Tools and Strategies for Grinding of Riblets on Freeformed Compressor Blades

A major goal in the design of turbomachinery is the increase of efficiency. To attain this increase, the flow losses must be reduced. A substantial proportion of the losses is generated by skin friction between compressor blades and working fluid. With respect to smooth surfaces, micropatterns (riblet-structures) reduce skin friction in turbulent flow by up to 10%. Grinding with multiprofiled wheels is an effective method for the manufacturing of riblet-structures on large plane surfaces. However, the grinding wheel wear affects the accuracy of the riblet geometry and the efficiency of the manufacturing process. Therefore, this paper shows the potential of different grinding wheel types for the manufacturing of riblet structures on an industrial scale with regard to tool wear. The results show that vitrified bonded tools are not suitable for the structuring of compressor blades. Here, axial forces lead to high profile wear. In contrast, grinding wheels with a metal bond are more wear resistant. However, the dressing process of metal bonded tools is time-consuming and causes 80% of the total machining time. As a consequence, just one blade can be structured per day. To increase the efficiency, a new grinding wheel was developed, which is bionically inspired by beaver teeth. The tool is constructed of alternating layers consisting of metal bonded diamonds and pure resin respectively. With this layer-by-layer setup, the tool does not have to be dressed and enables structuring of up to 50 compressor blades per day.BMBF/03V047

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

A new CAD/CAM/CAE integration approach to modelling flutes of solid end-mills

Milling is used widely as an efficient machining process in a variety of industrial applications, such as the complex surface machining and removing large amounts of material. Flutes make up the main part of the solid end-mill, which can significantly affect the tool’s life and machining quality in milling processes. The traditional method for end-mill flutes design is using try-errors based on cutting experiments with various flute parameters which is time- and resources-consuming. Hence, modeling the flutes of end-mill and simulating the cutting processes are crucial to improve the efficiency of end-mill design. Generally, in industry, the flutes are ground by CNC grinding machines via setting the position and orientation of grinding wheel to guarantee the designed flute parameters including rake angle, relief angle, flute angle and core radius. However, in previous researches, the designed flute profile was ground via building a specific grinding wheel with a free-form profile in in the grinding processes. And the free-form grinding wheel will greatly increase the manufacturing cost, which is too complicated to implement in practice. In this research, the flute-grinding processes were developed with standard grinding wheel via 2-axis or 5-axis CNC grinding operations. For the 2-axis CNC flute-grinding processes, the flute was modelled via calculating the contact line between the grinding wheel and cutters. The flute parameters in terms of the dimension and configuration of grinding wheel were expressed explicitly, which can be used to planning the CNC programming. For the 5-axis CNC flute-grinding processes, the flute was obtained with a cylinder grinding wheel via setting the wheel’s position and orientation rather than dressing the dimension of grinding wheel. In this processes, optimization method was used to determine the wheel’s position and orientation and evaluating the machined flute parameters. Beside, based on the proposed flute model, various conditions for grinding wheel’s setting were discussed to avoid interference of flute profile. A free-form flute profile is consequently generated in its grinding processes. However, in the end-mill design, the flute profile is simplified with some arcs and lines to approximate the CAD model of end-mills, which would introduce errors in the simulation of cutting processes. Based on the proposed flute-grinding methods, a solid flute CAD model was built and a CAD/CAM/CAE integration approach for the end-mill was carried out to predict the cutting forces and tool deflection. And also, the prediction results with various methods are verified to demonstrate the advantage of proposed approach. This work lays a foundation of integration of CAD/CAM/CAE for the end-mill design and would benefit the industry efficiently

Application of riblets on turbine blade endwall secondary flow control

© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Within the past 10 years, significant improvements have been achieved in the laser manufacturing process. It is feasible now to design various small-scale surface features (such as dimples, riblets, grooves, etc.) in gas turbine applications with the current manufacturing readiness level of laser surface texturing techniques. In this paper, the potential of adding riblets on a turbine endwall has been investigated through combined computational fluid dynamics and experimental studies in a low-speed linear cascade environment. Detailed comparisons of the flow structures have been made for cases with and without riblets on the endwall. The numerical results show that endwall riblets can effectively reduce the strength of the pressure side leg of the horseshoe vortex, lower the cross-passage pressure gradient, and alleviate the lift up of the passage vortex. Oil filmflowvisualization and exit aerodynamic loss survey in experiments support the computational fluid dynamics observations: The passage vortex loss core moves closer to the endwall with the addition of riblets. The present study consistently demonstrates that the addition of riblets can be an effective approach to reduce the endwall secondary flow. Further research questions are raised for the applicability of the riblets concept in actual engine conditions and options for design optimization

Parametric modelling of APT cutters and accurate calculation of their area moments of inertia

Due to cutting forces and the flexibility of the tool and its holder, the tool (or end-mill) deflects when it is engaging with the workpiece; unfortunately, large deflections can cost part accuracy, even break the tool. To produce high-precision parts, it is important to predict the deflections with high fidelity and then greatly reduce them through compensation in CNC tool paths. For this purpose, many research works have been successfully conducted on cutting forces prediction; however, another critical factor, the area moment of inertia of the tool, is always approximated, significantly reducing the accuracy of estimated deflections. The main reason for this is that the 3-D geometric model of end-mills is difficult to construct. To find the moment of inertia, in this work, first, a parametric model of APT cutters has been established and implemented in the CATIA CAD/CAM system by using its API. Then, a system of calculating the area moment of inertia for end-mills is built. Finally, a detailed discussion on the moment of inertia of end-mills is provided, along with comparison of this work with the existing methods. The major contributions of this work include the parametric end-mill modeling, which can automatically render the 3-D geometric model of an end-mill in seconds, and accurate calculation of the moments of inertia of end-mills. This work can be used, together with an existing cutting force calculation method, to accurately predict cutter deflections during milling in order to compensate them in CNC tool paths. It can also provide more precise 3-D solid models of end-mills for machining simulation by using finite element analysis

CAD of Solid Carbide End-Mills and its Applications

Nowadays, carbide end mills are widely utilized in the aluminum, titanium and steel cutting industries, so the more and more high-precision requirements to design of cutters are provided by users. Meanwhile, in order to finish the simulation and analysis of cutting processing, it is also important to design more free-control geometry model, and then transit into the CAD/CAM systems. For this purpose, many research works have been successfully conducted on optimizing the geometry model of cutters to get more real and easy controlled geometry; however, another critical factor, there are still more space to optimize the geometry model of cutters. To finish this task, in this work, first, a method has been established and implemented in the MATLAB to convert mathematic model into a free-form geometry model. Then, an accurate calculation system of area moment inertial of cutter is built. Finally, a detailed discussion on the cutting force of end-mills is provided, based on cutting simulation software. The major contributions of this work include the free-form end-mill modeling, which can render the 3-D geometric model of an end-mill in CATIA system, and a type of calculation of cutter area moment of inertial. This work can be used, together with an existing cutting force calculation method, to accurately predict cutting force during milling in order to get better geometry model of cutter. Meanwhile, solid modelling of the helical cutting tool can be carried out with computer graphics programming. It can also provide more precise 3-D solid models of end-mills for machining simulation by using finite element software

Optimization of Operation Sequencing in CAPP Using Hybrid Genetic Algorithm and Simulated Annealing Approach

In any CAPP system, one of the most important process planning functions is selection of the operations and corresponding machines in order to generate the optimal operation sequence. In this paper, the hybrid GA-SA algorithm is used to solve this combinatorial optimization NP (Non-deterministic Polynomial) problem. The network representation is adopted to describe operation and sequencing flexibility in process planning and the mathematical model for process planning is described with the objective of minimizing the production time. Experimental results show effectiveness of the hybrid algorithm that, in comparison with the GA and SA standalone algorithms, gives optimal operation sequence with lesser computational time and lesser number of iterations

Optimization of Operation Sequencing in CAPP Using Hybrid Genetic Algorithm and Simulated Annealing Approach

In any CAPP system, one of the most important process planning functions is selection of the operations and corresponding machines in order to generate the optimal operation sequence. In this paper, the hybrid GA-SA algorithm is used to solve this combinatorial optimization NP (Non-deterministic Polynomial) problem. The network representation is adopted to describe operation and sequencing flexibility in process planning and the mathematical model for process planning is described with the objective of minimizing the production time. Experimental results show effectiveness of the hybrid algorithm that, in comparison with the GA and SA standalone algorithms, gives optimal operation sequence with lesser computational time and lesser number of iterations