Malgorzata Rosochowska

Measurements of thermal contact conductance

Abstract During forging, the transfer of heat between the component, the tools and the environment has an impact on tool-life and the accuracy of the formed component. Consequently, the measurement of thermal contact conductance is of increasing interest to researchers and industrial engineers participating in the manufacture of high-precision components by plastic deformation. It is recognised that thermal contact conductance is a function of several parameters, the dominant ones being the type of contacting materials, the macro- and micro-geometry of the contacting surfaces, temperature, the interfacial pressure, the type of lubricant or contaminant and its thickness. A new steady-state method and measurement equipment are proposed in which the measurements are conducted on thin cylindrical specimens, which are retained under pressure between two tools. A clear advantage of this method is the ability to measure the thermal contact conductance under precisely controlled conditions. Due to the small aspect ratio of the specimen, the applied pressure may be of the same magnitude as that prevailing in industrial bulk-metal forming processes. In the present paper some experimental results on the dependence of h on the pressure and the specimen texture are presented.

A new method of measuring thermal contact conductance

Abstract The measurement of thermal contact conductance between forging work-material and tools is of interest to the assessment of temperature-change induced component-form errors derived during metal-forming operations and also to tool-life. Methods of measurement of the thermal contact conductance are reviewed and evaluated and a new steady-state methodology and equipment for the measurement of conductance are proposed. Experiments were conducted on thin cylindrical specimens retained under axial pressure between two tool surfaces. A clear advantage of this method is the ability to measure the conductance under continuously sustained thermal conditions and under pressures in excess of the yield strength of the work-material. Experimental results are provided and experimental errors are defined.

FE Simulation of Ultrasonic Back Extrusion

The main benefit of using ultrasonic vibrations in metal forming arises from the reduction in the mean forming force. In order to examine mechanisms responsible for this effect FE simulations of ultrasonic back extrusion using ABAQUS/Explicit were carried out. In two analysed models, vibration of frequency of 20 kHz was imposed on the punch. In the first model, the die and the punch were defined as rigid bodies and in the second, the punch was modelled as an elastic body, this being the innovative feature of the research. The punch vibrated in a longitudinal mode. Simulations were performed for amplitude of vibrations of 8.5μm and different punch velocities for both friction and frictionless conditions. Results showed that the amplitude and the mean forming force depended on the process velocity. Further, the decrease in the mean forming force might be partly explained by the reduction in the friction force due to changes in the direction and magnitude of the frictional stress over the vibration period. A...

Severe plastic deformation by incremental angular splitting

A new way of generating large plastic strain in a billet by splitting it plastically by a reciprocating punch is investigated. The concept of incremental angular splitting (I-AS) is explained by referring to the severe plastic deformation process of incremental equal channel angular pressing (I-ECAP). Results of laboratory trials of I-ECAP and I-AS, using a purposely designed AA1070 billet, are presented and both processes are compared. Further comparison is based on Vickers hardness distribution in the billet subjected to I-ECAP and I-AS. FE simulation results give an indication of strain distribution in both processes. The main advantages of I-AS appear to be more flexibility in the billet choice and more uniform strain distribution in the first pass of the process. A possibility of creating a gradient material by I-AS with a flat punch is considered.

New SPD Process of Incremental Angular Splitting

A new way of severely deforming ductile metals in order to refine their microstructure is proposed. It is called incremental angular splitting and originates from the idea of orthogonal cutting. It is intended to intensify plastic deformation in the cutting zone and lead to faster refinement of the microstructure. A laboratory experiment carried out on Al 1070 has proved the technical feasibility of the process. As the first indication of process capability, micro hardness measurements have been used to compare incremental angular splitting and incremental equal channel angular pressing.

Tailored Sheared Blanks Produced by Incremental ECAP

Incremental equal channel angular pressing (I-ECAP) is a process used for production of continuous ultrafine grained bars, plates and sheets. Normally the thickness of the processed billet is kept unchanged in consecutive passes to enable repetitive insertion into the same die. This is achieved by controlling the bottom dead centre of the reciprocating punch. However, if a final product requires being thinner and therefore longer, the bottom position of the punch can be lowered before the last pass. Going further, the bottom position of the punch can be changed during the process, which opens up a possibility to vary billet thickness along its length. Such a product, especially sheet, can serve as a preform for further metal forming operations and is known as tailored blank. This paper will show examples of varying thickness sheets produced by different configurations of I-ECAP. Experimental and finite element results will be presented.

Lower Cost Automotive Piston from 2124/SiC/25p Metal-Matrix Composite

Engineered materials have made a breakthrough in a quest for materials with a combination of custom-made properties to suit particular applications. One of such materials is 2124/SiC/25p, a high-quality aerospace grade aluminium alloy reinforced with ultrafine particles of silicon carbide, manufactured by a powder metallurgy route. This aluminium matrix composite offers a combination of greater fatigue strength at elevated temperatures, lower thermal expansion and greater wear resistance in comparison with conventionally used piston materials. The microscale particulate reinforcement also offers good formability and machinability. Despite the benefits, the higher manufacturing cost often limits their usage in high-volume industries such as automotive where such materials could significantly improve the engine performance. This paper presents mechanical and forging data for a lower cost processing route for metal matrix composites. Finite element modelling and analysis were used to examine forging of an automotive piston and die wear. This showed that selection of the forging route is important to maximise die life. Mechanical testing of the forged material showed a minimal reduction in fatigue properties at the piston operating temperature.

Chemical etching as a method of combatting adhesive tool wear during severe plastic deformation of commercially-pure titanium

This paper investigates chemical etching as a potential temporary solution to severe adhesive wear experienced during forming of commercially-pure titanium. The aim was to identify contributing factors and experimentally quantify their effects on the etching of CP-Ti and Vanadis 23 tool steel. A comprehensive literature review identified a promising etchant solution, containing 6.5% hydrofluoric acid, 2% formic acid and 2% triethanolamine. A full factorial experiment was designed to test the effects of three factors – hydrofluoric acid concentration, temperature, and time – with statistical analysis to interpret and validate the results. The results confirmed that increasing any of the factors tested leads to a significant increase in titanium dissolution, while only temperature and concentration increases led to a significant increase in steel dissolution. Therefore, a 20°C solution of 3.5% hydrofluoric acid and an etching duration of 35 minutes is recommended for removing adhered titanium without significantly affecting the steel.

Modelling microstructure evolution in ATI 718Plus® alloy

The present study details the results of finite element analysis (FEA) based predictions for microstructure evolution in ATI 718Plus® alloy during the hot deformation process. A detailed description of models for static grain growth and recrystallisation is provided. The simulated average grain size is compared with those experimentally measured in aerofoil parts after forging trials. The proposed modified JMAK model has proved to be valid in the main body of the forging. The results predicted for the surface are less accurate. The recrystallised grain size on the surface is smaller than in the centre of the part which corresponds to the experimental results and reflects the main trend.