Removing The Boundaries of 3D Printing with Multi-Axis Additive

One of the major value propositions of additive manufacturing (AM) is the ability to create parts with complex geometries that are unable to be manufactured using traditional methods. Parts can be printed with a range of technologies from fused deposition modeling (FDM) to stereolithography (SLA) and even selective laser sintering (SLS). But while the materials are wildly different—extruded plastics, cured liquids and melted powder, respectively—the techniques have traditionally relied on two-dimensional tooling paths on the XY plane with those planar layers stacked in the Z direction. In some situations, this reliance upon planar print layers is a real limitation.

The next step in AM lies with state-of-the-art multi-axis printing and the software tools enabling this revolutionary printing technology.

3D metal printer producing a steel part. (All images provided by Siemens)

There are three major improvements to AM from adopting multi-axis printing operations—gravity can be effectively removed from the variables in printing, part performance under load can be improved, and large parts become far easier to print. Each of these benefits comes from the unique way multi-axis processes deposit material. Implementing multi-axis printing can provide an edge, if not a leading role, in industries looking to optimize complex geometries for performance, efficiency and weight.

Beating Gravity

Additive manufacturing has moved out of the trial phase, where the industry grappled with the basic parameters available for adjustment. Since then, AM has evolved into a valuable process for creating the most complex, most efficient and most unique components available in many industries. Multi-axis printing is the next generation additive manufacturing technology, enabling printed parts that would be difficult, if not impossible, to print with planar methods. Overhangs are a problem with many 3D printing technologies. Gravity causes many printed materials to distort or sag when heat is applied. However, this issue is mitigated when the printed component can be reoriented during printing to cancel gravity-induced distortion. However, resolving the distortion in this way means there is more complexity in creating the deposition paths for printing, requiring a greater dependance on coordinated software and hardware systems.

Using multi-axis printing to eliminate gravity-induced distortion enables more complex internal structures to be printed. Conformal cooling channels, internal vanes, complex lattices, and other hollow or thin-walled structures are possible without a need for support structures. By eliminating the planar production constraint, multi-axis technologies enable superior optimization for the remaining system requirements. This can lead to lighter weight parts, better cooling capacity, higher yield strength or many other positive design attributes. Multi-axis additive manufacturing is taking part design to new realms of complexity and performance.

Improve Stress Performance

In addition to the static stresses from gravity imposed on the print during manufacturing, multi-axis techniques can minimize the impact of loading stresses on a part in the field. Instead of relying exclusively on a planar layering approach, multi-axis can integrate 3-dimensional printing patterns to improve material strength. For example, planar printing often results in parts where stresses in the Z-direction cause the part to separate between layers.

Planar 3D printing often exhibits weakness between layers, where the differing heat characteristics between the previously printed layer and the layer being printed cause weaker bonds. The best solution to prevent this in a planar process is to attempt to optimize the orientation of the component within the print volume to maximize the force dissipation, thereby discouraging delamination failures. While this method can be effective, having the layers of a print aligned in a planar fashion will inherently introduce weakness.

Stress improvements with multi-axis prints are highly dependent on the geometry. However in general, printing in multiple directions improves the overall strength characteristics of a print. Multiple orientation printing allows for complex, continuous deposition paths like helixes where the deposition is moving uninterrupted in the X, Y, and Z directions all at once. This doesn’t alleviate the reduced bond strength between layers, but rather distributes the weakness in more than a single direction, leading to an overall improvement in strength characteristics. Furthermore, a multi-axis tool path may even be optimized to reduce overheating of print regions. Overheating changes the local material structure, providing another avenue for stress failure on top of the sheer planes previously discussed.

Regardless of the material used or method of deposition, multi-axis printing requires a far more nuanced printing path than seen with other technologies. Considerations like the best angle to deposit material, whether movement of the print head will interfere with the component or other systems inside the print area, and how much cooling time is needed before a part can be reoriented to prevent sagging must all be taken into consideration . However, modern software systems, such as multi-axis process simulation tools, feed into the print process to mitigate many of these concerns.

Printing Bigger

Many printing technologies have been limited in size because the final part had to fit within the footprint of the manufacturing machine, just as a CNC machining process is limited by the size of the machine. Large format 3D printing does exist, but the complexities associated with scaling up planar printing has restricted it to niche applications. Planar large format printers often require large gantries with minimal precision and most of the applications were limited to marine, housing, and architectural projects.

But multi-axis breaks away from the limitation of printing within a box while still providing all of the previous benefits of the technology. Rather than creating an enclosed printer large enough to contain the largest print, robotic arm-based machines can provide a more flexible printing area with better cost scaling compared to standard planar printing machines. Eliminating the space constraints associated with planar printing enables larger components for aerospace, marine and a variety of other industries seeking to improve the performance of their products.

Using robotics to print at larger scales also requires complex software to drive the hardware processes. Not only are the length scales very different compared to enclosed printing operations, but robotic arms also produce a very different printing area—resembling a hemisphere if the arm is mounted to the floor rather than the rectangular prism of more traditional printers.

When large format printing is combined with multi-axis machining, the parts produced can even compete with more traditional processes with regards to precision. When scaling up the 3D printing process, precision is created through a combination of software and hardware. The ability of a software package to define deposition paths that work with, rather than against, the part geometry combined with the proper hardware controls is what allows for printing to be scaled to large formats while retaining the necessary precision.

Figure 1 – Printing large format parts often requires multi-axis machines that can deal with parts of larger size.

Deposition paths for multi-axis printing can be very complex and can include a full six degrees of motion, requiring precision in the path definition, but also precision in the ability of the hardware to follow that path. A small deviation that is within tolerance in a normal 3D printer can become a large deviation that is far outside of allowable tolerance when scaled to large format sizes. This is why special software packages have been created to ensure that the deposition paths for large format multi-axis printing are exact. From that point it is the responsibility of the hardware to replicate those deposition paths accurately, and many large format printers use industrial controls for this reason. Over decades of use in CNC processes, industrial controls have been proven to have the accuracy necessary for complex three-dimensional motion. This is why the combination of innovative software and industrial controls is necessary for large-format multi-axis printing.

Making it Real

A great example of the benefits with multi-axis printing comes out of the renewable energy market, in wind turbine repair. The gears transferring the energy captured by the blades into the generator are massive, both figuratively and literally. Re-manufacturing the steel parts requires a large amount of energy even when using recycled material. However, with multi-axis additive, the cost in material and energy is only a fraction of what would be used to make a new gear. And while AM-based repairs have already been applied in other products, the scale of these gears called for multi-axis printing technology.

After grinding down the worn teeth on the gears, it is then rebuilt with AM which requires a rotating mount for the bulky gear and a robotic-arm mounted printer working in tandem. These multiple degrees of motion enable depositing material without regard to gravity. Each tooth on the gear is filled with an alternating deposition path for strength and covered in the steel contact surface for durability. Because this process requires machining, multi-axis printing, and post-processing, a comprehensive software solution is what enables a streamlined workflow to get parts like large turbine gears back in operation as quickly as possible.

Larger, More Complex Parts

Multi-axis printing is on the cutting-edge for additive manufacturing processes, enabling more-complex parts to be printed than were possible before.

Removing gravity as a constraint can refine design intent, because no compensations need to be made in creating once sag-prone geometries. Increased freedom of motion enables manufacturers to forgo planar layered parts, moving instead towards continuous deposition paths for improved stress characteristics. Furthermore, multi-axis printing lets engineers think outside the box, rather than being confined to smaller scales, robotic arms can scale up the manufacturable size of multi-axis printed parts.

Figure 2 – As with most print operations, multi-axis printing often requires post-print machining steps.

Underpinning all of these improvements are a software environment that can handle the new information associated with the processes. Siemens Software’s extensive background in modeling and printing will be highly valuable for companies looking to adopt the next era of printing technology, and we have invested our time and experience in creating a unique solution for multi-axis deposition paths for the future of additive manufacturing.

New Technology Era

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