Injection molded parts

Abstract

An injection molded part has a functional portion and a quality control portion. The quality control portion includes a set of protrusions that are adapted to visibly distort in response to injection molding shrinkage, thereby enabling a visual quality control inspection.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to injection molded parts. It particularly relates to shrinkage occurring during the molding process. BACKGROUND

[0002] Shrinkage during injection molding is a well-known problem. In fact, it is known that the mold is designed such that shrinkage is taken into account, and that the final produced product has the desired shape despite the shrinkage during the cooling and solidification phase of the injection molding process.

[0003] Some parts require a particularly good quality and repeatability of their shape, and this becomes more and more difficult as the size increases.

[0004] One example where the product shape is crucial for the product performance is injection molded lenses or lens arrays. Such lenses or lens arrays are for example applied in LED modules in order to provide uniform illumination of a flat surface. Of course, many other beam shaping optics can be designed as injection molded parts.

[0005] One approach to achieve flat surface illumination is to use a so-called batwing intensity distribution (also called wide beam intensity distribution). The term batwing refers to the high peak shape of the intensity distribution in polar coordinates.

[0006] Batwing light distributions allow for uniform illumination of a flat surface, for example even up to a beam angle of 140°. Such light distributions and thus lens designs are used for example in street lighting and wall washing applications. In these examples, the batwing distribution targets a flat surface in the far field: the illuminated surface is at a distance much larger than the light module size.

[0007] Figure 1 An example of a batwing intensity distribution is shown in polar coordinates. In this example, two wings 10, 12 have a peak intensity at 60 degrees on each side of the normal, and the goal is to provide uniform surface illumination over a range of 120 degrees. The intensity at grazing angles is higher because the surface area illuminated per unit angle increases sharply.

[0008] The ring 14 is the light intensity in the perpendicular direction. For a rotationally symmetric light distribution, this would also be a batwing distribution. For a linear light source, it is for example a circular (i.e. Lambertian) distribution.

[0009] In order to produce the desired batwing profile from an LED, optical components are needed to compensate for the well-known cosine fourth law applicable to Lambertian point sources (according to which the illuminance follows cos 4 function down). Thus, the optical design needs to change the Lambertian intensity distribution from the LED output intensity distribution to the batwing distribution.

[0010] There are two known lens designs that are able to change a Lambertian intensity distribution into a batwing intensity distribution.

[0011] The first example is the so-called peanut design, the second example is the so-called bubble optic.

[0012] By way of example, Figure 2 A peanut lens design 20 is shown in Fig. 1 (from above and from the side), and Figure 3 An array of such lenses is shown in Fig. 2.

[0013] Figure 3 Each lens 20 in Fig. 1 is placed above an LED 30 of an array of LEDs, forming a luminaire, such as a road lighting luminaire. The surface that changes the Lambertian distribution into a batwing is the outer lens surface of the peanut lens, while for the bubble optic it is the inner surface.

[0014] It is known that lenses and lens arrays of this type use injection molding. However, when manufacturing large lens plates as shown in Fig. 2, there is a risk of injection molding shrinkage on the optical surface. This will affect the light distribution accuracy. Figure 3

[0015] A known procedure to monitor the injection molding process is to laser scan or 3D scan the product when it is found that the light distribution has deteriorated, and thus the accuracy of the optical surface is suspected. This of course has a high cost.

[0016] Therefore, there is a need for a low-cost solution that enables the accuracy of the injection molding process to be monitored, in particular so that defects or problems can be identified as quickly as possible, so that production and sale of non-conforming products can be prevented. However, the number of photometric measurements should be kept to a minimum, as detailed optical analysis testing of a large number of already manufactured products is not practical in a mass production environment.

[0017] US20170291343A1 discloses a molding system capable of detecting abnormalities of each cavity.

[0018] DE102017003001A1 discloses an injection molding system including an image storage determination unit configured to determine whether to store an image of a molded product corresponding to a physical quantity obtained by a physical quantity acquisition unit and a condition set by an image storage condition setting unit, and to store the image according to the determination result. SUMMARY

[0019] The invention is defined by the claims.

[0020] According to an example in accordance with an aspect of the invention, there is provided an injection molded part, comprising:​

[0021] a functional part; and

[0022] a quality control part,

[0023] wherein the quality control part comprises at least one protrusion which is adapted to visibly distort in response to injection molding shrinkage, thereby enabling a visual quality control check.

[0024] By providing a quality control part for visual inspection, a large number of parts (or even each part) can be inspected at low cost. Any changes in the quality of the injection molding process can be monitored by visual inspection of the at least one protrusion. The protrusion may, for example, have a height which depends on the degree of shrinkage. Thus, as soon as a reduction in height is seen, a problem can be flagged. The size (i.e. width) of the protrusion is, for example, smaller than any protrusions in the functional part of the part.

[0025] The smallest dimension in a direction parallel to the general plane of the part, perpendicular to the height direction, is referred to herein as the "thickness". Thus, the thickness of the protrusion in the quality control part is smaller than the thickness of the features in the functional part (having a height corresponding to the protrusion).

[0026] The quality control part does not interfere with the main functional purpose of the part, and the part does not need to perform its main functional purpose. It is thus added as a dummy part, whose only purpose is to implement the visual quality check.

[0027] The functional part can have a smooth surface. Thus, based on visual inspection of the functional part, changes in the injection molding process are difficult to observe. The functional part is smooth because the height of the protrusion is larger than any features in the functional part having a corresponding thickness.

[0028] The functional part comprises, for example, a lens element. The lens function has a crucial dependency on the surface quality used as a refractive index boundary. Thus, early identification of injection molding problems is important to prevent making non-conforming products.

[0029] The functional part comprises, for example, an array of lens elements. These can be used to be mounted on top of a corresponding array of LEDs, with one lens providing beam shaping for a corresponding LED or sub-array of LEDs.

[0030] The part can comprise a set of protrusions having different sensitivity to deformation in response to injection molding shrinkage.

[0031] In this way, based on visual inspection of the set of protrusions and identification of which protrusions have visible cracks, different levels of performance of the injection molding process can be identified.

[0032] The set of protrusions comprises, for example, protrusions each having a different size.

[0033] The different sizes of the protrusions will or less easily shrink. For example, they can be arranged in a row. There can be a collection of protrusions, each having a different size, but there can be multiple instances of each different protrusion size. There can also be multiple collections of protrusions at different locations of the part, so that the uniformity of the injection molding quality across the part area can be checked.

[0034] The collection of protrusions for example comprises at least 3 different protrusions of the same height but different thickness, for example 5 different protrusion designs of the same height but different thickness.

[0035] Visible shrinkage in different protrusions can then indicate different levels of severity. For example, different levels of shrinkage will have different impacts on the final product, and different actions can be appropriate, such as performing photometric tests.

[0036] The different thicknesses for example each lie in the range of 0.1 mm to 1.0 mm. For example, there can be a collection of thicknesses 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm and 1.0 mm.

[0037] The collection of protrusions can comprise at least 2 different protrusions of the same thickness but different height. The different heights can each lie in the range of 1 mm to 5 mm.

[0038] For example, there can be protrusions of 2 mm height (or a collection of protrusions of different width, each protrusion having 2 mm height) and protrusions of 4 mm height (or a collection of protrusions of different width, each having 4 mm height).

[0039] The at least one protrusion for example comprises a column having a circular or rectangular (e.g. square) cross-section in a plane perpendicular to the direction of the column height.

[0040] The entire part for example has an area of more than 100 cm 2 The larger the size of the part, the more prone to shrinkage problems the part is during injection molding.

[0041] The part for example comprises a lens sheet for beam shaping of LED light. For example, the lens sheet can have a size of 30 cm length and 15 cm width, with 90 individual peanut-shaped lenses.

[0042] The invention also provides a luminaire comprising a housing, an arrangement of LED light sources mounted in the housing, and a lens sheet for beam shaping of the light output of the arrangement of LED light sources, the lens sheet comprising a part as defined above.

[0043] The invention also provides an injection molding method comprising forming a part using an injection mold, the part having: a functional part; and

[0044] a quality control portion,

[0045] wherein the quality control portion comprises at least one protrusion adapted to visibly distort in response to injection mould shrinkage, thereby enabling a visual quality control check.

[0046] These and other aspects of the application will become apparent from the following description of the (multiple) embodiments, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0047] For a better understanding of the present application, and to show how it can be put into effect, reference will now be made, purely by way of example, to the accompanying drawings in which:

[0048] Figure 1 A batwing intensity distribution is shown as an example of a polar plot;

[0049] Figure 2 A peanut shaped lens design is shown;

[0050] Figure 3 An array of peanut shaped lenses over an LED array is shown;

[0051] Figure 4 A component according to one example of the application is shown in plan view;

[0052] Figure 5 A cross section of the component of Figure 4 is shown; and

[0053] Figure 6 How the protrusion can change in response to injection mould shrinkage is shown. DETAILED DESCRIPTION

[0054] The present application will be described with reference to the accompanying drawings.

[0055] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of apparatuses, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the application. These and other features, aspects, and advantages of the apparatuses, systems and methods of the present application will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the drawings are only schematic and are not drawn to scale. It should also be understood that the term "couple" and variations thereof, as used herein, are intended to convey an operational connection or coupling between two entities that are in physical or communicative contact with each other, unless otherwise indicated.

[0056] The present application provides an injection moulded component having a functional portion and a quality control portion. The quality control portion comprises at least one protrusion adapted to visibly distort in response to injection mould shrinkage, thereby enabling a visual quality control check.

[0057] Figure 4 The components are shown in plan view.

[0058] Functional portion 40 is the main body of the component and has a three-dimensional shape designed to perform the desired function. This function can be optical, and for this purpose, a lens array 42 is shown. The lenses generally have smooth surfaces, making changes during injection molding difficult to observe based on visual inspection of the lenses. Each lens 42 is mounted over a corresponding LED (or LED group) in the LED array and provides beam shaping for the associated LED or LED group.

[0059] For example, the functional portion 40 comprises a lens plate 30 cm in length and 15 cm in width, with 90 individual peanut-shaped lenses (in Figure 4 Only 36 are shown in the schematic representation).

[0060] The quality control portion 44 is located in an area of ​​the component that does not detract from its primary function, ie, away from the functional portion 40 .

[0061] The quality control part Figure 4 For example, it may occupy an area with dimensions of less than 10 mm by less than 10 mm, while the entire component may have dimensions of several tens of centimeters for forming the light output window of a luminaire.

[0062] There can be a collection of quality control features at different locations on the component. These quality control features do not need to be located at the edges. Instead, these quality control features can be interspersed with features that have functional parts (in this example, lenses) if the spaces between those features do not serve a functional part.

[0063] The quality control portion includes at least one protrusion 46 adapted to visibly distort in response to injection molding shrinkage, thereby enabling visual quality control inspection.

[0064] This example shows a set 48 of five protrusions. The protrusions in this set have different sensitivities to deformation in response to injection molding shrinkage. They are all rectangular in plan view, but have different minimum dimensions (i.e., the length of the shorter rectangular side). This dimension is referred to in this document as thickness.

[0065] It is this thickness that is of particular importance. The longer dimension is less important. In practice, the protrusions may be square (or other shapes with a uniform aspect ratio, such as any regular polygon or circle), or they may be elongated, as shown in this example.

[0066] Table 1 below shows examples of possible sizes for the five protrusions of set 48 .

[0067] Table 1

[0068] Length Width Height Projection 1 3 mm 0.2 mm 2 mm Projection 2 3 mm 0.4 mm 2 mm Projection 3 3 mm 0.6 mm 2 mm Projection 4 3 mm 0.8 mm 2 mm Projection 5 3 mm 1.0 mm 2 mm .

[0069] In this example, the protrusions have a rectangular shape (when viewed from above) as shown in Figure 4 The width tapers, but the protrusions of the set all have the same height.

[0070] The different thicknesses are, for example, generally in the range 0.1 mm to 1.0 mm. This example has 5 different protrusion designs, but there can be fewer (for example 3 or 4) or there can be more than 5. In the extreme case, there can be only one protrusion.

[0071] An important parameter is the minimum dimension of the protrusion, which is referred to herein as the "thickness". For a circular shape, this would be the diameter. For a rectangle, this would be the shortest side length, and for any other shape it would be the shortest distance between opposite sides.

[0072] The size of the thickness is chosen so that the protrusion is easily contractible so that it visibly distorts, thereby enabling a visual quality control check.

[0073] Figure 5 A cross-section of the component is shown, and five different protrusions 46a to 46e are shown (not to scale). The functional part 40 is smooth because it has fewer abrupt features than the protrusions. The curved surface of the lens and the refraction of light through that surface makes it very difficult to visually identify any shape changes. The protrusions are designed to have a greater visual appearance of defined contractibility problems than any part of the functional part, including any non-smooth parts of the functional part.

[0074] The protrusions, for example, include vertical features with a thickness-to-height ratio that is less than any feature of the functional part. The protrusion designs described above have thickness-to-height ratios of 5:15, 4:15, 3:15, 2:15 and 1:15. More particularly, the protrusions include vertical features that have a thickness-to-height ratio that is less than any feature of the functional part for a corresponding height, for example, having a height above a threshold such as 1 mm. The quality control part thus has tall, thin protrusions. A protrusion of a given thickness will have a greater height than any feature in the functional part that has a corresponding thickness.

[0075] Alternatively or additionally, there can be protrusions of different heights.

[0076] For example, Table 2 shows a set of 10 protrusions, split into two groups of 5. Each group has the same length and width dimensions as in Table 1, but one group has a height of 2 mm and one group has a height of 4 mm.

[0077] Table 2

[0078] Length Width Height Projection 1 3 mm 0.2 mm 2 mm Projection 2 3 mm 0.4 mm 2 mm Projection 3 3 mm 0.6 mm 2 mm Projection 4 3 mm 0.8 mm 2 mm Projection 5 3 mm 1.0 mm 2 mm Projection 6 3 mm 0.2 mm 4 mm Projection 7 3 mm 0.4 mm 4 mm Projection 8 3 mm 0.6 mm 4 mm Projection 9 3 mm 0.8 mm 4 mm Projection 10 3 mm 1.0 mm 4 mm .

[0079] The different heights can generally be in the range of 1 mm to 5 mm.

[0080] By providing the quality control portion 44 for visual inspection, a large number of parts (or even each part) can be inspected at low cost. Any variation in the quality of the injection molding process can be monitored by visual inspection of at least one of the protrusions.

[0081] Figure 6 It is shown how the protrusions in Table 1 change in response to injection molding shrinkage.

[0082] Figure 6 A shows no shrinkage at all. Since the product produced is perfect, no action needs to be taken.

[0083] Figure 6 B shows very slight shrinkage. It has affected the thinnest protrusion 46e, for which a reduction in height can be seen visually. This can not affect the product, but it can be used to carefully monitor for any additional problems in production.

[0084] Figure 6 C shows slight shrinkage. It has affected the two thinnest protrusions 46d, 46e, for which a reduction in height can be seen visually. This can affect the product functionality, and it can be used to trigger further photometric testing. For example, a supplier quality engineer (SQE) can be notified.

[0085] Figure 6 D shows moderate shrinkage. It has affected the three thinnest protrusions 46c, 46d, 46e. The thinnest one has not formed at all. This will affect the product functionality, and thus can trigger the need for an inspection of all products from the production line, as well as further testing.

[0086] Figure 6 E shows severe shrinkage, and Figure 6 F shows very severe shrinkage.

[0087] It can be seen that the height of the protrusions depends on the degree of shrinkage. Thus, as soon as a reduction in height is seen, a problem can be flagged. Based on the visual inspection of the set of protrusions and the identification of which protrusions have visible cracks, different performance levels of the injection molding process can be identified. Appropriate remedial actions as well as further quality control measures and actions can then be taken.

[0088] The invention is particularly useful for large-area parts, such as parts with an area of more than 100 cm2 Particularly interesting are components for which it is difficult to guarantee the quality of the injection-moulding process, in particular for components for which the shape of the functional part is essential (such as a lens plate). Another advantage is that larger products have a higher cost. A simple inspection method can help to identify any defects early, thereby reducing the number of defective parts to be scrapped.

[0089] However, the application can be applied to other products and in general to the quality control of injection-moulding processes.

[0090] The application also provides an injection-moulding method comprising the use of an injection mould to form the component described above.

[0091] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single processor or other unit can fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program can be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state storage medium supplied together with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. If the term "adapted to" is used in the claims and / or the specification it should be taken as equivalent to the phrase "configured to". Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An injection molded part comprising: Functional part (40); and Quality Control Section (44), wherein the quality control portion (44) includes at least one protrusion (46) adapted to visibly distort in response to injection molding shrinkage, thereby enabling visual quality control inspection; wherein the at least one protrusion (46) comprises a collection (48) of protrusions (46a-46e) having different sensitivities to deformation in response to injection molding shrinkage.

2. The component according to claim 1, wherein the functional portion (40) has a smooth surface.

3. The component according to claim 2, wherein the functional portion (40) comprises a lens element.

4. The component of claim 3, wherein the functional portion comprises an array of lens elements.

5. The component of claim 1, wherein the set of protrusions (48) includes protrusions each having a different size.

6. The component according to claim 1 or 5, wherein the set (48) of protrusions comprises at least 3 different protrusions of the same height but different thickness.

7. The component according to claim 6, wherein the set (48) of protrusions comprises five different protrusions of the same height but different thicknesses.

8. The component of claim 6, wherein the different thicknesses each exist within the range of 0.1 mm to 1.0 mm.

9. The component according to any one of claims 1 to 5, wherein the set of protrusions comprises at least two different protrusions of the same thickness but different heights.

10. The component of claim 9, wherein the different heights each lie within the range of 1 mm to 5 mm.

11. The component of any one of claims 1-5, 7, 8, 10, wherein the at least one protrusion comprises a post having a circular or rectangular cross-section in a plane perpendicular to the height direction of the post.

12. The component according to any one of claims 1 to 5, 7, 8, and 10, having a diameter greater than 100 cm 2 area.

13. The component according to any one of claims 1-5, 7, 8, 10, comprising a lens plate for beam shaping of the LED light.

14. A luminaire comprising a housing, an LED light source arrangement mounted in the housing, and a lens plate for beam shaping of the light output of the LED light source arrangement, the lens plate comprising the component of claim 13.

15. An injection molding method comprising forming a component using an injection mold, the component having: Functional parts; and Quality control section, wherein the quality control portion comprises at least one protrusion adapted to visibly distort in response to injection molding shrinkage, thereby enabling visual quality control inspection; and wherein the at least one protrusion (46) comprises a collection (48) of protrusions (46a-46e) having different sensitivities to deformation in response to injection molding shrinkage.

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