Computational determination of the structure and hardness of rolls after induction hardening

The main problem of induction hardening consists in obtaining the requisite hardness of the surface layers of parts. In hardening rolls by currents of commercial frequency the hardness and thickness of the hardened layer are determined by the speed of motion of the inductor, its power, and the intensity of the sprayer cooling. The choice of these parameters with the help of a full-scale experiment is a very expensive and laborious operation. For this reason it is expedient to determine the regimes of induction hardening with the use of numerical experiments. The present work is devoted to the creation of software for computing the hardness in induction hardening from the cross section of the roll. Since the hardness of the steel is determined primarily by the structural state that dependes on the temperature regime, the software should included the solution of problems of thermal conduction, determination of the structural state, and calculation of the hardness as such. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 31–34, September, 1997.     

Experimental study of forming and tightening processes with thread forming screws

Thread forming screws are being increasingly used, particularly in the automobile industry. They are designed to directly assemble two parts by displacing material to form their own thread. This specificity implies knowledge of the screwing torque needed for the thread to be formed in the lower plate of the assembly and of the tightening torque necessary so as to establish the preload in the assembly. The experimental study presented in this paper is divided into two parts.The first concerns the thread forming process and shows the influence of the geometrical parameters of the thread forming screw and of the work-piece, and the influence of the process parameters on the maximum forming torque. A compromise can be proposed for the choice of the lead hole diameter, which is the most important parameter to be considered in order to keep a reasonable forming torque while obtaining threads deep enough to avoid stripping problems.The second part concerns the tightening process. An original experimental device is used to enable an empirical formula to be proposed, based on the ISO standard screw formula giving the tightening torque according to the preload applied inside the assembly.     

Optimization problem of the hardening of rolling mill rolls and methods of its solution

Conclusion At present it is suggested to use mathematical models, and not only for evaluating the quality of hardening. There is an increasing number of publications containing new models for optimizing regimes of heat treatment, for working out fundamentally new regimes, and also for the quantitative evaluation of rational parameters of the planned equipment. When the hardening regime for some product is chosen, and it is to be optimal according to some indices, a fairly complex problem of optimal control has to be solved. For that various means of solving optimization problems can be used: methods of statistical optimization (planning of extremal experiments, LP-search); methods of optimization with derivatives taken into account (nonlinear programming, successive linearization). On the basis of accumulated experience with the solution of problems of optimal control of the hardening process libraries of algorithms for optimization should be established.Judging by preliminary evaluations, the suggested trend of investigations will help improve the quality and reliability of engineering products on the basis of the computerassisted, deliberate use of all the available scientific information on processes of heat treatment.Central Research Institute of Metallurgy. All-Union Research and Design Institute for the Planning of Thermal Installations. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 19–23, September, 1989.     

The use of spatial impulse responses to characterise flexible forming processes with mobile tools

A novel test method for the characterisation of flexible forming processes is proposed and applied to four flexible forming processes: Incremental Sheet Forming (ISF), conventional spinning, the English wheel and power hammer. The proposed method is developed in analogy with time-domain control engineering, where a system is characterised by its impulse response. The spatial impulse response is used to characterise the change in workpiece deformation created by a process, but has also been applied with a strain spectrogram, as a novel way to characterise a process and the physical effect it has on the workpiece. Physical and numerical trials to study the effects of process and material parameters on spatial impulse response lead to three main conclusions. Incremental sheet forming is particularly sensitive to process parameters. The English wheel and power hammer are strongly similar and largely insensitive to both process and material parameters. Spinning develops in two stages and is sensitive to most process parameters, but insensitive to prior deformation. Finally, the proposed method could be applied to modelling, classification of existing and novel processes, product-process matching and closed-loop control of flexible forming processes.     

成型塑件内螺纹抽芯结构设计

针对传统脱螺纹结构附加设备多、生产保养复杂、脱模效率低等缺陷,提出了一种利用顶出动作脱螺纹的模具结构,该结构设计在顶出的同时利用顶出行程控制机构与同步顶出机构解决部件间运动矛盾,实现高效的内螺纹抽芯,可为类似塑件的模具设计提供一定的参考。     

Experience in TMT with the use of cold lengthwise rolling in dead rolls

Experience in the thermomechanical treatment of long stepped preforms for shafts (including torsion ones), studs, forcing bolts, and other articles from high-strength and maraging steels with the use of cold lengthwise rolling in dead rolls is described. The used variants of TMT make it possible to obtain hardened highly loaded machine parts with high quality and performance parameters. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 34–37, January, 2007.     

Development of deterministic-stochastic surface structures to improve the tribological conditions of sheet forming processes

In sheet-forming processes with mixed frictional state the tribological system is characterized to a great extent by the sheet-surface structure. This structure has the functions of storage, transport, and distribution of the lubricant, and take-up and transport of surface-abrasion particles. These functional characteristics are achieved by different of surface structure, the so-called stochastic and deterministic structures. The presence of micro channels connecting the surface pockets in stochastic structures allows the distribution of the lubricant in all directions but it is not possible to detain this lubricant in areas under high pressure, it simply flows aside. This ability is given by the isolated surface pockets (hydrostatic lubrication pockets) in deterministic structures. From this micro reservoirs the lubricant can be transported directly into the deformation zone by means of building up a hydrostatic pressure. However, because of the absence of micro channels it is not possible to transport the lubricant to all areas of micro contact between tool and sheet, the risk of cold-welding effects increases. Therefore, a new type of surface structure is developed by the combination of a deterministic and a stochastic sheet-surface structure. The results of strip-drawing experiments point out that the combination between isolated lubrication pockets and a network of micro channels to transport the lubricant in the space between these surface pockets leads to a improvement of the forming behaviour.     

Welding current prediction in GMAW and UGMAW processes using response surface methodology

Abstract

Among all process variables in gas metal arc welding (GMAW) process, welding current is the most influential variable affecting heat input and weld quality. Its dependence on other process variables in GMAW and universal gas metal arc welding (UGMAW) processes (which makes use of a specially designed torch to preheat the filler wire independently, before its emergence from the torch) has been investigated using four factor five level central composite rotatable design to develop relationship for predicting welding current, which enables to quantify the direct and interactive effects of four numeric factors, namely wire feedrate, open circuit voltage, welding speed and electrode stickout and one categorical factor preheat current. Mathematical models developed show that welding current increased linearly with increaseing wire feedrate and open circuit voltage, whereas it decreased with increasing electrode stickout and preheat current. Numerical optimisation was carried out, and the optimal solutions generated indicate that under the same input conditions higher deposition rates are achievable in UGMAW process.