Dashboard

Vehicle body engineering and safety

● The dashboard is defined as that component, or rather that group of components, which makes up the front passengers compartment.

● The dashboard of today, (Fig. 6.52) is very different from that seen on the first cars.

● At the beginning of the last century, the vehicle had a structural wall under the windshield which was used to contain gages, instruments, switches, the hole for the ignition key and some warning lights; in luxury cars a wood frame and a glove box were added (Fig. 6.53).

● Over time the instruments, some switches and warning lights were grouped together into one panel and protected by an anti-reflection visor in front of the driver to improve visibility and for assembly and service requirements; afterwards air vents and various other controls, glove compartments etc., were added until a single self-supporting component evolved, enabling all the elements mentioned above to be incorporated:

this component is called the dashboard

● The dashboard is a very important component of the passenger compartment of a car because it contributes to some of the most important functions of the vehicle such as:

● Aesthetic function: Since the dashboard is noticed immediately after opening the door and entering the car, it becomes the key element in the aesthetic judgment, important in determining the rating of the vehicle; furthermore, while driving, the dashboard is the primary interface between the driver and the vehicle;

● safety function, for both active and passive safety.● Active safety, since it is possible to correctly distribute the air

on the windshield and on the glass front door, and thus obtain a high level of visibility through the appropriate apertures (defroster/demister) which are present on the dashboard,

● Passive safety, since in situations of impact of the head against the dashboard, the criteria of biomechanical performance required must be respected, as well as ensuring the absence of dashboard breaks that could injure the occupants.

● Besides, the dashboard acts as a support to the passenger air-bag and to the knee air-bags when present.

● In the case of passenger air-bag with cover integrated into the dashboard, the dashboard itself is part of the safety system, and as such it is subject to traceability.Additional functions are:• Ergonomic function, consisting, for instance, in the easy operation of

the controls located on the dashboard and, to see correctly the instruments on the dashboard;• comfort climate function, contributing to a proper distribution of the air

in the passenger compartment, through air-vents located on the dashboard;• objects containment function, with specific areas (drawers) on the

dashboard, with appropriate sizes, in which to place objects.

Type of dashboard

● The dashboards, according to their main characteristics and respective production technologies (table of Fig. 6.55), may be classified into:

● Stiff;● covered;● foamed.

Stiff dashboards

● Stiff dashboards are those which, for their economy and lightness, and for the freedom in the design of their shapes and therefore for the stylistic versatility, represent the best solution for the lower segment cars.

● The technology used is the injection moulding of thermoplastic materials, mainly belonging to the family of Polyolefin (Polypropylene) by adding mineral (talc) and elastomeric fillers or, mixtures of ABS and Polycarbonate.

● The desired appearance is achieved by coloring the polymer in mass and by embossing.

● Before continuing the examination of the dashboard, it is necessary to spend some time on the embossing process because it is a process widely used to characterize the appearance of elements made by plastic materials.

● What exists in nature has its own roughness or texture which give to the Plastic materials, in themselves do not possess any of these characteristics;

● simply by appropriate preparation and processing of the mould’s surfaces, specific features can be given to the plastic material components. This process is called embossing.

● Besides embellishing the plastic components (including the rubber components), embossing allows:• To mask the defects in the injection molding process and

reduce the production waste;• to make the surfaces of the plastic components more

resistant to scratches and abrasion;• to make the plastic objects more functional (for example

less slippery).

● The topography of an embossed surface is identified by a measurement of roughness parameters (mean and maximum) and consists of a scale of roughness

● There are two embossing processes:• The texture;• the spark-erosion.

Texturing

● Texturing is the most used embossing process, expertise in which is jealously guarded by a few specialized companies.

● After having defined and protected the areas of the mould not to be embossed, the area which must be embossed is covered by a film that reproduces the embossing design to be reproduced.

● With the use of a special chemical solution it is possible to engrave the mould surface which is not protected by the film through the corrosion, so as to obtain the embossing depth and the look of embossing design required.

● The steel blocks used to make moulds for which this type of embossing is required, should be free from any defects, such as inclusion and porosity.

spark-erosion

● This embossing process, unlike the texturing, is a well-known process which is also used to make moulds, generally of small sizes or for particular operations.

● The spark-erosion is a physical phenomenon performing a material removal as a result of electric shock.

● If the removal of material is limited to the surface area of the mould to be embossed, it is possible to achieve a similar removal of material like in the texture.

● A fundamental difference with the texture is that the design which can be obtained is only one (like sandblasting), for which the only manageable variable is the depth that makes the embossing more or less engraved.

● factor affecting aesthetic- various plastic components with the same embossing and moulded with the same material

● Another affecting aesthetics of a molded plastic component is the gloss which influences the effect of the embossing, especially when the design is less marked. The gloss is measured by using a simple instrument: The glossmeter.

● If the gloss is low (dull), the embossing may appear less pronounced and, on the contrary, if the gloss is high (bright), the embossing may seem deeper than it is in reality.

● If the gloss is low (dull), the embossing may appear less pronounced and, on the contrary, if the gloss is high (bright), the embossing may seem deeper than it is in reality.

● It is possible to change the brightness of the embossed plastic surface through the dulling, chemical and mechanical treatments (sandblasting and shot peening); the duration of these treatments is limited in time and therefore it is necessary to remake them.

● ABS and Polycarbonate blend-based materials which, for their nature, can already be classified as engineering resins, as seen in Fig. 6.56, have characteristics that do not require the use of fillers and, for their high costs, they are mainly used for the dashboard having a design which can create problems of thermal resistance and impact strength, especially at low or high temperature.

● Their use is more frequent in technical components which are present on the dashboard, such as the air vents, for which is not thinkable, for example, to guarantee the resistance to the impact, especially at low temperatures, by using Polypropylene materials.

section of a stiff injection molding dashboard: Defroster air duct A, demister air duct B, cross beam C, tilting glove box compartment D, aesthetic cover E, body dashboard F, vents air duct G.

Stiff injection molding dashboard

● The moulding process optimization and the embossing can improve the aesthetics, but cannot remove the plastic effect, which is inherent to plastic moulding injection process.

● The way to really remove the plastic effect is the painting. ● The result that is achieved is such that it is used to apply the

same component (painted or not), on different cars, giving a significant difference.

● Besides painting, there are other processes which characterize the surfaces of plastic components.

● One of these processes, started in the automotive industry, is the cubic-printing system.

● The element that must be treated is immersed in a tank containing water on whose surface floats a gelatinous film reproducing the design that you want to reproduce.

● During the emergence the element is covered by the film. Then, after the drying, the surface on which the film is deposited, is protected with a finishing paint coat.

With this process it is possible to reproduce the most varied types of finishes such as: Wood, textile materials, carbon fibers, etc.

Covered dashboard

● This type of dashboard represents an intermediate solution between stiff and foamed dashboards (Fig. table 6.55), and being such, it tries to recover the aesthetic and tactile performance without penalizing too much weight and cost.

● The covered dashboard is, in fact, a stiff dashboard on which a covering consisting of an embossed laminated plastic plus an expanded plastic layer having a thickness of about two millimeters is joined by bonding.

● This covering, with its color and embossing has an esthetical function and, with its expanded part, even a tactile function

● Covering material. Initially the material used was the laminated PVC (polyvinylchloride), now the most widely material used is the TPO (polyolefin based material).

● The adoption of the TPO was made possible bonding processes and preparation processes of the surface to be bonded (flaming and plasma treatment in open environment).

● The elimination of PVC, besides the ecological benefits resulting from the non-use of chlorides, has also enabled the reduction of the fogging (deposition of volatile compounds present in PVC that, by condensing on the windshield, cause an effect of fogging).

● It has also improved the resistance to the prolonged sunlight exposure by improving the tactile sense and eliminating the feeling of greasiness, typical of PVC.

● Support materials. In parallel to the TPO adoption, instead of using PVC for the covering and instead of using PC (polycarbonate) and ABS (acrylic-butadiene-styrene) blend for the support material, PP (Polypropylene) materials have been recently used.

● Moreover, the covered dashboard, just for the covering that characterizes it, has a better ability to absorb energy and to resist to the impact compared with a stiff dashboard.

● Therefore it is possible to use PP with more filler talc (25÷30%) and without EPDM (elastomeric filler) with a consequent increase of the flexural modulus and cost reduction.

● The impact strength reduction is compensated by the presence of an expanded covering which is glued on the support.

● Covering process. The process used to apply the covering on the support is the Vacuum Thermo-forming process and, for this reason, the covered dashboard is also known as Vacuum Thermo-formed Dashboard.

Vacuum Thermo-formed Dashboard.

Phase 1: Positioning of the support on the thermo-forming mould and application of a thermal bi-component adhesive, through a robot. The use of a robot is important in order to ensure that the repeatability of the adhesive application is correct both in terms of distribution on the support surface and in terms of quantity.

Phase 2: Thermo-heating of the covering material and thermo-heating of the adhesive applied on the dashboard support.Phase 3: Vacuum thermo-forming that, by sucking the covering material on the support, through the vacuum channels of the thermo-forming mould, enables the adhesion between the dashboard support and the covering.

● Finishing process. This is an important process for the covered and foamed dashboards. It consists in trimming and finishing on the perimeter and in the parts that need to be opened such as the locations for the air vents (see Fig. 6.61).

● To conclude the examination of the covered dashboard, which represents the type of least used dashboard, it should be remembered that this technology in order to guarantee the same foamed dashboard finish, but with less cost and weight.

Foamed dashboard

● It is certainly the dashboard type that, more than the other two that were considered above, contributes in a fundamental way, with the seats and the door panel, to the car passenger compartment furnishing.

● In fact, from the table in Fig. 6.55, it is possible to see that this solution ensures the best design freedom for style and form, and then also, achieves the best performances in aesthetics and touch (see Figs. 6.62 and 6.63).

● The dashboard importance in characterizing the vehicle passenger compartment is also evident by the fact that, since the 1990s, the use of the foamed dashboards has become more and more extended. Today they are also used on economy cars.

● While the covered dashboard is made up on a stiff support, in the foamed dashboard between the support and the covering, there is a soft layer with about 5÷10 mm of thickness. The process with which this soft layer is made, is called foaming.

● The three most important parts of the foamed dashboard are: The support, the foam and the covering.

● The support. It is the structural part of the foamed dashboard which is put into the foaming mould.

● The first characteristic of the support is that, in this case, unlike stiff dashboards, is much more simple: It must not have an esthetical function, it must not guarantees impact strength and resilience as well as a good absorption energy capacity as a result of collision, because the set of the support, the foaming layer and the covering guarantee the performance required.

● The material used is always an injection-moulded thermoplastic, it is possible to adopt materials with a better structural performance like higher flexural modulus and high temperature resistance.

● These materials could be the following: Heat-resistant ABS reinforced with glass fibers or Polypropylene copolymer with mineral filler (talc), as shown in the table of Fig. 6.56.

● For dashboards to be assembled on low-production vehicles like buses or heavy trucks, in order to limit the investments, other technologies can be used such us low-pressure moulding processes, which use thermosetting resins or vacuum thermo-forming process and thermoplastic plates having a thickness of 3÷5 mm.

● The covering. The covering is the dashboard skin. One of the technologies which is currently most used is the vacuum thermo-forming, already seen with respect to the covered dashboard.

● The covering consists of an embossed laminated material obtained by calendaring in compact TPO. Normally the thickness is about one millimeter (the thickness depends on the dashboard geometry), but it does not exceed 1.2 mm.

● The vacuum thermo-forming process represented in Fig. 6.64 may be classified into five phases:

Phase 1: Heating the laminated material top and bottom through two heating lamp panels.

Phase 2: Supporting the warm laminated material through the air, in order to prevent, as a heating result, the softening and deforming downward of the laminated material, coming into contact with the mould forming and generating a localized pre-stretched.

Phase 3: Vacuum thermo-forming; by means, of vacuum application through appropriate channels obtained in the thermo-forming mould, the laminated material is sucked on the same mould.

Phase 4: Cooling by spraying atomized water on the thermo-formed covering; even the mould forming, with cold water, participates in the covering cooling.Phase 5: De-moulding by means of blown air; the laminated material, which has now taken the new three-dimensional conformation, is detached from the forming mould and is ready to be put into the foaming mould.

● The vacuum thermo-forming is a process that allows one to have the laminated material transformation in the three-dimension skin and that represents the shape of the foamed dashboard.

● This happens through the stretching of the flat embossed laminated material.

● If the stretching exceeds certain limits, it will damage the laminated material embossing, and a gloss variation by damaging the dashboard aesthetic.

● After stretching simulation, during the car development process, it is possible to produce, very quickly, by means of the CAS, the vacuum forming mould, to get immediately the real situation (Fig. 6.65).

slush molding

● Fig. 6.67. Covering production cycle by slush technology. ● Phase 1: mould heating.● Phase 2: starting rotation (170÷180◦C), fixing to the mould of the powders container.● Phase 3: rotation, mould filling with the PVC powders. Phase 4: rotation with return● to initial position and PVC sticking on the mould walls. Phase 5: sintering, separation● of the mould from the powders container. Phase 6: cooling. Phase 7: demoulding.

● The foaming. Through the foaming it is possible to obtain the expanded material that characterizes the foamed dashboard.

● The foam is the material that, by interposing between the support and the covering, provides the required softness.

● The material used is a thermosetting (polyurethane), obtained by mixing in the mould, at low-pressure, polyol and isocyanate.

● The attempts to use thermoplastic materials (polypropylene), because the polyurethane is not recyclable, have not given encouraging results.

● The foaming mould, due to the low pressures used, is composed of an aluminum male and of a thermostatically controlled resin female, with possible aluminum spacer block.

The support is usually placed on the male, while the covering is placed in the female, where it is held in position by the vacuum created through the suction channels (phase 1).

After the mould closure, a pre-heated polyurethane is injected (phase 2); in some cases the polyurethane is poured into the mould when it is still open.After a suitable reaction time and formation of the foam, it is possible to de-mould the dashboard (phase 3)

● Finishing process. The process is similar to the one described for the covered dashboards with the addition of the need to remove the foam that, during the foaming, may have infiltrated on the support part that should be released for the subsequent assembly operations (e.g. welding).

● The removal of the foam is facilitated by a preventive process of waxing, consisting in the application of a wax layer on the support surface that must be free of foam.

Monolithic and non-monolithic dashboards

● After having examined the dashboard classification in terms of technologies and characteristics and before starting the examination of the most important dashboard components as well as the assembling technologies, it is necessary to remember that the dashboard design can be:• Monolithic (Fig. 6.70), when the dashboard body is made up

of a single piece;• decomposed (Fig. 6.71), when the dashboard body is made

up of more than one piece.

Monolithic dashboard

Decomposed dashboard