process of simulating the manufacture of a part by plastic injection

Abstract

The invention relates to a method for digitally simulating the injection-molding of a plastic part (101, 105, 110) comprising aluminum particles to give a metallic appearance to said part (101, 105, 110). According to the invention, said method comprises the following steps: - a step of simulating the flow of the plastic material loaded with aluminum particles (103, 106, 111), - a step of developing a map of a quantity representative of the orientation of the aluminum particles (103, 106, 110) after injection, - a step of establishing a diagnosis on the quality of the part (101, 105, 110) obtained by viewing in particular areas of said map which would be likely to contain defects (104, 109, 112), Figure for the abstract: Figure 1

Description

Title of the invention: method for simulating the manufacture of a part by plastic injection

[0001] The present invention relates to a method for simulating the manufacture of a part by plastic injection.

[0002] Certain parts of a vehicle, such as a front bumper or a rear bumper, are manufactured by plastic injection. During this manufacturing process, aluminum particles can be mixed with the plastic in order to give a metallic tint to the manufactured part. However, the aluminum particles each have an elliptical shape and can be poorly positioned relative to the direction of flow of the plastic in the mold, this poor positioning of the aluminum particles can lead to the appearance of defects on the manufactured part such as black marks. This type of defect is perfectly visible to the customer, who will then have the impression that his vehicle was manufactured in a hurry and in a sloppy manner. The presence of black marks on the parts of the vehicle will degrade the visual appearance of said vehicle and will therefore not be likely to satisfy the customer.

[0003] A control method according to the invention is a digital simulation method making it possible first to control the perceived quality of a part manufactured by plastic injection in the presence of aluminum particles, then to modify the geometry of the part, in particular the imprint in the mold, and / or the geometry of the feed system if this quality was not satisfactory until satisfactory quality is obtained.

[0004] The subject of the invention is a method for digitally simulating the injection molding of a plastic part comprising aluminum particles to give a metallic appearance to said part, said method being controlled by software. According to the invention, the method comprises the following steps: - a step of creating a specific mesh of an imprint intended for the manufacture of the part, - a step of fixing at least one parameter conditioning the flow of the plastic material comprising the aluminum particles, —a step of simulating the flow of the plastic material loaded with aluminum particles in the mold, - a step of developing a map of a quantity representative of the orientation of the aluminum particles after injection relative to the flow direction, - a step of establishing a diagnosis on the quality of the part obtained by visualizing in particular areas of said mapping which are likely to contain defects, - a step of stopping said process if no area likely to contain defects is detected, - a step of modifying said at least one parameter if at least one area likely to contain defects is detected, followed by a new step of developing a map, itself followed by a new step of establishing a new diagnosis on the quality of the part obtained, said steps being repeated until the part no longer shows any defects.

[0005] Such a method is a numerical simulation method which is used prior to a manufacturing process of a part. A method according to the invention is based on the fixing of a certain number of input parameters which will condition the formation of the part by plastic injection, then on a simulation of the orientation of the aluminum particles in the impression. The diagnosis on the quality of the part is carried out in the following way: -Either the aluminum particles are oriented in the direction of flow, and in this case the part to be manufactured will be of good quality. The actual manufacturing of the part can then be launched on the basis of the parameters which will have been stopped to carry out the numerical simulation, -Either the aluminum particles are disoriented relative to the flow direction in certain areas of the plastic material. These more disoriented areas of the aluminum particles appear on the map and the part will then be judged to be of poor quality. For this configuration, the process is then repeated at least once after modifying at least one of the input parameters which will condition the numerical simulation. As long as the part obtained by numerical simulation shows areas of higher disorientation of aluminum particles, the process will be repeated until a good quality part is obtained for which the aluminum particles will be oriented in the flow direction within the part. The quantity which is representative of the orientation of the aluminum particles can for example be a certain measure of the orientation tensor in each area of ​​the imprint.The part resulting from the digital simulation can be judged to be of good quality even if it shows areas of accentuated disorientation of aluminum particles, provided that said areas are no longer visible once the part has been fixed in its destination location which could for example be in a vehicle.

[0006] The aluminum particles each have an elliptical shape, and can be poorly positioned relative to the direction of flow of the plastic material in the mold, which phenomenon which could justify an uncontrolled orientation of the aluminum particles in the mold.

[0007] According to a possible characteristic of the invention, the defect to be detected in the part is a dark trace reflecting a local disorientation of aluminum particles. These dark traces degrade the appearance of the part, giving the customer the impression that this part was manufactured in haste, without particular care. If the part is intended to be mounted on a vehicle which is a structure of limited size, the dark traces will appear even more blatantly, hence the need to take particular care in the manufacture of the part.

[0008] According to a possible characteristic of the invention, said at least one parameter which will condition the flow of the plastic material comprising the aluminum particles in the mold is to be chosen from the shape of the cavity of the mold containing the plastic material, the thickness of the cavity, the insertion of a localized relief in the cavity, the position of the feed orifice of the mold within said mold. This is a non-exhaustive list of the parameters which will govern the simulation of the flow of the plastic material in the cavity. It is therefore sufficient to vary at least one of these parameters to modify the flow conditions of the plastic material in the cavity and therefore modify the distribution of the aluminum particles in said plastic material.

[0009] In particular, said at least one parameter which will condition the flow of the plastic material comprising the aluminum particles is to be chosen from the shape of the part, the geometry of the part, the position of the feed point of the mold within said mold.

[0010] According to a possible characteristic of the invention, the mapping appears in the form of a variation of colors in the area delimited by the contour of the cavity, each of said colors being representative of the orientation of aluminum particles. A simple visualization of the mapping allows at a glance to know whether the simulated part is of good or poor quality. Generally, if the part is of good quality the mapping will only show one color.

[0011] According to a possible characteristic of the invention, the mapping consists of a variation of gray in the area delimited by the contour of the cavity, each of said gray shades being representative of the orientation of the aluminum particles in the direction of flow. In this way, a simple visualization of the mapping makes it possible at a glance to know whether the simulated part is of good or poor quality. Generally, if the part is of good quality the mapping will only show the same shade of gray.

[0012] According to a possible characteristic of the invention, the step of establishing the diagnosis on the quality of the part obtained is carried out automatically by the software after having defined in said software the representative quantity of the orientation of the aluminum particles, a representative value of the form factor of the particles and a rheological model with specific parameters governing the interaction, that is to say the orientation, of the particles with the polymer matrix. In this way, the diagnosis on the quality of the part is carried out automatically without the intervention of an operator who could give an erroneous opinion based on a simple visualization of the mapping.

[0013] According to a possible characteristic of the invention, the method stops when no visible area of ​​the part once it has been fixed at its destination location is likely to contain defects. In other words, the method stops when: - no area of ​​disorientation of the aluminum particles is detected on the part, which will then have a uniform color reflecting good quality, -areas of higher aluminum particle misorientation are detected, but these areas will be masked once the part is mounted in its destination location.

[0014] According to a possible characteristic of the invention, the software controlling said method operates from a mesh of the geometry of the cavity comprising the aluminum particles, said mesh consisting of dividing said geometry into unit cells, the software performing a simulation of the flow of the plastic material loaded with aluminum particles in the cavity, from near to far cell by cell.

[0015] According to a possible characteristic of the invention, the plastic material is polypropylene and / or polypropylene with a certain quantity of talc (CaCO3).

[0016] According to a possible characteristic of the invention, the part to be manufactured is a front bumper or a rear bumper of a vehicle. These are two illustrative examples of parts to be manufactured for which a simulation method according to the invention is particularly suitable, but which are in no way limiting examples.

[0017] A simulation method according to the invention has the advantage of being able to simulate with great precision a flow of plastic material loaded with aluminum particles in a mold, in order to know if the part which will be manufactured under the same conditions will have defects. As a result, it makes it possible to generate a saving of time and savings on a process of manufacturing a part, by avoiding having to manufacture said part each time under different conditions before arriving at a part without defects. It also has the advantage of being able to carry out a very large number of simulations in a short time, by varying the input parameters with a large amplitude, making it possible to test a plurality of configurations.

[0018] The invention further relates to a method for manufacturing a plastic part comprising a simulation step according to the simulation method of the invention, said manufacturing method being devoid of a punching step in the manufacturing flow of the part.

[0019] A detailed description of a preferred embodiment of a simulation method according to the invention is given below, with reference to the following figures:

[0020] [Fig-1] [Fig.l] is a flowchart showing the main steps of a simulation method according to the invention,

[0021] [Fig.2] [Fig.2] is a side view of a first part simulated by means of a method according to the invention, and showing defects,

[0022] [Fig.3] [Fig.3] is a side view of the first part of [Fig.2] having much fewer defects, after the modification of a first parameter conditioning the flow of the plastic material loaded with aluminum particles in the mold,

[0023] [Fig.4] [Fig.4] is a side view of a second part simulated by means of a method according to the invention, and showing defects,

[0024] [Fig.5] [Fig.5] is a side view of the second part of [Fig.4] without defect, after the modification of a second parameter conditioning the flow of the plastic material loaded with aluminum particles in the mold,

[0025] [Fig.6] [Fig.6] is a side view of a third part simulated by means of a method according to the invention, and showing defects,

[0026] [Fig.7] [Fig.7] is a side view of the third part of [Fig.6] having much less defects, after the modification of a third parameter conditioning the flow of the plastic material loaded with aluminum particles in the mold,

[0027] The detailed description which follows focuses on the manufacture of a part which is intended to be fixed to a vehicle, said part being able for example to be a front bumper or a rear bumper.

[0028] The part is generally produced by plastic injection, the plastic material preferably being polypropylene. In order to obtain a metallic tint for said part, aluminum particles are introduced into the plastic material.

[0029] However, these aluminum particles have an elliptical shape and can be poorly positioned relative to the direction of flow of the plastic material in the mold. This poor positioning can result in a heterogeneous orientation of the aluminum particles in the plastic material, resulting in the appearance of dark traces on the manufactured part. These dark traces represent areas in which the orientation of aluminum particles is abnormally high compared to a relatively homogeneous orientation of said aluminum particles in said part. These dark traces, which are visible on the part, are unsightly and give the impression to the customer that the manufacturing of the part was carried out in a rushed and sloppy manner.

[0030] One way to remedy the appearance of these dark traces is to modify certain parameters of the injection process in order to better orient the aluminum particles, then to repeat the part manufacturing operation each time. This way of proceeding is not acceptable, because it is very time-consuming and very expensive, since for each part manufacturing operation with new parameters, it is necessary to mobilize manufacturing equipment and sacrifice raw material.

[0031] A method according to the invention makes it possible to quickly know, by means of digital simulations, whether the manufactured part will have defects or not, without having to manufacture said part each time.

[0032] Referring to [Fig.l], a numerical simulation method according to the invention makes it possible to simulate a manufacturing process by injection of a plastic part comprising aluminum particles. This method is controlled by software and comprises the following steps: -step 10 of creating a mesh of an imprint intended for the manufacture of the part. The mesh is representative of the general shape of the part to be manufactured. -a step 20 of fixing at least one parameter conditioning the flow of the plastic material comprising the aluminum particles in the mold. Among these parameters, we can cite the shape of the cavity, the dimensions of the cavity, the thickness of the cavity, the position of the entry point through which said cavity will be supplied with plastic material loaded with aluminum particles. It is important to emphasize that any structural modification of the mold, such as for example a localized change in the radius of curvature of said mold, will have a significant influence on the flow of the plastic material loaded with aluminum particles in said mold. -a simulation step 30 of the flow of the plastic material loaded with aluminum particles in the mold. The simulation of this flow is carried out by software based on finite element modeling, consisting of creating a mesh of the mold and then evaluating the flow of the plastic material loaded with aluminum particles within each unit cell constituting this mesh. - a step 40 of developing a map of a quantity representative of the orientation of the aluminum particles after injection relative to the flow direction. This quantity can for example be represented by a measurement of the orientation tensor relative to the flow direction. This map can be produced in the form of different colors appearing inside the contour materializing the mold, each of said colors being representative of a defined concentration of aluminum particles. - a step of establishing 50 a diagnosis on the quality of the part obtained by visualizing in particular the different colors appearing on the mapping produced in the contour materializing the mold: -If only one homogeneous color appears in the said outline, the simulated part can then be considered as being of good quality 60, even if slight changes in shade compared to this majority color can appear in a very localized way on the map, -if a color appears in the majority and if areas of different colors appear in said majority color, then the simulated part will be considered to be of poor quality 70,

[0033] In the case where the simulated part is of good quality the first time, a method according to the invention stops 80.

[0034] In the case where the simulated part is not of good quality, a method according to the invention is again applied involving the following steps: - a step of modifying said at least one parameter managing the flow of the plastic material loaded with aluminum particles in the mold, - a step of simulating the flow of the plastic material loaded with aluminum particles in the mold, - a step of developing a new map, - a step of establishing a new diagnosis deduced from said new map.

[0035] The different steps of a method according to the invention will be repeated as long as the simulated part is of poor quality.

[0036] For purely illustrative purposes, referring to Figures 2 and 3, a first part 101 is simulated by means of a method according to the invention, by modifying the position of the feed point 102 of the mold 103, made of plastic material loaded with aluminum particles. Referring to [Fig.2], when the feed point 102 is placed in an upper zone of the mold 103, the first part 101 obtained by simulation has defects 104 in the form of dark traces, placed at the ends of said first part 101. Referring to [Fig.3], when this feed point 102 is placed in a lower zone of the mold 103, the first part 101 has fewer defects. This simulation highlights the influence of the position of the feed point 102 on the quality of the obtained part 101.

[0037] Purely for illustrative purposes, referring to Figures 4 and 5, a second part 105 is simulated by means of a method according to the invention, by modifying in all the areas concerned the shape of the cavity 106. Referring to [Fig. 4], when the mold 106 has a lower face 107 with some curved sectors 108, the second part 105 obtained by simulation has defects 109 in the form of dark traces, placed in a scattered manner on said part 105. Referring to [Fig.5], when the lower face 107 is made more rectilinear by making the curved sectors 108 disappear, the defects 109 have disappeared from the second part 103. This simulation highlights that the slightest modification of the mold 106 can decisively influence the quality of the part 105 obtained.

[0038] For purely illustrative purposes, referring to [Fig.7], a third part 110 obtained by means of a method according to the invention, by modifying the geometry of the cavity. Referring to [Fig.6], the third part obtained by conventional numerical simulation has defects 112 at its two ends in the form of dark traces. Referring to [Fig.7], when the geometry is modified in accordance with the method according to the invention, the defects 112 are less accentuated in the third part 110. This simulation highlights that the slightest modification of the geometry of the cavity at certain locations thereof can decisively influence the quality of the part 110 obtained.

Claims

Claims

1. Method for digital simulation of the manufacture by injection (103, 106, 111) of a part (101, 105, 110) made of plastic comprising aluminum particles to give a metallic appearance to said part (101, 105, 110) said method being controlled by software and being characterized in that it comprises the following steps: - a step of creating a specific mesh of an imprint (103, 106, 111) intended for the manufacture of the part (101, 105, 110), - a step of fixing at least one parameter conditioning the flow of the plastic material comprising the aluminum particles (103, 106, 111), - a step of simulating the flow of the plastic material loaded with aluminum particles (103, 106, 111), - a step of developing a mapping of a magnitude representative of the orientation of the aluminum particles (103, 106, 110) after injection, - a step of establishing a diagnosis on the quality of the part (101, 105,110) obtained by visualizing in particular areas of said mapping which would be likely to contain defects (104, 109, 112), -a step of stopping said method if no area likely to contain defects (104, 109, 112) is detected, -a step of modifying said at least one parameter if at least one area likely to contain defects (104, 109, 112) is detected, followed by a new step of developing a mapping, itself followed by a new step of establishing a new diagnosis on the quality of the part obtained (101, 105, 110), said steps being repeated until the part (101, 105, 110) no longer shows any defects.,

2. Digital simulation method according to claim 1, characterized in that the defect (104, 109, 112) to be detected in the part (101, 105, 110) is a dark trace reflecting a local accumulation of aluminum particles and appearing on the map.

3. Numerical simulation method according to any one of claims 1 or 2, characterized in that said at least one parameter which will condition the flow of the plastic material including the aluminum particles is to be chosen from the shape of the part, the geometry of the part, the position of the mold feed point within said mold.

4. Digital simulation method according to any one of claims 1 to 3, characterized in that the mapping appears in the form of a variation of colors in the zone delimited by the contour of the mold (103, 106, 110), each of said colors being representative of the orientation in aluminum particles.

5. Digital simulation method according to any one of claims 1 to 3, characterized in that the mapping consists of a variation of gray in the zone delimited by the surface of the part (103, 106, 110), each of said gray shades being representative of the orientation of the aluminum particles.

6. Numerical simulation method according to any one of claims 1 to 5, characterized in that the step of establishing the diagnosis on the quality of the part (101, 105, 110) obtained is carried out automatically by the software after having defined in said software the quantity representative of the orientation of the aluminum particles, a value representative of the form factor of the particles and a rheological model with specific parameters governing the interaction, that is to say the orientation, of the particles with the polymer matrix.

7. Digital simulation method according to any one of claims 1 to 6, characterized in that said method stops when no visible area of ​​the part once it is fixed at its destination location is likely to contain defects (104, 109, 112).

8. Numerical simulation method according to any one of claims 1 to 7, characterized in that the software controlling said method operates from a mesh of the plastic material comprising the aluminum particles, said mesh consisting of dividing the cavity of the mold containing said plastic material into unit cells, and in that the software performs a simulation of the flow of the plastic material loaded with aluminum particles, from near to far cell by cell.

9. Simulation method according to any one of the preceding claims, characterized in that the plastic material is polypropylene or a composite of polypropylene with talc (CaCO3).

10. Simulation method according to any one of claims 1 to 9, characterized in that the part (101, 105, 110) to be manufactured is a front bumper or a rear bumper of a vehicle.

11. Method for manufacturing a plastic part comprising a simulation step according to the simulation method according to any one of the preceding claims, said manufacturing method being devoid of a punching step of the manufacturing flow of the part.

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