ET COMPOSITES DANS LES VEHICULES RENAULT
MASS PRODUCTION COMPOSITES
Aimé Jardon, Vice Président and Michel Costes, Head of Plastic Research
Imagine a car
which never rusts even if you scratch it.
Imagine a car yen never have to take to the repair shop even if yen accidentally scrape it against a tree. And imagine that this car is cheaper than what you are used to paying.
Is it fiction? Not really
That is what composites can lead to if they are used in the automotive industry.
Of course, up to now, composites were rather related to "High Performance/Low Volume" industries like Aerospace or Surgery. They have enabled major advances in these fields. Revolution has been a widely used word for qualifying the benefits they brought to the industrial product.
And yet new materials are net confined to "High Performance/low Volume" industries. From a french study (BIPE 1986) (figure 1), the automotive industry accounts for 25% of new materials outlets. The came paper estimates composites growth (High Performance and Mass Production) at 8% during the period 1983-1990.
In this presentation I will examine the possibility of composites entering the "Mass Production" industry and 1 will base my talk on the industry 1 know best: the automotive industry.
The first question to be addressed is:
Why are composites now so widely used in 'High Performance/Low Volume" industries and why are they less employed in "Mass Production" industries (figure 2).
As a basis for discussion,. let°s tape two examples:
The aim of these
two sectors is profitability. So the answer must bc in terms of
In every rase, the complote cost of a service is composed of.
An examination of the aerospace and automotive industries shows a difference in the relative share of these three components:
In this field, the
selling price (and so the manufacturing cost) of the vehicle is
We can indeed notice that:
Customers of aircraft mantifacturers watch their operating costs very carefully. And as for "non-reliability", its conséquences are catastrophic:
From this analysis we can deduce a completely différent approach to costs in thé two industries.
Whereas in thé automotive industry, manufacturing costs are a major considération, in the aerospace industry they are just one of many criteria. Two figures highlight this point (figure 3)
Moreover, volumes in thé two sectors are quite différent and so thé balance between costs and investment is not thé came. The automotive industry can afford higher investment to reduce cost per unit.
We can give some figures here:
Finally, constraints in Aerospace are very often more difficult than in thé automotive industry:
All these factors
explain thé fact that composites were first used in "High
Performance/Low Volume" industries.
But what about the future?
Before going any further into the discussion, the first point we need to clarify is the definition of composites.
Of course the general definition of a "Composite" is very well known. A composite is a material containing two or more distinct phases on a macroscopic scale. Ar first, we will limit this definition to materials which contain a fiber reinforcing material supported by an organic binder or matrix.
points out that, within this very definition, the word
"Composite" refers to different kinds of products
depending on the people yon speak to.
If you talk to an aerospace designer, he will immediately think of "High Performance" materials. The product vill bc composed of various specifically oriented layers, the fibers will bc made from carbon or aramid and will often be continuous.
The processes will generally bc complex and the volume of production will not need a drastic cut in cycle times.
If you talk to a
car manufacturer, he will immédiately think of less expensive
composites. The process will have to be fast, the fibers will
have to be cheap (and so generally made of glass) and will often
So in this paper we will use as our definition
all reinforced plastic materials.
Plastic rnaterials entered automotive sector in the sixties and their growth was very fast (figure 4). Composite materials appeared in the seventies. In 1971, a mass production application was decided in RENAULT: bumpers of small vehicles Renault 5 (volume 2,000 to 3,000 cars a day) (photo 1).
This application spread to side protections of the same car and then to other models: Renault 18 (medium range), Renault 25 (upper range).
In the eighties, the interesting characteristics of these materials together with a good knowledge of how to industrialize them brought the designer to consider their use for other parts:
_ Exterior body panels
For instance, RENAULT lias been manufacturing, since 1985, on the Renault Express vehicle:
- Suspension parts
Renault Trafics have been on the road since 1986 with composite leaf springs and so have other vehicles.
- Frame parts
- Underhood parts
The consumption of
composites in RENAULT today is about 80 tons a day (figure
development makes us wonder: "Are we now in a balanced
position? Or are we heading for a breakthrough of these materials
in a "Mass Production" industry?
To answer such a question, we propose having a look at the different applications:
and in each case to point out:
BUMPERS AND SIDE PROTECTIONS COMPOSITES IN COMPETITION WITH THERMOPLASTICS
This is where composites were first applied in the automotive industry :
- :For bumpers, two types of design are competing :
- As for side protections, they must :
match the aspect of bumpers (and this generally leads to the use of a material similar to the one used for bumpers)
factors into consideration, composite materials (SMC, that is
polyester reinforced with glass fibers) were chosen for bumpers
and side protections.
For example, at RENAULT the mass produced Renault 5 (low range vehicle) and Renault 25 (upper range vehicle) are assembled with SMC bumpers and side protections.
The other models (Renault 9, Renault 11 and Renault 21, medium range) are designed with a polypropylene skin.
However, this application of composites is today threatened. The reasons are:
These two reasons are closely linked together .
A strong trend in
the european market is the success of vehicles whose stvle
features smooth surface, body-colored bumpers. And such a result
cannot be achieved, at the right cost, using SMC type composites.
For, unfortunately, the use of SMC causes :
Of course this damage can bc corrected, but only with a cost penalty.
In parallel, competing materials are improving very quickly (figure 6 ):
- thermoplastic materials.
Several technical factors explain the growth of these materials:
- improvement of painting
The cheaper materials (polyolefins) are net easy to paint. So the coating system tends to bc complex and expensive. Big improvernents in this field are on the way.
- development of new thermoplastics, especially alloys
As today's materials do not easily pass specifications, a lot of research programs have been launched to develop new thermoplastics. As the cost to create a new molecule is verv high, chemical industries are chiefly working on manufacturing alloys. These are now appearing on the market.
The productivity of these materials has been greatly increased by the use of an internal release agent.
Key factors of the trend
Car manufacturers are interested, for a given specification, in the cheapest design. Composites can romain a very good solution, providing that they allow the manufacture of body-colored, smooth surface bumpers.
So a lot of research and development work is going on along Chose fines. It concerns :
Moreover, a great deal of effort is being put into increasing SMC productivity. Work is being done on :
BODY PANELS : IN STRONG COMPETITION WITH STEEL FOR MEDIUM VOLUMES
There is a big challenge.
For the automotive industry, composites are only a member of a larger family, the "plastics" family. To take a look at composites in body panels, we must proceed in two stages:
STAGE 1: HOW DO PLASTICS COMPARE WITH STEEL IN BODY APPLICATIONS?
At first sight, plastic materials scem very well adapted to building car bodies. Thev offer indeed many technical advantages.
However the economic profit is very much dependent on volume.
This is especially a consequence of the balance between tooling costs and part manufacturing costs.
While to make a steel part, von always need three or four stamping tools irrespective of volume; in plastics processing the number of tools and also the cost of tooling are very much dependent on volume. For small quantities, one tool will bc sufficient. As volume increases, so too do the number of tools and the cost of tooling.
variable cost of a plastic part is generally higher than the
variable cost of a steel part.
So it is clear that there exists a cost breakeven poing between steel and plastics. This breakeven point depends on many factors and so can only bc set for a given application.
A general trend, however, is that the higher the volume the more difficult it is for plastics to be cost effective.
So for low volumes cars we can note a conjunction of technical advantages for customers and profit for the car manufacturer.
So it is not
surprising that today nearly every low volume car (up to 100
vehicles a day) has a plastic body.
We can give two examples, at RËNÂULT:
We can also point out the benefits of plastic materials for truck and bus bodies. In this field, where production is typically under 70 vehicles a day, specific advantages can bc obtained in addition te those already rnentioned:
- For medium volumes (100 to 1,000 vehicles a day) there is some hard fighting going on.
progress brings the price of plastic applications down, the
breakeven point is moving up to higher volumes.
So we can notice several medium-volume cars on the market with plastic body panels, for example:
What can we foresee .in the future?
The above analysis shows that, today, the break aven point is between 100 and 1,000 parts a day, depending on the part and/or vehicle design. We may wonder if this breakeven point is likely to move to higher volumes.
in fact, if we can say that in the near future, the probability of seeing a lot of cars on the market with plastic bodies is low, in the more distant future (5 to 10 years) certain factors may promote the move :
The decrease in the price of plastics applications.
This can be
achieved through different complementary ways:
At first through experience of designing with plastic materials. The designer will learn to take advantage of the consolidation possibilities (part integration)
This cati lead to a completlv new approach of the whole vehicle.
We cannot design a plastic body car in the same way as we design a steel car :
A customer-driven trend.
specifications require the body to have an appearance similar to
that of steel (smoothness, class "A" surface finish).
The requirement has a strong impact on cost.
The specifications can bc modified in time.
STAGE 2: WHAT PART WILL COMPOSITES PLAY IN THE GROWTH OF PLASTICS?
For the automotive industry, composites are only a class of plastic material like any other. Everything we said before can be applied to composites.
However composites feature some characteristics of their own:
The main limit to the use of composites in body panels today is the low productivity of the process. Although the price of the material is not so expensive, cycle times are still too long and too many finishing operations are needed. This is for example the case in the SMC process.
However, some improvements are now on the way. Some more productive processes like BMC have been developed for automotive applications. At the present time, the process does not however provide the high properties of SMC. The future lies with those processes that combine the properties of SMC and the productivity of BMC.
Given this view of
plastic materials, we can say that at the present time the
balance is in favor of composite materials.
Very few parts are now made of unreinforced plastics. But for some kinds of parts, especially vertical parts which need less rigidity, there may bc strong competition in the future from other materials.
TO MORROW / MECANICALS PARTS?
For this type of
application, the materials used are higher performance materials.
They are closer, property-wise, to those commonly employed in
"High Performance/Low Volume" industries.
The fibers are generally continuons and not chopped. And, on accourut of costs, only glass fibers can be used.
A vehicle's suspension system has different functions :
A suspension system is always composed of :
And one of the main characteristics of composites is precisely their "spring property", that is their ability to store high specific strain energy.
So it is logical to consider their use for the spring component of the suspension. Development along these lines has started with the leaf spring and torsion bar. Studies are also being conducted on coils but in this case the problem is much more difficult.
The easiest way to start is to replace a metal leaf-springs set by a composite leaf spring. Several vehicles with such a suspension are afready on the roads :
As for. RENAULT, a research program was launched in 1980 and led in 1986 to the on-line assembly of leaf springs on the Trafic Van (payload: 1,300 kg; volume: 40 vehicles a day) (photos 3 and 4)
The advantages of the application are :
The springs are indeed unbreakable: if a fallure occurs, the leaf spring will just lose properties but will not break.
The aim of the car manufacturer is to utilize the advantages that composites can bring to the suspensions of passenger cars. This means rethinking designs for suspension systems. In this case, composite materials can, at similar and perhaps lower costs than conventional systems, offer :
Keys to development
They are mainly :
Several processes are today in use or in the development stage. We can point out :
The choice of the process is strongly dependent on :
We must stress that studies in the field were only recently undertaken and so there seems to bc a high potential for innovation in this area.
Severe control of the process.
Total reliability must bc obtained. This needs :
FRAME PARTS: STUDIES IN AN EARLY STAGE
Recently, several developments have been undertaken for frame parts: chassis system, floorpan, front structure, front end, whole frame.
This type of rescarch is now in its carly stages.
The advantages of composites for these applications are their "parts consolidation" ability (replacement of a large number of parts by a very few). Through such designs, the costs (parts and investment) can be cut drastically. The stakes are high but the battle is far from over.
To reach this goal, it is absolutely necessary :
To learn to design a structure using composites.
A major problem is the fastening of parts together. Welding is a very well known way of joining materials together. But for composites, new methods must be developed :
Bonding is a very attractive solution. It is :
lnserting is another one.
To control better the material, its consistency and its reliability
One critical point is crash behavior. There is not so much experience on how composites react in crashes.
To improve significantly the productivity of the processes.
The processes existing on the market are very slow and so expensive. They are :
The challenge is a drastic decrease in cycle times and automation.
The first question to bc addressed is : is it possible to make a plastic engine?
In fact, many
engine parts are feasible using plastic materials. Some companies
have for instance rnanufactured cylinder-blocks. But the cost of
such applications are much too high for a mass production.
However plastic materials and especially composite materials can be very profitable in the following applications:
The advantages of composites over steel are:
Photo 6 and figure 4 show various interesting applications.
From the beginning
of mankind, materials have been the weapons of progress. The
first ages were even named after them: Stone Age, Copper Age,
Yet today we cannot qualify our age after just one material. For our era is the era of choice. We have the possibility of using
the right material at the right place.
So there is strong competition. And in this fight, composites are very well-armed. Orie of their main strengths is their wide range of properties. Let's take another look at the benefits they cari offer to the car customer: no corrosion, resistance to minor impact, new shapes...
competitors also have a strong weapon: their low cost. So
initially, composites could only conquer the "High
Performance/Low volume" industry.
But today, major changes are on the move. Using the automotive sector as an example we have shown that the colt of in-composites designs cari bc decreased :
The stakes are very high :
The play has begun
but has only just started. If composites cari confirm that they
are able to combine economic benefits with technical advantages,
then a new era of composites may be emerging:
the era of `,Mass Production' composites.
Exposé présenté au Congrès ICCM 1987 par Aymé Jardon et Michel Costes
Document scané et converti en fichier HTLM en mai 2016.