DE102019001199A1 - Process and 3D printer for additional stiffening of 3D printed objects built up in layers using stiffening elements - Google Patents

Abstract

Method and device (3D printer) for stiffening 3D printed objects built up in layers, characterized in that one or more building materials are used across layers, the layers being anchored to one another.

Description

Layer by layer by means of e.g. Objects created using the FDM method suffer from the disadvantage that they do not have anisotropic strength values. This means that an object will have significantly lower values in the axis of the printhead than at right angles to it.

A layer tears under tension because the layers are not optimally connected to one another.

This can be remedied by printing weak point areas particularly slowly (to ensure that the layers merge better) or by increasing the temperatures in the extruder (hot end) to allow this. In addition, in the process of calculating the layer layers, called slicing, the area of the layer can be increased by laying partially wider or more pressure tracks (paths), or the% of the infill can be maximized (but undesirable weight increase)

Disadvantage: long printing time, high heat input (tendency to warp), material decomposes, and the goal of the desired strength is not achieved.

The invention embodied here shows a simple way of increasing the strength of the object.

In the simplest case, this is achieved by inserting cavities, which are filled with hot material (let run into them) by the print head which is temporarily standing (or moving at very low speed).

The cooled material in an expanded form (see illustrations) can now absorb forces that would otherwise lead to breakage.

Variants of the process of filling cross-layer cavities use additional materials and not just one or two FDM materials available in neighboring HotEnds, which do not require any modifications but only a modified slicing algorithm.

The process of filling cavities in various ways can be used in various 3D printing techniques. See claim 1.

Further materials are described in claim 2.

For example, a fiber-reinforced strip can be pushed into a cavity and glued in using FDM material (or a separately supplied resin).

See also the texted list of the reference symbol list.

• 1a The specimen for the tensile test was sliced parallel to the axis of the tensile forces. That means the paths on which the FDM technology print head deposits the melted material.
• 1b In 1b the tracks were sliced at right angles to this axis. It turns out that the test rod in 1a delivers significantly higher strength values than the one 1b The reason for this is the lower strength with which the individual strips are laid on top of one another and melt together. An object always has a lower strength along the layer level and can break or tear apart particularly quickly at these points. See also 13th and explanations there.
• 1a + b test specimen according to 1b tends to separate along the layers. The cohesion of the layer (layer adhesion) is influenced by several conditions, mainly: printing speed, temperature of the applied layer, temperature of the layer that has already cooled down, material parameters such as melt viscosity, as well as parameters relating to the structure of the filling (shape and fill percentage). If all of these parameters have been optimized, it is hardly possible to further increase the overall strength of the object if the material is only deposited in layers (as is usual with the FDM method). Store layer by layer in the direction of the Z-axis (usual selection in the XYZ system)
• 2 Print object view from the front. Inside, more thinly lined, two extensive cavities, with pearl-like bulges, which, when filled with material, are supposed to act as stiffening, anchoring elements.
• 2a Print object side view,
• 2 B Print object perspect. View; the two cavity structures appear on the top surface R1 .
• 2c Print object view from the side, with R2 , indicated the breakdown into layers
• 2d Print object front view, with R2 ,
• 2e Print object perspect. View; Detail: R2 does not extend to the ceiling, but starts at the floor
• 2f perspective. Look into an object 2 , which does not have a special hollow structure according to the invention for stiffening, but only the typical filling structure ( 7th ), here about 15% filling, as it is created when printing according to the FDM method (also FFM) in a "slicing" procedure. Here with a rectangular filling structure. It should be pointed out that this typical structure or parts thereof, created according to previous sclicing methods, can also be filled with a material according to claims 1-7 and is thus claimed as a cavity structure according to the invention according to claims 1-7.
• 2g perspective. Look into an object 2 , which is a particular cavity structure according to the invention R2 for stiffening
• 3 Simplified representation of the FDM process, layered structure not shown separately, an oblique object has cavity structures R. , which were filled in the upper part of the object with the building material of the object (with R4 designated)
• 4th FDM process cavity structures empty, filled; different versions
• 4a unfilled cavity structures bulging here R3 , oblique or perpendicular in the object; Bulged forms anchor better with the object
• 4b unfilled, cavity structures R3 , oblique or perpendicular in the object
• 4c Representation with two hotends (dual pushers) that convey two different materials. One for the property. ( 10 ), one for the cavity structures ( 11 ) Note: The cavity structures can also be used by FDM printers with only one material ( 10 ) are filled. That means that no modifications are necessary. ( 18th ) indicates escaping air that wants to escape when filling with material. R4 is thus a cavity with an additional opening (hole in the wall), preferably arranged at the other end than the opening for filling. please refer 6a
• 4d filled, unbuilt cavity structure.
• 4e the thin fluid material 12a gets into the cavity R. filled, the more fluid (shown here as small droplets) the better the filling of the cavity and entanglement (anchoring) on the walls of the cavity structure.
• 5 Representation of the FDM process, a strand emerging from the hotend is stored in layers
• 6th if there is no base under the hotend in the layer spacing, the filament is extruded "into the air". The escaping material typically becomes curled up because it cools down and shrinks very quickly (depending on the installation space temperature).
• 6a Applies to FDM and sintering processes. Cavity structure, already filled, bulged and constricted, with an air outlet ( 18th ) at the bottom, three arrows symbolizing escaping air.
• 7th The shown curling of the exiting strand leads to inhomogeneous filling of the cavity.
• 8th However, if the temperature of the strand material is increased, this is very often accompanied by a reduction in viscosity, this flows better and the material can fill the installation space more evenly. For example, the material 1 is printed to the object at 240 ° C, but the cavity structures according to the invention (with material 1 ) printed at 260 °. Alternatively, is building material 1 Printed at 240 ° C, another building material 2 but has the same temperature as the material 1 a lower viscosity (therefore flows better) and is therefore applied from a second hotend. One material is preferred 3 used, which also has higher strength values than material 1 owns. However, this is not absolutely necessary, since the cavity structure according to the invention already has a strength-increasing effect by anchoring the layers to one another.
• 9 FDM method As an alternative to filling with molten filament, filling with profile segments that are taken from the supply ( 13th ) cut into the cavity structures are proposed. If these are sprinkled with a resin or cast, and then exposed to actinic light, a solid, stably filled cavity structure results. The resin can just as well be a thermosetting or multi-component resin.
• 9a a profile bar in a cavity structure without filling with resin
• 9b Cavity structure with several profile pieces
• 9c Cavity structure, more closely packed with profile pieces
• 9d obliquely arranged cavity structure
• 9e Cavity structure, tightly packed, resin flows in (stylized by drops)
• 9f Cavity structure, filled, the curing, here by UV light, takes place
• 10 stylized an SLS process, the layers are produced by sintering with a laser from a powdery starting material.
• 11 stylized: Binder Jetting, powdery starting material at selected points with a binder from a print head ( 15th ) glued.
• 12 The print object is created from a powdery starting material, see 10 and 11 .
• 12a a suction device ( 16 ) sucks the non-solidified powder out of the cavity structure
• 12b Profile pieces are filled
• 12c Profile pieces were filled in, but not with a resin as in 12d , shed
• 12d Resin flows into the cavity structure, which has already been filled with profile pieces
• 12e Curing by UV light or other actinic radiation, or by heat, or by using self-curing resins (2K)
• 13th Stylized illustration, top row: • left, object built up in layers in the FDM process • middle: application of forces; Object breaks along layers as these usually have the lowest strength among each other • right: the cavity structures according to the invention act like tie rods that hold the layers of the object together lower row: • left: object built up in layers using the SLS method or the binder jetting method. • middle: the object does not break on the line of parallel layers, but rather irregularly • right: the cavity structures according to the invention act like tie rods which generally hold the layers and the object together
• 14th Stylized, FDM printer with more than the usual degrees of freedom, usually 3 axes can be approached, here the print bed is also movable, as well as the hotend. The layer thicknesses can vary.
• 15th Device for supplying hot air for the purpose of preheating the cavity structure. If its walls are preheated, molten material can flow better and cools down more slowly.
• 16 Left: A special cavity in an FDM object is created using a dosing device after the 3D printing process 26th filled with a resin. The special cavities have filling openings for this process 20th on the outside of the property. The object can also have cavities 21st that do not have a filling opening. At the opening 22nd either excess resin escapes or displaced air escapes. Right: An object made of sintered, fused or bonded particles can be filled with resin in the same way as an FDM object.
• 17th If the resin is electrically conductive, the result is an electric circuit through the object.
• 18th a hotend 24 , has a slim design and sinks into the cavity (FDM object) and fills it as it moves out of the cavity again. This ensures that even a filament which does not melt very thinly is brought to the bottom of the cavity and can thus fill it completely
• 19th a hotend 24 The (FDM method) has a slim design and sinks into the cavity of an SLS object (also known as a binder jet or jet fusion object) and fills it while it moves out of the cavity again.

List of reference symbols

1

The supply of material, shown here in the form of a coil, contains a filament for the FDM process

2

stylized printed object, two hollow structures R1 containing,

2a

Print object with R1 ,

3

Hotend, also called liquefier (for the filament)

4th

Filament before it is fed to a guide tube.

5

Guide tube

6th

Construction platform

7th

Filling structure (after a slicing procedure) of an object, here with a square shape

8th

stylized, squeegee, moves the loose grains to a smooth surface

9

actinic light, e.g. UV light for curing curable resins

10

Filament material 1

11

Filament material 2

12

Filament that melts with a low viscosity

12a

Filament very thin, viscosity very low, drop-shaped ejection from the hotend, it is to be expected that such a thin filament fills the cavity homogeneously and fuses with the walls (anchored)

13

symbolic material reserve (whether wound or unwrapped), which is cut open (piece by piece) and filled into the cavity. The material can be a profile made of a thermoplastic polymer, a thermosetting plastic, a metallic material such as a steel profile, a fiber-reinforced profile, e.g. in rectangular shape, a flat band (e.g. fiber-reinforced) or other solid, e.g. be made of ceramic. If possible with comparatively high strength values

15th

symbolic, print head that emits a teardrop-shaped binder binder jetting process)

16

Extraction, to remove particles. Extraction of non-sintered grains from a laser sintering process or from non-bonded grains from a binder jetting process. These grains are metallic, made of plastics or of mineral origin.

17th

Tubes for dispensing a hardenable liquid, e.g. an actinic curing resin, a photopolymer, or a thermosetting polymer in resin form.

18th

Air (three small arrows) escapes through an opening according to the invention in the cavity structure

19th

stylized, laser beam in a laser sintering process

20th

Filling opening

21st

Cavity, anchor-shaped, which has no filling opening

22nd

Opening, outlet for air or superfluous material

23

electrical contact surface

24

slim designed hotend,

25th

Filament supply

26th

stylized, dosing device with here double feed and mixing elements

R.

Identification for a cavity structure, divided into R1-R5

R1

A cavity structure with pearl-like bulges extends in this illustration from the bottom to the top of the object. R1 is already "planned" into the object as a reinforcing structure when the object is designed. For example from the designer, architect or structural engineer.

R2

The cavity structure R2 on the other hand, in the print preparation, i.e. if this cavity structure was not planned into the object by the designer etc., but only calculated using a software procedure and combined with the layers to be built up. R1 and R2 can have different, but also the same forms.

R3

unfilled cavity structure

R4

Cavity structure already filled with building material across layers

R5

Void structure that is currently being filled

Claims (7)

Method and device (3D printer) for stiffening 3D printed objects built up in layers, characterized in that one or more building materials are used across layers, the layers being characterized by the a) FDM process with filaments b) Selective Laser Sintering Process (SLS) c) Direct Metal Laser Sintering d) Binder Jetting e) Jet Fusion f) pasty deposits are formed and anchored to one another. Procedure and device (3d printer) Claim 1 , characterized in that to stiffen the print object to be created, 1) special cavities are constructed in the object before a slicing procedure or 2) when calculating the arrangement of the layers for the 3D printing of the object by means of a slicing Program, special cavities are calculated. These are extended over several layers and are partially or completely filled in a subsequent process with one or different materials, one of the materials being a) FDM filament A (first main building material) or further FDM building materials B + C or more , b) non-thermoplastic material, e.g. crosslinking hardening resin (2K), by process heat or actinic hardening resin c) an aqueous, pasty material, e.g. cement, ceramic mix, wood concrete, a d) a fiber-reinforced strip (tape), (e.g. made of carbon fibers, glass fibers or Kevlar) e) a meltable powder, metallic, made of plastics or ceramics (laser sintering) f) a powder that can be bonded with a binder (binder jetting) g) Profile bars (round, rectangular, polygonal, made of metal, plastic, fiber-reinforced material) h) a combination of a - g, e.g. an FDM filament and a fiber-reinforced strip, or a combination of a hardening resin and a profile bar i) or may be an electrically conductive resin or conductive powder. Special cavities after Claim 1 - 2 , characterized in that these extend over either 1) more than one adjacent layer, 2) preferably more than 2 - 10 layers, most preferably 10-500 or even more, depending on the object size, or 3) more than 1 - 5 mm in one direction of the axis of construction progress, layer laying axis (usually called the z-axis), preferably 5 - 20 mm or most preferably over 20 - 500 mm or or a multiple thereof depending on the object size, 4) viewed side by side, in the direction of the layering axis preferably overlap one another. ( 4th ) and 5) have an opening (hole) for the escape of displaced air, 6a , (18) 6) optionally have one or more filling openings 20, and optionally exit openings 22 for displaced air or excess material on the outside of the object, and anchor the layers to one another. Special cavities after Claim 1 - 3 , characterized in that this after filling with a material Claim 2 a) warmed up using hot gas, e.g. air or a radiant heat source, b) blown out or sucked out (to remove loose particles from the sintering technique), c) moistened (for the purpose of better flow of a paste, mixture) d) or filled with a primer (adhesion promoter) become. Cavities after Claim 1 - 4th , characterized in that these are filled with a material whose viscosity at the temperature of the filling is by a factor of 1.5, preferably a factor of 2-10, particularly preferably 10-50 or 50-100, or 100-10,000 times higher than that Viscosity of the building material at the working temperature of the hotend (with the FDM process). 3d printer after Claims 1 - 5 , characterized in that this according to the type FDM printer via a device for filling a cavity either with a) profile rods (round, rectangular, polygonal, made of metal, plastic, fiber-reinforced material) and preferably a cutting device for this or b) fiber-reinforced Strip (tape), (e.g. made of carbon fibers, glass fibers or Kevlar) and preferably a cutting device for this. These (profiles and / or strips) are preferably placed in the cavity at an angle greater than 1 ° to the layer, particularly preferably greater than 30 °, 45 ° or particularly preferably at an angle of 90 °, or c) a liquid resin, d) over a hotend 24 has a particularly slim design, which dips into the cavity by moving downwards ( 18th ) and liquid filament can flow in, e) and a device for supplying warm, hot air (preferably close to the temperature of a building material. 3d printer after Claims 1 - 6th , characterized in that this according to the type laser-sinter printer, binder jetting or jet fusion, via a device for filling a cavity either with a) profile rods (round, rectangular, polygonal, made of metal, plastic, fiber-reinforced material) and preferably one Cutting device for this or b) fiber-reinforced strips (tape) (for example made of carbon fibers, glass fibers or Kevlar) and preferably a cutting device for this. These (profiles and / or strips) are preferably placed in the cavity at an angle greater than 1 ° to the layer, particularly preferably greater than 30 °, 45 ° or particularly preferably at an angle of 90 °, or c) a liquid resin, d) a melted filament, preferably using a hotend 24 (see 19th ), as well as • a suction device for loose particles • a device for supplying warm, hot air (preferably close to the temperature of a building material.

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