NTU Singapore: Robotic Post-Processing System Removes Residual Powder from 3D Printed Parts

Researchers from Nanyang Technological University in Singapore wrote a paper, titled “Development of a Robotic System for Automated Decaking of 3D-Printed Parts,” about their work attempting to circumvent a significant bottleneck in 3D print post-processing. In powder bed AM processes, like HP’s Multi Jet Fusion (MJF), decaking consists of removing residual powder that sticks to the part once removed. This is mostly completed by human operators using brushes, and for AM technologies that can produce hundreds of parts in one batch, this obviously takes a long time. Manual labor like this is a significant cost component of powder bed fusion processes.

An operator manually removing powder (decaking) from a 3D printed part.

“Combining Deep Learning for 3D perception, smart mechanical design, motion planning, and force control for industrial robots, we developed a system that can automatically decake parts in a fast and efficient way. Through a series of decaking experiments performed on parts printed by a Multi Jet Fusion printer, we demonstrated the feasibility of robotic decaking for 3D-printing-based mass manufacturing,” the researchers wrote.

A classic robotic problem is bin-picking, which entails selecting and removing a part from a container. The NTU researchers determined that 3D perception, which “recognizes objects and determining their 3D poses in a working space,” would be important in building their bin-picking system. They also used a position-controlled manipulator as the baseline system to ensure compliant motion control.

The NTU team’s robotic system performs five general steps, starting with the bin-picking task, where a suction cup picks a caked part from the origin container. The underside is cleaned by rubbing it on a brush, then flipped over, and the other side is cleaned. The final step is placing the cleaned part into the destination container.

Proposed robotic system design for automated decaking.

Each step has its own difficulties; for instance, caked parts overlap and are hard to detect, as they’re mostly the same color as the powder, and the residual powder and the parts have different physical properties, which makes it hard to manipulate parts with a position-controlled industrial robot.

“We address these challenges by leveraging respectively (i) recent advances in Deep Learning for 2D/3D vision; and (ii) smart mechanical design and force control,” the team explained.

The next three steps – cleaning the part, flipping it, and cleaning the other side – are tricky due to “the control of the contacts” between the parts, the robot, and the brushing system. For this, the researchers used force control to “perform compliant actions.”

Their robotic platform made with off-the-shelf components:

  • 1 Denso VS060: Six-axis industrial manipulator
  • 1 ATI Gamma Force-Torque (F/T) sensor
  • 1 Ensenso 3D camera N35-802-16-BL
  • 1 suction system powered by a Karcher NT 70/2 vacuum machine
  • 1 cleaning station
  • 1 flipping station

The camera helps avoid collisions with the environment, objects, and the robot arm, and “to maximize the view angles.” A suction cup system was found to be most versatile, and they custom-designed it to generate high air flow rate and vacuum in order to recover recyclable powder, achieve sufficient force for lifting, and firmly hold the parts during brushing.

Cleaning station, comprised of a fan, a brush rack, and a vacuum outlet.

They chose a passive flipping station (no actuator required) to change part orientation. The part is dropped down from the top of the station, and moves along the guiding sliders. It’s flipped once it reaches the bottom, and is then ready to be picked by the robot arm.

Flipping station.

A state machine and a series of modules make up the software system. The machine chooses the right module to execute at the right time, and also picks the “most feasible part” for decaking in the sequence.

The software system’s state machine and modules perform perception and different types of action.

“The state machine has access to all essential information of the system, including types, poses, geometries and cleanliness, etc. of all objects detected in the scene. Each module can query this information to realize its behavior. As a result, this design is general and can be adapted to many more types of 3D-printed parts,” the researchers explained.

The modules have different tasks, like perception, which identifies and localizes visible objects. The first stage of this task uses a deep learning network to complete instance detection and segmentation, while the second uses a segmentation mask to extract each object’s 3D points and “estimate the object pose.”

Example of the object detection module based on Mask R-CNN. The estimated bounding boxes and part segmentations are depicted in different colors and labelled with the identification proposal and confidence. We reject detection with confidence lower than 95%.

“First, a deep neural network based on Mask R-CNN classifies the objects in the RGB image and performs instance segmentation, which provides pixel-wise object classification,” the researchers wrote.

Transfer learning was applied to the pre-trained model, so the network could classify a new class of object in the bin with a high detection rate.

“Second, pose estimation of the parts is done by estimating the bounding boxes and computing the centroids of the segmented pointclouds. The pointcloud of each object is refined (i.e. statistical outlier removal, normal smoothing, etc.) and used to verify if the object can be picked by suction (i.e. exposed surfaces must be larger than suction cup area).”

Picking and cleaning modules are made of multiple motion primitives, the first of which is picking, or suction-down. The robot picks parts with nearly flat, exposed surfaces by moving the suction cup over the part, and compliant force control tells it when to stop downward motion. It checks if the height the suction cup was stopped at matches the expected height, and then lifts the cup, while the system “constantly checks the force torque sensor” to make sure there isn’t a collision.

Cleaning motion primitives remove residual debris and powder from nearly flat 3D printed parts. The part is positioned over the brush rack, and compliant force control moves the robot until they make contact. In order to maintain contact between the part and the brushes, a hybrid position/force control scheme is used.

“The cleaning trajectories are planned following two patterns: spiral and rectircle,” the researchers explained. “While the spiral motion is well-suited for cleanning nearly flat surfaces, the rectircle motion aids with removing powder in concave areas.”

A combination of spiral and rectircle paths is used for cleaning motions. Spiral paths are in red. The yellow dot denotes the centroid of the parts at beginning of motion. Spiral paths are modified so they continue to circle the dot after reaching a maximum radius. The rectircle path is in blue, parameters include width, height, and direction in XY plan.

The team tested their system out using ten 3D printed shoe insoles. Its cleaning quality was evaluated by weighing the parts before and after cleaning, and the researchers reported the run time of the system in a realistic setting, compared to skilled human operators.

In terms of cleaning quality, the robotic system’s performance was nearly two times less, which “raised questions how task efficiency could be further improved.” Humans spent over 95% execution time on brushing, while the system performed brushing actions only 40% of execution time; this is due to a person’s “superior skills in performing sensing and dexterous manipulations.” But the cleaning quality was reduced when the brushing time was limited to 20 seconds, which could mean that the quality would improve by upgrading the cleaning station and “prolonging the brushing duration.”

Additionally, humans had more consistent results, as they are able to adjust their motions as needed. The researchers believe that adding a cleanliness evaluation module, complete with a second 3D camera, to their system would improve this.

Average time-line representation of actions used for cleaning.

“We noted that our robot ran at 50% max speed and all motions were planned online. Hence, the sytem performance could be further enhanced by optimizing these modules,” the team wrote. “Moreover, our perception module was running on a CPU, implementations of better computing hardware would thus improve the perception speed.”

While these results are mainly positive, the researchers plan to further validate the system by improving its end-effector design, optimizing task efficiency, and adapting it to work with more general 3D printed parts.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below. 

The post NTU Singapore: Robotic Post-Processing System Removes Residual Powder from 3D Printed Parts appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Is This the Best Way to Manually Post-Process an FDM 3D Printed Part?

Researchers Jinjin LiuHai GuBin LiLu ZhuJie Jiang, and Jie Zhang from the Nantong Institute of Technology and Jiangsu Key Laboratory of 3D Printing Equipment and Application published a paper, titled “Research on Artificial Post-Treatment Technology of FDM Forming Parts,’ about using manual post-processing on 3D printed parts made with FDM technology, which has a low molding accuracy that can cause stair-stepping.

“Due to the “step effect”, the printed parts have rough surface, obvious stripes, poor surface quality, and cannot meet the customer’s or specified requirements, so post-processing is very important. This paper mainly studies and summarizes the manual post-processing technology of FDM printed parts, and provides the specific implementation method of post-processing, providing reference for the post-processing of FDM formed parts and other forming processes,” the researchers wrote.

Figure 2. The vase model.

In order to “further improve the surface quality and strength” of 3D printed models, post-processing is often necessary. Some of the more common methods of post-processing FDM formed parts include:

  • Chemical treatment with organic solvent
  • Heat treatment
  • Mechanical treatment with a sander or grinder
  • Surface coating treatment

In this paper, the researchers focused on a manual post-treatment process, which requires several items to work properly, such as a spray pen air pump with air storage tank, a coloring pen and tool set, gloves, a mask, water-diluted solvent in a solvent bottle, quick dry small fill soil, 80 to 3000 mesh sandpaper, a cleaning agent, a file, and others.

The team fabricated a post-treatment vase model as an example, using PLA material and an Einstart 3D printer. Once the vase was printed, they removed the plate with the model on it from the printer.

Figure 4. Model finished printing. Figure 5. Demolition of support.

“…the model is smoothly removed from the bottom plate with a shovel, and then to check whether there is strain concentration model, relatively weak parts with small first stripping knife to spin out the model and the support, and then has a long nose pliers clamping a direction support, applying a constant force, the location of the tiny support can use the file to remove,” they wrote.

To clean up a rough surface, the researchers noted that you can use low mesh sandpaper to sand and polish it. The model and the low mesh sandpaper should be immersed in water and sanded along the model’s texture, as this can both extend the sandpaper’s life and smooth out the model’s surface.

Then, they moved on to a technique called quick dry small fill, which involves the addition of a small amount of filling material to gaps in the model; then, the fill is evenly daubed with a hard scraper.

Figure 7. Apply small patch of soil evenly. Figure 8. Polished to make it smooth.

“Then wait for 30 seconds, after filling soil has hardened, using 1200 mesh to 1500 mesh sandpaper in, as shown in figure 8, If there are still tiny grooves and repeat the above steps,” the researchers wrote. “To be in addition to the groove after no large-area fill soil, feel smooth, can proceed to the next step.”

The next step is spray can water fill soil spraying. First, the model’s surface should be washed with water, and then the spray pot is used to fill the soil, before the model is wiped with a non-woven cloth and sprayed at “the ventilated position,” keeping the nozzle at about 20 cm and uniformly spraying the model one to three times, quickly.

“Generally, choose gray spray pot water to fill the soil, because gray is a neutral color,” the team explained.

Figure 10. High mesh sandpaper grinding.

Once the water is sprayed and the soil is filled, air drying takes place. Then, 2000-3000 high-mesh sandpaper is applied for “slight grinding” along one direction, before moving on to the coloring phase.

The 3D printed, polished and processed model should first be washed and dried before pigments are applied. A spray gun can be used to add either a base color or one that covers a large area of the model; you’ll need a 1:2 ratio of diluent to pigment for spraying, and you should be able to adjust the amount of air injection while you’re spraying.

“Brushes of different thicknesses and sizes can be used to paint the details,” the team wrote. “It is accessible to use 00000 pens to paint the detailed parts of the figures, or use different widths of the cover tape to cover and then spray the spray gun to paint.”

Once the paint and spray paint have dried completely, you can uniformly spray protective paint on the model; the research team used B603 water-based extinction for their 3D printed vase.

The team shared a few more notes on making the post-treatment process run smoothly, such as the importance of using software to reduce the amount of unnecessary support structures, coating the print plate with a thin layer of glue to prevent deformation, and observing the model while it’s being printed.

Figure 13. The vase is finished after processing.

“Secondly, in the manual post-processing should look to the protection work, grinding water mill is the best way to model processing, be patient, 80-2500 mesh, use each mesh sandpaper required time from long to short, low mesh sandpaper grinding along the texture of the model, high mesh sandpaper grinding should be turned around,” the researchers concluded. “When mixing colors, you should understand in advance the relationship between light and shade, brightness and purity of various colors, warm and cold color selection, etc.”

They noted that “the degree of difficulty” for post-processing methods, and the methods themselves, can vary with different 3D printing technologies – what works for FDM may not necessarily work for SLA, and so on.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the comments below.

The post Is This the Best Way to Manually Post-Process an FDM 3D Printed Part? appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

3D Printing News Briefs: February 22, 2019

We’ve got some exciting dental news to share first in today’s 3D Printing News Briefs – Stratasys just announced its new full-color dental 3D printer at LMT Lab Day. Moving on, Farsoon has been busy developing an advanced pure copper laser sintering process, and Aether is working with Procter & Gamble on a joint development project. DyeMansion has announced a new UK distributor for its products, and three researchers address the challenges of adopting additive manufacturing in a new book about best practices in the AM industry.

Stratasys Introduces Full-Color Dental 3D Printer

This week at LMT Lab Day Chicago, the largest dental laboratory event in the US, Stratasys has introduced its new full-color, multi-material J720 Dental 3D printer which lets you have 500,000 color combinations for making very high resolution, patient-specific models. Its large build tray can print six materials at the same time, and it’s backed by GrabCAD Print software.

“Labs today operate in a very competitive space where differentiation counts on mastering the digital workflow and expanding into new products and services. The J720 Dental 3D Printer is designed to change the game – allowing levels of speed, productivity and realism the market has never seen,” said Barry Diener, Dental Segment Sales Leader for Stratasys. “This powers laboratories to meet the demands of a competitive market and push the boundaries of digital dentistry.”

See the new J720 Dental 3D printer at LMT Lab Day Chicago today and tomorrow at Stratasys Booth A9. It’s expected to be available for purchase this May.

Farsoon 3D Printing Pure Copper

Pure copper heat exchanger

Two years ago, after Farsoon Technologies had introduced its metal laser sintering system, the company’s application team began working with industrial partners to develop an advanced 3D printing process that could additively produce components made of pure copper. Copper is a soft, ductile metal with both high electrical and thermal conductivity, and it’s often used in industries like shipbuilding, electronics, automotive, and aerospace. But most additive copper is based on alloys, and not the pure metal itself, which is hard for lasers to regularly and continuously melt and can cause problems like thermal cracking and interface failure.

That’s why Farsoon’s work is important – all of its metal laser sintering systems can successfully create cost-effective, high-quality pure copper parts. The company’s process and unique parametric design is able to meet custom needs of customers, and to date, it’s launched 13 process parameters for metal powder sintering, including pure copper. Some of the parts that have come out of Farsoon’s recent collaborations include a pure copper heat exchanger, which featured a 0.5 mm wall thickness, complex spiral geometry and was printed in a single piece. Farsoon is open for additional partners seeking to further develop the 3D printing of pure copper and other specialized materials.

Aether and Procter & Gamble Begin Joint Development Project

Aether CEO Ryan Franks and Director of Engineering Marissa Buell with an Aether 1

San Francisco 3D bioprinting startup Aether has entered into a two-year joint development agreement with Procter & Gamble (P&G) in order to develop 3D printing and artificial intelligence technologies. The two will use the multi-material, multi-tool Aether 1 3D printer as a technology creation platform, and will create several hardware and software capabilities that hope to automate and improve P&G’s product research applications and develop a next-generation Aether 3D printer. An interconnected network of computer vision and AI algorithms aims to increase automation for multi-tool and multi-material 3D printing, while high-performance cameras will enable new robotics capabilities. Aether is also working on additional software that will help P&G automate and speed up image processing.

“Aether is working with P&G to completely redefine 3D printing.  It’s no longer going to be just about depositing a material or two in a specific pattern. We’re building something more like an intelligent robotic craftsman, able to perform highly complex tasks with many different tools, visually evaluate and correct its work throughout the fabrication process, and constantly learn how to improve,” said Aether CEO and Founder Ryan Franks.

DyeMansion Names New UK Distributor

3D print finishing systems distributor DyeMansion, headquartered in Munich, announced that Cheshire-based 3D printing services supplier Europac3D will be the UK distributor for its range of machines. Per the agreement, Europac3D will now offer all of the AM finishing systems in DyeMansion’s Print-to-Product workflow, which includes its Powershot C powder blasting system, DM60 industrial coloring system, and the PowerShot S, which delivers homogeneous surface quality to 3D printed, powder-based plastics. Because of this, Europac3D is one step closer to achieving its mission of being a one-stop shop for 3D printing, scanning, and post-processing services.

“DyeMansion’s post-production systems are worldclass and add the all important finish to additive manufacturing,” said John Beckett, the Managing Director of Europac3D. “Their systems are perfect for companies or 3D print bureaus that have multiple SLS or HP 3D printers and allow us to extend our offer by providing market leading additive manufacturing finishing systems for 3D-printed polymer parts.”

New 3D Printing ‘Best Practices’ Book

We could go on and on about the many benefits offered by 3D printing (and we do), but there are still industry executives who remain unconvinced when it comes to adopting the technology. But a new book, titled “Additive Manufacturing Change Management: Best Practices” and released today, is here to provide some guidance for those still holding back. The book, which addresses some of the challenges of adopting 3D printing, was published by CRC Press as part of its Continuous Improvement Series and written by Dr. Elizabeth A. Cudney, an associate professor of engineering management and systems engineering at the Missouri University of Science and Technology, along with Divergent 3D’s VP of Additive Manufacturing Michael Kenworthy and Dr. David M. Dietrich, who is an Additive Manufacturing Engineering Design Fellow for Honeywell Aerospace and Dr. Cudney’s former doctoral student.

Dr. Cudney said, “If company leaders are interested in bringing additive manufacturing online, this book can help them decide if it makes sense for their industry.

“There’s often a lack of planning, a lack of understanding, a resistance to change and sometimes fear of the unknown. Our hope is that this book will provide a good road map for managers to advance additive manufacturing at a faster pace.

“We wanted to take a look at how companies can roll out a new technology, new processes and equipment and integrate that in such a way that you have a good product in the end.”

In the 17-chapter book, the authors present what Dr. Cudney refers to as a ‘road map’ for business leaders looking to adopt 3D printing. The eBook format costs $52.16, but if you want that shiny new hardcover version, it will set you back $191.25.

Discuss these stories and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the Facebook comments below.