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附錄
附錄1
英文原文
Journal of Materials Processing Technology 187–188 (2007) 19–25
Micro deburring for precision parts using magnetic
abrasive finishing method S.L. Ko a,., Yu M. Baron b, J.I. Park a
a Center for Advanced E-System Integration, Konkuk University, 1 Hwayang-dong,
Kwangjin-gu, Seoul 143-701, Republic of Korea
b Saint-Petersburg State Polytechnic University, St.-Petersburg, Russia
Abstract
Using the developed electromagnetic inductor for deburring micro burr, more detail characteristics of the performance are analyzed. Experiments were carried out to verify the influence of each conditions: volume of powder, height of gap, rotational frequency of the inductor and feed velocity. Proper deburring conditions are suggested to satisfy the productivity and the accuracy. In addition to deburring efficiency, the influence to surface roughness is analyzed. To improve the surface roughness and impurity, a method of coolant supply and component of abrasive powder are investigated. It is proved that the continuous flow of coolant and the Fe powder without abrasive is effective for deburring and surface quality.
. 2006 Elsevier B.V. All rights reserved.
Keywords: Magnetic abrasive finishing (MAF); Micro burrs; Electromagnetic inductor; Deburring
1. Introduction
The quality of precision parts can be evaluated by the surface and edge quality. The geometry of edge is determined by deburring process for removing burr and rounding process, which is
necessary for its function. The surface quality is determined by surface roughness and the stress state of the surface. As one of the finishing methods, magnetic abrasive finishing method
(MAF) has been used for a long time [1–3]. MAF is based on the magnetization property of ferromagnetic iron and the machining property of abrasives, which is made of Al2O3 and SiC. Along the magnetic flow, which is formed by the magnetic inductor, the magnetic powders will be arranged like brushes and the strength and stiffness of the magnetic brushes can be controlled by the electric current supplied. As a first application of MAF technology for deburring, the burr formed on plane after drilling was tried to be removed. An inductor for removing the burr formed in drilling was produced and analyzed for effective deburring [4]. The precise part used as samples in this work contains 5–10 m averaged burr height . Corresponding author.
E-mail addresses: slko@konkuk.ac.kr (S.L. Ko),
baron@burr.hop.stu.neva.ru (Y.M. Baron), jungil78@hanmail.net (J.I. Park).
and 0.30–0.40 m surface roughness on surface after piercing operation. In the previous work, electromagnetic inductor for deburring this part was designed and manufactured. Some conditions were applied to evaluate the performance of the inductor [5]. The proper powders are selected based on the previous work using the evaluation method to characterize performance
of powder [6]. The characteristic equation can be obtained from simply developed experiment method, which enables to predict the productivity and powder tool life [6]. In this paper, proper
finishing conditions are to be recommended for precision deburring. Volume of powder, rotational frequency of inductor, height of gap and the feed velocity of table are the main factors to be determined from the more detail experiment based on the result from the experiment in previous work. As a result, the optimized conditions are suggested to improve productivity. The vibration table is applied to improve the performance, which was verified in previous work also as in Fig. 1. The efficiency for deburring and the surface roughness can be improved using this vibration table [5].
In the case of micro deburring for precision parts, improvement of surface roughness during deburring becomes one of the most important task. Most influencing factors for surface roughness are component of powder and the coolant supply method. Fe-powder without abrasive is proved to be efficient by protecting adhesion on the surface which results in 0924-0136/$ – see front matter . 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2006.11.183
S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 Fig. 1. Overall view of inductor EMI-2 (a) and the scheme of its application (b). improved surface roughness. And continuous supply of coolant improves the surface roughness. The influence of flow rate is also investigated.
2. Experiment equipment
The electromagnetic inductor EMI-2 was designed and manufactured specially for burrs removal on surfaces of small parts made from ferromagnetic or non-magnetic materials. The view of the inductor and the scheme of the experiments are shown in Fig. 1. Three kinds of movements are involved in this case: inductor rotation; feed of the sample (workpiece); oscillation of the top plate with a sample in the direction normal to the feed direction. The sample moves inside the working gap filled by magnetic abrasive powder. The powder flows over the sample and performs finishing and deburring for both sides at the same time. The smaller working gap height is, the larger magnetic intensity B and cutting forces are (Fig. 2). These data were obtained from the working gap without powder. Magnetic intensity increases to 10% when the gap is filled by magnetic abrasive Fig. 2. Magnetizing curves for magnetic inductor EMI-2 at the different height δof the working gap. powder. The positive peculiarities of magnetic inductor EMI-2 are the homogeneity of the process of the surface process through the working gap and the continuous contact between a workpiece and magnetic abrasive powder during process. Mag-Fig. 3. The sample from alloy Fe (60%) + Ni (40%) (a) and geometry of micro burrs and edges cross-section (b and c).
S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 netization curves for EMI-2 with different working gaps are shown in Fig. 2. The vibrating table was used to activate abrasive cutting and to improve the quality of worked surfaces. It is claimed that the extra oscillation movement at MAF guarantees self-sharpening of the powder and higher productivity and better quality of a worked surface as a result [2]. The used vibrating table creates longitudinal or transverse oscillation of its top plate to the feed movement direction. The top plate is exchangeable and can be made from ferromagnetic or non-magnetic material.
3. Characterization of inductor EMI-2
The main differences of the electromagnetic inductor EMI-2 to EMI-1, which was developed for the burr on plane [4] are following: a sample is continuously at contact with magnetic abrasive powder during process; both sides of the sample are Fig. 4. Influence of MAF parameters to process productivity using the inductor EMI-2: volume of the powder (a), height of the work gap (b), inductor rotation frequency (c) and feed (d). Fig. 5. Influence of coolant to MAF productivity and the work surface rough-ness: at different methods of cooling (a and c) and at different discharge of coolant flow (b). S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 processed at the same time. But this inductor can be used only for small parts, which can be placed inside gap. 3.1. Determination of deburring conditions Parts of electric guns from Fe–Ni alloy were used as samples to determine MAF conditions for removal of micro burrs by inductor EMI-2 (Fig. 3a). There are three holes with diameter 0.1 mm made by piercing. It is necessary to remove micro burrs to improve edge quality of holes and surface quality. The geometry of initial burrs and edge cross-section are shown in Fig. 3b and c. The experiments were carried out using the scheme shown in Fig. 1b. Workpieces were fastened to aluminum top plate. The specific removed allowance is defined as the removed volume per
unit area, which is used for comparison of deburring conditions [6]. MAF conditions are: working gap height 4 mm; magnetic intensity in the gap 0.48 T; coil current I = 1–1.5 A; inductor rotation frequency n = 95–280 min.1; feed f = 127 mm/min; oscillation frequency of vibration table nosc = 500 min.1; amplitude of oscillation Aosc = 2.5 mm; MAF duration corresponds to number of the table strokes in feed N = 1, 2, 4, 8 (it corresponds to 0.5, 0.9, 1.9, 3.8 min); magnetic abrasive powder Fe(CH2); volume of the powder portion Vp = 11–27 cm3. Influence of parameters Vp, n, f, nosc, were investigated. Fig. 6. View of a hole edge after punching: (a) 200×and (b) 1000×.
3.1.1. Amount of the powder for process
The powder is packed inside the working gap by magnetic forces, and the amount of powder is important for productivity and cost of MAF operation. The volume of the working gap (the gap height δ = 4 mm) at inductor EMI-2 equals to Vg =19cm3. This volume was calculated as 100% of the powder for one-time process Vp. Other conditions are: n = 95 rpm; f = 127 mm/min; I =1.0A (B = 0.45 T); N = 2; coolant (cutting Fig. 7. Rounding of edges by MAF (100×). S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 oil) flow rate 0.96 l/mm. The experimental result is shown in Fig. 4a. Increase of the amount of powder is accompanied by larger magnetic forces and leads to increase of the productivity but not very much, because there is free space where the extra powder may be located in the gap near the poles.
3.1.2. Height of the work gap δ
The design of inductor EMI-2 allows to change the height of the work gap from 2 up to 10 mm according to the height of a workpiece. Influence of the wok gap was examined over
the range δ = 4–10 mm at Vp = 130% Vg. Other conditions were the same as at previous experiment. Increase of the work gap induces the decrease of productivity by the decrease of magnetic intensity inside the gap. The coil current was constant during this experiment. It can be observed from Fig. 4b that magnetic intensity becomes smaller as work gap δ increases.
3.1.3. Inductor rotational frequency and feed
When the volume of powder equals to 100% Vδ and the height of the gap δ = 4 mm at this experiment, the influence of the rotation frequency of inductor is shown in Fig. 4c. The duration of the contacts of powder grains with the work surface increases proportionally to the rotation frequency n, which increases the productivity either. But rate of the increase of productivity becomes slow at the frequency larger than 180 rpm as shown in Fig. 4c. This might be caused by the increase of centrifugal forces as the rotational speed increases, by which most part of the grains is thrown out of the gap. The experiment of feed optimization was carried out at following conditions: n = 95 rpm; f = 127–507 mm/min; nosc = 500 min.1; Aosc = 2.5 mm; δ = 4 mm; B = 0.48 T; MAF duration—two work strokes (4–15 s of processing correspondingly to the feed value); with coolant. The result is shown in Fig. 4d. The influence of the feed over range of 127–342 mm/min is not very large. But best surface roughness was obtained at f = 342 mm/min. 3.1.4. Role of a coolant
The use of chemical active and surface-active coolants is very important for MAF process [2]. Induced currents are generated inside a workpiece material and especially inside of its blanket during MAF. The electric charged surface of the workpiece activates chemical processes and an action of surface-active matters. This fact was verified at the research of deburring by MAF [6]. The research on the role of coolant was continued at these experiments. The experiment was carried out with n = 95 rpm; Vp = 100% Vg; δ = 4 mm. Others conditions were same as the previous ones. The specific removed allowance increases when the coolant is periodically injected inside the work gap, and it increases more when the coolant is used like the constant flow as shown in Fig. 5a. The flow of the coolant guarantees the supply of the coolant to all sections of the work surface inside the work gap and increases the productivity. Increase of the coolant flow rate increases the productivity. But too big discharge of the coolant reduces the productivity, since the strong stream of the coolant washes out the powder from the work gap (Fig. 5b). The presence of the surface-active coolant is very important for good surface roughness. The dependences of the surface roughness Ra to the coolant supply method during MAF process are shown in Fig. 5c. MAF process without coolant and with cooling by periodical injections worsen the roughness. The case without coolant, which is shown as . in Fig. 5c generates worst surface roughness. It may be explained by phenomena of an adhesion of the powder component on the work surface due to the heat generated during MAF. The process without coolant reveals more severe deterioration of surface than the periodic supply of coolant (. in Fig. 5c). The adhesion is activated with the electrically charged work surface. Cooling by periodically injection of the coolant decreases adhesion but does not avert it fully. Cooling by the continuous coolant flow (. in Fig. 5c) prevents the adhesion and improves the roughness. So the proper conditions for removal of micro burrs at parts obtained from the experiment can be summarized as: EMI2 inductor rotation frequency n = 180 rpm; f = 342 mm/min; nosc = 500 min.1; Aosc = 2.5 mm; δ = 4 mm; Vp = 1.3Vg; method of cooling—the continuous flow of coolant with the discharge rate 1 l/min. The iron powder without abrasive particles was used here as magnetic abrasive powder. The test of MAF deburring using the determined conditions showed that burrs with initial height 1.5–2.5 m are removed for 15 s.
4. Analysis of edges and surface quality
after MAF The samples shown in Fig. 3 were used. The edges after piercing had several kinds of defects: burrs, scratches and rough surface roughness (Fig. 6). Magnetic abrasive finishing deletes all these defects. And it takes longer to remove all the defects than to remove burrs. For example burrs were completely removed after one stroke of feed and the rounding of edges was Fig. 8. Edge quality before (a) and after MAF (b) (1000×). S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 Fig. 9. The top worked surface after MAF using (8500×) mixture powder CH2 +Al2O3 (a) and CH2 (b). performed after two and more strokes. The rounding of edge of 4.1. Worked surface quality hole after one, two, and four strokes is shown in Fig. 7a–c. One can see, that it is possible to control the radius of the edge: the The top surface is polished during deburring or rounding on longer MAF duration is, larger the radius is. The quality of the edge of holes by MAF. Influence of MAF conditions to surface edge before and after MAF is shown in Fig. 8. The iron powder roughness was described above. MAF process has the characterCH2 was used for deburring and edge rounding in this case. istic that work surface becomes to be electrically charged at the Fig. 10. Views at 1500× and the EDS diagrams of the attached particle after MAF using mixture powder (a), the same after MAF using iron powder (b) and grain of iron powder (c). S.L. Ko et al. / Journal of Materials Processing Technology 187–188 (2007) 19–25 25 Table 1 Chemical composition of the worked surface, powder grain and the attached particles Chemical element Amount of an element (%) Work surface Work surface after Work surface after A grain of the An attached particle An attached particle before MAF MAF with powder MAF with powder CH2 after MAF with after MAF with
CH2 mixture powder mixture powder powder CH2 C 2.47 0 1.46 23.11 5.84 Si 0.40 0.30 0.71 1.99 Mn 0.51 0.44 0.64 1.09 0.36 0.35 Fe 55.94 58.70 58.07 96.42 39.90 50.34 Ni 38.88 40.34 40.73 25.96 34.17 Cu 0.18 0.23 0.07 Er 1.61 0 1.09 Al 0.56 0.37 Others Co (0.32) O (6.78); Ca (0.72); O (4.79); Ca (3.35); Cl (0.61); K (0.20) Cl (0.20) Total 100 100 100 100 100 100 process, and this promotes adhesion of the component of powder to the work surface. We showed above that a surface-active coolant hinders from adhesion. The experiments were carried out
at conditions: n = 180 rpm; f = 127 mm/min; nosc = 500 min.1; Aosc = 2.5 mm; B = 048 T; MAF duration for two strokes. The coolant (cutting oil) was periodically injected into the gap. Two sorts of powders were used: mechanical mixture of powders of iron CH2 (50% vol.) and Al2O3 (50% vol.); iron powder CH2 [4]. The top surface of sample has tracks of abrasive cutting when deburring was performed by the mixture powder (Fig. 9a). There were no tracks on the surface when iron powder was used (Fig. 9b). The tracks may be made by the hard particles, Al2O3, in the mixture powder, which deteriorates the surface roughness. However the specific removed allowance is almost same in both cases. It was also found that there are some particles attached on the worked surface even after cleaning by alcohol, and chemical composition of the surface was changed. The pictures of attached particles are shown in Fig. 10, and their chemical composition is described in Table 1. The chemical composition of worked surface was changed after MAF. Carbon and erbium vanished, and silicon was decreased or deleted. Small amount of aluminum appears when MAF was made using mixture powder containing Al2O3. That is why the iron powder is recommended for micro deburring of precision parts with soft material. The attached particles consist of the workpiece material (chips) and chemical elements of the coolant. Ultrasonic cleaning of workpieces after MAF is necessary to keep initial chemical composition of worked surfaces. The extra experiment showed that ultrasonic cleaning in a tank with distilled water guarantees removing of coolant films and the attached particles fully.
5. Conclusions
(1) Electromagnetic inductor for deburring and surface finishing of the part of electric gun is developed before. More detail characteristics of deburring are investigated by changing the main parameters.
(2) As deburring conditions, volume of powder, height of gap, inductor rotational frequency, feed velocity and the method of coolant supply are analyzed by experiment more detail.
(3) In addition to the performance of deburring, the influence to surface roughness is also analyzed. To improve the surface roughness, several systems of coolant supply are applied. The continuous coolant flow improves the surface quality.
(4) The remained particle on surface after MAF consists of the component of the coolant and abrasive. Ultrasonic cleaning can remove the particles completely. And the iron powder is recommended to prevent adhesion and the particles on surface.
Acknowledgement This work was supported by the Ministry of Science and Technology of Korea through the 2001 National Research Laboratory (NRL) program. References
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