Method for producing an object from mortar by 3D printing

Abstract

The invention relates to a method for producing an object from mortar by 3D printing, comprising: printing a multitude of layers one on top of another, the layers being visible on at least one surface (S) of the object in the form of beads (B); then a step of finishing the at least one surface (S) of the object by applying vibrations to the at least one surface (S) of the printed object via a vibrating contact surface (210) and by shaping the at least one surface (S) of the printed object, treated by the vibrating contact surface (210), by a shaping surface (300), the shaping surface (300) being applied, at the earliest, at the same time as the vibrating contact surface (210).

Description

Method of creating an object using 3D printing

[0001] The invention relates to the three-dimensional printing of an object made with mortar or concrete, more generally a construction material. Previous art

[0002] 3D printing of construction materials such as concrete or mortar is a well-known technique for creating building elements or even entire buildings. Mortar is defined as a material containing a hydraulic binder (such as cement or plaster) and possibly aggregates. This 3D printing process involves a vat of material. A pump is used to transfer the material from the vat to a print head. This print head includes an opening / closing mechanism used to enable or stop printing. This opening / closing mechanism is used during the creation of an object or building.

[0003] The resulting object is then composed of a multitude of layers superimposed on one another to form said object.

[0004] These superimposed layers have the disadvantage of being visible. This means that the finished object has a non-smooth surface, that is, one that leaves the strata, the layers of material, visible. Aesthetically, this results in an unflattering appearance, made up of striations (also called ridges).

[0005] One existing method to overcome this drawback involves equipping the print head with at least one smoothing tool. This smoothing tool takes the form of a plate that is applied during printing to smooth the surface simultaneously with the printing process. The disadvantage of this solution is that this step occurs during printing. This necessitates rotating the nozzle and tool assembly during printing, which is difficult for complex shapes.

[0006] Another solution is to include a surface finishing step after hardening. This finishing step involves adding or removing material to achieve a smooth surface. A material is then applied to conceal any striations in the case of material addition, or a grinder or sander is used in the case of material removal.

[0007] In the case of adding material, we end up with an object that is composed of two different materials or two blocks of the same material but not linked.

[0008] In the case of material removal, the risk is that the object will become fragile. Furthermore, this material removal has a negative environmental and economic impact. First, it generates dust. Second, it generates waste. Therefore, to achieve the same level of strength, this material removal must be compensated for by using a larger initial material, thus requiring more resources.

[0009] The invention then seeks to provide a solution to the aforementioned drawbacks by providing a method for improving and modifying the surface of a three-dimensionally printed mortar object.

[0010] To this end, the invention relates to a method for producing a mortar object by means of a printing system comprising a printing head by which the material is deposited, said printing head being mounted on a structure enabling said printing head to move along at least three axes, said printing head being connected to a reservoir, in which the mixture used for printing is stored, by means of a main conduit, said method comprising the following steps:- To equip the printing system and to print the object using the mortar so as to form an object composed of a multitude of layers superimposed one on the other, said layers being visible on at least one surface of the object in the form of ridges;- To carry out a surfacing step of said at least one surface of the object, using the following steps:▪ To equip a vibrating contact surface and a shaping surface;▪ Apply vibrations to the printed object to apply vibrations to said at least one surface of the printed object via a vibrating contact surface; ▪ Conform said at least one surface of the printed object treated by the vibrating contact surface by the conforming surface, said conforming surface being applied at the earliest at the same time as said vibrating contact surface.

[0011] In one example, the application of the shaping surface is simultaneous with the application of the vibrating contact surface.

[0012] According to one example, the application of vibrations is carried out by a first tool.

[0013] In one example, the application of the conforming surface is carried out by a second tool.

[0014] In one example, the application of vibrations and the application of the forming surface are operated by the same tooling.

[0015] According to one example, the surfacing step is carried out when the printed material forming the object has a threshold stress with a defined value.

[0016] In one example, the value of the threshold constraint is determined using a database.

[0017] According to one example, the value of the threshold stress is determined with a measuring device that allows obtaining a value of the threshold stress.

[0018] According to one example, the threshold stress measurement is carried out continuously or at intervals.

[0019] According to one example, the threshold stress value is between 50 and 130 kPa for a printable material.

[0020] Preferably, the surfacing step is carried out within a time frame of between 30 minutes and 5 hours after the printing step.

[0021] Preferably, the surfacing step is done without removing material.

[0022] The thickness of the layers is preferably at least 5 mm, in particular between 5 and 100 mm.

[0023] In one embodiment, the surfacing step produces a smooth surface. This process eliminates the characteristic ridges or striations of 3D printing.

[0024] In another embodiment, the surfacing stage produces a surface with an aesthetic or functional texture. This process not only eliminates ridges or striations but also creates a texture, preferably regular, for example in the form of patterns.

[0025] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying drawings, in which: - a view of a printing system according to the invention; - a diagram of the printing system according to the invention; - a profile view of a printed object; - a vibrating contact surface according to the invention; - Figures 5 to 8 represent different ways of carrying out the surfacing step of a printed object according to the invention. Detailed description

[0026] Figure 1 shows a three-dimensional material printing system. This printing system is used to create an object. This object can be a construction item such as a brick, a concrete block, a wall, or even an entire building. It can also be an object such as street furniture. The printing system includes a print head 10 through which the material (mortar) is deposited. The print head 10 is mounted on a structure 2 that allows it to move along at least three axes: length, width, and height, to perform the printing. This structure can be in the form of an articulated arm or gantries. The print head 10 is controlled by a control unit 60, which controls the movement of the print head and its material flow rate.

[0027] The print head 10, visible in the figure, is connected to a reservoir 20 via a conduit called the main conduit 40. The reservoir 20 is a tank in which the printing mixture is stored. The reservoir 20 is also called a mixer when it is equipped with means for mixing the mixture (typically a hydraulic binder, water, and possibly granules) such as a screw conveyor or rotating blades.

[0028] The printing system 1 also includes a pump 50 to bring the mixture from the reservoir to the print head.

[0029] The print head 10 optionally includes opening-closing or sealing means 100, such as a flap or valve, allowing the mixture to exit the print head and be deposited.

[0030] Thus, printing is done by pumping the mixture from the reservoir to the print head while the head moves along a programmed path to create the object by layering several layers on top of each other. The layer thickness is preferably at least 5 mm, typically between 5 and 100 mm, or even between 5 and 50 mm, or between 5 and 20 mm.

[0031] According to the invention, the printed object undergoes a surfacing step. This surfacing step is performed to modify the appearance of at least one surface S of the object O and eliminate the unsightly appearance of the various superimposed layers. This unsightly appearance takes the form of ridges B (or striations) visible on the surface of the object O, as seen in [reference]. These ridges B are visible on external or internal surfaces of the object, depending on its configuration. The surfacing step is preferably performed on an external surface but can also be performed on an internal surface, depending on the configuration of the printed object. It is understood that it is necessary to be technically capable of performing this surfacing step. This modification of the appearance is preferably carried out without removing any material.In the case of material removal, this is as small as possible, and generally results from slight losses of mortar that can adhere to the tools.

[0032] This surfacing step is based on the use of vibrations. These vibrations are applied to the printed material and used to locally modify it. This local modification consists of refluidifying the material. The vibrations applied to the material cause the bonds formed during its hardening to break. Breaking these bonds allows the material to be reshaped over time.

[0033] The vibrations are generated by a vibration generator. This vibration generator can use various technologies such as a pneumatic or ball vibrator. Such a vibrator, for example, is capable of generating vibrations of 1700 N at a frequency of 16,000 VPM (vibrations per minute).

[0034] These vibrations are applied to the printed material by a tool 200 which has a vibrating contact surface 210 as seen in figures 4 and 5.

[0035] These vibrations are accompanied by the application of a 300 shaping surface. This 300 shaping surface is used to shape the freshly reflowed material to give it the desired appearance. This appearance can be smooth or have an aesthetic or functional texture.

[0036] The application of vibrations and the application of the 300 shaping surface can be simultaneous or staggered. In the case of staggered applications, the application of the 300 shaping surface occurs after the application of vibrations.

[0037] To achieve this, vibration and shaping can be carried out with the same tooling or with different tooling.

[0038] With a single tooling 200, it's clear that the application of vibrations and the application of the forming surface are simultaneous, as can be seen in the diagram. Thus, the vibrating contact surface and the forming surface are one and the same. Alternatively, one could imagine a tooling surface 200 divided into two portions: the vibrating section and the forming section.

[0039] Tool 200, for example, takes the form of a trowel. This trowel is operated manually or mounted on a robotic arm. It comprises a working surface and a vibration generator designed to transmit vibrations to the surface. This working surface can be flat or patterned. The pattern is then replicated on the surface of the object.

[0040] The advantage is saving time with surfacing done in a single pass.

[0041] With two 200 toolings, we understand that the application of vibrations and the application of the forming surface are simultaneous or staggered.

[0042] In the case of offset applications, as seen in the image, each tool is used for a specific function. The first tool is used to provide vibrations and reflow the printed material, while the second tool is used to mark the material and replicate a pattern. The first tool is an application tool designed to be in contact with the printed material. This tool can take any shape, such as a trowel. Its contact surface with the printed material is flat to prevent marking. The second tool is designed to present a contact surface. This contact surface displays a pattern intended to be reproduced on the printed object.

[0043] Each tool is handled manually or, preferably, mounted on a robotic arm.

[0044] In the case of simultaneous applications, as seen in the illustration, a first tool is used to impart vibrations and reflow the printed material, while a second tool is used to mark the material and replicate a pattern. The first tool is an application tool designed to be in contact with the printed material. This first tool can take any shape, such as a trowel. Its contact surface with the printed material is flat to prevent marking. The second tool is an interlayer. This interlayer is positioned between the first tool and the printed object. It is a flexible material such as a sheet, film, membrane, or strip with two opposing faces. One face contains the pattern to be replicated. The second tool then works in conjunction with the first tool to replicate the pattern.This interaction occurs through vibrations that are not transferred directly to the printed material but rather through the second tool. In this case, the vibrations from the first tool are transmitted to the second tool, which then transmits them to the printed material. The printed material, receiving the vibrations, experiences a refluidification of its surface. The pattern created on the second tool is then replicated onto the refluidified surface of the printed material.

[0045] The advantage of having two different tool sets is that it allows for greater flexibility since the number of usable tools is larger.

[0046] The surfacing step according to the invention is such that it allows the printed material to be momentarily reflowed for resurfacing. This reflowing implies that bonds between the materials are formed and that hardening is underway. It is therefore necessary to determine the optimal moment to perform the surfacing. Indeed, if the bonds have not yet been formed, the reflowing will be too significant and less localized, resulting in overall deformation or sagging of the printed part. If the bonds are too strong, then the hardening is too advanced, and therefore reflowing does not occur.

[0047] The time interval within which surface finishing is possible is linked to a physical quantity called the "threshold stress." This threshold stress is associated with the material's stiffness over time after printing. The range of threshold stress values ​​for which the surface finishing step according to the invention is effective has been determined. Indeed, if this threshold stress value is too low, then overall deformation or sagging of the part may occur due to excessive reflowing, and if this value is too high, then the material is too dry and brittle.

[0048] The threshold stress is, within the framework of the present invention, measured with a falling cone penetrometer of mass 80.1 g and angle 15°.

[0049] Preferably, this value range is between 50 and 130 kPa for a mortar-based printable material. This range ensures that the printed material can be resurfaced. Preferably, the resurfacing step is carried out between 30 minutes and 5 hours after the printing step, specifically between 1.5 and 4 hours after printing.

[0050] In one embodiment, this threshold stress value is extracted from a database. This database contains threshold stress values. These threshold stress values ​​are simulated (theoretical) and / or previously measured during tests. Advantageously, this database includes numerous simulations or tests, providing values ​​for different environmental conditions such as humidity and temperature. It is therefore understood that the threshold stress is an intrinsic property of the material, which makes the use of a database possible. Thus, by knowing the start time of printing, it is possible to determine the time from which the surfacing stage can begin.

[0051] In another embodiment, this threshold stress value is measured. This measurement is performed by a sensor that allows the direct measurement of the threshold stress or of a physical quantity that allows this threshold stress to be obtained. The measurement is made continuously or at regular intervals.

[0052] Of course, the present invention is not limited to the illustrated example but is susceptible to various variants and modifications which will become apparent to those skilled in the art.

Claims

A method for producing a mortar object using a printing system comprising a printing head (10) through which the material is deposited, said printing head (10) being mounted on a structure (2) allowing said printing head to move along at least three axes, said printing head (10) being connected to a reservoir (20) in which the mixture used for printing is stored, via a main conduit (40), said method comprising the following steps: - To equip the printing system and print the object using mortar so as to form an object composed of a multitude of layers superimposed one on top of the other, said layers being visible on at least one surface (S) of the object in the form of ridges (B); - To perform a surfacing step on said at least one surface (S) of the object, using the following steps: ▪ To equip a vibrating contact surface (210) and a surface of conformation (300);▪ Apply vibrations to the printed object to apply vibrations to said at least one surface (S) of the printed object via the vibrating contact surface (210); ▪ Conform said at least one surface (S) of the printed object processed by the vibrating contact surface (210) by the conforming surface (300), said conforming surface (300) being applied at the earliest at the same time as said vibrating contact surface (210). Method according to the preceding claim, wherein the application of the shaping surface (300) is simultaneous with the application of the vibrating contact surface (210). A method according to any one of the preceding claims, wherein the application of vibrations is carried out by a first tool. A method according to any one of the preceding claims, wherein the application of the conforming surface (300) is carried out by a second tool. A surfacing method according to claim 2, wherein the application of vibrations and the application of the conforming surface (300) are carried out by the same tooling. A method according to any one of the preceding claims, wherein the surfacing step is carried out when the printed material forming the object has a threshold stress having a defined value. A method according to the preceding claim, wherein the threshold stress value is between 50 and 130 kPa. A method according to any one of the preceding claims, wherein the surfacing step is carried out without material removal. A method according to any one of the preceding claims, wherein the thickness of the layers is at least 5 mm, in particular between 5 and 100 mm. A method according to any one of the preceding claims, wherein the surfacing step makes it possible to obtain a smooth surface. A method according to any one of claims 1 to 9, wherein the surfacing step makes it possible to obtain a surface with an aesthetic or functional structure. A method according to any one of the preceding claims, wherein the surfacing step is carried out within a time between 30 minutes and 5 hours after the printing step.

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