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Temperature control is an effective approach to ensure the weld quality produced by friction stir welding (FSW). In this study, the temperature of the tool–workpiece interface was controlled by a predictive PI (PPI) control method during bobbin-tool friction stir welding (BT-FSW). When the interface temperature was constant, the temperature of the heat affected zone (HAZ) was recorded at different welding speeds. The influence of interface temperature control on the thermal cycle of the HAZ was analyzed. The influence of interface temperature control on the material flow behavior was discussed using a theoretical model. The results of tensile tests showed that the tensile properties were not affected by changes in the tool rotational speed caused by controlling the interface temperature. In addition, regardless of the welding speed, there were optimal welding interface temperatures that caused a weld to have the highest tensile strength or elongation. The weld with the highest tensile strength broke in the HAZ, while the weld with the lowest tensile strength broke on the advancing side in the weld nugget zone because of the tunnel defects in this area. The high interface temperature will lead to these kinds of defects, because the high interface temperature will make the friction coefficient drop sharply, so that the driving effect of the tool on the material will be greatly weakened. The results of tensile tests indicated that interface temperature control can effectively ensure the weld quality. [ABSTRACT FROM AUTHOR]

This paper presents a new dynamic two-axis interpolation test method for dynamic accuracy calibration of rotary axis in a five-axis machine tool based on the double ball bar(DBB). The proposed method only requires synchronous movement of a single rotary axis and a single linear axis which is parallel to the average line of the rotary axis. The measurement trajectory is a spatial curve formed by the intersection of spherical and cylindrical surface, which are the reachable operating space of the DBB and the reachable operating space of the two moving axes, respectively. Compared to the circular tests described in ISO10791.6, which need at least three axes to synchronize motion, the proposed method can be effectively applied to the matching of servo parameters and the adjusting of the dynamic errors of the rotary axis, without the interference of additional linear axes. Meanwhile, the error trajectory pattern obtained by this method has the characteristics of orthogonality and regular variation, which is similar to the circular test of linear axis. So it can guide the calibration and optimization of rotating axis conveniently and effectively. Simulation results show that the proposed method can effectively identify the inverse error, scaling mismatch error, servo mismatch error, squareness error, and other error sources of the rotary axis. The proposed method is verified through experiments on a five-axis machine tool. [ABSTRACT FROM AUTHOR]

Press working causes structural deformation of the machine tool, especially the machine tool with large-span gantry or double columns used for the large-sized workpiece. The structural deformation makes the press tool out of accurate positioning, which leads to dimension deviation of the pressed workpiece. Even more, for thin-walled panel riveting, the structural deformation of the riveting machine will cause local deformations of the panel at rivet joints; this accumulated deformation will make the panel out of tolerance. An online deformation measurement and compensation method is developed for adaptive riveting with high accuracy and efficiency in this paper. During the process of servo driving riveting combined with force measurement, the force-displacement data points can be online obtained, and the recognized feature data points by a robust algorithm can represent the critical points during rivet deformation. Combined with the analytical springback of the rivet joint, the deformation of the machine tool can be accurately solved and compensated to the displacement of press tool for high­precision riveting. Simultaneously, with this innovative measurement method, the online quantity inspection for rivet joints can be realized synchronously. Also, a contrast experiment is conducted to validate the effectiveness of the online adaptive deformation compensation based on force-displacement data analysis. The results demonstrate the feasibility of the proposed method in riveting error compensation and riveting quantity inspection. [ABSTRACT FROM AUTHOR]

This paper presents an approach to optimize the shape of a general rotary cutter for five-axis flank milling of ruled and non-ruled surfaces. Based on the observation that tool shape optimization is equivalent to repositioning the control points of its B-spline meridian, the optimization of tool surface is reduced to that of a B-spline curve. Then, the meridian of rotary tool surface is represented by cubic B-spline curve, and it is used to obtain the analytic tool envelope surface. Subsequently, the flank milling error is measured by the distance between a point sampled from envelope surface and the design surface. On this basis, shape optimization of a general rotary cutter is formulated as an optimization problem from the perspective of approximating the tool envelope surface to the designed surface. Two examples are given to confirm the validity of the proposed method. The approach also applied to multi-pass five-axis flank milling. [ABSTRACT FROM AUTHOR]

For the joints of bobbin tool friction stir welding (BT-FSW), welding factors such as welding speed, tool rotation speed, and shoulder pinching gap have significant effects on the ultimate tensile strength (UTS) and tensile elongation (TE). This work developed empirical models to describe the relationships between the welding factors and the tensile properties of bobbin tool friction stir-welded 2219-T87 aluminum alloy. Based on the models, the factor effects can be analyzed quantitatively and graphically, and the UTS and TE of the joints can be predicted and optimized effectively. Firstly, experiments were carried out according to a three-factor and five-level central composite design (CCD). Secondly, empirical models were developed by fitting experimental data points. Adequacies of the models were checked by the analysis of variance (ANOVA). Thirdly, the analysis and optimization processes were conducted. Based on the expressions and plots of the developed models, the individual and interactive effects of the welding factors were investigated. By the multiple-desirability function and three-dimensional response surface methodology (RSM), the optimum welding factors were calculated from the models. The validation trial has been carried out, and the result shows that the models are adequate for predicting and optimizing the BT-FSW factor effects. [ABSTRACT FROM AUTHOR]

Shape of flexible part is easy to be out of tolerances due to deformations in the clamping and machining process. These deformations are generated randomly and hard to be predicted. Surface normal drilling and countersinking of flexible part is commonly necessary in aircraft assembly process. An online high precision surface normal measurement and cutter orientation compensation method is developed for adaptively drilling of flexible part in this paper. During the process of normal measurement and adjustment, the distance from tool nose to drilling point is accurately measured and adjusted synchronously, which is critical for countersinking. To accurately measure the current normal of the deformed workpiece, two 2D laser displacement sensors are applied to measure the surface profiles of the workpiece and sample two sets of geometrical points each time. Two crossed spatial curves are respectively fitted by the two sets of geometrical points, and the surface normal at the intersection point of the crossed curves is computed. After the deviation between the measured normal and tool orientation is calculated, an online compensation method is used to eliminate the deviation and meet the perpendicularity requirement of the cutter axis to the workpiece surface, and the distance from tool nose to drilling point is measured and adjusted to the setting value synchronously. The compensation method is based on the kinematic transformation of a five-axis machine tool and is implemented by NC compensation. Simulations and experiments are conducted to validate the feasibility and effectiveness of the online adaptive measurement and adjustment method. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) is a promising welding technology and is being extensively researched because it can produce high-quality joints. In the welding process, due to improper clamping, deformation of back support and other process variations, the axial force can vary significantly and produce welding defects. To solve this problem, a feedback controller of FSW axial force is desirable. However, time-delay, which widely exists within the FSW systems, may degrade the controller effect and make the system unstable. To regulate the axial force and compensate the time delay, this paper designs an axial force controller for FSW system with delay. At first, by utilizing a time delay compensation scheme, FSW systems with delayed control actions is transformed into standard differential equations without time delay terms. Then, an axial force controller is designed based on the linear-quadratic regulator (LQR) technique. Since the time delay is incorporated in the system model throughout the whole controller design process, the system performance and stability are assured and the control system is also simplified. Utilizing the LQR technique, aspects of system dynamic properties and simplicity are considered simultaneously. Experimental validations were carried out on a FSW platform. The experimental results demonstrate that the time delay is compensated effectively. The controller maintains the constant axial force and shows desirable dynamic behavior, even when the disturbance is encountered during the welding process. [ABSTRACT FROM AUTHOR]

Geometric error is among the most important fundamental elements that significantly affect the machining accuracy of multi-axis machine tools. This paper developed an efficient, accurate, and automatic geometric error measurement and identification method for rotary axis of a five-axis machine tool based on on-machine measurement by using a touch-trigger probe with a test piece. Before on-machine measurement, the test piece is installed and pre-machined to a designated geometry. Then, the coordinates of the reference points on the test piece are indirectly measured at different rotary axis positions. The geometric errors of each rotary axis then can be identified individually and the calculation algorithm is easy to establish and solve. Due to the special features of this method, neither the geometric inaccuracy of the test piece nor its installation error on the workbench affects the geometric error measurement and identification results. Geometric errors of a five-axis machine tool with double table rotary axes are measured as an example to validate the efficiency and effectiveness. [ABSTRACT FROM AUTHOR]

A new method is proposed to improve cutter life and cutting efficiency of five-axis plunge milling by solving two problems during plunge milling processes. First, the increase of radial depth often happens at the end of plunging phase, which will lead to large increase of cutting force. Second, friction between the cutter and the component always exists during the rising phase and low rising feedrate has to be used. Two suggestions, gradually decreasing the plunge depth and rising without engagement, are given by cutter companies to improve the cutter life and cutting efficiency. It is easy to realize them in three-axis plunge milling. However, in five-axis plunge milling, it is difficult because of the complexity of the material removing process. In this paper, a method to realize the above suggestions for five-axis plunge milling was proposed with the help of simulation. The tool path optimization method was validated by experiments and they showed that the cutter life and cutting efficiency were both improved. [ABSTRACT FROM AUTHOR]

A new plunge milling tool path generation method using medial axis transform is proposed to control the radial depth to improve the cutting efficiency and cutter life. Radial depth have great influences on cutting force and cutter life. Traditional plunge milling tool path generation methods such as zigzag may lead to large radial depth on some cutter locations. It is hard for these methods to judge and adjust the real radial depth. The method proposed in this paper is based on the inscribed circle of the offset contour generated by medial axis transform. Radial depth can be easily controlled in this method. Experiments showed that both the cutting efficiency and the cutter life were improved. [ABSTRACT FROM AUTHOR]

This paper investigates the analytical envelope surface model formed by specially designed cutting edge under cutter runout error, including axis offset error and tilt error, in five-axis flank milling. This model, which is independent of the machine tool type, is determined by the tangency condition in envelope theory. First, the cutter runout is defined by four parameters, namely offset distance, offset direction angle, locating angle, and tilt angle. Then, the cutting edge represented by cubic B-spline curve is used as the generator of cutter rotation surface to formulate the closed-form envelope surface model. In particular, the runout error and feedrate are both integrated into the model. In addition, we study special cases of the analytical model and the runout effect on envelope surface. Finally, computer example validates the feasibility of the proposed model with runout. We find that envelope surface formed by cutter edge is different from each other at the existence of runout, and envelope surface dedicated to final machined surface is generated by the composition of some segments of cutter edges. The results can be applied to tool path optimization in five-axis flank milling and NC simulation with cutter runout. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) has recently emerged as a solid-joining technology for high-strength aluminum alloys and light metal welding. The large axial force to be maintained between the welding tool and workpiece is the primary requirement of FSW process, which has also been a great obstacle to the design and application of FSW in manufacturing. Further complicating the issue is the need to perform FSW over three-dimensional contours, which requires a mechanism dexterous enough to set the stir pin used in welding to track a predefined trajectory with prescribed poses. Apart from the position specification, the design of a dexterous mechanism to pose the orientation of stir pin is a great challenge. This paper proposed the application of 3-PRS (P, R, and S standing for prismatic, revolute, and spherical joint, respectively) parallel mechanism as a welding tool head and employed it to form a five-axis welding machine tool for FSW. In order to accommodate the orientation capability requirements, the kinematic feature has been analyzed. With the dimensionless treatment of the Jacobian matrix of 3-PRS manipulator, a global condition index is proposed to estimate the kinematic dexterity in the whole orientation workspace. Finally, by means of an optimal design method and performance atlas, optimal designs of the 3-PRS parallel mechanism is carried out. A preferable set of optimized geometric parameters are obtained to achieve a compact and dexterous design, and the optimization results are used in development of a prototype machine for FSW. [ABSTRACT FROM AUTHOR]

Aiming at the special requirements of a shoe last high-speed machining process and the large dataset which could be gained by the reverse engineering technique, this paper analyzes the conventional tool-offset methods and presents a B-spline tool-offset model. A simple vector-analyzed algorithm to smooth the tool-offset curve in which there are local strange points is proposed, and then the second tool-offsetting, which obtains the fine data of the machining tool’s center points, is directly processed. To reduce the error from tool offsetting of the C2 continuity curve, this paper gains a smoother curve after processing via the edge points joint algorithm, which effectively solved the overcut or undercut problems in the high-speed machining of the spline curve. [ABSTRACT FROM AUTHOR]

In complex high-speed machining of consecutive small line blocks, the tool path segments can be so short that a machining center moving at a high feedrate cannot accelerate or decelerate fast enough to make direction changes accurately. Aiming at adjusting the feedrate automatically to achieve maximum productivity, this paper present a novel mathematical model considering the key and representative factors, and then based on it, propose an algorithm to seek the approximate optimal feedrate by evaluating the toolpath ahead. Simulation results demonstrate the machine using the proposed model and algorithm can go fast where possible and to slow down just enough where needed and the productivity can be improved dramatically . [ABSTRACT FROM AUTHOR]

In order to achieve high accuracy in the laser measuring of free-form surfaces, equal step-length sampling usually involves much more measurement data than necessary. An equal arc-length sampling method based on tangent extrapolation of cubic spline curves is introduced to solve this problem. By this method, step-length is adjusted adaptively according to the slope variation of the sampled curve with arc-length maintained to be constant, thus the small slope region is sampled sparsely while the large slope region is sampled densely. Sampling simulation of a typical surface proves that the data amount of equal arc-length sampling is much less than that of equal step-length sampling under the same circumstance. [ABSTRACT FROM AUTHOR]