Reinforced rotomolded body

Abstract

The invention relates to a process for manufacturing parts, for example a vehicle body (01), said process involving rotomolding a compact outer layer (11, 21), rotomolding a compact inner layer (12, 22), and treating the inner layer in order to enhance the mechanical properties of the part.

Description

[0001] Reinforced rotomolded body

[0002] CORRESPONDING REQUEST

[0003] The present application claims priority from the earlier European application No. 23184269.1 filed on July 7, 2023 in the name of SOFTCAR SA, the contents of this earlier application being incorporated by reference in its entirety into the present application.

[0004] TECHNICAL FIELD

[0005] The present invention relates to the manufacture of a vehicle body with a low CO2 footprint, low ecological impact, and favorably comprising one or more layers of recycled polymer allowing it to be reinforced, and the means for manufacturing it. These means and the steps of the method according to the invention comprise the rotational molding of the outer layer of the body parts preferably in a new material. The present invention also relates to production methods making it possible to improve the mechanical characteristics of the body, for example by using material from the recycling of a previous vehicle body.

[0006] PRIOR TECHNIQUE

[0007] Since 1938, vehicles have been universally manufactured with steel body frames. The modulus of steel is very high, generally between 190 and 220 GPa, and the body frame, once assembled by welding, has an optimum quadratic moment. However, today many problems arise.

[0008] Formed from coke, steelmaking in a blast furnace generates a huge amount of CO2. During the transformation of raw steel into sheet metal in the rolling mill, the energy required and CO2 emissions are equally intense. The sheet metal is then greased for corrosion protection before being rolled into coils, which are transported by ship, train, and truck. Due to the density of the steel, the mass requires a significant amount of energy for transport. Once they arrive at the factory, the coils are stored away from the elements before being unwound and degreased. The steel enters the ironwork line for stamping. The hull frame consists of approximately 350 stamped parts, each requiring roughing tools, semi-finishing tools, and finishing tools. A change of style requires a new investment in all these tools.The ironworks line also requires a very significant investment in capital expenditure (several billion Swiss francs). Finally, the footprint is very significant. The ironworks line's presses consume a lot of energy and are dependent on the supply network. A micro-power outage has very significant consequences. Steelworking generates noise, dust, vibrations, and the use of heavy solvents. The stamped part is cut from the sheet metal, which on average generates 35% waste. This sheet metal waste is transported to blast furnaces and cannot be used to produce automotive sheet metal, as it contains silicon to make it more easily plastically deformable. The steel from the press waste will be remelted and will therefore be used in degraded secondary applications.

[0009] The parts are transferred from one press to another by robots because the sheets are sharp, dirty, and heavy. The sheets are then welded together by robots to form the body frame. The frame is then protected against oxidation in a cataphoresis bath. Preferably, four layers of anti-corrosion protection are then applied, before the final thermosetting paint (non-recyclable). Once the body frame is completed, the assembly of heavy interior functions, such as the seats and dashboard, requires robots or motorized assistance, as manual assembly of the body frame is very difficult due to the masses and trajectories from the door openings to the interior of the vehicle. Ultimately, the energy used on the body frame line is difficult to reconcile with the creation of an ecological vehicle, and the higher the automation, the more intense the CO2 generation.

[0010] Another fundamental problem is that the density of steel does not allow for the construction of lightweight vehicles consistent with electric propulsion. Lighter structures improve vehicle performance and allow for reduced energy consumption. In the case of an electric motor, lightness becomes performance and increased autonomy. The sheet metal forming line is noisy, dirty, dusty, and requires a very large amount of energy. The capex of a line is very high, occupying a very large floor space to chain operations in line.

[0011] Sheet metal chassis are generally 0.8 mm thick, and these sheets have the major problem of being susceptible to hail damage. In addition, corrosion remains the biggest problem with steel automobiles.

[0012] Rotational molding is known as one of the first polymer transformation processes, generally used to make containers (such as tanks, vats, hydrogen tank bladders, etc.), kayaks, and other large parts. These parts are not very technical, do not generally require significant mechanical strength, and the surfaces are not very tense. Polyethylene, polypropylene, or polyamides are used, which have very low moduli compared to steel: for example, polyethylene has a very low modulus of around 700 MPa.

[0013] To produce a vehicle body, significant mechanical strength is required, particularly at the A-pillars, seat belt anchor points and doors to protect passengers from a side impact.

[0014] For mechanically loaded parts, such as canoes and kayaks, two-layer parts are produced. In this configuration, the outer layer of the wall (called the "first layer" or "skin") is preferably thin and compact, and the inner layer (called the "second layer"), which is rotomolded, can also be compact, or foamed depending on the desired mechanical properties.

[0015] The fusion of the two layers is carried out during the same mold heating operation. If the polymers constituting the two layers are chemically compatible, there is then chemical adhesion between the two layers, this cohesion being a key element for the final mechanical resistance of the sandwich produced.

[0016] Foaming the second layer (inner layer) creates an expansion of the material which increases the wall thickness, and therefore the quadratic moment of the section and the mechanical resistance of the part. The foam thus created has a lower density than the compact part, but the part made with foaming the second layer has a much greater mechanical resistance than that made with a single layer.

[0017] SUMMARY OF THE INVENTION AND METHODS OF CARRYING OUT THE INVENTION

[0018] An aim of the present invention is to improve the processes, methods and products of the state of the art, in particular for using recycled material from a used bodywork to reinforce a new production. In this application, we will use the term "Upcycling" to describe this use. The present invention makes it possible to overcome all of the drawbacks mentioned above, by producing a bodywork reinforced by recycled material from a previously produced shell (called "previous shell"). In embodiments, the present invention comprises four industrial processes for increasing the quadratic moment of the shell, produced by using recycled material from a previous shell, thus following the principles called "upcycling" in the state of the art.

[0019] The hull is molded in a single piece, with no waste during production since all the material goes entirely into the mold and the finished part, dyed directly in the mass, stainless, entering the short circuit circular economy by incorporating recycled polymer from a previous hull.

[0020] The invention integrates the production by rotational molding of an outer layer (called "first layer") preferably formed from new material (but which may incorporate recycled material), for example colored, and one or more inner reinforcing layer(s) made from recycled polymer (called "second layer", "third layer" etc.). For this / these inner layer(s), the following methods, described as non-limiting embodiments of the present invention, can be used.

[0021] The first method of upcycling reinforcement to increase the mechanical characteristics consists of carrying out a full foaming: in this method, the material, preferably from a previous shell, is micronized and introduced as a second layer by a "drop box" (i.e. a heat-insulated tank mounted on the mold) during the rotation of the mold after the realization of the first layer. The expansion phase of the second layer takes place in the section considered. The foaming reaction is preferably triggered by an exothermic agent - example: OSBH or 4,4'-oxydibenzene sulphonohydrazide (the reaction can also work with endothermic agents) and the full foaming is created by the runaway of the thermal reaction associated with the heating of the mold.Full foaming is a local reinforcement in the bodywork, for example in the A, B, C pillars and / or at the seat belt anchor points, door crash protection, or vehicle seats.

[0022] In this method, the drop box entrance will preferably be positioned roughly in the center of the vehicle, in the middle of the passenger-side roof. This reinforced area offers great strength and then becomes the best upper anchor point for seat belts for front passengers, for example.

[0023] The second method to increase the mechanical characteristics in upcycling is as follows: first, the outer layer is made by rotational molding, preferably made of new material, for example colored. The second layer is preferably made of recycled material from a previous micronized shell and mixed with expansion agents that can favorably contain nucleating agents. This material to form the second layer is sent during the rotation of the mold by a drop box to create a foamed layer. To obtain a third inner layer denser than the foam, a large expansion of the bubbles on the surface of the second foamed layer is carried out. Also during the heating phase, hot air is injected inside the two-layer rotational molded part at a temperature higher than the softening or melting temperature of the polymer.Depending on the location of the hot gas injection point(s), it is possible to locally or completely create a third layer (called "skin") of compact polymer, the surface of the second foamed layer.

[0024] More precisely: at the end of the expansion of the foamed layer (i.e. the second layer produced), the third layer is created by sending a flow of hot air into the mold cavity preferably located in the center of the mold in the middle of the pavilion on the inside. Preferential hot air circulation is achieved by vents as shown in Figures 1 and 2.

[0025] This increase in temperature causes the bubbles on the surface of the second layer to expand. The bubbles burst under the action of temperature, the material falls back onto the foam while creating the skin (the so-called third layer). The expansion is obtained after the programmed expansion phase has ended. The part thus has an external compact layer (first layer) resulting from the two-layer rotational molding, an internal compact layer resulting from the injection of hot gas (expansion of the bubbles of the external layer of the foam, third layer), and a middle foamed layer (intermediate, second layer) resulting from the two-layer rotational molding. The part therefore has a mass similar to that of a two-layer part, but with an internal compact layer closing the sandwich by greatly increasing its quadratic moment.This system makes it possible to increase the mechanical characteristics locally or across the entire bodywork, in the same part footprint and without increasing the mass of the said part.

[0026] The third method of reinforcement by upcycling involves the simultaneous heating of particles of different sizes - powder and microgranules - to increase the mechanical characteristics. First, an outer layer is produced by rotational molding, preferably from new material, for example colored. The second layer is preferably formed by upcycling recycled material from a previous hull that has been reformulated and then micronized.

[0027] The second and third layers are made according to two different particle size spectra. The first powder, loaded with blowing agents, has a fine particle size (for example, the particles range from 150 pm to 550 pm depending on a particular distribution) and will allow the second layer (foamed) to be made. The second powder has a larger particle size than the first (for example, the particles range from 500 pm to 750 pm depending on a particular distribution and a narrow particle size spectrum) and will allow the third layer (compact) to be made.

[0028] The first outer layer of the part is preferably made of virgin material. The second and third inner layers are sent into the mold, preferably at the same time via a drop-box containing the mixture of the two particle sizes of recycled material. The finest particles melt first, so the powder loaded with expansion agent is deposited on the first layer of virgin material, forming a second layer, then the larger particles adhere to the second layer (which has not yet reacted) forming a third layer. As the temperature continues to increase in the mold, this triggers the expansion of the second layer previously covered by the third layer. The result is a three-layer "sandwich" structure. This reinforcement will be favorably achieved throughout the part.

[0029] It is possible to carry out the expansion of the second layer before the deposition of the third, by using expansion agents with a lower trigger temperature.

[0030] The fourth method for improving mechanical characteristics is as follows: the outer layer is first made by rotational molding, preferably made of new material, for example colored. The material of the second layer is preferably made of recycled material from a previous micronized and reformulated shell. During this reformulation operation, it is possible to integrate nanometric fillers into the recycled material to improve mechanical resistance, such as nanotubes, Graphene for example, or other equivalent reinforcement materials. To ensure the traceability of the recycled material, it is also possible to introduce nanometric tracers to guarantee the origin and quality of the recycled material.

[0031] The first outer layer of the part is preferably made of virgin material. The second inner layer is sent into the mold via a hopper containing the mixture of recycled powder with the additives described above. This reinforcement can be carried out locally or throughout the part.

[0032] These four methods make it possible to increase the mechanical characteristics of the parts produced, in the same part size and without increasing the mass of said part.

[0033] By means of the methods and processes described above, shells are obtained having the characteristics required for their use, for example as vehicle bodies.

[0034] In embodiments, local reinforcements can be added, particularly in places where the strength must be high and / or in places where the material sections are limited, for example at the level of the A-pillars where the width is limited so that the driver can maintain a good angle of vision and see the road clearly to the sides. The invention makes it possible to reinforce the rigidity according to one of the four methods described above (full foaming of the section, addition of a third layer by heating the foam, addition of a third layer by adjusting the grain size of the raw material and / or addition of nanometric fillers in the raw material).

[0035] The anchor points of the front passenger seat belts, which will be favorably located in the middle of the vehicle, will also be heavily stressed, particularly during possible crashes. The invention makes it possible to stiffen the entire roof on which the anchor points are located. This stiffening can be done using one of the four methods described above (full foaming of the section, addition of a third layer by heating the foam, addition of a third layer by adjusting the grain size of the raw material and / or addition of nanometric fillers in the raw material).

[0036] The same reinforcement methods can be applied to rotomolded doors to resist side impacts, front and rear bumpers to resist frontal and rear impacts, rear seat belt anchor points to withstand crash forces, the C-pillar to resist rollovers, or any other high-stress area.

[0037] Another way to stiffen locally is to make material re-bonding pads, also called "kiss-offs" in the field of rotational molding. In the case where these kiss-offs are made directly in the first external layer, due to the shrinkage of the material during its cooling, sink marks appear on the external surface of the first layer, which is not the desired level of quality for the automobile. In order to overcome this problem, the material re-bonding is carried out with the second layer and / or the third layer, which avoids the formation of hollows on the external surface of the part concerned. More precisely, said kiss-offs are formed by making bosses on the rotational molding molds of the formed objects (for example, body or door). During rotational molding of the first (external) layer, there is no material re-bonding.The material is bonded during the formation of the second (foamed) layer and / or the third layer, as described above. This results in considerably reinforced parts that meet the crash resistance requirements required for the construction of a car body.

[0038] These reinforcement kiss-offs are favorably located in the most mechanically loaded areas of the parts, for example at the front and rear seat belt anchor points, on the A-pillars, on the C-pillars, on the roof, on the front and rear bumpers, or on any other mechanically stressed area. They provide protection for passengers in the event of a side, frontal or rear crash, in the event of a rollover. On the doors, they can be favorably located at the hip point at the level of the hidden storage compartments, or at the level of the passengers' shoulders.

[0039] The material resulting from regrinding a body and body panels has an even higher economic value if it is re-additive and micronized according to a defined spectrum. It can be resold on the market to manufacture other industrial parts and provide a sufficiently attractive economic value for the user to complete the recycling process.

[0040] In embodiments, the invention relates to a method of manufacturing parts, for example a vehicle body, said method comprising rotational molding of a compact outer layer, rotational molding of a compact inner layer and treating the inner layer to increase the mechanical characteristics of the part.

[0041] In embodiments, at least one of the layers is formed, in part or in whole, from recycled and micronized materials from a previous body.

[0042] In embodiments, treating the inner layer comprises foaming at least the compacted inner layer to obtain a foamed inner layer.

[0043] In some embodiments, the treatment locally includes foaming the entire thickness of the part.

[0044] In embodiments, at least the foamed inner layer is heated to obtain a compact inner layer and a foamed middle layer. In embodiments, the heating of the foamed inner layer(s) is carried out by injecting and / or circulating a hot gas, for example air or the like, inside said bodywork.

[0045] In some embodiments, the foamed surface then serves as a guide for the hot gas by the Coanda effect.

[0046] In some execution modes, dropboxes and / or vents are used to realize the hot gas inlets and / or outlets.

[0047] In execution modes, during the micronization of a previous bodywork, this is produced with at least two different granulometry spectra and introduced into the mold by a drop box to produce the second foamed layer and a third layer.

[0048] In embodiments, a first particle size spectrum is preferably fine and a second particle size spectrum is larger than the first spectrum.

[0049] In embodiments, particles of both spectra are fed into the mold, the finer particles melt first forming a second layer on the first layer, then the larger particles adhere to the second layer forming a third layer. In embodiments, expansion of the second layer is carried out before deposition of the third layer using expansion agents having a low trigger temperature.

[0050] In some embodiments, when recycling a previous shell, grinding, reformulation, and then micronization are carried out in which nanometric fillers such as nano tubes and graphene are integrated, improving the mechanical characteristics of the second foamed layer and the third layer.

[0051] In some embodiments, a pad is formed on the compact outer layer during rotational molding, said pad or (called a "kiss off") allowing the materials to be reattached during the treatment of said inner layer.

[0052] In embodiments, the invention relates to a part produced by a manufacturing method as described in the present application.

[0053] In some embodiments, the part is a vehicle shell or a body part such as a door or the like.

[0054] In some embodiments, the bodywork is made in three layers at the belt anchor points, and / or the A-pillar, and / or the C-pillar.

[0055] In some embodiments, the part comprises at least one material bonding pad. In some embodiments, the part is a door, a leaf, a seat or a hood and is made in three layers.

[0056] In embodiments, the invention relates to a vehicle comprising a part or body as described in the present application.

[0057] In some embodiments, the vehicle includes seat belt anchor points that are located in the center of the roof, on the inside of the vehicle.

[0058] In embodiments, the invention relates to a structure forming the passenger compartment of a vehicle, comprising a shell and openings, said structure being manufactured by rotational molding and forming the complete body of a vehicle, where each part such as the shell and the openings is a hollow body comprising at least one compact outer layer and a foamed inner and / or middle layer manufactured from the same polymer base as the outer layer, with the addition of a foaming agent.

[0059] In embodiments of the invention, the structure forming the passenger compartment of a vehicle comprises a shell made in a mold comprising dropboxes and vents at the wheel arches and the roof, said dropboxes containing the material intended to form the inner and middle layers. In embodiments of the invention, the rotomolded parts of the structure are reinforced by reinforcements in the particularly stressed areas, in particular the belt anchor points, the A-pillars, the C-pillars, the front bumper, the rear bumper, the doors or the hoods, the reinforcement being made possible by the proximity of dropboxes in the mold used to form said parts.

[0060] In embodiments of the invention, the foamed middle and / or foamed inner and / or compact inner layers of the parts are made entirely or partially from materials derived from the recycling of previous structural parts forming a passenger compartment.

[0061] In embodiments of the invention, obtaining reinforcements may consist of locally foaming the entire thickness of the rotationally molded part.

[0062] In embodiments of the invention, obtaining reinforcements may comprise heating the foamed inner layer to obtain a compact inner layer and a foamed middle layer.

[0063] In embodiments of the invention, the heating of the foamed inner layer(s) is carried out by the injection and / or circulation of a hot gas, for example air, inside the part.

[0064] In embodiments of the invention, the foamed surface serves as a guide for the hot gas by the Coanda effect. In embodiments of the invention, the structure comprises a shell made in a mold in which dropboxes and / or vents are used both to supply material to the internal layers, and to provide the inlets and / or outlets for hot gas.

[0065] In embodiments of the invention, in which structure one or more parts have one or more bridging elements or re-bonding or kiss-off pads produced during rotational molding on the compact outer layer, said bridging element allowing re-bonding of the materials during the treatment of said inner layer.

[0066] In embodiments of the invention, the structure comprises at least one part in which, during the micronization of one or more previous structural / cabin parts, said part is produced with at least two different particle size spectra and introduced into the mold by one or more drop boxes to produce the second foamed layer and a third layer.

[0067] In embodiments of the invention, a first particle size spectrum is fine and a second particle size spectrum is larger than the first spectrum.

[0068] In embodiments of the invention, particles of both spectra are fed into the mold from the dropbox(es), with the finer particles melting first to form a second layer on the first layer, and then the larger particles adhering to the second layer to form a third layer.

[0069] In embodiments of the invention, the expansion of the second layer is carried out before the deposition of the third layer using expansion agents having a low initiation temperature.

[0070] In embodiments of the invention, when recycling structural parts forming a previous passenger compartment, grinding, reformulation, then micronization are carried out in which nanometric fillers such as nano tubes or graphene are integrated, improving the mechanical characteristics of the second foamed layer and / or the third layer.

[0071] In embodiments of the invention, the structural parts forming a passenger compartment are a shell, a door, a leaf, a hood, a tailgate, a front or rear bumper.

[0072] In embodiments of the invention, seat belt anchor points are located in the center of the roof, on the inside of the vehicle.

[0073] In embodiments, the invention relates to a mold for forming a shell of the structure forming the passenger compartment of a vehicle as described in the present application, said mold comprising dropboxes and vents at the wheel arches and the roof of said structure, said dropboxes containing the material intended to form the inner and middle layers.

[0074] In embodiments of the invention, dropboxes and / or mold vents are used both to supply material to the inner layers, and to provide hot gas inlets and / or outlets.

[0075] In embodiments, the invention relates to a rotomolded vehicle seat produced according to a method identical to that of the structural parts forming the passenger compartment as described in the present application.

[0076] SUMMARY DESCRIPTION OF THE DRAWINGS

[0077] The present invention and its advantages will appear better in the description below of embodiments given as non-limiting examples, with reference to the appended drawings in which:

[0078] - Figure 1 represents a bottom view of the rotomolded shell of a vehicle manufactured according to embodiments of the invention;

[0079] - Figure 2 represents a sectional view of the rotomolded shell of a vehicle manufactured according to embodiments of the invention;

[0080] - Figure 3 represents a sectional view of a wall of the vehicle after rotational molding of the two layers, where the inner layer may be recycled from a previous body (or shell) according to embodiments of the invention; - Figure 4 represents a sectional view of a wall of the vehicle after foaming of the inner layer according to embodiments of the invention;

[0081] - Figure 5 represents a sectional view of a wall of the vehicle after formation of the third inner layer according to embodiments of the invention;

[0082] - figure 6 represents a sectional view of a wall of the vehicle completely foamed according to embodiments of the invention;

[0083] - Figures 7 to 9 illustrate seat belt attachments / anchor points according to embodiments of the invention;

[0084] - Figures 10 to 13 illustrate methods of performing kiss-offs (or material re-bonding pads) on parts, used to reinforce the structure.

[0085] - Figure 14 illustrates the complete body of a vehicle, i.e. the structural parts that make up the vehicle's interior, such as the body, doors, hood, or tailgate. Figure 14 also shows the seats that are not part of the body.

[0086] DIGITAL REFERENCES OF THE ELEMENTS

[0087] - 01: hull

[0088] - 02: roof

[0089] - 03: belt anchor points

[0090] - 04: pillar A

[0091] - 05: C pillar

[0092] - 06: wheel arch

[0093] - 07: rocker panel - 08: windshield bottom

[0094] - 09: bumper

[0095] - 10: body wall

[0096] - 11: compact outer layer

[0097] - 12: compact inner layer

[0098] - 13: foamed inner layer

[0099] - 14: compact inner layer

[0100] - 15: foamed middle layer

[0101] - 20: passenger compartment wall

[0102] - 21: compact outer layer

[0103] - 22: compact inner layer

[0104] - 23: foamed inner layer

[0105] - 24: compact inner layer

[0106] - 25: foamed middle layer

[0107] - 30: dropbox

[0108] - 31: vent

[0109] - 32: seat belts

[0110] - 33: bridging elements or layer re-bonding pad or "kiss-off"

[0111] - 34: material joint

[0112] - 35: shape of layer 21 to create the "kiss-off"

[0113] - 40: hood

[0114] - 41: doors or leaves

[0115] - 42: Rear bumper

[0116] - 43: Tailgate

[0117] - 44: Seat DETAILED DESCRIPTION OF MODES OF EXECUTION OF THE INVENTION

[0118] The invention is not limited to the embodiments or modes of execution described, but is capable of being modified by using means equivalent to those described. The invention and its principle therefore relate both to a vehicle body (or a part thereof), and to a method of manufacturing said body or parts thereof.

[0119] With reference to the figures, the shell 01, given as a non-limiting example, is designed to be rotomoldable. As such, it has a hollow body delimited by a bodywork wall 10 and a passenger compartment wall 20. It is provided with entry points for the polymer material, for example dropboxes 30, and air exit points, for example vents 31. The dropboxes 30 and the vents 31 are elements present on the manufacturing molds of said shell 01 rather than elements of said shell 01 itself, but these entry and exit points will be named as such in the figures and in the present description, to correspond to the vocabulary commonly used by those skilled in the art. Favorably, said dropbox 30 and vents 31 are positioned in the roof 02 and in the wheel arches 06 of said hull 01. They can however be placed at any other location of the hull 01.

[0120] The manufacture of said shell 01 according to the present invention is carried out in several successive phases described below: a phase of rotational molding of the outer layer and then the production of the inner layer(s) according to the methods described below.

[0121] Rotational molding phase of the outer layer 11: polymer in the form of powder or pellets for example is inserted into a rotational molding mold either poured directly into the cavity of the open mold, or poured into the closed mold via said dropboxes 30. The mold is heated and rotated on two axes so that the polymer becomes pasty or liquid and lines all the walls of said mold. This phase forms the compact outer layer 11 of said body wall 10 and the compact outer layer 21 of said passenger compartment wall 20. These layers are called compact because they contain little or no porosity and their physical and mechanical properties correspond to those of the materials (for example polymer) constituting them.

[0122] Rotational molding phase of the inner layer: polymer in the form of virgin or recycled material powder, added to an expansion agent coupled or not to a nucleating agent, is inserted into the closed rotational molding mold through said dropboxes 30. The mold is heated and rotated so that the polymer becomes pasty or liquid and covers said compact outer layers 11 and 21 of said body wall 10 and passenger compartment 20. The heating temperature of the mold is set to be lower than the decomposition temperature of the expansion agent. This phase forms the compact inner layer 12 of said body wall 10 and the compact inner layer 22 of said passenger compartment wall 20 as illustrated in Figure 3. These layers are called compact because they contain little or no porosity and their physical and mechanical properties correspond to those of the polymer constituting them.

[0123] Foaming phase of the inner layer: the heating temperature of the mold is increased until reaching the decomposition temperature range of the foaming agent integrated into the polymer of said compact inner layers 12 and 22 of said bodywork 10 and passenger compartment 20 walls. The blowing agent triggers the germination then the expansion of a gas bubble (preferably nitrogen), its volume expands, which creates porosities in the polymer and increases the thickness of the inner walls. Said compact inner layers 12 and 22 of said bodywork 10 and passenger compartment 20 wall are transformed to form the foamed inner layer 13 of said bodywork 10 wall and the foamed inner layer 23 of said passenger compartment 20 wall as illustrated in Figure 4. These layers are said to be foamed because they are formed of polymer cells forming gas pockets. Their thickness is greater than when they were compact.Their mechanical and physical properties are inferior to those they had when they were compact.

[0124] At this stage, the manufacturing process is the same as for making a standard two-layer part.

[0125] Heating phase of the inner layer: hot air (or any other gas) is injected into the part, between said foamed inner layer 13 of said body wall 10, and said foamed inner layer 23 of said passenger compartment wall 20. The air circulates between an entry point and an exit point in the part. These points can be said dropboxes 30 and / or said vents 31, and / or other points made specifically for this function. The temperature of the gas is higher than the decomposition temperature of the foaming agent. The temperature is high enough for the air in the bubbles located on the surface to expand and then for the bubbles to burst. There is then coalescence and a compact skin is thus formed on the foam layer. Said foamed inner layer 13 of said body wall 10 is thus transformed to form a compact inner layer 14 and a foamed middle layer 15.In the same way, said foamed inner layer 23 of said passenger compartment wall 20 is thus transformed to form a compact inner layer 24 and a foamed middle layer 25. This structure is illustrated in figure 5.

[0126] This process produces a three-layer part (compact outer layer, foamed middle layer and compact inner layer) even though the part was rotationally molded with only two layers of polymer.

[0127] According to a particular embodiment, certain parts of said shell 01 are foamed until said foamed inner layer 13 and said foamed inner layer 23 join, as illustrated in Figure 6. This can be achieved by a particular part design, i.e. a locally thinner part thickness which causes the foams to join during the foaming phase. This can be achieved by locally increasing the thickness of the compact inner layers. There is thus locally a greater quantity of foaming agent, and therefore a greater foam thickness at the end of the foaming phase. This can be achieved by increasing the foaming temperature, for example locally outside the mold, so that the exothermic sublimation reaction of the foaming agent runs away and results in a thicker (but therefore less compact) foam in the part.

[0128] Merging said body wall 10 and said passenger compartment wall 20 can have several advantages. This makes it possible to stiffen the part locally, without resorting to the third layer (for example in areas in which the circulation of a hot air flow is difficult to achieve). This can also make it possible to form preferential channels for the circulation of hot air during the heating phase of the inner layer. For example, the rocker panels 07, the bottom of the windshield 08 and the bumper 09 can be fully foamed as illustrated in Figure 6. When hot air is then injected into said dropbox 30 located in said wheel arch 06 at the front of said shell 01, and the hot air outlet is placed in said dropbox 30 located on the roof, the air will pass entirely into the A-pillar 04, creating the third layer in this location specifically.The combination of complete foaming of the thickness in places and the creation of a third layer by circulation of hot air in other places, makes it possible to specifically reinforce the most mechanically loaded zones of said shell 01, for example said pillar A 04, pillar C 05, or the anchor points 03 of belt 32 (see figures 7 to 9), without increasing the mass of said shell 01. The third and fourth methods described above can also be applied to the constructions illustrated in figures 1 to 9.

[0129] Figure 10 illustrates an embodiment of a layer bonding pad 33 called "kiss-off" in a door. The base of the pad 33 is made in the layer 21 during the rotational molding thereof. The material bonding (illustrated by the reference 34) is carried out between 2 internal layers, one belonging to the bodywork wall 10, the other belonging to the passenger compartment wall 20. In Figure 10, it is the layers 14 and 24 which join but these kiss-offs can be formed with any of the internal layers of the embodiments of Figures 3 to 5 (respectively 12 / 22, 13 / 23, 14 / 24), the aim being to avoid doing this on the external walls (11, 21) to avoid having visible shrinkage from the outside. This results in considerably reinforced parts that meet the necessary strength requirements.

[0130] Figures 11 to 13 illustrate methods of performing the kiss-offs 33 at different locations on a bodywork, these methods being illustrative and not limiting, such kiss-offs being able to be placed at other locations as well.

[0131] Figure 11 illustrates an exterior perspective and sectional view of a door with its outer 10, inner 20 layers, the shape 35 of the layer 21 to create the kiss-off during rotational molding, and the layer bonding pad 33. Said kiss-off 33 creates a connection between the bodywork wall 10 and the passenger compartment wall 20. The assembly will thus be much more difficult to deform because to deform one of the two walls, it will also be necessary to deform the other at the same time while these are linked by the material joint 34. In the event of a side impact, said door will therefore sink much less, ensuring better safety for the passengers.

[0132] Figure 12 illustrates a perspective and sectional view of the interior of a door with its outer 10 and inner 20 layers, the shape 35 of the layer 21 to create the kiss-off during rotational molding, and the layer re-bonding pad 33.

[0133] Figure 13 illustrates a rear perspective and sectional view of the front of a shell (as illustrated in figures 7 to 9) with its outer 10, inner 20 layers, the shape 35 of the layer 21 to create the kiss-off during rotational molding, and the layer bonding pad 33. In this example, the kiss-offs are placed at the roof level and make it possible to reinforce the structure at the seat belt anchor points (see figures 7 to 9). Said kiss-off 33 creates a connection between the body wall 10 and the passenger compartment wall 20. The assembly will thus be much more difficult to deform because to deform one of the two walls, it will also be necessary to deform the other at the same time while they are linked by the material joint 34.In the event of a frontal impact projecting the passenger forward, thus pulling on the seat belts and their anchor points 03, said anchor points will resist the traction of said seat belts much better, ensuring better safety for the passengers.

[0134] Figure 14 illustrates examples of parts of a body such as the shell 10, openings or doors 41 and a hood 40. Other parts formed according to the invention are for example a seat 44, a rear bumper, a tailgate 42 etc... all parts which are known in the field of automobile construction.

[0135] Embodiments have been described to provide a comprehensive understanding of the principles of structure, function, manufacture, and use of the systems and methods described in this application. One or more of these embodiments are illustrated in the accompanying drawings. The systems and methods specifically described in this application and illustrated in the accompanying drawings are non-limiting embodiments, and the scope of the present invention is not defined solely by the claims. Features illustrated or described in connection with one embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. A number of problems with conventional methods and systems are noted herein, and the methods and systems described herein may solve one or more of these problems.Additionally, while this invention has been described in conjunction with a number of embodiments, alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention are also covered by this application.

Claims

CLAIMS 1. Structure forming the passenger compartment of a vehicle, comprising a shell (01), and openings (40, 41), said structure being manufactured by rotational molding and forming the complete body of a vehicle, where each part such as the shell (01) and the openings (40, 41) is a hollow body comprising at least one compact outer layer (11) and a foamed inner and / or middle layer (13, 15, 23, 25) manufactured in the same polymer base as the outer layer, with the addition of a foaming agent.

2. Structure forming the passenger compartment of a vehicle according to the preceding claim, comprising a shell (01) produced in a mold comprising dropboxes (30) and vents (31) at the wheel arches (06) and the roof (02), said dropboxes (30) containing the material intended to form the inner (12-14, 22-24) and middle (15-25) layers.

3. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, the rotomolded parts being reinforced by reinforcements in the particularly stressed areas, in particular the anchor points (03) of the belt (32), the A pillars (04), the C pillars (05), the front bumper (09), the rear bumper (42), the doors (41) or the hoods (40), the reinforcement being made possible by the proximity of dropboxes (30) in the mold used to form said parts.

4. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, the foamed middle layers (15, 25) and / or foamed inner layers (13, 23) and / or compact inner layers (12, 14, 22, 24) of the parts being made entirely or partially from materials resulting from the recycling of previous structural parts forming the passenger compartment of a vehicle.

5. Structure forming the passenger compartment of a vehicle according to one of claims 3 or 4, obtaining said reinforcements consisting of locally foaming the entire thickness of the rotomolded part.

6. Structure forming the passenger compartment of a vehicle according to one of claims 3 to 5, obtaining said reinforcements consisting of heating the foamed inner layer (13, 23) to obtain a compact inner layer (14, 24) and a foamed middle layer (15, 25).

7. Structure forming the passenger compartment of a vehicle according to the preceding claim, in which the heating of the foamed inner layer(s) (13, 23) is carried out by the injection and / or circulation of a hot gas, for example air, inside the part.

8. Structure forming the passenger compartment of a vehicle according to the preceding claim, in which the foamed surface serves as a guide for the hot gas by the Coanda effect.

9. Structure forming the passenger compartment of a vehicle according to one of claims 7 or 8, comprising a shell (01) produced in a mold in which dropboxes (30) and / or vents (31) are used both to supply material to the internal layers (12-14, 22-24), and to produce the hot gas inlets and / or outlets (24, 24).

10. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, in which one or more parts have one or more bridging elements or re-bonding or kiss-off pads (33) produced during rotational molding on the compact outer layer (11, 21), said bridging element (33) allowing re-bonding of the materials during the treatment of said inner layer (12-15, 22-25).

11. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, comprising at least one part in which, during the micronization of one or more previous structural parts forming the passenger compartment of a vehicle, this is produced with at least two different particle size spectra and introduced into the mold by one or more drop boxes to produce the second foamed layer (13, 15, 23, 25) and a third layer (14, 24).

12. Structure forming the passenger compartment of a vehicle according to the preceding claim, in which a first granulometric spectrum is fine and a second granulometric spectrum is greater than the first spectrum.

13. Structure forming the passenger compartment of a vehicle according to claim 11 or 12, in which the particles of the two spectra are sent into the mold from the dropbox(es), the finest particles melting first to form a second layer (13, 15, 23, 25) on the first layer (11, 21), then the larger particles adhering to the second layer to form a third layer (14, 24).

14. Structure forming the passenger compartment of a vehicle according to the preceding claim, in which the expansion of the second layer (13, 15, 23, 25) is carried out before the deposition of the third layer (14, 24) using expansion agents having a low trigger temperature.

15. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, in which, upon recycling structural parts forming the passenger compartment of a previous vehicle, grinding, reformulation, then micronization are carried out in which nanometric fillers such as nano tubes, graphene are integrated, improving the mechanical characteristics of the second foamed layer (13, 15, 23, 25) and / or of the third layer (14, 24).

16. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, said structural parts forming the passenger compartment of a vehicle are a shell (01), a door (41), a leaf (41), a hood (40), a tailgate (43), a front bumper (09) or rear bumper (42).

17. Structure forming the passenger compartment of a vehicle according to one of the preceding claims, in which anchoring points (03) of the seat belts (32) are located in the center of the roof (02), on the interior side of the vehicle.

18. Mold for forming a shell (01) of the structure forming the passenger compartment of a vehicle according to one of the preceding claims 1 to 17, said mold comprising dropboxes (30) and vents (31) at the wheel arches (06) and the roof (02) of said structure, said dropboxes (30) containing the material intended to form the inner (12-14, 22-24) and middle (15, 25) layers.

19. Mold according to the preceding claim, in which dropboxes (30) and / or vents (31) are used both to supply material to the inner layers (12-14, 22-24), and to provide the hot gas inlets and / or outlets.

20. Rotomoulded vehicle seat produced using a process identical to that of the structural parts forming the passenger compartment according to one of the preceding claims.

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