Effect of turning-induced initial roughness level on surface roughness and residual stress improvements in subsequent burnishing

Abstract

The hydraulic support column of comprehensive mining equipment is the most important part, subjecting to corrosion, wear and collision. The scrapped columns are restored by laser cladding to replace plating process for enhancing service life. All that is required after laser cladding is subtractive machining to improve the surface quality of the laser cladded coatings. This work focused on the remanufacturing machining strategy for re-contouring the laser cladding restored columns. First, surface roughness model of the laser cladded coatings by turn-burnishing was presented based on the surface generation mechanism. Then the effect of turning-induced roughness level on the surface roughness improvements by subsequent burnishing is addressed. Results indicated that the reduction of surface roughness by burnishing showed positive correlation with the feed in initial turning with conventional inserts, while was negatively correlated with the feed in initial turning with wiper inserts. In addition, the initial turning-induced surface roughness level generated great influence on the residual stress improvement in subsequent burnishing. Based on the findings, proper remanufacturing machining strategies for re-contouring the laser cladding-restored hydraulic support columns were presented.

Introduction

Research motivation

Laser cladding has been commonly utilized for remanufacturing key parts with high values. The durability and strength of the remanufactured parts by laser cladding are improved and, as a result, service life is extended when compared to the electroplating process [1]. The energy consumption and emissions are quantitatively estimated by laser cladding [2]. In addition, the surfaces can be updated by laser cladding to resist wear, corrosion and/or fatigue. Liu et al. [3] showed that the corrosion current of 45 steel can be reduced by orders of magnitude by laser cladding with Ni60CuMoW alloy powder. Xu et al. [4] also showed that both the wear and corrosion resistance of 45 steel can be improved with 304/Al2O3 composite coatings by laser cladding.

However, the poor surface quality becomes a key technological barrier that restricts the widespread applications of laser cladding, especially when the restored parts come to high-quality and high-accuracy requirements. In general, dense microstructure, metallurgical bonding, a low dilution and a shallow heat-affected zone (HAZ) can be achieved with the use of high-density laser beam [5]. It means all that is required after the laser cladding is to subtractive machining the laser-cladded coatings for improving surface quality. However, the laser-cladded coatings belong to the category of difficult-to-cut materials, which are commonly finish machined by grinding method. In our previous studies, turning process was utilized for finish machining the laser-cladded coatings to replace the grinding process [6]. Though the coatings can be processed to a finishing level, stress concentration induced by wave-shaped roughness and tensile residual stresses weakens the corrosion resistance of the coatings [7]. Hence, subsequent burnishing is used to flatten the peak-to-valley and promote the formation of compressive residual stresses on the laser-cladded coatings.

Literature review

During the burnishing process, the coarse coating surface is smoothed by a ceramic/steel ball/roller under the role of hydraulic pressure. Rolling of the ball/roller against the coarse coating surface reduces the surface irregularities [8].

Hiegemann et al. [9] predicted the surface roughness of HVOF-sprayed coatings finished by the ball burnishing process as a function of the burnishing parameters. The surface roughness after burnishing is proportional to the original surface roughness of the coarse coatings [10]. As a chip-less processing, the rolling effect of burnishing process is restricted since there is no material removal. The coarse coating surface should be first via subtractive machining to a low surface roughness level before the burnishing process to get additional reduction of surface roughness.

A combination of subtractive machining and, subsequently, burnishing is utilized to improve the surface integrity of the coatings. The reason is because turning and burnishing processes are similar in kinematical characteristics, both of which can be conducted in one machine tool at given rotation speeds and feed. Sova et al. [11] indicated that ball burnishing following with hard turning made severer and deeper plastic deformation of the surface additionally. Due to the rolling effect of the burnishing ball, the deflected and elongated boundaries along the burnishing direction were formed. As a result, surface roughness of the laser cladded coatings decreased from Sa = 35 μm (coarse surface) to Sa = 1.8 μm (semi-finishing level) by hard turning and Sa = 0.5 μm (finishing level) by turn-burnishing process. Maiß et al. [12] also indicated that the turn-burnishing process improves surface quality by plastic deformation of the surface roughness peaks, where the surface roughness decreases by 24% by the process chain when compared to those obtained by turning individually.

Zhang and Liu [13] found that the laser-cladded Fe−Cr−Ni coatings are smoothed by subsequent burnishing compared to the turned one. In addition, the residual stresses in near-surface shifted from tensile to compressive state by burnishing because of severe plastic deformation. Courbon et al. [14] further indicated that the affected depth of burnishing could reach 300 μm in the cladded coatings with deep and intense stresses down to − 1 GPa.

In the above studies, the improvements in surface roughness and residual stresses by burnishing are obvious, but the quantitative relationship improved by burnishing is unknown. Moreover, the degree of improvement by burnishing should be related to the surface roughness level after turning, rather than a percentage.

Research objectives

This work focuses on remanufacturing machining strategy belonging to the surface engineering project by laser cladding and turn-burnishing processes. First, the evolution of surface roughness during turn-burnishing process is modelled based on the surface generation mechanism. Second, the effect of turning-induced roughness on the surface roughness and residual stress improvements by burnishing are addressed. In particular, surface roughness and residual stress improvements by burnishing after initial turning with conventional vs. wiper inserts are experimentally compared. Finally, remanufacturing machining strategies are proposed for laser cladding restored hydraulic support columns to meet the surface roughness requirement. On the basis of this work, the laser cladding and subtractive machining methods are hopeful to be a promising process to restore key components, aiming for surface engineering and remanufacturing fields.

Analytical models

Surface roughness induced by initial turning

The laser cladding restored hydraulic support columns are first machined by turning to improve the surface quality. The use of wiper inserts (i.e., multi-radii design for the nose of cutting inserts) can improve the surface roughness level of the laser-cladded coatings at high material removal rate [6, 15].The mechanism of wiper inserts is the adoption of a large transit arc or straight line linking the tool nose and main/minor cutting edges. This special configuration of the wiper inserts extends the actual contact length between the cutting tool and workpiece, which, as a result, decreases the surface roughness. Comparing to turning with conventional inserts, surface roughness level can be decreased to half by using wiper inserts under the same feed, or maintained in comparable surface roughness level using wiper inserts with double feeds [16,17,18], as schematically illustrated in Fig. 1.

Fig. 1
figure1

The effects of tool nose and feed on surface roughness generation in turning with (a) conventional insert, (b) and (c) wiper inserts

The prediction model for surface roughness by subsequent turning is established based on the definitions of surface roughness Ra and Rz, which are defined as the arithmetical mean deviation of surface profile and peak–valley spacing along the measured length, as shown in Fig. 2.

Fig.2
figure2

The surface roughness profile of the coatings by turning with (a) wiper vs. (b) conventional inserts

First, the surface profile (R(δ)) of the coatings after turning with wiper inserts as a function of position angle (δ) is derived based on the cutting tool nose geometry as well as the kinematics. As shown in Fig. 2a, the surface profile depends on the multi-radii geometry of the tool nose. It can be proved that the secondary cutting edge is not involved for wiper inserts when the feed does not exceed 0.5 mm/rev. The surface profile is given by

$$R\left( \delta \right) = \left\{ {\begin{array}{*{20}l} {(r_{1} + \Delta r)(1 - \cos \delta ),} \hfill & {\delta < 0} \hfill \\ {r_{1} (1 - \cos \delta ),} \hfill & {\delta \ge 0} \hfill \\ \end{array} } \right.,$$
(1)

where Δr is defined as the increment of wiper radius (r2) to the normal tool nose radius (r1), i.e., Δr = r2 − r1. The tool tip is defined as the point with a position angle of δ = 0, which shifts to a negative angle in the clockwise direction or positive angle in the counterclockwise direction.

As shown in Fig. 2a, the line that bisects the area surrounded by the machined surface profile is taken as the mean line. For ease of calculation, the length of arc is regarded as the width of each micro-element. The mean value, hence, is given by

$$R_{{{\text{mean}}}} = \frac{{\int_{{\delta_{\min } }}^{0} {\left( {r_{1} + \Delta r} \right)^{2} \left( {1 - \cos \delta } \right)d\delta } + \int_{0}^{{\delta_{\max } }} {r_{1}^{2} \left( {1 - \cos \delta } \right)d\delta } }}{{r_{1} \sin \delta_{\max } - \left( {r_{1} + \Delta r} \right)\sin \delta_{\min } }},$$
(2)

where δmin and δmax represent the boundary of the cutting zone in one feed:

$$\delta_{\min } = - \left( {\arctan \frac{f}{\Delta r} - \arccos \frac{{2r_{1} \Delta r + 2\Delta r^{2} + f^{2} }}{{2\left( {r_{1} + \Delta r} \right)\sqrt {f^{2} + \Delta r^{2} } }}} \right)$$
(3)

and

$$\delta_{\max } = \arccos \frac{{\left( {r_{1} + \Delta r} \right) \cdot \cos \delta_{\min } - \Delta r}}{{r_{1} }}.$$
(4)

Thus, the surface roughness of the coatings by turning with wiper inserts can be expressed by the following equations according to the definition of surface roughness:

$$R_{a} = \frac{1}{{r_{1} \sin \delta_{\max } - \left( {r_{1} + \Delta r} \right)\sin \delta_{\min } }} \cdot \left( \begin{gathered} \int_{{\delta_{\min } }}^{0} {\left| {\left( {r_{1} + \Delta r} \right)\left( {1 - \cos \delta } \right) - R_{{{\text{mean}}}} } \right| \cdot \left( {r_{1} + \Delta r} \right)\cos \delta d\delta } + \hfill \\ \int_{0}^{{\delta_{\max } }} {\left| {r_{1} \left( {1 - \cos \delta } \right) - R_{{{\text{mean}}}} } \right| \cdot r_{1} \cos \delta d\delta } \hfill \\ \end{gathered} \right),$$
(5)
$$R_{z} = \left( {r_{1} + \Delta r} \right)\left( {1 - \cos \delta_{\min } } \right) = r_{1} \left( {1 - \cos \delta_{\max } } \right).$$
(6)

In particular, the wiper inserts convert to conventional inserts when r2 equals to r1, as shown in Fig. 2b. Taking Δr → 0 in Eqs. (1)–(6), surface roughness Ra0 and Rz0 in turning with conventional inserts are expressed by

$$R_{a0} = \frac{1}{{ - r_{1} \sin \delta_{\min } }} \cdot \int_{{0}}^{{ - \delta_{\min } }} {\left| {r_{1} \left( {1 - \cos \delta } \right) - R_{{{\text{mean}}}} } \right| \cdot r_{1} \cos \delta d\delta } ,$$
(7)
$$R_{{z{0}}} = r_{1} - \sqrt {r_{1}^{2} - \frac{{f^{2} }}{4}} .$$
(8)

Surface roughness improvement by ball burnishing

The roughness peaks induced by turning can be estimated by ball burnishing as a result of the severe plastic deformation. In this way, the surface roughness level of the laser-cladded coatings can be improved. Hiegemann et al. [9] had proposed a surface roughness model by ball burnishing. However, this mathematical model does not consider the influence of the initial surface roughness induced by turning on the subsequent burnishing process. In fact, the initial surface roughness induced by turning converts continuous to discontinuous contact between the burnishing ball and machined surface, which, in turn, leads to different improvements of surface roughness during subsequent ball burnishing. In the present study, the surface roughness model is expected to be extended by considering the initial surface roughness Rz (i.e., Eq. (6)) induced by turning.

By treating the turned surface as a one-dimensional wavy surface, the surface can be compressed to continuous contact if the pressure was large enough during the burnishing process. The required contact pressure p* contact can be given by [19]

$$p_{{{\text{contact}}}}^{*} = \frac{{\pi ER_{z} }}{2f}.$$
(9)

However, the surface morphology shows that the burnishing ball and the turned surface are in discontinuous contact. These two surfaces contact at the peaks and separate from each other at the valleys. The mean contact pressure pcontact (smaller than p* contact) between the burnishing ball and machined surface can be calculated by the following equation due to the similar contact conditions between Brinell hardness measurements (contact of an indenter against a surface) and ball burnishing [20]:

$$p_{{{\text{contact}}}} = \left( {\frac{{{{\left( {\frac{\pi }{4}d^{2} } \right) \cdot p_{{{\text{fluid}}}} } \mathord{\left/ {\vphantom {{\left( {\frac{\pi }{4}d^{2} } \right) \cdot p_{{{\text{fluid}}}} } {F_{{{\text{HBW}}}} }}} \right. \kern-\nulldelimiterspace} {F_{{{\text{HBW}}}} }}}}{{\frac{{d^{2} }}{{D_{{{\text{HBW}}}}^{2} }}}}} \right)^{{{{\left( {n - 2} \right)} \mathord{\left/ {\vphantom {{\left( {n - 2} \right)} n}} \right. \kern-\nulldelimiterspace} n}}} \cdot {\text{HBW}} = \left( {\frac{\pi }{4} \cdot \frac{{p_{{{\text{fluid}}}} \cdot D_{{{\text{HBW}}}}^{2} }}{{F_{{{\text{HBW}}}} }}} \right)^{{{{\left( {n - 2} \right)} \mathord{\left/ {\vphantom {{\left( {n - 2} \right)} n}} \right. \kern-\nulldelimiterspace} n}}} \cdot {\text{HBW,}}$$
(10)

where n is the Meyer index (n = 2.20 for black metal and its alloys) [21], FHBW and DHBW are the applying load and indentation diameter in Brinell hardness measurement, pfluid is the fluid pressure, and d is the diameter of burnishing ball. Equation (10) indicates that the mean contact pressure between burnishing ball and machined surface is independent of the ball size.

As shown in Fig. 3, it is considered that the burnishing ball compresses the surface roughness peak into flat because that the diameter of the burnishing ball is much larger than the feed adopted in the burnishing process. The width of the flat band can be calculated by

$$a = \frac{2f}{\pi }\arcsin \left( {\frac{{p_{{{\text{contact}}}} }}{{p_{{{\text{contact}}}}^{*} }}} \right)^{{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}}} .$$
(11)
Fig. 3
figure3

The surface roughness model by ball burnishing based on machined surface after turning

In addition, the flat band is limited in the intervals δ > δ1, and δ < δ2. The boundary can be derived based on

$$\delta_{{1}} = \arccos \frac{{\left( {r_{1} + \Delta r} \right) \cdot \cos \delta_{{2}} - \Delta r}}{{r_{1} }},$$
(12)
$$\delta_{{2}} = - \left( {\arctan \frac{f - a}{{\Delta r}} - \arccos \frac{{2r_{1} \Delta r + 2\Delta r^{2} + \left( {f - a} \right)^{2} }}{{2\left( {r_{1} + \Delta r} \right)\sqrt {\left( {f - a} \right)^{2} + \Delta r^{2} } }}} \right).$$
(13)

Thus, the surface roughness R' z after burnishing can be determined by

$$R^{\prime}_{z} = \left( {r_{1} + \Delta r} \right)\left( {1 - \cos \delta_{{2}} } \right)$$
(14)

Thus, the surface profile (R'(δ)) by burnishing can be expressed by

$$R^{\prime}\left( \delta \right) = \left\{ {\begin{array}{*{20}l} {R^{\prime}_{z} ,} \hfill & {\delta^{\prime}_{\min } \le \delta < \delta_{2} } \hfill \\ {(r_{1} + \Delta r)(1 - \cos \delta ),} \hfill & {\delta_{2} \le \delta \le 0} \hfill \\ {r_{1} (1 - \cos \delta ),} \hfill & {0 < \delta \le \delta_{1} } \hfill \\ {R^{\prime}_{z} ,} \hfill & {\delta_{1} < \delta \le \delta^{\prime}_{\max } } \hfill \\ \end{array} } \right.,$$
(15)

where δ' min and δ' max represent the boundary of the plastic deformation of surface roughness peaks in subsequent burnishing:

$$\delta^{\prime}_{\min } = \arctan \left( {\frac{{\left( {r_{1} + \Delta r} \right)}}{{r_{1} + \Delta r - R^{\prime}_{z} }} \cdot \sin \delta_{\min } } \right)$$
(16)

and

$$\delta^{\prime}_{\max } = \arctan \left( {\frac{{r_{1} }}{{r_{1} - R^{\prime}_{z} }} \cdot \sin \delta_{\max } } \right).$$
(17)

The mean value of the surface profile after burnishing is further given by

$$R^{\prime}_{{{\text{mean}}}} = \frac{{\int_{{\delta^{\prime}_{\min } }}^{{\delta_{2} }} {R^{\prime}_{z} (r_{1} + \Delta r)d\delta } + \int_{{\delta_{2} }}^{0} {(r_{1} + \Delta r)^{2} (1 - \cos \delta )d\delta + \int_{0}^{{\delta_{1} }} {r_{1}^{2} (1 - \cos \delta )d\delta + } } \int_{{\delta_{1} }}^{{\delta^{\prime}_{\max } }} {R^{\prime}_{z} r_{1} d\delta } }}{{r_{1} \sin \delta^{\prime}_{\max } - \left( {r_{1} + \Delta r} \right)\sin \delta^{\prime}_{\min } }}.$$
(18)

Thus, the surface roughness after burnishing can be derived by

$$R^{\prime}_{a} = \frac{1}{{r_{1} \sin \delta^{\prime}_{\max } - \left( {r_{1} + \Delta r} \right)\sin \delta^{\prime}_{\min } }} \cdot \left( \begin{gathered} \int_{{\delta^{\prime}_{\min } }}^{{\delta_{{2}} }} {\left| {R^{\prime}_{z} - R^{\prime}_{{{\text{mean}}}} } \right| \cdot \left( {r_{1} + \Delta r - R^{\prime}_{z} } \right)d\delta } + \hfill \\ \int_{{\delta_{{2}} }}^{{0}} {\left| {(r_{1} + \Delta r)(1 - \cos \delta ) - R^{\prime}_{{{\text{mean}}}} } \right| \cdot \left( {r_{1} + \Delta r} \right)\cos \delta d\delta } { + } \hfill \\ \int_{{0}}^{{\delta_{{1}} }} {\left| {r_{1} (1 - \cos \delta ) - R^{\prime}_{{{\text{mean}}}} } \right| \cdot r_{1} \cos \delta d\delta + } \hfill \\ \int_{{\delta_{{1}} }}^{{\delta^{\prime}_{\max } }} {\left| {R^{\prime}_{z} - R^{\prime}_{{{\text{mean}}}} } \right| \cdot \left( {r_{1} - R^{\prime}_{z} } \right)d\delta } \hfill \\ \end{gathered} \right).$$
(19)

By substituting Eqs. (14) and (18) into Eq. (19), the influence of turning-induced roughness level, determined by the tool nose geometry and feed adopted in initial turning, on surface roughness evolution by subsequent burnishing can be obtained. However, Eq. (19) is derived by considering only kinematic factors, but not physical factors.

In special, the surface roughness R' a0 and R' z0 in turn-burnishing with conventional inserts can be expressed by the following equations when Δr tends to 0:

$$R_{a0}^\prime = \frac{1}{{ - {r_1}\sin \delta _{\min }^\prime }}\left( {\int_0^{ - {\delta _2}} {\left| {{r_1}(1 - \cos \delta ) - R_{{\text{mean}}}^\prime } \right| \cdot {r_1}\cos \delta {\text{d}}\delta + \int_{ - {\delta _2}}^{ - \delta _{\min }^\prime } {\left| {R_z^\prime - R_{{\text{mean}}}^\prime } \right| \cdot \left( {{r_1} - R_z^\prime } \right){\text{d}}\delta } } } \right),$$
(20)
$$R^{\prime}_{z0} = r_{1} \left( {1 - \cos \delta_{{2}} } \right).$$
(21)

It should be noted that the surface roughness by ball burnishing depends on the initial roughness level induced by turning (determined by tool nose radii and feed parameters), Brinell hardness and elastoplastic of the laser-cladded material, and the fluid pressure adopted in subsequent burnishing process. This model solves the problem of discontinuous contact during the subsequent burnishing of machined surfaces. Therefore, this model is suitable for the burnishing process under different materials and different turning conditions. This model also shows that the elastoplastic properties of the material limit the improvement of surface roughness by burnishing. If appropriate measures are taken, such as the use of warm plastic burnishing, it is conducive to shifting discontinuous contact into continuous contact, thereby improving the strengthening effect of burnishing.

Experimental setups

Laser-cladded Fe–Cr–Ni coatings (approx. 2 mm in thickness) were prepared on AISI 1045 steel rod with Φ120 mm in diameter and 300 mm in length. A combination of subtractive machining and, subsequently, burnishing is utilized to improve the surface integrity of the coatings. Advantage of the machining process chain lies in that turning and burnishing processes are similar in kinematical characteristics, both of which can be conducted on one machine tool (DAEWOO PUMA200MA computer numerical control (CNC) turning center) at given rotation speeds and feed. First, the cladded coatings were machined by rough and finish turning in sequence. Feeds covering from 0.2 to 0.45 mm/rev were selected during finish turning to generate different surface roughness levels, while the cutting speed and depth of cut were kept as 50 m/min and 0.15 mm in constant, respectively. Then low plasticity burnishing (LPB) equipped with a Si3N4 ceramic ball (Φ 6.3 mm in diameter) was carried out. The detailed burnishing parameters were listed as follows: burnishing speed 50 m/min, feed 0.05 mm/rev, fluid pressure 18 MPa, penetration depth 0.4 mm, and Nos. of tool passes 2.

After the turn-burnishing operations, surface topographies were measured by a laser scanning confocal microscopy (Keyence Co., Ltd.), and all the surface roughness was measured in a surface area of 1427.08 μm × 1069.96 μm with a sampling interval of 1.395 μm after the processes of tilt removal and Gaussian regression filter with the short-wavelength cutoff of λs = 25 μm. Residual stresses along cutting/burnishing speed and feed directions were measured by the μ-X360 portable X-ray residual stress analyzer (Pulstec Industrial Co., Ltd.), which calculates residual stress using the cosα method. The machined specimen was placed on a robust table, while the detector gun of the residual stress analyzer was inclined at an angle of 35°, establishing a red spot of laser on the machined surface where the X-ray beam would incident. A diffraction profile (Debye ring) was obtained as distribution of the diffraction intensity along radial directions from the location of the incidence beam determined above. The Debye ring was derived from α = 0° to α = 360° with an interval of 0.72° and were used for residual stress analysis.

Figure 4 shows the comparison between the predicted values of surface roughness Ra based on the proposed model and the experimental results. The percentage errors can generally be controlled within 10%, indicating that the model can reliably predict the surface roughness of turn-burnishing process. When the combination of wiper insert and small feed is adopted, the friction between the flank face of cutting tool and the machined surface generates excessive heat, which softens the surface material. As a result, the prediction value in subsequent burnishing deviates greatly from the experimental result, as shown in Fig. 4d.

Fig. 4
figure4

Comparison of the predicted and measured surface roughness by turn-burnishing process

Results and discussions

Effect of turning-induced roughness on surface roughness improvement by subsequent burnishing

Effects of the tool nose geometry and feed on surface roughness in turn-burnishing process

Figure 5 shows the influences of tool’s nose geometry and feed adopted in initial turning on surface roughness Ra evolution before vs. after burnishing based on the calculation results from the model. The surface roughness acquired by ball burnishing shows dependence on the initial surface roughness levels.

Fig. 5
figure5

Influences of tool nose geometry and feed on surface roughness Ra by turning vs. burnishing

For initial turning, the surface roughness Ra increase with feed increasing. As a matter of fact, the residual material volume above the machined surface determines the surface roughness after machining. For this reason, the increasing feed will induce larger residual material volume, which is detrimental to surface roughness level of the machined surface. Luca et al. [10] indicated that the adoption of larger tool nose radii in turning can improve the surface roughness. However, the introduction of larger tool nose radii increases the magnitude of cutting force. In this case, wiper inserts are more suitable for improving the surface roughness on account of the rolling action of the transit arc/larger radii. The wiper inserts are preferred for initial turning in high-feed conditions, which can generate low surface roughness level without sacrificing the cutting efficiency for re-manufacturing machining process.

For burnishing, the rolling action of burnishing ball against the machined surface after initial turning can further reduce the surface roughness. Hiegemann et al. [9] utilized burnishing process as a finishing method to improve the surface roughness of the HVOF-sprayed coatings. However, the rolling action of burnishing process is restricted since there is no material removal volume. As a result, burnishing is limited to the thermally sprayed coatings with low levels of surface roughness. In general, the surface roughness formed by laser cladding has a range of up to hundreds of microns. Therefore, lower surface roughness level provided by initial turning process is required before burnishing. As can be seen from Fig. 5, the surface roughness level before vs. after burnishing process is proportionally reduced. The larger the initial roughness value, the greater the reduction in roughness by burnishing.

Figure 6 shows the sensitivity of surface roughness on the tool nose geometry and feed used in the initial turning process. As shown in Fig. 6a, the contour map indicates that the wiper inserts are less sensitive to the feed adopted in turning than the conventional inserts. In addition, the sensitivity to feed further decreases with the transit radius increases. It means that the surface roughness can be kept at a low level when using wiper inserts. The contour map also indicates that the surface roughness is less affected by tool nose geometry at small feed. The result replies that the wiper inserts are preferred in initial turning of the laser cladded parts with large feed. As a result, machining efficiency is significantly improved. Figure 6b shows that the surface roughness has a minimum value in burnishing the machined surface by initial turning with feed f = 0.3 mm/rev and tool nose radius increment Δr = 2.0 mm. It indicates that the plastic deformation of the machined surface in subsequent burnishing is the most sufficient at this time. Otherwise, the residual surface material will be reduced, which will weaken the rolling effect during the subsequent burnishing.

Fig. 6
figure6

Sensitivity analysis of surface roughness Ra by (a) turning and (b) turn-burnishing on tool nose geometry vs. feed used in the initial turning process

Comparison of surface roughness improvements by burnishing after turning with conventional versus wiper inserts

Figure 7 compares the surface roughness generation of the coatings finished by initial turning with various feeds. It can be found that the surface roughness Ra increases linearly with increasing feed in the initial turning operations. Moreover, the Ra can be maintained at low levels regardless of the feeds in initial turning equipped with wiper inserts when comparing to the conventional ones. The reason can be attributed to the rolling actions by the multi-radii geometry as well as the small end cutting edge angle.

Fig. 7
figure7

Effect of feed on initial turning on surface roughness Ra generation

Surface roughness can be further reduced due to the rolling effect of burnishing ball against the machined surface. Besides burnishing parameters, the surface conditions after ball burnishing also depend on the surface roughness induced by initial turning process, which is affected by the tool nose geometry and the feed parameter. Sova et al. [11] found that the turn-burnishing process permitted to decrease the surface roughness to Ra = 0.5 μm under specific processing conditions. However, the feeds used in the initial turning were restricted below f = 0.15 mm/rev, where the machining efficiency is too low to be accepted by the production practice. Luca et al. [10] studied the influence of tool nose radius on surface roughness induced by the turn-burnishing process. The feed adopted in initial turning can be increased from 0.075 to 0.18 mm/rev when tool nose radius increases from 0.2 to 0.8 mm while the surface roughness Ra is kept less than 0.5 μm by subsequent burnishing. However, the machining efficiency is relatively low in initial turning with the conventional inserts because of the low feed to be used.

This section attempts to reveal the evolution of surface roughness by subsequent burnishing. As shown in Fig. 8, the reduction of surface roughness by subsequent burnishing is proportional to the feed used in the initial turning process. For initial turning with conventional inserts, increasing feed results in larger amount of residual material on the machined surface. This facilitates severer plastic deformation during the subsequent burnishing process, resulting in a significant reduction of surface roughness. As a result, the reduction of surface roughness shows a positive correlation with the feed levels adopted in initial turning with conventional inserts. In contrast, most material is removed via the multi-radii geometry equipped with a small end cutting edge angle for initial turning with wiper inserts. Plastic deformation, in turn, is significantly weakened during the subsequent burnishing, causing less reduction of surface roughness. Consequently, the reduction of surface roughness is negatively correlated with the feed in initial turning with wiper inserts.

Fig. 8
figure8

Effect of subsequent burnishing on surface roughness evaluation vs. feed used in the initial turning operation

It is easier to understand the evolutionary history of surface roughness induced by turn-burnishing from the viewpoint of surface topography and corresponding surface profile. Figure 9a, c shows that the surface topographies of coatings machined by initial turning are periodically fluctuated in the wave shapes. Feed marks exhibit parallel and equidistant, which are formed due to the feed motions of the cutting tool. In addition, the surface profiles further show that the peak of the surface machined by turning is relatively very sharp, which will cause stress concentration on the machined surface. Figure 9b, d shows that the surface profiles become blunt by subsequent burnishing. However, the surface profile by subsequent burnishing is similar to that obtained by the initial turning process, indicating the dependence of burnishing on the previous machining process. The reason may be due to the anisotropy of the machined surface by initial turning. Borkar et al. [22] indicated that the plastic deformation during burnishing displaced the material from surface roughness peaks into valleys by the rolling actions. That is, the side flow of materials along the feed direction contributes to flatter surface topography by turn-burnishing process. Maiß et al. [12] also indicated that the turn-burnishing process improves surface quality by the plastic deformation of surface roughness peaks, where the surface roughness by subsequent burnishing shows proportional to the original surface roughness. In present study, the surface roughness peaks are almost eliminated by wiper inserts, as shown in Fig. 9c. As a result, the rolling effect of burnishing after initial turning with wiper inserts is weakened.

Fig. 9
figure9

Typical surface topographies and corresponding profiles of laser cladded coatings finished by turning (f = 0.4 mm/rev) and turn-burnishing processes

Effect of turning-induced roughness on residual stress improvement by burnishing

The residual stress of machined surface is another key parameter which determines the service performance of the parts. In case of turn-burnishing processes, it is crucial to highlight how subsequent burnishing modifies the residual stress conditions induced by initial turning. Sova et al. [11] indicated that tensile residual stresses were commonly induced by turning and shifted to compressive states by subsequent burnishing. In fact, the residual stresses on machined surface are anisotropy, where the residual stresses by subsequent burnishing shows a correlation to the initial conditions by initial turning. This section attempts to reveal the evolutionary history of residual stress by subsequent ball burnishing.

Figure 10 first compares the initial residual stresses along the cutting speed and feed directions induced by initial turning process. In general, tensile residual stresses are prone to be generated on machined surface during turning processes. The tensile residual stresses shift to compressive conditions with larger feeds in initial turning with conventional inserts, as can be seen from Fig. 10a. The reason can be explained by severer side flow between the machined surface and tool flank face.

Fig. 10
figure10

Effect of feed on residual stress in initial turning process

Conversely, the adoption of wiper inserts induces an opposite evolution history of residual stresses. As shown in Fig. 10b, the residual stresses shift from compressive to tensile conditions with larger feeds in turning with wiper inserts. The reason should be considered as the coupling effects of cutting forces and cutting temperature. On one hand, Gaitonde et al. [23] indicated that larger cutting forces were generated in turning with wiper inserts than those of conventional ones. It is beneficial to generate compressive residual stress under the action of mechanical load. Consequently, the extrusion on the machined surface by the multi-radii geometry in turning with wiper inserts results in the compressive residual stresses at low feed. On the other hand, the contact length between cutting tool and workpiece increases with feed increasing, resulting in poor heat dissipation and high cutting temperature. Hence, the machined surface promotes the establishment of tensile residual stresses.

As for the subsequent burnishing process, the evolution of residual stresses exhibits sensitivity to the burnishing directions. The residual stresses along feed direction are significantly improved due to the plastic deformation of surface roughness peaks. In the present study, all machined surfaces turn into deep compressive residual stresses under the rolling effect of burnishing ball. As for machined surfaces by initial turning with conventional inserts, the residual stresses after subsequent burnishing reach − 616 MPa and − 987 MPa along the burnishing and feed directions, respectively. As for machined surfaces by initial turning with wiper inserts, the residual stresses after subsequent burnishing reach − 516 MPa and − 1035 MPa along the burnishing and feed directions, respectively.

The burnishing process has a more pronounced effect on the improvement of residual stresses along feed direction, as shown in Fig. 11. In fact, the improvements of residual stresses by subsequent burnishing significantly depend on the initial surface roughness/residual material volume conditions, i.e., the feed and tool inserts adopted in the initial turning process. As a result, the improvements of residual stresses by subsequent burnishing are negatively correlated with the feed in initial turning with conventional inserts, while shows positive correlation with the feed in initial turning with wiper inserts.

Fig. 11
figure11

Effect of subsequent burnishing on the improvement of residual stresses comparing to the machined surface by initial turning

Case study: remanufacturing machining strategies for laser cladding restored hydraulic support columns

The column of the hydraulic support of comprehensive mining equipment is the most important component for bearing loads, which plays an important role in its usability and reliability. The column is subjected to corrosion, wear and collision after working for a long time. As reported, the scrapped hydraulic support columns are about 450,000 tons/year in China. At present, the scrapped columns are commonly repaired by electroplating process. However, the scrapped columns cannot be repaired to the new product size after repairing two times due to the thickness limitation of the plating layer. The only way to deal with the scrapped columns is re-melting, which consumes a lot of energy, and the resulting CO2 and SO2 have serious environmental pollution.

Laser cladding is a very promising repairing technique to replace electroplating. All that is required after laser cladding is subtractive machining to improve surface quality. The subsequent machining process is closely related to the usage of columns. For different applications, the columns are mainly used in single- and double-telescopic forms. The single-telescopic column possesses advantages of wide adjustment, high reliability and low cost, while the double-telescopic column is much more flexible in use besides a wide range of adjustment. Besides, the double-telescopic column has a complex structure, as well as a high-precision requirement and high cost. In general, the surface roughness requirement of a double-telescopic hydraulic support column (i.e. Ra ≤ 0.8 μm) is tighter than the single-telescopic one (i.e. Ra ≤ 1.6 μm). Therefore, the remanufacturing process of the two different hydraulic columns needs to adopt different machining strategies to meet the requirements of surface roughness.

This section attempts to provide suitable process planning for remanufacturing machining of the laser cladding restored hydraulic support columns based on the present research. Figure 12 implies the distributions of the surface roughness and residual stress on the machined surface by different machining strategies. As for the turning method, the using of wiper inserts can achieve the surface roughness requirement of single-telescopic columns, while not using conventional inserts. However, the residual stresses on the surface of the remanufacturing machined columns tend to be in tensile or a shallow compressive residual stress using turning method individually, which is not beneficial for the service life.

Fig. 12
figure12

Comparison of the remanufacturing machining strategies for re-contouring the single-telescopic and double-telescopic hydraulic support columns

With subsequent burnishing (i.e., by turn-burnishing process), surface roughness of the laser-cladded coatings can be further reduced. As a result, the machined surface by initial turning with wiper inserts can be burnished to meet the surface roughness requirement of double-telescopic columns, while the machined surface by initial turning with conventional inserts can be burnished to meet the requirement of single-telescopic columns. Luca et al. [10] proposed that the feed in initial turning should be controlled within 0.18 mm/rev in turn-burnishing process to a finishing machined level. By adopting turning with wiper inserts as initial machining method, the feed can be increased to 0.4 mm/rev while maintains an acceptable surface roughness level.

Moreover, the residual stresses on the remanufacturing machined surface of the columns are in deep and intense compressive conditions down to − 1 GPa after ball burnishing, which is beneficial to prolong the service life. Common grinding and honing processes were not able to induce such high compressive stresses, as illustrated by Guo et al. [24].

Conclusions

The hydraulic support columns of the comprehensive mining equipment are the most important part, subjecting to corrosion, wear and collision. Laser cladding provides an effective way to restore the worn-out columns. All that is required after laser cladding is subtractive machining to improve surface quality. This work focused on remanufacturing machining strategy for re-contouring the laser cladding restored columns. The key conclusions are summarized as follows:

  • Surface roughness induced by hybrid turn-burnishing process is modelled and predicted based on surface generation mechanism.

  • The reduction of surface roughness by burnishing shows a positive correlation with the feed in initial turning with conventional inserts, while is negatively correlated with the feed in initial turning with wiper inserts.

  • The improvements of residual stresses by burnishing are negatively correlated with the feed in initial turning with conventional inserts, while show positive correlation with the feed in initial turning with wiper inserts.

  • On the basis of this work, laser cladding restored single-telescopic columns can be remanufacturing machined by turn-burnishing process with conventional inserts in the initial turning, while the restored double-telescopic columns should be remanufacturing machined by turn-burnishing process with wiper inserts. Moreover, the residual stresses of the remanufactured columns are in deep and intense compressive conditions by turn-burnishing process.

References

  1. 1.

    Chen C, Wang Y, Ou H, He Y, Tang X. A review on remanufacture of dies and moulds. J Clean Prod. 2014;64:13–23.

    Article  Google Scholar 

  2. 2.

    Morrow W, Qi H, Kim I, Mazumder J, Skerlos S. Environmental aspects of laser-based and conventional tool and die manufacturing. J Clean Prod. 2007;15:932–43.

    Article  Google Scholar 

  3. 3.

    Liu H, Wang C, Zhang X, Jiang Y, Cai C, Tang S. Improving the corrosion resistance and mechanical property of 45 steel surface by laser cladding with Ni60CuMoW alloy powder. Surf Coat Technol. 2013;228:S296–S300.

    Article  Google Scholar 

  4. 4.

    Xu P, Lin C, Zhou C, Yi X. Wear and corrosion resistance of laser cladding AISI 304 stainless steel/Al2O3 composite coatings. Surf Coat Technol. 2014;238:9–14.

    Article  Google Scholar 

  5. 5.

    Hemmati I, Ocelík V, De Hosson JTM. Dilution effects in laser cladding of Ni–Cr–B–Si–C hardfacing alloys. Mater Lett. 2012;84:69–72.

    Article  Google Scholar 

  6. 6.

    Zhang P, Liu Z, Guo Y. Machinability for dry turning of laser cladded parts with conventional vs. wiper insert. J Manuf Process. 2017;28:494–9.

    Article  Google Scholar 

  7. 7.

    Zhang P, Liu Z, Su G, Du J, Zhang J. A study on corrosion behaviors of laser cladded Fe−Cr−Ni coating in as-cladded and machined conditions. Mater Corros. 2019;70:711–9.

    Article  Google Scholar 

  8. 8.

    Tekkaya AE, Kleiner M, Biermann D, Hiegemann L, Rausch S, Franzen V, Kwiatkowski L, Kersting P. Friction analysis of thermally sprayed coatings finished by ball burnishing and grinding. Prod Eng Res Devel. 2013;7:601–10.

    Article  Google Scholar 

  9. 9.

    Hiegemann L, Weddeling C, Khalifa NB, Tekkaya A. Prediction of roughness after ball burnishing of thermally coated surfaces. J Mater Process Technol. 2015;217:193–201.

    Article  Google Scholar 

  10. 10.

    Luca L, Neagu-Ventzel S, Marinescu I. Effects of working parameters on surface finish in ball-burnishing of hardened steels. Precision Eng. 2005;29:253–6.

    Article  Google Scholar 

  11. 11.

    Sova A, Courbon C, Valiorgue F, Rech J, Bertrand P. Effect of turning and ball burnishing on the microstructure and residual stress distribution in stainless steel cold spray deposits. J Therm Spray Technol. 2017;26:1–13.

    Article  Google Scholar 

  12. 12.

    Maiß O, Denkena B, Grove T. Hybrid machining of roller bearing inner rings by hard turning and deep rolling. J Mater Process Technol. 2016;230:211–6.

    Article  Google Scholar 

  13. 13.

    Zhang P, Liu Z. Enhancing surface integrity and corrosion resistance of laser cladded Cr–Ni alloys by hard turning and low plasticity burnishing. Appl Surf Sci. 2017;409:169–78.

    Article  Google Scholar 

  14. 14.

    Courbon C, Sova A, Valiorgue F, Pascal H, Sijobert J, Kermouche G, Bertrand P, Rech J. Near surface transformations of stainless steel cold spray and laser cladding deposits after turning and ball-burnishing. Surf Coat Technol. 2019;371:235–44.

    Article  Google Scholar 

  15. 15.

    Zhang P, Liu Z. Machinability investigations on turning of Cr–Ni-based stainless steel cladding formed by laser cladding process. Int J Adv Manuf Technol. 2016;82:1707–14.

    Article  Google Scholar 

  16. 16.

    Guddat J, M'saoubi R, Alm P, Meyer D, Hard turning of AISI 52100 using PCBN wiper geometry inserts and the resulting surface integrity. Proc Eng. 2011;19:118–24.

    Article  Google Scholar 

  17. 17.

    Grzesik W, Wanat T. Surface finish generated in hard turning of quenched alloy steel parts using conventional and wiper ceramic inserts. Int J Mach Tools Manuf. 2006;46:1988–95.

    Article  Google Scholar 

  18. 18.

    Davim JP, Figueira L. Comparative evaluation of conventional and wiper ceramic tools on cutting forces, surface roughness, and tool wear in hard turning AISI D2 steel. Proc Inst Mech Eng Part B. 2007;221:625–33.

    Article  Google Scholar 

  19. 19.

    Johnson KL, Johnson KL. Contact mechanics. Cambridge: Cambridge University Press; 1987.

    Google Scholar 

  20. 20.

    Hiegemann L, Weddeling C, Tekkaya AE. Analytical contact pressure model for predicting roughness of ball burnished surfaces. J Mater Process Technol. 2016;232:63–77.

    Article  Google Scholar 

  21. 21.

    Berg G, Grau P. Meyer's hardness law and its relation to other measures of ball hardness tests. Cryst Res Technol. 1997;32:149–54.

    Article  Google Scholar 

  22. 22.

    Borkar A, Kamble P, Seemikeri C. Surface integrity enhancement of Inconel 718 by using roller burnishing process. Int J Curr Eng Technol. 2014;4:2595–8.

    Google Scholar 

  23. 23.

    Gaitonde V, Karnik S, Figueira L, Davim JP. Machinability investigations in hard turning of AISI D2 cold work tool steel with conventional and wiper ceramic inserts. Int J Refract Metal Hard Mater. 2009;27:754–63.

    Article  Google Scholar 

  24. 24.

    Guo Y, Sahni J. A comparative study of hard turned and cylindrically ground white layers. Int J Mach Tools Manuf. 2004;44:135–45.

    Article  Google Scholar 

Download references

Funding

This work was supported by the National Natural Science Foundation of China [grant numbers 51425503, 51675289], Key Technology Research and Development Program of Shandong [grant number 2018GGX103023] and Open Research Fund of Shandong Provincial Key Laboratory of Mine Mechanical Engineering, Shandong University of Science and Technology [grant number 2019KLMM209].

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Correspondence to Peirong Zhang.

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Zhang, P., Du, J., Zhang, H. et al. Effect of turning-induced initial roughness level on surface roughness and residual stress improvements in subsequent burnishing. Archiv.Civ.Mech.Eng 20, 80 (2020). https://doi.org/10.1007/s43452-020-00083-5

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Keywords

  • Remanufacturing
  • Laser cladding
  • Burnishing
  • Surface roughness
  • Residual stress