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ISSN : 1598-6721(Print)
ISSN : 2288-0771(Online)
The Korean Society of Manufacturing Process Engineers Vol.18 No.7 pp.42-47
DOI : https://doi.org/10.14775/ksmpe.2019.18.7.042

A Study on the Squareness of Circular Pocket Machining of SCM415 Steel

Jin-su Kim*, Chul-Woong Choi**, Mi-Jung Shin***#
*College of Computer Application Mechanical, Korea Polytechnic UNIV.
**Daemyung High-Tech.
***S&S Tech LTD.
Corresponding Author : lifevoyage@naver.com Tel: +82-55-253-1917, Fax: +82-55-253-1918
10/05/2019 29/05/2019 07/06/2019

Abstract


In this research, we try to study the change of squareness in the cutting process while changing cutting conditions such as feed rate and spindle rotational speed with chromium molybdenum steel (SCM415) material and TiCN, TiAlN coated end mill tool. The TiCN coating tool had the best straightness at 4,000 rpm at a feed rate of 200 mm/min. The TiAlN coating tool was best measured at 3,000 rpm at a feed rate of 200 mm/min. TiAlN coated tools had excellent dimensional tolerance when comparing the coating tool specifics.



SCM415강의 원형포켓 가공시 직각도에 관한 연구

김 진수*, 최 철웅**, 신 미정***#
*한국폴리텍대학 컴퓨터응용기계과
**대명하이텍
***(주)S&S Tech

초록


    © The Korean Society of Manufacturing Process Engineers. All rights reserved.

    This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

    1. Introduction

    With recent rapid industrial development, high-quality machining technology that achieves accuracy of machined surface while satisfying the requirements of improving productivity and reducing costs for various products is urgently needed in the mould industry[1].

    Major factors that have a direct influence on machining accuracy include cutting speed, feed rate, and cutting depth. Generally, form error increases when feed rate increases, while the life of the equipment becomes shorter when the speed of main spindle increases[2,3].

    In particular, technological development of various factors affecting machining accuracy is needed for machining. To reduce friction and wear, machining process technology that can reduce process time while maintaining ideal surface roughness by means of improved performance of coated tools is needed[9,10].

    Even though cutting speed, feed, or step over can be increased to improve cutting efficiency (i.e., to increase chip disposal per unit time), it is difficult in practice to freely manipulate these three factors in terms of economic and technical aspects[4]. Increasing the main spindle speed and feed rate has been developed to the top-level for machining centers, but the optimal cutting conditions have not been well developed[5,7,8].

    Due to the demand for increasing the feed rate and high accuracy of products, the simple geometric precision of each motion axle should be measured, and the interpolation motion precision needs to be evaluated. There is, however, no special dedicated measuring instrument for the precision measurement of linear interpolation motion, and ISO stipulates that square, dial gauge, electrical micrometer, and laser interferometer as measuring instruments[6].

    The present study investigated changes in squareness during the cutting process as the cutting conditions such as feed rate and main spindle speed are changed using chromium molybdenum steel (SCM415) and TiCN-coated and TiAlN-coated end mills.

    2. Experimental apparatus and materials

    2.1 Experimental apparatus

    The equipment used in the present study was Doosan Infracore’s VX500, and the specification details are presented in Table 1. Fig. 1 shows the processing schematic diagram, which shows cutting edge protruding from the collet. Fig. 2 shows a squareness-measuring instrument (Indicator). Fig. 3 shows the measurement drawing, and datum A represents the squareness measuring location using A as a datum point while maintaining a flat surface.

    2.2 Cutting tools

    The thickness of the TiCN coating is only a few microns, but it is known to be harder than metal as well as being chemically stable. It is frequently used in machining tools or difficult machining during punching and forming work, because it reduces wear of tools and molds, cold deposition, and friction, improving the productivity of products. Its color is dark gray, and its major features are wear resistance and hardness enhancement compared to TiN. Applications include cutting tools; STS high-strength steel-plate processing; and forming, drawing, and punching molding[1].

    The purpose of TiAlN coating is the high-efficiency cutting of high-hardness material rather than extending tool life, like TiN. In particular, the coating material not only has to have outstanding oxidation-resistance at high temperatures (500 °C or higher during machining) generated during machining but also has to be resistant to wear, shock, and thermal stress, which makes the material advantageous for high-speed cutting of difficult material and possibly for dry machining of high-hardness steel because of excellent oxidation-resistance and thermostability. The color is black gray, and the major features are high-temperature hardness and high-speed work. Applications include cutting tools, dry machining, and high-hardness machining[1].

    The cutting tools used in the present study were TiCN-coated and TiAlN-coated two-flute end mills, and one tool was used per circular pocket. The shapes and specification details are presented in Table 2 and Fig. 4.

    2.3 Experimental materials

    The material used in the present study was chromium molybdenum steel, which is created by adding 0.15–0.35% Mo to chrome steel to improve tempering characteristics and reduce sensitivity to tempering brittleness. It is mainly used in gears, heavy-duty bolts, axles such as a large crankshaft, automotive equipment, and defense equipment. In addition, it appears to be appropriate for improving productivity through machining because the influence of cutting conditions of main spindle speed and feed rate during the machining of chromium molybdenum steel on surface roughness and shape characteristics is considerable, problems associated with high speed machining are minimal, and in some cases, it exhibits thermal resistance and its mechanical properties even improve[8,9].

    The workpiece used as a specimen was cut into 12 pieces of 80x80x40 mm hexahedrons. Their appearances before and after processing are shown in Fig. 5 and Fig. 6, respectively, and the chemical composition is shown in Table 3.

    3. Experimental method and considerations

    3.1 Experimental methods

    The present study created circular pockets by 3-D modeling them using Hyper CAD, a CNC processing software by OpenSolution, creating processing data (NC date) using Hyper Mill, and then transmitting the data to the machining center. First, the workpiece material was firmly fixed so that it does not vibrate or detached from the vise during machining, and the coated end mill was inserted into the collet chuck so that a 38-mm cutting edge protruded from the chuck.

    For machining, helical circular interpolation method was used with 5 mm depth per cut, which was repeated a total of three times so that the total machined depth was 15 mm. Eight holes were machined per experimental sample, and cutting oil was applied when 12 samples were machined.

    After the first drilling, circular pockets were created using end mills, and measurements were made using an indicator attached to the machining center. The changes in machining conditions of cutting speed and feed rate are shown in Table 4.

    3.2 Squareness measurement

    The squareness of the machined surface was measured using a dial test indicator after machining to determine the condition for ideal squareness.

    The measurements of machined surface of the TiCN coated tool are presented in Fig. 7, and those of TiAIN coated tool are presented in Fig. 8.

    Figure 7 shows that the dimensional tolerance of the TiCN coated tool was the most accurate, with the error range of +0.0044 mm at main spindle speed of 4,000 rpm and feed rate of 200 mm/min when the spindle speed was varied from 1,000 rpm to 6,000 rpm in 1,000 rpm steps. Squareness measurements showed that error range was greatly changed at the feed rate of 400 mm/min regardless of cutting speed.

    Figure 8 shows that the dimensional tolerance of TiAlN coated tool was most accurate with error range of +0.003 mm at cutting speed of 3,000 rpm and feed rate of 200 mm/min, and the large error range of squareness was observed at the feed rate of 400 mm/min regardless of coated tool.

    In addition, the dimensional tolerance of TiAlN coated tool was better when the squareness of each coated tool was compared.

    4. Conclusion

    The present study obtained the following conclusions on squareness through an experiment in which circular pockets were created using SCM415 steel by changing cutting conditions such as cutting speed and feed rate using TiCN-coated and TiAlN-coated end mills.

    1. The squareness of the TiCN-coated tool was best at the main spindle rate of 4,000 rpm and feed rate of 200 mm/min, while that of the TiAlN-coated tool was best at 3,000 rpm and feed rate of 200 mm/min.

    2. The dimensional tolerance of the TiAlN-coated tool was better when the squareness of each coated tool was compared.

    3. The error range of squareness increased when feed rate increased rather than cutting speed.

    Figure

    KSMPE-18-7-42_F1.gif
    Schematic diagram of experimental apparatus
    KSMPE-18-7-42_F2.gif
    Dial test indicator
    KSMPE-18-7-42_F3.gif
    Measurement drawing
    KSMPE-18-7-42_F4.gif
    TiAlN and TiCN tools
    KSMPE-18-7-42_F5.gif
    Previous experiments
    KSMPE-18-7-42_F6.gif
    After the experiments
    KSMPE-18-7-42_F7.gif
    Measurement of squareness after cutting TiCN coating end mill tool
    KSMPE-18-7-42_F8.gif
    Measurement of squareness after cutting TiAlN coating end mill tool

    Table

    Machining center specification
    Dimension and shape of end mill(mm)
    Chemical composition of SCM415
    Experimental conditions of cutting process

    Reference

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    3. Doo, S., Hong, J. W., and Suh, N. S., “A Study on the Cutting Force and Machining Error on the Inclined Plane in Ball-end Milling”, Journal of the Korean Society of Manufacturing Process Engineers, Vol. 18, No. 7, pp. 112-119, 2001.
    4. Lee, J. K., Yoo, J. H., and Kim, M. K., Kook, J. H., “A Study on the Evaluation of End Mills for High Speed Machining”, Proceedings of the Korean Society of Precision Engineering Conference, Vol. 2000, No. 10, pp. 833-837, 2000.
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