Effects of milling condition on the surface integrity of hot forged steel

This paper presents a study on the influence of milling condition on workpiece surface integrity focusing on hardness and roughness. The experimental work was carried out on a CNC machining center considering roughing and finishing operations. A 25 mm diameter endmill with two cemented carbide inserts coated with TiN layer were used for end milling operation. Low carbon alloyed steel Cr-Mo forged at 1200 degrees C was used as workpiece on the tests. Two kinds of workpiece conditions were considered, i.e. cur cooled after hot forging and normalized at 950 degrees C for 2 h. The results showed that finishing operation was able to significantly decrease the roughness by at least 46% without changing the hardness. on the other hand, roughing operation caused an increase in hardness statistically significant by about 6%. The machined surface presented deformed regions within feed marks, which directly affected the roughness. Surface finish behavior seems to correlate to the chip ratio given the decrease of 25% for roughing condition, which damaged the chip formation. The material removal rate for finishing operation 41% greater than roughing condition demonstrated to be favorable to the heat dissipation and minimized the effect on material hardness.

Numerical and experimental study of the thermal behaviour of coining and upsetting processes

A numerical simulation technique has been employed to study the thermal behavior of hot-forging type forming processes. Experiments on the coining and upsetting of an aluminum billet were conducted to validate the numerical predictions. Typical forming conditions for both the coining and upsetting processes were then studied in detail. an electrical analogy scheme was used to determine the thermal contact resistance. This scheme can conviniently provide the interface characteristics for typical processing conditions, which normally involve high pressures and temperatures. A single forging cycle was first considered, and then a batch of twenty-five forgings was studied. Each forging cycle includes the billet mounting, ascent, loading, dwelling, unloading, descent, and billet removal stages. The temperature distribution in the first forging to be formed is found to be significantly different from that at the end of the batch. In industry, forging is essentially a batch operation. The influence of forming speed and reduction on thermal characteristics was investigated also. The variations that can occur in the process design by considering differences in temperature characteristics are discussed also.

A virtual inspection framework for precision manufacturing of aerofoil components

The finite element method plays an extremely important role in forging process design as it provides a valid means to quantify forging errors and thereby govern die shape modification to improve the dimensional accuracy of the component. However, this dependency on process simulation could raise significant problems and present a major drawback if the finite element simulation results were inaccurate. This paper presents a novel approach to assess the dimensional accuracy and shape quality of aeroengine blades formed from finite element hot-forging simulation. The proposed virtual inspection system uses conventional algorithms adopted by modern coordinate measurement processes as well as the latest free-form surface evaluation techniques to provide a robust framework for virtual forging error assessment. Established techniques for the physical registration of real components have been adapted to localise virtual models in relation to a nominal Design Coordinate System. Blades are then automatically analysed using a series of intelligent routines to generate measurement data and compute dimensional errors. The results of a comparison study indicate that the virtual inspection results and actual coordinate measurement data are highly comparable, validating the approach as an effective and accurate means to quantify forging error in a virtual environment. Consequently, this provides adequate justification for the implementation of the virtual inspection system in the virtual process design, modelling and validation of forged aeroengine blades in industry.

Análise do coeficiente de atrito no ensaio do anel para o forjamento a quente.

O presente trabalho, apresenta resultados da investigação experimental e da análise computacional acerca do método de ensaio de anéis de aço para obtenção do valor do coeficiente de atrito, existente na região de contato entre as matrizes e os corpos de prova. Buscando atingir os objetivos, foi feito um planejamento do experimento, através do programa MINITAB (2000), levando-se em consideração as variáveis do processo para forjamento a quente de peças para indústria automotiva, os experimentos foram realizados nos laboratórios da Universidade Federal do Rio Grande do Sul (UFRGS). A simulação do ensaio de anel permitiu uma boa estimativa da redução de diâmetros dos mesmos, bem como, do fluxo de material no interior dos anéis e da superfície neutra. A análise estatística dos resultados mostrou que a variável mais importante a afetar o coeficiente de atrito foi a temperatura, seguindo-se do tipo de revestimento das ferramentas, velocidade e material. Para um estudo mais pormenorizado do efeito do material a ser forjado, do recobrimento das ferramentas e da rugosidade das mesmas no coeficiente de atrito será necessário um maior número de repetições dos experimentos.

Application of wear resistant coatings by the brush plating technique

The development of cobalt molybdenum and cobalt tungsten brush plating electrolytes is described. Their optimum compositions and operating conditions for commercial applications have been determined. The effects of composition, pH, applied voltage, stylus speed and pressure upon deposit composition and efficiency have been investigated. Transmission and Scanning Electron Microscopy have been employed to study the cobalt alloy deposits produced. Evaluation of the wear resistant properties of the cobalt alloys developed in this work was carried out in the laboratory using a pin and disc technique and a simulated hot forging test, and by industrial trials involving the "on site" plating of hot forging dies and cold pressing tools. It was concluded that the electrolytes developed in tl1is work enabled cobalt alloys containing 6% Mo or 8% W to be deposited at 17-20V. Brush plated cobalt deposits possessed a mixed CPU and FCC crystallographic structure at room temperature. The application of 13µm of either of the cobalt alloys resulted in improved wear performance in both pin and disc and simulated hot forging tests. The results of the industrial trials indicated that by the use of these alloys, the life of hot forging dies may be increased by 20-100%. A commercial forging organisation is using electrolytes developed in this work to coat dies prior to forging nimonic alloys. Reductions in forging temperature and improved forging qualities have been reported. Cold pressing tools coated with the alloys showed a reduced tendency to "pick-up" and scoring of the pressed panels. Reports of a reduced need for lubrication of panels before pressing have also been received.

American standard safety code for forging and hot metal stamping.

Mode of access: Internet.

Influence of electroslag refining on the hot ductility of AISI 4340 steel in torsion

Electroslag refining is a useful remelting process by which clean steels can be produced for sophisticated applications. In this investigation, AISI 4340 steel has been electroslag refined and the improvement in its hot ductility has been assessed using hot torsion tests; electroslag refining has improved the hot ductility considerably. The temperature at which peak ductility is obtained has also increased — from 1473 K in the unrefined steel to 1573 K in ESR steel. Results indicate that it should be possible to subject the ESR ingot to much higher strains per unit operation during industrial hot working processes such as forging, which would result in a considerable saving of power. The improvement in hot ductility in ESR steel has been attributed primarily to the removal of non-metallic inclusions and the reduction in sulphur content. From the apparent activation energy estimated from the hot torsion data, the dynamic recrystallization process is identified as the mechanism controlling the rate of hot deformation.

Development of a computer code to predict cooling of die and billet in forging

A hot billet in contact with relatively cold dies undergoes rapid cooling in the forging operation. This may give rise to unfilled cavities, poor surface finish and stalling of the press. A knowledge of billet-die temperatures as a function of time is therefore essential for process design. A computer code using finite difference method is written to estimate such temperature histories and validated by comparing the predicted cooling of an integral die-billet configuration with that obtained experimentally.

Effect of process variables on die-billet temperature history in a slow speed hot coining type process

A computer code is developed as a part of an ongoing project on computer aided process modelling of forging operation, to simulate heat transfer in a die-billet system. The code developed on a stage-by-stage technique is based on an Alternating Direction Implicit scheme. The experimentally validated code is used to study the effect of process specifics such as preheat die temperature, machine ascent time, rate of deformation, and dwell time on the thermal characteristics in a batch coining operation where deformation is restricted to surface level only.

Microstructural control in hot working of IN-718 superalloy using processing map

The hot-working characteristics of IN-718 are studied in the temperature range 900 °C to 1200 °C and strain rate range 0.001 to 100 s−1 using hot compression tests. Processing maps for hot working are developed on the basis of the strain-rate sensitivity variations with temperature and strain rate and interpreted using a dynamic materials model. The map exhibits two domains of dynamic recrystallization (DRX): one occurring at 950 °C and 0.001 s−1 with an efficiency of power dissipation of 37 pct and the other at 1200 °C and 0.1 s−1 with an efficiency of 40 pct. Dynamic recrystallization in the former domain is nucleated by the δ(Ni3Nb) precipitates and results in fine-grained microstructure. In the high-temperature DRX domain, carbides dissolve in the matrix and make interstitial carbon atoms available for increasing the rate of dislocation generation for DRX nucleation. It is recommended that IN-718 may be hot-forged initially at 1200 °C and 0.1 s−1 and finish-forged at 950 °C and 0.001 s−1 so that fine-grained structure may be achieved. The available forging practice validates these results from processing maps. At temperatures lower than 1000 °C and strain rates higher than 1 s−1 the material exhibits adiabatic shear bands. Also, at temperatures higher than 1150°C and strain rates more than 1s−1, IN-718 exhibits intercrystalline cracking. Both these regimes may be avoided in hotworking IN-718.

Microstructural control in hot working of IN-718 superalloy using processing map

The hot-working characteristics of IN-718 are studied in the temperature range 900 degrees C to 1200 degrees C and strain rate range 0.001 to 100 s(-1) using hot compression tests. Processing maps for hot working are developed on the basis of the strain-rate sensitivity variations with temperature and strain rate and interpreted using a dynamic materials model. The map exhibits two domains of dynamic recrystallization (DRX): one occurring at 950 degrees C and 0.001 s(-1) with an efficiency of power dissipation of 37 pct and the other at 1200 degrees C and 0.1 s(-1) with an efficiency of 40 pct. Dynamic recrystallization in the former domain is nucleated by the delta(Ni3Nb) precipitates and results in fine-grained microstructure. In the high-temperature DRX domain, carbides dissolve in the matrix and make interstitial carbon atoms available for increasing the rate of dislocation generation for DRX nucleation. It is recommended that IN-718 may be hot-forged initially at 1200 degrees C and 0.1 s(-1) and finish-forged at 950 degrees C and 0.001 s(-1) so that fine-grained structure may be achieved. The available forging practice validates these results from processing maps. At temperatures lower than 1000 degrees C and strain rates higher than 1 s(-1), the material exhibits adiabatic shear bands. Also, at temperatures higher than 1150 degrees C and strain rates more than 1 s(-1), IN-718 exhibits intercrystalline cracking. Both these regimes may be avoided in hot-working IN-718.

Air pollution levels measured at traffic hot spots : Brisbane urban corridor study

Air pollution levels were monitored continuously over a period of 4 weeks at four sampling sites along a busy urban corridor in Brisbane. The selected sites were representative of industrial and residential types of urban environment affected by vehicular traffic emissions. The concentration levels of submicrometer particle number, PM2.5, PM10, CO, and NOx were measured 5-10 meters from the road. Meteorological parameters and traffic flow rates were also monitored. The data were analysed in terms of the relationship between monitored pollutants and existing ambient air quality standards. The results indicate that the concentration levels of all pollutants exceeded the ambient air background levels, in certain cases by up to an order of magnitude. While the 24-hr average concentration levels did not exceed the standard, estimates for the annual averages were close to, or even higher than the annual standard levels.