Zhi Li Sun

Reflow Soldering Process Virtual Test Based on BPNN-GA and ANSYS

Experiment plays the prime method in soldering reflow profile forecasting. While its high cost and low efficiency makes the company hard to develop. According to the nonlinear relationship between the multi input and output, reflow profile input parameters setting method based on BP neural network and genetic algorithm(BPNN-GA) is proposed in the paper. Establish the finite element model of the PCB products with ANSYS software, and simulate the reflow profile. Temperature field in the PCBAs heat process is analyzed to help adjust to provide guidance for parameter settings partially. The result shows that the process of parameters set methods with BPNN-GA and simulating analysis with ANSYS is effective in establish the virtual test system. The obtained characteristic value meets product quality requirements well.

Real-Time Reliability Analysis and Optimal Distribution of the Reliability on Five-Axis Machining Center

The some five-axis machining center was investigated, and it divided ten subsystems. Based on analysis of fault data, the distribution of fault time submits to Weibull distribution, the distribution function and reliability function of each subsystem were confirmed. The reliability allocation model with the constraints of cost is established based on reliability prediction to get optimal reliability allocation results of the complicated mechano-electronic system. The most growth potential of the reliability of subsystem and growth situation of reliability of each subsystem could be got by using this method. The reliability allocation is an important part of reliability design, because its result influences system design directly. This provides reference for design improving of this series of new products.

Kinematic Reliability Analysis of Five-Axis Machine Tool

Five-axis CNC machine tool is the top product of numerically controlled machine tool. Kinmatic accuracy is an important index to evaluate the quality of mechanism. Kinematic accuracy analysis of the Five-axis machine tool in previous study ignores the randomness of each input error component, so the conclusions are imprecise. Using the homogeneous transformation, inverse kinematics of VMC650 Five-axis machine tool is calculated. Based on Multi-body System Theory, error model of the machine tool is presented. Considering the randomness of every input error components, applying the Monte Carlo method, math model of kinematic reliability of the mechanism is deduced. The calculation method of kinematics reliability are put forward applying point evaluation and track evaluation. Kinematic reliability analysis provides some theoretical reference for improving the machining accuracy and operation life of machine tool.

Study on Properties of Grinding Fluid Jet and Nozzle Position for Super-High Speed Point Grinding

Super-high speed point grinding is a new high-speed grinding technology with some excellent machining performances. In such a grinding process, there is a high-speed airflow rotating around the edge of grinding wheel which hinders the grinding fluid from injecting into the contact area and makes the fluid atomization and splash during grinding process, so as to decrease the ratio of effective grinding fluid into contact area and affect the surface integrity of workpiece. In this paper, the structure and properties of grinding fluid jet is analyzed, the velocity distribution field of the round turbulent jet is discussed theoretically and simulated. Based on the pressure balance principle, a mathematical model is established for the jet velocity at the fluid nozzle, which enables the grinding fluid to pass through the high speed airflow and enter into the contact area. According to the analysis of the grinding fluid velocity in the jet core, an engineering formula is given to calculate the position limit of nozzle during grinding process, as well as a practical design example for the high speed grinding machine is presented.

Analysis of Thermal Properties of Super-High Speed Hybrid Journal Bearing Based on ANSYS

Hybrid journal bearings are used in the high and super high speed cases mainly, such as the super-high speed spindle system. Since the bearing operates under high speed conditions, the excessive temperature rise of the bearing is a major reason to lower the accuracy of the main shaft system and limit the bearings working speed higher, as a result, restrict the bearing applications. In this paper, the thermal properties and the heat mechanism of such bearings are analyzed. The mathematical model of hybrid journal bearing is established to analyze the mechanism of generating heat. In addition, the temperature field distribution for the certain hybrid journal bearing at speed of 10000 rpm is studied by means of software ANSYS considering the heat transfer characters between fluid and solid. An improved measure about temperature rise of hybrid journal bearing is presented.

Study on Thermal Properties of Hybrid Journal Bearing for Super High Speed Grinding Machine

As the high speed bearings, hybrid journal bearings are usually used in high and super high speed grinding machine spindle system. Since the bearing operates under high speed conditions, the excessive temperature rise of bearing is a key factor to lower the accuracy of the spindle system and limit the bearings working speed, so restrict the bearing applications. In this paper, the model of hybrid journal bearing is established to analyze the heat mechanism. In addition, the temperature field distribution for the certain hybrid journal bearing at high speed is studied by ANSYS considering the heat transfer characters between fluid and solid. The experiment of temperature for hybrid journal bearing system in super high speed grinding machine is also performed. The thermal properties and the measure for controlling temperature rise of such bearings are analyzed.

The Reliability Virtual Experiment Based on Deep Groove Ball Bearing

With the application of explicit dynamics and probability finite element method, reliability virtual experiment of deep groove ball bearing is carried out. Based on self –adaptive mesh module of the ANSYS/LS-DYNA, true numerical simulation of the working process is presented after the three-dimensional finite element bearing model is built. Then, the contact stress and strain among balls, retainer and inner (outer) race and also the pressure law during the contact process are obtained. As the randomness of manufacture and assemblage tolerance is inevitable, Monte Carlo method is adopted when samples the bearing system. From the random sampling, a large sample data of the maximum contact stress is got and the reliability coefficient is calculated; and the contribution of each original manufacture error to the reliability sensitivity of the bearing is analyzed. Reliability virtual experiment offers a theoretical reference to fatigue strength calculation and dynamic optimum design of the bearing system, and the analysis process is easy to be program controlled.

Considering Thermal Deformation in Gear Transmission Error Calculation

This research analyze the gear for body temperature field, according to the body temperature field, it calculates comprehensive deformation of the loaded gear by using the contact method. It extracts the deformation of gear surface along the gear thickness and gear tall direction, calculating the gear non-involute error. It calculates the gear transmission error considering the thermal deformation. The results show that: Considering thermal deformation non-involute error of addendum is maximum, and there are no mutations in gear non-involute error the transmission error caused by mutation of elastic deformation mutate at single and double tooth alternating position. The bigger mutation becomes, the bigger vibration amplitude will be. The results of the study provide a solid basis to improve the motion transmission accuracy of gear.

Calculate Transient Availability of Complex Repairable System Base on Coherent System

Repairable system is complex, because of its diversity distribution form of units’ lives and its complex structure. In this paper we studied on a complex system. Lives and repairing time of units obey general distributions, we got the unit transient availability by using Markov renewal process, then got the system transient availability by using the character of coherent system. Finally gave example which verified by Monte Carlo method. This paper provided calculation base for more complex system.

Variation of Aerodynamic Load Engineering Analysis during Wind Turbine Run

In order to improve design reliability of wind turbine, it is needed that calculating method of aerodynamic load during wind turbine run. In paper from the angle of the project, NACA special airfoil of wind turbine is analyzed. Combined with thin-theory, airfoil angle of attack variation is deduced, meanwhile wind turbine actual force is calculated in each blade location point when blade of wind turbine is running based on wind shear theory and tower shadow effect. According to actual condition calculation method is engineering amplified, aerodynamic load calculation method of wind turbine blade is obtained. By this method aerodynamic load which is calculated match with experiment result, it fits better.