Studying Curve Interpolator for CNC System

2019

CNC machine tools incorporate the interpolators to generate reference points due to physical movement. In this study, initially the NURBS curve has been generated and sent to interpolator. By consideration of NURBS curve properties and other dynamic conditions like maximum velocity, the maximum acceleration and the maximum jerk of the reference points have been generated for each sample time. The current interpolators generally work based on 2nd degree Taylor series, but the numerical errors which are produced because of the nature of numerical truncations are not considerate. In this report, the real time interpolation of feed rates has been investigated in order to precisely control position on 3 axis CNC table with Milne-Simpson predictor corrector. In this approach, the numerical errors have been reduced with correction of the main calculating core of the interpolation unit that has been led to the higher accuracy. This claim has been proved by experimental tests on 2 axis CNC t...

2007

Abstract. In this work, the influence of the tool interpolation method on the HSC of free form surfaces with sharp edges is analyzed. The traditional linear interpolation was compared to polynomial interpolation by application of three different values of CAM tolerance. The results were analyzed in terms of machined surface roughness, contour dimensional form error measurements and dynamic behavior of the tool machine, through the real time acquisition of feed rate in x and z axes. It was shown that polynomial interpolation offers accuracy and surface quality gains if compared to linear interpolation, in the same cutting conditions. However the decision for applying both interpolation methods has to consider the CAM tolerance value in terms of lead-time reduction. By using of linear interpolations the programmer has to decide for opener CAM tolerances due to the NC program size and consequently the time to process the program. When the CAM programmer decides for applying polynomial ...

Procedia Engineering, 2014

Parametric representation has become a standard form in product design, graphics design, computer-aided geometric design as well as machining. Stamping, forging and extrusion dies and tools, rolling shapes, turbine blade profile, air craft and automobile body, ship hull, etc is designed in CAD and uses parametric curves to define the shapes. Past few decades have witnessed formulations of many novel mathematical representations of free form curves aspiring to make them more computers compatible. Parameterization of a curve have availed some important advantages of being bounded in parameter range, independent of coordinate system over implicit representation as well as part family and coding in Group Technology (GT). Parametric programming also referred to as macro programming being a critical feature in GT and Computer Aided Process Planning (CAPP) is a powerful but less explored feature of the CNC technology. Machining using parametric programming is judged against the CAM system for program length, machining time and accuracy through Coordinate Measuring Machine results. Few Bezier curve profiles have been constructed, by joining of which gives tangent continuity throughout the curve for the purpose of machining and their CNC and Parametric programs have been discussed. The results found for the same geometry, work material and cutting parameters are discussed in the paper in detail.

INTERNATIONAL JOURNAL OF DESIGN AND MANUFACTURING TECHNOLOGY

A circular interpolation algorithm used to determine the parameters of separate circular paths was used to generate round shapes on a computer-controlled numeric (CNC) turning machine. It is suggested that this calculation should be included in the CNC lathes ' resident software program. This would decrease the amount of blocks of data required for part of the program. In a single block, a complete circular interpolation cycle for the number of passes could be specified. The suggested algorithm is optimized for minimal machining time and enhanced surface roughness. The programming of the new interpolation scheme, using circular and linear segments, must be applied to the specific part.

International Journal of Advance Engineering and Research Development, 2014

Cubic Bézier Surface (CBS) is powerful design tool, used in various parts. Formulation using control points to evaluate surface by mathematical calculation. Improve surface accuracy using various parameters gives as variation in, convex hull property, curve interpolation etc. Condition for proper machining of surface gives smoothness and accuracy. Scallop height and tool selection gives exactness of machining. Tool path generation shows motion of the tool during actual machining process. Length of path depends on cutting tool diameter larger diameter have short path and vice-versa. During machining tool and surface contact must remain tangentially for smoothness. Generation of NC code for machining is based on tool path data using CAM software i.e. SURFCAM , it's easily generated by giving input data like machine controller, tool, scallop height etc.Applying this code to machine a surface on CNC milling machine gives pre-defined effect and measurement is taken on Coordinate Measuring Machine (CMM).

The International Journal of Advanced Manufacturing Technology, 2014

The recourse to the high-speed machining for the manufacture of warped shapes imposes an evolution towards a very high technicality of the CAM methods and of the machining operation execution. Due to its own characteristics, the high-speed machining (HSM) implies the use of new machining interpolations, in such a way that it assures the continuity of advances in the best way possible. Among these interpolations, we mention the polynomial interpolation. In this article, we propose a complete study of the interpolation type influence on the HSM machine dynamic behavior and also on the generated errors. For this, we have measured the feed rate of the cutting tool path for each type. Then, in terms of accuracy, we have measured the errors. In order to validate our approach, we have compared the simulated results to the experimental ones.

The International Journal of Advanced Manufacturing Technology, 2014

The aim of this study is to propose a five-axis toolpath smoothing method in order to improve the quality of machined surfaces. Currently, toolpaths are commonly computed from CAD models presenting small geometrical discontinuities. These discontinuities may be caused by an insufficient quality of the CAD model (geometrical discontinuities) and the use of meshed surfaces (e.g., stereolithography (STL) files). Normally, CAM systems generate linearly interpolated toolpaths. CNC options are then used on the machine to smooth the toolpath. The geometrical discontinuities of CAD models and linear toolpath interpolation may induce an unsmooth toolpath. This type of toolpath causes marks on the machined workpiece even if classical enhanced CNC options are used. Generally, these marks are unacceptable for the functionality of the workpiece. To reduce this problem, this study proposes a method to efficiently smooth toolpaths and consequently improve the obtained surface quality. The proposed method may be employed with high-end controllers commonly used on five-axis CNC machines. First, a five-degree polynomial interpolation method is presented. This interpolation is computed to ensure geometrical continuity in the slope and curvature of the obtained toolpath. Next, a concatenation method is proposed to reduce the size of the CNC program and to improve the toolpath smoothness. Moreover, the purpose of this concatenation is to obtain an optimized repartition of points along the toolpath. Furthermore, in a reverse engineering process, this method avoids surface reconstruction, decreasing the process time and improving the quality of the obtained surface. The efficiency of these methods is validated by the machining of biomedical prostheses. The CAD model used for the test is a meshed surface.

This paper purposed an efficient and effective methodology to generate optimal tool path for machining operation using Numerical Control (NC) machine. Tool path design is highly desirable factor as point of view of high-speed machining (HSM) of sculptured surface, where frequent change of tool position and direction may lead to inefficient machining. NC paths with controlled accuracy using optimal tool path based on such an algorithm which is depends on a number of factor like selection of surface, part geometry, Cutter location (CL) points, scallop height, side step, forward step etc. The CL points are generated directly from part surfaces and interpolated by desired curves/surface. This work proposes a new approach for generating accurate iso-scallop tool paths in the process planning for parts that are subjected to Bézier surface. The simulation results shows that the effectiveness of the proposed methodology.

The parametric interpolators of modern CNC machines use Taylor’s series approximation to generate successive parameter values for the calculation of x, y, z coordinates of tool positions. In order to achieve greater accuracy, higher order derivatives are required at every sampling period which complicates the calculation for contours represented by NURBS curve. In addition, this method calculates the chordal error in a given segment through estimation of the curvature neglecting a fraction of the error. In order to avoid calculating higher derivatives and make the calculations simpler, this paper proposes the classical fourth-order Runge-Kutta (RK) method for the determination of successive tool positions requiring the calculation of the first derivatives only. Furthermore, a method of estimating the chordal error on the average value of parameters at the end points of a given curve segment is proposed here that does not require the calculation of curvature at every segment. Finally, a variable feedrate interpolation scheme is designed combining the RK method of parameter calculation and the proposed method of chordal error calculation. Results show that reduced chordal error and feedrate fluctuations are achievable with the proposed interpolator compared to the conventional interpolator based on Taylor’s approximation with higher order terms.

Free-form surfaces are used for many industrial applications from aeronautical parts, to molds or biomedical implants. In the common machining process, CAM software generates approximated tool paths because of the limitation induced by the input tool path format of the industrial CNC. Then, during the tool path interpolation, marks on finished surfaces can appear induced by non smooth feedrate planning. Managing the geometry of the tool path as well as the kinematical parameters of the machine tool are two key factors for quality and productivity improvements. The aim of this paper is to present a unified method to compute the trajectory directly on the surface to be machined avoiding CAM approximations and producing a smoother trajectory. This paper proposes an interpolation of the trajectory based on the free form surface mathematical model while considering the kinematical limitations of a high speed milling machine (velocity, acceleration and jerk). The amelioration of the data exchange between CAD/CAM and CNC opens new ways to optimize the manufacturing process. The Direct Trajectory Interpolation on the Surface (DTIS) method allows to obtain both a higher productivity and a better surface quality. Machining experiments carried out with an Open CNC on a 5-axis high speed milling machine show the benefits of the proposed method compared to the classical strategies available with an industrial CNC.