Centrifugal barrel polishing method

Abstract

To suppress variation in surface roughness of an inner peripheral surface when performing centrifugal barrel polishing of the inner peripheral surface of a hollow part for a work-piece having a shape with the hollow part.SOLUTION: According to a centrifugal barrel polishing method for polishing a work-piece 50 having a hollow part 52, in a polishing process, the work-piece 50, into the hollow part of which a polishing material is inputted, is held by a barrel case, and a rotation speed n and a revolution speed N of the barrel case are set so that a relative centrifugal acceleration F falls within a range defined by 10<F<40, and a rotational speed ratio n / N falls within a range defined by -0.9<n / N<-0.1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a technique for centrifugal barrel polishing of a workpiece. [Background technology]

[0002] Patent Document 1 describes a centrifugal barrel polishing method in which a barrel case is rotated about its rotation axis while revolving about its revolution axis, thereby polishing a workpiece placed inside the barrel case. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-069545 A Summary of the Invention [Problem to be solved by the invention]

[0004] In some cases, the inner surface of a hollow part of a workpiece is subjected to centrifugal barrel polishing while an abrasive is poured into the hollow part and sealed. In such cases, for example, depending on the shape of the hollow part of the workpiece, the variation in surface roughness of the inner surface may become large.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to suppress variation in surface roughness of the inner surface when the inner surface of a hollow portion of a workpiece having a hollow portion is centrifugal barrel polished. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a centrifugal barrel polishing method for polishing a workpiece, which includes a holding step of holding a workpiece with abrasive material charged into a hollow part in a barrel case, and a polishing step of polishing the workpiece held in the barrel case by rotating the barrel case around a rotation axis while revolving the barrel case around a revolution axis. In the polishing step, when N is the revolution rotation speed of the barrel case, n is the rotation rotation speed of the barrel case, the revolution direction of the barrel case is defined as positive, R is the revolution radius around the revolution axis of the barrel case, and F = 4π 2 ×N 2 ×R / g is defined as the relative centrifugal acceleration, which is the ratio of the gravitational acceleration g to the centrifugal acceleration applied to the barrel case due to the revolution of the barrel case, the rotation rotation speed n and the revolution rotation speed N of the barrel case are set so as to be in the range defined by 10 < F < 40 and -0.9 < n / N < -0.1. Here, the abrasive material refers to any one of those in which an abrasive is contained in a base material, those composed only of the base material, or those in which an abrasive is coated on the surface of the base material. In addition to these, an abrasive may be added separately as needed.

[0007] The inventor has come up with the idea that if the abrasive can reach every corner inside the hollow part of the workpiece, the inner peripheral surface of the hollow part can be suitably polished. Generally, the relationship between the rotational speed n of the barrel case and the orbital speed N is such that the rotational speed n is in the opposite direction to the orbital speed N and has the same absolute value, so that it is known that the workpiece can be suitably polished while suppressing the wear of the abrasive (that is, n / N = -1). However, for example, even when n / N = -1, when the relative centrifugal acceleration F is small (for example, less than 10), sufficient centrifugal acceleration does not act on the abrasive, and the abrasive may bounce inside the hollow of the workpiece and cannot sufficiently polish the inner peripheral surface. In this regard, as a result of intensive research, the inventor has found that by making the absolute value of the rotational speed n in the barrel case slower than the absolute value of the orbital speed N, it is possible to make it easier to polish the abrasive inside the hollow part of the workpiece. Note that when the barrel case does not rotate, the abrasive does not flow, so the workpiece cannot be polished. That is, it is set to -0.9 < n / N < -0.1. Also, by increasing the force applied to the abrasive by the centrifugal force associated with the revolution of the barrel case, the flow of the abrasive associated with the rotation of the barrel case becomes stable, and the inner peripheral surface of the hollow part can be suitably polished. In this regard, as a result of intensive research, the inventor has found that by setting the relative centrifugal acceleration F in the range of 10 < F < 40, it is possible to suppress the wear of the abrasive while stabilizing the flow of the abrasive inside the hollow part. Note that when the relative centrifugal acceleration F significantly exceeds 40, the polishing efficiency indicating the wear amount of the abrasive with respect to the polishing amount of the workpiece significantly decreases, so the upper limit value is set to 40. Thereby, when centrifugally barrel-polishing the inner peripheral surface of the hollow part in the workpiece, it is possible to suppress the variation in surface roughness in the hollow part.

Advantages of the Invention

[0008] According to the present invention, when centrifugally barrel-polishing the hollow part of a workpiece, it is possible to suppress the variation in surface roughness in the hollow part.

Brief Description of the Drawings

[0009] [Figure 1] Configuration diagram of the polishing device. [Diagram 2] FIG. 1 is a diagram illustrating a workpiece having a hollow portion. [Diagram 3] FIG. 13 is a diagram for explaining the movement of an abrasive within a conventional workpiece. [Figure 4] 4A to 4C are diagrams for explaining the movement of an abrasive within a workpiece according to the present invention. [Diagram 5] 5 is a diagram illustrating the relationship between the polishing amount, the polishing efficiency, and the relative centrifugal acceleration. [Figure 6] FIG. 2 is a process diagram illustrating the centrifugal barrel polishing process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Embodiment> The polishing apparatus according to the present embodiment will be described with reference to the drawings. The polishing apparatus 100 shown in Fig. 1 is an apparatus capable of performing centrifugal barrel polishing on a workpiece. The polishing apparatus 100 includes an operation panel 10, a sequencer 11, a revolution drive circuit 12, a rotation drive circuit 13, and a barrel mechanism unit 20.

[0011] First, the configuration of the barrel mechanism 20 will be described. The barrel mechanism 20 mainly includes a sun shaft 21, a turret plate 22, a barrel case 23, a revolution motor 24, and a rotation motor 25. The sun shaft 21 is a shaft member attached so as to be rotatable in a predetermined direction, and in this embodiment, is an example of a revolution shaft. The turret plate 22 is penetrated by the sun shaft 21 and is held so as to be rotatable around the sun shaft 21.

[0012] The barrel case 23 is a holding member capable of holding the workpiece 50. The barrel case 23 has a rotation shaft 28, and is rotatably attached to the turret platen 22 via the rotation shaft 28. Specifically, the barrel case 23 has a gripping member such as a clamp, and holds the workpiece 50 in the polishing apparatus 100 by gripping the outer periphery of the workpiece 50 with the gripping member. In FIG. 1, four barrel cases 23 are rotatably attached to the turret platen 22. The rotation shafts 28 of the barrel cases 23 are disposed eccentrically by the revolution orbit radius R from the center of the position where the sun axis 21 passes through the turret platen 22.

[0013] The revolution motor 24 is a drive source for rotating the turret platen 22. A revolution drive pulley 26 is attached to the output shaft of the revolution motor 24. A revolution driven pulley (not shown) is provided on the outer periphery of the turret platen 22 and is connected to the revolution drive pulley 26 via a V-belt. When the output shaft of the revolution motor 24 rotates, the V-belt is driven, and the turret platen 22 can be rotated.

[0014] The rotation motor 25 is a drive source for rotating the barrel case 23. A rotation drive pulley 27 is attached to the output shaft of the rotation motor 25. The rotation of the rotation motor 25 is transmitted to the barrel case 23 via a known planetary gear mechanism, causing the barrel case 23 to rotate in a direction D2 opposite to the rotation direction D1 of the turret board 22. For example, the planetary gear mechanism includes a sun pulley fixed to the sun shaft 21, a sun gear fixed to the sun shaft 21 and rotating together with the sun pulley, a planetary gear fixed to the output shaft of the rotation motor 25, and a reduction gear that reduces the rotation speed of the sun gear and transmits it to the planetary gear. In addition, a V-belt, which is a transmission member, is stretched between the rotation drive pulley 27 and the sun pulley. As a result, the sun pulley rotates in response to the rotation of the output shaft of the rotation motor 25, causing the sun shaft 21 and the sun gear to rotate. The rotation speed of the sun gear is reduced by the reduction gear and transmitted to the planetary gear, causing the barrel case 23 to rotate in the direction of rotation D2 around a rotation shaft 28 fixed to the planetary gear.

[0015] The sequencer 11 is a programmable controller having a predetermined program stored in a memory. Signals corresponding to the operating conditions of the polishing apparatus 100 are input to the sequencer 11 from the operation panel 10. The operating conditions that can be set by operating the operation panel 10 include, for example, the rotation speed n, the revolution speed N, the polishing time, and the acceleration / deceleration time.

[0016] The output from the sequencer 11 is input to the revolution drive circuit 12 and the rotation drive circuit 13. The revolution drive circuit 12 outputs a drive signal for controlling the revolution speed N of the revolution motor 24 and the polishing time in response to a signal corresponding to the operating conditions input from the sequencer 11. In this embodiment, the revolution drive circuit 12 feedback controls the rotation speed of the revolution motor 24 so as to bring the rotation speed of the turret platen 22 detected by the sensor closer to a target speed. The rotation drive circuit 13 outputs a drive signal for controlling the rotation speed n of the rotation motor 25 and the polishing time in response to a signal corresponding to the operating conditions input from the sequencer 11. In this embodiment, the rotation drive circuit 13 feedback controls the rotation motor 25 so as to bring the rotation speed of the barrel case 23 detected by the sensor closer to a target speed. Alternatively, the revolution drive circuit 12 and the rotation drive circuit 13 may be configured to open-control the rotation speeds of the revolution motor 24 and the rotation motor 25, respectively.

[0017] In the polishing apparatus 100 having the above configuration, when centrifugal barrel polishing is performed on the inner peripheral surface of the hollow portion of the workpiece, the abrasive M is poured into the hollow portion of the workpiece and the hollow portion is sealed with a lid or a plug, and then centrifugal barrel polishing is performed while the workpiece is held by the barrel case 23. At this time, the surface roughness of the hollow portion of the polished workpiece may vary.

[0018] FIG. 2 is a cross-sectional view of a workpiece 50 having a hollow portion as an example. The workpiece 50 has an opening 51 formed on the outer peripheral surface and a hollow portion 52 which is a space extending continuously from the opening 51. In the workpiece 50 shown in FIG. 2, the inside of the hollow portion 52 is partially shown, and other parts are not shown. In this embodiment, the hollow portion 52 extends in a curved state inside the workpiece 50. In addition, the maximum dimension of the inner diameter of the hollow portion 52 varies as it advances from the opening 51 to the back. Specifically, the maximum dimension of the inner diameter becomes smaller as it advances from the vicinity of the opening 51 in the hollow portion 52. In other words, when the maximum dimension of the inner diameter near the opening 51 in the hollow portion 52 is L1, and the maximum dimensions of the inner diameter at the points deeper than this point are L2 and L3, respectively, the relationship of each dimension is L1>L2>L3.

[0019] 3 and 4 are cross-sectional views of the workpiece 50 centered on a part of the hollow portion 52. For ease of explanation, the amount of abrasive M shown in Figs. 3 and 4 is less than the actual amount of abrasive M. As the barrel case 23 rotates in the D2 direction, the abrasive M in the hollow portion 52 flows along the inner circumferential surface of the hollow portion 52 and polishes the inner circumferential surface of the hollow portion 52.

[0020] Regardless of the shape of the hollow portion 52, if the abrasive M can be spread to every corner inside the hollow portion 52 as the barrel case 23 rotates, the variation in the flow rate of the abrasive M on each inner peripheral surface of the hollow portion 52 can be reduced. Here, in order to spread the abrasive M to every corner of the hollow portion 52, it is advisable to slow down the rotational speed n of the barrel case 23. In particular, since the maximum dimension of the inner diameter of the workpiece 50 becomes smaller as it advances into the hollow portion 52 from near the opening 51, if the rotational speed n is increased, the abrasive M may flow in all at once, and there is a risk of clogging. Generally, the relationship between the rotational speed n and the revolution speed N of the barrel case 23 is such that the rotational speed n is in the opposite direction to the revolution speed N and the absolute values are the same (i.e., n / N = -1). In this way, it is known that the device structure is simple, the consumption of the abrasive M can be suppressed to a certain extent, and the workpiece 50 can be polished well. On the other hand, when the barrel case 23 does not rotate (i.e., n = 0), the abrasive M does not flow inside the barrel case 23, so it becomes impossible to polish the workpiece 50.

[0021] Therefore, in the polishing device 100 of the present invention, when polishing the workpiece 50, the rotational speed n and the revolution speed N are determined so that the ratio of the revolution speed N to the rotational speed n satisfies the following (Equation 1). Note that the minus sign indicates that the rotational speed n and the revolution speed N are in opposite directions. -0.9 < n / N < -0.1 … (Equation 1)

[0022] Also, inside the hollow portion 52, if the abrasive M is slightly moved while being pressed against the inner peripheral surface, the abrasive can be slid along the inner peripheral surface to stabilize the polishing, and the polishing force on the inner peripheral surface of the hollow portion 52 can be improved. As shown in FIG. 4, a centrifugal acceleration Fc associated with the revolution of the barrel case 23 is applied to the workpiece 50 and the abrasive M inside the barrel case 23. The centrifugal acceleration Fc is a force that presses the abrasive M inside the hollow portion 52 against the inner peripheral surface of the hollow portion 52. In FIG. 4, a centrifugal acceleration Fc larger than the centrifugal acceleration Fc shown in FIG. 3 is applied to the abrasive M.

[0023] In this embodiment, the centrifugal acceleration Fc applied to the abrasive M due to the revolution of the barrel case 23 is determined from the viewpoint of suppressing wear of the abrasive M as much as possible while maintaining a high level of polishing force. Fig. 5 is a graph in which the horizontal axis represents the relative centrifugal acceleration F and the vertical axis represents the polishing amount Q and the polishing efficiency E. The relative centrifugal acceleration F is the ratio of gravity g to the centrifugal acceleration Fc applied to the barrel case 23 due to the revolution of the barrel case 23, and is a value calculated by the following (Equation 2). The unit of the relative centrifugal acceleration F is dimensionless. F=4π 2 ×N 2 ×R / g … (Formula 2) Here, N is the revolution speed in [rps]. R is the revolution orbit radius shown in Figure 1 in [m]. g is the gravitational acceleration in [m / s 2 The acceleration due to gravity is 9.8 [m / s 2 ] may also be used.

[0024] The polishing amount Q is the amount of workpiece polished (weight of workpiece removed during polishing) per unit time (e.g., 30 minutes), and is expressed in mg. The polishing efficiency E is a value defined as the ratio of the amount of workpiece polished per unit time Q to the amount of wear of the abrasive per unit time W, and is calculated by the following formula 3. The polishing efficiency E is dimensionless. E=Q / W … (Equation 3)

[0025] The polishing efficiency E is a value obtained by dividing the polishing amount Q of the work 50 by the wear amount W of the abrasive, and is therefore an index showing how much polishing of the work 50 has progressed when the wear of the abrasive M has reached a predetermined amount. In other words, it can be said to be an index showing how much the wear of the abrasive M has been suppressed when the polishing of the work 50 has reached a predetermined amount, and is an index showing how efficiently the abrasive M has contributed to the polishing of the work 50, taking into account the progress of the polishing of the work and the progress of the wear of the abrasive M.

[0026] The polishing apparatus 100 polishes the inner peripheral surface of the workpiece 50 by applying centrifugal acceleration Fc caused by revolution to the abrasive M while causing the abrasive M to flow within the workpiece 50 by the rotation of the barrel case 23, so there is a correlation between the relative centrifugal acceleration F and the polishing amount Q and polishing efficiency E. That is, it is considered that the polishing amount Q of the workpiece 50 is affected by the flow amount proportional to the rotation speed n of the barrel case 23 and the relative centrifugal acceleration F. Therefore, in the diagram shown in FIG. 5, a range of the relative centrifugal acceleration F in which the polishing amount Q and the polishing efficiency E are optimal is determined.

[0027] As shown in FIG. 5, as the relative centrifugal acceleration F increases, the polishing amount Q of the workpiece 50 increases, while the polishing efficiency E generally tends to decrease. On the other hand, the polishing efficiency E transitions to a downward convex shape with an inflection point (minimum value) at point Eβ, and then transitions to an upward convex shape with an inflection point (maximum value) at point Eγ. These will be described in detail by defining the range of the relative centrifugal acceleration F (areas a, b, c, d, and e). Note that the area a is an area showing a value smaller than the relative centrifugal acceleration F at the polishing efficiency Eα. The area b is an area from the relative centrifugal acceleration F at the polishing efficiency Eα to a value excluding the relative centrifugal acceleration F at the polishing efficiency Eβ. The area c is an area from the relative centrifugal acceleration F at the polishing efficiency Eβ to a value excluding the relative centrifugal acceleration F at the polishing efficiency Eγ. The area d is an area from the relative centrifugal acceleration F at the polishing efficiency Eγ to a value excluding the relative centrifugal acceleration F at the polishing efficiency Eδ. The region e is a region equal to or greater than the relative centrifugal acceleration F at the polishing efficiency Eδ. Here, in the polishing efficiency E, the point Eα is a value that shows the same value as the inflection point Eγ (maximum point) of the polishing efficiency E. The point Eδ is a value that shows the same value as the inflection point Eβ (minimum point) of the polishing efficiency E.

[0028] When the relative centrifugal acceleration F is within the range of region a, although the polishing efficiency E is higher than those in regions b, c, d, and e, the polishing amount Q is extremely small, so it cannot be said to be a good region. In addition, when the relative centrifugal acceleration F is less than 10, the force pressing the abrasive M against the inner peripheral surface of the work 50 attached to the barrel case 23 is weak. Moreover, when n / N = -1, the abrasive M bounces inside the work 50 and cannot be pressed against the inner peripheral surface, which increases the likelihood of variations in the surface roughness. On the other hand, when the relative centrifugal acceleration F is within the range of region e, although the polishing amount Q is high, the polishing efficiency E significantly decreases. In particular, when the relative centrifugal acceleration F greatly exceeds 40, there is concern that indentations will be caused on the inner peripheral surface of the work 50 by the abrasive M. At this time, if the work is made of a brittle material, there is also concern that the abrasive M will chip and crack.

[0029] From this, when the relative centrifugal acceleration F is a value near regions b, c, d (10 < F < 40), the polishing efficiency E is maintained at a high value and can be said to be a good region. In particular, when the relative centrifugal acceleration F is a value near regions c, d (15 < F < 35), the value of the polishing efficiency E is maintained at a particularly high value (Eβ < E < Eγ).

[0030] In the present embodiment, in the polishing apparatus 100, when polishing the work 50, the value of the公转 rotation speed N is determined so that the relative centrifugal acceleration F calculated by the above (Equation 2) satisfies the following (Equation 4). 10 < F < 40 … (Equation 4)

[0031] Also, from the viewpoint of maintaining both the polishing amount Q and the polishing efficiency E at high values, the value of the公转 rotation speed N may be determined so that the relative centrifugal acceleration F satisfies the following (Equation 5). 15 < F < 35 … (Equation 5)

[0032] Next, the procedure of the centrifugal barrel polishing method using the polishing apparatus 100 will be described with reference to FIG. 6. It should be noted that there may be some inaccuracies in the translation due to the possible ambiguity of the original text in some places. For example, the term "公转回転速度" is directly translated as "公转 rotation speed" here, and it may need to be further determined according to the specific context whether it is a more accurate translation such as "revolution rotation speed".6, an operator inputs operating conditions of the polishing apparatus 100 by operating the operation panel 10. The operating conditions include the revolution speed N, the rotation speed n, the polishing time, and the operating time. Note that these operating conditions are not limited to values ​​directly input by the operator operating the operation panel 10, and may be values ​​read by the sequencer 11 according to the workpiece type selected by the operator operating the operation panel 10. In this case, the sequencer 11 may store the operating conditions in association with the workpiece type.

[0033] In step S11 (hereinafter, step will be simply referred to as S), a charging step is carried out in which an abrasive M is charged into the hollow portion 52 of the workpiece 50. As the abrasive M used in the charging step, for example, a grinding stone in which an abrasive is bonded with a binder as a base material is used. The abrasive contained in the abrasive M can be an abrasive having a hardness higher than that of the workpiece 50. In the charging step, a grinding stone having a tap density of 2 [g / cm 3 ] or more of abrasive is charged into hollow portion 52. Here, "tap density" refers to the density obtained by putting powder into a container under specified conditions, tapping the container, and dividing the powder weight by the container volume in the state where the gaps between the powder particles are filled. When abrasive stones are used as the abrasive M, this refers to the density of the abrasive stones obtained by filling a container with the abrasive stones and tapping the container. Note that when the abrasive is added separately, the tap density excluding the abrasive added separately is 2 g / cm or more. 3 The above is used. There is a concern that the polishing power of the abrasive M may decrease if the maximum dimension of the abrasive M is reduced according to the inner dimension of the hollow portion 52. Therefore, in this embodiment, the tap density is set to 2 [g / cm 3 By using the above abrasive M, it is possible to suppress the decrease in abrasive power caused by the reduction in the dimensions of the abrasive M. As a specific method for introducing the abrasive M into the workpiece 50, the abrasive M is introduced into the hollow portion 52 of the workpiece 50, and water and a compound (detergent for barrel polishing) are introduced if necessary, and the hollow portion is sealed to prevent leakage.

[0034] In S12, a holding step is performed in which the workpiece 50, into which the abrasive M has been charged, is held in the polishing apparatus 100 by the barrel case 23. Specifically, the outer periphery of the workpiece 50 is held by the gripping member of the barrel case 23, thereby holding the workpiece 50 in the polishing apparatus 100.

[0035] In S13, the barrel case 23 is rotated on its axis while being revolved by the rotation of the turret plate 22, thereby executing a polishing process for polishing the inner peripheral surface of the workpiece 50. Specifically, the operator operates the operation panel 10 to cause the sequencer 11 to start the rotation and rotation of the barrel case 23. The sequencer 11 outputs signals according to the operating conditions to the revolution drive circuit 12 and the rotation drive circuit 13, thereby causing the revolution drive circuit 12 to drive the revolution motor 24 and causing the rotation drive circuit 13 to drive the rotation motor 25.

[0036] In the polishing process executed in S13, the rotation speed n and revolution speed N output from the sequencer 11 are determined so that the relative centrifugal acceleration F and the rotation speed ratio "n / N" satisfy the above (Equation 1) and (Equation 4). Note that the polishing process executed in S13 may be performed multiple times depending on the type of workpiece.

[0037] When the operating time in the polishing process in S13 has elapsed, the driving of the revolution motor 24 and the rotation motor 25 is stopped, and after a predetermined period of time has elapsed, the process proceeds to S14, where the recovery process is executed. In the recovery process, the workpiece 50 is removed from the barrel case 23, the workpiece 50 and the first abrasive material M1 are separated, and the workpiece 50 is washed and dried.

[0038] <Example> Next, an example in which a workpiece 50 was centrifugal barrel polished according to the steps shown in FIG. 6 will be described. In the examples, as shown in Table 1, Examples 1 to 8 were carried out under different operating conditions including the relative centrifugal acceleration F and the rotational speed ratio n / N. In Examples 1 to 8, the polishing process was carried out for 480 minutes. In Examples 1 to 8, a ceramic polishing stone manufactured by Tipton was used as the polishing material M. The ceramic polishing stone is an abrasive material in which an abrasive material is sintered and bonded with a clay binder. The polishing stone diameter (maximum dimension) is one-third or less of the minimum value of the internal dimension of the workpiece 50, and the tap density is 2 [g / cm 3 ]That's all.

[0039] In the comparative example, the same process as in the example was carried out, but the relative centrifugal acceleration F and the rotational speed ratio n / N were set under conditions different from those of (Equation 1) and (Equation 4) above.

[0040] [Table 1]

[0041] In the examples and the comparative examples, the surface roughness Ra [μm] of the hollow portion 52 after the polishing process was measured. Specifically, the surface roughnesses Ra1, Ra2, and Ra3 were measured at the first measurement point, the second measurement point, and the third measurement point, which are different in distance from the opening 51, in the hollow portion 52 of the workpiece 50. The first measurement point is the point in the hollow portion 52 that is closest to the opening 51 compared to the other measurement points, and in FIG. 2, it is the point with the inner dimension L1. The third measurement point is the point in the hollow portion 52 that is farthest (deeper) from the opening 51 compared to the other measurement points, and in FIG. 2, it is the point with the inner dimension L3. The second measurement point is the intermediate point between the first measurement point and the third measurement point in the hollow portion 52, and in FIG. 2, it is the point with the inner dimension L2. In addition, the standard deviations of the surface roughnesses Ra1, Ra2, and Ra3 were calculated in each example.

[0042] The results of measuring the surface roughness in Examples 1 to 8 will be described. In any of Examples 1 to 8, the values of surface roughness Ra1, surface roughness Ra2, and surface roughness Ra3 increase in this order. That is, even after centrifugal barrel polishing, in the hollow portion 52 of the workpiece 50, the surface roughness Ra increases as the distance from the opening 51 increases.

[0043] In Examples 4 to 8 where the relative centrifugal acceleration F is within the range of "19 < F < 40", the surface roughness Ra1 at the first measurement location is a value of "1.61" or less, the surface roughness Ra2 at the second measurement location is a value of "3.77" or less, and the surface roughness Ra3 at the third measurement location was "4.86" or less. Here, the above range of "19 < F < 40" is a range set from the viewpoint of maintaining both the polishing amount Q and the polishing efficiency E at high values in FIG. 5 and the above (Equation 5). In Examples 4 to 8 where the relative centrifugal acceleration F is within the range of "19 < F < 40", compared with other examples, the surface roughnesses Ra1, Ra2, and Ra3 at all measurement locations are generally small values. Also, in Examples 4 to 8, the standard deviation of the surface roughness Ra is a value of "0.79" or more and "1.38" or less, and the variation was small compared with other examples.

[0044] Furthermore, in Examples 7 and 8 where the relative centrifugal acceleration F is within the range of "19 < F < 40" and the rotation speed ratio "n / N" is within the range of "-0.7 < n / N < -0.5", the surface roughness Ra1 at the first measurement location is a value of "1.28" or less, the surface roughness Ra2 at the second measurement location is a value of "2.61" or less, and the surface roughness Ra3 at the third measurement location was "3.22" or less. Also, in Examples 7 and 8, the standard deviation of the surface roughness Ra is a value of "0.79" or more and "0.81" or less, and the variation was generally small compared with other examples.

[0045] In Examples 4 to 8, the polishing stone diameter [mm] (maximum dimension) of the polishing stone is the smallest compared with other embodiments. However, in Examples 4 to 8, the tap density of the polishing stone is 2 [g / cm 3] or more, the surface roughness Ra1, Ra2, Ra3 and the standard deviation were not significantly different from those of the other examples. In particular, the tap density was 3 [g / cm 3 In Examples 7 and 8, where [ ], the surface roughnesses Ra1, Ra2, and Ra3 and the standard deviation were smaller than those of the other Examples.

[0046] Next, the results of measuring the surface roughness in the comparative example will be described. In both Comparative Examples 1 and 2, the surface roughness Ra1, the surface roughness Ra2, and the surface roughness Ra3 are larger in this order. That is, even after centrifugal barrel polishing, the surface roughness Ra is not improved from the state before polishing as the distance from the opening 51 increases in the hollow portion 52 of the workpiece 50. Furthermore, in Comparative Examples 1 and 2, the standard deviations of the surface roughness Ra were "1.99" and "1.90", which were larger than all of Examples 1 to 8.

[0047] The results of measuring the surface roughness in the examples and comparative examples will be summarized. In the comparison between Examples 1 to 8 and Comparative Examples 1 and 2, at the first measurement location close to the opening 51, no significant difference was observed in the surface roughness Ra1. This is because in the hollow portion 52, at the first measurement location close to the opening 51, the abrasive stone is easily distributed, and the influence on centrifugal barrel polishing by the parameters (F, n / N) is low. On the other hand, in Comparative Examples 1 and 2, at the second measurement location where the distance from the opening 51 is farther than the first measurement location, the surface roughness Ra2 was generally a larger value compared to Examples 1 to 8. Also, in Comparative Examples 1 and 2, at the third measurement location where the distance from the opening 51 is the farthest, the surface roughness Ra3 became larger values (6.39, 6.55) than those in Examples 1 to 8. Furthermore, in Comparative Examples 1 and 2, the standard deviation of the surface roughness Ra was a larger value than that in Examples 1 to 8. This is because as the distance from the opening 51 increases, it becomes difficult for the abrasive stone to spread inside the hollow portion 52, so the influence on centrifugal barrel polishing by the parameters (F, n / N) increases. That is, in the polishing apparatus 100, by setting the公转 rotation speed N and the自转 rotation speed n so as to satisfy the above (Equation 1) and (Equation 4), the variation in the surface roughness of the hollow portion 52 in the workpiece 50 could be reduced.

[0048] In the present embodiment described above, the following effects can be achieved. In the centrifugal barrel polishing method, in the polishing step of polishing the workpiece 50 held in the barrel case 23, the relative centrifugal acceleration F is in the range of "10 < F < 40", and the rotation speed ratio n / N is in the range defined by "-0.9 < n / N < -0.1". The自转 rotation speed n and the公转 rotation speed N are set accordingly. Thereby, when centrifugally barrel-polishing the inner peripheral surface of the hollow portion 52 in the workpiece 50, the variation in the surface roughness on the inner peripheral surface can be suppressed.

[0049] In the polishing step, the自转 rotation speed n and the公转 rotation speed N are set so that the relative centrifugal acceleration F is in the range defined by "19 < F < 40". Thereby, the variation in the surface roughness of the inner peripheral surface in the hollow portion 52 with respect to the workpiece 50 can be suitably suppressed while suppressing the wear of the abrasive M.

[0050] In the polishing process, the rotation speed ratio n / N is in the range defined by "-0.7 < n / N < -0.5", and the rotation speed n of self-rotation and the rotation speed N of revolution are set. Thereby, the variation in the surface roughness of the inner peripheral surface in the hollow portion 52 with respect to the workpiece 50 can be further suppressed.

[0051] The maximum dimension of the abrasive M is 1 / 3 or less of the minimum inner dimension of the hollow portion in the workpiece 50. Thereby, even when the hollow portion 52 does not extend linearly within the workpiece 50, the abrasive M can be easily spread to every corner within the hollow portion 52 as the barrel case 23 rotates, and the variation in the surface roughness of the inner peripheral surface in the hollow portion 52 can be suppressed.

[0052] In the holding process, an abrasive M with a tap density of 2 [g / cm 3 or more is charged into the hollow portion 52 of the workpiece 50. Thereby, even when the dimension of the abrasive M is reduced according to the inner dimension of the hollow portion 52, the decrease in the polishing force can be suppressed, and thus the surface roughness of the inner peripheral surface in the hollow portion 52 can be reduced.

[0053] <Other Embodiments> Make it into stone. The technology disclosed in this specification is not limited to the above-described embodiments, and can be deformed into various forms without departing from the gist thereof. For example, the following deformations are also possible. In the above-described embodiment, the abrasive M was a ceramic abrasive stone in which an abrasive was contained in a ceramic binder. Instead of this, an abrasive M in which the binder as the base material is made of a synthetic resin may be used. Further, the abrasive M is not limited to one in which the abrasive is contained in the binder, and may be one having only the base material, or one in which the abrasive is coated on the surface of the base material. In addition to these, an abrasive obtained by further adding the abrasive as a separate body may also be used.

[0054] In the above-described embodiment, the polishing apparatus 100 drives each of the revolution motor 24 and the rotation motor 25 to rotate and revolve the barrel case 23. Alternatively, the barrel case 23 may be rotated and revolved by driving only the revolution motor 24. In this case, the rotation of the output shaft of the revolution motor 24 may be transmitted to the sun shaft via a transmission mechanism. [Explanation of symbols]

[0055] 100... polishing device, 23... barrel case, 50... workpiece, 52... hollow portion, M... polishing material

Claims

1. A centrifugal barrel polishing method for polishing a workpiece, comprising the steps of: a holding step of holding the workpiece having the abrasive material placed in the hollow portion in a barrel case; a polishing step of polishing a workpiece held in the barrel case by rotating the barrel case about a rotation axis while revolving the barrel case about a revolution axis; Run N is the revolution speed of the barrel case, n is the rotational speed of the barrel case, The revolution direction of the barrel case is positive, R is the radius of revolution about the revolution axis of the barrel case, When F=4π2×N2×R / g is defined as the relative centrifugal acceleration, which is the ratio of gravity g to the centrifugal acceleration applied to the barrel case due to the revolution of the barrel case, In the polishing step, 10<F<40, -0.9<n / N<-0.1, The rotation speed and the revolution speed of the barrel case are set so as to be within a range defined by A centrifugal barrel polishing method, wherein the maximum dimension of the abrasive is one-third or less of the minimum inner dimension of the hollow portion in the workpiece.

2. 2. The centrifugal barrel polishing method according to claim 1, wherein in the polishing step, the rotation speed n and the revolution speed N of the barrel case are set so that the relative centrifugal acceleration is in the range specified by 19<F<40.

3. 3. The centrifugal barrel polishing method according to claim 2, wherein in the polishing step, the rotation speed n and the revolution speed N of the barrel case are set to be within the range defined by −0.7<n / N<−0.

5.

4. 4. The centrifugal barrel polishing method according to claim 1, wherein the abrasive charged into the hollow portion of the workpiece in the holding step has a tap density of 2 g / cm3 or more.

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