Binder Jetting is an indirect metal 3D printing technology in which metal powders and binders are bonded layer by layer to form a part blank, and then a metal part is manufactured through a degreasing and sintering process.
This production system is quite close to powder metallurgy (including metal injection molding process, MIM), but it does not use molds in its manufacturing process. This technology will enable manufacturers to significantly reduce their costs, making this technology an alternative to casting.
This indirect metal 3D printing process has aroused the interest of automakers. For example, Volkswagen will use HP's binder jet metal 3D printing technology to first carry out mass customization and the manufacture of decorative parts, and plans to use this technology as soon as possible. The structural components are integrated into next-generation vehicles, and focus on the ever-increasing component sizes and technical requirements.
However, before the binder jet metal 3D printing technology moves towards mass production applications, effective control of sintering deformation is a problem that must be solved. Using simulation software to control sintering deformation instead of trial and error and empirical judgment is an obvious trend in the field of binder jet metal 3D printing.
Desktop Metal, a technological innovation company in the field of binder spray metal 3D, recently launched Live Sinter, a simulation software for sintering deformation control. The software will first be delivered to users of its workshop system Shop System (delivered at the end of 2020) and Production System (delivered in 2021).
The challenge of sintering
Sintering is a key step in powder metallurgy manufacturing processes (including binder jet metal 3D printing). The sintering process heats the part close to melting to give it strength and integrity, but this process usually shrinks the part, shrinking by up to 20% relative to its original 3D printed or molded size. During the sintering process, improperly supported parts will also face a great risk of deformation, which will cause the parts to crack or deform from the furnace or require expensive post-processing to achieve dimensional accuracy.
For decades, sintering deformation has been a reality in the powder metallurgy industry. For most of the time, the solution has been to combine part design adjustments with various sintered supports or "fixers" by experienced people through repeated trial and error and experience to achieve stable mass production.
Change the rules of the game
According to Desktop Metal, the Live Sinter simulation software will change the rules of the game through simulation technology by minimizing the dependence on trial and error. With the blessing of this software, users do not need to be powder metallurgy experts, but can also manufacture accurate parts.
Live Sinter can not only correct the shrinkage and deformation that are usually encountered during the sintering process, but also reduce the challenges of creating complex geometric structures with the binder jet metal 3D printing technology. By improving the shape and dimensional tolerances of the sintered parts, the complex geometry is improved The first success rate of shaped parts, and the first success rate of parts with complex geometric shapes.
Desktop Metal states that in many cases, the software can even support part sintering without the use of supports/locators.
"Negative offset" geometry can compensate for distortion
Live Sinter can be calibrated for a variety of alloys. It can predict the shrinkage and deformation of the part during the sintering process, and automatically compensate for this change, thereby creating a "negative offset" geometric shape, which will be sintered to the original expected design specifications after printing. The software can actively pre-deform the geometry of the part with a precise amount in a specific direction, so that it can achieve the desired shape during sintering.
Sintering simulation is a complex multiphysics problem, involving how the modeled parts and materials respond to many factors, including gravity, shrinkage, density changes, elastic bending, plastic deformation, friction resistance, etc. In addition, the thermodynamic and mechanical transformations that occur during the sintering process occur under intense heat, so it is difficult to observe them without stopping the sintering process or observing the deformation of the high-temperature captured image.
But this kind of method may be acceptable in new product development and application, but due to the severe delay in production time, this kind of method is difficult to accept in mass production applications.
The Live Sinter software is designed to meet the challenges of sintering and provide additive manufacturing engineers with fast and predictable sintering results. According to Desktop Metal's data, the simulation results can be completed in five minutes, while the negative offset geometry can be completed in twenty minutes.
High-speed simulation
Live Sinter can perform high-speed simulation prediction of sintering, which is related to GPU and simplified calibration.
Live Sinter runs on a GPU-accelerated multi-physics engine and can model the collision and interaction between hundreds of thousands of connected particle masses and rigid bodies. The dynamic simulation of the multi-physics engine has been improved using integrated meshless finite element analysis (FEA), which can calculate the stress, strain and displacement between part geometries, not only to predict shrinkage and deformation, but also to predict risk And failure. The feasibility of sinter-based additive manufacturing of parts is verified before starting.
With this dual-engine method that balances speed and accuracy, Live Sinter can simulate a typical sintering furnace cycle in five minutes compared to a general simulation tool that uses complex grids and requires complex settings and man-hours to complete , And generate a negative offset geometry to compensate for shrinkage and deformation within twenty minutes. In addition, the software can be calibrated compatible with new materials, sintering hardware, and process parameters.
The Live Sinter sintering process simulation software will be available to users of Desktop Metal's binder jet metal 3D printing system starting in the fourth quarter of 2020, as well as any sinter-based powder metallurgy process.
Compared with the PBF powder bed-based selective laser melting metal 3D printing process, the Binder Jetting metal 3D printing technology has several key advantages: more economical powder materials (similar to the metal powder materials used in the MIM process ); Efficient printing speed is suitable for mass production applications, including automobiles, aircraft parts, and medical applications.
Binder Jetting metal 3D printing technology is unique compared to almost all other metal 3D printing processes because it does not generate a lot of heat during the 3D printing process. This makes high-speed printing possible and avoids the problem of residual stress in the metal 3D printing process.
Binder Jetting Binder Jetting metal 3D printing technology transfers the thermal processing process to the sintering step, which makes it easier to manage thermal stress because the sintering temperature is lower than the complete melting temperature required in other types of metal 3D printing processes, and the heat can be Apply more evenly. However, this does not completely eliminate the challenges of temperature gradients and residual stress.
Binder Jetting metal 3D printing technology has the potential to replace low-volume, high-cost metal injection molding. It can also be used to produce complex and lightweight metal parts in other fields (such as gears or turbine wheels), greatly reducing the cost of 3D printing. And shorten the delivery time.
But managing and compensating for the massive shrinkage that occurs during the sintering stage is one of the biggest challenges facing Binder Jetting's 3D printing technology. The parts shrink by 30-40% in the furnace and linearly shrink by 15-20%. If the part is small and the wall thickness is uniform, the shrinkage can be predicted.
However, the sintering process of large parts with different thicknesses will cause very complicated geometric problems. According to Bering 3D's market research, sintering shrinkage currently severely limits the applicable geometry and application types of Binder Jetting metal 3D printing technology.
These shortcomings of binder jet metal 3D printing technology are gradually disappearing in the development of simulation software. Internationally, general-purpose simulation software companies and sinter-based indirect metal 3D printing technology companies have introduced sintering simulation technology to the market.
When manufacturers hope to use the flexibility of sintering-based indirect metal 3D printing technology for mass production, such as binder jetting, simulation reveals the "mystery" of the sintering process and becomes the key "companion" to this type of indirect metal 3D printing technology.