JPS6139361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to powder metallurgy technology when compressing products such as gears that require high concentric precision.
This invention relates to a method for adjusting the non-uniformity (denseness) of filling that occurs when filling a mold cavity with powder.

When compression molding metal powder using a mold, the method of filling the metal powder into the mold is to pass the powder from the hopper into the powder box through the powder supply hose, and then pour the powder onto the mold cavity to be filled. Often used are the powder drop method, in which the cavity is filled by shaking the box, or the powder suction method, in which the powder box is placed on a mold, and the mold is pulled down to create a space for filling, and at the same time, the powder is filled. It will be done. In either method, after filling the powder, excess powder remaining on top of the filled powder is removed and weighed by returning the powder box to its original position.

If the powder is filled unevenly during this powder filling process, it will adversely affect the properties of the sintered body, especially the dimensional accuracy, in the subsequent compression and sintering processes. Therefore, it is important to uniformly fill the powder into the mold.

Various methods have been developed in the past to uniformly fill powder into the cavity of a mold, such as installing partition plates of various shapes in the powder box, moving the partition plate, and moving the powder box. Various improvements have been made, such as controlling the speed and grinding the powder after filling, but all of these have problems such as the amount of filling changing when the powder box is shaken or moved back and forth, and the need for sufficient powder. Because it was not possible to replenish the amount, it was not possible to accurately supply the required amount to the required location, and in the end, modifications such as machining were required to manufacture products with high concentric precision.

The present invention provides a powder filling method that makes it possible to uniformly fill a powder in the circumferential direction when filling a mold with powder, thereby obtaining a molded body with high concentricity accuracy.

That is, in the filling method of the present invention, when a powder filling device is used to fill a mold with powder and form a circular powder compact, a powder shortage area in the obtained compact is detected in advance, and the powder is After filling the mold, use a powder filling adjustment device to place the insufficient amount of powder on one or more places on the filling powder of the mold, or
Press a spot or two or more powder-deficient spots with a rod of a predetermined thickness to create a recess on the filled powder surface, and fill the recess with additional powder to spread the powder in the circumferential direction of the green compact. This method is characterized by replenishing the powder so as to eliminate unevenness in the amount of filling.

The apparatus used in the filling method of the present invention will be explained using figures while comparing it with a conventional apparatus.

In general, as shown in FIG. 1, a molding powder is filled into a mold and compression molding is performed. powder box 5
The powder 4 in the cavity is filled by pressing the powder 4 inside the cavity by lowering the upper punch 6. Powder filling is carried out by placing the powder box 5 between guide rails provided on the upper end reference surface of the die 1b and moving the powder box 5 onto the cavity. A hopper 9 is connected to the powder box 5 via a flexible hose 10, and the inside of the box is filled with powder. The powder box 5 is first moved to the left in the figure by the operation of the hydraulic cylinder 8, and is carried to the cavity portion of the die 1b. Once the powder 4 is filled in the area, the cylinder 8 is operated to return it to the position shown, but at this time, the left end of the powder box 5 scrapes off the filled powder. In the figure, 11 represents a guide bar, 12 represents a punch holder, and 13 represents a piston rod.

However, in the above-described conventional configuration device, the powder is often not filled uniformly, and the resulting green compact has poor concentricity between the inner and outer diameters,
The perpendicularity of the end face with respect to the inner diameter or outer diameter was distorted.

In order to eliminate the above drawbacks, conventionally, for example, a second
As shown in the figure, there is a cylindrical partition plate 1 inside the powder box 5.
4 is provided, and the height of the powder 4 filled in this partition plate 14 is made higher than the height of the powder 4' outside of it, so that the weight of powder filled under each is different, and In this method, the inner ring-shaped partition plate 14 is moved in accordance with the desired position to uniformly fill powder into a desired position within the cavity.
Additionally, although not shown in the figure, the amount of powder filled at the front and back positions of the powder box is often different during sanding, and countermeasures such as attaching rubber to the front and back of the powder box to change the amount of sanding are taken. However, none of these measures fundamentally solved the drawback of poor concentricity accuracy.

As a result of various studies on circular compacted powder bodies, the present inventors found that there is a certain correlation in the deflection of the compact. In other words, if powder is added little by little in one direction around the circumference of a circular molded body of a fixed shape, the concentricity error will increase according to the amount of artificially added powder, and this will depend on which direction of the circumference the powder is added. A similar correlation can be seen. For example, when a hollow cylindrical body with an inner diameter of 30 mmφ, an outer diameter of 70 mm, and a weight of 500 g is used as a molded product, the resulting molded product has the following properties:
As shown in Figure 3, the deflection in each direction when 10g of weight is added to ○A is on the line shown by the solid line in the figure,
The deflection portion weighing 5 g is on the line shown by the broken line. Therefore, by adding an appropriate amount of powder to a position opposite to the direction of the deflection, or removing an appropriate amount of powder from a position in the direction of the deflection, the conventional problem of uneven powder filling can be satisfactorily solved.

The powder filling adjustment device used in the present invention is, for example, the powder filling device shown in FIG. An example of the structure of the powder adding device is shown in FIGS. 4A and 4B. As shown in the figure, a sub-hopper 18 to which a hose 17 for supplying powder from the hopper is connected is provided at the top of the powder addition box 15, and a shutter 19 is interposed between the addition box 15 and the sub-hopper 18. The powder addition box 15 is provided with a spacer 20 for adjusting the volume of the powder addition box, and the amount of powder to be added is determined by adjusting the spacer 20. On the other hand, a sub-hopper 18 is connected to the upper part of the powder addition box 15 via a shutter 19, and the powder is transferred from the hopper 18 to the addition box 15.
It is supplied falling to. Powder flows into the powder addition box 15 from the sub-hopper 18 at the return position (the state shown in the figure), and the structure is such that powder does not flow out from the sub-hopper 18 when the addition box 15 is moved by the operation of the cylinder 16. Further, a lid 21 is provided at the lower end of the additional box 15, and the lid 21 is resiliently supported by a spring 22 whose one end is fixed to the piston rod 16'. A rod 23 separately attached to the lid 21 contacts the stopper 24, overcomes the force of the spring 22, and opens the lid 21.

The stroke and moving direction of the cylinder 16 can be set freely, and the cylinder 16 is fixed to a die holder.

A powder filling adjustment device having the above configuration is provided above the die 1 in a route separate from the powder box 5, and the deflection of the obtained green compact is detected in advance, and the adjustment device is moved according to the deflection, Further, the amount of additional powder is adjusted using the spacer 20, and the optimum amount of powder for the amount of flaring is added to the minimum portion of flaring. In this case, the added powder is in a state of being raised from the upper end surface of the die of the mold, but it is press-molded as it is to obtain a green compact.

Next, an example of another apparatus used in the present invention is shown in FIG. In this example, in the powder filling apparatus having the structure shown in FIG. This is how it was done. The powder filling adjustment device is approximately the same size as the powder box 5, and has adjusting press pins 28, 28 attached therein, and after the powder is filled into the cavity by the powder box 5, it is moved onto the cavity. However, the pressing pins 28, 28 are lowered to locally press the powder in the cavity. After forming a recess in the filling powder in the cavity in this way, the powder box 5 is again pulled to the right in the figure and moved onto the cavity, so that the recess is filled with the powder to be replenished. If the powder box is further pulled to the right, it returns to its original position while stopping at the left end of the powder box 5, completing one cycle of powder filling.

In addition, in the adjustment device, the pressing pins 28, 28 are attached to the pressing board 29, and the pressing pins 28, 28 are attached to the pressing board 29.
When the cam base connected to 9 is pressed downward, it also descends. There are various methods of pressing the cam base 27 downward, but in the example shown in the figure, the upper surface of the cam base 27 is made into a slope, and the cam 26 having a corresponding slope is pushed out from the horizontal direction by the cylinder 31. I'm going. Note that when the spring 32 is not pressed, the pins 28 and 2
This is to make it appear that 8 is floating.

In the above example, the number of pins is two, but the number of pins is not limited to this. The run-out correlation diagram of the powder compact is detected in advance, and the location where the supply of powder is insufficient is proportional to the amount of shortage. An appropriate number of pins may be provided to make the holes, and by adjusting the pin thickness, pin position, and downward stroke, an appropriate amount of powder can be added to the desired position.

During mass production, the sintered body obtained by powder filling using the above device had a concentricity error of 0.05 TIR compared to 0.1 TIR of the sintered body obtained using the conventional device.

As is clear from the above description, according to the method of the present invention, a product with high concentric precision can be obtained by eliminating the density of packed powder in the circumferential direction. It is possible to correct small amounts of non-uniformity in the filling powder, which cannot be adjusted using existing filling equipment, in a cycle time that is almost the same as with conventional methods, and it is possible to easily improve the concentricity accuracy of the product. Furthermore, depending on the shape of the product, it may be necessary to split the punch, or if an unbalance in the density of the compact is unavoidable, powder can be forcibly added to the necessary areas, resulting in good compaction. The present invention has various advantages, such as the ability to obtain a healthy body.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an example of a conventional powder filling device, Fig. 2A is a cross-sectional view of a powder box having a ring-shaped partition plate, B is a longitudinal sectional view thereof, and Fig. 3 is a cross-sectional view of a powder box having a ring-shaped partition plate. FIG. 4A is a vertical cross-sectional view showing an example of a device according to the method of the present invention, FIG. 4B is a top view thereof, and FIG. 5 is a vertical cross-sectional view showing another example of a device according to the method of the present invention. In the figure, 1...Die, 2...Lower punch, 3...Core, 4
...Powder, 5...Powder box, 6...Upper punch, 8...Cylinder, 9...Hopper, 15...Powder addition box, 18...Sub hopper, 26...Cam, 27...Cam base, 2
8...represents a pressure pin.

Claims (1)

[Claims] 1 Fill the mold with powder using a powder filling device,
In the method of forming a circular powder compact, the powder-deficient spots in the resulting compact are detected in advance, and after the powder is filled into the mold with the powder filling device, the powder is filled with the powder using the powder filling adjustment device. Place the insufficient amount of powder on one or more places of the filling powder of the mold, or press the one or more places where the powder is insufficient with a rod of a predetermined thickness to the filling powder surface. Make a recess,
A powder filling method characterized by further filling the recess with powder so as to eliminate non-uniformity in the amount of powder filling in the circumferential direction of the green compact.