Manufacturing Of Freeform Surfaces Research Articles

Application of the Improved Grinding Technology to Freeform Surface Manufacturing

In order to meet the manufacturing requirements of modern space remote sensors for high-precision freeform optical parts, the grinding technology and its application were studied. The objective of this paper was to improve the application effect of traditional grinding technology in the processing of hard and brittle materials, and then apply it in specific fields. Therefore, the influence of key process factors such as cutting speed and removal depth on subsurface damage (SSD) was studied based on orthogonal experiments, and an improved grinding technology characterized by low SSD and high surface shape accuracy was formed. Then, the effect of this grinding technology was further verified by the high-precision manufacturing of freeform surfaces. A surface of a 130 mm diameter freeform surface was machined by improved grinding technology and combined polishing technology, the final root mean square of surface shape reached 12.1 nm. The improved grinding technology can reduce SSD from 20 μm to 10 μm, and improve the manufacturing efficiency of freeform surfaces above 30% when the cut speed is 20 m/s and the remove depth is 10 μm. The proposed technology can be applied to the extreme manufacturing of hard and brittle materials.

CAD modelling of the chip shape in case of ball-end milling

The manufacturing of free form surfaces is a common task in the field of mould and die manufacturing. The changing circumstances of the finishing milling with ball-end milling cutter has effect on the shape and the volume of the chip, the load of the cutting tool and the generated surface roughness. The aim of the article is to investigate the changing of the chip thickness and volume in case of ball-end milling by 3D CAD modelling, and to analyse the changing of the circumstances in case of milling of a convex and a concave surfaces.

Ductile machining of single-crystal germanium for freeform surfaces diamond turning based on a long-stroke fast tool servo

Freeform surfaces of single-crystal germanium are required increasingly in advanced infrared optics, but there are difficulties in processing due to the high hardness, brittleness and low fracture toughness of germanium itself. In the present study, the machining mechanisms and parameters of single-crystal germanium were investigated via ultra-precision diamond turning based on a long-stroke fast tool servo. To realize ductile regime machining, a ductile machining model in ultra-precision turning of germanium considering both feed rate, cutting depth and surface slope of freeform surface was proposed and discussed. A novel taper cutting test was adopted to determine the critical ductile–brittle transition depth. Subsequently, XYPFS were fabricated under different cutting parameters to demonstrate the effectiveness of proposed model. The morphologies of machined surfaces and cutting chips were identified and compared. Finally, a smaller feed rate and cutting depth should be used to reduce its maximum undeformed chip thickness and realize the ductile machining for a freeform surface having a large surface slope. The freeform surface of single-crystal germanium with a form error of ~1258 nm PV and surface roughness of ~1.92 nm Ra was successfully fabricated. In summary, this research provides a comprehensive understanding of ductile machining mechanisms of diamond turning based on a LFTS as well as is meaningful in the manufacturing of freeform surfaces on germanium or other brittle materials with optically qualified surfaces and high-precision.

Investigations on a novel process chain for manufacturing of freeform surfaces

Freeform optical surfaces have become increasingly important in recent years, as they can be used to construct optical assemblies with a reduced number of optical surfaces compared to systems without freeform surfaces, and thus optical systems can get more compact and lighter. However, the flexible and efficient production of precise optical freeform surfaces poses a major problem. This manifests itself in insufficient precision of the optics, long delivery times and high prices. It is shown, that ultrasonic grinding processes, combined with an ultra-fine grinding process and subsequent plasma jet polishing, are very well suited for the production of freeform optics and have a high technical and economic potential. Therefore, the aim is to validate an industrially suitable process chain based on this combination, in order to produce freeform optics of high accuracy (shape deviations <100 nm RMS) that can be manufactured in significantly fewer steps than before.

Micro milling of areal material measures –Study on surface generation for different up and down milling strategies

Abstract Ball end micro milling is a suitable process for the manufacturing of freeform surfaces and therefore appropriate for the manufacturing of material measures according to ISO 25178-70. In previous studies of the authors, ball end micro milling of areal material measures with specified microstructures was experimentally investigated and the influence of the cutting parameters, as well as the influence of the control dataset parameters and the tilt angle were systematically analyzed. The influences of the surface generation strategy (up or down milling) and the chosen tool path on the surface quality of the manufactured structure are investigated experimentally in this study. For this purpose, a full factorial experimental design is created in which two different areal material measure geometries (ACS and AFL as described in ISO 25178-70) are examined applying two different tools in two different surface generation strategies (up or down milling). In addition, two different cases per surface generation strategy are tested: the tool is retracted in the milled groove (case 1: reverse movement with engaged tool) or the tool is lifted between two paths (case 2: reverse movement without tool contact). On the basis of these two cases it is possible to evaluate how the repeatability of the z-axis (case 1) or the smaller short-wavelength roughness due to the second cut (case 2) influences the surface quality of the milled structure. In addition, a meander-shaped tool path is tested as reference: the tool moves alternately in up and down milling direction without lifting from the workpiece. The meander-shaped tool path is the most time-efficient and was applied in previous studies. As a result, information on the influence of the milling strategy on dimensional accuracy and surface roughness is provided. The quality of the manufactured surfaces is compared both quantitatively (based on areal surface texture parameters) and qualitatively (measured topography compared to nominal geometry).

Ball end micro milling of areal material measures: influence of the tilt angle on the resulting surface topography

Topography measuring instruments are calibrated by using material measures to estimate the measurement uncertainty and to ensure traceability. In ISO 25178-70, areal material measures are standardized, but no manufacturing process for their generation is defined. Therefore, previous studies examined the capabilities of multiple manufacturing principles for this application. Micro milling is an adequate process when the manufacturing of freeform surfaces in metal is required; it was proven that micro milling also is a generally suitable process for the manufacturing of material measures. In previous investigations, a study analyzing the influence of the control dataset design on the resulting surface quality of the micro milled material measures was carried out. It was shown that some control data parameters have a crucial influence on the surface quality, e.g. the tilt angle. When using ball end micro mills, a tilt angle prevents a cutting speed equal to zero in the mill’s center. When too small tilt angles are applied, ploughing of the material instead of a cutting occurs. However, at high tilt angles other effects that can lead to deviations between the target geometry dataset and machined geometry occur. In this experimental study the tilt angle’s influence on the resulting roughness and machined geometry was examined by micro milling sinusoidal freeform surfaces at different tilt angles. In addition to the deviation between intended and machined geometry and the roughness of the manufactured surfaces the correlations of the mentioned parameters to the tilt angle were additionally evaluated.

Optimization of the STEP-NC compliant online toolpath generation for T-spline surfaces using convolutional neural network and random forest classifier

Deep implementation of principals of the intelligent STEP-NC compliant manufacturing implies enabling a CNC system with integrated CAM functionality to perform all tasks autonomously. This means that most of the responsibilities of a CAM engineer need to be delegated to the CNC system. When it comes to manufacturing of freeform surfaces, the implementation of this approach becomes very challenging. One of the most important issues is the autonomous online toolpath generation. Making a choice of optimal machining strategies and other manufacturing parameters, that might be a trivial task for an expert, turns out to be not an easy problem for a machine, and often can be hardly solved using the traditional approach of explicit programming. Therefore, this paper proposes a method to optimize toolpath generation for T-spline surfaces, in particular, the process of choosing an optimal machining strategy for a given surface region using Machine Learning. The selection model has been trained to make a choice of the appropriate freeform machining strategy (two different strategies have been considered) based on the shape of an input surface.

Effect of Feed Rate, Tool-Path and Step over on Geometric Accuracy of Freeform Surfaces when 3 Axis CNC Milling

The use of freeform (sculptured) surfaces in the product design process is accelerating at an exponential rate driven by functional as well as esthetics demands. CAD/CAM software is a must in their design are relatively well-covered, issues still remain when it comes to the actual manufacture of freeform surfaces. The major issues are related to the chosen feed rate, toolpaths and step over that would assure the required surface quality, the minimization of the total machining time, etc. This research presents an experimental study to define the effects of machining’s parameters (including: feed rate; toolpath and step over) for CNC 3-axis ball end milling process. The result shows a model for cutting is formulated and incorporated into the parameters of machining that is compatible with all CAD/CAM systems. This result can be used to choose parameters of optimum including federate, toolpath and step over when machining of other freeform surfaces. Keywords: Freeform surface; tool path; ball end milling

Prospects for using T-splines for the development of the STEP-NC-based manufacturing of freeform surfaces

For successful development of the intelligent manufacturing of freeform surfaces using STEP-CNC with online toolpath generation capability, it is required to make a choice of the optimal representation of a 3D model which will be used for machining. Traditionally, most existing CAD-CAM systems use NURBS to design freeform surfaces and to perform toolpath generation in order to machine them. The introduction of T-splines to CAD systems and some reported results of using them in manufacturing makes it possible to consider T-splines, or more generally T-NURCCs (Non-Uniform Rational Catmull-Clark Surfaces with T-junctions), as a good solution for the development of the STEP-NC-based manufacturing of freeform surfaces because of their advantages over NURBS. Therefore, this paper gives an overview of the main arguments in favor of choosing the T-spline surface representation for integration within STEP-CNC systems. We examine the prospects for T-splines to become an integral part of modern manufacturing systems, and highlight some important properties of T-splines which are the most beneficial for manufacturing processes. The paper presents the results of the development of a complete T-spline-enabled STEP-CNC system which can strategically support online toolpath generation for three-axis ball end machining of simple T-spline surfaces using four different freeform strategies defined in ISO 14649-11. These results represent the implementation of the first stage of the development process of intelligent STEP-CNC systems, and in the future more research is needed in this direction.

Tool path generation for milling of free form surfaces with feed rate scheduling

The use of freeform (sculptured) surfaces in the product design process is accelerating at an exponential rate driven by functional as well as esthetics demands. CAD/CAM software is a must in their design and manufacture. While the geometric aspects of the design are relatively wellcovered, issues still remain when it comes to the actual manufacture of freeform surfaces. The major issues are related to the generation of the proper toolpaths that would assure the required surface quality, the minimization of the total maching time, the control of the magnitude of the cutting forces, etc. This paper presents an algotithmic procedure for tool path generation based on the criterion of maintaing the cutting forces at a constant pre-defined level for 3-axis ball end milling processes. To this end, a model for cutting force prediction is formulated and incorporated into the tolpath generation algorithm and software that is compatible with all CAD/CAM systems. It has been experimentally confirmed that the proposed algorithm offers a number advantages over the machining strategies used in commercial CAD/CAM software.

Dynamic Education as a Modern Education System of University

Abstract The contribution discusses the issue of modern education system of university. This method of education was designed within the KEGA project. Implementation of on-line classroom for dynamic education of the secondary technical school and university students focused on the design and manufacturing of freeform surfaces. The main objective of this teaching method of is improving the parent faculty cooperation with training centres and increasing the interest of secondary school students in the university studies of technical orientation.

On–Line Classroom for Dynamic Education

The article discusses the issue of on-line learning for Faculty of Materials Science and Technology in Trnava. This method of education was designed within the project KEGA: Realisation of on-line classroom for dynamic education of secondary technical school and university students focused on design and manufacturing of freeform surfaces. The main objective of this method of teaching is improving parent ́s faculty cooperation with detaches workplaces and increasing of the interest of secondary school students about studying on the college with technical orientation.

Tool Selection for Machining of Free Form Surfaces

The most important factor that affects the cost of the processing of free-form surfaces are cutting tool data. Therefore in this study, we develop a tool selection algorithm to manufacture of free form surfaces with minimum cost and time. This system can read surface information from IGES file and convert to NURBS and than determine convenient tools. The developed system in this study is implemented with Visual C++ and tested with machining of free form surfaces. As a result of testing, we have seen the tool path with developed system is shorter than conventional methods.

Five-axis STEP-NC controller for machining of surfaces

Five-axis machining is more widely used in manufacturing of freeform surfaces. However, in five-axis machining of freeform surfaces, incomplete information exchange between computer numerical control (CNC) and computer-aided design/computer-aided manufacturing (CAM) results in many limitations need to be rectified. In the paper, a new structure of CNC based on STEP-NC standard is proposed, where tool path planning, tool offset, and inverse kinematics are transferred from CAM to CNC. In order to guarantee good openness, open platform and standard interface are applied in the development. Technology of module collaboration and design of data flow are studied. A five-axis real-time interpolator for non-uniform rational B-spline surfaces machining is realized. Based on these technologies, a five-axis CNC is developed in the manner of software realization, which consists of interpreter, task coordinator, axis group, softPLC, etc. The software CNC system has been applied on a tilt-rotary type five-axis machine tool, where the milling experiment has been performed successfully.

A freeform surface manufacturing approach by integration of inspection and tool path generation

Freeform surfaces have been widely used in various engineering applications. Increasing requirements for the accuracy of freeform surfaces have led to significant challenges for the manufacturing of these surfaces. A method for manufacturing of freeform surfaces is introduced in this paper by integrating inspection and tool path generation to improve manufacturing quality while reducing manufacturing efforts. Inspection is conducted by comparing the digitised manufactured surface with the design surface to identify the error regions. In this new inspection technique, the areas on the manufactured surface that are beyond the design tolerance boundaries are used as the objective function during the localisation process, in order to minimise post-inspection machining efforts. The tool path generation methods are then selected based on the geometric characteristics of the identified error regions, for creating tool paths to remove the errors. Computational efficiency, machining efficiency, and quality are considered in this integrated method.

Control by virtual gauge of skew surfaces for correction process

The automation of production has been considerably developed in recent years in all its phases from design and manufacturing to control. The design and manufacture of free form surfaces are a current practice in the industry; thus, the conformity problem of complex geometry parts is felt more and more. The co-ordinate measurement machine (CMM) has largely reduced the acquisition and processing time in the take up measurement operation, which explains the wide use of the CMM in the mechanical industry over the last decade. The modelling and controlling procedure proposed within this paper enables correction of complex surfaces during the parts manufacturing process. The method is based on real surfaces modeled by finite elements starting from cloud points obtained by a digitalizing procedure in the co-ordinate measurement machine. The procedure was applied on a tooth gear which equips the gear box manufactured in the Algeria Engines and Tractors Factory. A comparison between the real and ideal model has been established showing the defects of form in order to correct the grinding process. This comparison is carried out by associating a surface of perfect geometry to a group of palpated dots. The selected criterion of optimisation is the least squares method.

A certification method for the milling process of free-form surfaces using a test part

It is generally admitted that the manufacturing of free-form surfaces requires the use of a CAD-CAM system. The toolpath accuracy and dimensional quality of the final shape have to be in accordance with the geometrical specifications. But most of the time, the final parts present deviations from the expected shape. These deviations may be due to either the toolpath calculation (CAM system) or the cutting process itself. In this paper, we propose an analysis of the whole milling process to point out the possible sources of errors. These errors generally lead to geometrical deviations and the final part does not meet the required specifications. As the errors can be linked to geometrical particularities of the shape, we propose a test part associated with check means to bring out problems. The milling of this part using two different techniques of toolpath generation shows that obviously both toolpaths are not error-free, and that errors result from different geometrical particularities of the part surfaces.

A New Concept for the Design and the Manufacturing of Free-Form Surfaces: The Machining Surface

This paper deals with a modeling method of free-form surfaces based on the new concept of the machining surface. The machining surface is built so that design intents and manufacturing requirements are ensured and so that it completely defines the tool movement necessary to produce a part. Therefore, approximations appearing during the elaboration process (CAD modeling, tool path calculation and free-form machining) are minimized. The concept of the machining surface described here relies on an analysis of the process quality.

Design and manufacture of free-form surfaces

Design and manufacture of free-form surfaces

Generating NC data at the machine tool for the manufacture of free-form surfaces

SUMMARY This paper describes the progress to date in the development of a software package for the machining of free-form surfaces by the real-time generation of NC control blocks at the machine tool. The salient features of the system are the complete elimination of paper-tape from the machining process and increased flexibility at the machine tool, particularly allowing production-orientated decisions to be made on the shop-floor rather than on the CAD system.