3D Printing of metal components is gaining in popularity. This is partly because it can reduce production times and improve part quality in many applications. 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. Additive manufacturing (AM) has been adopted in the medical industry due to these advantages over conventional subtractive machining.
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 a key reason that additive manufacturing is gaining momentum.
CAM Works with AM
The traditional thinking of CAM vendors to only focus on cutter path techniques is no longer sufficient. Additive manufacturing is not separating itself from CAM; indeed, it is moving even closer together. To address the changing requirements of component post-finishing processes, a closer collaboration between CAM and AM is needed.
The post-finishing processing of a 3D printed component can take more time than the printing itself, so critical finishing operations should not be neglected. The techniques to complete a 3D printed raw part and transform it into a final implant component is a new strategy for CAM. This is both a tool path generation capability to remove stabilizing structures, as well as an ability to consider alignments of the additive component in relation to the actual part model.
New technologies that are connected to AM developments can also replace traditional thinking and can reduce manufacturing workload and convert complex tasks to simpler ones. Directed-Energy Deposition (DED) procedures are emerging within AM to enable multi-material benefits and also complete processing (subtractive and additive) on one machine tool.
Where Additive and Subtractive Manufacturing Meet
Experience shows that the interface of the 3D printing machine and milling machine bring many challenges. Besides removing the remaining powder, CAM programming and correct fixturing of printed components often prove to be very difficult. Frequently, there is thermal deformation during 3D printing. This distortion must be compensated in the shift/alignment of the part origin during subsequent subtractive machining. Manual alignments are insufficient for this because they are too time consuming and error prone.
By using a machine probe device, the error-prone manual intervention can be eliminated. Best Fit CAM technology calculates 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 tool path simulation must be run to confirm the cutter paths based on the new position. The material distortion is compensated and thus the finishing of the complete implant is guaranteed.
Easy-to-Use Programming
CAM programming tasks within a family of -parts, such as drilling or engraving applications, are often quite similar. The bone plate systems to be used for the stabilization and repair of simple fractures or for reconstruction cancer surgeries are often similar other than overall geometry that is unique for each case. A key advantage in CAM software is the ease of programming. With a modular principle, recurring programming tasks can be easily standardized and automated without significant user interaction. So, it 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 tool paths 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 tool paths, 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 quality and are more resistant to wear. In addition to seamless finishing, advanced CAM techniques also provide imperceptible blend regions and minimize the need for subsequent polishing work.
Synergistic Effect of Additive and Subtractive — DED Advantages
Standard bone plates are often deformed manually. This procedure deforms the plate but adds stress concentration, weakening the component in the area of deformation. For highly stressed implants such as a lower jaw plate, manual deformation can lead to fractures and shorter implant life due to the permanent high load.
However, DED technology opens new methods of component design. Standard tool paths can be converted into additive processing paths, so 5-axis coating operations can be programmed in a targeted and automated manner.
To compensate for mechanical weaknesses in a material, different materials can be combined. Well-known examples with multi-materials in everyday life are car tires and reinforced concrete. Medical technology can also benefit from multi-material components or cladding high-performance materials atop a base material. One manner to obtain a multi-material solution is to deposit a mix of two different powders, essentially making a new alloy.
Another is to deposit one material onto another, utilizing the 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. Also, reinforcement of highly stressed areas leads to more durable implants.
DED processing has other strong benefits that can simplify the manufacturing process. By having multi-axis deposition potential, structural supports are not needed and so the post-finishing processing requiring support removal is eliminated. Also, DED processes are often applied on a traditional machine tool (milling or mill-turn). In these cases, many of the alignment and refixturing 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 afterward on the same machine. The implant is precisely adapted to the customer’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.
The future-equipped CAM system delivers suitable solutions in addition to tool path generation, and it opens up new innovative manufacturing opportunities in medical technology. To achieve maximum process performance, the CAM modules should work seamlessly together.
This article was written by Manfred Guggemos, Product Manager, and David Bourdages, Product Manager, OPEN MIND Technologies. For more information, visit here .
