WO2020043647A1

WO2020043647A1 - Method of manufacturing an object by means of 3d printing

Info

Publication number: WO2020043647A1
Application number: PCT/EP2019/072671
Authority: WO
Inventors: Rifat Ata Mustafa Hikmet; Paulus Albertus VAN HAL
Original assignee: Signify Holding B.V.
Priority date: 2018-08-28
Filing date: 2019-08-26
Publication date: 2020-03-05

Abstract

The invention relates to a method of manufacturing an object (1100) by means of 3D printing using a 3D printer (1200) with an extrusion head (1210) and a build platform (1220). The extrusion head (1210) has a nozzle (1211) with an opening (1212) through which printable material (1300) can be deposited onto a receiver item. During printing the extrusion head (1210) moves relative to the build platform (1220) along a tool path (1230) in a plane parallel to the build platform (1220) to create a layer (1110) of the object (1100). When the opening (1212) of the nozzle (1211) has a non-circular boundary with a rotational symmetry of order n (n being an integer equal to or larger than 2), the tool path (1230) should consist of two or more straight tool path segments, wherein each angle between two adjoining straight tool path segments is an integer multiple of 360/n when n is an even integer, and an integer multiple of 180/n when n is an odd integer. This method allows the manufacture of printed objects (1100) of which the layers have faceted side surfaces that may give an aesthetically appealing effect, while preventing inaccuracies in the layer structure.

Description

METHOD OF MANUFACTURING AN OBJECT BY MEANS OF 3D PRINTING

FIELD OF THE INVENTION

The invention relates to a method of manufacturing an object by means of 3D printing. The invention also relates to an object obtainable with such a method of

manufacturing, and to a lighting device comprising such an object. The invention further relates to a computer program product comprising instructions which, when the computer program product is executed by a 3D printer, cause the 3D printer to carry out the method of manufacturing.

BACKGROUND OF THE INVENTION

Digital manufacturing is expected to increasingly transform the nature of global manufacturing. One of the main processes used in digital manufacturing is 3D printing. The term“3D printing” refers to processes wherein a material is joined or solidified under computer control to create a three-dimensional object of almost any shape or geometry. Such three-dimensional objects are typically produced using data from a three-dimensional model, and usually by successively adding material layer by layer.

Many different 3D printing technologies are known in the art.

US5121329 discloses an apparatus incorporating a movable dispensing head provided with a supply of material which solidifies at a predetermined temperature, and a base member, which are moved relative to each other along X, Y, and Z axes in a

predetermined pattern to create three-dimensional objects by building up material discharged from the dispensing head onto the base member at a controlled rate. This 3D printing technology is known as fused deposition modeling (FDM), sometimes also referred to as fused filament fabrication (FFF) or filament 3D printing (FDP).

FDM is one of the most commonly used forms of 3D printing. In an FDM process, a 3D printer creates an object in a layer-by-layer manner by extruding a printable material (typically a filament of a thermoplastic material) along tool paths that are generated from a digital representation of the object. The printable material is heated just beyond solidification and extruded through a nozzle of an extrusion head of the 3D printer. The extruded printable material fuses to previously deposited material and solidifies upon a reduction in temperature. In a typical 3D printer, the printable material is deposited as a sequence of planar layers onto a substrate that defines a build plane. The position of the extrusion head relative to the substrate is then incremented along a print axis (perpendicular to the build plane), and the process is repeated until the object is complete.

FDM printers are relatively fast, low cost and can be used for printing complicated three-dimensional objects. Such printers are used in printing various shapes using various 3D printable materials. The technique is also being further developed in the production of LED luminaires and lighting solutions.

An FDM printer has an extrusion head with a nozzle. The nozzle has an opening, and the shape of this opening defines the side surfaces of the printed object.

Typically, the nozzle has a circular opening. This results in the characteristic“ribbed” surface structure of objects manufactured by means of FDM.

FDM printers having an extrusion head with a non-circular nozzle opening are also known in the art. See for example US-2017/0312985, which discloses a nozzle having a polygonal outline that defines a plurality of clamping features for producing a textured printed layer.

Further examples of non-circular nozzle openings are disclosed in WO- 2018/067178, in the form of bores with a polygonal shape, such as a rectangle with equal or unequal sides, a diamond, a triangle, a star and a cross.

SUMMARY OF THE INVENTION

In certain circumstances it may be desired to use a nozzle with a non-circular opening, such as a triangular, square or hexagonal opening, to provide the object with a surface structure that may give an aesthetically appealing effect, especially if the object is to serve as light-transmissive optical component.

Non-circular nozzle openings maybe used to obtain printed objects of which the layers have faceted side surfaces. In the context of the present invention, the term “faceted surface” refers to a surface with at least two adjoining flat or curved faces. The characteristic“ribbed” surface structure obtained with an FDM printer having a circular nozzle opening is not an example of a faceted surface. Here, the side surfaces of the layers do not have two or more adjoining flat or curved faces. Instead, the side surfaces of the layers are semi-cylindrical. Examples of layers with faceted side surfaces are layers with a polygonal cross section. The inventors have realized that for non-circular nozzle openings the printing strategy must be adjusted to prevent inaccuracies in the layer structure.

Consider for example an extrusion head having a square nozzle opening. The extruded filament has a different cross-sectional profile when the extrusion head moves in a direction parallel to a side of the nozzle opening than when it moves in a direction parallel to a diagonal of the nozzle opening. More particularly, the width and height of the extruded filament are larger when the extrusion head moves in a direction parallel to a diagonal of the nozzle opening. In FDM, the layer height is a setting in the slicing software. Typically, the layers are flattened in the stack direction and they can even be slightly distorted by pressure exerted by the extrusion head on the layers. The larger the height of the extruded filament, the higher the degree of distortion will be. In other words, for an extrusion head having a square nozzle opening, the degree of distortion of the layers depends on the direction in which the extrusion head moves in the XY -plane. This means that when printing with a square nozzle opening, the tool path (i.e. the path in the XY-plane followed by the extrusion head) should be carefully chosen to prevent undesired differences layer distortions.

Further to the above, moving an extrusion head with a square nozzle opening in a direction parallel to a side of the nozzle opening results in faceted side surfaces that have a different configuration than when the extrusion head moves in a direction parallel to a diagonal of the nozzle opening. Also, to prevent such different configurations of the faceted side surfaces, the tool path should be chosen carefully.

A solution would be to have a 3D printer wherein the extrusion head and/or the build platform can perform a rotational movement. However, for various practical reasons this solution is not always feasible.

It is an object of the present invention to at least partly overcome one or more of the aforementioned disadvantages.

In a first aspect, the invention provides a method of manufacturing an object by means of 3D printing using a 3D printer having an extrusion head and a build platform. The extrusion head has a nozzle with an opening through which printable material can be deposited onto a receiver item (such as onto the build platform, or onto a previously- deposited layer of printed material). The method comprises the step of moving the extrusion head relative to the build platform along a tool path in a plane parallel to the build platform to create a layer of the object. The opening of the nozzle has a boundary that is a curve of non constant width with a rotational symmetry of order n, n being an integer equal to or larger than 2. The tool path consists of two or more straight tool path segments. Each angle between two adjoining straight tool path segments is an integer multiple of 360/« when n is an even integer, and an integer multiple of 180 In when n is an odd integer.

In the method according to the first aspect of the invention, the nozzle opening is defined as having a boundary that is a curve of non-constant width. A“curve of non constant width” is a planar shape whose width is different for at least two different orientations of the curve. Herein, the“width” of the curve is defined as the perpendicular distance between two distinct parallel lines each having at least one point in common with the shape’s boundary but none with the shape’s interior.

A circle is an example of a curve of constant width. There are no two different orientations of the same circle that have a different width. The width of a circle is constant, and equal to the circle’s diameter. An example of a non-circular curve of constant width is a Reuleaux triangle.

Examples of curves of non-constant width are polygons. A polygon is a plane figure that is bounded by a finite chain of straight line segments closing in a loop. Examples of polygons are a triangle, a quadrilateral or tetragon (for example a trapezoid and a parallelogram, such as a rectangle or a square), a pentagon, a hexagon, a heptagon, an octagon, a nonagon, and a decagon. Other polygons that are examples of curves of non constant width are cross-shaped and star-shaped polygons.

The method comprises the step of layer-wise depositing a printable material to create an object. In other words, during the method a printable material is deposited to form a stack of layers.

The term“printable material” refers to the material to be deposited or printed.

It may especially refer to the material in an extrusion head or extruder at elevated temperature. The printable material is printed as a filament and deposited as such. It may be provided as a filament or it may be formed into a filament.

The printable material typically comprises a polymeric material. The term “polymeric material” may refer to a blend of different polymers, but it may also refer to essentially a single polymer type with different polymer chain lengths. Hence, the term “polymeric material” (or“polymer”) may refer to a single type of polymer but also to a plurality of different polymers. Similarly, the term“printable material” may refer to a single type of printable material but also to a plurality of different printable materials.

In general, the polymeric materials used as printing material have a glass transition temperature (Tg) and/or a melting point (Tm). The glass transition temperature is in general not the same as the melting point. Melting is a transition which occurs in crystalline polymers when the polymer chains fall out of their crystal structures and become a disordered liquid. The glass transition is a transition which happens to amorphous polymers, which are polymers whose chains are not arranged in ordered crystals, but are just strewn around in any fashion, even though they are in the solid state. Polymers can be amorphous, essentially having a glass transition temperature and not a melting point or they can be (semi) crystalline having both a glass transition temperature and a melting point, with in general the latter being higher than the former.

Before the printable material leaves the nozzle, it will be heated by the 3D printer to a temperature of at least the glass transition temperature, and in general at least the melting point. For example, the printable material may comprise a thermoplastic polymer having a glass transition temperature and/or a melting point, and in the extrusion head the printable material is heated to a temperature above the glass transition temperature, and if the material is a semi-crystalline polymer above the melting point. The printable material may alternatively comprise a thermoplastic polymer having a melting point, and in the extrusion head the printable material is heated to a temperature of at least the melting point.

Materials that may qualify as printable materials can be selected from the group consisting of metals, glasses, (thermoplastic) polymers, and silicones. Especially, the printable material may comprise a (thermoplastic) polymer selected from the group consisting of polystyrenes (such as acrylonitrile butadiene styrene (ABS)), polyamides (such as nylon), polyacetates (such as polylactic acid (PLA), polyesters (such as polyethylene terephthalate (PET)), polyacrylates (such as polymethylmethacrylate (PMMA)), polyolefins (such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polypropylenes, polyvinyl chloride (PVC), polycarbonate (PC), sulfide containing polymers (such as polysulfone), and polyurethanes.

While performing the method, the printable material is printed on a receiver item. The receiver item can be the build platform, or it can be part of the build platform. The expression“printing on a receiver item” and similar expressions include amongst others directly printing on the receiver item, or printing on a coating on the receiver item, or printing on material that has already been deposited (printed) on the receiver item in an earlier stage of the method. The term“receiver item” may therefore refer to a build platform, a print bed, a substrate, a support, or a build plate, but it may also refer to a pre-existing layer of printed material.

The layer-wise deposition of printable material is done by moving the extrusion head relative to the build platform along a tool path in a plane parallel to the build platform, resulting in the creation of an object. In other words, during the method a printable material is deposited along a tool path on a substrate while moving at least one of the extrusion head and the build platform at a tool path speed, thereby forming a stack of layers that have been deposited on top of each other.

A tool path describes the movement of the extrusion head and the build platform relative to each other. Tool paths are created by means of so-called slicing software. The object that should be manufactured is first designed by means of 3D modelling software, such as computer-aided design (CAD) software. The 3D model of the object is then“sliced” by means of the slicing software, which effectively means that the 3D model is translated into G-code (being a generic name for a control language) that a 3D printer can understand.

Slicing software will create tool paths for a 3D printer to follow when printing. These tool paths comprise geometrical instructions, and instructions on what speed to print at for various points and what layer thicknesses to adopt.

Unless the tool path is designed in a special way, nozzle openings having a boundary that is a curve of non-constant width give rise to the following issues: (i) undesired differences in distortion of the layers, and (ii) undesired differences in the configuration of faceted side surfaces.

When the nozzle opening has a rotational symmetry of order n ( n being an integer equal to or larger than 2), the tool path should be designed such that it consists of two or more straight tool path segments. In the context of the present invention, the term“straight tool path segment” refers to a geometric object that has a length and a direction, comparable to a vector. Each angle between two adjoining straight tool path segments should be an integer multiple of 360/w when n is an even integer, and an integer multiple of 180/« when n is an odd integer. Applying this rule prevents the issue of undesired differences in distortion of the layers, which would otherwise occur for nozzle openings having a boundary that is a curve of non-constant width.

For example, when the nozzle opening has a boundary in the form of a triangle (i.e. a curve of non-constant width with a rotational symmetry of order 3), the tool path may only contain straight tool path segments that make an angle of 60 degrees (180/3) relative to each other. When the boundary of the nozzle opening has a square shape (i.e. a curve of non constant width with a rotational symmetry of order 4), the tool path may only contain straight tool path segments that make an angle of 90 degrees (360/4) relative to each other.

If at least part of the object that should be manufactured has a cylindrical shape, and the nozzle opening has a boundary in the form of a curve of non-constant width, the cylindrical shape cannot have a circular cross section. For example, if the nozzle has a square opening, the cylindrical shape of the object should be approximated by a curve consisting of straight tool path segments at right angles to each other. The cross section of such a cylindrical shape has the form of an aliased circle.

As mentioned above, when the tool path is designed such that it consists of two or more straight tool path segments, wherein each angle between two adjoining straight tool path segments is an integer multiple of 360/w when n is an even integer, and an integer multiple of l80/« when n is an odd integer, the issue of undesired differences in distortion of the layers is prevented. To also ensure that the issue of undesired differences in the configuration of faceted side surfaces is prevented, each angle between two adjoining straight tool path segments should always be an integer multiple of 360/w, irrespective of whether n is an even integer or an odd integer.

In a second aspect, the invention provides an object obtainable with the method according to the first aspect.

In a third aspect, the invention provides a lighting device comprising an object according to the second aspect. The lighting device according to the third aspect also comprises a light source. The object has a stack of light-transmissive layers, each of these light-transmissive layers having an inner side surface that faces towards the light source.

In a fourth aspect, the invention provides a computer program product for being executed by a 3D printer. The 3D printer has an extrusion head and a build platform, and the extrusion head has a nozzle with an opening through which printable material can be deposited onto the build platform. The computer program product comprises instructions which, when the computer program product is executed by the 3D printer, cause the 3D printer to carry out the method according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 schematically shows a method of manufacturing an object by means of 3D printing;

Figure 2 shows several nozzles with different openings through which a printable material can be deposited; Figure 3 serves to further explain the concept of a curve of non-constant width;

Figure 4 shows the formation of a layer upon extrusion of a filament through a nozzle that travels along a tool path in the XY -plane;

Figure 5 shows the deposition of a filament through nozzles with different nozzle openings;

Figure 6 shows deposited filaments that are distorted due to pressure exerted on them by an extrusion head;

Figure 7 shows the deposited filaments of Figure 5 as part of a layer stack in cross-sectional view along a direction parallel to the direction of movement of the nozzle;

Figure 8 shows different tool paths for nozzles with a triangular opening, a square opening, a pentagonal opening, and a hexagonal opening; and

Figure 9 shows a lighting device with a light source and an object that has been manufactured with a method according to the invention.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 schematically shows a method of manufacturing an object by means of 3D printing, in particular by means of FDM.

A 3D printer 1200 has an extrusion head 1210 and a build platform 1220. The extrusion head 1210 has a nozzle 1211 with an opening 1212. Printable material 1300 is deposited through the opening 1212 of the nozzle 1211 in the form of an extruded filament, thereby creating a layer 1110 of object 1100. The extrusion head 1210 moves relative to the build platform 1220 in a direction 1230 to follow a tool path in an XY-plane, being a plane parallel to the build platform 1220. Typically, the extrusion head 1210 moves in the XY- plane, while the build platform 1220 moves in the Z-direction.

Figure 2 shows several nozzles with different openings through which printable material 1300 can be deposited. The nozzles are drawn as seen in a direction indicated by the arrow. Nozzle 121 la has a circular opening l2l2a. In other words, the boundary of opening l2l2a is a circle. Nozzle 121 lb has a triangular opening l2l2b. Nozzle 121 lc has a square opening l2l2c. Nozzle 121 ld has a pentagonal opening l2l2b. Nozzle 121 le has a hexagonal opening l2l2e. Nozzle 121 lf has a heptagonal opening l2l2f. Nozzle 121 lg has an octagonal opening !2l2g. Nozzle 121 lh has a nonagonal opening 1212L Nozzle 121 li has a decagonal opening 1212L Nozzle 121 lj has a cross-shaped opening 1212 j . Nozzle 121 lk has a star-shaped opening l2l2k.

Figure 3 serves to further explain the concept of a curve of non-constant width. The first curve shown in Figure 3 is that of circle 310. Circle 310 is a planar shape having a width w. The width w can be found by drawing two straight lines that are distinct and parallel to each other, each having at least one point in common with the shape’s boundary but none with the shape’s interior. These two distinct parallel lines are shown in Figure 3 as dashed vertical lines. The width of the curve is then found by measuring the distance between the two dashed lines in a horizontal direction, perpendicular to the extension of the lines. Clearly, for the circle 310 there are no two different orientations resulting in a different width. The width of circle 310 is constant, and equal to the diameter of circle 310.

The second curve shown in Figure 3 is that of square 320. In one orientation, the square 320 has a width wl, while in another orientation the same square 320 has a width w2, wherein the width w2 is larger than the width wl. The circle 310 is an example of a curve of constant width, while the square 320 is an example of a curve of non-constant width. All polygons, being plane figures that are bounded by a finite chain of straight line segments, are examples of curves of non-constant width. Plane figures bounded by a finite chain of line segments that are not all straight may also be examples of curves of non-constant width.

Based on the above, an overview of the nozzles illustrated in Figure 2 is presented in Table 1.

Table 1: Overview of nozzles illustrated in Figure 2.

Nozzle openings l2l2b-k all have a boundary that consists of straight line segments. It is noted that this is not required, and that the invention is equally applicable for nozzle openings with boundaries that have curved line segments, provided that the boundary is a curve of non-constant width with a rotational symmetry of order n, n being an integer equal to or larger than 2.

As mentioned before, when manufacturing an object by means of 3D printing, in particular by means of FDM, typically the extrusion head moves in the XY -plane, while the build platform moves in the Z-direction. This movement may result in a rotation (or twist) of the extruded filament, as schematically illustrated in Figure 4.

Figure 4 shows the formation of a layer upon extrusion of a filament through a nozzle that travels along a tool path in the XY-plane. Two different nozzles are used: one with a circular opening 411 and another with a square opening 412. For each nozzle, two different tool paths are used: a square tool path 421 and a triangular tool path 422.

Figure 4(a) shows the combination of a circular nozzle opening 411 and a square tool path 421. By depositing a filament along the square tool path 421, a square layer 431 is obtained. The left part of Figure 4(a) shows the movement of the nozzle in a counter clockwise direction (indicated by the arrows) along the tool path 421. The small black dot included in the nozzle’s circular opening 411 is an orientation marker for illustration purposes only. As shown in the right part of Figure 4(a), when the nozzle completes the square tool path 421 the orientation marker tracks a route in the layer 431 that alternately brings it in the center of the layer 431, the inner side of the layer 431, the center of the layer 431, and the outer side of the layer 431, thereby illustrating the aforementioned rotation (or twist) of the extruded filament. Despite the rotation (or twist) of the extruded filament, the layer 431 has a constant layer width w.

Figure 4(b) shows the combination of a circular nozzle opening 411 and a triangular tool path 422. By depositing a filament along the triangular tool path 422, a triangular layer 432 is obtained. The rotation (or twist) of the extruded filament is again evident from the route of the orientation marker, but, similar to Figure 4(a), the layer 432 has a constant layer width w. Although in Figures 4(a) and 4(b) only two different tool paths are shown, extrusion of a filament through a circular nozzle opening will result in the formation of a layer that has a constant width for any tool path.

Figure 4(c) shows the combination of a square nozzle opening 412 and a square tool path 421. By depositing a filament along the square tool path 421, a square layer 433 is obtained. The rotation (or twist) of the extruded filament is evident from the route of the orientation marker, and the layer 433 has a constant layer width w.

Figure 4(d) shows the combination of a square nozzle opening 412 and a triangular tool path 422. By depositing a filament along the triangular tool path 422, a triangular layer 434 is obtained. In contrast to the square layer 433 of Figure 4(c), and in contrast to the triangular layer 432 of Figure 4(b), the triangular layer 434 has a non-constant layer width. One side of the triangular layer 434 has a width wl, while the other two sides have a width w2, wherein w2 is larger than wl .

For nozzles with a circular opening, which are commonly used in 3D printing, particularly in FDM, rotation of the extruded filament typically does not result in a visible effect in the printed object, at least not in the configuration of the object’s side surfaces.

Non-circular nozzle openings maybe used to obtain printed objects of which the layers have flat or faceted side surfaces. For such non-circular nozzle openings, rotation of the extruded filament may result in a visible effect in the side surfaces of the printed object, which effect may negatively impact the object’s desired appearance. Such undesired visible effects due to rotation of the extruded filament may occur for all nozzle openings that have a boundary in the form of a curve of non-constant width.

Figure 5 shows the deposition of a filament through nozzles with different nozzle openings: a circular opening 511, a square opening 521, and a triangular opening 531. When travelling along a tool path, the nozzles move in directions indicated with arrows along the lines A-A.

Figure 5(a) shows the deposition of a filament through a nozzle with circular opening 511. The deposited filament 512 has a width wl .

Figure 5(b) shows the deposition of a filament through a nozzle with square opening 521. The nozzle moves in a direction that is parallel with a side of the square opening 521. The deposited filament 522 has a width w2. Figure 5(c) again shows the deposition of a filament through a nozzle with square opening 521, but now the nozzle moves in a direction that is parallel with a diagonal of the square opening 521. The deposited filament 532 has a width w3, which is larger than width w2. Furthermore, the configuration of the side surfaces of the deposited filament 532 is different than that of the side surfaces of the deposited filament 522. In Figure 5(b), the deposited filament 522 has flat side surfaces, while in Figure 5(c) the deposited filament 532 has faceted side surfaces, wherein each side surface has two flat faces adjoining at a right angle.

Figures 5(d), 5(e) and 5(f) show the deposition of a filament through a nozzle with triangular opening 531. In Figures 5(d) and 5(e), the nozzle moves in a direction that is parallel with a vertex of the triangular opening 531. In Figure 5(f), the nozzle moves in a direction that is parallel to a side of the triangular opening 531. The deposited filaments 542, 552 and 562 have widths w4, w5 and w6, respectively. Widths w4 and w5 are equal, and larger than width w6. Furthermore, for the deposited filaments 542, 552 and 562 the configuration of the side surfaces is different.

In Figure 5, the deposited filaments are shown as undistorted filaments.

Because in 3D printing the layer height is a setting in the slicing software, the deposited filaments are typically flattened in the Z direction and distorted due to pressure exerted by the extrusion head on the deposited filaments. The larger the height of the deposited filament, the higher the degree of distortion will be.

Such distortion is illustrated in Figure 6. The upper left part of Figure 6 again shows deposited filament 512, in cross-sectional view along a direction parallel to the direction of movement of the nozzle, being a direction along lines A-A as shown in Figure 5. Deposited filament 512 has a circular cross section with height hl equal to width wl. The upper right part of Figure 6 shows deposited filament 512’, being distorted by a pressure exerted by the extrusion head on the deposited filament. The pressure is exerted because the desired layer height h2 is smaller than hl. The lower left part of Figure 6 shows deposited filament 532 in the same cross-sectional view. Deposited filament 532 has a square cross section with height hl equal to width wl. The lower right part of Figure 6 shows deposited filament 532’, being distorted by a pressure exerted by the extrusion head on the deposited filament. For both cases it can be clearly seen that the upper surfaces of the deposited filaments are flattened, and that the distortion has an effect on their side surfaces.

In a similar way as Figure 6, Figure 7 shows the deposited filaments 512’, 522’, 532’, 542’, 552’ and 562’, but now as part of a layer stack in cross-sectional view along a direction parallel to the direction of movement of the nozzle, being a direction along lines A-A as shown in Figure 5.

For each of the layer stacks, the layers have the same height h, which, in 3D printing processes such as FDM, is a setting in the slicing software. The layers are flattened in the stack direction and their side surfaces are distorted due to pressure exerted on the layers by the extrusion head. The degree of distortion of the side surfaces depends on the direction in which the extrusion head moves in the XY-plane. Filaments 542’ and 552’ have both been deposited by an extrusion head having a triangular opening, wherein the extrusion head moves in a direction that is parallel with a vertex of the triangular opening. In other words, for filaments 542’ and 552’ the extrusion head moves along a tool path that consists of straight tool path segments, wherein each angle between two adjoining straight tool path segments is an integer multiple of 60 degrees. Although the configuration of the side surfaces is reversed for deposited filaments 542’ and 552’, the degree of distortion is the same. If, when using an extrusion head with a triangular nozzle opening, the degree of distortion and the configuration of the side surfaces should both be uniform, each angle between two adjoining straight tool path segments should be an integer multiple of 120 degrees.

Figure 8 shows different tool paths (dashed lines) for nozzles with a triangular opening 810, a square opening 820, a pentagonal opening 830, and a hexagonal opening 840.

Triangular nozzle opening 810 has a boundary that is a curve of non-constant width with a rotational symmetry of order 3. Triangular nozzle opening 810 travels along tool paths 811, 812 and 814 in directions indicated with arrows. Tool path 811 consists of a single straight tool path segment, while tool path 812 has two straight adjoining tool path segments. In the context of the present invention, a straight tool path segment should be interpreted as a geometric object that has a length and a direction, comparable to a vector. In a way similar as for vectors, the angle between two straight adjoining tool path segments can be determined. The angle 813 between the two straight adjoining tool path segments of tool path 812 is 60 degrees. Tool path 814 also has two straight adjoining tool path segments, wherein the angle 815 between these segments is 120 degrees. In other words, tool paths 812 and 814 both consist of two straight tool path segments, wherein the angle between the two adjoining straight tool path segments is an integer multiple of 180/3, 3 being the order of rotational symmetry of triangular nozzle opening 810.

Square nozzle opening 820 has a boundary that is a curve of non-constant width with a rotational symmetry of order 4. Square nozzle opening 820 travels along tool paths 821 and 822 in directions indicated with arrows. Tool path 821 consists of a single straight tool path segment. Tool path 822 has two straight adjoining tool path segments, wherein the angle 823 between these segments is 90 degrees. In other words, tool paths 822 consists of two straight tool path segments, wherein the angle between the two adjoining straight tool path segments is an integer multiple of 360/4, 4 being the order of rotational symmetry of square nozzle opening 820. Pentagonal nozzle opening 830 has a boundary that is a curve of non-constant width with a rotational symmetry of order 5. Pentagonal nozzle opening 830 travels along tool paths 831, 832 and 834 in directions indicated with arrows. Tool path 831 consists of a single straight tool path segment. Tool paths 832 has two straight adjoining tool path segments, wherein the angle 833 between these segments is 36 degrees. Tool path 834 also has two straight adjoining tool path segments, wherein the angle 835 between these segments is 72 degrees. In other words, tool paths 832 and 834 both consist of two straight tool path segments, wherein the angle between the two adjoining straight tool path segments is an integer multiple of 180/5, 5 being the order of rotational symmetry of pentagonal nozzle opening 830.

Hexagonal nozzle opening 840 has a boundary that is a curve of non-constant width with a rotational symmetry of order 6. Hexagonal nozzle opening 840 travels along tool paths 841, 842 and 844 in directions indicated with arrows. Tool path 841 consists of a single straight tool path segment. Tool paths 842 has two straight adjoining tool path segments, wherein the angle 843 between these segments is 60 degrees. Tool path 844 also has two straight adjoining tool path segments, wherein the angle 845 between these segments is 120 degrees. In other words, tool paths 842 and 844 both consist of two straight tool path segments, wherein the angle between the two adjoining straight tool path segments is an integer multiple of 360/6, 6 being the order of rotational symmetry of hexagonal nozzle opening 840.

The method according to the first aspect of the invention can be used to manufacture an object, which object can be applied in a variety of situations. For example, when at least part of the object comprises a light-transmissive material, the object may be used as optical component in a lighting device. This is schematically illustrated in Figure 9.

Figure 9 shows a lighting device 910 having a light source 920 and an object 930 that has been manufactured with a method according to the first aspect of the invention. The object 930 comprises a stack of layers 931-934. Each of the layers 931-934 has been deposited using a nozzle with a hexagonal nozzle opening. The layers 931-934 are stacked on top of each other such that each of them has faceted inner side surfaces 93 la-934a facing towards the light source 920 and faceted outer side surfaces facing away from the light source 920, each faceted side surface having two adjoining flat faces with an interior angle of 120 degrees.

In operation, the light source 920 emits light rays 921-928 towards object 930, each of the light rays 921 -928 being incident on a flat face of one of the faceted inner side surfaces 93 la-934a. The layers 931-934 are light-transmissive, allowing light rays 921-928 to pass through the object 930. The faceted inner side surfaces 93 la-934a cause light rays 921- 928 to be alternately refracted in upwards and downwards directions, thereby essentially splitting the light output of light source 920 in two separate parts so that lighting device 910 is arranged to provide an appealing optical effect.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that the person skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb“to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article“a” or“an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a product claim enumerating several means, two or more of these means may be embodied by one and the same item of hardware. 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.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined.

Claims

CLAIMS:

1. A method of manufacturing an object (1100) by means of 3D printing using a 3D printer (1200), wherein the 3D printer (1200) has an extrusion head (1210) and a build platform (1220), the extrusion head (1210) having a nozzle (1211) with an opening (1212) through which printable material (1300) can be deposited onto a receiver item, wherein the method comprises the step of moving the extrusion head (1210) relative to the build platform (1220) along a tool path (1230) in a plane parallel to the build platform (1220) to create a layer ( 1110) of the obj ect ( 1100), wherein the opening ( 1212) of the nozzle (1211) has a boundary (1213) that is a curve of non-constant width with a rotational symmetry of order n, n being an integer equal to or larger than 2, wherein the tool path (1230) consists of two or more straight tool path segments, and wherein each angle between two adjoining straight tool path segments is an integer multiple of 360/w when n is an even integer, and an integer multiple of 180/« when n is an odd integer.

2. The method according to claim 1, wherein each angle between two adjoining straight tool path segments is an integer multiple of 360/w, irrespective of whether n is an even integer or an odd integer.

3. The method according to any of claims 1 and 2, wherein the boundary (1213) is a polygon.

4. An object (1100; 930) obtainable by the method according to any of claims 1 to 3.

5. A lighting device (910) comprising a light source (920) and an object (930) according to claim 4, wherein the object (930) comprises a stack of light-transmissive layers

(931-934), each of the light-transmissive layers (931-934) having an inner side surface (93 la- 934a) that faces towards the light source (920).

6. A computer program product for being executed by a 3D printer (1200), the

3D printer (1200) having a extrusion head (1210) and a build platform (1220), the extrusion head (1210) having a nozzle (1211) with an opening (1212) through which printable material (1300) can be deposited onto the build platform (1220), wherein the computer program product comprises instructions which, when the computer program product is executed by the 3D printer (1200), cause the 3D printer (1200) to carry out the method according to any of claims 1 to 3.