FR2784050A1 - Finishing profiled structural section with flexible plastic skin involves conformation, even reversal, of skin before molding to final shape and bonding, achieving difficult re-entrant sections with ease - Google Patents

Abstract

Between extraction of the skin from the mold (21) and bonding with the structural section, the skin has a first form, differing from its final form. During bonding, the skin is conformed, bringing it to its final predetermined shape. An Independent claim is included for the finished structural section. Preferred features: During introduction, plastic is injected under pressure. The initial skin form has one or more re-entrant zones less than in the final form. During bonding, the skin (21) is placed in a further molding cavity. Plastic is introduced to form the structural section which adheres to the skin. A further variant of this method is described, in which a flexible bonding plastic is introduced, especially a foam, to expand between skin and structural section, also achieving bonding. A zone of the skin is reversed, such that convex parts become concave and vice versa, to produce the final form.

Description

] The invention relates to a method for producing a finished part

  comprising a structural element covered with a flexible skin of plastic material, such as in particular a thermoplastic material or

  thermosetting, having a determined shape, as well as the finished part.

  The part obtained by the method of the invention particularly finds its application in the automotive field and can constitute all or part of a dashboard, door panels,

  amounts or other "cabinet" elements of the vehicle.

  Processes are already known comprising the following steps: a) bringing plastic material into a molding cavity, b) demolding the skin thus obtained,

  c) bind the skin to the structural element.

  The addition of plastic may in particular consist of an injection. However, the forms of part which it is possible to obtain by implementing these methods are limited. Figure 1 illustrates step a) of such a method. FIG. 1 represents a mold 2 mainly comprising two parts constituted by a punch 4 and a die 6. The punch 4 and the die 6 are movable relative to each other between an open position and a closed position. In the closed position, they come into contact with one another along a main joint plane 9 surrounding a molding cavity 5

spared them.

  The matrix comprises two elements 6a, 6b movable with respect to each other and coming into contact with one another along a secondary joint plane 7 in the closed position of the mold, in order to allow the demoulding of

  the molded object, the latter in fact having an undercut zone 10.

  For the same reason, the punch 4 comprises two elements 4a, 4b movable with respect to each other and coming into contact with each other along a plane

  secondary seal 3 in the closed position of the mold.

  In a first step, plastic is introduced into the molding cavity 5, mold 2 closed. After cooling, the mold is opened, the elements 4a, 4b, 6a, 6b of the mold deviate from each other and

  a skin 1 is released from the cooled plastic.

  This skin 1 has a shape closely corresponding to the shape it must have on the finished part. It includes an aspect face 1a which will be visible on the finished part and a non-visible face 1b. The intersection of the secondary joint planes 3, 7 with the molding cavity 5 define lines along which marks, respectively, 8b, 8a develop,

  visible on the skin 1 after demolding.

  The skin will then be introduced into a second mold, in which a support made of structural material, intended to structure the finished part, will be linked to the non-visible face 1b of the skin 1. The mark 8b will therefore be camouflaged, but the mark 8a being on the visible face will constitute a defect of prohibitive aspect which it will be necessary to mask under penalty of rendering the skin unusable commercially. This is why, the injection technique was hardly used until now to make skins in

plastic material.

  Thermoforming or rotational molding techniques were then used to make the skin when it had to have an undercut shape. However, these are more expensive, increase the material falls and do not make it possible to obtain grain variations or

  desired thicknesses on the skin.

  The solution of the invention, aiming to remedy these various drawbacks, consists in that: - during step a), plastic material is brought into the molding cavity to which a shape different from said is given. determined shape of the part, so that between steps b) and c), the skin has substantially a first shape, distinct from its final determined shape, - during step c), the skin is conformed to the 'bring it into its final determined form. It is therefore a question of arriving at the determined shape of the skin in two stages. It is simpler to produce, by the selected molding process (injection, even rotational molding according to the so-called "slush molding" technique; supply of fine powder), the first form than to directly produce the corresponding "determined form". This therefore makes it possible to reduce the cost of the skin and to modify the characteristics which do not allow its

  satisfactorily performed in injection.

  According to an advantageous characteristic of the invention, the first shape will be determined so that in this first shape, the skin has at least one undercut area less than in

its final determined form.

  An advantageous solution proposed by the invention for performing step c) consists in that: - the skin is placed in another molding cavity without having previously heated it, and - plastic material is introduced into the cavity molding

  to constitute the structural element adhering to it.

  The pressure and the heat of the plastic material introduced into the molding cavity shape the skin, without altering its appearance qualities and in particular without stretching its grain if it is grainy (insofar as o

you don't stretch the skin).

  This characteristic makes it possible to obtain even more

  simple and therefore less expensive the finished part.

  Another characteristic of the invention consists in turning over - as a glove - an area of the skin between the first shape and the final shape, so that in this area the convex part (s) (s)

  becomes (become) concave (s) and vice versa.

  The inversion of an area of the skin makes it possible in certain cases to facilitate demoulding or to simplify the mold while the deformations of the skin caused by this inversion do not alter

  practically no appearance qualities of the skin.

  The invention also relates to a finished part. According to the invention, the finished part comprises a structural element covered with a flexible skin of injected plastic material having at least one zone in

  undercut and has no seal mark on the skin.

  The invention will appear even more clearly in the

  description which follows, made with reference to the drawings attached in

  which: - Figure 1 illustrates a step of a process of the prior art, - Figure 2 illustrates a first step of a process according to the invention, - Figure 3 illustrates a second step of the process according to l invention, - Figure 4 illustrates a third step of the method according to the invention, - Figure 5 illustrates a variant of the first step of the method according to the invention, - Figure 6 illustrates a first variant of the second step of the process according to the invention, - Figure 7 illustrates a second variant of the second step of the process according to the invention, - Figure 8 illustrates a third variant of the second step

  of the process according to the invention.

  FIG. 2 illustrates a mold 12 comprising a punch 14 and a die 16 each consisting of a single element. The punch and the die are movable between them and enclose between them a mold cavity 15. The mold cavity 5 is intended to produce a skin 21 forming part of a part 40 illustrated in FIG. 4. The skin 21 has a face of appearance 21a and a non-visible face 21b. In FIG. 4, the skin 21 has a determined shape including a concave part 33, which generates a

undercut area 30.

  In FIG. 2 illustrating the embodiment of the skin 2, the concave part is replaced by a convex part 20. This convex part is not

  simply the image in a mirror of the concave part 33 of the finished part.

  It has been slightly modified to allow the release of the skin

  although the mold 12 has only two elements.

  To make the skin, plastic material 11 is injected under pressure into the molding cavity 15. The plastic material is chosen so that the skin is flexible at room temperature and may in particular be made up of polyolefins, polyvinyl chloride and

polyurethane.

  After opening the mold, the skin is removed from the mold and then introduced

  in another mold as illustrated in Figure 3.

  FIG. 3 illustrates a mold 22 close, in its constitution, to that illustrated in FIG. 1. It mainly comprises two parts constituted by a punch 24 and a matrix 26. The punch 24 and the matrix 26 are movable relative to one another to the other between an open position and a closed position. In the closed position, they come into contact with one another along a main joint plane 29 surrounding a molding cavity 25

spared them.

  The shape of the molding cavity 25 corresponds to the shape of the finished part 40. In order to allow the finished part to be removed from the mold, the matrix comprises two elements 26a, 26b which are movable relative to each other and coming into contact one of the other along a secondary joint plane 27 in the closed position of the mold. For the same reason, the punch 24 comprises two elements 24a, 24b movable with respect to one another and coming into contact with one another along a secondary joint plane 23 in the closed position of the mold. After demolding, the skin is introduced into the molding cavity 25, its appearance face 21 being disposed opposite the matrix 26. When the mold 22 is closed, the convex part 20 of the skin 21 is turned over to become concave . The skin then has a shape close to that which it must have on the finished part. We could also return the game

  convex 20 before putting the skin in the mold 22.

  Plastic material 32 is then injected under pressure from the punch 24. The plastic material comes into contact with the non-visible face 21b of the skin to which it adheres. The pressure of the plastic material 32 applies the skin 21 against the matrix 26 and thus finishes shaping the skin. The line 28a formed by the intersection of the joint plane 27 and the molding cavity 25 does not create a mark since the plastic does not

  does not come into contact with it (the skin 21 is disposed between).

  The line 28b formed by the intersection of the joint plane 23 and the molding cavity 25 creates a mark on the finished part 40, but this is

  not visible side of the finished part. It therefore poses no problem.

  After the plastic material 32 has cooled, the mold 22 is opened. The finished part then comprises the skin 21 and a rigid structural element 31 forming a support for the skin to which it adheres. The arrows 34a, 36a and 36b illustrate the direction of the opening movement respectively

elements 24a, 26a and 26b.

  The finished part 40 is then removed from the element 24a as indicated

by arrow 34b.

  FIG. 5 illustrates a variant of FIG. 2. The elements of the

  Figure 5 corresponding to those of Figure 2 have a mark increased by 30.

  This variant is essentially distinguished in that the convex part 20 is replaced by a concave part 50 corresponding

  substantially in the image in a mirror of the convex part 20.

  Thus, the shape of the skin obtained after obtaining by molding plastic material 41 in the cavity 45 differs from its shape on the finished part 40, in that the part corresponding to the undercut area 30 is adapted so as not to present undercut while remaining fairly

  close to its shape on the finished part 40.

  FIG. 6 illustrates a variant of FIG. 3. A mold 52 comprises a punch 54 and a die 56 each comprising two elements. The punch and the die reserve between them a molding cavity 55. This mold 52 will not be further detailed since it is very close in its constitution and in its forms to the mold 22 from which it differs notably only in the slightly greater thickness. from the cavity of

molding 55.

  After production and demoulding, the skin 21 is introduced into the cavity 55. It is arranged facing the matrix 56. There is also in the cavity 55, facing the punch 54, a rigid structural element 58 produced beforehand. This element 58 is close to the element 31 described above. After closing the mold, a flexible plastic material 57 is introduced into the molding cavity, between the structural element 58 and the skin 21. The flexible plastic material 57 expands in the molding cavity and fills the space left free between the structural element 58 and the skin 21. It binds together the structural element 58 and the skin 21 and introduces between a

  flexible element improving the feel of the finished part.

  The expandable plastic material 57 is advantageously made up

by polyurethane foam.

  Figure 7 illustrates a variant close to that illustrated in Figure

  6. The corresponding elements have a mark increased by 10.

  These variants essentially differ in that in FIG. 7, the plastic material 67 introduced between the skin 21 and the support 68 is constituted by expanded balls, advantageously constituted by

polypropylene.

  After having introduced the balls into the molding cavity 75, water vapor is injected which, by its heat, welds the balls together, with the skin 21 and with the support 68. The balls of expanded plastic material 67

  are then agglomerated together and bind together the skin and the support 68.

  FIG. 8 illustrates a variant of the solutions illustrated in FIGS. 3, 6 and 7. A mold 72 comprises a punch 74 and a die 76 each comprising two elements. The punch and the die reserve between

them a mold cavity 75.

  We will not detail this mold 72 further since it is very

  close in its constitution and in its forms of the mold 72.

  After production and demolding, the skin 21 is introduced into the cavity 75. It is arranged facing the matrix 76. Expanded plastic balls are introduced between the punch 74 and the skin 21,

advantageously made of polypropylene.

  Then, steam is injected into the molding cavity 75

  which, by its heat, welds the beads together and makes them adhere to the skin 21.

  The expanded plastic balls 67 are then agglomerated together and bonded to the skin. They form a structural element to which the skin 21 conforms. Advantageously, at least for certain plastics, after production, the skin will be placed in the mold 22 binding it to the structural element, or at least turned over before it is fully cooled. Of course, the invention is in no way limited to the embodiments

  which have just been described and which are given only by way of example.

  Thus, the mold 22 for injecting plastic material binding the skin to the structural element could be replaced by a foaming mold,

thermoforming or other.

Claims (10)

Claims   1. Method for producing a finished part (40) comprising a structural element (31) covered with a flexible skin (21) of plastic material having a determined shape, comprising the following steps: a) supplying plastic material (11, 41) in a molding cavity (15, 45), b) demolding the skin (21) thus obtained, c) bonding the skin to the structural element, characterized in that: - during step a), brings plastic material into the molding cavity which has been given a shape different from said determined shape of the part, so that between steps b) and c), the skin has substantially a first shape, distinct from its final determined shape, - during step c), the skin is conformed to bring it into its final determined form.   2. Method according to claim 1, characterized in that during   step a), plastic material is injected under pressure.   3. Method according to claim 1 or 2, characterized in that the first shape is determined so that in this first shape, the skin has at least one undercut area less than in its final determined form.   4. Method according to any one of the preceding claims,   characterized in that during step c), the following steps are carried out: - the skin (21) is placed in another molding cavity (25), and - plastic material (32) is introduced into the cavity of   molding to constitute the structural element (31) adhering to the skin.   5. Method according to any one of claims 1 to 3,   characterized in that during step c): - the skin (21) and the structural element (58) are placed in a second molding cavity (55), - a flexible plastic connecting material (57, 67) in the mold cavity between the skin and the structural element for binding   together the skin and this structural element.   6. Method according to claim 5, characterized in that the flexible plastic material is an expandable material (57) such as polyurethane foam, which is made to expand between the skin and this element structural to link them together.   7. Method according to claim 5, characterized in that the plastic material is a material constituted by expanded balls (67), such as polypropylene balls, which are agglomerated together in the second mold cavity, between the skin and the structural element to link them together.   8. Method according to any one of claims 1 to 3,   characterized in that during step c): - the skin (21) is placed in a second molding cavity (75), and - a plastic material is introduced into this cavity consisting of expanded balls (77), such as polypropylene beads, in this cavity in contact with the skin to create and adhere to the skin said structural element.   9. Method according to any one of the preceding claims,   characterized in that an area of the skin is turned over between the first shape and the final shape, so that in this area the part (s)   convex (s) (20) becomes (become) concave (s) (33) and vice versa.   10. Finished part (40) comprising a structural element (31) covered with a flexible skin (21) injected in plastic material having at least one undercut zone and devoid of joint plane mark on the skin.