Key Technologies to Improve the Performance and Precision of Binder Jetting Metal Parts

　　General size accuracy of binder jetted metal parts is usually within ± 0.1 mm/100 mm, reaching a maximum of ± 0.05 mm, with roughness ranging from 3 to 5 micrometers, and a maximum of 2 micrometers, but this may sacrifice some printing speed. Compared to Selective Laser Melting (SLM) technology, BJ has significant advantages in roughness. Currently, the density of BJ parts is > 99%. In the past, BJ was often described as having low accuracy and poor performance.

　　This article is divided into three parts:

　　I. Analysis of Influencing Factors

　　There are seven main factors affecting the accuracy of BJ technology, including:

• 　　Mechanical accuracy
• 　　Motion control
• 　　Data accuracy: Data accuracy affects part accuracy because data is usually described by raster data. Higher resolution means higher accuracy, but also larger data processing and storage content. Additionally, higher resolution means more adhesive droplets and volume. If the volume of adhesive is too high, it will significantly affect the printing process.
• 　　Inkjet accuracy: Inkjet positioning accuracy is a unique accuracy factor of BJ technology. The size and speed of adhesive droplets affect positioning accuracy. Larger and heavier droplets improve accuracy but affect powder beds, leading to surface roughness. Adjusting the appropriate droplet size and speed reduces the impact.
• 　　Binder droplet penetration: Binder droplet penetration directly affects the accuracy of the powder bed boundary and even the bottom surface. If properly controlled, the entire surface of the part will be smooth after de-powdering.
• 　　Shrinkage deformation: BJ technology involves sintering, and uniform shrinkage is easy to compensate for through software. Non-uniform shrinkage significantly affects printing accuracy, which can be addressed by considering powder uniformity, density, and shape retention.
• 　　Nozzle defects

　　Nozzle clogging is a persistent issue in BJ technology. Many manufacturers are committed to addressing nozzle clogging and tilted spraying.

　　EASYMFG has a set of methods to solve factors affecting accuracy, including:

• 　　Online data processing: Solving the problem of large data volume and low memory usage. Different resolutions can be used for contour surfaces and internal entities to facilitate data processing, and partitioned data processing, transmission, and printing can reduce storage content.
• 　　Waveform control: Achieving stable inkjetting and reducing the influence of environmental wind speed on the ink droplet motion curve. Adjusting adhesive droplets to appropriate inkjet speeds reduces the influence of powder beds.
• 　　Penetration control: Achieving similar accuracy and roughness on all sides of the part (top, bottom, left, and right).
• 　　New powder laying methods: Compatible with powders of different shapes and diameters, improving the uniformity and density of powder laying.
• 　　Nozzle anti-clogging printing
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　　Factors affecting part performance

• 　　Various factors affect part performance. Here are four main factors affecting part performance:
• 　　Sintering activity of powder: The sintering activity of powder is a key factor determining the final part performance. The activity of powder can affect the density and strength of the sintered part.
• 　　Green density: Generally, the higher the density of the green part, the lower the shrinkage rate and the lower the likelihood of deformation. Therefore, controlling the density of green parts during manufacturing is crucial.
• 　　Binder residue: The amount of binder residue left in the part after sintering affects its performance. Less residue is better. Even with residue, it does not significantly affect the performance of the part.
• 　　Cleanliness of the sintering furnace: The cleanliness of the sintering furnace also affects the performance of the part. Different materials may require different sintering furnaces.

　　Solutions corresponding to these factors include:

• 　　High-density powder laying method: It is essential to use compacting mechanisms to achieve high-density powder laying.
• 　　Low-residue adhesive: Using adhesives with almost no residue during high-temperature decomposition can minimize any negative effects of residue.
• 　　Grain refinement additives: Adding grain refinement additives can effectively slow down grain growth during high-temperature sintering, improving part performance.
• 　　High-cleanliness sintering furnace: Using sintering furnaces with low volatile substances in the furnace chamber and heating components can help maintain a clean environment and achieve better part performance.

　　II. Key Technology Analysis

　　1. Printing Data Processing Software (RIP)

　　Printing data processing software is crucial for the success of BJ Metal 3D printing. This software converts sliced contour data into bitmap data that the printer can accept. Several functions are essential for printing data processing software:

　　Region-based data processing: For large-sized and high-precision data, the data volume may be enormous. Assuming the part size is 700mm x 700mm with a resolution of 1200x1200 DPI. In this case, monochrome bitmap data reaches 1.02 GB, and full-color bitmap data reaches 3.06 GB. If only one layer of data can be calculated and stored at a time, the memory usage during computer operation will typically double, making the computer overwhelmed. Region-based data output gradually outputs printing data in a region-based manner during printing, meaning that data processing is performed simultaneously with printing. This method achieves "large data with small memory processing", enabling processing of larger sizes and higher resolutions of data, allowing the printer to print normally.

　　Online data processing: Offline data processing does not allow real-time calculation and transmission of printing data in a region-based manner. This issue may not be exposed in small-sized machines, but for large-sized and high-precision printing, online real-time data processing is needed to ensure normal computer operation.

　　3D printing requires high precision in part size accuracy, and RIP algorithms used in the traditional inkjet printing industry use interpolation to improve printing resolution, which can improve color fidelity. However, interpolation methods cannot guarantee the physical position accuracy of bitmaps. Full mapping data processing technology maps high-precision bitmap data to every physical position actually sprayed by the nozzle without any data errors.

　　2. Binder Volume Adjustment Technology

　　Controlling the size and shape of droplets is often necessary, but adjusting droplets is far from enough. The volume of adhesive also needs to be controlled. BJ metal printing is very sensitive to the amount of adhesive; too much or too little adhesive per layer will affect printing quality. EasyMFG uses waveform modulation technology to control droplet size of the printhead. Then, it distinguishes contour areas (accuracy description) and filling areas (strength and adhesive volume description) used for droplet adjustment to achieve fine adhesive volume control.

　　3. Precision Contour Reproduction Technology: Internal Offset Contour Algorithm

　　Printing defects can lead to poor local inkjetting, thereby affecting the performance of parts. However, using printing control technology, blockages can be avoided by adjusting the data printed by each nozzle using RIP algorithms during each printing session. This technology also randomly rearranges the positions of nozzles on the current layer and upper and lower layers during printing, dispersing defects within the part instead of accumulating them in one position, effectively avoiding local inkjetting defects caused by nozzle blockages that lead to fractures.

　　In BJ metal printing, the printing spraying area is divided into two zones: contour and fill, both obtained from the vector data of model slicing. The amount of inkjetting in the contour area directly affects the horizontal penetration of the adhesive, leading to larger part sizes.

　　Contour Width: Setting a certain width for the contour may cause an "outward shift" beyond the actual contour area (as shown in the red area on the right in the figure), directly resulting in part "overflow" and larger dimensions. Additionally, the contour may appear too thick, or adjacent contours may "touch" and lose detail.

　　Internal Offset Contour Algorithm: Traditional contour offset algorithms compensate for horizontal sheet penetration and pen width offset, but due to inherent flaws in offset algorithms, contour details may be lost, resulting in unclear or incorrect details in the part. The internal offset contour (optical plate compensation) algorithm only "widens" the interior of the contour based on contour vector data, without affecting the contour data. The final contour data is displayed in the black area on the right.

　　4. Adaptive Anti-clogging Technology

　　Printing defects can lead to poor local inkjetting, thereby affecting the performance of parts. However, using printing control technology, blockages can be avoided by adjusting the data printed by each nozzle using RIP algorithms during each printing session. This technology also randomly rearranges the positions of nozzles on the current layer and upper and lower layers during printing, dispersing defects within the part instead of accumulating them in one position, effectively avoiding local inkjetting defects caused by nozzle blockages that lead to fractures.

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　　Printing effects at blockage 40% are observed

　　5. Fully Automatic Powder Feeding and Spreading System

　　The M400Pro uses a fully automatic powder feeding and spreading system that features high powder compatibility, high-density powder spreading, uniform powder spreading, and an integrated "powder valve" developed in-house, which ensures free powder transmission shutdown. The entire powder spreading mechanism uniformly spreads the powder over the entire working surface and then compacts it.

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　　High-Density Shaped Powder

　　The M400Pro uses high green metal powder with reduced particle size, which increases the sintering activity and the loose packing density to ensure fluidity. Additionally, the spherical shape of the high shaped metal powder is retained by combining water-gas combined atomization powder and gas atomization powder, which improves the powder flowability for easy spreading.

　　6. Low-Residue Environmentally Friendly Water-Based Binder

　　The M400Pro uses a binder that is environmentally friendly and has little residue during high-temperature sintering. The binder's penetration rate needs to be controlled within a certain range, and different binders are generally used for different powders.

　　III. New Equipment that Integrates Various Technologies

　　The M400Pro, a third-generation BJ printing equipment from EasyMFG, integrates various technologies to create a system that is highly automated and closed-loop. The equipment has not been officially launched yet.