Effects of Milling on Surface Integrity of Low-Carbon Steel

This work measured the effect of milling parameters on the surface integrity of low-carbon alloy steel. The Variance Analysis showed that only depth of cut did not influence on the workpiece roughness and the Pearson's Coefficient indicated that cutting speed was more influent than tool feed. All cutting parameters introduced tensile residual stress in workpiece surface. The chip formation mechanism depended specially on cutting speed and influenced on the roughness and residual stress of workpiece.

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.

Influence of the tool edge geometry on specific cutting energy at high-speed cutting

This paper presents specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. The experimental work was carried out on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power. Hardened steels ASTM H13 (50 HRC) were machined at conventional cutting speed and high-speed cutting (HSC). TiN coated carbides with seven different geometries of chip breaker were applied on dry tests. A special milling tool holder with only one cutting edge was developed and the machining forces needed to calculate the specific cutting energy were recorded using a piezoelectric 4-component dynamometer. Workpiece roughness and chip formation process were also evaluated. The results showed that the specific cutting energy decreased 15.5% when cutting speed was increased up to 700%. An increase of 1 °in tool chip breaker chamfer angle lead to a reduction in the specific cutting energy about 13.7% and 28.6% when machining at HSC and conventional cutting speed respectively. Furthermore the workpiece roughness values evaluated in all test conditions were very low, closer to those of typical grinding operations (∼0.20 μm). Probable adiabatic shear occurred on chip segmentation at HSC Copyright © 2007 by ABCM.

Analysis on turning Ti-6Al-4V with different cooling methods

The aim of this paper is to optimize the machining of Ti-6Al-4V alloy, by studying the chip formation, roughness and tool wear for different cooling conditions. The results were compared between cooling methods, minimal quantity of fluid (MQF) and flooding, and also without fluid for the tool H13A. The turning of Ti-6Al-4V has shown good results on roughness (0, 8μm) and tool life, which was 11% lower with MQF than with the flooding method. The tool wear causes variation of the shear angle, which promotes strength hardening of the chip. As a result, the machined surface could be damaged. The use of the cutting fluid helps to save the cutting edge and could reduce the strength hardening. Nevertheless, it could also facilitate the formation of built-up edge. The nucleation of alpha lamellar colonies can occur due to a combination of deformation rates and temperature, mainly when the flooding is used, but it's not conclusive. The lamellar colonies were also found with the MQF in some regions, however, this structure did not show hardness variation compared to equiaxial. For all this reasons, the machining parameters might be carefully chosen.

A valiação da integridade superficial e usinabilidade de engrenagens forjadas utilizando fresamento com alta velocidade de corte

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo dos mecanismos governantes do efeito de escala na microusinagem

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito do fresamento com alta velocidade de corte na usinabilidade de aços ferríticos com grãos ultrafinos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hot turning of a difficult-to-machine steel (sae xev-f) aided by infrared radiation

A possible way for increasing the cutting tool life can be achieved by heating the workpiece in order to diminish the shear stress of material and thus decrease the machining forces. In this study, quartz electrical resistances were set around the workpiece for heating it during the turning. In the tests, heat-resistant austenitic alloy steel was used, hardenable by precipitation, mainly used in combustion engine exhaustion valves, among other special applications for industry. The results showed that in the hot machining the cutting tool life can be increased by 340% for the highest cutting speed tested and had a reduction of 205% on workpiece surface roughness, accompanied by a force decrease in relation to conventional turning. In addition, the chips formed in hot turning exhibited a stronger tendency to continuous chip formation indicating less energy spent in material removal process. Microhardness tests performed in the workpieces subsurface layers at 5 m depth revealed slightly higher values in the hot machining than in conventional, showing a tendency toward the formation of compressive residual stress into plastically deformed layer. The hot turning also showed better performance than machining using cutting fluid. Since it is possible to avoid the use of cutting fluid, this machining method can be considered better for the environment and for the human health.

Fresamento de aço para moldes e matrizes em condições criogênicas

Pós-graduação em Engenharia Mecânica - FEIS