Five-axis milling for large sculpture surface parts
Five-axis milling for large sculpture surface parts
The traditional processing method of "sand mold casting → manual shovelling → stereoscopic sample inspection" is mostly used in the processing of large sculptural surface parts. Due to the low manufacturing precision of stereoscopic sample and the influence of its geometric deformation, it is difficult to improve the processing precision of such curved surface parts.
With the development of computer technology, the CAD/CAM technology has made great progress. Five-axis CNC boring and milling machine and some excellent CAD/CAM software have appeared, among which SDRC/CAMAND software is relatively flexible in five-axis CNC machining programming.
At present, for the processing of large sculpture surface parts, it is the best processing method to use large diameter surface milling cutter to process along the curve parameter direction. This processing method has the characteristics of high processing precision and efficiency, good surface quality of parts and excellent cutting state.
First, the sculpture surface three-dimensional modeling technology
In order to complete the nc programming of the surface, the 3d model of the surface should be made on the computer first.
The design data of sculpture surface is usually described by lattice data, while the source of surface lattice data is mainly in two ways: one is by means of design, which is calculated by designers according to the design theory of the product, and is usually given in accordance with certain rules and regulations, and three-dimensional modeling is relatively easy;
The other is to obtain the point cloud data of the surface by using three-dimensional measuring instruments on the hand-made wooden mold prototypes or real objects. There is no accurate rule of the dot matrix distribution of this kind of data, so it is relatively difficult to model the surface three-dimensional.
Therefore, according to the different situations of the original data of the surface, the 3d modeling of the sculpture surface can be divided into regular lattice and irregular lattice.
1. Three-dimensional modeling of regular lattice sculpture surfaces
Regular lattice sculptural surface means that the surface lattice data is given strictly in accordance with certain laws.
Generally, the surface data array is divided into several parametric spline node data, and THE THREE-DIMENSIONAL modeling adopts NURBS surface modeling to complete the required sculpture surface.
The modeling steps in the SDRC/CAMAND software are described below.
(1) The original bitmap data of the sculpture surface is generated into Pointset with the function of "Pointset". It should be noted that independent point sets should be generated according to each parameter spline.
(2) Using the "B-spline" function, choose to use "Thru Points" and "non-uniform" parameters, and then directly select the corresponding set of various strip Points to generate all parameter splines of the construction surface.
(3) Use the "Surface" Modeling feature, execute the "Loed Surface" sub-function, select each spline in a certain order, and click ok to generate the sculpture Surface.
2. Three-dimensional modeling of point cloud data sculpture surface
Point cloud surface data means that the surface lattice data is not accurately given in accordance with a certain law, and it is impossible to form a spline curve before modeling the surface to get a better sculpture surface model.
Therefore, only the function of "point cloud data modeling Surface" is adopted, while there is no similar function in CAMAND. In practice, we make use of the "Fit Points to Surface" function in I-DEAS to generate point cloud into Surface, and then convert it into CAMAND file format in i-DEAS software, and use it as the numerical control programming model.
Two, large sculpture surface numerical control processing technology design
In the actual production and manufacturing, to realize the five-axis nc machining of large sculpture surface parts, we should first solve the clamping alignment scheme of the surface parts, considering how to determine the zero point of the workpiece, the tool point, the machining tool scheme and the detailed machining sequence.
1, large sculpture surface CNC machining clamping alignment principle
For general large sculpture surface parts, its clamping and locating have certain rules to follow, so after analysis, large sculpture surface can be divided into two categories, its clamping and locating principle is as follows.
If there are characteristic datum planes such as plane and cylinder on the sculpture surface parts, then the characteristic surface of the plane will be used as the locating datum of the clamping device, which can simplify the locating process, improve the locating efficiency of the clamping device and ensure the locating precision of the surface.
If all sculpture surface composed of sculpture surface, no sure benchmark, then the general on the curved surface parts is found on the casting or welding plane block, pin hole or find is benchmark benchmark pin and other auxiliary, use 3 d measurement technology of large curved surface, and the use of computer software adaptation technology get blank allowance distribution, to guide the alignment of the sculpture surface parts.
Of course, these two ways are to determine the first large sculpture surface parts of the benchmark, and then nc processing program to find the benchmark for processing as a guiding ideology.
Now, some manufacturers also have another way of craft.
For large-scale sculpture surface no sure base, its freedom is placed directly on the machine tool worktable, after clamping reliable distribution of measurement points on the surface according to certain grid, then the measuring point data processing, find out the location of the curved surface in free space, make sure that the surface machining allowance, adjust the processing coordinate system, the nc machining program, and then return to complete parts of this machine tool processing.
The biggest advantage of this process is that there is no need to determine the benchmark for clamping and alignment, and the parts can be placed freely.
But on the other hand, this process method increases the auxiliary time of machine tool processing and processes more data, which also brings difficulties to the production organization.
2, large sculpture surface parts of CNC machining tool selection
For the five-axis nc machining of large sculpture surface parts, it is better to use the large diameter surface milling cutter.
At present, more famous tool manufacturers include Sandvik, Ingersoll, Kennametal, Seco, etc. Among them, Sandvik CoroMill 200 series circular cutter unilateral milling cutter, which is especially suitable for semi-finishing and finishing of sculpture surface parts.
MORE's 220/221 series of cutting tools have the advantages of good impact resistance and rigidity, and are suitable for rough and fast machining with large draft.
The diameter of the tool should be selected according to the size of the curvature of the sculpture surface parts to determine, the principle is that the tool radius should be less than the minimum radius of curvature of the sculpture surface concave surface, but should not be too small, otherwise it will reduce the processing efficiency.
The curvature radius changes too much sculpture surface parts, can also divide the whole part into different areas, choose different diameters of cutting tools, in order to improve the processing efficiency.
Three, five axis CNC machining tool position calculation and simulation
Sculpture surface parts of nc machining tool for five-axis linkage calculation in CAMAND software INTERP (interpolation), NORMAL (NORMAL), TILT (TILT) and TANGTO (tangent) and so on a variety of ways, but for the huge sculpture surface parts, the most commonly used in TILT to machining, the machining method of tool axis and cutting point surface method before and after the vector into a certain Angle (Lead/Lag Angle) or roll Angle (Right/Left Angle).
1, five axis CNC machining tool position calculation
In the CAMAND software, TILT was used to process sculptural surface parts, and the cutter position calculation process: first select the function of "Flowline Surfaces" under "Numerical Control". This processing mode of "Flowline Surfaces" is actually machining along the parametric line direction of the surface.
Second set tool name (or "New" or "Rename" function), select processing coordinate system and the cutting point, then input the corresponding tool parameters (diameter, length, shape of cutting edge dimension of tools and cutting parameters, etc.), the parameters set in and out of the knife, choose after interference surface and set parameters, then click on the tool computing functions, select the processing surface and define the cutting direction and the way the tool axis control TILT, general Settings before Angle, namely along the cutting direction forward a 2 ~ 10 ° Angle;
Finally, the five-axis machining tool position calculation is completed.
2. Cutting simulation and machine tool simulation
For large sculpture surface parts, due to the high cost of blank, and for the safety of the machine tool, tool and tooling, after the five-axis nc machining tool position calculation is completed, the cutting simulation and machine tool simulation must be carried out to check the correctness of the tool position, and finally the processing program can be used in the actual production and manufacturing.
In OUR software, a set of simple cutting inspection and machine tool simulation can meet the requirements of ordinary simulation.
If you need more precise simulation tools, use CGTech's Vericut software, which is more specialized.
The software can not only perform cutting simulation and machine tool simulation, but also optimize tool position trajectory.
The simulation inour software is briefly described here.
For the cutting simulation of the five-axis tool position, the over-cutting phenomenon of the tool in the calculation of the pre-order five-axis tool position can be checked and corrected.
Generally, the processed surface should be rendered and colored, and then the cutter position should be gradually simulated with the function of "Simulation" and the interference of the cutter should be checked. If there are overcuts and collisions, the cutter position must be recalculated or modified.
For machine tool Simulation, we mainly check the NC milling head (large five-axis gantry boring and milling machine is two axis NC milling head) and artifacts, clamp interference situation, therefore, can according to the actual machine tool NC milling head shape and size to establish three-dimensional model of NC milling head, and then use "Simulation" function plus NC milling machine tool Simulation, you can check out the NC milling head, cutting tool and fixture, interference of artifacts.
Four, five axis knife position after treatment
After the five-axis machining tool position calculation of the curved surface is completed, the intermediate tool position file needs to be converted into the G code program that can be recognized by the CNC machine through the post-processing technology.
The tool position file in CAMAND is given by the tool point coordinates and the tool axis vector, then the post-processing must convert the tool position data into X, Y, Z, B, C coordinate values.
The post-processor is designed according to the numerical control system of specific machine tools and machine tool parameters (such as the stroke of each coordinate axis, the maximum feed speed, rotation speed, etc.), and then the post-processing function in more's Main NC is utilized to convert the five-axis tool position data into G code program that can be executed by the numerical control system of machine tools.
The five-axis linkage machining technology of large sculptural surface parts can effectively solve the contradiction between the machining precision and the machining efficiency of such parts. This technology involves computer-aided 3d surface modeling, computer-aided manufacturing, machining technology and other multidisciplinary comprehensive technologies
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