Titanium alloys are used in various industries due to their superior mechanical strength and corrosion resistance. However, titanium is classified as a difficult-to-machine material due to its low thermal conductivity that consequently causes poor tool life. In this study, cryogenic+MQL milling was performed to improve the machinability of Ti-6Al-4V; a cryogenic coolant and a minimum quantity fluid were sprayed simultaneously. The machinability was analyzed according to the cooling and lubrication conditions, focusing on the cutting force and tool wear. When the minimum quantity fluid was injected using two nozzles during cryogenic machining, the cutting force remained low despite the increase in machining distance due to the effective lubrication. The average cutting force at the long machining distances (82-86 passes) was 14.8% lower than that under the wet condition. The tool wear progressed without chipping, and the flank wear length was 55.5% lower than that of the wet machining because the cryogenic cooling and minimum quantity lubrication reduced the tool temperature, friction, and thermal shock.

Tool-center-point (TCP) calibration and geometric error identification procedures are proposed to improve the accuracy of a 6-axis manipulator with a tilting rotary table. The accuracy of a 6-axis manipulator is affected by the accuracy of TCP calibration. In general, TCP calibration of the 6-axis manipulator uses a conical fixture provided by the manufacturer. However, since a TCP cannot be accurately positioned to the tip of the conical fixture repeatedly, a large positional deviation occurs at the calibration depending on the worker proficiency. Thus, accuracies of TCP calibration and the 6-axis manipulator are reduced. In this paper, a 3-DOF measuring device, consisting of a nest with three dial gauges and a precision ball, is developed to calibrate the TCP and to improve the accuracy of the 6-axis manipulator. Then, geometric errors of a tilting rotary table are identified via double ball-bar measurements according to the ISO 10791-6 with TCP initial alignment using an extension fixture. Finally, proposed TCP calibration and geometric error identification procedures are validated experimentally, and they show improvements in positional accuracy by 55 and 90%, respectively.

In ultra-precision processes, such as aerospace parts and precision mold machining, the accuracy of a feed drive system should be secured to achieve sufficient form accuracy. Dual-Servo stages, which compensate for multi-DOF motion errors, are being developed depending on the applied processes. This paper deals with the fine stage of a dual-servo stage to compensate for 6-DOF motion errors of a linear stage. The proposed fine stage measured 6-DOF errors of the linear stage motion with capacitive sensors, a reference mirror, and an optical encoder. It compensated for the errors using the flexure hinge mechanism with piezo actuators. The error equations and the inverse kinematics were derived to calculate the 6- DOF errors and displacements of piezo actuators for 6-DOF motions, respectively. Performance evaluation was implemented to verify feasibility of the developed fine stage of the fabricated dual-servo stage. Through the step response test of the fine stage, compensation resolutions for the translational and the rotational motion were confirmed to be less than 10 nm and 1/3 arcsec, respectively. The 6-DOF motion errors in the verification test were reduced by 73% on average.

The directed energy deposition (DED) process has been used for enhancement of the mechanical property, repair, and part manufacturing. Post-process machining is required due to the low quality of the DED printed part. Even if the part is printed under similar conditions, dimensional variations occur frequently due to the accumulation of small printing errors. Due to tool overfeeding and the occurrence of the non-cutting area due to this variation, the quality of the finished part is not guaranteed. Therefore, the post-process machining should be carried out considering the actual printed part shape. Herein, the flexible post-process machining is proposed by utilizing the shape information through the on-machine measurement (OMM) of DED printed parts. The process margin for machining the design shape is calculated through the OMM of the geometric dimension of the printed part. Feedrate (Override) and machining path of each printing parts are flexibly determined depending on the process margin. This technique is applied to the pocket shape part printed with STS 316L material, and the rough and finish machining conditions are established. Rough machining time was reduced by adjusting the feedrate flexibly. The final form of accuracy and surface roughness were achieved under 30 and 0.25 μm, respectively.

Industrial robots are widely used for part manufacturing besides simple task (welding, assembly). A parallel kinematic machine (PKM) with extending axes have been utilized in large volume machining because of their adequate stiffness and agility. Parallelism error in the PKM with an extending axis causes deterioration of dimensional accuracy of machined parts. This paper proposes a technique for compensating the parallelism error through measurement of the squareness error between the PKM with its extending axes using a laser interferometer. The four squareness errors are estimated to reduce the parallelism errors. The squareness error is calculated by measuring linearity of the extending axis and the PKM moving axis, and through the measurement of diagonal displacement error and position dependent geometric errors. Compensation of the parallelism error was done by transforming the basic coordinate system of the PKM. The parallelism error was significantly reduced from 0.735 to 0.022 mm and further verified experimentally.

In the manufacture of mechanical components, volumetric errors of a machine tool should be checked and reduced to meet the required tolerance levels. In this paper, we propose a quick and simple method of measurement for checking and compensating geometric errors which include scaling and squareness errors. During the measurement, which usually takes approximately 5 minutes to complete, the machine tool is first commanded into four vertices sequentially on a virtual regular tetrahedron. Subsequently, the six lengths between four vertices are measured using a double ball-bar and geometric errors are calculated from the measured lengths. In order to verify the measurement result, the measured geometric errors are compensated using NC-code and the six lengths are re-measured to confirm the error correction. In conclusion, a double ball-bar circular test on XY-, YZ-, ZX-plane is done, first without compensation and then with the compensation of the measured geometric errors to check the effect of compensation practically.

The squareness measurement of driving axes of a machine tool is very important to evaluate the performance of the machine. Laser interferometer measurement system is one of the most reliable equipment to measure the squareness. However, squareness measurement using laser system with an optical square result in restriction of straightness optics setup and Abbe’s offset. This offset combines with angular errors during the motion of an axis to cause Abbe’s error. In addition, the difficulty in optical square setup causes restriction of other optics and limitation of measurable range. In this paper, mathematical approaches are presented to eliminate the Abbe’s error and to estimate squareness for full range by using the best fit of straightness data measured without an optical square. Experiments for squareness measurement of 3 axis machine tool were conducted and the proposed techniques were used for squareness evaluation with elimination of Abbe’s error and squareness estimation for the full travel range.