Advanced Materials Research Vols. 291-294

Abstract: In practical production, the heavy forgings of the largest diameter 1225 mm larger than its length 905 mm are unqualified for supersonic inspection. By means of acid-eroding, scanning electron microscopy and energy spectrum analysis on defects, it is shown that the defects are originated from inclusions made up of Al₂O₃, Fe₂O₃ and a little CaO. In order to improve forging quality, the controlling mechanism of defects is analyzed, and forging process of two times upsetting and stretching process is researched to eliminate the cracks originated from inclusions. The result shows that the inclusions in forgings can be controlled and the inner cracks recovered effectively by two times upsetting and stretching process. All of the forgings meet the supersonic standard which indicates that this process is better fit for heavy forgings with largest diameter larger than its length.

Abstract: Mold steel 3Cr2Mo has been used widely in manufacturing of plastic mold formed parts, owing to fine mechanical properties. However, it is also very difficult to cut mold formed parts of steel 3Cr2Mo due to high hardness. Ordinary NC cutting method of steel 3Cr2Mo is unable to relate to modern mold manufacturing due to bad cutting property, so it is extremely significant for improving cutting property of steel 3Cr2Mo to study the high speed milling technology. On the basis of improving the traditional cutting force formula, the mathematical model of high speed milling force for steel 3Cr2Mo was derived and solved by using the experimental data and constructing matrix equation based on MATLAB software. Comparing with experimental data, the error of mathematical model of high speed milling force could be controlled within 6 percent. Due to high precision the model of high speed milling force can meet practical engineering requirement and has great value in the fields of CAD/CAM/CAE.

Abstract: Micro-texturing self-lubricated cutting tools named MTR-1 and MTR-3 were designed and made based on micro-texturing lubricating idea and laser micro-texturing technology. Dry cutting tests on 45^# hardened steel were carried out with these self-lubricated cutting tools and conventional cemented carbide tools named MT0. The cutting temperatures and the morphology of chips were measured. The results indicated that the cutting temperatures with the micro-texturing self-lubricated cutting tools were reduced compared with that of MT0 cemented carbide tools, and the chip coiling was improved.

Abstract: A SiC_p/Cu composite with excellent performance is prepared by using the advanced powder injection molding technology. The microhardness and tensile strength of the composite are detected, and the surface microstructure and the tensile fractures are observed. The results show that SiC particles are uniformly distributed in Cu matrix and excellently bonded with the Cu matrix. With the increase of the SiC content, the microhardness of the composite is increased while the tensile strength is increased first and then decreased. A crackle source of the composite for tensile fracture mainly includes two kinds: cracking of the Cu matrix in vicinity of the SiC particles and debonding of an interface of the SiC particles and the Cu matrix.

Abstract: Tool life and tool wear, cutting forces and cutting temperature, surface finish, chip formation and surface generation were investigated when milling SiC_p/2009Al composites at the cutting speed of 1200m/min using PCD tools. The results showed that PCD tool life was 150min when the 0.1mm tool wear criterion was chosen. PCD tool mainly suffered from tool grain breaking-off, chipping, abrasive wear, micro cracks and adhesive wear due to he very high-frequency impact and scrape of SiC particles. The peak value of the cutting force Fy (the radial direction) was over 1300N and the cutting vibration was very severe. The cutting temperature was 523.7°C. Pits, voids, matrix tearing and scratch were the main defects on the machined surface. The deformation layer thickness was about 20-35μm. The chip for the vol.20%SiC_p/2009Al composite took the form of flow type and the mechanisms of the chip formation were the combination of dynamic behavior of voids/micro-cracks and adiabatic shear. For the vol.35%SiC_p/2009Al composite, the chip was non-continuous and had the tendency of saw-toothed type. Material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, removal mode of SiC particles were the main mechanisms of surface generation.

Abstract: For gaining strip edge drop controllability and increasing roll grinding precision, the edge drop control work roll (EDW) was developed and designed in 1700 mm tandem cold rolling mill. During the rolling trial, the roll configuration between EDW and conventional backup roll didn’t match well because of the large fluctuation of strip edge drop, the lower shape control ability and non-uniform roll wearing, so the new roll configuration between EDW and varying contact backup roll (VCR) was proposed. After analyzing by finite element model, the result showed that the roll system configuration of VCR and EDW was better by 10.7% larger roll gap crown adjustable scope, 19.1% larger roll gap stiffness characteristics and 21.6% smaller pressure peak between rolls than before. The new roll system configuration has been applied to 1700 tandem cold rolling mill at WISCO after industrial testing.

Abstract: On the basis of technologies of gas atomization, supersonic gas atomization, surface effect of electric charge and jet, we design a new-style device of two fluids atomization with the combination of solid atomization and electric field utilizing a LAVAL nozzle, a delivery tube of sectional type and the electrical field dispersion technique. The soldering tin of 63 A was atomized with the air, and the powder prepared was analyzed by optical granularity analyzer, nanometer magnetic particles and Zeta potential analyzer. The results show that the particle size with less than 8μm can reach 75%; the average particle size is 1.7612μm, and the first peak in the distribution curve is about 500 nm, which is an order of magnitude smaller than that the existing reported peak. The compound atomization device can refine the particle size of powers effectively, improve uniformity, yielding rate, and the purity of atomized powders and has a significant effect on atomizing, thus provides powerful supports for preparing ultra fine metal powders with high efficiency and low energy consumption and has a good prospect in application.

Abstract: Aiming at the key problem of tool choice presented at high speed machining, this paper analyses the characteristic of existing materials of high speed machining tool from three aspects of mechanics, physics and chemistry, and sums up the cutting property of work materials combining with some experimental results and literatures. By integrated comparison of the property of materials of tool and workpiece, a method of choosing tool material for corresponding to workpiece is offered. Finally, some matched materials of tool and work are provided for convenient choice, which can acquire better effects than used testing or experience ways and means.

Abstract: In the present, by using rotating electromagnetic field (REMF) equipment, the effects of REMF for crystal growth processes in cast ZA27 alloy were investigated. It was found that the growth of the primary and secondary dendrites was restrained by alternative REMF and solidification microstructure transformed from dendrite to non-dendrite and globular crystal. The grain refinement effects were further improved with increasing of voltage.

Abstract: The effects of machining methods such as high pressure water jet cutting, laser cutting, mechanical cutting on the geometry accuracy,macro aspect of UHMWPE fiber reinforced epoxy composite laminates are studied.Compare the property of geometry accuracy, macro aspect after the UHMWPE fiber reinforce composites laminates, find the processing method and the optimal parameters to provide the best choice for the machining of UHMWPE reinforce composites laminates and further speed up the study of composite dynamic property.