From computer-aided to intelligent machining: Recent advances in computer numerical control machining research

The aim of this paper is to provide an introduction and overview of recent advances in the key technologies and the supporting computerized systems, and to indicate the trend of research and development in the area of computational numerical control machining. Three main themes of recent research in CNC machining are simulation, optimization and automation, which form the key aspects of intelligent manufacturing in the digital and knowledge based manufacturing era. As the information and knowledge carrier, feature is the efficacious way to achieve intelligent manufacturing. From the regular shaped feature to freeform surface feature, the feature technology has been used in manufacturing of complex parts, such as aircraft structural parts. The authors’ latest research in intelligent machining is presented through a new concept of multi-perspective dynamic feature (MpDF), for future discussion and communication with readers of this special issue. The MpDF concept has been implemented and tested in real examples from the aerospace industry, and has the potential to make promising impact on the future research in the new paradigm of intelligent machining. The authors of this paper are the guest editors of this special issue on computational numerical control machining. The guest editors have extensive and complementary experiences in both academia and industry, gained in China, USA and UK

Discrete modeling of sculptured surface machining for robust automatic feedrate selection

Traditional feedrate selection techniques currently used in three and five-axis CNC machining reduces milling efficiency. Manually estimated feedrates tend to be conservative and constant, greatly increasing mill time. The goal of this research is to develop robust techniques and software tools for automatically generating optimized feedrates for use on three and five-axis CNC mills, to both simplify the feed selection process and to increase the safety and efficiency of the milling operation through milling process simulation. The simulation software estimates milling force vectors for each tool move, and identifies a feedrate that maintains a desired peak force. The desired cutting force value may be selected to prevent cutter breakage, maintain part tolerance, or meet some other criteria. Other conditions are also considered, such as maximum allowable chip thickness and machine constraints. This allows for the generation of variable feedrates that are optimized for each tool move. The software consists of three distinct portions: a discrete mechanistic model, a discrete geometric model, and a CNC machine model. The mechanistic model estimates cutting forces as a function of cut geometry, cutter/stock relative velocity, and material constants. The geometric model keeps track of the changing in-process stock geometry and provides the cut geometry parameters required by the mechanistic model. The CNC machine model calculates the cutter/stock relative velocity based on feed inputs, machine kinematics, and controller behavior. A feed value is calculated in an iterative manner for each tool move based on the force estimates. The results of this research have produced accurate force estimates during sculptured surface machining, and have also demonstrated that this approach at automatic feedrate selection is feasible. Testing of feedrate selection has included the five-axis milling of production turbomachinery in an industrial environment. An average improvement in efficiency of 20% has resulted from the use of the optimized feeds

Multi-Axis Machining Project Development

Multi-axis milling is a manufacturing material removal process in which computer numerically controlled (CNC) tools cut away excess material through movement in four or more axes. Compared to traditional three-axis machining, multi-axis machining greatly increases the capability and accuracy of the CNC machining processes by reducing the amount of operations required to completely machine a part. Currently, the Industrial and Manufacturing Engineering Department at Cal Poly lacks an advanced CNC class that incorporates fourth and fifth axis CNC machining in the curriculum. This report describes the process behind creating a project for such a class. The class will demonstrate the increased capability of multi-axis machining through a multi-axis positioning machining project. To create the project for the class, a demo part was designed on SolidWorks to be machined on a multi-axis CNC mill. The part required initial operations to create a machining blank and workholding for the multi-axis mill, so these items were developed prior to the fabrication of the part. Each operation required a computer-aided design, computer-aided manufacturing, post-processing files, and engineering documentation. The project resulted in a multi-sided demonstration part that reflects the increased capabilities of fourth and fifth axis machining to be used in a class project in Cal Poly’s IME 336 Computer Aided Manufacturing II course

Towards efficient 5-axis flank CNC machining of free-form surfaces via fitting envelopes of surfaces of revolution

We introduce a new method that approximates free-form surfaces by envelopes of one-parameter motions of surfaces of revolution. In the context of 5-axis computer numerically controlled (CNC) machining, we propose a flank machining methodology which is a preferable scallop-free scenario when the milling tool and the machined free-form surface meet tangentially along a smooth curve. We seek both an optimal shape of the milling tool as well as its optimal path in 3D space and propose an optimization based framework where these entities are the unknowns. We propose two initialization strategies where the first one requires a user’s intervention only by setting the initial position of the milling tool while the second one enables to prescribe a preferable tool-path. We present several examples showing that the proposed method recovers exact envelopes, including semi-envelopes and incomplete data, and for general free-form objects it detects envelope sub-patches

End mill tools integration in CNC machining for rapid manufacturing processes: simulation studies

Computer Numerical Controlled (CNC) machining has been recognized as a manufacturing process that is capable of producing metal parts with high precision and reliable quality, whereas many additive manufacturing methods are less capable in these respects. The introduction of a new layer removal methodology that utilizes an indexing device to clamp the workpiece can be used to extend CNC applications into the realm of rapid manufacturing (CNC-RM) processes. This study aims to improve the implementation of CNC machining for RM by formulating a distinct approach to integrate end mill tools during finishing processes. A main objective is to enhance process efficiency by minimizing the stair-casing effect of layer removal so as to improve the quality of machined parts. In order to achieve this, different types of end mill tools are introduced to cater for specific part surfaces during finishing operations. Virtual machining simulations are executed to verify the method and the implications. The findings indicate the advantages of the approach in terms of cutting time and excess volume left on the parts. It is shown that using different tools for finishing operations will improve the capabilities of CNC machining for rapid manufacturing applications

A Practical and Optimal Approach to CNC Programming for Five-Axis Grinding of the End-Mill Flutes

For a solid carbide tapered end-mill, every flute includes a flute surface and a rake face along a helical side cutting edge, and the end-mill core is at the center and is tangent to all the flutes. The flutes significantly affect the tools cutting performance and life, and the core radius mainly affects the tools rigidity. Mainly, two methods are adopted in industry to grind the flutes; these are: the direct method and the inverse method. In the direct method, a flute is ground using a standard grinding-wheel moving in multi-axis machining to generate the rake face and the flute surface. However, the flute is the natural outcome of the grinding process without any control. On the other side, the inverse method employs the concept of inverse engineering to build a grinding-wheel that accurately grinds the end-mill flutes. This yields a free-form grinding-wheel profile that is used on a 2-axis grinding machine; however, the flute shapes are only exact on one section of the end-mill; when the grinding-wheel moves along the side cutting edge to smaller sections; the deviation of the generated flute from the designed one will be increased. Thus, neither can this method grind the rake face with the prescribed normal rake angle, nor generate the side cutting edge in good agreement with its design. Moreover, the grinding-wheel profile is very difficult and expensive to make. To address these problems, a practical and optimal approach for five-axis grinding of prescribed end-mill flutes is proposed by; first, establishing a 5-axis flute grinding theory describing the wheels locations and orientations during grinding the rake faces with constant normal rake angles; Second, introducing a simple grinding-wheel consisting of lines and circular arcs; and finally, applying an optimization algorithm to optimize the grinding-wheel shape and path. Overall, this approach significantly advances the CNC programming technique for the 5-axis flute grinding, and can substantially increase the quality of the solid carbide end-mills and lays a good foundation for the CAD/CAE/CAM of end-mills. The advantages of this approach over the other approaches are verified using computer simulation

Manufacturing Processes of Integral Blade Rotors for Turbomachinery, Processes and New Approaches

Manufacturing techniques applied to turbomachinery components represent a challenge in the aeronautical sector. These components are commonly composed of high resistant super-alloys; in order to satisfy the extreme working conditions, they have to support during their useful life. Besides, in the particular case of Integrally Bladed Rotors (IBR), they usually present complex geometries that need to be roughed and finished by milling and grinding processes, respectively. Thermoresistant superalloys present many challenges in terms of machinability what leads to find new alternatives to conventional manufacturing processes. In order to face this issue, this work presents a review of the last advances for IBR manufacturing and repairing processes.We are grateful to Basque Excellence university Groups IT IT1337-19, and Ministry of economy project IBRELIABLE (DPI2016-74845-R), and Elkartek PROCODA KK 2019-004

Computer Numerical Controlled (CNC) machining for Rapid Manufacturing Processes

The trends of rapid manufacturing (RM) have influenced numerous developments of technologies mainly in additive processes. However, the material compatibility and accuracy problems of additive techniques have limited the ability to manufacture end-user products. More established manufacturing methods such as Computer Numerical Controlled (CNC) machining can be adapted for RM under some circumstances. The use of a 3-axis CNC milling machine with an indexing device increases tool accessibility and overcomes most of the process constraints. However, more work is required to enhance the application of CNC for RM, and this thesis focuses on the improvement of roughing and finishing operations and the integration of cutting tools in CNC machining to make it viable for RM applications. The purpose of this research is to further adapt CNC machining to rapid manufacturing, and it is believed that implementing the suggested approaches will speed up production, enhance part quality and make the process more suitable for RM. A feasible approach to improving roughing operations is investigated through the adoption of different cutting orientations. Simulation analyses are performed to manipulate the values of the orientations and to generate estimated cutting times. An orientations set with minimum machining time is selected to execute roughing processes. Further development is carried out to integrate different tool geometries; flat and ball nose end mill in the finishing processes. A surface classification method is formulated to assist the integration and to define the cutting regions. To realise a rapid machining system, the advancement of Computer Aided Manufacturing (CAM) is exploited. This allows CNC process planning to be handled through customised programming codes. The findings from simulation studies are supported by the machining experiment results. First, roughing through four independent orientations minimized the cutting time and prevents any susceptibility to tool failure. Secondly, the integration of end mill tools improves surface quality of the machined parts. Lastly, the process planning programs manage to control the simulation analyses and construct machining operations effectively

Optimization of Three-Axis Vertical Milling of Sculptured Surfaces

A tool path generation method for sculptured surfaces defined by triangular meshes is presented in this thesis along with an algorithm that helps determine the best type of cutter geometry to machine a specific surface. Existing tool path planning methods for sculptured surfaces defined by triangular meshes require extensive computer processing power and result in long processing times mainly since surface topology for triangular meshes is not provided. The method presented in this thesis avoids this problem by offsetting each triangular facet individually. The combination of all the individual offsets make up a cutter location surface. A single triangle offsetting results in many more triangles; many of these are redundant, increasing the time required for data handling in subsequent steps. To avoid the large number of triangles, the proposed method creates a bounding space to which the offset surface is limited. The original surface mesh describes the bounding surface of a solid, thus it is continuous with no gaps. Therefore, the resulting bounding spaces are also continuous and without gaps. Applying the boundary space limits the size of the offset surface resulting in a reduction in the number of triangular surfaces generated. The offset surface generation may result in unwanted intersecting triangles. The tool path planning strategy addresses this issue by applying hidden-surface removal algorithms. The cutter locations from the offset surface are obtained using the depth buffer. The simulation and machining results show that the tool paths generated by this process are correct. Furthermore, the time required to generate tool paths is less than the time required by other methods. The second part of this thesis presents a method for selecting an optimal cutter type. Extensive research has been carried out to determine the best cutter size for a given machining operation. However, cutter type selection has not been studied in-depth. This work presents a method for selecting the best cutter type based on the amount of material removed. By comparing the amount of material removed by two cutters at a given cutter location the best cutter can be selected. The results show that the optimal cutter is highly dependent on the surface geometry. For most complex surfaces it was found that a combination of cutters provides the best results

Geometry and tool motion planning for curvature adapted CNC machining

CNC machining is the leading subtractive manufacturing technology. Although it is in use since decades, it is far from fully solved and still a rich source for challenging problems in geometric computing. We demonstrate this at hand of 5-axis machining of freeform surfaces, where the degrees of freedom in selecting and moving the cutting tool allow one to adapt the tool motion optimally to the surface to be produced. We aim at a high-quality surface finish, thereby reducing the need for hard-to-control post-machining processes such as grinding and polishing. Our work is based on a careful geometric analysis of curvature-adapted machining via so-called second order line contact between tool and target surface. On the geometric side, this leads to a new continuous transition between “dual” classical results in surface theory concerning osculating circles of surface curves and oscu- lating cones of tangentially circumscribed developable surfaces. Practically, it serves as an effective basis for tool motion planning. Unlike previous approaches to curvature-adapted machining, we solve locally optimal tool positioning and motion planning within a single optimization framework and achieve curvature adaptation even for convex surfaces. This is possible with a toroidal cutter that contains a negatively curved cutting area. The effectiveness of our approach is verified at hand of digital models, simulations and machined parts, including a comparison to results generated with commercial software