Additive manufacturing techniques may generate a three-dimensional object on a layer-by-layer basis through the solidification of a build material. In examples of such techniques, build material is supplied in a layer-wise manner and a solidification method may include heating the layers of build material to cause melting in selected regions. In other techniques, other solidification methods, such as chemical solidification methods or methods of binding materials, may be used. In some examples, the temperature of the build material is increased prior to the melting process.
Some non-limiting examples of the present disclosure are described in the following with reference to the appended drawings, in which:
In some 3D printing processes a layer of a build material in the form of a particle material, e.g. powder, is laid down on a build platform of a fabrication chamber. Then a fusing agent is selectively applied where the particles are to fuse together. The layer of build material is subsequently exposed to fusing energy. The process is then repeated until a part has been formed. In some 3D printing systems a heating structure is used to heat the top layer of build material to a uniform temperature just below the melting point of the build material and before fusing energy is applied. A heating element structure, for example mounted over the build platform may be used for heating. In other examples, a scanning, fusing and warming lamp configuration is used. Some heating element structures have arrays of heating elements that are selectively controllable to provide energy in the form of heat to the build platform.
In a 3D printing system, a fusing agent is applied on portions of the top layer of build material (e.g. powder). The fusing agent acts as a heat absorber to absorb more heat than portions on which no fusing agent is present, The action causes those portions with fusing agent to melt and fuse. The heat is applied at predefined temperatures or temperature ranges so that the build material to be fused. Heating at temperatures below or above a predefined temperature or temperature range, may degrade the quality of the printed product. A way to maintain the heating temperature within the prescribed temperature ranges is by measuring accurately the surface temperature of the printing area.
The heat sensor 150 may be used to monitor the powder temperature. The heat sensor 150 may be designed to measure temperature from a distance by detecting an object's infrared (IR) energy. The heat sensor 150 may comprise thermopile sensors that may convert the temperature radiation of an object surface to an electrical signal (voltage) by thermocouples, e.g. by using the thermoelectric or Seebeck effect. The sensor's output voltage may be related to the objects temperature and emissivity (radiation) as well as to the sensor chip temperature (housing temperature) and surrounding temperature (radiation) and may be calculated by the following equation:
VS=K*ε(TOn−TSn) (Equation 1)
where, VS may be the sensor output voltage, K may be a constant apparatus factor, ε may be the object's emissivity, TO may be the object's temperature, TA may be the ambient (surrounding) temperature, TS may be the sensor (housing) temperature and n may be an exponent corresponding to the temperature dependency of the signal voltage.
According to the above formula, the parameters K, TA & TS may either be measured by external sensors or may be predetermined and remain constant over time. However, the object emissivity (ε) may depend on the build material properties. Even if the theoretical emissivity for an object may be provided, e.g. in a datasheet of the object, the emissivity may change over time, from one material to another or when an agent is printed on the object.
Therefore, in order to obtain accurate temperature measurements a calibration process may be performed periodically. Such calibration process may be performed at the beginning of each printing process, e.g. during formation of the first layers.
The build platform 305, may contain as many temperature sensors 315 as may be the number of zones the thermal camera 310 may remotely measure.
By using external temperature sensors located on the build platform, e.g. the build platform of a 3D printing system, the powder surface temperature may be accurately measured because the thermal resistance from powder to sensor is very low. This temperature value may be compared with the temperature measurements received from the heat sensor, e.g. the thermal camera, in order to calculate and apply a factor correction per region or zone of the printing surface.
The calibration process may start once enough powder is deposited onto the build platform and the powder's temperature has reached a steady state. Then, temperature Ts obtained by the temperature sensor 315 and the measurement obtained from the thermal camera may be compared and a calibration factor may be calculated per each zone. When further layers are deposited, the controller may apply the calculated calibration factor for each zone.
Additionally, this method can be used to obtain calibration factors of different agents by, for instance, printing the powder deposited above a sensor with an agent and by comparing local and remote temperature measurements when the powder is printed with the agent.
In an example application, in a 3D printing system, the temperature may be regulated within 12 regions or zones of the build platform. In order to accurately calibrate the thermal camera across the build platform, one thermopile sensor, e.g. a negative temperature coefficient (NTC) sensor, may be used per each zone in order to calibrate the thermal camera. In one example, the thermal camera used may have an accuracy of +/−3% or +/−3° C. (+/−12° C. at 400° C.). By using high resolution temperature sensors the accuracy may be improved and provided in a range of +/−2.5° C. at 400° C. Therefore, in this example, this method may improve the thermal camera temperature acquisition accuracy by almost 5 times.
The example implementations discussed herein allow for accurate measurement of the temperatures on a build platform of a 3D printing system. For a certain build platform, the proposed calibration method may allow for lower energy consumption and for improved quality of the finished printed object. Thus, they may improve the efficiency of a 3D printing system.
It will be appreciated that examples described herein may be realized in the form of hardware or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disc or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, some examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, some examples may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the operations of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or operations are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.
Although a number of particular implementations and examples have been disclosed herein, further variants and modifications of the disclosed devices and methods are possible. For example, not all the features disclosed herein are included in all the implementations, and implementations comprising other combinations of the features described are also possible. As such, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the disclosure, which is intended to be defined by the following claims—and their equivalents—in which all terms are meant in their broadest reasonable sense unless otherwise indicated.
Filing Document | Filing Date | Country | Kind |
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PCT/US2017/043482 | 7/24/2017 | WO | 00 |