Five-axis simultaneous CNC machining to solve the processing of irregularly curved human skeleton models
Taking the individualized modelling and machining of the human skeleton as the research object, based on its complex shape and irregular machining difficulties, we analyze the machining process of key areas and develop an overall machining plan. After verification by Vericut simulation software, the five-axis CNC machining centre was used to complete the machining of the human skeleton model, which improved the machining efficiency and quality of the product.
Preface
The quality of human skeleton model processing will directly affect the effect of medical treatment. Currently, 3D printing technology is relatively mature. Still, due to the influence of materials and processing costs, it has not been fully popularized, so the 3D modelling and manufacturing processing of human skeletal models is an urgent problem. This project uses the human skeleton images obtained from CT (computed tomography) to complete the modelling of human skeleton models through UG software. Combined with PowerMILL software to compile the machining toolpath and post-processing to generate NC code that CNC machine tools can recognize, and then based on Vericut simulation software, simulate the correctness of the toolpath trajectory to verify the NC code, and finally, use i5 system AC cradle type five-axis machining centre to complete the machining of the human skeleton model. This machining method greatly reduces machining time, improves productivity and workpiece quality, and reduces medical costs.
Process solution
The human skeleton model is generated by UG 3D inverse, and the maximum size of the product is φ78mm×80mm (excluding the base), and there are more curved surfaces and circular arc transitions in the model. The test selection of the blank profile is φ80mm nylon bar, the choice of model i5M8.4 five-axis CNC machine tools, the highest speed of 12000r/min, stable accuracy up to 0.005mm, to meet product quality requirements.
Human skeleton model processing process card and PowerMILL processing parameters settings. The machining process strategy of the human skeleton model is divided into: model area clearance (three-axis fixed-axis rough machining), rotary finishing (four-axis base finishing), model residual area clearance (3+2 axis semi-finishing), point projection finishing and linear projection finishing (five-axis linkage finishing).
Three-axis fixed-axis roughing
Three-axis fixed-axis roughing uses the machining strategy of model area removal for model roughing. By fixing the tool axis direction and A/C axis rotation angle, the 5-axis machine is converted into a traditional 3-axis vertical machining centre for roughing, which improves machining efficiency. When machining the second side blank with Post2 as the machining coordinate system and machining the second side blank, when the tool is machined to the middle thin wall position, the tool will vibrate and bounce due to the vibration of the machine tool because there is not enough support at the bottom of the model, which affects the machining quality of the model. The residue of the third and fourth sides cannot be machined, so the process is improved, and the model is divided into 4 areas for machining. When processing with Post1 and Post2 as the coordinate processing system, the distance of 20-30mm above the centre of the model should be limited to the tool processing on one side; at this time, when processing the second side with Post2 as the coordinate processing system, the distance of 20-30mm reserved for processing the first side exists at the bottom, and the distance of 20-30mm reserved for processing the second side itself, the bottom has sufficient thickness when processing (about 40~60mm), the tool will not vibrate and pop. Then use Post3 and Post4 as the machining coordinate system to machine the third and fourth side, and machine to 2~5mm below the centre line to ensure the complete removal of the blank part of the model. When machining the third and fourth sides, the model itself is used as the support, so there will be no vibration of the tool and no popping of the tool, thus improving the machining efficiency and quality of the human skeleton model.
3+2 axis fixed-axis semi-finishing machining
Take the i5 system AC cradle type 5-axis CNC machining centre as an example, the essence of the 3+2-axis machining method is to change the table of 5-axis CNC machining centre to the fixed direction and fixed angle, and the axial tool direction will not change, to process the 3D surface of the model. 3+2-axis semi-finishing machining. The human skeleton model is first fixed in an inclined position using two rotary axes A/C, i.e., the table of A/C axis is turned to A-45° and C = DC (0°) according to the needs of the human skeleton model profile, and then the tool is fed along the X, Y and Z directions for machining. When the current area is machined, the A/C axis angle is adjusted to continue machining other areas according to the machining needs.
3+2 axis machining of the curved surface. Where vf is the feed rate, and α is the inclination angle between the tool axis and the cutting surface normal vector. The 3+2 axis CNC machining method treats the surface as an approximate plane for machining by tilting the tool axially to avoid zero-cutting speed machining to obtain the ideal machining effect. The machine’s A/C axis rotary table defines the rotary work plane in space, where 2D or 3D machining programming operations can be performed. Other parameters are reasonably set to generate the tool path trajectory for the semi-finishing of the model.
5-axis simultaneous finishing
The human skeleton model has an irregular shape, irregular surface distribution, large side distortion, and inverted areas on the top skeleton, if the traditional three-axis machine tool is used for processing, it requires multiple sets of special fixtures, and repeated disassembly, clamping and positioning, which cannot guarantee the processing quality, and the processing efficiency is low. i5 system AC cradle type five-axis CNC machining centre, each axis movement direction, using five-axis linkage PowerMILL provides five types of projection finishing strategies: point projection finishing, linear projection finishing, plane projection finishing, projection curve finishing and surface projection finishing. According to the structural characteristics of the human skeleton model, point projection finishing and linear projection finishing are used, respectively.
Program generation
The coordinate system of the 5-axis machine tool is different from that of the 3-axis machine tool. The origin of the X and Y axes in the 5-axis machine is the centre point of the rotary disc’s C axis, and the Z axis is the intersection of the axis of rotation A and the C axis of the rotary disc. NC parameters selection during post-processing. When NC parameters are selected, ensure the human skeleton model position coordinate system is consistent with the output user coordinate system, and make the machining coordinates at programming time consistent with the coordinate system at workpiece clamping time. When outputting the tool position point, select the tool centre as the tool position point when the machining tool is an end mill, and select the tooltip as the tool position point when a machining tool is a ball-head tool, and the output file type can be set to.NC or. TXT format.
Vericut simulation and CNC machining
The i5 system AC cradle type five-axis CNC machining centre matches the post-processing, and the post-processor generates the NC code recognizable by the machine tool. To ensure the feasibility and correctness of the NC code, it is necessary to simulate the simulation by Vericut simulation software, and the simulation verifies that there is no interference, overcutting and undercutting. Through the human skeleton model simulation after the light shade image, verify the error-free, through the DNC (DistributedNumericalControl) direct digital control transmission to CNC machine tools for human skeleton model processing. The actual product of the human skeleton model after processing (the blank material is a nylon rod)
Conclusion
This project is based on the characteristics of modern intelligent manufacturing processing, the human skeleton model five-axis linkage CNC machining as the research object, through UG reverse generation of the three-dimensional model, using PowerMILL for five-axis machining tool path writing, generate machining tool trajectory. After the NC code file was generated by the special 5-axis post-processor of the i5 system and verified by Vericut simulation, the machining of the human skeleton model was completed by applying the i5 system AC cradle type 5-axis simultaneous CNC machining centre.
The research adopts 3-axis fixed-axis roughing to rough all four sides of the human skeleton model, which improves the stiffness of the product during machining and reduces the phenomenon of tool bouncing caused by vibration; 3+2-axis fixed-axis semi-finishing removes the inverted buckle area that cannot be machined by 3-axis fixed-axis roughing, reduces the residual machining amount of the product, provides less and uniform residual amount for the subsequent 5-axis finishing, and ensures the tool finishing with It also provides a reference for the machining of other similar products.
