Dept of Mechanical Engineering, Faculty of Industrial Engineering of Terrassa (UPC), C/ Colom 11 Terrassa (Barcelona), SPAIN

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1 Materials Science Forum Online: -- ISSN: -, Vol., pp - doi:./ Trans Tech Publications, Switzerland Analysis of the behaviour effect of face cutting edge inserts on surface roughness when milling steels with MQL lubrication. X. Salueña-Berna a, J.A. Ortiz-Marzo b, J. Casals-Terré c Dept of Mechanical Engineering, Faculty of Industrial Engineering of Terrassa (UPC), C/ Colom Terrassa (Barcelona), SPAIN a xavier.saluena@upc.edu, b jose.antonio.ortiz@upc.edu, c jasmina.casals@upc.edu Keywords: Face milling, Face cutting edge inserts, MQL, Surface finish. Abstract. The main objectives of this work are the study of the obtained surface roughness on steels, using face cutting edge inserts milling tools in finishing face milling operations with microlubrication (MQL), and comparison of the results obtained with the widely-used radius inserts. This experimental study analyzes the roughness and surface appearance obtained with both sort of inserts. The interest about this study is to determine the steel types and the optimal cutting conditions for milling with this face cutting edge inserts. Another result analysed is the utility of the MQL implementation compared to the dry system. Introduction At the moment, due to the forced reduction of costs and environment protection, the conventional machining process has evolved with longer life of tools, substitution or suppression of operations, and wasting treatments (lubricant), new tools and new methods of lubrication-refrigeration have been implanted. Between the new tools we emphasized the face cutting edge ones, with which it is possible to obtain smaller roughness, but with an increase of heating due to the friction with the piece. The lubrication-refrigeration systems reduce this coefficient of friction or cool the tool. Between these systems of reduction or elimination of fluid, they emphasize the microlubrication (lubrication) and the cold air ejector (cooling) []. In this experimental study, made in the laboratory of the Technical School of Industrial Engineering of Terrassa, the combination of face cutting edge inserts with the microlubrication in different steel is analysed. Figure. End tip of a radius tool (left) and a face cutting edge tool (centre). Face milling with MQL (right). General parameters The equipment used in the tests is: a vertical milling machine CORREA and a MQL system, NOGA MC.Roughness measurement digital portable Surface Roughness Tester, RT- of SM S.L (Resolution./. mm). In the experiments the roughness was determined according to norm ISO :. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID:..., Pennsylvania State University, University Park, USA-//,::)

2 Advances in Materials Processing Technologies, A commercial face mill of mm diameter from "Toshiba Tungaloy", have been used in face milling operations. The radial and axial deviation of the position of the end of the teeth has not exceeded μm to avoid that the roughness depends on a single tooth []. The facet of the insert of the face mill has a face relief angle, α (corner angle) = º and an β(face cutting edge angle) = º. When working with microlubrication a flow of.ml/min has been used in agreement with the flow limit that is approximately of.ml/min in milling []. In order to evaluate the influence of the type of end on the surface quality uncoated inserts have been used (Cermet). After tests with face cutting edge, CVD carbide coated inserts, have been made to observe the coat influence on the friction coefficient and the surface roughness. Table. Grade, corner and reference of used tools. Grade tool Corner tool Ref. NS (Cermet) r =, [mm] SPMN NS (Cermet) face cutting edge SPKN ED T (CVD coated carbide) face cutting edge SPKN ED Table. Materials and cutting conditions (cutting speed, feed rate per tooth, cutting width and cutting axial depth). Work piece steel Vc [m/min] fz [mm/tooth] a e [mm] a p [mm] Stainless steel AISI- (W-Nr.) Mould steel UNE F- (W-Nr.) Carbon steel UNE F- (W-Nr.),,,,,, Next, in Table, we can appreciate the steel used in test series, as well as the cutting conditions. The face milling tool has been always working down milling. Only face milling operations where done in order to eliminate effects of tilting spindle []. Roughness analytical expressions There are analytical expressions to calculate arithmetical mean roughness in milling operations []. Two analytical equations are distinguished depending on the type of insert corner. The equations consider that the cut is perfect, the roughness is small, and the tools are arranged in the same symmetrical position on the mill tool.

3 Materials Science Forum Vol. Insert with corner radius Ra ( μ m) = f z * R () Insert with face cutting edge f z tanα * tan β R a ( μm) = * () tanα + tan β Being f z : feed per tooth [mm/tooth] R : corner radius [mm] α : corner angle β : face cutting edge angle Following the surface roughness for each material are plotted, respect to the feed rate per tooth. Results Type of corner In the Fig., the analytical mean roughness is plotted comparing the uncoated tools (Cermet) with different corners, using MQL lubrication. Nose radius, mm and "MQL" Face cutting edge insert and "MQL" Acero Moldes Mould steel Carbon steel Stainless steel Theoretical Ra Acero al Carbono Acero Inoxidable Ra teórica Acero Carbon al steel Carbono Acer Stainless Inoxidable steel Figure. Graphics comparing mean roughness, with MQL, when milling different steels and theoretical Ra. Inserts with radius corner (left) and inserts with face cutting edge (right). Microlubrication influence In the Fig., the analytical mean surface roughness, obtained when using inserts with face cutting edge uncoated (Cermet) and comparing dry and MQL milling.

4 Advances in Materials Processing Technologies, Face cutting edge and "dry" Face cutting edge insert and "MQL" Acero Carbon al steel Carbono Acero Stainless Inoxidable steel Ra Theoretical teórica Ra..... Acero Carbon al steel Carbono Acer Stainless Inoxidable steel..... Figure. Graphics comparing mean roughness between inserts with face cutting edge dry milling (left) and inserts with face cutting edge MQL milling. Coating influence In the Fig., the mean surface roughness obtained when using coated CVD inserts with face cutting edge, with dry milling and MQL milling. Face cutting edge insert and "dry" Acero Carbon Carbono steel Acer Stainless Inoxidable steel..... Face cutting edge insert (CVD) and "MQL" Acero Carbon Carbono steel Acero Stainless Inoxidable steel..... Figure. Graphics comparing mean roughness between dry milling (left) and MQL milling (right), using inserts with face cutting edge CVD coated carbide. Surface texture Sometimes, in some applications, we wish a good texture finish in addition to roughness surface. In the Fig. and Fig., we can appreciate the difference between the surface finish in dry milling and MQL milling.

5 Materials Science Forum Vol. Figure. SEM pictures of the surface roughness of stainless-steel with dry milling (left) and MQL milling (right), with face cutting edge coated CVD inserts. Figure. SEM pictures of the surface roughness of carbon-steel with dry milling (left) and MQL milling (right), with face cutting edge coated CVD inserts. Results In the Fig., we can observe that the surface roughness obtained when using tools inserts with face cutting edge, is less than corner radius tools in MQL lubrication milling and it is closer to the theoretical calculated roughness, Eq. and Eq.. The tools with corner radius produce higher surface roughness when milling with feed rates higher than. mm/tooth. From Fig., we can see that, in the interval feed rates and cutting speeds analyzed, mean surface roughness for stainless steels and mould steels is higher in dry milling than in MQL milling. However, for carbon steels it is similar. This is due to heating produced by the friction between tool and piece allowing part of the material removed to weld (see Fig. ). In Fig., the behaviour of CVD coated inserts is analyzed and it can be verified that coated inserts have smaller friction coefficients. In the case of carbon steels and mould steels, in the interval feed rates and cutting speeds analyzed, the same mean roughness is obtained in dry milling and in MQL milling. In stainless steel the mean roughness increases, in dry, because the friction increases due to built-up edge effect [] causing the welding of the chips to the work material (see Fig. ), when machining at feed rates higher than. mm/tooth. It can be corrected using MQL lubrication. Although the mean roughness is acceptable in dry milling, in Fig., we can appreciate a remarkably improvement when working with MQL lubrication, since the cut is more homogenous.

6 Advances in Materials Processing Technologies, Conclusions In steel face-milling lower mean surface roughness can be obtained when using inserts with face cutting edge. The main problem of this type of inserts is its heating due to the friction. From the point of view of surface roughness and in the interval of used parameters during the experimental evaluation, it is advisable to use microlubrication in uncoated Cermet insert when milling stainless steels and mould steels. It is not necessary in carbon steels. With CVD coated inserts, it is advisable to use MQL lubrication when milling stainless steels at higher feed rate per tooth than. mm/min. From the point of view of the surface texture, it is advisable to use MQL lubrication when face milling all types of steels tested. References [] S. Inoue, T. Aoyama: Application of Air Cooling Technology and Minimum quantity lubrication to relief grinding of cutting tools Advances in Abrasive Technology VI, Trans Tech Publications, p.. [] P. Franco et al: Influence of tool error on surface roughness during face milling operation, XIX National Congress of Mechanical Engineering, Cadiz, Spain. (in Spanish) [] A. Celaya et al: Experimental and analytical study of the effects of MQL lubrication on high speed milling, XIV Congress of Machine Tools and Manufacturing Technologies. Vol I. p. -. San Sebastián, Spain. (in Spanish) [] Cieloszyk J: The effect of tilting spindle during modern face milling, th International Research/Expert Conference, TMT, p.-, Spain. [] A B Sandvik Coromant, Modern machining. Sweden. [] J. Casals et al: Experimental analysis of relation between the surface roughness and fundamental machining parameters of milled surfaces, TMT, p.-. Spain.

7 Advances in Materials Processing Technologies,./ Analysis of the Behaviour Effect of Face Cutting Edge Inserts on Surface Roughness when Milling Steels with MQL Lubrication./