NC Machine Tools Research Articles

A novel tool path generation algorithm for plane envelope grinding convex surface based on constant scallop height method

This paper introduces a discovery about the geometric property of the tangent vectors of a constant scallop height (CSH) curve. Based on this discovery, a new tool path generation algorithm for plane envelope grinding a convex surface is presented, which aims at grinding convex surface with a cup wheel on five-axis NC machine tool. First, the envelop surface generated by a family of tangent planes of the convex surface is researched. Based on the research result, a method for computing the characteristic lines of the envelope surface is proposed, and then, an algorithm for searching the points of a CSH curve is presented. Second, the geometric properties of a CSH curve are researched, and an important discovery that the tangent vectors of a CSH curve are perpendicular to its corresponding normal vectors of the convex surface is made, which gives a method for precisely calculating the tangent vectors. Finally, on the basis of the research above, especially the tangent vectors of a CSH curve, a tool path generation algorithm is constructed. This algorithm can avoid computing the closed form expression of envelope surface and derive the largest width of grinding row with maintaining a CSH.

The Application of Maglev Supporting Technology in NC Machine

Feed motion guides driven by linear motor in NC machine for industrial applications mostly adopt mechani- cal support and they easily produce wear because of impact and high speed. For above characteristic and the requirement of machining accuracy, application of maglev supporting technology in NC Machine is raised. By analyzing the structure of maglev feed motion guide, the mechanical model of single-degree-freedom and multi-degree-freedom magnetic sus- pension system is proposed. By MATLAB, the curve of stiffness and damper in steady state is gained from the two groups of PID parameters, so that the influence of the controller parameters on the stiffness and damper is obtained and the vibra- tion area of feed motion guides is made smaller. The conclusion can be reached that the performance of maglev feed mo- tion guides is optimized by adjusting the parameters of controller properly that has an important theoretical significance for improving machining accuracy of NC machine tools.

Quasi-Close Loop Control of NC Machine Tools

There are some problems existing in open loop system with stepping motor as driving motor, such as lower servo precision, without compensation for step losing of stepping motor and so on. This paper presented a new approach called quasi-close loop control. With the help of the method, the control accuracy will be similar to that of close loop system and can be obtained, and the system will have the same stability as that of open loop system. With MCS-51 single-chip microcomputer as control unit and grating scales for measuring displacement, a quasi-close loop control system was built on NC lathe. The practice shows that the quasi-close loop control system has advantages such as high control accuracy, good stability and high cost performance. It is suited to economical NC machine tools and has wide application prospects.

Multiple Weibull Statistical Model of Random Censored Data of NC Machine Tools and Optimal Estimation of Parameters

According to the truncation feature of NC machine tools, this paper adopts Johnson rank adjustment method to deal with censored data, finding the distribution model of time between failures. At the same time, in order to increase the accuracy of parameter estimation of reliability data distribution model of NC machine tools, and to avoid the shortcoming that conventional optimization algorithms is difficult to get global optimal solution due to the influence of iteration initial value, this paper uses particle swarm optimization to solve the parameter of weibull mixture model. The result shows that particle swarm optimization can balance solution efficiency and convergence performance, it is not only feasible to estimate the parameter of mixture weibull distribution, but also to get more accurate results.

Research on Modification Algorithm of Cubic B-Spline Curve Interpolation Technology

Based on cubic B-Spline curve mathematical properties, theoretical analysis the cubic B-Spline curve recursive formula of Taylor development of first-order, derivation of two order in the interpolation cycle under the condition of certain interpolation increment only and interpolation speed, change the interpolation increments can be amended cubic times B-Spline curves purpose The simulation results show that meet the high-speed and high-accuracy NC machine tool require-ments of CNC systems.

Defects Cause Analysis Generated by Five-Axis NC Machine Tool and Optimization

In view of defects-"chew cutting" generated by the five-axis nc machine tool in the process of machining the S sample, the machine tool motion error model is established based on multi-body system theory. After that,combining sensitivity analysis theory with the research of machine tool processing defect causes.Then find out the main error terms which take great responsibility of machining defects and optimize related motion components,to meet accuracy requirements before leaving the factory.

Software Tool Used for Simulation of Metal Spinning Process for Complex Rotational Parts

Metal spinning on NC machine-tools is a very flexible and complex manufacturing method which has a high efficiency for small series of parts and prototype parts. The algorithms used for calculating the roller trajectory during the metal spinning process are usually complicated and hard to apply into production. This article presents an original application developed using Visual LISP that can be used for calculating and then simulating and testing the roller trajectory in the case of manufacturing rotational complex parts by metal spinning. The simulation prevents any errors that can occur during the process of manufacturing before the parts are actually put into production.

The Study of Compensation Method to Numerically-Controlled Machine Tool Geometrical Error

In this paper, the cause of nc machine tool geometric error made a more detailed analysis, the system error compensation methods are summarized, and on this basis this paper expounds the applications of all kinds of error compensation method, in order to further realize the accuracy of machine tool software upgrade to lay the foundation.

Characteristic Analysis and Optimization for the Tailstock Body of the NC Lathe

The characteristics of the NC Lathe tailstock has great influence on the machining accuracy of NC machine tools. Solidworks software is used to establish the tailstock body entity model, then import it into the Workbench software for finite element analysis and conclude its dynamic and statics characteristics. According to the result of the analysis on the topology optimization. Guarantee after optimization, the tailstock body not only can satisfy the requirement of machine tool, the quality can also be reduced by 5%. In saving material at the same time also can reduce the motion inertia, improve the machining accuracy.Keywords: tailstock body; statics analysis; modal analysis; topology optimization; Workbench;

Optimizing of Integral Impeller NC Program Based on the Material Removal Rate

It is a general processing technology that multi-axis NC machine tools is used for machining impeller at present. In order to improve the machining accuracy of the five-axis NC machine tools, the paper analyzes the computing interpolation error of the Multi-axis CNC system in detail. Some of the measures of tools selection have been proposed in purpose of diminishing the accumulative error of the system. The paper also establishes the optimized objective function to optimize the process parameters of the CNC machining based on the material removal rate. All these measures will improve the machining efficiency significantly and increase the stationary of the machining process.

Reliability Modeling on Time between Failures of NC Machine Tools

A reliability modeling method is proposed based on the time between failures of NC machine tools. According to the field data of the time between failures of a certain type of NC machine tools, parameter estimation of reliability model is made by use of particle swarm optimization (PSO)-based correlation coefficient optimization method, and it is proved that time between failure of CNC machine tool obeyed mathematical model of 3-parameter Weibull distribution via hypothesis testing. This provides the basis for reliability assessment of NC machine tool as well as the development of maintenance strategy in the future. Meanwhile, it also provides a theoretical reference for the reliability prediction of the whole NC machine tool.

Typical Workpiece Contour Surface NC Milling Tool Path Determination

In NC milling tool path reflects all the processing process, the tool path is reasonable or not, related to the workpiece processing quality and production efficiency, through several parts of the typical contour shape analysis, determination method of NC machining tool path, determined by the combination of NC milling tool path, to reduce the surface roughness of the workpiece, improve workpiece processing quality objective.

Correct Use and Maintenance of Nc Machine Tools

A country's level of Nc machine tool and ownership, is to measure the level of manufacturing and industrial modernization level of important indicators, is also an important index to measure national comprehensive competitiveness. Therefore, how to better use and maintenance of Nc machine tool is an important issue. This paper introduced how to reasonable use of Nc machine tools, as well as the use of the numerical control system and inspection.

Feed speed scheduling method for parts with rapidly varied geometric feature based on drive constraint of NC machine tool

As the existence of rapidly varied geometric feature and during the NC manufacturing process of this kind of parts, the actual moving speed of the workbench of the NC machine tool cannot reach the feed speed set in the NC program timely due to the drive constraint of NC machine tool. Furthermore, the machine tool would vibrate violently with the drive constraint when employing the constant machining parameter to process the parts with rapidly varied geometric feature, which seriously restricts the improvement of processing this kind of parts with high quality and high efficiency. In order to manufacture such parts with high quality and high efficiency, a sub-regional processing method with variable machining parameters is proposed. Firstly, the generation mechanism of the machining error is studied, and its mathematical model is built. Then the change rule of the machining error influenced by the curvature and the NC programmed feed speed is found out. Finally, taking the drive constraint and the machining error requirement into account, the relationship between the programmed feed speed and the curvature is established, and the corresponding programmed feed speeds to different curvatures are obtained. Taking the NC machining of the edge line of spiral microstrip antenna, which is an equiangular spiral, for example, the experiment results show that compared with the machining result with constant machining parameter, the maximum machining error of the sub-regional processing method with variable machining parameters decreases by 35.51% and the average value of the machining error decreases by 46.65%. For another example, the clover rose line is machined and the processing quality is also improved. This study proves that the method distributing the programmed feed speeds based on the curvature variation can improve the machining precision and ensure processing efficiency, and provides an effective method to manufacture parts with rapidly varied geometric feature.

Maintainability Modeling of NC Machine Tools Based on Repair Time

According to 62 field fault data from a certain type of 8 NC machine tools, maintainability distribution model is established based on the repair time. Hypothesis testing shows that the repair times of NC machine tools fit mathematical model of lognormal distribution. This provides the basis for maintainability assessment of NC machine tool as well as the development of maintenance strategy in the future.

Measurement of Transmission Nonlinearities in Servodrives

Paper presents transmission nonlinearities of servodrives. These nonlinearities directly affect the performance and precision of industrial machines such as robots, manipulators, NC machine tools etc. For measuring purpose of these nonlinearities a measurement test bench was created. Presented measuring test bench is used for static and dynamic measurements of servodrives as well as for precision and gear error evaluation. Paper focuses on properties, analysis and experimental measurements of angular transmission error, torsional elasticity and repeated position accuracy.

Failure Mode Analysis for High-Speed Motorized Spindle of NC Machine Tools

High-speed motorized spindle of NC machine tools is the core component for high speed machining. Production efficiency, machining accuracy, processing quality are greatly improved, and production cost is reduced by high speed machining. The paper describes the common failure modes of high-speed motorized spindle. By the fault tree analysis method, failure modes of motorized spindle are modeled, and the main fault reasons of motorized spindle for NC machine tools are gotten. Qualitative analysis is performed for the fault tree by the mean of the structure function. At the end of this paper, the minimal cut sets which are the main sets of failure modes are all obtained. It has laid a good foundation for further study of quantitative analysis of motorized spindle failure modes.

Application Analysis of Machining Simulation and Post-Processing of NC Turning Center

NC machining simulation, as one of the key technology in the field of CAD/CAM, can effectively check out the interference collisions that may occur in the machining process, significantly improve the safety usage of NC machine tools, has important practical significance to prevent the occurrence of machine accidents. Based on the integrated simulation module of UG NX software, this paper established the simulation model of NC turning center and elaborated the establishing process of machining simulation system, including the creation and verification of tool path, the digital model assembly, machine driver and motion model and so on. So tool path simulation and processing simulation were achieved, and the phenomenon of over-cutting and under-cutting between the parts and the cutting tool can be discovered timely. Meanwhile, on the basis of UG/Post module, the special postprocessor for NC turning center was developed to automatically output NC program, and the generated NC program can directly enter the NC machine tool for processing without manual modification, which will improve the efficiency and quality of automatic programming of machine tools, thereby shortening production cycle and reducing processing costs. Finally, the product processing examples verify the correctness and practicability of the special post-processor and process simulation system.

Approach to Study Bearing Thermal Preload Based on the ThermoMechanical Information Interaction Net

Owing to all the advantages of angular contact ball bearings (ACBB), including little energy consumption and low friction, etc, ACBB becomes the prior options for supportive components of NC machine tool spindle units. Thermal and mechanical behaviors of rigidpreloaded-ACBB are highly coupled, which produces the thermal preload. For investigating the effects of thermal preload on the bearing performances, this paper presents an ACBB thermo-mechanical information interaction net which is constructed on a collaborative computing platform. During the case study process, the thermo-mechanical information interaction net of a NSK ACBB 70BNR10X is realized. Thermal preload of the given ACBB is then predicted and analyzed through the information interaction net. In addition, effects of thermal preload on the ACBB operational stiffness are studied. With the help of temperature inspecting instrument, temperature tests are provided on the bearing thermo-mechanics test platform to validate the interaction net. Great agreements are found between the results predicted by the interaction net and the datum obtained through experimentation. The proposed information interaction net is useful for investigating the behaviors of runningbearing.

Preventive Maintenance Optimization of Availability for NC Machine

This paper addresses the problem of preventive maintenance optimization for NC machine tool. Firstly, the NC machine tool is divided into four subsystems according to the function module. The failure probability density function of each subsystem is estimated with the fault information records. Then, the optimal preventive maintenance period is estimated for each subsystem considering the availability. The optimal periods of all the subsystems are used to derive the preventive maintenance strategy of the whole machine. Finally, a numerical case is presented and the result shows the performance of the proposed approach.Keywords: NC machine tool, subsystem, availability, preventive maintenance