CN110884036B

CN110884036B - Multiple injection molding method for transparent plastic part of car lamp

Info

Publication number: CN110884036B
Application number: CN201911096450.4A
Authority: CN
Inventors: 蔡卫撑
Original assignee: ZHEJIANG TIANCHONG VEHICLE LAMP GROUP
Current assignee: ZHEJIANG TIANCHONG VEHICLE LAMP GROUP
Priority date: 2019-11-11
Filing date: 2019-11-11
Publication date: 2022-04-29
Anticipated expiration: 2039-11-11
Also published as: CN110884036A

Abstract

The invention belongs to the technical field of illumination, and discloses a multiple injection molding method of a transparent plastic part of an automobile lamp, which is suitable for the transparent plastic part with uneven thickness. The method can effectively solve the problem of low surface quality caused by overlarge difference between the surface shape and an ideal state due to uneven shrinkage. Particularly, the problem that the light distribution quality is influenced by the surface shrinkage of the plastic part caused by the wall thickness is effectively solved for the transparent plastic part used for light distribution in the vehicle lamp.

Description

Multiple injection molding method for transparent plastic part of car lamp

Technical Field

The invention belongs to the technical field of illumination, relates to a processing technology of a vehicle lamp plastic part, and particularly relates to a forming method of a vehicle lamp transparent plastic part.

Background

Along with the development of chemical technology, plastic parts are widely applied in daily production and life, have the advantages of low cost, easy processing and the like, and have the tendency of gradually replacing materials such as metal, wood, glass and the like at present. Especially for glass materials, transparent plastic parts have been used in various applications such as optical applications and surface decoration.

During the injection molding process of the plastic part, the plastic part shrinks during cooling and forming. The proportion of material shrinkage during molding is called molding shrinkage, the molding shrinkage is determined by the factors of the material, pressure, temperature difference and the like, and the molding shrinkage of the same material is determined under specific conditions.

When the injection molding piece is a plastic piece made of a single material and uneven in thickness, the molding shrinkage rate is the same, and the shrinkage size of the thick-wall part is larger than that of the thin-wall part. This results in the curvature and normal direction of the surface being different from the design goal. In the case of a transparent plastic part for light distribution used for a vehicle lamp, the light distribution effect is directly determined by the curvature and the normal direction of any part surface.

According to the injection molding practice, the fusion effect of the interface is very good even if the injection molding of plastics of different materials is carried out twice in sequence and the fusion effect of the interface is also very good, and experiments show that the interface can not be observed when the injection molding of the same material is carried out twice in sequence, and the effect is the same as that of the injection molding of one time.

Disclosure of Invention

The invention aims to provide a molding method based on a multiple-injection molding technology aiming at a transparent plastic part used in a vehicle lamp so as to avoid the influence of molding shrinkage on surface precision.

Aiming at the purposes, the technical scheme provided by the invention is as follows: a multiple injection molding method of a transparent plastic part of an automobile lamp is suitable for the transparent plastic part with uneven thickness, and is characterized in that the transparent plastic part needs to be subjected to injection molding at least three times, the method divides the transparent plastic part into a surface layer, an intermediate body and a bottom surface layer in the thickness direction, wherein the surface layer takes the upper surface of the transparent plastic part as the upper surface and takes a layer with basically even thickness, the bottom surface layer takes the lower surface of the transparent plastic part as the lower surface and takes a layer with basically even thickness, and the intermediate body is the rest part of the transparent plastic part after the surface layer and the bottom surface layer are removed; in the injection molding, the bottom layer is firstly injected, then the intermediate body is injected once or more times on the bottom layer, and finally the surface layer is injected on the intermediate body.

Preferably, in order to further reduce the molding shrinkage difference of the surface layer, a shrinkage compensation layer is separated from the intermediate body by taking the upper surface of the intermediate body as the upper surface, and the injection molding of the intermediate body is completed in two times, wherein the shrinkage compensation layer is firstly injected on the bottom surface layer at the part below the shrinkage compensation layer of the intermediate body for the first time, and is injected on the part of the intermediate body which is subjected to the first injection molding for the second time.

Preferably, the relatively flat one of the two surfaces of the transparent plastic part is used as the lower surface of the transparent plastic part.

The basic thicknesses of the surface layer and the bottom layer can be the same or can be selected differently according to the respective conditions, and preferably, the value of the basic thicknesses of the surface layer and the bottom layer is preferably larger than the product of the maximum thickness and the molding shrinkage rate of the transparent plastic part. The basic thickness of the surface layer and the bottom layer is as much as 5 to 10% of the maximum thickness of the transparent plastic part according to the general molding yield of the transparent plastic part.

The basic thickness of the surface layer refers to the thickness of the part of the surface layer except the thin wall part, the thin wall part of the surface layer refers to the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer, the middle part is the part of the surface layer, and the thickness of the thin wall part of the surface layer is smaller than the basic thickness of the surface layer. Similarly, the basic thickness of the bottom layer refers to the thickness of the part of the bottom layer except the thin wall part, the thin wall part of the bottom layer refers to the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer, the part of the bottom layer is arranged below the middle part, and the thickness of the thin wall part of the bottom layer is smaller than the basic thickness of the bottom layer.

For the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer, the division between the surface layer and the bottom layer can be selected in various ways, wherein two kinds of parts are relatively preferred, and one of the parts is as follows: the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer is bounded by the middle part, the part above the middle part is classified as the surface layer, and the part below the middle part is classified as the bottom layer. The second step is as follows: the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer but larger than the basic thickness of the surface layer takes the basic thickness of the surface layer, and the part below the basic thickness of the surface layer is classified as the bottom layer; the part of the transparent plastic part with the thickness less than the basic thickness of the surface layer is totally classified as the surface layer.

The method is more suitable for the transparent plastic part with the thickness gradually reduced from the center to the edge. The plastic is particularly suitable for transparent plastic parts with plane lower surfaces and paraboloid upper surfaces.

In the implementation of the method of the invention, a preferred mold design scheme is as follows: the upper surface of the surface layer, the lower surface of the surface layer and the upper surface of the intermediate body are designed to be the same in shape, and injection molding is achieved through a lower die, a fixed upper die and a movable upper die, wherein the surface shape of a cavity of the lower die is the same as the lower surface of the bottom layer, the surface shape of a cavity of the fixed upper die is the same as the upper surface of the bottom layer, and the surface shape of a cavity of the movable upper die is the same as the upper surfaces of the surface layer and the intermediate body.

The invention has the beneficial effects that: aiming at the transparent plastic part with uneven thickness, the surface layer, the intermediate body and the bottom layer are divided, and the surface layer, the intermediate body and the bottom layer are respectively subjected to injection molding at least three times, so that the problem that the surface quality is low due to overlarge difference between the surface shape and the ideal state caused by uneven shrinkage can be effectively solved. Particularly, the problem that the light distribution quality is influenced by the surface shrinkage of the plastic part caused by the wall thickness is effectively solved for the transparent plastic part used for light distribution in the vehicle lamp.

Drawings

FIG. 1 is a schematic view of example 1 divided into a surface layer, an intermediate body, and a bottom layer in the thickness direction.

Fig. 2 is an enlarged view at B in fig. 1.

FIG. 3 is an enlarged view at A in FIG. 1, illustrating a method of taking the basic thickness of the surface layer in the thickness direction in example 1.

FIG. 4 is an enlarged view of a section taken in FIG. 1, illustrating injection molding of example 1 in three shots.

FIG. 5 is a comparison between before and after the first injection cooling molding in example 1.

FIG. 6 is a comparison of the injection-molded product of example 1 before and after the second injection-cooling molding.

FIG. 7 is a comparison of the injection-molded article of example 1 before and after the third injection-cooling molding.

Fig. 8 is a schematic view of example 2 divided into a surface layer, an intermediate body, and a bottom layer in the thickness direction.

Fig. 9 is a hair growth diagram at C in fig. 8.

FIG. 10 is a schematic view of example 3 showing the surface layer, shrinkage compensation layer, intermediate body, and bottom layer divided in the thickness direction.

FIG. 11 is an enlarged view of the section taken in FIG. 10, illustrating four shots of example 2.

FIG. 12 is a comparison of the injection-molded product of example 3 before and after the second injection-cooling molding. (the first injection molding in example 2 is the same as in example 1 and is omitted)

FIG. 13 is a comparison of the injection-molded article of example 3 before and after the third injection-cooling molding.

FIG. 14 is a comparison of the injection-molded article of example 3 before and after the fourth injection-cooling molding.

Fig. 15 is a schematic view of example 4 divided into a surface layer, an intermediate body, and a bottom layer in the thickness direction.

Fig. 16 is a hair growth diagram at D in fig. 15.

In the figure: the

surface layers

1, 11 and 11 'are represented by surface layer portions, the intermediate body 2, the first dividing line 100, the second dividing line 200, the second dividing line 300, the

sole layers

3, 31 and 31' are represented by a first dividing line 6, a second dividing line 7, a first segment basic thickness h1, a second segment basic thickness h2, a shrinkage compensation layer 8, which are represented by sole layer portions, a first dividing line 4, a second dividing line 5, a first dividing line 6, a second dividing line 7, which are represented by sole layer portions, a first dividing point 4, a second dividing point 5, a first dividing point.

Detailed Description

The technical solution of the present invention will be further explained below by way of examples with reference to the accompanying drawings.

Parts in automobile lamps are widely made of glass material PMMA (acrylic, commonly called organic glass), in particular to a car lamp light-transmitting sheet. However, the light-transmitting sheet has ultrahigh requirements on light transmission, dimensional accuracy, use environment and the like, and particularly, the light-transmitting sheet with large thickness has high production difficulty and high accuracy requirement on surface production, and the accuracy requirement of a product is difficult to achieve by common injection molding. For convenience of description, examples 1 to 3 of the following light-transmitting sheet each employ a portion taken from a portion thereof like a convex lens shape.

Example 1

Referring to fig. 1, the thickness is gradually reduced from the center to the edge, the maximum thickness reaches 10mm, the surface layer 1 with a thickness of 1mm, the bottom layer 3 with a thickness of 1mm, and the rest is the intermediate body 2, the maximum thickness of the intermediate body is 8mm, and the first boundary line 100 and the second boundary line 200 are formed as a dummy, as shown in fig. 4. When the thinnest part of the left and right ends is divided, the first boundary line 100 and the second boundary line 200 intersect, and the surface layer and the bottom layer have overlapped parts, and the overlapped parts are classified as the surface layer. Specifically, the thinnest 1mm thick portion 11 is classified as the surface layer, and the remaining 0.2mm thick portion 31 is classified as the bottom layer, so as to ensure the uniform thickness of the surface layer 1 and the uniform shrinkage of the surface layer when the surface layer is cooled by injection molding, as shown in fig. 2.

The thicknesses of the surface layer and the bottom layer are basically uniform, one choice is that the distances between any point on the upper surface and projection points of the point on the lower surface along the normal direction are basically equal, the other choice is that the distances between any point on the upper surface and projection points of the point on the lower surface along the vertical direction are basically equal, and the first choice is adopted in the embodiment, as shown in fig. 3: any points 4 and 5 are taken on the arc surface of the upper surface of the surface layer, tangent lines 6 and 7 of the points are made, then a normal line is made perpendicular to the tangent line overcut point, and the distances h1 and h2 from the point where the normal line intersects with the lower surface of the surface layer to the point are both 1 mm. The first boundary line may be specifically defined as follows: sampling a plurality of tangent points on the arc of the upper surface of the surface layer at equal intervals from one end to the other end, taking a normal line towards the lower surface direction through each tangent point, taking a point with the distance of 1mm from the tangent point on the normal line to the designed thickness as a reference point, and connecting all the reference points to obtain a first boundary line. It is conceivable that the denser the sampling tangent point, the closer the obtained boundary is to the design target, but the more the calculation amount is.

Before injection molding, a mold needs to be designed, in the embodiment, three times of injection molding are carried out, and a lower mold and a fixed upper mold need to be designed, namely the surface shape of the cavity of the lower mold is the same as the lower surface of the bottom surface layer, and the surface shape of the cavity of the fixed upper mold is the same as the upper surface of the bottom surface layer. It is also necessary to design a movable upper mold to realize the case that the surface layer upper surface, the surface layer lower surface, and the intermediate body upper surface are the same shape in this embodiment, that is, the cavity surface shape of the movable upper mold is the same as the surface layer upper surface and the intermediate body upper surface. The injection molding of the bottom layer is realized by one lower die and one fixed upper die, the injection molding of the intermediate is realized by one fixed upper die and one movable upper die, and finally the injection molding of the surface layer is realized by the upward displacement and movement of the upper die.

The molding shrinkage of the material needs to be considered in the injection molding, the molding shrinkage of the PMMA material is 0.5-1.8%, 1.0% is taken, the maximum thickness of the embodiment reaches 10mm, the cooling shrinkage of the maximum thickness in one injection molding is 0.1mm, the shrinkage of the thin part of the edge is less than 0.1mm, and the shrinkage of the whole upper surface is inconsistent, so that the shape of the upper surface and the expected design are slightly changed, and the optical performance of the PMMA material is not influenced slightly. Fig. 5 to 7 show schematic views of the three-time injection molding process of the present embodiment: the bottom layer is injected for the first time, and the bottom layer shrinks from 1mm to 0.99 mm; performing secondary injection molding on the intermediate, wherein the maximum actual injection molding amount of the intermediate is 8.01mm, and the maximum thickness of the intermediate is shrunk from 8.01mm to 7.9299 mm; and (3) performing third injection molding on the surface layer, wherein the actual injection molding thickness of the surface layer is 1.0801mm, the surface layer is shrunk to 1.069299mm from 1.0801mm, and the actual shrinkage of the surface layer is 1.0801mm-1.069299mm =0.010801 mm. And the actual shrinkage at the maximum thickness and the thinnest part is uniform, and the actual shrinkage of the surface is uniform, so that the optical performance of the surface is basically not influenced.

Example 2

Referring to fig. 8 and 9, the difference from example 1 is that the intersection of the first and second dividing lines connects the midpoints of the left and right ends to form a third dividing line 300 which is also dummy, and when the left and right ends are divided to be thinnest, the upper half portion 11 'is classified as the surface layer 1 and the lower half portion 31' is classified as the bottom layer 3.

Example 3

Referring to fig. 10 and 11, the difference from example 1 is that a shrinkage compensation layer 8 having a maximum thickness of 1mm is divided from an intermediate body 2, and the remaining intermediate body 3 has a maximum thickness of 7mm, and this example is formed by four injection molding: as shown in fig. 12 to 14, the first injection molding is the same as embodiment 1; the second time of actual injection molding of the intermediate body with the maximum thickness of 7.01mm, the maximum thickness of which is shrunk from 7.01mm to 6.9399mm, and the third time of actual injection molding of the shrinkage compensation layer with the maximum thickness of 1.0701mm, the maximum thickness of which is shrunk from 1.0701mm to 1.059399 mm; fourthly, actually injection-molding a surface layer with the maximum thickness of 1.010701mm, and shrinking the maximum thickness from 1.010701mm to 1.00059399 mm; the actual shrinkage of the surface is 1.010701mm-1.00059399mm =0.01010701 mm. The molding shrinkage difference of the surface layer was more reduced than that of example 1.

The thickness of the transparent plastic part in actual production varies greatly, and fig. 15 is taken as an example, and the method of the present invention is also applicable thereto, example 4:

the transparent plastic part is uneven in thickness, and the surface of the transparent plastic part is formed in one-step injection molding mode, so that the forming shrinkage of the surface of the transparent plastic part is inconsistent, the actual shape of the surface of the transparent plastic part is greatly different from that of the original design, particularly the part with relatively thick thickness has obvious difference change, and the precision of the surface of a product is influenced. In order to improve the precision of the surface of the product, the present embodiment was formed by three-shot injection molding, dividing the surface layer 1 having a substantially uniform thickness of 0.5mm in the thickness direction, dividing the bottom layer 3 having a substantially uniform thickness of 0.5mm, and classifying the remaining portion as the intermediate body 2. At the thin wall at the tail end, the thickness of the thin wall is less than 1mm of the sum of the thicknesses of the surface layer and the bottom layer, the thickness of the thin wall is divided equally, the part above the middle is classified as the surface layer, and the part below the middle is classified as the bottom layer. For the part with smaller surface curvature of the transparent plastic part, when the surface layer and the bottom layer are divided, another method can be adopted: as shown in fig. 16, the surface layer can be divided by taking a portion of the surface layer with a smaller curvature and translating the upper surface of the surface layer directly downward by 0.5mm to obtain a dummy boundary line. The bottom layer is divided by the method. The design principle and the injection molding process of the mold are the same as those of embodiment 1.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art may make various modifications, additions or substitutions to the specific embodiments described, which may vary depending upon factors such as the operating environment, but which may be readily substituted without departing from the spirit of the invention.

Claims

1. A multiple injection molding method for a transparent plastic part of a car lamp is suitable for the transparent plastic part with uneven thickness, and is characterized in that the transparent plastic part needs to be subjected to injection molding at least three times,

the method comprises the steps of dividing a transparent plastic part into a surface layer, an intermediate body and a bottom layer in the thickness direction, wherein the surface layer takes the upper surface of the transparent plastic part as an upper surface and takes a layer with basically uniform thickness, the bottom layer takes the lower surface of the transparent plastic part as a lower surface and takes a layer with basically uniform thickness, and the intermediate body is the part of the transparent plastic part left after the surface layer and the bottom layer are removed;

in the injection molding, the bottom layer is firstly injected, then the intermediate body is injected once or more times on the bottom layer, and finally the surface layer is injected on the intermediate body.

2. The multiple injection molding method for the transparent plastic part for the vehicular lamp according to claim 1, wherein the upper surface of the intermediate body is an upper surface, a shrinkage compensation layer is separated from the intermediate body, and the injection molding of the intermediate body is performed in two steps, wherein the shrinkage compensation layer is firstly injected on the bottom surface layer at a portion below the shrinkage compensation layer of the intermediate body, and is secondly injected on the first injection molded portion of the intermediate body.

3. The multiple injection molding method for a transparent molded article for vehicle lamps according to claim 1, wherein a relatively flat one of the two surfaces of the transparent molded article is used as the lower surface of the transparent molded article.

4. The method of claim 1, wherein the basic thickness of the surface layer and the bottom layer is greater than the product of the maximum thickness and the molding shrinkage of the transparent plastic part.

5. The multiple injection molding method for a transparent plastic part for vehicle lamps as claimed in claim 4, wherein the basic thickness of the surface layer and the bottom layer is 5-10% of the maximum thickness of the transparent plastic part.

6. The multiple injection molding method for the transparent plastic part of the vehicular lamp according to claim 1, wherein the part of the transparent plastic part with the thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer is defined by the middle, the part above the middle is classified as the surface layer, and the part below the middle is classified as the bottom layer.

7. The multiple injection molding method for the transparent plastic part of the vehicular lamp according to claim 1, wherein the surface layer has a basic thickness at a portion of the transparent plastic part having a thickness smaller than the sum of the basic thickness of the surface layer and the basic thickness of the bottom layer but larger than the basic thickness of the surface layer, and the portion below the basic thickness of the surface layer is classified as the bottom layer; the part of the transparent plastic part with the thickness less than the basic thickness of the surface layer is totally classified as the surface layer.

8. The multiple injection molding method for the transparent plastic part of the automobile lamp according to claim 1, wherein the thickness of the transparent plastic part is gradually reduced from the center to the edge.

9. The method of claim 8, wherein the lower surface of the transparent plastic part is a plane and the upper surface is a paraboloid.

10. The method of claim 1, wherein the upper surface of the surface layer is the same as the lower surface of the surface layer and the upper surface of the intermediate body, and the injection molding is performed by a lower mold, a fixed upper mold and a movable upper mold, wherein the lower mold has a cavity surface of the same shape as the lower surface of the bottom layer, the fixed upper mold has a cavity surface of the same shape as the upper surface of the bottom layer, and the movable upper mold has a cavity surface of the same shape as the upper surface of the surface layer and the upper surface of the intermediate body.