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  • 5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

    Guwahati, Assam, India

    25-1

    Turning of Hardened H13 Steel with Interrupted and Continuous

    Surfaces using Multilayer Coated Carbide Tool

    R. Suresh1* and S. Basavarajappa2 1* Department of Mechanical Engg., Alliance College of Engineering and Design,

    Alliance University, Bangalore-562106, Karnataka, India *Email: sureshchiru09@gmail.com

    2Department of Mechanical Engineering, U.B.D.T. College of Engineering, Davangere- 577004, Karnataka, India,

    Email: basavarajappas@yahoo.com

    Abstract

    Turning of hardened steels has been used increasingly to replace grinding/finishing operations due to the

    development of advanced tool materials and rigid machine tools, which can ensure the same accurate geometrical

    and dimensional tolerances. However, when turning of interrupted surfaces, the tool requires not only these

    properties but also sufficient toughness to resist impacts against work piece interruptions. In the present study,

    performance of multilayer hard coatings (TiC/MT-TiCN/Al2O3) on cemented carbide substrate using chemical vapor

    deposition (CVD) for turning of hardened AISI H13 steel (50 HRC) was evaluated. Performance evaluation of the

    multilayer coated carbide tool was done on the basis of tool flank wear and was supplemented by cutting force and

    surface roughness analyses. The results show that the thrust force and cutting force increases with increased depth of

    cut and feed rate, while reduces with increase in cutting speed in both continuous and interrupt cutting. The tool

    flank wear was influenced mainly by the cutting speed followed by feed rate. Within the investigated range, abrasion

    and plastic deformation were deliberated to be the active wear mechanisms for the multilayer coated carbide tool.

    The feed rate was the dominant factor affecting work piece surface quality. The main conclusions of this work were

    that in both continuous and interrupted cutting, the multilayer coated tools exhibited a better performance with

    respect to both tool life and workpiece surface roughness. Keywords: Hard turning, Coated Carbide tool, Cutting forces, Tool Wear, Surface Roughness.

    1. Introduction

    Hard turning has been used increasingly in industry.

    Numerous studies have been reported on the successful

    implementation of hard turning. Most of these studies

    involve work materials with hardness values in the range

    of 45–65HRc and also they involve the use of coated

    carbide, ceramic and CBN cutting tools. Hard turning

    offers a number of potential benefits over traditional

    grinding like reducing manufacturing lead time, process

    flexibility, compitable surface finish, higher material

    removal rate and the possibility of dry machining (Ozel et

    al. 2008 and Bartarya and Choudhury (2012)).

    In industrial applications, many components that are

    heat treated before the finish turning operation have

    surfaces interrupted by keyway slots, holes, lubrication

    flow channels and fins. Interrupted turning of hardened

    surfaces imposes extra difficulties on machining

    operations (Diniz and Oliveira (2008), Oliveira et al. 2009

    and Vitor et al. 2009). In such cases, advanced tools are

    preferable, due to its high hardness allied to moderate

    toughness. PCBN and ceramic tools have good

    properties for use in hardened steel turning, such as

    hot hardness, wear resistance and excellent chemical

    stability.

    Diniz and Oliveira [3] studied the effect of cutting

    parameters on tool wear during hard turning with

    continunous and interrupted surfaces using CBN

    tools. Their results shown that high CBN content

    (90% of CBN) is sufficiently resistant to the impacts

    inherent in the cutting of interrupted surfaces and

    provided the longest life. Oliveira et al. (2009)

    performed experiments with a PCBN and whisker

    reinforced ceramic tool for hardened AISI 4340 steel

    turning of continuous and interrupted surfaces. The

    results indicated that, in continuous turning, the

    longest tool life was achieved using PCBN, but

    similar tool longevity was attained in interrupted

    turning using both PCBN and ceramic tools. In terms

  • Turning of Hardened H13 Steel with Interrupted and Continuous Surfaces using Multilayer Coated Carbide Tool

    25-2

    of surface roughness, the PCBN tools showed better

    results for continuous and interrupted surfaces.

    Dogra et al. (2012) investigated the effect of cutting

    parameters on tool wear and surface roughness in finish

    hard turning of continuous and iterrupted surfaces with

    CBN and coated carbide tools. They concluded that the

    surface integrity achieved with carbide tools was

    comparable with that of CBN tools. The surface

    roughness value observed with both tools was below

    1.6 µm. No white layer was observed while turning the

    interrupted and fully interrupted surfaces with both tools.

    As can be seen from the above literatures, cutting

    performance of PCBN and ceramic tool materials has

    been widely measured in hard machining field and

    observed to be acceptable. However, these tools are very

    costly. Undoubtedly, a relatively low cost cutting tool

    material needs to be searched to perform in an acceptable

    range of hard machining. Coated carbide insert is the

    proposed alternative in this regard, which is

    comparatively when cheaper compared to CBN and

    ceramic tools. However the usage of coated carbide insert

    in machining of hardened steel is still lacking during

    turning of interrupt surfaces. Hence, it is necessary to

    investigate the machinability assessments in turning

    hardened steels under dry environment to verify the

    cutting performance and economical viability.

    In the present work, attention is paid towards the

    study on the influence of cutting speed (Vc), feed rate (f)

    and depth of cut (d), which affect the machinability

    characteristics such as cutting forces, tool wear and

    surface roughness during turning of hardened H13 steel

    with continuous and interrupt surfaces using multilayer

    CVD(TiN/MT-TiCN/Al2O3) coated carbide inserts.

    Moreover, analysis of the workpiece surface roughness

    and of the tool wear lands using scanning electron

    microscopy (SEM) were carried out.

    2. Experimental Procedure

    The dry turning experiments were carried out on a

    ‘MAZAK CNC’ lathe with 22kW of spindle power and

    5000rpm of spindle speed. The work piece material was

    AISI H13 steel with 50 HRC of hardness. Round bars of

    100 mm diameter and 400 mm length were selected. The

    chemical composition of the work piece material is given

    in Table 1. These work pieces were produced in order to

    obtain continuous and interrupted surfaces (slot width of

    12mm x 4 interruptions) as shown in Figure 1. Axial

    interruptions were cut in the round bar before hardening.

    The multilayer CVD coated (TiC/TiCN/Al2O3) carbide

    insert grade KCP05 with ISO geometry CNMG 120408

    was used. The experimental setup is as shown in Figure 2.

    The average width of flank wear and nose wear was

    measured using a tool maker’s microscope connected to a

    digital camera and computer. The average surface

    roughness average (Ra) on turning surface was

    measured by ‘Surftest-201’ roughness tester. Cutting

    conditions were specified in accordance with

    recommendations from the insert suppliers. In each

    experiment a fresh cutting tool was used for fixed

    cutting time of 6.0min and the experiments were

    repeated twice at each condition in order to keep

    experimental error at a minimum.

    Table 1 The chemical composition of AISI H13 steel

    in percentage by weight.

    C Si Mn Cr Ni Mo V

    0.4 1.0 0.35 5.3 0.3 1.4 1.0

    Figure 1 Types of work piece surfaces (a) continuous

    surface (b) Interrupt surface.

    Figure 2: Experimental setup

    (a)

    (b)

    Tool Turret

    Axial slots

    Tool

    Dynamomete

    r

  • 5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

    Guwahati, Assam, India

    25-3

    3. Results and Discussions 3.1 Effect of cutting parameters on cutting forces

    The cutting forces acting on tool is an important facet in hard machining. The cutting forces directly influence

    on heat generation, tool wear, quality of machined surface

    and accuracy. Hence, in the present work, influence of

    cutting parameters on cutting forces during turning of

    AISI H13 steel during continuous and interrupted cutting

    with multilayer coated carbide tool has been studied. Fig. 3(a) shows the effect of cutting speed on cutting

    forces at constant feed rate of 0.14 mm/rev and depth of

    cut of 0.45mm. It is observed that the increase in cutting

    speed