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ISSN : 1598-6721(Print)
ISSN : 2288-0771(Online)
The Korean Society of Manufacturing Process Engineers Vol.20 No.6 pp.10-16
DOI : https://doi.org/10.14775/ksmpe.2021.20.06.010

Cutting Conditions of Carbide Insert Drill

Sung-Yun Choi*, Chul-Woong Hwang*, Sang-Tae Lee**#
*Graduate School, Kyungnam Univ.
**Korea Polytechnics Dep. of Mechanical System
#Corresponding Author : 1eest12000@hanmail.net Tel: +82-55-279-1751, Fax: +82-55-284-7802
24/03/2021 16/04/2021 27/04/2021

Abstract


Drilling is a crucial process that takes up a significant amount of weight during machining operations. In addition, drill tip-type tools and related operations have been developed for manufacturing industries to achieve economic efficiency. In this study, SM45C carbon steel, widely used for machine structures, was utilized as the working material after quenching and tempering. Insert-tip types of carbide tools, such as TiN and TiAlN, were used as tool materials. Drilling conditions such as the spindle revolution, feed rate, step of cut, and tool diameter were used to measure roughness, roundness, and straightness using the orthogonal array table statistical method. The surface roughness, roundness, and straightness characteristics based on the conditions were analyzed using ANOVA. The results showed that the spindle speed and feed rate were the main factors influencing carbide insert-tip drilling under the same conditions as the experimental conditions.



초경 인서트 드릴의 절삭 조건에 관한 연구

최 성윤*, 황 철웅*, 이 상태**#
*경남대학교대학원
**한국폴리텍대학 기계공학과

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

    Drill processing is one of the important processes accounting for the majority of the machine cutting process. With regard to the tools used in drill processing, there has been an increase in the demand for development and marketing of cutting tools with enhanced processing efficiency, reduced processing cost, and reduced processing time in various industries, including automobile and aerospace ones; owing to these, there have been numerous research developments out on tool forms, tool coatings, and processing conditions.[1]In drill processing, to conduct a stable and productive drilling process in a machine, research is being actively conducted on the selection of suitable tools, processing characteristics of cutting oil, and processing conditions such as drain processing temperature of processing chip.[2~3] Till date, the high-speed steel (H.S.S) twist drill developed half a century ago is still being utilized in many drill processes, and the necessity for research on the drill processing cutting conditions using the hard metal insert tip drill, which can have an enhanced wear resistance compared with the existing H.S.S drill, is on an increase.[4~5]

    In this study, the SM45C carbon steel for machine structural use, which is generally widely used in industrial sites, was subjected to quenching– tempering and utilized as a workpiece, and the drill tool with the hard metal insert tip was used to determine factors such as main-axis revolution, transfer speed, the status of step processing, and coating type of the insert tip. To investigate the effect of each factor on the surface roughness, roundness, and straightness of the processing results, the drilling processing was performed based on the design of experiments. Furthermore, in terms of the factors affecting the cutting force and processing results under different processing conditions, their characteristics were investigated through analysis of variation.

    2. Experimental Equipment and Methods

    2.1 Experimental Equipment

    The processing equipment used to conduct the drilling processing herein is Hyundai WIA F500 PLUS Machining Center. The workpiece specimen used is the SM45C, a carbon steel for machine structural use. This specimen in a rectangular parallelepiped shape of was subjected to quenching– tempering (HRC21±3) at a hardness lower than the cutting processing limit hardness HRC33–40), six sides of the specimen were subjected to milling processing, and the surface polishing was performed to prepare the specimen and to perform the tests for measuring surface roughness, roundness, and straightness under the same conditions.

    Fig. 1(a) is the picture of the specimen being processed using the hard metal insert tool at a machining center, and Fig. 1(b) shows the specimen form after the hard metal insert processing.

    Fig. 2(a) presents the two types of the hard metal insert tip drills with a processing diameter of ø18.5 mm and ø15.0 mm for drill processing and Fig. 2(b) shows the two types of insert tips coated with TiN and TiAlN. The surface roughness analyzer (Mitutoyo, SJ-410: Japan) that measured the surface roughness of the drilling processed surface is presented in Fig. 3, and the three-dimensional analyzer (Brown & Sharpe Corp. USA) that can simultaneously measure the roundness and straightness was used herein (Fig. 4).

    2.2 Experimental Methods

    For the hard metal insert tip drill, two types of drills with processing diameters of ø18.5 mm and ø15.0 mm along with two types of insert tips coated with TiN and TiAlN were used. The length of the drill was four times the diameter of the drill, and the insert tip was replaced after each processing. To analyze the results with the statistical method and obtain maximum information with a minimum number of tests, the design of experiments was utilized. Five experimental factors were investigated herein, namely (A) the number of revolutions of a spindle, (B) transfer speed, (C) cutting depth, (D) drill diameter, and (E) insert coating. For each factor, the hard metal insert tip drill processing experiments were conducted at two different levels of the factor.

    The experimental plans were established using the orthogonal matrix, and the five factors and their levels were arranged as shown in Table 1.

    The processing methods for different levels of (C) level are explained in Fig. 5. Level 0 of Fig. 5(a) is the method of one-time drill processing, and level 1 of Fig. 5(b) is the method of three-time processing.

    In terms of the experimental procedure, the experiments were performed using the manufactured specimen (SM45C) randomly selected following the experimental methods tabulated in Table 2.

    To measure the surface roughness of the processed specimen, it was arranged parallel to the heading direction of the stylus probe of the illuminance meter, and the reference point was obtained such that the measurement could be performed at the same point at all times. Furthermore, four points in the 90° direction were set by having the cross-section of the experimental workpiece as the reference point, as shown in Fig. 6, and the measurement section was measured while going backward from the 15-mm point based on the cross-section.

    In terms of the experimental procedure, the experiments were performed using the manufactured specimen (SM45C) randomly selected following the experimental methods tabulated in Table 2.

    To measure the surface roughness of the processed specimen, it was arranged parallel to the heading direction of the stylus probe of the illuminance meter, and the reference point was obtained such that the measurement could be performed at the same point at all times. Furthermore, four points in the 90° direction were set by having the cross-section of the experimental workpiece as the reference point, as shown in Fig. 6, and the measurement section was measured while going backward from the 15-mm point based on the cross-section.

    The roundness and straightness of the processed specimen were measured with the three-dimensional analyzer (CMM). In terms of the measurement section, the continuous surface contact method was used by dividing the drill-processed hole into 5-, 15-, 25-, and 35-mm sections and touching them with the probe. Fig. 7 presents the roundness measurement method, and the measurement conditions are tabulated in Table 3.

    3. Results and Discussion

    Drill processing was carried out based on the experimental plans. Based on the measurement results of the surface roughness, roundness, and straightness, the surface roughness was observed to be in the range of 0.949 μm to 3.502 μm, and the roundness and straightness were determined to be 8.0–36 μm and 2–16 μm, respectively. Table 4 shows the measurement results under different experimental conditions.

    The measurement results are presented in Fig. 8. Experiments 1–4 were performed when the spindle revolution was set to 1,000 rpm, while experiments 5–8 were conducted at a spindle revolution of 1,400 rpm. After comparing the revolution of factor (A) main axis, the surface roughness, roundness, and straightness were observed to be more precise when the spindle revolution was set at 1,000 rpm rather than 1,400 rpm.

    Fig. 9 shows the comparison of measurement results with different transfers per revolution for the tool diameter. The surface roughness, roundness, and straightness were precise at 0.06 mm/rev transfer per revolution of the tool, which corresponds to experiments 1 and 2 with a main-axis revolution of 1,000 rpm and transfer speed of 60 mm/min.

    Based on the average values of the surface roughness change with the change in cutting conditions, variance analysis was performed to investigate the effect of each factor on the process using the statistical program (Mini tap).

    In the analysis results of surface roughness presented in Table 5, the number of spindle revolutions (A) was the factor with a P value less than 0.05, and the transfer speed (B) was also found to have an impact although its P value was higher than 0.05.

    On the basis of the comparison results of each main effect plot graph (Fig. 10), when the main-axis revolutions and the transfer speed were set to S1400 and F100, respectively, the precision of surface roughness was identified to result in a rough surface. Furthermore, under the conditions of this study, utilizing a 15-mm tool, dividing cutting steps and processing by steps, and using TiN coating rather than TiAlN coating were observed to be favorable for the precise surface roughness.

    Based on the analysis results of roundness as presented in Table 6, the spindle revolutions (A), transfer speed (B), and drill diameter (D) were observed to be the main factors affecting the results.

    According to the compared results of the main effect plots provided in Fig. 11, when the main-axis revolutions, transfer speed, and drill diameter were S1400, F100, and 18.5 mm, the precision of the roundness appeared to worsen. Under the experimental conditions of this study, even if the diameter of the tool increases to 18.5 mm, the main-axis revolution and transfer speed were observed to have a more significant effect on the precision of the roundness. Moreover, dividing cutting steps and processing by following the steps along with using the TiAlN coating rather than TiN coating was more favorable for more precise roundness.

    Based on the analysis results of straightness (Table 7), the spindle revolutions (A) and transfer speed (B) were identified to be the main factors affecting the processing of straightness, and the drill diameter (D) was also observed to have an impact on straightness although it was not the main factor.

    After comparing the results of the main effect plot shown in Fig. 12, the precision of the straightness was identified to deteriorate when the main-axis revolutions were S1400, the transfer speed was F100, and the drill diameter was 18.5 mm. The precision of the straightness is significantly affected by the main-axis revolutions and transfer speed rather than the diameter of the tool, and dividing cutting steps followed by the processing of steps was more preferred for precise straightness.

    4. Conclusions

    In this study, the crude-processed SM45C material was processed at the machining center utilizing the design of experiment methodology, and the factors affecting the processing were comparatively analyzed based on the variance analysis, i.e., statistical analytical method, of the measurement results of surface roughness, roundness, and straightness under different cutting conditions. The following list summarizes major conclusions drawn from this study.

    • 1. In the hard metal insert tip drill processing, the main-axis revolutions and transfer speed were the main factors affecting the processing results. It was thus identified that selecting a suitable number of main-axis revolutions and transfer speed is important to obtain precise processing results under the experimental conditions herein in the hard metal insert tip drill processing.

    • 2. During the hard metal insert tip drill processing, the surface roughness Ra was rougher at main-axis revolutions of 1,400 rpm compared with that of 1,000 rpm. Moreover, in the case that the transfer speed was set at F60 rather than F100, Ra demonstrated a remarkable tendency. This suggests that when the main-axis revolutions and transfer speed is high, the vibration attributed to the machining road is generated, and hence, a suitable number of main-axis revolutions and transfer speed are favorable for enhancing the precision of the surface roughness.

    • 3. Under the investigated experimental conditions, setting the number of main-axis revolutions and transfer per revolution of the tool to 1,000 rpm and 0.06 mm/rev, respectively, was preferred to obtain the high precision of the surface roughness.

    • 4. Based on the straightness measurement results, the precision of the roundness deteriorated when the number of main-axis revolutions was S1400, transfer speed was F100, and drill diameter was 18.5 mm. Under the investigated experimental conditions, suitable main-axis revolutions and transfer speed have a more significant impact on the precision of the straightness compared with the tool diameter.

    • 5. In the straightness analysis, the precision of the straightness was more significantly affected by the main-axis revolutions and transfer speed, rather than the tool diameter and type of insert tip coating. Furthermore, processing by cutting steps was more preferable for precise straightness.

    Figure

    KSMPE-20-6-10_F1.gif
    Test piece after processing of test piece during processing
    KSMPE-20-6-10_F2.gif
    Experimental tool holder and insert tip
    KSMPE-20-6-10_F3.gif
    Photographs of surface roughness measurement
    KSMPE-20-6-10_F4.gif
    Photograph of coordinate measuring machine
    KSMPE-20-6-10_F5.gif
    Factor (c) step of cut level comparison
    KSMPE-20-6-10_F6.gif
    The location of surface roughness measurement
    KSMPE-20-6-10_F7.gif
    Roundness, straightness measurement
    KSMPE-20-6-10_F8.gif
    Measurement result of surface roughness, Roundness, straightness
    KSMPE-20-6-10_F9.gif
    Comparison surface roughness of Feed per revolution
    KSMPE-20-6-10_F10.gif
    Main effect analysis graph of surface roughness
    KSMPE-20-6-10_F11.gif
    Main effect analysis graph of value of roundness
    KSMPE-20-6-10_F12.gif
    Main effect analysis graph of straightness

    Table

    Five factors and two levels for drilling experiments
    L8 (27) in place of the five factors
    Measurement conditions for surface roughness
    The experimental results of measurement of hole diameter
    ANOVA of surface roughness
    ANOVA of roundness
    ANOVA of straightness

    Reference

    1. Shin, H. G., Kim, J. T., Kim, M. H., Lee, H. G., "A Study on the Drilling Characteristics of a TiAlN Coated Twist Drill", Journal of the Korean Society of Manufacturing Process Engineers, Vol. 3, No. 4, pp. 29-36, 2004.
    2. Choi, S. Y., Kwon, D. G., "A Study of the Effectives for Surface Roughness by Cutting Angle and Cutting Fluid", Journal of the Korean Society of Manufacturing Process Engineers, Vol. 17 No. 1, pp. 57-62, 2018.
    3. Sin, C. H., Jang J. G., "Effect of chemical treatment and variations of the physical properties of waste water-soluble cutting oil", Journal of Environmental Science International, Vol. 13, No. 4, pp. 403-412, 2004.
    4. Heo, Y. N., Oh, J. Y., Jung, Y. G., Cho, S. L., "A Study on the Development of a Step Cutter with Hybrid Process of Drilling and Boring", Journal of the Korean Society of Manufacturing Process Engineers, Vol. 7, No. 3, pp. 30-35, 2008.
    5. LEE, J. H., S, J. H., Oh, S. H., "Cutting Characteristics with Drilling Temperature of Composite Materials PDF icon", Journal of Korean Society of Mechanical Technology, Vol. 21, No. 64, pp. 1193-1197, 2019.