Eccentricity and hardness control in cold rolling mills with a dynamically constructed neural controller

The main objective of a steel strip rolling process is to produce high quality steel at a desired thickness.  Thickness reduction is the result of the speed difference between the incoming and the outgoing steel strip and the application of the large normal forces via the backup and the work rolls.  Gauge control of a cold rolled steel strip is achieved using the gaugemeter principle that works adequately for the input gauge changes and the strip hardness changes.  However, the compensation of some factors is problematic, for example, eccentricity of the backup rolls.  This cyclic eccentricity effect causes a gauge deviation, but more importantly, a signal is passed to the gap position control so to increase the eccentricity deviation.  Consequently, the required high product tolerances are severely limited by the presence of the roll eccentricity effects.
In this paper a direct model reference adaptive control (MRAC) scheme with dynamically constructed neural controller was used.  The aim here is to find the simplest controller structure capable of achieving an optimal performance.  The stability of the adaptive neural control scheme (i.e. the requirement of persistency of excitation and bounded learning rates) is addressed by using as the inputs to the reference model the plant's state variables.  In such a case, excitation is due to actual plant signals (states) affected by plant disturbances and noise.  In addition, a reference model in the form of a filter with a desired transfer function using Modulus Optimum design was used to ensure variance in the desired dynamic characteristics of the system.  The gradually decreasing learning rate employed by the neural controller in this paper is aimed at eliminating controller instability resulting from over-aggressive control.  The moving target problem (i.e. the difficulty of global neural networks to perfrom several separate computational tasks in closed -loop control) is addressed by the localized architecture of the controller.  The above control scheme and learning algorithm offers a method for automatic discovery of an efficient controller.
The resulting neural controller produces an excellent disturbance rejection in both cases of eccentricity and hardness disturbances, reducing the gauge deviation due to eccentricity disturbance from 33.36% to 4.57% on average, and the gauge deviation due to hardness disturbance from 12.59% to 2.08%.

Unlawful acts, unkind architecture and unhelpful perceptions: a case study of Market Square Mall, Geelong

On a quiet Sunday afternoon in January 2015, a 12 year old girl was assaulted in Geelong’s Market Square mall. The attack sparked a media furore over what should be done to address the ongoing safety and amenity issues of this intractable public space. The city’s mayor, Cr Darryn Lyons, responded to the situation by declaring the mall a ‘haunt for bogans and scumbags’ and renewed calls for its demolition. Such rhetoric highlights the exclusionary mindset that casts certain types of people as undesirable inhabitants of public spaces. It also bolsters negative public perceptions of the mall. Once formed, such attitudes are difficult to shift, despite an overall improvement in the area’s crime rates over recent years. Poor perceptions are further reinforced by the soulless nature of the mall’s built fabric and weak urban interfaces. Its formal language is one of hostility, not only towards would-be delinquents, but to all people. The space is furnished with cold stainless steel seats, CCTV cameras and limp, pavement water spouts, while its inactive edges consist of loading bays, security grilles and neglected facades. This paper considers how a more inclusive architecture might be utilised to create a kinder, more generous physical environment that reflects the public nature of the space. While not a quick fix, fostering an architecture that encourages a more equitable use of the mall may diminish the sense of fear, anxiety and suspicion that the space currently elicits, tackling the problem at both a structural and social level.

Ultrafine grained ferrite formed by interrupted hot torsion deformation of plain carbon steel

A plain carbon steel was deformed using a hot torsion deformation simulator. A schedule known to produce strain-induced ferrite was used with the strain interrupted for increasing intervals of time to determine the effect of an isothermal hold on the final microstructure. Microscopy and electron back-scattered diffraction (EBSD) were used to analyse the changes that occurred in the partially transformed microstructure during the hold and the subsequent applied strain. The strain-induced ferrite coarsened during the hold and this coarsened ferrite was refined during the second deformation. These results were compared to those obtained for a different plain carbon steel deformed in single pass rolling close to the Ar3 temperature.

Fragmentation of orientation within grains of a cold-rolled interstitial-free steel

The formation of a favourable recrystallization texture in interstitial-free (IF) steels depends on the availability and activation of particular nucleation sites in the deformed microstructure. This paper presents a description of the deformed microstructure of a commercially cold-rolled IF steel, with particular emphasis on the microstructural inhomogeneities and short-range orientational variation that provide suitable nucleation sites during recrystallization. RD-fibre regions deform relatively homogeneously and exhibit little short-range orientational variation. ND-fibre regions are heavily banded and exhibit considerable short-range orientational variation associated with the bands. While the overall orientational spread of ND-fibre grains frequently is about the ND-axis, the short-range orientational variation often involves rotation about axes in the TD-ND plane that are nearer to the TD than the ND.

Understanding the deformed microstructure of cold-rolled IF and LC steel

This paper presents an overview of a series of investigations of the microstructure and texture of cold-rolled IF and LC steel. The investigations made extensive use of orientation mapping using electron backscattered diffraction (EBSD) in a field emission gun scanning electron microscope (FEG-SEM). The effect of grain boundaries on the deformed microstructure was examined by comparing the textures of regions near grain boundaries and in the interiors of grains.  A general weakening of the texture, but a strengthening of the {OOI}<110> component, occurs in the vicinity of grain boundaries. Misorientation angle and axis distributions were used to characterise the fragmentation of grains belonging to different orientation classes. The influence of carbon on the deformed microstructure and nucleation during recrystallization was clarified by examining the microstructures of LC and IF steels during rolling and annealing. The
results of the investigations emphasize the important role of shear banding in determining the fragmentation behaviour of ND-fibre grains and the orientations of viable recrystallization nuclei within the deformed microstructure.

Development of the sheared edge in the trimming of steel and light metal sheet, part 1 - experimental observations

Trimming experiments were conducted on sheet metals including two drawing steels, an aluminum alloy and a magnesium alloy, using a specially designed die in a mechanical press. The punch-die clearance was varied and data obtained on the rollover and burr height as a function of the clearance. Samples were also partially trimmed to examine crack initiation, the generation of the fracture surface profile and mechanism of burr formation. The results showed that while the burr height and rollover depth generally increased with increasing clearance for all examined materials, there were differences in the fracture surface profile shape, the burr shape, and the mechanism of burr formation, between the two steels and the two light alloys. The major cause of these differences appeared to be the rate of crack propagation through the sheet material.

Development of the sheared edge in the trimming of steel and light metal sheet, part 2 - mechanisms and modelling

The shearing behavior of a drawing-steel and aluminum alloy were investigated using hardness contours of partially deformed samples and a finite element model of the trimming process. Results showed that the stress and strain distributions within the work-piece were more strongly dependent on the punch penetration than the material properties of the work-piece. Differences in the final fracture surface profile and burr formation of the drawing-steel and aluminum alloy were a consequence of the shape of the stress and strain distribution when the crack in the sample became unstable, not when it was initiated. Results and existing literature suggest that a correlation may exist between the strain-rate sensitivity of the work-piece material and the burr mechanism and fracture surface profile of the trimmed part.

Experimental and numerical investigation of low pressure tube hydroforming on 409 stainless steel

Tube hydroforming has been widely used to produce automotive structural components due to the superior properties of the hydroformed parts in terms of their light weight and structural rigidity. Compared to the traditional manufacturing process for a closed-section member including stamping and followed by welding, tube-hydro forming leads to cost savings due to reduced tooling and material handling. However, the high pressure pumps and high tonnage press required in hydroforming, lead to increased capital investment reducing the cost benefits. This study explores low pressure tube hydro forming which reduces the internal fluid pressure and die closing force required to produce the hydroformed part. The experimental and numerical analysis was for low pressure hydro formed stainless steel tubes. Die filling conditions and thickness distributions are measured and critically analysed.

Experimental stress analysis of a steel light truck wheel

The development of a new automotive wheel requires extensive testing and possible design changes. The wheel investigated had three major changes during development. These three designs were subjected to a stress analysis, by experimental methods, to allow a comparison to be made between each design. The experimental program tested the wheels under conditions designed to simulate the loading of the front wheels whilst cornering. A loading frame was built for this purpose and all testing was performed statically by multiple loading for different directions of bending moment. Brittle lacquer coatings were used on each wheel to highlight high strain areas and indicate optimum locations for the placement of strain gauges. The strain gauges were then used to evaluate the strains. Wheel stud loads were also monitored via strain gauges applied to two of the wheel studs. All data was stored on magnetic tapes and the stress analysis performed by means of a minicomputer. The results of the stress analysis showed quantitatively the improvement in design from the first to the third wheel design. The analysis of the stud loads and their variation during loading indicated the optimum wheel mounting face geometry to ensure nut loosening would not occur in service.

Fine structure of shear bands formed during hot deformation of two austenitic steels

Shear bands formed during both cold and hot plastic deformation have been linked with several proposed mechanisms for the formation of ultrafine grains. The aim of the present work was to undertake a detailed investigation of the microstructural and crystallographic characteristics of the shear bands formed during hot deformation of a 22Cr-19Ni-3Mo (mass%) austenitic stainless steel and a Fe-30 mass%Ni based austenitic model alloy. These alloys were subjected to deformation in torsion and plane strain compression (PSC), respectively, at temperatures of 900°C and 950°C and strain rates of 0.7s_-1 and 10s_-1, respectively. Transmission electron microscopy and electron backscatter diffraction in conjunction with scanning electron microscopy were employed in the investigation. It has been observed that shear bands already started to form at moderate strains in a matrix of pre-existing microbands and were composed of fine, slightly elongated subgrains (fragments). These bands propagated along a similar macroscopic path and the subgrains, present within their substructure, were rotated relative to the surrounding matrix about axes approximately parallel to the sample radial and transverse directions for deformation in torsion and PSC, respectively. The subgrain boundaries were largely observed to be non-crystallographic, suggesting that the subgrains generally formed via multiple slip processes. Shear bands appeared to form through a co-operative nucleation of originally isolated subgrains that gradually interconnected with the others to form long, thin bands that subsequently thickened via the formation of new subgrains. The observed small dimensions of the subgrains present within shear bands and their large misorientations clearly indicate that these subgrains can serve as potent nucleation sites for the formation of ultrafine grain structures during both subsequent recrystallisation, as observed during the present PSC experiments, and phase transformation.

Prediction of ductile fracture in the cold forging of steel

The thesis describes the development of a model of the cold forging process that accurately predicts the initiation of ductile fracture. The effect of the deformation history of the material during multiple forming operations is considered. Both two- and three-dimensional numerical models of the forging process were combined with a ductile fracture criterion to predict the material ductility and damage distribution in the workpiece.

Deformation behaviour of ultrafine grained steel produced by cold rolling of martensite

An ultrafine grained Nb microalloyed steel was produced by cold rolling of martensite followed by annealing heat treatments at different times to study its effect on the microstructure and mechanical behaviour of the ultrafine grained steel. High strength was achieved by this thermomechanical processing due to the formation of cell and subgrain dislocation substructure; however annealing reduced both strength and elongation.

Stability of oxide films formed on mild steel in turbulent flow conditions of alkaline solutions at elevated temperatures

In the industries involving alkaline solutions in different process streams, the nature and stability of oxide films formed on the metallic surfaces determine the rates of erosion–corrosion of the equipment. In the present study the characteristics of the oxide films formed on AISI 1020 steel in a 2.75 M sodium hydroxide solution at temperatures up to 175°C, have been investigated by employing electrochemical techniques of cyclic voltammetry and chronoamperometry. The experiments were carried out in an autoclave system based upon a ‘rotating cylinder electrode’ geometry to determine the effects of turbulence on the stability of the films. The results suggest that little protection is afforded in the active region (at about −0.8 V_SHE). In the passive region at low potentials (−0.6 V to −0.4 V_SHE), it appears the films are compact and more stable, and therefore provide good protection. At higher potentials (>−0.4 V_SHE) in the passive region, the results suggest that film formation and dissolution occur simultaneously and the increase in temperature and turbulence causes a breakdown of the passive film resulting in a situation similar to nonprotective magnetite growth.