JP7628282B2 - Centrifugal barrel polishing method - Google Patents

Description

The present invention relates to a technology for centrifugal barrel polishing of workpieces.

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 to polish a workpiece placed inside the barrel case.

JP 2020-069545 A

For workpieces with a hollow section inside, the inner surface of the hollow section may be centrifugal barrel polished with an abrasive placed inside the hollow section and sealed. In such cases, for example, depending on the shape of the hollow section of the workpiece, the surface roughness of the inner surface may vary greatly.

The present invention has been made in consideration of the above problems, and aims to suppress the variation in surface roughness of the inner circumferential surface when centrifugal barrel polishing is performed on the inner circumferential surface of a workpiece having a hollow portion.

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 the workpiece, with an abrasive charged in a hollow portion, in a barrel case, and a polishing step of polishing the workpiece held in the barrel case by rotating the barrel case about its rotation axis while revolving the barrel case about its revolution axis. In the polishing step, the rotation speed n and the revolution speed N of the barrel case are set so as to be within the ranges defined by 10<F<40 ^{and -0.9} <n/N<-0.1, where N is the revolution speed of the barrel case, n is the rotation speed of the barrel case, the revolution direction of the barrel case is positive, R is the revolution radius around the revolution axis of the barrel case, and F=4π2× ^N2 ×R/g is the relative centrifugal acceleration, which is the ratio of gravity g to the centrifugal acceleration applied to the barrel case by the revolution of the barrel case.
Here, the abrasive refers to one in which the abrasive is contained in a base material, one made of only a base material, or one in which the abrasive is coated on the surface of a base material. In addition, the abrasive may be added separately as necessary.

The inventor came up with the idea that if the abrasive can be distributed throughout the hollow part of the workpiece, the inner circumferential surface of the hollow part can be polished appropriately. It is generally known that the relationship between the rotation speed n and the revolution speed N of the barrel case is such that the rotation speed n is in the opposite direction to the revolution speed N and has the same absolute value, thereby suppressing wear of the abrasive and polishing the workpiece appropriately (i.e., n/N=-1). However, even when n/N=-1, for example, if the relative centrifugal acceleration F is small (for example, less than 10), sufficient centrifugal acceleration may not act on the abrasive, causing the abrasive to jump around inside the hollow part of the workpiece and not be able to polish the inner circumferential surface sufficiently. In this regard, the inventor has conducted extensive research and has come to the knowledge that the abrasive can be easily polished inside the hollow part of the workpiece by making the absolute value of the rotation speed n of the barrel case slower than the absolute value of the revolution speed N. If the barrel case does not rotate, the abrasive does not flow, and the workpiece cannot be polished. In other words, it is set to -0.9<n/N<-0.1. In addition, by increasing the force applied to the abrasive by the centrifugal force accompanying the revolution of the barrel case, the flow of the abrasive accompanying the rotation of the barrel case can be stabilized, and the inner surface of the hollow portion can be polished suitably. In this regard, the inventor has found, as a result of extensive research, that by setting the relative centrifugal acceleration F in the range of 10<F<40, it is possible to stabilize the flow of the abrasive in the hollow portion while suppressing wear of the abrasive. If the relative centrifugal acceleration F significantly exceeds 40, the polishing efficiency, which indicates the amount of wear of the abrasive relative to the amount of polishing of the workpiece, is significantly reduced, so the upper limit is set to 40. This makes it possible to suppress the variation in surface roughness in the hollow portion when centrifugal barrel polishing the inner surface of the hollow portion of the workpiece.

According to the present invention, when the hollow portion of a workpiece is subjected to centrifugal barrel polishing, the variation in surface roughness in the hollow portion can be suppressed.

FIG. FIG. 1 is a diagram illustrating a workpiece having a hollow portion. FIG. 13 is a diagram for explaining movement of an abrasive within a conventional workpiece. 4A to 4C are diagrams for explaining the movement of an abrasive within a workpiece according to the present invention. 5 is a diagram illustrating the relationship between the polishing amount, the polishing efficiency, and the relative centrifugal acceleration. FIG. 2 is a process diagram illustrating the centrifugal barrel polishing process.

<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.

First, the configuration of the barrel mechanism 20 will be described. The barrel mechanism 20 mainly comprises 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 an axial member that is attached so as to be rotatable in a predetermined direction, and in this embodiment, is an example of a revolution axis. The turret plate 22 is pierced by the sun shaft 21 and is held so as to be rotatable around the sun shaft 21.

The barrel case 23 is a holding member capable of holding the workpiece 50. The barrel case 23 has a rotation axis 28 and is rotatably attached to the turret platen 22 via this rotation axis 28. Specifically, the barrel case 23 has a gripping member such as a clamp, and holds the workpiece 50 in the polishing device 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 axis 28 of the barrel case 23 is eccentrically disposed on the turret platen 22 by the revolution orbit radius R from the center of the position where the sun axis 21 passes through.

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.

The rotation motor 25 is a drive source for rotating the barrel case 23. The output shaft of the rotation motor 25 is attached with a rotation drive pulley 27. The rotation of the rotation motor 25 is transmitted to the barrel case 23 via a well-known planetary gear mechanism, causing the barrel case 23 to rotate in the opposite direction D2 to the rotation direction D1 of the turret plate 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 rotational speed of the sun gear is reduced by the reduction gear and transmitted to the planetary gear. As a result, the barrel case 23 rotates in the direction of rotation D2 around the rotation axis 28 fixed to the planetary gear.

The sequencer 11 is a programmable controller that stores a predetermined program in 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.

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 plate 22 detected by the sensor closer to the 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 the target speed. In addition, the revolution drive circuit 12 and the rotation drive circuit 13 may openly control the rotation speed of the revolution motor 24 and the rotation motor 25, respectively.

When centrifugal barrel polishing is performed on the inner surface of a hollow portion of a workpiece in the polishing device 100 configured as described above, abrasive M is poured into the hollow portion of the workpiece, the hollow portion is sealed with a lid or plug, and centrifugal barrel polishing is performed while the workpiece is held by the barrel case 23. At this time, there may be variation in the surface roughness of the hollow portion of the polished workpiece.

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 that 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, if 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 points deeper than this point are L2 and L3, respectively, the relationship of each dimension is L1>L2>L3.

Figures 3 and 4 are cross-sectional views of the workpiece 50, centered on a part of the hollow portion 52. Note that, for ease of explanation, the amount of abrasive M shown in Figures 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.

Regardless of the shape of the hollow portion 52, if the abrasive M can be distributed to every corner of the hollow portion 52 with the rotation of the barrel case 23, the variation in the flow amount of the abrasive M can be reduced on each inner peripheral surface of the hollow portion 52. Here, in order to distribute the abrasive M to every corner of the hollow portion 52, it is advisable to slow down the rotation speed n of the barrel case 23. In particular, since the maximum dimension of the inner diameter of the workpiece 50 decreases as it advances through the hollow portion 52 from the vicinity of the opening 51, if the rotation speed n is increased, the abrasive M may flow in all at once and cause clogging. In general, it is known that the relationship between the rotation speed n and the revolution speed N of the barrel case 23 is such that the rotation speed n is in the opposite direction to the revolution speed N and has the same absolute value (i.e., n/N = -1), the device structure is simple, and the workpiece 50 can be polished well while suppressing wear of the abrasive M to a certain extent. On the other hand, if the barrel case 23 does not rotate (i.e., n = 0), the abrasive M does not flow inside the barrel case 23, making it impossible to polish the workpiece 50.

Therefore, in the present invention, when polishing the workpiece 50 in the polishing apparatus 100, the rotation speed n and the revolution speed N are determined so that the ratio of the rotation speed n to the revolution speed N falls within a range that satisfies the following (Equation 1). Note that minus indicates that the rotation speed n and the revolution speed N are in the opposite directions.
-0.9<n/N<-0.1... (Formula 1)

In addition, by slightly moving the abrasive M inside the hollow portion 52 while pressing it against the inner peripheral surface, the abrasive can be slid along the inner peripheral surface to stabilize the abrasive, and the abrasive force against the inner peripheral surface of the hollow portion 52 can be improved. As shown in FIG. 4, the workpiece 50 and the abrasive M inside the barrel case 23 are subjected to centrifugal acceleration Fc accompanying the revolution of the barrel case 23. The centrifugal acceleration Fc becomes 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.

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 abrasive power. Fig. 5 is a graph in which the horizontal axis represents the relative centrifugal acceleration F and the vertical axis represents the amount of polishing 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 FIG. 1 in [m]. g is the gravitational acceleration in [m/ ^s2 ]. The gravitational acceleration may be 9.8 [m/ ^s2 ].

The polishing amount Q is the amount of workpiece polished (weight of workpiece scraped off 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)

The polishing efficiency E is the value obtained by dividing the amount Q of the workpiece 50 polished by the amount W of wear of the abrasive, and is therefore an index showing how much polishing of the workpiece 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 wear of the abrasive M has been suppressed when the polishing of the workpiece 50 has reached a predetermined amount, and is an index showing how efficiently the abrasive M has contributed to the polishing of the workpiece 50, taking into account the progress of polishing of the workpiece and the progress of wear of the abrasive M.

The polishing device 100 polishes the inner surface of the workpiece 50 by applying centrifugal acceleration Fc due to 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. In other words, 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 Figure 5, the range of relative centrifugal acceleration F in which the polishing amount Q and polishing efficiency E are optimal is determined.

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 explained in detail by defining the range of the relative centrifugal acceleration F (areas a, b, c, d, e). Note that area a is an area showing a value smaller than the relative centrifugal acceleration F at the polishing efficiency Eα. 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. 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. 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. 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, point Eα is a value that shows the same value as the inflection point Eγ (maximum point) of the polishing efficiency E. Point Eδ is the same value as the inflection point Eβ (minimum point) of the polishing efficiency E.

When the relative centrifugal acceleration F is in the range of region a, the polishing efficiency E is higher than in regions b, c, d, and e, but the polishing amount Q is significantly small, so it cannot be said to be a good region. In addition, when the relative centrifugal acceleration F is smaller than 10, the force pressing the abrasive M against the inner surface of the workpiece 50 attached to the barrel case 23 is weak, and when n/N=-1, the abrasive M jumps around inside the workpiece 50 and is not pressed against the inner surface, which increases the possibility of causing variation in surface roughness. On the other hand, when the relative centrifugal acceleration F is in the range of region e, the polishing amount Q is high, but the polishing efficiency E is significantly reduced. In particular, when the relative centrifugal acceleration F significantly exceeds 40, there is a concern that the abrasive M will cause indentations on the inner surface of the workpiece 50. In this case, if the workpiece is made of a brittle material, there is a concern that the abrasive M will chip.

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

In this embodiment, when polishing the workpiece 50 in the polishing apparatus 100, the value of the revolution 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... (Formula 4)

From the viewpoint of maintaining both the polishing amount Q and the polishing efficiency E at high values, the value of the revolution speed N may be determined so that the relative centrifugal acceleration F satisfies the following (Equation 5).
15<F<35... (Formula 5)

Next, the procedure of the centrifugal barrel polishing method using the polishing apparatus 100 will be described with reference to FIG.
6, an operator operates the operation panel 10 to input operating conditions for the polishing apparatus 100. 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 being directly input by the operator operating the operation panel 10, and may be values read out 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 corresponding to the workpiece type.

In step S11 (hereinafter, step will be simply referred to as S), a charging step is performed in which an abrasive M is charged into the hollow portion 52 of the workpiece 50. For example, a grinding stone in which an abrasive is bound with a binder, which is a base material, is used as the abrasive M used in the charging step. 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, an abrasive having a tap density of 2 g/cm ³ or more is charged into the hollow portion 52. Here, the "tap density" is a density obtained by putting a powder into a container under a set condition, tapping the container, and dividing the powder weight by the container volume in a state in which the gaps between the powder are filled. When a grinding stone is used as the abrasive M, the density of the grinding stone obtained by filling the container with the grinding stone and tapping the container is referred to. In addition, when the abrasive is added separately, a grinding stone having a tap density of 2 g/cm ³ or more excluding the abrasive added separately is used. There is a concern that the polishing power of the abrasive M may decrease when the maximum dimension of the abrasive M is reduced according to the inner dimension of the hollow portion 52. Therefore, in this embodiment, the abrasive M having a tap density of 2 [g/cm ³ ] or more is used to suppress the decrease in polishing power caused by the reduction in the dimension 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 workpiece is sealed to prevent leakage.

In S12, a holding process is performed in which the workpiece 50, into which the abrasive M has been added, is held in the polishing device 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 device 100.

In S13, the barrel case 23 is rotated on its axis while revolving due to the rotation of the turret plate 22, thereby executing a polishing process for polishing the inner 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.

In the polishing process performed 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). Depending on the type of workpiece, the polishing process performed in S13 may be performed multiple times.

When the operating time for the polishing process in S13 has elapsed, the revolution motor 24 and the rotation motor 25 are 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.

<Example>
Next, an example in which a workpiece 50 is 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 with 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 smallest value of the internal dimensions of the workpiece 50, and the tap density is 2 [g/cm ³ ] or more.

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

In the examples and comparative examples, the surface roughness Ra [μm] of the hollow portion 52 after the polishing process was measured. Specifically, the surface roughness Ra1, Ra2, and Ra3 were measured at the first measurement point, the second measurement point, and the third measurement point, which are different distances 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 (rear) 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 point in the hollow portion 52 between the first and third measurement points, and in FIG. 2, it is the point with the inner dimension L2. In addition, the standard deviation of the surface roughness Ra1, Ra2, and Ra3 was calculated in each example.

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

In Examples 4 to 8, where the relative centrifugal acceleration F is in the range of "19<F<40", the surface roughness Ra1 at the first measurement point was "1.61" or less, the surface roughness Ra2 at the second measurement point was "3.77" or less, and the surface roughness Ra3 at the third measurement point was "4.86" or less. The above-mentioned 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 (Formula 5). In Examples 4 to 8, where the relative centrifugal acceleration F is in the range of "19<F<40", the surface roughness Ra1, Ra2, and Ra3 at all measurement points are generally small values compared to other Examples. In addition, in Examples 4 to 8, the standard deviation of the surface roughness Ra was "0.79" or more and "1.38" or less, and the variation was smaller than in other Examples.

Furthermore, in Examples 7 and 8, where the relative centrifugal acceleration F was in the range of "19 < F < 40" and the rotational speed ratio "n/N" was in the range of "-0.7 < n/N < -0.5", the surface roughness Ra1 at the first measurement point was "1.28" or less, the surface roughness Ra2 at the second measurement point was "2.61" or less, and the surface roughness Ra3 at the third measurement point was "3.22" or less. In Examples 7 and 8, the standard deviation of the surface roughness Ra was "0.79" or more and "0.81" or less, and the variation was generally smaller than in the other Examples.

In Examples 4 to 8, the grinding stone diameter [mm] (maximum dimension) of the grinding stone is the smallest compared to the other embodiments. However, in Examples 4 to 8, the tap density of the grinding stone is 2 [g/cm ³ ] or more, so the surface roughnesses Ra1, Ra2, Ra3 and standard deviations are not significantly different from the other Examples. In particular, in Examples 7 and 8, where the tap density is 3 [g/cm ³ ], the surface roughnesses Ra1, Ra2, Ra3 and standard deviations are smaller than the other Examples.

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. Also, 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.

The results of measuring the surface roughness in the examples and comparative examples will be summarized.
In comparison between Examples 1 to 8 and Comparative Examples 1 and 2, no significant difference was observed in surface roughness Ra1 at the first measurement point close to the opening 51. This is because the polishing stone is easily distributed at the first measurement point close to the opening 51 in the hollow portion 52, and the effect of the parameter (F, n/N) on the centrifugal barrel polishing is low. On the other hand, in Comparative Examples 1 and 2, at the second measurement point farther from the opening 51 than the first measurement point, the surface roughness Ra2 was generally larger than that of Examples 1 to 8. Furthermore, in Comparative Examples 1 and 2, at the third measurement point farthest from the opening 51, the surface roughness Ra3 was larger than that of Examples 1 to 8 (6.39, 6.55). Furthermore, in Comparative Examples 1 and 2, the standard deviation of the surface roughness Ra was larger than that of Examples 1 to 8. This is because the influence of the parameter (F, n/N) on the centrifugal barrel polishing increases as the distance from the opening 51 increases, since the polishing stone is less likely to penetrate into the hollow portion 52. That is, in the polishing apparatus 100, by setting the revolution speed N and the rotation speed n so as to satisfy the above (Equation 1) and (Equation 4), it is possible to reduce the variation in the surface roughness of the hollow portion 52 in the workpiece 50.

The present embodiment described above can provide the following advantages.
In the centrifugal barrel polishing method, in the polishing step of polishing the workpiece 50 held in the barrel case 23, the rotation speed n and the revolution speed N are set so that 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". Thereby, when the inner peripheral surface of the hollow portion 52 in the workpiece 50 is centrifugal barrel polished, the variation in surface roughness on the inner peripheral surface can be suppressed.

In the polishing process, the rotation speed n and the revolution speed N are set so that the relative centrifugal acceleration F is in the range defined by "19 < F < 40". This makes it possible to suitably suppress the variation in surface roughness of the inner surface of the hollow portion 52 of the workpiece 50 while suppressing wear of the abrasive M.

In the polishing process, the rotation speed n and the revolution speed N are set so that the rotation speed ratio n/N is in the range defined as "-0.7<n/N<-0.5". This makes it possible to further suppress the variation in the surface roughness of the inner circumferential surface of the hollow portion 52 of the workpiece 50.

The maximum dimension of the abrasive M is one-third or less than the minimum inner dimension of the hollow portion in the workpiece 50. As a result, even if the hollow portion 52 does not extend linearly within the workpiece 50, the abrasive M can be easily distributed throughout the hollow portion 52 as the barrel case 23 rotates, and the variation in the surface roughness of the inner surface of the hollow portion 52 can be suppressed.

In the holding process, an abrasive M having a tap density of 2 g/cm ^or more is poured into the hollow portion 52 of the workpiece 50. As a result, even if the dimensions of the abrasive M are reduced to match the inner dimensions of the hollow portion 52, a decrease in the abrasive power can be suppressed, and the surface roughness of the inner peripheral surface of the hollow portion 52 can be reduced.

<Other embodiments>
Turn to stone.
The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.
In the above-described embodiment, the abrasive M is a ceramic grinding stone in which an abrasive is contained in a ceramic binder. Alternatively, an abrasive M in which the binder, which is the base material, is made of a synthetic resin may be used. Furthermore, the abrasive M is not limited to one in which an abrasive is contained in a binder, but may be one in which only the base material is present, or one in which the surface of the base material is coated with an abrasive. In addition to these, abrasive may be added separately.

In the above-described embodiment, the polishing apparatus 100 rotates and revolves the barrel case 23 by driving the revolution motor 24 and the rotation motor 25. Alternatively, the barrel case 23 may rotate and revolve 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.

100... polishing device, 23... barrel case, 50... workpiece, 52... hollow section, M... polishing material

Claims (4)

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 . The centrifugal barrel polishing method according to claim 1, wherein in the polishing process, 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 defined by 19<F<40. The centrifugal barrel polishing method according to claim 2, wherein in the polishing process, the rotation speed n and the revolution speed N of the barrel case are set to be in the range defined by -0.7<n/N<-0.5. 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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