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LFT: the future of reinforced thermoplastics?
LFT: the future of reinforced thermoplastics? The application
of long fibre
the automotive
industry
commercially Breugel,
Centre
advantages
F
ibre
available
reinforced
where
large production
processing
of Lightweight
thermoplastics
equipment.
Structures,
reinforced
plastics
(FRP) are
many cases the properties of these materials allow their application as a construction material where they replace, for example, metals. A second group of FRP is fibre reinforced thermoplastics, where thermoplastic material is used as the matrix for the fibre reinforcement. Compared to thermosets, these materials often show better impact properties, increased toughness and they can be processed a fast and clean way.
in
Ferrie
van Hattum
Large-scale application of these materials has so far been limited to short fibre reinforced injection moulding materials. The material properties in these cases are about two to three times higher than the unreinforced material. In the automotive industry glass mat reinforced thermoplastic (GMT) (often glass reinforced polypropylene) is widely used in semi-structural, compression moulded parts. ‘High end’ applications can be found in, for instance, the use of high quality thermoplastic matrices like polyetheretherketone (PEEK) with carbon fibre reinforcement. In spite of the excellent properties of this group of materials, their high cost and processing limitations allow only limited application in, for example, aerospace products.
Price
42
relationship
REINFORCEDplastics
between different
Ju n e 2 0 0 1
fibre reinforced
thermoplastics.
limited
to
I
and Sjef van
discuss the potential
a more economical
Continuous fibre reinforced plastics
Figure I: Price-property
mainly
runs offset the high cost of
the Netherlands,
of LFT over GMT and introduce
used in products where weight savings, reduced production costs, low maintenance costs and freedom of design are an issue. In these cases, thermosets are traditionally used, reinforced with glass or carbon fibres. In
has been
production
machine.
In terms of price and properties there is a huge gap between short fibre reinforced thermoplastics and GMT on the one hand and continuous fibre reinforced thermoplastics on the other hand. This keeps fibre reinforced thermoplastics from wider application as (semi-)structural materials in relatively cheap and fast processes for large production series.
LFT A relatively new group of materials, long fibre reinforced thermoplastics (LFT) can exactly fill this gap. LFTs are thermoplastics reinforced with discontinuous long fibres (a few centimetres in length) and (unlike GMT) are available in different fibre and matrix combinations. As a result, for every application the right material combination can be used. This characteristic enables LFT to fill the gap between GMT and continuous fibre reinforced thermoplastics (see Figure 1). Furthermore some specific advantages make LFT a serious competitor in terms of price for products in which GMT is traditionally used. In addition, the compression moulding process for these materials has not yet been fully optimised. Better control of the effect of the process on fibre distribution in the final product, and therefore on the material properties, can result in considerably improved product properties using the same materials.
0034-3617/07/$ see front matter 0 2001 Elsevier Science Ltd. All rights reserved.
LFT: the future of reinforced
The potential compared product
cost reduction
to
GMT
quality
and
has been
of LFT improved
demonstrated
in the front-ends of the Volkswagen Passat series which are currently made of LFT, at the expense of the GMT previously used. In this example
some advantages
of LFT over GMT are: the
possibility
semi-finished
of working materials
without
(in-line
extru-
sion compression moulding): less labour intensive; greater freedom of materials; lower
easier to recycle;
compression
forces
due
to
better flow which results in cost savings
with
respect
to
thermoplastics?
moulds
and
machinery; better surface quality; shorter cycle times; and less rejected products.
Economic advantages
of LfT
One of the reasons why the application of LET has so far been mainly limited to the automotive industry lies in the high equipment costs of commercially available LPT processing machines. Large production series are required to counterbalance these costs. CPI indicates that using its (direct) LFT process for glass/polypropylene (PP) LPT can be economically justified if the equipment is used to process approximately 450 000 kg of material annually. This can usually only be attained with applications in the automotive industry. By using its in-line process, savings of
In the West European automotive industry alone, it is expected that by 2008 LFT will account for 20% of the total amount of fibre reinforced thermoplastics used. Products in other markets are also suitable for the application of LFT. Examples include street furniture, self-supporting housing and machine parts.
approximately $O.SS/kg of material can be re&sed. This implies that using such a process, one has to take into account approximately $2SQ 000 of capital ar ld I royalty expenses annually. This is mainly caused by the high equipment costs of such a machine, The machine developed by the CLS costs only a fraction of its commercially available counterparts. This reduces required investments and associated risks to a minimum. This makes the LPT technology accessible for new markets, where much smaller production series are common.
[a) Melting the material
(b) Material ejection and insertion in the mould
(c) Compression and cooling
(d) Release product
The process The processing of LFT (see Figure 2) is very similar that of GMT and, to a lesser extent, sheet moulding compound (SMC), and can be described in a simplified way by four steps: melting the material; ejection and insertion in the mould;
Figure
2:
The processing steps
moulding
for LFT.
-
l
l
l
l
compression moulding; and cooling under pressure and release of the product.
In the processing of LFT the conservation of fibre length (and hence the mechanical properties of the final product) is vital. The first step, the melting of LFT, is therefore not done using a traditional extruder. Traditionally extruders work with high shear forces in the mat-erial, which causes considerable fibre breakage. Several companies have developed extruders especially for LFT, which melt the material whilst conserv-
ing the fibre length. However, these machines require a significant investment (about go.51 million), one reason why their application has so far been mainly limited to the automotive industry. In processing LFT two different methods are used, mainly differing in the initial materials used. Indirect LFT processing uses semi-finished materials supplied by several manufacturers in pellet form which are then melted in the extruder. Manufacturers that supply LFT with different fibre/matrix combinations include DSM, LNP, Asahi,
RTP and Ticona. To take advantage of the economy of the LFT process to the greatest extent fibres and matrix material can also be mixed in the extruder, so called direct LFT processing. This eliminates the need for semifinished materials. As a result of this cost reduction this is the preferred method in the automotive industry (still only in combination with glass/ polypropylene), where traditionally cost plays a dominant role. After melting, the desired quantity of material is ejected from the extruder and cut-off by a cutting device. The molten June
2001
RElNFoRCEDplastics
43
LFT: the future
of reinforced
thermoplastics?
at a pressure of at least SO-100 bars, after which the mould is opened and the product
can be taken out.
the
machine’s
sibility
New developments Because
of the
go with
the
large
investments
purchase
of the
to the automotive
in a ‘cold’
that
required
--t l
s
Structures
the
of Aerospace
ing fibre length
10
15
20
25
30
35
v, W)
1t
Ygure
4:
Stiffness versus fibre fraction for different LFh.
300
PP-GF
itj 100
ranging
polypropylene
from
reinforced
glass
fibre
(PP) to
polyamide
3) LFT combinreincarbon
(PA) have
and tested. The possibil-
ness and bending
strength
of the LFT
(in this case the two extremes: glass fibre
reinforced
in
stiff-
PP and
12.5 mm 25 mm
carbon fibre reinforced PA 12) versus fibre volume fraction are plotted. It is clearly shown that by modifying material combinations and fibre fractions a wide range of stiffnesses can be attained (the shaded area). In this way properties can be tailored to the final desired product properties. Extension of this area is possible by further change of the parameters mentioned. For comparison, the properties of GMT are also given, which clearly shows the position of LFT relative to this material. Note that in Figure 5 at higher fibre fractions the strength of the glass/PP material decreases. Too high a fibre fraction does not necessarily result in better properties. Apart from possible applications of LFT and attainable properties (Figure 1: New material combinations) the research at the CLS also aims at process control (Figure 1: Control): the relation between processing parameters, fibre orientation, and distribution and fibre length W product properties.
0
0
.-.'_
50
0
5
10
15
20
v, WI
rigwe 5: Strength versus fibre fraction for different L-s.
44
ations forced fibre
(Figure
fibre/matrix
=?Ix 0
D
and
(see Figure 3). Because of
0
l
5
of
of Technology,
Engineering,
l
0
Centre
(CLS TUD-TNO), a
A(
5000
machine
Figures 4 and 5, where the tensile
At
PP-GF PA12-CF (25 mm) GMT
10000 15000
this
different
ities that LFT offers are clearly shown
sector.
E w
Using with
motive
25000
20000
sector, but it’s
TN0 Industrial Technology, research is being directed LFT. As part of this work a patented piston-blender has been developed for melting the LFT while conserv-
mould, which then closes at relatively high speed. On closing the LFT material will start to flow to fill the mould cavity. During cooling the mould is kept closed
LFT at only minor
nities for the material outside of the auto-
faculty inserted
of processing
been processed
merger of Delft University is then
its
evident that there are also many opportu-
Lightweight
LFT material
construction,
investments.
extruder and press for the processing of LFT, the material’s use has mainly been limited
simple
cost is only a fraction of that of conventional LFT extruders and it offers the pos-
REINFoRCEDplastics
I un e 2 00 1
25
30
35
CLS TUD-TN0 is looking for companies interested in the application of LFT in products or in further development of the piston-blender to an industrial level. Aldert Verheus, CLS TUD-TNO, Delft, the Netherlands; tel: +31-l 52781778.
of long fibre
the automotive
industry
commercially Breugel,
Centre
advantages
F
ibre
available
reinforced
where
large production
processing
of Lightweight
thermoplastics
equipment.
Structures,
reinforced
plastics
(FRP) are
many cases the properties of these materials allow their application as a construction material where they replace, for example, metals. A second group of FRP is fibre reinforced thermoplastics, where thermoplastic material is used as the matrix for the fibre reinforcement. Compared to thermosets, these materials often show better impact properties, increased toughness and they can be processed a fast and clean way.
in
Ferrie
van Hattum
Large-scale application of these materials has so far been limited to short fibre reinforced injection moulding materials. The material properties in these cases are about two to three times higher than the unreinforced material. In the automotive industry glass mat reinforced thermoplastic (GMT) (often glass reinforced polypropylene) is widely used in semi-structural, compression moulded parts. ‘High end’ applications can be found in, for instance, the use of high quality thermoplastic matrices like polyetheretherketone (PEEK) with carbon fibre reinforcement. In spite of the excellent properties of this group of materials, their high cost and processing limitations allow only limited application in, for example, aerospace products.
Price
42
relationship
REINFORCEDplastics
between different
Ju n e 2 0 0 1
fibre reinforced
thermoplastics.
limited
to
I
and Sjef van
discuss the potential
a more economical
Continuous fibre reinforced plastics
Figure I: Price-property
mainly
runs offset the high cost of
the Netherlands,
of LFT over GMT and introduce
used in products where weight savings, reduced production costs, low maintenance costs and freedom of design are an issue. In these cases, thermosets are traditionally used, reinforced with glass or carbon fibres. In
has been
production
machine.
In terms of price and properties there is a huge gap between short fibre reinforced thermoplastics and GMT on the one hand and continuous fibre reinforced thermoplastics on the other hand. This keeps fibre reinforced thermoplastics from wider application as (semi-)structural materials in relatively cheap and fast processes for large production series.
LFT A relatively new group of materials, long fibre reinforced thermoplastics (LFT) can exactly fill this gap. LFTs are thermoplastics reinforced with discontinuous long fibres (a few centimetres in length) and (unlike GMT) are available in different fibre and matrix combinations. As a result, for every application the right material combination can be used. This characteristic enables LFT to fill the gap between GMT and continuous fibre reinforced thermoplastics (see Figure 1). Furthermore some specific advantages make LFT a serious competitor in terms of price for products in which GMT is traditionally used. In addition, the compression moulding process for these materials has not yet been fully optimised. Better control of the effect of the process on fibre distribution in the final product, and therefore on the material properties, can result in considerably improved product properties using the same materials.
0034-3617/07/$ see front matter 0 2001 Elsevier Science Ltd. All rights reserved.
LFT: the future of reinforced
The potential compared product
cost reduction
to
GMT
quality
and
has been
of LFT improved
demonstrated
in the front-ends of the Volkswagen Passat series which are currently made of LFT, at the expense of the GMT previously used. In this example
some advantages
of LFT over GMT are: the
possibility
semi-finished
of working materials
without
(in-line
extru-
sion compression moulding): less labour intensive; greater freedom of materials; lower
easier to recycle;
compression
forces
due
to
better flow which results in cost savings
with
respect
to
thermoplastics?
moulds
and
machinery; better surface quality; shorter cycle times; and less rejected products.
Economic advantages
of LfT
One of the reasons why the application of LET has so far been mainly limited to the automotive industry lies in the high equipment costs of commercially available LPT processing machines. Large production series are required to counterbalance these costs. CPI indicates that using its (direct) LFT process for glass/polypropylene (PP) LPT can be economically justified if the equipment is used to process approximately 450 000 kg of material annually. This can usually only be attained with applications in the automotive industry. By using its in-line process, savings of
In the West European automotive industry alone, it is expected that by 2008 LFT will account for 20% of the total amount of fibre reinforced thermoplastics used. Products in other markets are also suitable for the application of LFT. Examples include street furniture, self-supporting housing and machine parts.
approximately $O.SS/kg of material can be re&sed. This implies that using such a process, one has to take into account approximately $2SQ 000 of capital ar ld I royalty expenses annually. This is mainly caused by the high equipment costs of such a machine, The machine developed by the CLS costs only a fraction of its commercially available counterparts. This reduces required investments and associated risks to a minimum. This makes the LPT technology accessible for new markets, where much smaller production series are common.
[a) Melting the material
(b) Material ejection and insertion in the mould
(c) Compression and cooling
(d) Release product
The process The processing of LFT (see Figure 2) is very similar that of GMT and, to a lesser extent, sheet moulding compound (SMC), and can be described in a simplified way by four steps: melting the material; ejection and insertion in the mould;
Figure
2:
The processing steps
moulding
for LFT.
-
l
l
l
l
compression moulding; and cooling under pressure and release of the product.
In the processing of LFT the conservation of fibre length (and hence the mechanical properties of the final product) is vital. The first step, the melting of LFT, is therefore not done using a traditional extruder. Traditionally extruders work with high shear forces in the mat-erial, which causes considerable fibre breakage. Several companies have developed extruders especially for LFT, which melt the material whilst conserv-
ing the fibre length. However, these machines require a significant investment (about go.51 million), one reason why their application has so far been mainly limited to the automotive industry. In processing LFT two different methods are used, mainly differing in the initial materials used. Indirect LFT processing uses semi-finished materials supplied by several manufacturers in pellet form which are then melted in the extruder. Manufacturers that supply LFT with different fibre/matrix combinations include DSM, LNP, Asahi,
RTP and Ticona. To take advantage of the economy of the LFT process to the greatest extent fibres and matrix material can also be mixed in the extruder, so called direct LFT processing. This eliminates the need for semifinished materials. As a result of this cost reduction this is the preferred method in the automotive industry (still only in combination with glass/ polypropylene), where traditionally cost plays a dominant role. After melting, the desired quantity of material is ejected from the extruder and cut-off by a cutting device. The molten June
2001
RElNFoRCEDplastics
43
LFT: the future
of reinforced
thermoplastics?
at a pressure of at least SO-100 bars, after which the mould is opened and the product
can be taken out.
the
machine’s
sibility
New developments Because
of the
go with
the
large
investments
purchase
of the
to the automotive
in a ‘cold’
that
required
--t l
s
Structures
the
of Aerospace
ing fibre length
10
15
20
25
30
35
v, W)
1t
Ygure
4:
Stiffness versus fibre fraction for different LFh.
300
PP-GF
itj 100
ranging
polypropylene
from
reinforced
glass
fibre
(PP) to
polyamide
3) LFT combinreincarbon
(PA) have
and tested. The possibil-
ness and bending
strength
of the LFT
(in this case the two extremes: glass fibre
reinforced
in
stiff-
PP and
12.5 mm 25 mm
carbon fibre reinforced PA 12) versus fibre volume fraction are plotted. It is clearly shown that by modifying material combinations and fibre fractions a wide range of stiffnesses can be attained (the shaded area). In this way properties can be tailored to the final desired product properties. Extension of this area is possible by further change of the parameters mentioned. For comparison, the properties of GMT are also given, which clearly shows the position of LFT relative to this material. Note that in Figure 5 at higher fibre fractions the strength of the glass/PP material decreases. Too high a fibre fraction does not necessarily result in better properties. Apart from possible applications of LFT and attainable properties (Figure 1: New material combinations) the research at the CLS also aims at process control (Figure 1: Control): the relation between processing parameters, fibre orientation, and distribution and fibre length W product properties.
0
0
.-.'_
50
0
5
10
15
20
v, WI
rigwe 5: Strength versus fibre fraction for different L-s.
44
ations forced fibre
(Figure
fibre/matrix
=?Ix 0
D
and
(see Figure 3). Because of
0
l
5
of
of Technology,
Engineering,
l
0
Centre
(CLS TUD-TNO), a
A(
5000
machine
Figures 4 and 5, where the tensile
At
PP-GF PA12-CF (25 mm) GMT
10000 15000
this
different
ities that LFT offers are clearly shown
sector.
E w
Using with
motive
25000
20000
sector, but it’s
TN0 Industrial Technology, research is being directed LFT. As part of this work a patented piston-blender has been developed for melting the LFT while conserv-
mould, which then closes at relatively high speed. On closing the LFT material will start to flow to fill the mould cavity. During cooling the mould is kept closed
LFT at only minor
nities for the material outside of the auto-
faculty inserted
of processing
been processed
merger of Delft University is then
its
evident that there are also many opportu-
Lightweight
LFT material
construction,
investments.
extruder and press for the processing of LFT, the material’s use has mainly been limited
simple
cost is only a fraction of that of conventional LFT extruders and it offers the pos-
REINFoRCEDplastics
I un e 2 00 1
25
30
35
CLS TUD-TN0 is looking for companies interested in the application of LFT in products or in further development of the piston-blender to an industrial level. Aldert Verheus, CLS TUD-TNO, Delft, the Netherlands; tel: +31-l 52781778.