Printing metal components in 3D is gaining in popularity. This is partly because it often reduces production time while improving part quality. Its growth is also due to the use of generative design tools that produce topology-optimized shapes, as well as its ability to create special surface textures. These advantages over conventional subtractive machining has led the medical industry to increasingly adopt additive manufacturing (AM).
Manufacturing process development trends and market analysis also indicate that traditional subtractive techniques are increasingly taking on a smaller role in medical manufacturing. The elimination of material-wasting roughing operations found in conventional machining operations is one key reason that additive manufacturing is gaining momentum.
To address the changing requirements of component post-finishing processes, a closer collaboration between CAM and AM is needed. A future-equipped CAM system delivers suitable solutions in addition to toolpath generation, and opens up new innovative manufacturing opportunities in medical technology. To achieve maximum process-performance, the CAM modules should work seamlessly together.
The traditional thinking of CAM vendors is to focus only on cutter path techniques. This is no longer sufficient. Additive manufacturing, on the other hand, is not separating itself from CAM; indeed, it is moving even closer to CAM. The post-finishing processing of a 3D printed component can take more time than the printing itself. Critical finishing operations should not be neglected. The techniques to complete a raw part printed in 3D and transform it into a final implant component is a new strategy for CAM. This new strategy requires both generating a new toolpath to remove stabilizing structures as well as aligning the additive component in relation to the actual part model.
New technologies from AM advancements can also reduce manufacturing workload while converting complex tasks to simpler ones. For example, directed energy deposition (DED) procedures are emerging within AM that enable multi-material designs. They also offer complete processing (subtractive combined with additive) on one machine tool.
Experience shows there are challenges in the interface between 3D printing and milling machines. Besides removing the remaining powder, CAM programming and correct fixturing of printed components often prove to be difficult. Frequently, there is thermal deformation during 3D printing. This distortion must be compensated for in the shift and alignment of the part origin during subsequent subtractive machining, and trying to manually align it is too time consuming and error prone.
Using a machine probe eliminates error-prone manual intervention. Best Fit CAM technology then uses the probe data to calculate an improved position of the part on the CNC machine. The position and alignment are corrected so that the virtual part is contained within the raw 3D printed part. A simple datum correction on the machine tool controller will not fulfill the geometric needs; machine limit violations and collisions with the fixture and machine components could arise when the shift is larger than expected. A toolpath simulation must be run to confirm the cutter paths based on the new position. The material distortion is compensated for and thus the finishing of the complete implant is guaranteed.
CAM programming tasks within a family of parts, such as drilling or engraving applications, are often quite similar. The bone plate systems used for stabilizing and repairing simple fractures, or for complex reconstruction cancer surgeries, are often similar other than the geometry unique for each case. A key advantage in CAM software is how easy it is to program. With a modular principle, recurring programming tasks can be easily standardized and automated without significant user interaction. This also makes it easy to program CT-scanned, individual bone-derived prostheses. The user needs only minimal training to handle the programming templates.
High-quality, efficient toolpaths are of great importance to complete 3D printed components. Support structures are often removed manually, but this process is time consuming and risky. Alternatively, with the right toolpaths, machine tools can safely and quickly perform these tasks. For example, high-strength surgical stainless steel often requires special machining strategies with novel tools such as conical barrel cutters (aka Circle Segment). Due to their shape, these tools are capable of finishing surfaces faster, achieving finer surface finish quality and are more wear resistant. In addition to seamless finishing, advanced CAM techniques also provide imperceptible blend regions and minimize the need for subsequent polishing work.
A good application for future DED work is when standard bone plates are deformed manually, a common operation.
While it is an effective method, it also adds stress concentration, weakening the component in the deformed area. For highly stressed implants such as a lower jaw plate, manually deforming can lead to fractures and shorter implant life due to the high permanent load.
However, DED technology opens new methods of component design. Standard toolpaths can be converted into additive processing paths, so five-axis coating operations can be programmed to target weak areas. Another way to compensate for mechanical weaknesses in a design is to combine different materials. Well-known multi-material examples in everyday life include car tires and reinforced concrete. Medical technology can also benefit from multi-material components or cladding high-performance materials atop a base material. One way to obtain a multi-material solution is to deposit a mix of two different powders, creating a new alloy. Another is to deposit one material on another, using a material with special properties for contacts and wear surfaces. These advanced solutions may have better material properties such as slower material fatigue, better bending load capacity and higher elasticity. Reinforcement of highly stressed areas leads to more durable implants.
DED processing has other strong benefits that can simplify the manufacturing process. With its potential to deposit material on arbitrary orientation, structural supports are not needed and neither is post-finishing to remove them. Also, DED processes are often applied on a traditional machine tool (milling or mill-turn). In these cases, many of the alignment and re-fixturing tasks that are required when moving a component from a 3D printer to a finishing machine are also eliminated, saving time and improving efficiency.
Another advantage of DED processing is its customizability. For example, after a CT scan, material can be applied to the base body in a targeted manner and hybrid machining can be used to apply material and finish it afterwards on the same machine. The implant is precisely adapted to the patient’s bone. The DED method also has an advantage when it comes to processing speed—it is faster and more efficient than the powder bed process.
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