Methods and apparatus relating to substructures for three-dimensional objects are described. In an example, a method comprises receiving a lattice model having a consistent dimensionality and determining a substructure model representing a three-dimensional material structure, the substructure model being based on the lattice model and specifying a variable material distribution. The substructure model may be populated with halftone threshold data to provide a three-dimensional halftone threshold matrix

In some examples, an additive manufacturing technique for forming a vacuum insulator. For example, a method including forming an article including a first layer, a second layer, and at least one support member extending between the first and second layer by depositing a filament via a filament delivery device, wherein the filament includes a sacrificial binder and a powder, and wherein the first layer, second layer, and at least one support member define an open cavity within the article; removing the binder; and sintering the article to form the vacuum insulator, wherein the vacuum insulator defines a vacuum environment in the cavity.

In some examples, an additive manufacturing technique for forming a vacuum insulator. For example, a method including forming an article including a first layer, a second layer, and at least one support member extending between the first and second layer by depositing a filament via a filament delivery device, wherein the filament includes a sacrificial binder and a powder, and wherein the first layer, second layer, and at least one support member define an open cavity within the article; removing the binder; and sintering the article to form the vacuum insulator, wherein the vacuum insulator defines a vacuum environment in the cavity.

A sensor may be to detect a property indicative of a print dead zone caused by a defect of build material to be used for generating the three-dimensional object or a malfunction of a heater that is to heat the build material, a build material distributor that is to provide the material, or a carriage. A processor may be to receive, from the sensor, dead zone data relating to the print dead zone, and to prevent the malfunction of the heater, the build material distributor, or the carriage, or to modify data representing the three-dimensional object to cause the three-dimensional object to be shifted such that three-dimensional object is to be printed outside the print dead zone.

Adjustment of a halftoning threshold can, in an example implementation, include assigning a relative energy value, relative to a reference energy value, to a location of a build area and adjusting a halftoning threshold based on the relative energy value.

Agent calibration can, in an example implementation, include generating a calibration based on a quantity of energy absorbed by a build material treated with different quantities of an agent and converting a portion of a three-dimensional object model to a quantity of agent based on the calibration.

Agent calibration can, in an example implementation, include generating a calibration based on a quantity of energy absorbed by a build material treated with different quantities of an agent and converting a portion of a three-dimensional object model to a quantity of agent based on the calibration.

At least one agent distributor may be to selectively deliver coalescing agent onto portions of a layer of build material at a first density and at a second density lower than the first density. A controller may be to control the at least one agent distributor to selectively deliver the coalescing agent at the first and second densities onto respective first and second portions of the layer in respective first and second patterns derived from data representing the three-dimensional object to be generated, so that when energy is applied to the layer the build material may coalesce and solidify to form a slice of the three-dimensional object in accordance with the first pattern. The second portion may be in proximity to a boundary of the first portion. Presence of the coalescing agent in the second portion may be to prevent at least some heat from flowing away from the first portion when the energy is applied.

A three-dimensional shaped object using a plurality of materials can be shaped, and replenishment of the materials is implemented during shaping without stopping an apparatus. A three-dimensional laminating and shaping apparatus includes a shaping chamber in which a three-dimensional laminated and shaped object is shaped, at least two material spreaders that are provided in the shaping chamber and spread materials of the three-dimensional laminated and shaped object, at least two material suppliers that supply the materials to the material spreaders, a controller that controls movements of the material spreaders and the material suppliers, and a beam irradiator that irradiates the materials with a beam. The material spreaders and the material suppliers are respectively paired, and the controller controls the movements of the material spreaders and the material suppliers so that each of the material spreaders is supplied, at a predetermined timing, with the material from a paired one of the material suppliers.

A disclosed system includes an additive manufacturing printer that performs a layer by layer three-dimensional printing process generating a casting mold based on a three-dimensional numerical specification. The numerical specification is based on a desired casting shape, including internal features such as hollow areas formed by cores, and is further based on a thermo-mechanical model of a casting process. The numerical specification describes variations in material and geometric properties of one or more layers of the casting mold corresponding to variations in the thermal and mechanical properties of the casting processes, as predicted by the thermo-mechanical model. The system may vary the thickness of features of the casting mold, based on predicted cooling rates, to reduce cooling non-uniformities and to provide for controlled, predictable cooling of the casting. The system may further generate trusses and heat sinks in the mold to respectively strengthen and weaken various features of the mold.