The use of potentiostatic techniques in the development of improved stainless steels for chemical plant

It is possible by potentiostatic methods to exactly forecast the behaviour of unusual material/corrodent systems; such methods may, consequently, be used for the development of corrosion resistant alloys. A new alloy on iron base (with, %, 25 Cr, 5.5 Ni, 3.0 Cu, 2.5 Mo) combines very good mechanical properties with resistance to general corrosion, pitting and crevice corrosion. Industrial applications include impellers for pumps operating in acid slurries (30% P₂O₅, 30% CaSO₄ as solids, 2% H₂SO₄, HF, H₂SiF₆; 60–80°C, three years without corrosion); pump impeller for sulfuric acid and other corrosive products shipped in tank ships; impeller for a sea water pump (no corrosion after 4 years' operation).     

A chip-breaking system for mild steel in turning

The reliability of machining operations is an essential requirement of modem automatic manufacturing systems. In the case of turning operations, in which unbroken chips are the major obstacles for automation, reliability implies chip control as a major aspect. Chip control in turning is difficult in the case of mild steel because chips are continuous. Thus the development of a chip breaker for mild steel is an important subject for the automation of turning operations. The presented experimental research deals with the modeling of the chip flow formation process using different insert geometrics, and leads to important characteristic parameters in chip control. This study has focused on the chip-breaker design and experimental cutting of mild steel with the chip breaker. The characteristics of chip breakage for mild steel with respect to cutting speed, depth of cut and feed were analyzed from the experimental results.     

数控车削加工编程方法

数控加工中,加工程序编制的合理与否直接关系到加工的可行性、加工质量的获得、生产效率的提高及允许的最低经济成本.编程人员在工作时,应立足于以上原则进行,做到编制的程序最合理、最实用.     

闭式压力机一种偏心齿轮加工机构

偏心齿轮是闭式单双点压力机最常用的曲柄核心构件,其加工过程较为繁琐,而且精度不容易保证。本文介绍了一种加工偏心旋转体的机械机构,能够有效保证偏心齿轮的加工精度。     

Automatic tool selection for rough turning operations

A method of automatically selecting cutting tools for rough turning operations on a CNC lathe is presented. While the selection procedure can deal with various economic objectives, only the minimum cost per component is considered in this paper. Selection is made from an appropriate tool library and in order to reduce the search time a heuristic method is employed.

The cost of machining with a given tool is estimated following the determination of the cutting conditions consistent with the constraints acting on the process. From a detailed examination of the constraints it is possible to ascertain whether the next tool in the library will give improved cutting conditions and the possibility of a lower cost. This procedure eliminates the need for an exhaustive search of the library and results in a very fast and efficient algorithm.

The results of ten tool selections are presented. In all cases the computation time for the heuristic approach was less than 5% of that for the exhaustive search. In eight out of ten cases the heuristic method selected the same tool as the exhaustive search; in the two cases where the tools selected were different, those selected by the heuristic method produced only a marginal increase in the operation cost.     

改造型花纹铣床加工工艺的研究与应用

针对普通CW61100车床被改造成数控花纹铣床后遇到主轴温度高报警、花纹辊寿命低、花纹辊易剥落等问题,采取优化机械结构和加工工艺、改善花纹孔型等措施,使花纹铣床满足了产品生产的需要,节约了成本,提高了生产效率。     

Thermal modeling for white layer predictions in finish hard turning

Part thermal damage is a process limitation in finish hard turning and understanding process parameter effects, especially, tool wear, on cutting temperatures is fundamental for process modeling and optimization. This study develops an analytical model for cutting temperature predictions, in particular, at the machined-surfaces, in finish hard turning by either a new or worn tool.A mechanistic model is employed to estimate the chip formation forces. Wear-land forces are modeled using an approach that assumes linear growth of plastic zone on the wear-land and quadratic decay of stresses in elastic contact. Machining forces and geometric characteristics, i.e. shear plane, chip–tool contact, and flank wear-land, approximate the heat intensity and dimensions of the shear plane, rake face, as well as wear-land heat sources. The three heat sources are further discretized into small segments, each treated as an individual rectangular heat source and subsequently used to calculate temperatures using modified moving or stationary heat-source approaches. Temperature rises due to all heat-source segments are superimposed, with proper coordinate transformation, to obtain the final temperature distributions due to the overall heat sources. All heat sources are simultaneously considered to determine heat partition coefficients, both at the rake face and wear-land, and evaluate the final temperature rises due to the combined heat-source effects.Simulation results show that, in new tool cutting, maximum machined-surface temperatures are adversely affected by increasing feed rate and cutting speed, but favorably by increasing depth of cut. In worn tool cutting, flank wear has decisive effects on machined-surface temperatures; the maximum temperature increases 2–3 times from 0 to 0.2 mm wear-land width. White layers (phase-transformed structures) formed at the machined-surfaces have been used to experimentally validate the analytical model by investigating tool nose radius effects on the white layer depth. The experimental results show good agreement with the model predictions.The established model forms a framework for analytical predictions of machined-surface temperatures in finish hard turning that are critical to part surface integrity and can be used to specify a tool life criterion.     

Sliding mode cutting force regulator for turning processes

Continuous sliding mode control is applied to turning processes for cutting force regulation. The motivation of the use of the slide mode control scheme is to solve the nonlinearity problem caused by the feedrate override command element in the commercial CNC machine tool. When the adaptive control algorithm is applied to the commercial CNC machine tool, it is one of the practical methods that the programmed feedrate is overridden after the control algorithm is carried out. However, most CNC lathe manufacturers offer limited number of data bits for feedrate override, thus resulting in nonlinear behavior of the machine tools. Such nonlinearity brings ‘quantized' or discrete effect so that the optimal feedrate is rounded off before being fed into the CNC system. To compensate for this problem, continuous sliding mode control is applied. Simulation and experimental results are presented in comparison with those obtained from applying adaptive control which is a widely used approach in cutting force regulation. Adaptive control loses its effectiveness in the presence of nonlinearity since it generally requires linear parametrization of the control law or the system dynamics. Experiments are conducted under various machining conditions, subject to changes in spindle speed, material of work-piece, and type of machining process. The suggested slide mode controller shows smoother cutting force fluctuation, which cannot be achieved by the conventional adaptive controller. The experimental set-up reflects the emphasis on the practicality of the sliding mode controller. In order to avoid the use of a dynamometer in the course of measuring the cutting force, the indirect cutting force measuring system is used by means of feed drive servo-motor current sensing.     

An adaptive fuzzy control system for turning operations

In the paper, an adaptive fuzzy control system is developed and then applied to control turning processes with highly non-linear and time-varying cutting characteristics. The control system employs linguistic rules to obtain a constant turning force under varying cutting conditions. In order to improve the performance of the non-adaptive fuzzy logic controler, and adaptive algorithm using a turning process identifier to adapt the output scaling factor of the fuzzy logic controller is included. It is shown, by experimentation, that the adaptive fuzzy control system is capable of providing an effective solution to the control of the constant turning force under varying cutting conditions.     

铸造车间旧砂冷却问题浅析

介绍了热砂形成的原因和不良影响,以及热砂冷却的方法.旧砂处理的核心部分是热旧砂的冷却.过高温度的砂子,对型砂性能、生产率以及环境有许多负面影响.热砂冷却方法可根据辐射、传导、对流及水分蒸发的原理进行,其中增湿并促使水分蒸发是使热旧砂迅速冷却的有效方法,每蒸发1%的水,砂温可降约24.5℃.增湿冷却的控制方法,主要有ZS系列旧砂增湿冷却系统和LIPPKE自动水份在线测量和控制系统两种方式.实际生产中主要的冷却设备有:冷却提升机、落砂冷却滚筒、振动沸腾冷却器、双盘搅拌冷却机.     

Low vibration control system in turning

This paper presents a system developed for on-line vibration control on a CNC lathe. The on-line vibration control system is composed of two subsystems, namely, the vibration monitoring subsystem, and the vibration reduction subsystem. A simple chatter criterion was adopted in the vibration monitoring subsystem in order to detect the occurrence of chatter as soon as possible. The vibration reduction subsystem is then triggered to suppress vibrations when chatter was detected. It was shown that chatter can be detected by comparing the standard deviation of signal collected on-line to an off-line experimentally determined value. The vibration reduction subsystem provides possible ways to reduce vibrations by adjusting cutting parameters including cutting speed and feed rate. Series of experimental tests were conducted to verify the feasibility of the proposed system. It was shown that the proposed system can generally detect the occurrence of chatter and reduce vibrations effectively when chatter occur.     

基于强冷策略的连铸小方坯二冷纵-横均匀冷却研究

以国内某钢厂ML40Cr钢连铸小方坯为研究对象,考虑凝固过程中结晶器气隙的形成,建立了连铸小方坯二维凝固传热模型。在避开钢的第三脆性温度区(674~814℃)与二冷强冷的前提下,将二冷比水量由0.89 L/kg增加到1.29 L/kg,二冷区2段铸坯表面喷淋水覆盖率调整为90%。结果表明,配水优化后,矫直点处连铸坯角部温度为802℃,处于钢的脆性温度区,最大回温速率较大,为122℃/m;调整喷淋水覆盖率后,矫直点处连铸坯角部温度为821℃,避开了钢的脆性温度区,最大回温速率为80℃/m,且角部温度升高了136℃,改善了角部过冷问题,较好地实现了连铸坯纵-横均匀冷却。     

Predictive machinability models for a selected hard material in turning operations

In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. Process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machinability models. Two important data mining techniques are used; they are response surface methodology and neural networks. Data of 28 experiments when turning austenitic AISI 302 have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the considered material.     

A grey prediction fuzzy controller for constant cutting force in turning

Constant force control is gradually becoming an important technique in the modern manufacturing process. Especially, constant cutting force control is a useful approach in increasing the metal removal rate and the tool life for turning systems. However, turning systems generally have non-linear with uncertainty dynamic characteristics. Designing a model-based controller for constant cutting force control is difficult because an accurate mathematical model in the turning system is hard to establish. Hence, this study employed a model-free fuzzy controller to control the turning system in order to achieve constant cutting force control. Nevertheless, the design of the traditional fuzzy controller (TFC) presents difficulties in finding control rules and selecting an appropriate membership function. To solve this problem, a grey-theory algorithm was introduced into the TFC to predict the next output error of the system and the error change, rather than the current output error of the system and the current error change, as input variables of the TFC. This design of the grey prediction fuzzy controller (GPFC) cannot only simplify the TFC design, but also achieves the desired result in TFC implementation. To confirm the applicability of the proposed intelligent controllers, this work retrofitted an old lathe for a turning system to evaluate the feasibility of constant cutting force control. The GPFC has better control performance in constant cutting force control than does the TFC, as verified in experimental results.     

Cycle optimization in cam-lobe grinding for high productivity

Cycle optimization in cam-lobe grinding is presented for improving productivity. It includes novel modeling of the instantaneous geometry, kinematics and temperature for any workpiece form. A technical assessment of three process-control strategies – (1) constant specific material removal rate, (2) constant power, and (3) constant temperature – is made. The constant-temperature process provides the shortest cycle time without thermal damage. A detailed analysis of this process considers the role of machine limitations, including maximum speed, acceleration, and jerk, as well as the cam-lobe geometrical effects. The optimization results are validated by grinding tests in an actual production line.     

A comprehensive dynamic cutting force model for chatter prediction in turning

This paper presents a model of the dynamic cutting force process for the three-dimensional or oblique turning operation. To obtain dynamic force predictions, the mechanistic force model is linked to a tool–workpiece vibration model. Particular attention was paid to the inclusion of the cross-coupling between radial and axial vibrations in the force model. The inclusion of this cross-coupling facilitates prediction of the unstable–stable chatter phenomenon which usually occurs in certain cases of finish turning due to process non-linearity. The dynamic force model developed was incorporated into a computer program to obtain time-saving chatter predictions. Experimental tests were performed on AISI 4140 steel workpieces to justify the chatter predictions of the dynamic cutting process model in both the finishing and roughing regimes. Experimental results corroborate the unstable–stable chatter predictions of the model for different cases of finish machining. In addition, experimental results also confirmed the accuracy of chatter predictions for various cases of rough turning.     

Mechanism for material removal in diamond turning of reaction-bonded silicon carbide

Reaction-bonded silicon carbide (RB-SiC) is a new ceramic material that has extremely high strength and hardness. Diamond turning experiments were performed on RB-SiC to investigate the microscopic material removal mechanism. Diamond tools with large nose radii of 10 mm were used for machining. It was found that the surface roughness was not significantly affected by the tool feed rate, but was strongly dependent on the tool rake angle. The mechanism for material removal involved plastic deformation, microfracture and dislodgement of 6H-SiC grains. Raman spectroscopy revealed that the silicon bond component underwent amorphization, while no phase transformation of 6H-SiC grains was observed. Tool wear was also investigated and two types of wear patterns were identified. Under the experimental conditions used, a surface finish of 23 nm Ra was obtained even at an extremely high tool feed rate of 72 μm/rev. This study demonstrates the feasibility of precision machining of RB-SiC by diamond turning at a very high material removal rate.     

Modeling of turning process cutting forces for grooved tools

A mechanistic modeling approach to predicting cutting forces for grooved tools in turning has been developed. The model assumes the existence of an equivalent orthogonal cutting operation for any oblique operation. The effects of tool nose radius and chip flow have been incorporated by defining a set of equivalent groove parameters. Two calibration methods have been presented for the model. A variety of commercial grooved inserts were chosen to validate the model. The workpiece material used was AISI 1018 steel. The force predictions from the model were found in good agreement with the measured forces. The effects of cutting conditions and groove parameters on the cutting forces and their implication in designing grooved tools were also determined.     

Development of a chip flow model for turning operations

A model is presented which predicts the chip flow direction in turning operations with nose radius tools under oblique cutting conditions. Only the tool cutting edge geometry and the cutting conditions (feed and depth of cut) are required to implement the model. An experimental study has verified the chip flow model and shown that the model's predictions are in good agreement with the experimental results.