real time observation of binder jetting printing process using high-speed x-ray imaging

by:INDUSTRIAL-MAN     2019-09-19
A high-
Synchronous Accelerator X
X-ray imaging technology is used to study the manufacture of adhesive injection additives (AM)process.
A commercial binder injection printer with dropletson-demand ink-jet print-
Head is used to print a single line on a powder bed.
Record the printing process in real time using high-highspeed X-ray imaging. The ink-
The jet droplets are in an obvious elongated shape, with a spherical head and a long tail and three to five tail satellite droplets.
Significant drift was observed between the main drop and the impact point of the satellite drop.
The impact of droplets on the powder bed results in the movement and injection of powder particles.
The disturbing depth of motion and injection to the powder bed is defined as the depth of interaction and it is found that this depends on the size, shape and material of the powder particles.
For smaller powder particles (
Less than 10 μm in diameter)
Three consecutive adhesive droplets were observed to combine to form a large reunion.
The observations reported here will help to understand the underlying physics that guides the adhesive injection process, which will help to improve the quality of the parts manufactured using this AM process.
Additive Manufacturing (AM)
Is a disruptive technology that adds material to a layer
A wise way to make complex parts. The layer-by-
The layered approach offers a variety of advantages compared to traditional manufacturing, including the ability to manufacture complex parts, design flexibility, shorter lead time, prototyping, custom items, reduced stock storage and online
Demand manufacturing.
According to the selected process, the material selection of AM is almost unlimited.
With these advantages, AM\'s use in the medical, aerospace, automotive and defense industries is growing rapidly.
ASTM F42 identifies seven categories of AM, and this paper specifically studies the adhesive injection AM.
Adhesive spray AM using iterative ink
Spray printing of adhesive material on powder bed to make parts.
In a typical process, a layer of powder is dispersed to the required thickness, and the adhesive is accurately deposited on the powder bed, applying the adhesive liquid to locally combine the powder particles.
This process is repeated layer by layer, creating a series of 2D crossoversections.
The combined part is cured at low temperatures to produce a \"green\" part that can be used directly as a sand mold, as a component, or as a composite material by penetration of a third material.
Fusion processes such as selective laser melting or photography
Polymerization is mainly used in certain materials (
Metals and polymers for laser/electron beam and light
Aggregation separately)
Although there are some examples of ceramic materials made using a melting process in the literature.
Adhesive injection is used to manufacture metal parts from stainless steel and other ferroalloys, copper and nickel superalloys.
At the same time, the adhesive injection of ceramic parts has also been shown to be: bio-active glass containing ha, titanium acid and titanium acid ba, hench glass containing tricalcium phosphate, Paris plaster, mold containing 12% and silica sand.
The adhesive injection process has many other advantages.
Large heating and cooling rates in laser and electronic injection metal AM processes (
Usually in the order of 10-10 kbps K/s)
It usually results in harmful residual stress and poor microstructure.
Since the adhesive injection process separates the printing process from the subsequent compaction process
Processing steps (
Typical sintering)
It is possible to avoid the microstructure of thermal residual stress and height of the opposite sex.
As with all powder bed AM technologies, the adhesive spray uses the surrounding powder to support the subsequent layers, so there is no need to build the supporting structure of complex parts.
By adding multiple prints-
Head and nozzle, Binder injection can be easily scaled to speed up the printing of large parts.
In addition, functional gradient parts can be manufactured by changing the composition of each layer.
The quality of the adhesive injection components depends on several physical phenomena, including the formation of droplets in the nozzle, the flow and packaging of powder in the powder bed, the powder-
The adhesive interaction of the green part, the curing of the adhesive and the hot sintering.
The process parameters that control these processes can be divided into four different categories: 1.
Powder properties (
Material, shape, particle size distribution), 2.
Binder properties (
Adhesive properties, drop volume, drop velocity, separation between drops, saturation), 3.
Part properties (
Nominal size, direction, location, geometric features of the print bed), and 4. post-
Processing steps.
Some studies have examined the effects of various processing parameters on the density, dimensional accuracy and surface finish of the parts.
However, there is still limited understanding of the underlying mechanisms.
Previous studies used high
Speed visible light imaging to observe the effect of droplets on the powder bed.
It was observed that the particles gathered with the impact of the droplets to form a spherical prototype.
Due to the deformation of the powder bed moving the original body, an impact pit was observed to form around the original body.
In addition, due to the transfer of momentum from the adhesive droplets to the powder particles, it was observed that the particles around the droplets were ejected from the powder bed.
Post-mortem observations of the printing layer also show that from the injection of powder particles close to the printing line, buried printing lines are formed at the surface level of the powder bed.
Previously reported observations were recorded using a continuous jet drop print
Head with significantly different mechanisms of droplet formation-on-demand (DoD)ink-jet print-
Head commonly used on commercial adhesive jet printers.
In addition, optical imaging observations are limited to the surface of the powder bed. Hence, no sub-
Surface information about the dynamics and crushing of the powder bed has been obtained.
Because lines printed using the mod-
It is found that the head is under the surface of the powder bed and must be obtained
Fully understand the surface information of the physical processes involved in the adhesive injection. Therefore, high
Hard X synchronous accelerator
Here, the adhesive injection AM process of various high-space materials is studied using ray imaging technology (≈2u2009m)and temporal (≈5u2009s)resolutions. The X-
The ray image captures the highly dynamic phenomenon inside and outside the powder bed, revealing the different behavior of the adhesive droplets, the collision interaction between the droplets and the powder bed, and the powder movement after the impact.
Quantitative Experimental data provide important insights into the adhesive injection process, which not only helps reduce defects and improve the quality of adhesive injection components, but also helps to develop and validate numerical models.
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