Temperature control scheme using hot-gas bypass for a machine tool oil cooler

et al. 2022

Machines

Self Cite

Machine tool (MT) accuracy is an important factor in the industry and is affected by heat generation through internal and external moving parts; the electrical components used; and variable environmental temperatures. Thermal errors lead to 40–60% of all MT errors. To improve MT accuracy, efficient techniques to minimize thermal errors must be identified. This study investigated the coolant temperature effects under different rotating speeds of a standalone built-in spindle system and computer numerical control (CNC) machine with a direct-drive spindle on the accuracy of thermal deformation prediction. The z-axis thermal deformation of the standalone built-in spindle system and CNC machine with a direct-drive spindle was conducted at different spindle rotating speeds and coolant temperatures at a constant coolant flow rate of 5 LPM. All experiments were conducted in a steady and dynamic operation according to ISO 230-3. For the standalone built-in spindle system, in comparison to the Mares model, the developed new model based on the coolant temperature effect on the Mares model (Mares CT model) can improve the thermal deformation prediction accuracy by 18.17% to 39.50% at different coolant temperatures of 12 ∘C to 26 ∘C and the accuracy can be controlled within the range of 0.03 μm to 5.24 μm, while the supply coolant temperature is above 16 ∘C. However, the thermal compensation analysis of the Mares CT model for a CNC machine with a direct-drive spindle shows a thermal deformation prediction accuracy improvement of 58.30% to 66.35% at different coolant temperatures of 22 ∘C to 28 ∘C and the accuracy can be controlled within the range of 0.14 μm to 4.05 μm. To validate the feasibility of the compensation model in real machining processes, dynamic operational analysis was performed for a standalone built-in spindle system and a CNC machine with a direct-drive spindle, and the thermal deformation prediction accuracy improved by 12.19% to 35.53% with the standalone built-in spindle system and 40.25% to 60.33% with the CNC machine with a direct-drive spindle. The compensation model analysis shows that the coolant temperature has a high impact on thermal deformation prediction and markedly affects system accuracy within certain limits.

“…The accuracy improvement (AI) of the system between the Mares model (δ M ) and the Mares CT model (δ MCT ) can be calculated using Equation (10):…”

Section: Multiple Linear Regression (Mlr) Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Coolant Temperature on the Thermal Compensation of a Machine Tool

Maurya

et al. 2022

Machines

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“…However, the response time delay of the coolant temperature variation exists under the sudden cooling load variation, which may cause over cooling or insufficient cooling problems of the cooling system. For the latest literatures in 2018 and 2019, Chiang et al [20] presents a novel temperature control by MATLAB simulation software to determine the specifications of outlet temperature control using a hot-gas bypass scheme of high-precision oil cooler with refrigerant R-32. Simulation results revealed that the proposed control scheme presented better temperature control accuracy than the traditional PID control.…”

Section: Temperature Difference T Imentioning

confidence: 99%

Enhancement of Machining Accuracy Utilizing Varied Cooling Oil Volume for Machine Tool Spindle

Hong

et al. 2020

IEEE Access

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In this study, varied cooling oil volume (VOV) control was developed for the oil coolant of a machine tool. This allows adjustment of the oil circulation flow rate in terms of the machining loads and rotational speeds of the spindle to remove the generated heat effectively from the spindle. A mathematical model of the cooling oil flow rate in terms of the rotating speed and torque of the spindle for VOV method is developed. From the thermal deformation experiments with the VOV method, the thermal deformations in both the Y-axis and Z-axis can be greatly reduced, by 70.1 % and 73.5 %, respectively, in variable rotational speed operation with a short operational period (10 minutes). Moreover, the VOV method was applied to shorten the required warm-up time of the spindle. The required warm-up time of the spindle can be shortened by 50 %, while the three axes of the spindle attain stable thermal conditions. In practical machining experiments, the machining accuracy with the VOV method can be greatly enhanced by 34 % to 62 % in comparison with the current case of constant cooling oil volume (COV). The VOV control system in the machine tool spindle can effectively reduce the thermal deformation and shorten the required warm-up time. In addition, the machining accuracy can be greatly enhanced. INDEX TERMS Thermal deformation, thermal suppression, varied cooling oil volume, machining accuracy.

“…The spindle is the key element of a machine tool; its accuracy and performance have considerable influence on the accuracy and quality of a machined product [13]. Chiang et al [14] indicated that the temperature control of a machine tool cooling system can effectively reduce the thermal effect on accuracy. The Smith predictive method was adopted to control the coolant output temperature of a machine tool within 0.1 • C. Li et al [15] applied variable coolant volume control in the dynamical machining of a spindle to enhance the accuracies of workpieces.…”

Section: Introductionmentioning

confidence: 99%

Machining Accuracy Enhancement of a Machine Tool by a Cooling Channel Design for a Built-in Spindle

Wei

2020

Applied Sciences

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This study presents a multiphysics simulation analysis that was performed for the cooling channel of a built-in spindle. The design of experiments (DOE) method was employed to optimize the dimension of the cooling channel, and a practical machining experiment was performed to validate the effect of the design. In terms of the temperature, pressure drop, thermal deformation, manufacturing cost, and initial cost considerations, the paralleling type cooling channel of the front bearing and the helical type cooling channel of the motor were adopted in the study. After the optimal design of the cooling channel was applied, the bearing temperature was reduced by a maximum decrease of 6.7 °C, the spindle deformation decreased from 53.8 μm to 30.9 μm, and the required operational time for attaining the steady state of the machine tool was shortened from 185.3 min to 132.6 min. For the machining validation, the spindle with the optimal cooling channel design was employed for vehicle part machining, the flatness of the finished workpiece was increased by 61.3%, and the surface roughness (Ra) was increased by 52%. According to the findings for the optimal cooling channel, when the spindle cooling efficiency is increased by the optimal cooling channel design, the thermal deformation and warm-up period can be reduced effectively, and the machining precision can be enhanced. This method is an efficient way to increase the accuracy of a machine tool.