1 Introduction

The electro-hydraulic servo systems are widely used in aviation, aerospace vehicles, ships, and rockets. The servo valve, which serves as the foundation of an electro-hydraulic servo system, is primarily utilized to accomplish precise control over displacement, speed, and torque [1, 2]. The core of a servo valve is a pair of spool valves made up of a spool and a valve sleeve [3]. The manufacture and assembly accuracy of the spool and valve sleeve, including shape accuracy, position accuracy, dimensional accuracy, and surface roughness, are the primary determinants of its performance.

However, due to the special structure of the valve sleeve, the edge of the intersecting bore in the valve sleeve is easy to produce burrs. The precision, lifespan, and stability of the valve sleeve are significantly influenced by these burrs [4] which are difficult to remove. In the existing deburring process, burrs with a small size can be removed using a metal brush, but it would also do harm to the surface quality of the valve sleeve bore. While removal of the burrs with a big size can only rely on manual operation. Generally, a deburring process is already arranged prior to the final finishing of the valve sleeve. Arranging another deburring process after the finishing is not only inefficient but also would increase the scrap rate. Therefore, it is necessary to inhibit the burr generation during the finishing process.

Usually, the burr is unavoidable and its shape, size, and forming process are various with the machining methods. For example, the possible burr types in face milling are knife-type, wave-type, curl-type, edge breakout, and secondary burr [5, 6]. While those in face grinding are: positive burr, negative burr, and residual burr [7]. Among them, burrs with positive burr characteristics are the easiest to remove, so relevant research is usually aimed at generating such burrs and reducing their size.

In the orthogonal cutting process, the formation of burrs is related to cutting conditions, work material microstructure, and mechanical behavior. Increasing the uncut chip thickness will promote the formation of a negative burr while decreasing the uncut chip thickness will cause burr accumulation under continuous cutting. In the cutting process, significant local strain is the main cause of crack initiation, expansion, and eventually, fracture [8].

For machining methods with micro-removal characteristics, the most effective and commonly used method to study the burr formation process and influencing factors is finite element simulation (FES) analysis combined with a single-grain scratch test [9]. For example, in the grinding process, the factors that have a significant impact on the morphology and size of burrs are wheel granularity [10], uncut chip thickness [7, 10,11,12], negative rake angle of the abrasive grain [7, 12], grinding temperature [13], grinding force [12, 13], and the workpiece's chamfer size [11]. In the process of micro-milling, the burr size is determined by the relationship between the uncut chip thickness and the radius of the cutting edge [14, 15]. Pre-introduction of stress can inhibit the generation of burrs [16]. As for the honing process, the factors that affect the burr size include the penetration depth of the abrasive grain [17], the rake angle of the abrasive, and the number of times that the abrasive grain passes through the edge of the workpiece [18].

In recent years, researchers have paid more attention to how ultrasonic vibration (UV) influences the machining process at different machining methods. For the cutting process, Xu and Zhang [19] studied the advantages of applying UV on cutting, which showed high machining capabilities, including low cutting forces, long tool life, high surface integrity, and excellent cutting accuracy; Liang et al. [20] studied the material removal mechanism of high-frequency UV-assisted cutting. The defect-free surface can be obtained by making the cutting stroke in each vibration cycle less than 800 nm. Dynamic recrystallization can release the stress concentration. For the micro-milling process, Zhang et al. [21] proposed that applying high-frequency UV in the milling feed direction could reduce cutting temperature and cutting force, improve chip-breaking ability, and reduce burr formation; Chen et al. [22] conducted that the frequency of UV had a significant influence on the machining mechanism, e.g., suppression of burr formation and reduction of cutting forces and tool wear; Xu et al. [23] found that the longitudinal-torsional UV could reduce the burr length and cutting force as well as release the concentrated stress. For micro-drilling, Zhu et al. [24] found that UV showed an effect of decreasing cutting force, inhibiting the burr formation, improving surface quality and the dimensional accuracy, and effectively hindering bit wear; Chang and Bone [25] developed an analytical burr height model for UV assisted drilling; Zai et al. [26] and Li et al. [27] studied the influence between the drilling parameters and burr size. The studies show that using a bigger amplitude, higher spindle speed, and lower feed speed can reduce the burr size. Much research indicates that the UV effect can reduce cutting force and burr size. Xiang et al. [28] studied the mechanism of the UV effect which was the intermittent cutting and high-frequency impact characteristics of ultrasonic vibration would reduce the fracture strength of the material, making it more prone to crack and fracture.

Among many of the finishing processes, honing is commonly used in finishing the valve sleeve, which can improve the surface quality and shape accuracy. Presently, there is already some research on ultrasonic-assisted honing (UAH). For example, Gao et al. [29] proposed that UAH could effectively decrease honing torque and improve honing efficiency. However, the burrs formation during UAH is a lack of research. This paper will focus on the burr’s generation mechanism and the main influence factors on burr size during UAH process. The main work of this paper is as follows.

  1. (i)

    The finite element simulation is used to study the law of burr evolution.

  2. (ii)

    Single-grain scratch tests under UV and non-UV conditions are carried out to explore the influencing factors of burrs, and analyze the effect of UV on burrs with FES.

  3. (iii)

    Honing tests under UV and non-UV conditions are carried out to verify the effect of UV on inhibiting the burr’s generation during honing.

2 Method and materials

2.1 Motion analysis of UAH

To make the test and simulation more in line with the actual UAH situation, it is necessary to analyze the relative motion between the abrasive grain on the honing stone and the workpiece.

The relative motion of honing is compound, including rotation and reciprocation along the tool axis. Inside the honing tool, the axial feed of the expanding cone is converted into the radial feed of the honing stone through a cone surface, providing the normal force between the honing stone and the workpiece. The abrasive grains are fixed on the surface of the honing stone, cutting the workpiece under relative motion and normal force, and forming cross-grained lines on the surface of the valve sleeve bore after honing, as shown in Fig. 1.

Fig. 1
figure 1

Working principle of UAH

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In the UAH process, due to the complex structure of the honing tool, the UV is usually applied on the workpiece along the axis direction of the honing tool. The relative motion trajectory between the honing stone and the workpiece can be described as

$$\left\{\begin{array}{l}x\left(t\right)=r\text{cos}\left(\omega t\right),\\ y\left(t\right)=r\text{sin}\left(\omega t\right),\\ z\left(t\right)=A\text{sin}\left(2\uppi ft\right)+{v}_{\text{a}}t,\end{array}\right.$$
(1)

where \(\omega \) is the angular velocity of the tool, \(r\) the radius of the honing tool, \(A\) the vibration amplitude, \(f\) the vibration frequency, \({v}_{\text{a}}\) the axial velocity, and \(t\) is the time.

In this study, the frequency of the UV is set as 18 000 Hz, and the amplitude is set as 4 μm. Figure 2 shows the diagram of local trajectory of the honing stone under UV and non-UV conditions.

Fig. 2
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Local trajectory of honing stone under UV and non-UV conditions

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The abrasive grains are in a continuous cutting state during the honing process, and the cutting depth of any single grain on the honing stone is less than 5 μm, which is much smaller than the curvature radius of the valve sleeve bore. Therefore, in the simulation and experiment study, the movement of a single grain can be simplified as a continuous curve with a fixed cutting depth.

2.2 Single-grain scratch test setup

The most commonly used material of the sleeve is 9Cr18MoV, which belongs to high-carbon and high-chromium martensitic stainless steel. It has high hardness, high wear resistance, and high corrosion after quenching. The test surface of the workpiece is 10 mm × 3 mm in size, pretreated on the WAZA415X-NC ultra-precision forming surface grinder, which has a minimum feed of 0.1 μm. The roughness of the test surface was 0.4 μm and the flatness was 1 μm after pretreatment. The grain material is CBN, which is commonly used in metal cutting. It has high hardness, good wear resistance, high thermal stability, and good chemical stability. The diameter of grain used in the single-grain scratch test was 325−380 μm.

The single-grain scratch test was conducted at the DMG Ultrasonic 20 Linear ultrasonic assisted machining center, as shown in Fig. 3. The workpiece was fixed on the Kistler 9129AA dynamometer, measuring the cutting force during the test process. The CBN grain was brazed on the self-made UV tool, moving with the spindle of the machining center.

Fig. 3
figure 3

Single grain scratch test platform

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The relative motion between the grain and the workpiece is shown in Fig. 4. The main cutting motion of the grain is along the x-axis. The cutting depth is altered along the y-axis. The UV motion is applied along the z-axis.

Fig. 4
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Relative motion between single-grain and workpiece

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To correct the installation error of the workpiece and achieve accurate tool feed, the test cutting plane is calibrated by the ruby probe to make it perpendicular to the y-axis before cutting. The feeding reference position is confirmed by moving the grain along the y-axis until the dynamometer detects the force signal. After the experiment, the morphology and size of burrs were measured by a 3D video microscope (KH-77003Dviewer) and a 3D laser confocal profilometer (S-Neox, SENSOFAR). The test parameters are listed in Table 1.

Table 1 Parameters of single-grain scratch test
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2.3 Finite element simulation model setup

The properties of CBN grain and 9Cr18MoV are listed in Table 2. The simulation parameters are the same as the test parameters. The cutting depth of single-grain is less than 5 μm during the honing process. To save computing resources, the cutting layer mesh is locally refined, and its mesh size is set to 0.1 μm. The hardness of the CBN grain is far higher than that of the 9Cr18MoV workpiece, so the grain is set to an analytically rigid body.

Table 2 Materials properties [30]
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The material constitutive relation for the workpiece was simulated by the Johnson and Cook constitutive model [31], which has the form of

$$\sigma =\left(A+B{\varepsilon }_{\text{p}}^{n}\right)\left(1+C\left(\text{ln}\frac{\dot{{\varepsilon }_{\text{p}}}}{\dot{{\varepsilon }_{0}}}\right)\right)\left(1-{\left(\frac{T-{T}_{\text{tran}}}{{T}_{\text{melt}}-{T}_{\text{tran}}}\right)}^{m}\right),$$
(2)

where B, C, m, n are material constants; \({\varepsilon }_{\text{p}}\) represents the equivalent plastic strain; \(\dot{{\varepsilon }_{\text{p}}}\) and \(\dot{{\varepsilon }_{0}}\) are the equivalent plastic strain rate and reference strain rate respectively; \({T}_{\text{melt}}\) and \({T}_{\text{tran}}\) are melting temperature and transition temperature, respectively. The parameters used in this study are listed in Table 3.

Table 3 Parameters of J-C plasticity model
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For the contact between the CBN grain and workpiece, separation was allowed in the normal direction, and sliding was allowed in the tangential direction, with coulomb frictional resistance. The frictional stress was calculated by

$$\tau =\left\{\begin{array}{c}\mu p \,\left(\text{if}\, \mu p \le {\tau }_{\text{lim}}\right), \\ {\tau }_{\text{lim}} \,\left(\text{if} \,\mu p >{\tau }_{\text{lim}}\right),\end{array}\right.$$
(3)

where \(p\) is the normal pressure; friction coefficient \(\mu \) is set to be 0.3; and \({\tau }_{\text{lim}}\) is the maximum frictional stress. When the stress becomes larger than \({\tau }_{\text{lim}}\), the tangential sliding would occur.

The shear damage criterion was applied in this FES model. The damage state variable \({\omega }_{\text{s}}\) was used to numerically describe the material failure process, which increased monotonically with the plastic strain of the elements. It can be calculated as

$${\omega }_{\text{s}}=\int_0^{\varepsilon_{\text{P}}}\frac{\text{d}{\varepsilon }_{\text{p}}}{{\varepsilon }_{\text{s},\text{pl}}\left({\theta }_{\text{s}},\dot{{\varepsilon }_{\text{p}}}\right)}\left(0\le {\omega }_{\text{s}}\le 1\right),$$
(4)

where \({\varepsilon }_{\text{s},\text{pl}}\left({\theta }_{\text{s}},\dot{{\varepsilon }_{\text{p}}}\right)\) is a variable determined by shear ratio \({\theta }_{\text{s}}\) and strain rate \(\dot{{\varepsilon }_{\text{p}}}\). When \({\omega }_{\text{s}}\) reaches 1, the corresponding elements start to fail due to the large plastic strain. In the post-processing, the material state is used to display the final state of each element, which is

$$\text{State } \, \text{value}=\left\{\begin{array}{l}1\, \left(\text{if}\, {\omega }_{\text{s}}<1\right),\\ 0\, \left(\text{if}\, {\omega }_{\text{s}}=1\right).\end{array}\right.$$
(5)

3 Results and analysis

3.1 Indicators of the burr size

Figure 5a shows the simulated burr under 2 m/min of the cutting speed and 3 μm of the cutting depth and non-UV. Figure 5b shows the test result under the same condition measured by the 3D laser confocal profilometer (S-Neox, SENSOFAR). It can be seen from the morphology that the shape of the burr is composed of a top and root. Two indicators are used to evaluate the burr size, which is burr height \(h\) and burr thickness \(b\) [7]. In simulation, \(h\) is 9.4 μm and \(b\) is 8.8 μm. In test \(h\) is 8.6 μm and \(b\) is 10 μm. The discrepancy between the test and simulation results for burr size is less than 15%, which shows good reliability of the simulation.

Fig. 5
figure 5

Burr morphology of simulation and test results

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3.2 Results of the single-grain scratch tests

3.2.1 Influence of various cutting depths on burr size

The test conditions are 2 m/min of cutting speed and 1−5 μm of cutting depth, under UV and non-UV. Figure 6 shows the burr morphology of the test results, and Fig. 7 shows the burr size correspondingly. In both cases, with the increase of the cutting depth, the burr size increased first and then decreased. Under non-UV, the burr size grows with the cutting depth. When the cutting depth is 1 μm, the burr thickness is 5.98 μm, and the burr height is 2.47 μm. When the cutting depth grows to 4 μm, the burr size reaches its maximum which is 13.45 μm in thickness and 8.9 μm in height. When the cutting depth reaches 5 μm, the breakage of the burr happens and the burr size reduces greatly. The burr size drops to 8.68 μm in thickness and 5.13 μm in height.

Fig. 6
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Test burr morphology at various cutting depths

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Fig. 7
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Test burr size at various cutting depths

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The trend of burr size under UV is similar to that under non-UV, which is growing initially and then reducing. However, there is a significant difference when the cutting depth is 3 μm. Under UV, the burr partially fractures, leading to an increase in the burr’s thickness from 13.27 μm to 15.8 μm and a decrease in its height from 7 μm to 6.4 μm. When the cutting depth is 4 μm, the burr is completely fractured, causing a significant reduction of the burr height. As the cutting depth increases to 5 μm, the breakage is further enlarged, and the burr size drops to 7.47 μm in thickness and 3.21 μm in height. Overall, under UV, the burr size is bigger before the breakage, and smaller after the breakage.

Figure 8 shows the scratch depths of the test results and Fig. 9 shows the cutting forces of the test results. Where \({F}_{\text{n}}\) is the normal force and \({F}_{\text{t}}\) is the tangential force. In both situations, the scratch depth and cutting force increase with the cutting depth, but the scratch depths are less than the predetermined cutting depth. Compared to under non-UV, under UV the scratch depth is deeper, and the cutting force is smaller.

Fig. 8
figure 8

Scratch depths at various cutting depths

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Fig. 9
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Cutting forces at various cutting depths

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3.2.2 Influence of various cutting speeds on burr size

The test conditions are 1−5 m/min of cutting speed and 2 μm of cutting depth, under UV and non-UV. Figure 10 shows the burr sizes at various cutting speeds. The different cutting speed under non-UV has little effect on the burr size, while under UV, the increment of the cutting speed reduces the burr size.

Fig. 10
figure 10

Burr sizes at various cutting speeds

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Figure 11 shows the scratch depths at various cutting speeds and Fig. 12 shows the cutting forces at various cutting speeds. In both situations, the scratch depth and the cutting force show a reduction when the cutting speed grows. The scratch depth under UV is deeper than under non-UV, meanwhile, the cutting force is smaller.

Fig. 11
figure 11

Scratch depths at various cutting speeds

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Fig. 12
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Cutting forces at various cutting speeds

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4 Mechanism analysis of UV inhibition of burr generation

4.1 Burr’s generation stages under non-UV

According to the simulation result, the formation of burrs under non-UV mainly goes through 4 stages. The first stage is the transition stage, as shown in Fig. 13a. As the abrasive grain approaches the edge of the workpiece, the rake face material accumulates, causing the stress to concentrate on the edge of the workpiece gradually. The stiffness of this area reduces as the material decreases. Under the action of the negative rake angle of the grain, the rake face material gradually produces a tendency of plastic deformation.

Fig. 13
figure 13

Generation process of burrs

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The second stage is the bending deformation stage, as shown in Fig. 13b. As the abrasive grain moves further forward, the degree of plastic deformation intensifies. The material at the edge of the workpiece bends around a rotation hinge point O. The actual cutting depth keeps decreasing as the material bends. The cutting action of abrasive grains keeps weakening. More rake face material bends into burrs and less forms chips.

The third stage is the burr development stage, as shown in Fig. 13c. The burr’s root is nearly formed when the major of the material finishes its bending deformation. Most of the rake face material is currently situated beneath the cutting layer, so there are almost no chips forming during this period. As the grain keeps moving forward, the rake face material bends and extends, gradually turning into the burr’s top.

The last stage is the final formation stage, as shown in Fig. 13d. When the grain completely cuts out of the workpiece, the burr is completely formed.

4.2 Analysis of the UV effect on burrs

According to the formation stages of burrs, the burr size mainly depends on the volume of the material on the rake face of the abrasive grain at the bending deformation stage. When the cutting depth grows, the rake face material volume increases and more material rotates around the hinge point, turning into burrs, as shown in Fig. 14. Thus, in both situations, the burr size first grows with the cutting depth.

Fig. 14
figure 14

Relationship between the rake face material volume and burr size

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When the cutting depth is 3 μm, the breakage of the burr is incomplete, making part of the burr extend outward and causing the burr height to increase. But the breakage of the root causes the burr thickness to decrease. When the cutting depth increases to 4 μm, the burr fractures under UV, but not under non-UV. Since the burr fractures at the rotating hinge point, the bending deformation stage of burr formation is crucial in determining whether it breaks. Figure 15 shows the stress diagram of the bending deformation stage at 4 μm of cutting depth. The hinge point under UV is higher than under non-UV, closer to the bottom of the grain which will thin the burr’s root during the development stage. Meanwhile, the higher the hinge point, the more complete the burr fracture, and the smaller the residual burr. Besides, an apparent stress dividing line (SDL) appears near the hinge point. Under the UV effect, the abrasive grain continuously impacts the rake face material and promotes the separation of the stress field. The uneven stress distribution is more susceptible to fatigue fracture in the subsequent bending deformation and reduces the burr size.

Fig. 15
figure 15

Stress diagram of the bending deformation stage at 4 μm of cutting depth

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In the actual honing process, due to the great amount of the abrasive grains contacting with the workpiece at the same time, the actual cutting depth and normal force of a single grain are usually small which would cause a significant rebound effect. When the grain moves away, the elastic deformation of the material will be released, causing the actual scratch depth to be less than the predetermined cutting depth. While under the effect of UV, the moving direction of the grain is constantly changing, as shown in Fig. 16. The motion trajectory of the grain can be divided into an upward trajectory and a downward trajectory. There are many cross areas between these two, and the rebound material in these areas will be cut again, improving the material removal rate. At the UV parameters used in the tests, for the single-grain scratch process, the cross-area accounts for 29.59% of the total scratch area. And in the honing process, the proportion of crossing trajectories is higher because of the overlap between multi-grain trajectories.

Fig. 16
figure 16

Schematic diagram of ultrasonic vibration weakening rebound effect

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Besides, the high-frequency vibration makes the cutting process of abrasive grain change from continuous cutting to high-frequency intermittent cutting, thus weakening the continuous extrusion effect of the abrasive on the material. The material will withstand multiple alternating loads under the impact of the abrasive, and the pores and cracks increase, reducing the fracture strength of the material [28]. As a result, UV can promote the separation of chips and reduce the cutting force [19].

So, the reason for scratch depth under UV being deeper than non-UV can be explained from two aspects. On the one hand, the normal force is much lower, which will weaken the rebound effect. On the other hand, part of the rebound material is removed. As mentioned before, the burr size is mainly dependent on the rake face material volume before the burr fractures, and the material volume is mainly dependent on the actual scratch depth. Since that, when the cutting depth does not exceed 3 μm, the burr size under UV is larger than that under non-UV. In that case, the cutting speed under UV may affect the size of the burr. Due to the fixed frequency and amplitude of UV, the faster the cutting speed, the less the number of vibrations at the edge of the workpiece, which will weaken the UV effect. Besides, the increment of the cutting speed will also lower the cutting force, which weakens the rebound effect. As a result, under the joint action of these two aspects, the scratch depth is decreased as well as the burr size.

5 Verification of the UV effect on burrs in UAH

5.1 UAH test platform set up

To verify the effect of UV on burrs in the honing process, a UAH platform was established to carry out experiments, as shown in Fig. 17. The platform was also built at the DMG ultrasonic 20 Linear ultrasonic assisted machining center. The workpiece is clamped by a UV device, which connects to an ultrasonic generator. The generator can provide a fixed frequency and amplitude of ultrasonic vibration. Dynamometer Kistler-9272 was used to collect the cutting force during the experiment.

Fig. 17
figure 17

UAH platform

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The workpiece material is 9Cr18MoV with the hardness of HRC58~64 after heat treatment. The bore of the workpiece was pre-processed to remove the burrs generated by the previous process. The honing tool used is a force-controlled single-stone structure, and the diameter of the abrasive grains fixed on the honing stone is between 165 μm and 198 μm. The parameters used in the honing test are listed in Table 4. When the tests are done, the workpieces are cut along the axis to measure the burr size and morphology by a 3D video microscope (KH-77003Dviewer) and a 3D laser confocal profilometer (S-Neox, SENSOFAR).

Table 4 Parameters of honing experiment
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5.2 Measurement and evaluation method of honing burr

The honing object is a bore, and the honing burrs are present throughout the circumference. The average burr size at four positions on the circumference is taken as the honing burr size. The measured positions are shown in Fig. 18.

Fig. 18
figure 18

Honing burr measurement method

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During the honing process, the final honing burrs are formed by all effective grains cutting the edge multiple times. Combined with the previous analysis, the growth of the burr is a process that accumulates with material removal. Therefore, to evaluate the honing burrs, the material removal volume needs to be considered. The aperture increment is used to represent the material removal, and it can be measured by a pneumatic aperture measuring instrument.

The growth rate of the burr \({b}_{\text{r}}\) is defined as the ratio of the cross-sectional area of the burr to the incremental radius \(\Delta r\) of the bore. As the cross-sectional shape of the burr is usually triangular, the growth rate of the burr can be calculated as follows

$${b}_{\text{r}}=\frac{bh}{2\Delta r}.$$
(6)

5.3 Analysis of the UV effect on burrs in UAH process

The burr sizes and radius increment of honing test results at various honing pressure are shown in Table 5. And the growth rate of the burr is shown in Fig. 19. It can be seen from the results that, in all cases, the radius increment under UV is bigger than under non-UV, and the growth rate of the burr under UV is smaller than under non-UV. The results prove that UV not only improves the material removal rate greatly but also inhibits the growth of the burr.

Table 5 Measurement results of honing tests
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Fig. 19
figure 19

Growth rate of burr at various honing pressure

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6 Conclusions

In this paper, based on the honing condition, the experimental scheme of cutting 9Cr18MoV with a single CBN abrasive grain is designed. How burr’s morphology and size change with the cutting parameters under UV and non-UV is studied. Besides, the corresponding simulation model is established. By analyzing the simulation results, the formation mechanism of burrs, the influence mechanism of cutting depth and cutting speed on burr size, and the suppression mechanism of ultrasonic vibration on burr growth are clarified. The conclusions are as follows.

  1. (i)

    The burr formation process can be divided into the following four stages: the transition stage, the bending deformation stage, the development stage, and the final formation stage. The plastic bending deformation of the rake face material when the grain approaches the edge of the workpiece is the main reason for burr formation. And the burr size is mainly depended on the rake face material volume during the bending deformation stage.

  2. (ii)

    When the cutting depth is smaller than 5 μm, the rebound effect is significant, making the actual scratch depth smaller than the predetermined cutting depth. The rebound effect is weakened under UV by reducing the cutting force and re-cutting the rebound material. The re-cutting area accounts for 29.59% of the total scratch area. The increment of cutting speed will reduce the proportion of the re-cutting area. The normal cutting force under UV is 31.4% lower than that under non-UV. And the actual scratch depth under UV is 87.5% deeper than that under non-UV. And that makes the burr size under UV bigger than that under non-UV before the burr fractures, which is 1.97 μm larger for burr height, and 3.51 μm larger for burr thickness on average.

  3. (iii)

    The hinge point under UV is closer to the grain’s bottom than non-UV, which makes the material easier to break when bending around the hinge point. In addition, the abrasive grains have impact characteristics, which can promote the tendency of dividing the stress field at the root of the burr. The uneven stress distribution will increase the possibility of material fracture, which will reduce the fracture strength of the material, so that in the subsequent bending deformation, the burr is more likely to fatigue fracture along the direction of the stress field interface, and ultimately greatly reduce the size of the burr. Under UV, the burr size after fracturing is 44.95% reduced in height and 18.53% reduced in thickness.

  4. (iv)

    In general, the growth rate of burr under UV is 21.7% lower than that under non-UV. When the honing pressure grows from 0.1 MPa to 0.3 MPa, the growth rate of burr reduces by 39.19%. When the honing pressure keeps growing from 0.3 MPa to 0.5 MPa, the growth rate of burr increases by 39.97%. So, using a honing pressure of 0.3 MPa and applying UV can significantly inhibit the burr’s growth.