The International Journal of Advanced Manufacturing Technology

A novel high-order discretization method for the prediction of milling stability is proposed in this paper to increase the accuracy and efficiency considering the differential of directional cutting coefficient and vibration velocities. Same to the existing full-discretization method (FDM) and semi-discretization method (SDM), the milling system is expressed as a linear time-periodic equation and the time period is discretized into discrete time intervals to approximate the solution. In this algorithm, the cutting force coefficient matrix of the whole integrand is reconstructed to lay the foundation for the fast and accurate approximation. Then, the monodromy matrix (or the Floquet matrix) is calculated by the method used in the temporal finite element analysis (TFEA) instead of the multiple recursive algorithms which can improve the computational time. Finally, the computational efficiency is defined in a new way which gives quantitative comparisons for different discretization methods. It is shown that the proposed method can reduce the computational cost by 91–95% when the same errors are required.

Filler wire metallurgy was modified through temporally shaped laser pulses, controlling cooling cycles in a recently developed method. Trends were identified through efficient mapping while maintaining representative thermal cycles of welding processes. A primary pulse melted preplaced filler wires while a secondary, linearly ramped-down pulse elevated the nugget to re-austenization temperatures. Ramped-down pulses resulted in linear cooling rates comparable with and exceeding furnace-based methods, between 50 and 300∘C/s. The linear decay of laser output power guided the temperature through a regime to obtain desired microstructures. For three very high-strength steel filler wire chemistries, quenching resulted in smaller plates with cross-hatched microstructures, accompanied by grain boundary ferrite. Finer bainite microstructures started forming for fast linear temperature decay, about 250∘C/s. Slower decay or a weaker third cycle formed coarser microstructures with coalescent sheaves and less cross-hatching.

Do hình dạng phức tạp và chuyển động liên quan trong quá trình mài bánh răng liên tục, đặc điểm mài mòn của bánh xe mài khác với quy trình mài thông thường. Việc đánh giá mài mòn của bánh xe mài bằng thể tích vật liệu bị loại bỏ tích lũy đã được nghiên cứu thông qua các thí nghiệm tiến triển trạng thái mài mòn. Bằng cách thay đổi các tham số mài trong các thí nghiệm trực giao, bề mặt bánh xe mài với các trạng thái mài mòn khác nhau và độ nhám bề mặt bánh răng tương ứng đã được thu được. Kết quả cho thấy rằng kích thước phân diện có thể được sử dụng để định lượng sơ bộ trạng thái mài mòn của bánh xe mài. Một mối quan hệ gần như tuyến tính đã được tìm thấy giữa kích thước phân diện và thể tích vật liệu bị loại bỏ. Tốc độ mài, độ dày lớp gia công, tốc độ cho ăn và giá trị dịch chuyển đã được chứng minh là có ảnh hưởng lớn đến mài mòn của bánh xe mài. Một tương quan tiêu cực đáng kể đã được tìm thấy giữa kích thước phân diện và độ nhám bề mặt. Tuy nhiên, do chuyển động dịch chuyển, cả tham số mài thô và tham số mài hoàn thiện đều có thể ảnh hưởng đến bề mặt bánh răng. Kích thước phân diện nhỏ hơn được tìm thấy có liên quan đến bề mặt bánh răng mịn hơn và ngược lại. Dựa trên kết quả, các tham số mài trong quá trình mài tạo hình liên tục đã được khuyến nghị. Tốc độ mài nên được duy trì ở mức cao nhất có thể, với điều kiện lưu ý đến khả năng của dụng cụ máy. Độ dày lớp gia công bình thường từ 0.02–0.09 mm, tốc độ cho ăn từ 50–100 mm/phút, và giá trị dịch chuyển 7 mm nên được áp dụng trong quá trình mài hoàn thiện.

Sensorless contact force estimation methods facilitate the application of the serial manipulators to manufacturing as they enable robots to interact with unexpected collisions at low cost. In this paper, an external force estimation approach with no embedded sensors is proposed. The approach combines a Weighted Moving Average (WMA) with variable span, the standard Kalman filter (SKF), and its tuning routines. Improved confidence in the motor output torque is achieved due to the reduction of the measurement noise in the motor current by the WMA. The span of the filter adapts continuously to achieve optimal tradeoff between response time and precision of estimation in real time. With the comprehensive information of uncertainty in motor current noise and measurement errors of individual joints speed, an automatic tuning algorithm of the SKF is presented. Validation of the presented estimation approach in terms of estimation accuracy and response time was conducted on the Universal Robot 5 manipulator with differing end effector loads. It was found that the combined force estimation method leads to a reduction of the root-mean-square error and response time by 55.2% and 20.8% in comparison with the established method. The proposed method can be applied to any robotic manipulators as long as the motor information (current, joint position, and joint velocities) is available. Consequently, the cost of collision recognition could be reduced dramatically.

Modern cutting tools like end mills, drilling tools, and reamers underlie high requirements regarding geometrical accuracy, cutting edge quality, and production costs. However, the potential for process optimization is limited due to the process kinematics during grinding. Consequently, a novel tool grinding process for the manufacture of cutting tools has been developed recently at the Institute for Production Engineering and Machine Tools (IFW). This continuous generating grinding process allows the simultaneous production of all flutes and circumferential flank faces of rotational symmetrical cutting tools. The present paper focuses on the geometrical process design and develops a method to determine the necessary basic rack and process parameters in order to create a desired cutting edge geometry by continuous generating grinding. The developed method can define all parameters with an accuracy of up to 5 µm and 0.2° within a simulation in five iteration steps and allows not only the quantitative design of the cutting tool geometry but a qualitative modification of the flute geometry as well. Subsequently performed grinding tests showed that the presented method allows the design of grinding worms for continuous generating grinding of cutting tools and enables the successful implementation of these processes.

SiCp/Al composites are extensively used in aerospace, automotive, and civil applications, and the machining characteristic of SiCp/Al composites is an issue of great economic impact. This paper presents an experimental investigation of the drilling characteristics during machining of SiCp/Al composites with electroplated diamond drills; the drilling characteristics were evaluated in terms of drilling forces, tool wear, surface roughness, and entrance edge quality. Due to the very different machining properties between the SiC particles and Al alloy matrix, in a broader sense, the edge defect is defined as an undesirable effect generated at the edge of a workpiece after the machining process. The results demonstrate that with the increase of the drilling speed, both the thrust force and torques have no significant increase, while the surface roughness increased quickly. In addition, it is found that the formation of the entrance edge defects was associated with the varying of the drilling force and the electroplated diamond drills were subjected to an extremely rapid flank wear. The primary wear mechanism includes abrasive and adhesive wear of the flank face.

Because of its outstanding strength-to-density ratios, corrosion resistance, and other superior properties, Ti-6Al-2Zr-1Mo-1 V titanium alloy (TA15) is widely employed in aeronautics and astronautics. TA15 is a typical difficult-to-cut material with low heat conductivity, a high cutting temperature, and an easy adhesion characteristic. When machining difficult-to-cut materials, cryogenic machining is an efficient way to lower the cutting temperature. There is, however, few research on machining TA15 under cryogenic cooling conditions. In this study, tensile tests were performed under different low-temperature cooling conditions. By analyzing the changes of material properties under different low temperatures, the machining mechanism of TA15 under cryogenic cooling conditions was revealed. Then, cutting experiments were carried out under three cooling conditions: dry, cutting fluid (wet), and liquid nitrogen internal cooling (cryogenic). The results show that under cryogenic conditions, TA15 can effectively reduce plasticity and adhesion. The cutting experiments also prove that machining TA15 under the cryogenic cooling condition can reduce the surface adhesion, improve the machining quality of the machined surface, and effectively reduce the generation of tool adhesion wear.

There has been limited studies on corrosion behaviour of post-processed electron beam melted (EBM) Ti6Al4V, given that the factors affecting corrosion resistance of AM Ti6Al4V remain unclear. This paper proposes using heat treatment method to improve the pitting corrosion resistance of EBM Ti6Al4V. Different treatment profiles alter the microstructure of EBM Ti6Al4V. A clear trend is observed between microhardness and α lath width. As-printed EBM Ti6Al4V exhibits an inferior pitting potential, while heat treatment provided a significant improvement in the corrosion resistance. This study finds that the β phase fraction is a better indicator than the α lath width for pitting corrosion resistance. Solution air-cooled and ageing heat-treated EBM Ti6Al4V exhibits good mechanical and corrosion properties, and even performs better than commercial cast Ti6Al4V.

Laser metal deposition (LMD) has been a promising additive manufacturing technology widely used in mold rapid manufacturing. In order to improve the capacity of LMD for complex curved surface structures, a surface based variable thickness slicing (S-VTS) model is proposed to adaptively generate the LMD process based on the geometric characteristics of structures. Two deposition strategies in scanning and overlapping directions are designed to enable variable thickness of each cladding layer by dynamically adjusting the scanning speed and overlapping rate. To improve the surface quality and forming efficiency, the discrete particle swarm optimization (DPSO) algorithm is adopt to optimize the process parameters of S-VTS model, including the number of cladding layer, scanning pass, and segment per pass. Several experiments are conducted to form the cuboid samples with wavy and freeform surface and verify the feasibility of the S-VTS model. The results demonstrate that under the open-loop control condition, the geometric accuracy, surface quality, and efficiency of the proposed method is improved in comparison with uniform thickness slicing (UTS) deposition. Moreover, heterogeneous microstructure is always generated by the S-VTS method in terms of grain size and growth direction.