GB2344557A

GB2344557A - Process for injection moulding elements which can move rotationally with respect to each other

Info

Publication number: GB2344557A
Application number: GB9929042A
Authority: GB
Inventors: Jean-Paul Caoduro; Jean-Jacques Mathieu
Original assignee: MGI Coutier SA
Current assignee: Akwel SA
Priority date: 1998-12-10
Filing date: 1999-12-08
Publication date: 2000-06-14
Anticipated expiration: 2019-12-08
Also published as: FR2787054A1; GB2344557B; IT1314268B1; ES2166295B1; ITMI992551A0; CN1263817A; GB9929042D0; ITMI992551A1; DE19959656A1; BE1012591A3; ES2166295A1; BR9905825A

Abstract

An injection moulding process for a bar/blade assembly for ventilation of a motor vehicle passenger space is formed using a bi-injection mould cooperating with a rotating carriage. In a first moulding phase, in a first impression in the bi-injection mould and with the aid of pins 4, blades 1 are injection moulded. The blades 1 are produced with essentially conical hollow axes 3, having a low retaining strength and constituting the axes of rotation (X-X) of the elements with respect to each other. These blades are removed from the mould and are transferred into a second impression in the bi-injection mould by rotating the carriage. Pins 5 are introduced into the conical cavities of the axes 3 obtained during the first moulding phase and make it possible to open out the ends 6 of these cavities to thus obtain a permanent plastic deformation of the axes 3 at this point. In a second moulding phase, the bars 2 are over-moulded by injection, at least partially around the hollow axes 3 of the blades 1 previously opened out by the pins 5.

Description

PROCESS FOR INJECTION MOULDING ELEMENTS WHICH CAN MOVE ROTATIONALLY WITH RESPECT TO EACH OTHER The present invention relates to an injection moulding process for elements which are integrally attached to each other but can move in rotation with respect to each other, in particular for a bar/blade assembly intended for ventilation of the passenger area of a motor vehicle.

In recent decades the plastics industry has undergone a considerable increase and a large number of common objects are now produced by injection moulding from various plastics materials.

It is frequently the case that such objects are formed from a number of elements which are integrally attached to each other but can move in rotation with respect to each other; these are conventionally produced by moulding a first element from a first plastics material and then over-moulding thereupon a second element from a second plastics material having a melting point lower than that of the first; during this over-moulding process the first element constitutes an element of the mould.

The implementation of such a process causes difficulties linked to the fact that in order to obtain an assembly which cannot be disassembled but in which the two elements can move in rotation, it is necessary to provide retaining members on the part which is moulded first and this can cause problems when releasing it from the mould.

In order to overcome these problems, moulds are generally used which are formed from a number of parts. This can lead to the formation, on the moulded parts, of irregularities in relief at the parting planes of the various parts of the mould.

However, in order to give complete satisfaction, it is necessary for the connection surface of the two elements, which must be a turning surface, to be perfectly smooth.

Specialists have already proposed various means for overcoming these irregularities, which are fully satisfactory from a technical point óf view. However, these means require the implementation of sophisticated, and therefore expensive, apparatus and are consequently open to criticism in economic terms.

It is the object of the present invention to overcome these difficulties by proposing an injection moulding process for elements, which are integrally attached to each other but can move in rotation with respect to each other, using a biinjection mould cooperating with a rotating carriage, giving full satisfaction both technically and economically.

This process is especially suited to the injection moulding of bar/blade assemblies intended for ventilating the passenger area of motor vehicles but could, of course, be used to produce other objects without thereby departing from the scope of the invention.

According to the invention, this process is characterised in that: -in a first moulding phase, in a first impression in the bi-injection mould and with the aid of pins, a first element, preferably the blades of a bar/blade assembly as mentioned above, is injection moulded, being produced with essentially conical hollow axes, having a low retaining strength and constituting the axes of rotation of the elements with respect to each other, -the first element is removed from the mould, -it is transferred into a second impression in the bi-injection mould by rotating the carriage, -pins are introduced into the conical cavities of the axes obtained during the first moulding phase and make it possible to open out the ends of these cavities to thus obtain a permanent plastic deformation of the axes at this point, and -in a second moulding phase, the second element, preferably the bars of the bar/blade assembly, is over moulded by injection, at least partially around the hollow axes of the first element previously opened out by the pins.

It is clear that this process makes it possible to guarantee the absence of any irregularity on the external conical wall of each axis which corresponds to the surface of rotation of the elements with respect to each other.

For reasons linked to their function, the blades of the ventilation grilles of the passenger area of motor vehicles must generally be produced from a material having a melting point higher than 250 C.

Consequently, and in accordance with another feature of the invention, the blades which are produced first are preferably moulded from a plastics material having a melting point of the order of 260 C.

The bars which are moulded second must, of course, be produced from a material having a melting point lower than that of the material forming the blades, preferably from a plastics material having a melting point of the order of 200 C.

It should be noted that the moulding order (blades then bars) of the two elements of a bar/blade assembly corresponds to a particularly advantageous feature of the invention since it makes it possible to produce the bars from a common material with a low melting point; however, this would not be the case if the order of moulding were reversed because it would then be necessary to choose a plastics material for the bars which had a melting point higher than 260 C and this would considerably increase the cost price of the assembly.

It should also be noted that, at the end of the first moulding phase, the presence of the hollow axes having a retaining member is such as to cause difficulties during removal from the mould.

However, these problems can be overcome either by forced removal of the first element from the mould, or even by exploiting the shrinkage of the moulded material, which is, as a general rule, of the order of 1%, in order not to have to carry out such forced removal.

According to the invention, the shrinkage of the thermoplastic material forming the second element and the permanent deformation of the end of the axes of the first element are two parameters which make it possible easily to control the value of the braking forces of the rotation of the first element. In detail, these forces are controlled, after the mould is complete, by additional parameters such as the temperature of the thermoplastic material during injection, the injection pressure, the compacting time, the cooling time and the time of the full cycle.

The features of an example of an injection moulding process according to the invention will be described in more detail with reference to the attached drawing, in which: -Figure 1 is a diagram, of which the upper part (above axis X-X) corresponds to the first moulding phase of a bar/blade assembly while the lower part (below the axis X-X) corresponds to the second moulding phase; and -Figure 2 is a diagram similar to the lower part of Figure 1 but corresponding to a variation in the pins used in the process.

According to the figures, in a first moulding phase the moulding is carried out by injection of the blades 1 from a plastics material having a melting point of the order of 260 C, whereas in a second moulding phase, the bars 2, formed from a plastics material having a melting point of the order of 200 C, are over-moulded onto the blades 1.

According to the upper part of Figure 1, the moulding of the blades is carried out in a first impression in a biinjection mould cooperating with a rotating carriage.

The blades obtained during this phase are produced with hollow conical axes 3 having a low retaining strength, constituting the axis of rotation X-X of the blades 1 and of the bars 2.

The hollow axes 3 are moulded by the positioning of pins 4 of a suitable shape.

It should be noted that after this first moulding phase, the blades 1 are removed from the mould by force or by exploiting the shrinkage of the material forming these blades, and then transferred into a second impression in the biinjection mould by rotation of the carriage, into the position illustrated in the lower part of Figure 1 and in Figure 2 in order to carry out the over-moulding of the bars 2 by injection.

Before this over-moulding operation, pins 5 (Figure 1) or 5' (Figure 2) of a suitable shape are introduced into the conical cavities of the axes 3 of the blades 1 in order to open out the ends 6; in this way a permanent plastic deformation of these axes is obtained.

The over-moulding of the bars 2 around the axes 3 of the blades 1 is then carried out.

It is clear that the blades 1 and the bars 2 obtained in this way are integrally attached to each other while being able to move in rotation with respect to each other about the axis X-X.

Furthermore, the outer face 7 of the axes 3, which corresponds to the zone of contact of the blades 1 and of the bars 2 during this rotation, is smooth and free from any superficial faults.

Claims

CLAIMS:

1. An injection moulding process for first and second elements which are integrally attached to each other but can move in rotation with respect to each other, using a biinjection mould cooperating with a rotating carriage, wherein -in a first moulding phase, in a first impression in the bi-injection mould and with the aid of pins the first element is injection moulded, being produced with substantially conical hollow axes, having a low retaining strength and constituting the axes of rotation of the elements with respect to each other, -the first element is removed from the mould, -the first element is transferred into a second impression in the bi-injection mould by rotating the carriage, -pins are introduced into the conical cavities of the axes obtained during the first moulding phase and make it possible to open out the ends of these cavities to thus obtain a permanent plastic deformation of the axes at this point, and -in a second moulding phase, the second element is over-moulded by injection, at least partially around the hollow axes of the first element previously opened out by the pins.

2. A process according to claim 1, wherein the first element is moulded in a material having a melting point of the order of 260 C, whereas the second element is over-moulded around the first element in a material having a melting point of the order of 200 C.

3. A process according to claim 1 or 2, wherein, after the first moulding phase, the first element is removed from the mould by force.

4. A process according to claim 1 or 2, wherein the shrinkage of the material forming the first element is exploited during its removal from the mould.

5. A process according to any of claims 1 to 4, wherein the shrinkage of the material forming the second element and the permanent deformation of the end of the axes of the first element are two parameters which make it possible to control the value of the braking forces of the rotation of the first element.

6. A process according to any of claims 1 to 5, wherein the first element comprises the blades of a bar/blade assembly intended for the passenger area of a motor vehicle and the second element comprises the bars.

7. An injection moulding process substantially as hereinbefore described with reference to the drawing.

8. An article produced by a process according to any of claims 1 to 7.