Turning hardened steel using coated carbide at high cutting speeds

The present work studies some aspects of the turning process applied on hardened steel using multilayer coated carbide tools at high cutting speeds. The influence of cutting parameters (vc, f, and depth of cut - d.o.c.) on tool temperature, tool wear, cutting forces, and surface roughness were analyzed. The current literature reports many studies using PcBN on hardened steel, but it is also important to know the results when using coated carbide tools, mainly for economical reasons. Temperature was measured by a thermocouple positioned at the lowest insert face, underneath it. Temperature near the rake face was calculated using the measured gradient within the insert thickness. To measure the gradient a special technique was used with one embedded thermocouple near the rake face and one underneath. Tool wear measurements demonstrated the capability of such tools in turning hardened steel with reasonable tool life. Forces measured resulted in relatively low values, being the radial component the largest of all. For the different cutting conditions studied, the doc has the greatest influence on force and temperature. Additionally, the best surface roughness values were smaller than 0,4 µm Ra

Enhanced grinding performance by means of patterned grinding wheels

In this paper, a new and innovative method for the patterning of grinding wheels is presented. The patterns are machined with a patterning tool by using fly-cutting kinematics. By changing the patterning process parameters, different pattern sizes and densities can be machined in a flexible way. Surface and cylindrical grinding experiments show that grinding with patterned grinding wheels can significantly reduce process forces, grinding burn, and grinding power. The surface roughness increases because less active cutting edges remain when grinding with patterned wheels. But especially for roughing processes, the results show great potential for increasing the overall grinding performance. The final publication is available at Springer via http://dx.doi.org/10.1007/s00170-014-6579-8.DFGFAPES

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

An experimental method to determine the minimum uncut chip thickness (Hmin) in orthogonal cutting

Chip formation has been studied for more than a century using, initially, process description followed by experimental procedures and mathematical models. At first, cutting edges were modelled as perfectly sharp, but real cutting tools contain small radius. Some of them are as low as few micrometers. Micro-machining operations often need uncut chip thickness (h) lower than edge radius. In such conditions a minimum value (hmin) may be found, under which material may not be properly removed. There is an extensive range of values for hmin in literature, as a percentage only of the edge radius (re). The criterion for establishing hmin also extensively varies as well as the cutting conditions used. The present work proposes an innovative method to study hmin with realistic values of cutting and feed speed (vc and vf) in orthogonal cutting. Using the proposed method several edges were tested and two of them, one sharp (re = 6 μm) and one blunt (re = 120 μm), are here presented in 3 different conditions. Values of hmin were detected for each of the cutting conditions. They were found to depend on the cutting conditions, on the maximum hmax established and on the way it grows during the interaction between edge radius and workpiece material. It was also suspected that BUE can be formed in front of the tool, depending on the way the uncut chip thickness increases during the interaction. The method also proved to be capable of detecting hmin and several other associations with the main parameters affecting that minimum value10194207FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temmachinin

Qualidade do café-cereja descascado produzido na região sul de Minas Gerais Quality of the parchment coffee grown in the southern region of Minas Gerais

O café-cereja descascado vem conquistando cada vez mais espaço nas diversas regiões produtoras de café. Considerando os diversos questionamentos sobre a qualidade dos grãos resultantes desse tipo de processamento, os poucos estudos sobre o assunto e as contradições observadas nos resultados obtidos até o momento, com o presente estudo teve-se por objetivo caracterizar a qualidade do café-cereja descascado produzido na região sul do Estado de Minas Gerais, bem como averiguar a influência da altitude na qualidade desse café por meio de análises físicas, químicas e sensoriais das amostras em seu estado original e após a retirada de grãos defeituosos. Foram aleatoriamente selecionadas lavouras de empresas cafeeiras situadas em faixas de altitude que variaram de 720 a 920 metros e de 920 a 1120 metros. As amostras de café da safra 2001/2002 foram coletadas em 32 propriedades distribuídas em 10 municípios. No Pólo de Tecnologia em Qualidade do Café da Universidade Federal de Lavras (UFLA), foram realizadas as seguintes análises: teor de água, acidez titulável total, açúcares totais e análise sensorial. As análises físicas, químicas e sensoriais realizadas nos grãos de café demostraram que a maioria dos cafés descascados apresenta teor de água abaixo do valor recomendado; os valores médios de acidez titulável total e açúcares totais em todas as amostras analisadas encontram-se dentro dos valores característicos de bebidas finas; os cafés sem a presença dos defeitos, produzidos na faixa de altitude de 920 a 1120 metros, apresentam corpo e acidez mais fracos e doçura mais alta do que os produzidos na faixa de 720 a 920 metros; e que maiores altitudes possibilitam a produção de cafés de melhor qualidade.<br>The parchment coffee has been conquering more and more space in the several coffee growing regions. By taking into account the several questionings upon the quality of the berries resulting from this sort of processing, the few studies on the subject and the contradictions observed in the results obtained up to now, the present study aimed to characterize the quality of the parchment coffee produced in the Southern region of Minas Gerais state as well as to assess the influence of the altitude on the quality of these coffees by means of physical, chemical and sensorial analyses of the samples in their original state and after removal of defective beans. Crops of coffee enterprises situated in ranges of altitude varying from 720 to 920 meters and from 920 to 1120 meters were randomly selected. The coffee samples of the 2001/2202 crop were duly collected on 32 farms distributed in 10 towns. At the "Polo de Tecnologia em Qualidade do Café" of the "Universidade Federal de Lavras" (UFLA), the following analyses were performed: water content, total titrable acidity, total sugars and sensorial analyses. The physical, chemical and sensorial analyses accomplished on coffee beans showed that: most parchment coffees present water content bellow the value recommended; the average values of total titrable acidity and total sugars in all the samples analyzed lie within the values characteristic of fine beverages; hard beverage occurs in 75% of the parchment coffee samples with the presence of the defects; the coffees without the presence of the defects produced in the range of altitude of 920 to 1120 meters present body and acidity weaker and sweetness higher than the ones produced in the range of 720 to 920 meters; higher altitudes enable the production of better quality coffees