Knowing all the additive manufacturing constraints and challenges, the ESPRIT CAM team has been engaged in national and international research projects to develop dedicated toolpath simulation solutions for additive technologies. Article by Clément Girard, Product Manager for Additive at DP Technology.
While additive manufacturing (AM) has been around for the last 20 years, it is only in the last several years that metal AM has taken off. One of the key enablers for this new technology is material extrusion, more commonly known as 3D printing. While jetting technology (material or binder) is more suitable for 3D printing polymer and charged materials, engineers commonly apply power bed fusion (PBF) or direct energy deposition (DED) for the AM of metals.
All AM processes have some common characteristics. They use a power source, usually a laser or electron beam or a welding arc, and a material carrier, typically powder or wire, to build a three-dimensional object from a computer-aided design (CAD) model by adding molten material layer by layer. Powder processes most closely resemble traditional sintering processes, while wire processes (also called wire arc additive manufacturing) most closely resemble traditional welding.
Each method has advantages and disadvantages. For example, powder processes tend to have better surface quality—owing to the small size of the powder particles—but material loss can be high (as much as 80 percent when the tool is inclined in 5-axis applications). Wire processes lose less material, but the deposited bead tends to be larger, leading to a “rougher” surface quality. Powder processes require the use of shielding gas, as do some wire processes.
It is also important to remember that parts built by additive processes today more closely resemble raw stock of a particular shape than they do machined parts. This means that secondary subtractive processes are almost always needed to achieve the final part. Hybrid machines with both additive and subtractive capabilities may be an answer to this. However, because additive parts can take a considerable amount of time to make, it is generally more effective to machine additive parts in a separate CNC center.
Who Can Benefit from AM?
Currently aerospace, aviation, medical, energy, and defense are the main industries at the forefront of AM. For aerospace and aviation, AM’s ability to build complex, weight-saving shapes makes it a natural choice.
Particularly interesting for the medical field is AM’s ability to create custom shapes to match the morphology of each patient. These and other industries can also benefit from using additive processes to repair tools or parts made of costly alloys, or to apply coatings to tools.
The Challenges of Additive Toolpaths
Multi-axis additive toolpaths can be more difficult to program than those of a comparable subtractive operation, as additive toolpaths introduce a new level of complexity. For example, executing a toolpath twice in a subtractive process typically causes no issues, as the tool simply passes through air. However, the same toolpath in an additive process collides with recently deposited material, crashing the machine or re-melting the material, leading to an overheated deposition.
Optimal additive layers are not always planar, but creating non-planar additive layers is more complex than making non-planar subtractive cuts—the additive toolpath must consider support for such layers, which may involve an existing substrate or built-up additive material.
The additional complexity goes beyond just the toolpath, however. Additive processes require knowledge of the material, the power source technology, the proper temperature and rate of bead deposition, and the use of shielding gas. In some cases, separate controllers add complexity, as in the case of wire arc AM where a welding controller may handle the wire supply feed separately from the machine controller.
Accelerating Smart AM with Simulation
Knowing all the additive constraints and eager to provide new technologies to their end users, the ESPRIT CAM team has been engaged in national and international research projects, in collaboration with the research centers or companies primarily in the aerospace/aviation and energy industries, to develop dedicated toolpath simulation solutions for additive technologies. Today, these teams continue to contribute to additive technology research, providing a powerful tool to continue building knowledge.
Last year, in close collaboration with Mazak, ESPRIT conducted tests to validate additive toolpath trajectories (Figure 1). These tests have validated cycles on 3-axis and 5-axis machines and have shown good results. Testing continues to evaluate promising AM and robot technology.
Additive Simulation Validation
Two parts were chosen to validate 3-axis and 5-axis applications, respectively. The 3-axis part was designed to validate simple trajectories and the behavior of material deposition on acute angles. To achieve this, the part included spikes, slopes, and a pocket feature in the middle. Figure 2 shows the additive part as built in a Mazak Variaxis J-600 machine. The main idea was to test hybrid capabilities by building an additive stock in the basic shape of the part and then finishing it with subtractive machining.
To test a 5-axis cycle, the team selected a valve part. Similar to the 3-axis part, the idea here was to build a custom stock in the basic shape of the part to save money, material, and time over using bar stock. Figure 3 shows the additive stock as built.
Both of these test parts were built using a Variaxis J-600 machine and a Yaskawa robot with a Fronius head and wire arc AM technology. In both cases, the ESPRIT team found that fine-tuning of the job parameters is the key to a good deposition, with good results close to the simulated trajectories shown in Figure 4.
Additive Processes and ESPRIT
In the CAM environment, simulation of additive cycles lets end users verify additive toolpaths, including the results of thermal simulation and dwell time. Incorporating the full machine environment in the simulation has the added benefit of machine-aware capability, detecting and avoiding collisions in the virtual environment before they cause problems in the real world. As the technology matures, so too will CAM. By being on the ground floor and developing additive CAM technology in lockstep with the additive industry, ESPRIT shows strong promise to remain on the leading edge.
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