3D printing is revolutionizing the production of components in many industry sectors, creating new challenges in manufacturing processes. This is primarily because additive manufacturing (AM) most often requires subtractive machining as a secondary process. Using a digital process such as computer-aided manufacturing (CAM) software can streamline the workflow between the additive and subtractive processes and reduce the chance of error, helping to make the new manufacturing processes cost effective.
Because most additive processes do not produce a component with sufficient quality to be in “final” state, subtractive manufacturing is a natural process to complete the overall task. CAM programming can be applied to both additive and subtractive process steps, and when also considering the requirements of part alignment, numerical control (NC) programming takes on an increasingly large role for these applications.
Downstream milling and the associated generation of NC programs are key factors to complete the part. For example, many complex components require support structures during printing that are then removed afterwards. When the surface finish is rough or irregular, milling is required to achieve the desired surface qualities, accuracy or fit. Or the additive component may have some deformation due to thermal influences during the build. Additively manufactured components often have to fit together precisely with other parts. This requires the highest degree of precision and can only be achieved by having the right NC programs for subtractive manufacturing.
Medical implants have complex manufacturing requirements and are often prepared with AM. Patients need individual solutions for implants and prostheses, and this means that the CAD/CAM data must be adapted to suit each patient.
AM can also play an important role in production of aerospace components. Most aerospace components start with large solid stock and have high material removal. Adding features can be an interesting and effective alternative to material removal. Or in some cases, using AM for a few features can have large savings on the amount of initial stock required. Again, finish machining with traditional subtractive processes is required in most cases.
Whether a workpiece is milled from raw material or built up layer-by-layer, toolpaths generated by NC programs are always required. For optimal efficiency, CAD/CAM software packages should be capable of generating toolpaths for both five-axis machining centers as well as AM machines.
To minimize the amount of programming required, the CAM solution must provide standardization and automation functions for generating NC programs. CAM programming tasks, such as drilling, roughing, finishing or engraving are often similar within a family of parts. The difference is that the standard machining process is applied to the variant geometry. Bone plate systems for reconstructive surgery, after-cancer surgery or the stabilization and repair of fractures often differ only slightly. The software should be capable of recognizing specific geometries and manufacturing information in the CAD model feature, and provide templates that make programming significantly faster. A perfect example is when a prosthesis is derived from the computerized tomography (CT) scan of a bone. In the aerospace field, many components are similar over different airplane sizes, or the similarities are based on the change requirements of each airline when specifying the same airplane model.
When hybrid machines are used and 3D printing and rework machining take place consecutively, it is prudent to work with CAD/CAM software that is at home in both worlds. In many cases, the two process steps are carried out on different machines and the continuity between the digital model and the workpiece is lost. As a result, the additively generated semifinished product must be clamped in the milling machine in such a way that it is congruent with its counterpart in the CAM system to ensure the toolpaths can be calculated correctly.
The component is aligned using a dial gauge, control cycles, and a great deal of sensitivity. In a sense, the actual clamping is adapted to conform to virtual programming. This process is time and labor intensive, often needs to be repeated multiple times, and is fraught with uncertainty and risk. This is evident when something is not milled from generously dimensioned raw material, but from a part that’s already close to net shape, except for small irregularities.
CAM packages such as hyperMILL from Open Mind Technologies help manufacturers solve these problems. For example, the hyperMILL BEST FIT function offers an innovative answer to these challenges and thus achieves an unprecedented level of process reliability. BEST FIT aligns the component automatically. The unaligned stock is probed on the machine using 3D probing and the measurement report is sent to the CAM system. Based on the probing result, the software adapts the NC programs to match the existing clamping and actual part position. The adjusted NC code is then simulated in the virtual machine including collision check and optimization within the machine space.
Previous solutions tried to solve the problem by changing the zero point on the controller—an intervention that is not completely harmless. BEST FIT does not change anything at the machine control. It adapts the CAM model to the position of the component and also to the situation in the machining area, generating fully collision-checked toolpaths. This function is extremely important in connection with the AM used in various industries. The effort and costs if the component is scrapped are high, and therefore the CAD/CAM system plays a decisive role in making the process efficient and error free.
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