Additive Manufacturing: The Perfect Strategy for Reworking Components

CAD/CAM system ensures perfect handshake between metal 3D printing and rework machining

Additive metal printing has become an established industrial manufacturing process in recent years. Powder bed-based metal laser melting processes are particularly popular as they create a highly homogeneous, microstructure with minimal voids and a density exceeding 99.8 percent. Sven Skerbis, Additive Manufacturing Engineer and Managing Director of Parare GmbH in Frickenhausen, Germany, explains the resulting advantages: “The parts we produce with selective laser melting technology are, on average 20 to 30 percent more mechanically resilient than die-cast aluminum parts that can sometimes contain blowholes.”

Parare GmbH, which Skerbis founded in 2017 with his partner Matthias Bath, is a manufacturing service provider specializing in industrial metal and plastic 3D printing. The two industrial engineers had already recognized the potential of this technology back in their university days. Since 3D printing is a direct manufacturing process based on CAD data, no tools, molds or CAM programming is required to generate the part. However, production can take anywhere from a few hours to several days, depending on the material and component size. “The more complex a component is, or the more conventional consecutive manufacturing steps are required, the more sense it makes to resort to 3D printing,” Sven Skerbis points out. “This is because, with additive processes, complexity has little impact on cost. Therefore, our offer is primarily suitable for prototyping and small-batch projects where building time-consuming and costly die casting tools would not be viable. 3D printing also addresses scenarios such as the low-volume construction of replacement parts.”

“We recognized early on that the interface between 3D printing and rework machining is of great importance. This also applies to the CAD/CAM system used. hyperMILL® from OPEN MIND is the perfect solution for us.”

Parare Managing Director Sven Skerbis

Taking the Customer by the Hand

The name ‘Parare’ can be loosely translated from Latin as ‘to take by the hand’ – it is also the name of the game for Skerbis and Bath: “For us, this means that we transfer our knowledge to customers and show them where the use of 3D printing makes sense. We assist with the design and topology optimization stage and then produce the components. We also perform rework machining work, so our customers receive final products.”
The powder materials used in selective laser melting are traditional alloys comprising stainless steel, tool steel, titanium, aluminum and nickel-based materials. As the laser melts one layer at a time, the components require additional structures to support areas that cannot support themselves in the powder, such as walls with slopes exceeding 45 degrees. These supports have to be removed afterwards. In addition, further machining is required in some cases for functional and sealing surfaces, fits and threads to ensure the required level of precision and surface quality.

Important Rework Machining Interface

Previously, Parare outsourced this final step to partners. “Experience has taught us that the interface to rework machining is very critical,” explains Sven Skerbis. “If the person programming or machining the part did not create the raw data for 3D printing themselves, this will often result in long machining times and, in the worst case, errors. And the costs of generating rejects at this stage is very high.”
For this reason, in early 2019 the Parare management started to pursue the goal of handling rework machining themselves. They set out to find a suitable employee, a powerful 5-axis machining center, and suitable CAD/CAM software. With Michael Meyer, they found a machining professional who also brought more than ten years of experience with various CAD/CAM systems to the table. The company opted for a Hermle C30 U and introduced the hyperMILL® CAD/CAM system from OPEN MIND Technologies AG.
Michael Meyer, who is now in charge of programming and machining, is highly satisfied with hyperMILL® and the integrated hyperCAD®-S ‘CAD for CAM’ system: “I’ve been working with this software for over ten years, and I don’t know of any other system that can hold a candle to hyperMILL® when it comes to 5-axis machining. In addition, hyperCAD®-S allows me to easily add geometric solids and faces to the supplied 3D CAD data or repair faulty faces.”

Creating Printable Components with hyperCAD®-S

Most of the time, Parare receives 3D CAD part manufacturing data from the customer. Since this is not suitable for 3D printing, they are first transferred to hyperMILL® and then further processed using hyperCAD®-S . Michael Meyer checks the faces, touches them up, and adds support structures as well as clamping straps where necessary. For the places that need to be reworked, he calculates the required allowance to ensure optimal milling. He then transfers the file back to the CAD system, which outputs it as an STL file for the SLM process.
“Because of this preliminary work, I know exactly where my reference points are,” Michael Meyer explains. “If needed, I could even add a small cylinder as a reference, which I can then probe in the machine to properly align the component. This ensures that the stock is clamped on the machine table precisely as intended in the CAM program. This makes for very safe, reliable machining.”

The Right 5axis Strategy for any Application

Michael Meyer’s enthusiasm does not stop with the CAD side of hyperMILL®, but also extends to the CAM programming itself. The structures created in 3D printing are often very complex and can only be processed with 5-axis technology. “This is precisely one of the strong points of hyperMILL®, because it provides several tilt strategies. This allows me to select a suitable solution for every geometry, material and machine kinematics,” says the head of production. “Inconel, for example, must be machined radially, which is sometimes only possible in 5-axes. In this case, a frontal machining strategy would wear out the cutters very quickly. We have been able to significantly reduce tooling costs and component production by opting for a 5-axis swarf cutting instead. hyperMILL® delivers extremely strong 5-axis swarf cutting or 5-axis finishing machining cycles.”
hyperCAD®-S also played an important role in this project. This is because Parare wanted to print the complex component geometry without using any additional clamping straps. For example, Michael Meyer used the Boolean Difference function to generate a negative fixture for rework machining into which the component was inserted. His verdict: “That worked out quite brilliantly.”

Short Programming Times Thanks to Feature and Macro Technology

“What I personally like about hyperMILL® is macro programming,” says Michael Meyer. With its feature and macro technologies and associated process and macro databases, hyperMILL® provides a solid basis for automating programming. “This saves us a lot of time even at the programming stage,” adds Managing Director Skerbis. “Incidentally, this applies not only to rework machining but also to other complex milled parts, which are increasingly in demand from us.”
When working with features and macros, users specify the tools that they know are best suited for the operation. For Michael Meyer, a well-maintained tool database is a key to efficient programming and reliable machining. “In our daily work that involves a lot of different parts, I need a reliable database. hyperMILL® provides a very viable solution.”
Parare’s machining center, which is used both for finishing and roughing processes, must also be reliable. “Our Hermle C30 U meets our requirements perfectly,” attests the machining expert. “It is flexible to use, very precise, and rigid, which is important for roughing.” To program the pre-machining, he uses the roughing module of the hyperMILL® MAXX Machining performance package, which offers solutions for high-performance cutting (HPC) with spiral and trochoidal tool movements. The package combines optimal milling paths, maximum material removal and minimized machining times. Michael Meyer is pleased: “It’s really fun to watch the machine produce chips with it.”

www.parare.de


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