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22 March 2018 12:26
All You Need to Know About Metal Binder Jetting
Following our introductory guide to Binder Jetting last week, today we’ll be taking a look at Metal Binder Jetting, a technology that offers a variety of applications and versatile solutions. Widely used in a range of industries, including automotive, dental, healthcare, aerospace, jewellery and luxury fashion, metal Binder Jetting is particularly ideal for end-use production of low-cost, lightweight parts and small components with complex designs.
This guide will cover the benefits and limitations of metal Binder Jetting, the post-processing steps required and practical tips on getting the most out of the technology.
Post-processing Steps for Metal Binder Jetting
Traditional binder jetting technology works by using a print head to apply a liquid binding agent onto layers of powder.
When printing metals with Binder Jetting technology, however, the parts will require various post-processing steps as they are initially printed in their green state, which means that they possess low mechanical properties and are very often weak and brittle. The post-processing stage aims to strengthen the parts, and includes curing, sintering, infiltration and other finishing processes.
Curing increases the strength of the green parts so they can be safely removed from the printing bed. During the process the parts are hardened off in an oven at roughly 200°C for a period of several hours, resulting in much stronger parts.
Despite the curing, your metal parts will still be highly porous. However, you can significantly reduce the porosity of the parts through sintering or infiltration processes. Typically the sintering process takes place in a furnace with a controlled atmosphere, where the part is heat treated at roughly 100°C for 24–36 hours and the binding agent burnt away. This helps to fuse the metal particles together and results in strong metal part with a low porosity. Sintering, however, can cause non-homogenous shrinkage to the part and can be hard to predict – this must therefore be taken into consideration at the design stage.
To achieve high density, the part will need to be infiltrated to fill the voids left by the binding agent being burnt away. This is usually done by applying molten bronze to infiltrate the remaining voids in the part. Undergoing these post-processing steps will significantly enhance the mechanical properties of the metal part; for example, bronze infiltration of stainless steel can achieve a final density of 95%.
Finally, although optional, the part can be polished and plated with gold or nickel allowing aesthetically pleasing surface finishes.
The Benefits of Metal Binder Jetting
As a versatile AM technology with a range of industrial applications, metal Binder Jetting provides numerous advantages industrial AM:
- Metal Binder Jetting allows for the production of metal parts with complex geometries thanks to the large build size of binder jetting machines and the fact that no support structures are required.
- Metal Binder Jetting is significantly less expensive than its counterparts, namely DMLS and SLM. It is therefore ideal for low to medium volume production where high-performance parts are not a requirement. For metal objects with complex, intricate details and designs, it is therefore worth considering metal Binder Jetting.
- Metal Binder Jetting produces minimal waste as the metal powder is bonded selectively and any excess powder can be subsequently reused.
- The volume of the build platform of metal Binder Jetting machines makes it ideal for printing several parts in the same powder bed at once. In fact, current metal Binder Jetting printers, such as Digital Metal’s high-precision binder jet metal AM system, are able to produce a large quantity of small parts with great accuracy.
The Limitations of Metal Binder Jetting
In spite of the numerous advantages of metal Binder Jetting, there are a few factors that are worth taking into consideration:
- A key limitation of metal Binder Jetting is that the parts produced have a high porosity, resulting in weak mechanical properties, particularly when compared to DMLS and SLM. As a result, this technology unsuited to high-end applications. So where high part performance is a requirement, it is advisable to use DMLS or SLM.
- After printing the printing process, the part remains in what is termed a “green” state, and therefore requires secondary post-processing. It’s worth considering that post-processing will inevitably add considerable time and cost to the overall production process, so this should be taken into consideration beforehand. Additionally, metal Binder Jetting can also produce parts with a rough surface finish. Although the imperfections of the surface can be smoothed by post-machining (CNC machining or manual surface grinding, sandblasting, or polishing), this will also take additional time and cost.
Metal Binder Jetting: An Ideal Solution for Low Cost Metal Parts
Overall, metal Binder Jetting is an ideal AM technology for producing complex metal parts with almost full density at a significantly lower cost than DMLS or SLM technologies. With a wide range of materials to choose from, this is one technology that affords you greater flexibility.