Experimental investigation into the effect of abrasive ... - Springer Link

Int J Adv Manuf Technol (2017) 90:1881–1888 DOI 10.1007/s00170-016-9491-6

ORIGINAL ARTICLE

Experimental investigation into the effect of abrasive and force conditions in magnetic field-assisted finishing Jiang Guo 1 & ZhiEn Eddie Tan 1 & Ka Hing Au 1 & Kui Liu 1

Received: 2 June 2016 / Accepted: 16 September 2016 / Published online: 4 October 2016 # Springer-Verlag London 2016

Abstract This paper presents an experimental study on the key process parameters in magnetic field-assisted finishing (MFAF), aiming to investigate the relations between the magnetic abrasives, polishing force, material removal rate (MRR) and surface roughness. The experiments were conducted using a dual magnetic roller tool combining with a 6-axis robot arm. The effect of abrasive type and size on polishing force and MRR, wear of magnetic abrasives, surface roughness and surface morphologies obtained using different types of magnetic abrasives were evaluated quantitatively. The results show that the type of SiC-based magnetic abrasives had a higher MRR but lower polishing force than that of Al2O3-based magnetic abrasives. Due to the inability of carbonyl iron powder (CIP) carrier to hold large SiC or Al2O3 particles during the rotation motion of the magnetic roller tools, large particle

Highlights 1. A dual magnetic roller tool combining with a 6-axis robot arm was used to conduct the experiments. 2. The type of SiC-based magnetic abrasives had a higher material removal rate (MRR) but lower polishing force than that of Al2O3-based magnetic abrasives. 3. Due to the inability of carbonyl iron powder (CIP) carrier to hold large SiC or Al2O3 particles during the rotation motion of the magnetic roller tools, large particle size abrasives have a lower MRR as well as polishing force than small particle size abrasives. 4. The wear of magnetic abrasives was investigated through scanning electron microscope (SEM) observation and energy dispersive X-ray (EDX) analysis of abrasive particles before and after polishing. 5. The surface morphologies generated by the four different experimental conditions of magnetic abrasives were different although the surface roughness achieved a similar value. * Jiang Guo [email protected]

1

Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, Singapore 637662, Singapore

size abrasives have a lower MRR as well as polishing force than small particle size abrasives. The wear of magnetic abrasives was demonstrated through scanning electron microscope (SEM) observation and energy dispersive X-ray (EDX) analysis of abrasive particles before and after polishing. The surface morphologies generated by the four different experimental conditions of magnetic abrasives were different although the surface roughness achieved a similar value. Keywords Polishing . Magnetic abrasive . Magnetic field . Material removal rate . Surface roughness . Surface morphology

1 Introduction Inconel alloys possess various properties such as hightemperature strength and high resistance of corrosion, oxidation and chemical degradation which make them ideal for aerospace applications. However, due to the extreme toughness and work hardening characteristic, there is a significant difficulty in machining Inconel alloys, especially for those having complex structures [1–3]. A solution to circumvent this difficulty is the utilisation of metal additive manufacturing (AM) for Inconel components. Metal AM has recently begun picking up speed and emerges as an essential commercial manufacturing technology. Metal AM techniques enable a myriad of geometric features considered challenging prior to its inception. Some features include complex part geometries, porous cores, shell structures as well as internal part functionalities. Moreover, since metal AM parts are manufactured in one step, it negates complexities in assembly processes [4, 5]. Despite its momentum, metal AM faces a series of hurdles that bar its broader application in manufacturing. Although this process eliminates the need for complex assembly of parts

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and enables freeform fabrication, achieving a favourable surface condition from a metal AM part is challenging [6, 7]. This is due to a combination of a few issues. Firstly, AM processes like electron beam machining, produces surface defects and a high surface roughness that contribute to the material’s fatigue properties and thusly requires a significant amount of material removal from the surface in order to achieve a desired surface condition [8, 9]. Furthermore, the freeform capability of AM introduces complexities in part geometries designs that restrict the utilisation of conventional surface post-processing methods like parallel grinding for metals [10, 11]. This is especially the case when it comes to AM-built internal part structures that require a defined surface finish condition but have considerable difficulty for conventional tools to access due to internal design structure’s propensity to be enclosed. The current landscape of advanced processing manufacturing technologies demands a standard of quality in work components to meet the demand of complex industry applications. Many engineering components’ and their respective performance capabilities are very much dependent on material removal and surface finish. The utilisation of magnetic fieldassisted finishing (MFAF) allows for challenging geometry to be accessed for workpiece. Compared with other polishing technologies such as bonnet polishing [12], vibration-assisted polishing [13, 14] and fluid jet polishing [15], MFAF enables Fig. 1 a Schematic illustration of the MFAF configuration, b material removal mechanism model of the MFAF process

Int J Adv Manuf Technol (2017) 90:1881–1888

better geometry conformant capability for freeform surface, internal surface and even microstructured surface. Jayswal et al. did some theoretical investigations on modelling and simulation of magnetic abrasive finishing process [16]. Suzuki et al. realized the polishing of a curved surface using a magnetic fluid [17]. Yin et al. achieved 3D micro-curved surface finishing using vibration-assisted magnetic abrasive polishing [18]. Guo et al. proposed a new vibration-assisted magnetic abrasive polishing method to finish microstructured surface [19]. Yamaguchi et al. presented a new MFAF technique for finishing internal surfaces of alumina ceramic components [20]. It also exhibits good flexibility in controlling process parameters such as magnetic abrasive composition and polishing force, to reach target user requirements in work tolerances and surface conditions. Therefore, the adaptation of MFAF to Inconel alloys holds the potential to overcome postprocessing restrictions for metal AM. In order to optimize the process parameters so as to achieve the required surface conditions in a high efficiency, in this paper, the relations between key process parameters magnetic abrasives, polishing force, material removal rate (MRR) and surface roughness were investigated. The necessary scope which includes experimental setup, effect of abrasive type and size on polishing force and MRR, wear of magnetic abrasives,


z

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y x

Fig. 2 Experimental setup of the MFAF process

target positions around the rollers, enabling a reforming mechanism of the magnetic abrasives at each revolution [21]. The magnetic abrasives accumulated between the two rollers were used as the polishing tool to remove material from workpiece surface. As shown in Fig. 1b, magnetic abrasives are essentially composed of abrasive particles, ferromagnetic particles and a fluid that serves a lubricating and binding function for the abrasive and ferromagnetic particles. The abrasive particles, in this process, is the main contributor of work done within the magnetic abrasive composition. However, since it is non-magnetic, ferromagnetic particles are required in the composition to serve as a carrier for the abrasive particles to perform the

surface roughness and surface morphologies obtained using different types of magnetic abrasives will be detailed in the following sections.

2 Experimental A schematic illustration of the MFAF configuration is shown in Fig. 1a. In general, MFAF utilises magnetic field to control and manipulate magnetic abrasives to conduct its finishing work. In this paper, a dual magnetic roller design was adopted to generate the magnetic field. It was designed in a manner that exhibits differential magnetic flux densities at various

(a) µm

Length = 25.1 mm Pt = 62.4 µm Scale = 58.0 µm

20 15 10 5 0

h

-5 -10 -15 -20 -25 -30 -35 0

5

10

15

20

(b) Fig. 3 a Material removal measurement by stylus profilometer and b cross-sectional profile of the polished area

25 mm

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finishing work. When a magnetic field is applied to the magnetic abrasives, the particles adhere to the magnetic field lines and form a series of chain-like structures, transitioning the magnetic abrasives into a hardened and semi-solid state. The dual roller magnets not only provide the magnetic field necessary to assist the transition of the media states, but also provides a rotary relative motion to control and move the magnetic media. With the combined effect of the hardened magnetic media state and the relative motion provided by the dual roller magnets, the magnetic abrasives are able to perform the finishing process on the entire surface of workpiece. The experimental setup is shown in Fig. 2. It mainly consists of a dual magnet roller tool, a 6-axis robot arm (VM-6083M, DENSO WAVE INCORPORATED), a force dynamometer (Type 9119AA2, Kistler Instruments Pte Ltd), as well as a workpiece mounting fixture. The magnetic roller tool was attached to two rotary motors that provide a controlled variable speed motion up to 1800 rpm. During polishing process, the workpiece and the force dynamometer are secured onto a mounting fixture at the robot arm’s end effector. The use of the robot arm enables the use of a programmable work path to reach non-planar workpiece profiles. The force dynamometer takes force measurements in 3-axis (X, Y and Z) directions to observe the effect of the experimental variables on polishing force. Figure 3a and b shows the measurement of material removal by stylus profilometer and a typical measured result of a cross sectional profile of the polished area, respectively. The detailed conditions used in the experiments are listed in Table 1. The workpieces were cut into dimension of 30 mm × 30 mm × 15 mm by wire EDM, followed by surface preparation for target initial conditions via sandblasting with an initial surface roughness Ra over 2.0 μm. The rotation speed of the dual magnetic roller tool was set to 400 rpm while the robot arm fed in 288 mm/min (40 % of the maximum speed) with a travel range of 60 mm. The gap between the roller and the workpiece was set to 2 mm. Two kinds of magnetic abrasives were adopted for the experiments. SiC and Al2O3 have the same weight percentage in the magnetic abrasives so there is a slight difference in volume. For the type of SiC-based magnetic abrasives, the volume composition was Table 1

Fig. 4 Effects of abrasive size and type on a polishing force and b MRR

taken at 30.9 % carbonyl iron powder (CIP) CM grade, 6.8 % SiC powder, 54.2 % lubricating fluid and 8.1 % machining oil. For the type of Al2O3-based magnetic abrasives, the volume composition was taken at 30.5 % CIP CM grade, 8.3 % Al2O3 powder, 53.2 % lubricating fluid and 8.0 % machining oil. During experiments, lubricating fluid was replenished in the magnetic abrasives every 5 min. Different from other types of magnetic abrasives such as magnetorheological fluid (MRF) and magnetic compound fluid (MCF) slurry [22, 23], the magnetic abrasive composition used for this experiment was defined based on its binding requirements at the magnet roller’s speed and the pressurised proximity that the magnetic abrasives undergoes at the workpiece-to-roller area. Due to this requirement, a media composition of lower viscosity as well as a lower abrasive-to-CIP ratio is required to maintain a good binding during the MFAF process. Furthermore, to control the amount heat produced, Ecocool, a type of lubricating fluid, is used in place of conventionally used water in the media composition. This is necessary for higher tool speed experiment conditions that more heat is generated.

3 Results and discussions The results of effects of abrasive size and type on polishing force and MRR are shown in Fig. 4a and b, respectively. The force data used in this analysis was taken normal to the workpiece finishing surface. The material removal was measured every 10 min using a contact type, stylus profilometer (Form Talysurf PGI 2540, Taylor Hobson, UK). It is found that the

Experimental conditions

Equipment

Dual magnetic roller tool & 6-axis robot arm

Workpiece material Initial roughness Ra Tool rotation speed Robot arm feed speed Gap Abrasive type Abrasive size

Inconel 718 >2.0 μm 400 rpm 288 mm/min 1.5 mm Al2O3, SiC 5 μm, 30 μm Fig. 5 Change of MRR as a function of process time


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Fig. 6 SEM observation and EDX analysis of SiC (5 μm)-based magnetic abrasives. a SEM view of initial magnetic abrasives, b spectrum 1: EDX analysis of SiC particle, c spectrum 2: EDX analysis of CIP particle

polishing force was lower using SiC-based magnetic abrasives, but the MRR (averaged value in 40 min) was higher than that using Al2O3-based magnetic abrasives. Besides, large particle size abrasives had a lower MRR than small particle size abrasives. This is attributed to the inability of CIP carrier to hold large SiC or Al2O3 particles during the rotation motion of the magnetic roller tools. As a result of particle scattering and being dropped out from the abrasives which can be clearly observed during experiments, the volume of the SiC and Al2O3 particles lessened and was thusly represented in the MRR. Also, a large polishing force was observed in small particle size abrasives than that in large particle size abrasives. This is consistent with that a higher MRR was observed in small particle size abrasives than in large particle size one. Figure 5 shows the change of MRR as a function of process time. The results indicate that a decreasing trend in MRR was observed for each magnetic media type. The MRR begins to saturate at 30 min. This is due to the lifetime of the magnetic abrasives which is mainly caused by the scattering of SiC or Al2O3 particles and abrasive wear.

To further understand the wear mechanism, scanning electron microscope (SEM) observation and energy dispersive Xray (EDX) analysis were conducted on the SiC (5 μm)-based magnetic abrasives, which exhibited the highest MRR, using JSM-IT300LV SEM from JEOL coupled with EDS detector from Oxford Instruments. As shown in Fig. 6a and Fig. 7a, the SEM image was taken at the magnetic abrasives’ initial state and after 40 min of MFAF process, respectively. The EDX analysis conducted on the initial state of magnetic abrasives (see Fig. 6b, c) shows distinct indications of SiC particles and CIP particles. On the other hand, the EDX analysis of magnetic abrasives after 40 min of MFAF process, as shown in Fig. 7b and c, shows traces of iron at a target SiC particle, and traces of silicon at a target CIP particle. This shows that there is a degree of wear on the magnetic abrasives’ particles during the MFAF process, and it is exhibited in the magnetic abrasives’ MRR saturation trend. The effect of abrasive size and type on surface roughness was evaluated. As shown in Fig. 8, the surface roughness dropped dramatically in the first 10 min, and it was reduced faster using

Fig. 7 SEM observation and EDX analysis of SiC (5 μm)-based magnetic abrasives after 40 min of MFAF process. a SEM view of magnetic abrasives after 40 min of MFAF, b spectrum 3: EDX analysis of SiC particle, c spectrum 4: EDX analysis of CIP particle

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Fig. 8 Change of surface roughness as a function of process time

SiC (30 μm)-based magnetic abrasives than the other three types of abrasives due to the low polishing force condition. Then, it gradually saturated and reached about Ra 0.5 μm after 40 min polishing. Although the surface roughness using all four kinds of magnetic abrasives achieved the same Ra value, Fig. 9 Surface roughness profiles before polishing a initial status, and after 40 min polishing by b Al2O3 (5 μm)-based magnetic abrasives, c SiC (5 μm)-based magnetic abrasives, d Al2O3 (30 μm)-based magnetic abrasives and e SiC (30 μm)based magnetic abrasives


surface roughness profiles are different using different magnetic abrasives. Figure 9a–e shows the profiles of initial surface roughness and that after polishing by using four experimental conditions of magnetic abrasives, respectively. It is found that the workpiece polished by SiC (5 μm)-based magnetic abrasives was observed to have deeper and longer scratches on its surface than that polished by Al2O3 (5 μm)based magnetic abrasives. Deeper and longer scratches is determined by the type of abrasives although the polishing force for SiC (5 μm) is smaller than that for Al2O3 (5 μm). Both of the workpieces polished by SiC (30 μm)-based magnetic abrasives and Al2O3 (30 μm)-based magnetic abrasives have significant remnant surface blemish compared to those polished by 5-μm particle size abrasives. Beside, smaller pores were observed. The surface morphologies after polishing by using a microscope (Keyence VHX-2000, KEYENCE CORPORATION) as shown in Fig. 10a–e also correspond to the effect of abrasive size and type on surface roughness.


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Fig. 10 Surface morphologies before polishing a initial status, and after 40 min polishing by b Al2O3 (5 μm)-based magnetic abrasives, c SiC (5 μm)-based magnetic abrasives, d Al2O3 (30 μm)-based magnetic abrasives and e SiC (30 μm)based magnetic abrasives

4 Conclusions In this paper, inter-relations between the process parameters in MFAF process were investigated using the setup mainly composed by a dual magnetic roller tool and a 6-axis robot arm. It shows that MFAF is a suitable process to polish Inconel 718 to achieve surface roughness less than 1 μm Ra in 40 min. Based on the results obtained from this research, some conclusions can be drawn as follows: 1. The surface roughness and surface morphologies are mainly affected by the type and size of abrasives, and they are not affected by volume difference of SiC and Al2O3 in the magnetic abrasives. 2. The type of SiC-based magnetic abrasives has a good polishing performance represented by high MRR and low polishing force compared with that of Al2O3-based magnetic abrasives. 3. Due to the inability of CIP carrier to hold large SiC or Al2O3 particles during the rotation motion of the

magnetic roller tools, large SiC or Al2O3 particles were not well bound and dropped out from the abrasives, resulting in a lower MRR as well as polishing force than small particles. 4. Results of SEM observation and EDX analysis of magnetic abrasives demonstrate the wear of magnetic abrasives’ particles during the MFAF process and explain the reason for the saturation of the material removal. 5. The surface roughness dropped dramatically in the first 10 min before it gradually saturated and reached about Ra 0.5 μm after 40 min polishing. Although the surface roughness Ra value achieved by using the four different experimental conditions of magnetic abrasives was similar, the surface morphologies were different due to different functions of abrasive particles which results in different surface roughness Rz values. Acknowledgments We would like to express our thanks to Dr. Sato Takashi (ARTC) for the design of experimental setup and Mr. Wan Yin Chi (Machining Technology Group, SIMTech) for his help on SEM-EDX

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analysis. The acknowledgement is extended to Dr. Wang Xincai (Machining Technology Group, SIMTech) for his kind support.

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