: 2,977 parts); for aluminium, selective laser melting (SLM: 400 parts).
Volkswagen produced 194 parts,
representing 95% of all relevant
parts, as AM prototypes in Golf 7 development.
Meyer said VW uses AM to assess
"geometric integration" and visual
appearance. It should ideally not require post-processing, but VW also
really needs to develop parts "with
properties largely identical to serial
production parts, such as with injection moulding", in future also for prototypes capable of e.g. crash testing.
He said these issues are subject of
university research at e.g. IKV and industry partners. A 2018 IKV master
degree thesis compared PA, PP and
PC-ABS printed and injection moulded mechanical properties. A current
IKV research contract for VW aims at
development by 2022 of printed
parts with serial production mechanical properties.
Meyer told Plastics News Europe
that modified PP for 3D printing is still
very different to injection moulded PP.
Prof. Hopmann of IKV asked whether
research information would be proprietary to VW or if VW would cooperate with other automotive OEMs.
Meyer replied, "I can imagine sharing
VW additive manufacturing knowledge via e.g. the Formnext trade fair,
so it wouldn't be just for VW".

In 1979, Evonik launched the
thermoplastic elastomer polyether block amide.
Whether in sports equipment, hydraulic pressure
lines in trucks, medical devices or 3D printed hightech parts, Evonik's polyamide 12 elastomers kept
finding their way into new demanding applications
over the past four decades. www.vestamid.com

http://www.vestamid.com

Plastics News Europe - June 2019

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