JPS6254162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for processing machine components made from metal powder.

As a method of processing machine components using metal powder as a raw material, sintered products are hot-pressed using hot isostatic pressure (hereinafter abbreviated as HIP) or hot forging presses, and the remaining material remains inside the sintered product. A method of manufacturing parts with a density close to the true density (density of melted material) by compressing and crimping the pores is already known and is widely used industrially. However, with this conventional processing method, there are limitations on the shape of parts that can be obtained by powder press molding. Machine components are almost impossible to obtain by powder pressing.
In addition, density distribution tends to occur in powder molded products obtained by powder press molding, which causes uneven compression during sintering in the next step, making it impossible to obtain the desired product quality.

Precision casting is also available as a manufacturing method for the above-mentioned complex-shaped mechanical components, but it suffers from poor material yield and
Products are becoming extremely expensive due to high defect rates (defective rates). Furthermore, with the precision casting method, cost reductions due to mass production cannot be expected much, and there is an increasing demand for a manufacturing method that is an alternative to precision casting.

The present invention has been made in view of the above-mentioned needs, and it is an object of the present invention to provide a method for processing mechanical components using metal powder as a raw material, which makes it possible to process mechanical components with complex shapes by molding metal powder by injection molding. With the goal. The structure of the present invention that achieves this object is to add a thermoplastic material and a molding aid to metal powder with an average particle size of 2 μm to 10 μm, mix and knead the mixture while heating, and prepare a raw material for injection molding. An injection molded product as a machine component is obtained by injection molding using a molding raw material, and the thermoplastic material and molding aid contained in this injection molded product are heated to above their melting point and dewaxed under pressure. After dewaxing is completed, the porosity of the powder molded product is suppressed to less than 20%, and then sintered while heating in a vacuum or atmospheric gas, and then hot isostatically pressed to form a high-density product. It is characterized by

Hereinafter, specific examples of the present invention will be described in detail based on the drawings.

As shown in Figure 1, the basic process of the present invention is to add a binder and a molding aid to raw metal powder, mix and knead it, use this as a raw material for injection molding, and produce an injection molded product by injection molding. After dewaxing and further sintering, the product is manufactured through hot isostatic pressing, finishing and inspection processes.

Next, each process will be explained in detail.

As raw metal powder, reduction method, electrolysis method,
Various metal powders obtained by manufacturing methods such as water atomization, gas atomization, vacuum atomization, and rotating consumable electrode methods can be applied, and fine metal powder with an average particle size of about 2 to 10μ is suitable. ing. The raw material for injection molding is made by adding a thermoplastic material such as paraffin wax as a binder (a material added to give fluidity to the metal powder used as the raw material for injection molding) to the raw metal powder mentioned above, and then heating it. While kneading and plasticizing, ethylene acrylate (plasticizer), oil agent (wetting agent), and polyethylene (hardening agent) are added as molding aids, and the mixture is mixed and kneaded for 1 to 3 hours while heating to around 100℃. can be obtained.

There are various types of injection molding machines for molding this injection molding raw material, such as plunger type and in-line screw type, but the model does not matter as long as the injection molding pressure can be up to about 2000 kg/cm ² .

In addition, the design of injection molding molds differs depending on the product to be molded, but important factors include the position, number, and dimensions of the gate and liner, the degassing of the mold, and the position of the ejector pin. Become an element. An example of this mold is shown in FIG.

Dewaxing is a process of melting, burning, and burning away the binder interposed between metal powder particles, which is necessary during injection molding. During this dewaxing process, the binder is usually heated and thermally expanded, so in order to remove this effect, the binder is heated under a gas pressure of 10 to 50 kg/cm ² . The density ratio of the powder compact obtained when this dewaxing is completed is 80%, assuming the density of the ingot material as 100%.
% or more, and therefore a powder compact with a porosity of less than 20% is also desirable from the standpoint of post-processing (see Figure 7).

After dewaxing is completed, sintering is performed, and the sintering is performed in a vacuum or in a gas atmosphere.
Generally, if the porosity is less than 20% at the powder compact stage, by sintering it, a sintered product with a density ratio of 92 to 95% can be obtained, and the remaining porosity will be 5 to 8%. It is thought that all pores are trapped inside the sintered product, except for the pores on the outermost surface of the sintered product, and the next step, hot isostatic pressing (hereinafter referred to as
In the HIP (abbreviated as HIP) process, gas pressure is applied to the surface of the sintered product at high temperatures to compress and compress the pores remaining inside the sintered product, making it possible to obtain parts with close to true density. Incidentally, FIG. 5 shows an outline of the state in which the HIP process is performed in the HIP device. In the figure, 26 is a high pressure vessel, 2
7 is a seal for sealing an inert gas (for example, argon gas) as a pressure medium; 28 is a heat insulating layer;
29 is a heating element, 30 is an arrow explaining how gas pressure acts in a hydrostatic manner, and 31 is a sintered product to be subjected to HIP treatment.

Next, examples will be given to specifically explain the present invention and its effects. The object to be processed is the impeller shown in Fig. 2.

The impeller shown in Fig. 2 includes a blade 1, a shaft hole 2, a boss part 3,
The blade base 4 is made of super heat-resistant alloy (Inconel), and its dimensions are such that the outer diameter of the blade base 4 is approximately
80 mm, the total length of the boss portion 3 is about 60 mm, the ratio l/t of the blade thickness t to the length l, which is a factor governing moldability in injection molding, is about 25, and the number of blades is 6.

The metal powder used was Inconel 713C (nickel-based super heat-resistant alloy) manufactured by a rotating consumable electrode method, with a particle size distribution of 5% by volume of 2μ or less, 92% by volume of 2-10μ, and 3% by volume of 10μ or more.

Next, 18 volume% of paraffin wax as a binder and a total of 2 volume% of ethylene acrylate (plasticizer), oil agent (wetting agent), and polyethylene (hardening agent) as molding aids were added to 80 volume% of the above metal powder, Kneaded for 3 hours while heating to 100℃, once cooled to room temperature and solidified, milled to give an average of 2.
A method was adopted in which millimeter square granules were made and supplied from a hopper as raw material for injection molding. In addition, if the injection molding machine is of a type in which raw materials for injection molding are supplied directly from kneading to the heating cylinder, cooling, solidification,
No particular grinding is required.

An in-line screw type machine was used as the injection molding machine.

The granular raw material supplied to the injection molding machine is heated to approximately 100°C while being pumped through a heating cylinder with a screw, and after being plasticized again, it is injected into a mold through a nozzle and a gate and molded. This injection molded product is indicated by symbol 5 in FIG. Furthermore, Figure 4 shows the injection mold used in this example.
10 is an injection molded product in the mold, 11 is a runner, 12
is a gate between the runner and the injection molded product, 13 is a movable plate, 14 is a cooling water hole for mold cooling, 15 is a movable mold, 16 is a fixed mold, 17 is an ejector, 18
is the main ram, 19 is the movable plate, 20 is the sprue-use,
21 is a nozzle, 22 is a heating cylinder, 23 is a band heater, and 24 is a plasticized raw material. Also,
FIG. 4b is a front view of the runner 11, with one runner for each wing, as indicated by the broken line on the wing 1.

In addition, if the injection molding pressure is not sufficient for a part having a thin and long part such as the blade 1 of the impeller in this embodiment,
A phenomenon in which the material does not completely fill up to the tip of the blade (short shot) is likely to occur, and the ratio l/t between the thickness t and the length l is often used as a measure of formability. /t=25. As shown in Figure 6, which shows the results of a separate experiment, the horizontal axis represents the metal powder volume ratio in the raw material for injection molding, and the vertical axis represents the appropriate injection molding pressure.
This shows the injection molding pressure necessary to obtain a molded product that is completely filled with material up to the blade tip without any shot, and with the metal powder volume ratio of 80% in this example, 2000 kg/cm ² is appropriate. It can be seen that this is the injection molding pressure. In Figure 6, the curve shows an upward trend to the right because as the metal powder volume ratio increases, the binder volume ratio decreases, the viscosity increases, and fluidity decreases, which requires high injection molding pressure. It is. In this example, the metal powder volume ratio is 80
%, we found that 2000 kg/cm ² was the appropriate injection molding pressure and set the molding conditions.

Next, this injection molded product 5 is dewaxed. Dewaxing is a process in which 20% by volume of the binder and molding aids contained in the injection molded product are melted and burned out. Since paraffin wax thermally expands when heated, the test was performed while applying gas pressure of 10 to 50 kg/cm ² and heating to 400 to 500°C. The powder compact after this dewaxing is indicated by symbol 6 in FIG.
In this powder compact 6, pores are formed at the binder and the forming aid, so the porosity thereof is about 20%.

The powder compact 6 that has been dewaxed is sintered.
Sintering was carried out in vacuum at 1260° C. for 2 hours, and the density ratio of the powder compact 6 could be reduced from 80% to about 92% after sintering.

After this dewaxing, the relationship between the density ratio of the powder compact before sintering and the density ratio of the sintered product was investigated by experiment, and this is shown in FIG. The horizontal axis of FIG. 7 shows the density of the powder compact after dewaxing and before sintering, and the vertical axis shows the density ratio of the sintered product. Note that the hatched area in the figure indicates the range where the density ratio of the sintered product is less than 92%, where the pores are not trapped inside and the HIP treatment cannot be performed. As is clear from the figure, the density ratio of the sintered product in this example is 92%, and HIP treatment in the next step is possible. Further, this sintered product is indicated by symbol 7 in FIG. In order to obtain a sintered product with a high density ratio, high injection molding pressure is required, but this is limited by the structure of the injection mold, the capacity and capacity of the injection molding machine, etc. .

Next, this sintered product 7 was subjected to HIP treatment. As a result, the density ratio was improved to about 97%, which was extremely close to the true density.

FIG. 8 shows the HIP processing conditions set in this example. In the figure, the horizontal axis shows elapsed time, and the vertical axis shows set pressure (2000Kg/cm ² ) and set temperature (1200℃), and the set pressure and temperature are maintained within a certain range (horizontal line in the figure). range.

Here, the average particle size of the raw metal powder is set to 2 μm or more.
The reason for setting the thickness to 10 μm will be explained. If the particle size of the raw metal powder exceeds 10 μm, the raw material for injection molding produced by heating and kneading with the thermoplastic material will have poor viscosity and will become unsuitable for injection molding. On the other hand, it is possible to give the raw material for injection molding a predetermined viscosity by increasing the ratio by increasing the amount of thermoplastic material, but on the other hand, this is less than the lower limit of the metal powder volume ratio (see Figures 6 and 7). 80 at
The point indicated as %) is divided. As a result, the density ratio of the powder compact before sintering becomes low, and the density ratio of the sintered product does not reach 92%, which is possible for HIP, and the present application is not valid. In other words, although it depends on how the thermoplastic material is selected, the average particle size of the raw metal powder is 10μ.
If it exceeds m, it becomes difficult to use it as a raw material powder for injection molding.

Next, another example in which the binder added to the raw metal powder is changed will be described.

Polyethylene was used as the binder, and other raw material metal powders and the like were the same as in the previous example.
Furthermore, although the steps are the same, the temperature and pressure conditions are different.

Since polyethylene was used as the binder, the plasticization temperature during kneading and injection molding was slightly higher than that of paraffin wax, around 120℃, and the injection molding pressure was high due to the high viscosity and poor fluidity during plasticization.
It was necessary to reduce the weight to ^around 2700Kg/cm2. Furthermore, the relationship between the density ratio of the sintered product and the density ratio of the powder compact after dewaxing and before sintering is almost the same as in the case of paraffin wax shown in Fig. A necessary condition for HIP treatment is to have a density ratio of 80% or more. Therefore, the injection molding pressure was set to 2700Kg/ ^cm2 , and the dewaxing was performed by applying a gas pressure of about 50Kg/ ^cm2 to 700~700Kg/cm2.
It was heated to 800℃ to melt, burn, and burn out the polyethylene. Other conditions were the same as in the previous example, and the density ratio after HIP treatment was improved to 97%, which was extremely close to the true density.

The strength of the two examples of impellers thus obtained was investigated. In general, the impact strength of powder sintered parts is greatly influenced by its porosity, and in this example, the impact strength ratio was approximately 25% (approximately 1/of the strength of the ingot material) at the stage of the sintered product before HIP treatment. 4), but by applying HIP treatment, the density ratio of the sintered product can be improved to 97%, which also increases the impact strength ratio.
This was a significant improvement of 60%. The results are shown in FIG. The figure shows the relationship between the impact strength ratio of the sintered product and the density ratio of the sintered product, when the impact strength of the ingot material is taken as 100%. In addition, in the same figure, the shaded area is
Indicates the range where HIP processing is not possible.

Further, it was confirmed that the impeller manufactured in this example exhibited performance that sufficiently satisfied the specifications in a hot spin test, and it was confirmed that it could be sufficiently put to practical use.

As explained above in detail along with the examples, according to the method of the present invention, even if the machine component part has a complicated shape, it can be molded by injection molding to produce a uniform product with no density distribution, and the final It was confirmed that the obtained product had almost the same strength as the melted product. Furthermore, mass production becomes possible, contributing to cost reduction.

[Brief explanation of the drawing]

Fig. 1 is a process explanatory diagram of the processing method of the present invention, Fig. 2 is a perspective view of a blade wheel which is an example of the target product of the processing method of the present invention, Fig. 3 is a cross-sectional view of the molded product during each process, Fourth
Figures a and b show the injection mold used in the example, where a is a longitudinal sectional view, b is a front view of the runner, and the fifth
The figure is an explanatory diagram of the HIP process, Figure 6 is a graph showing the relationship between the metal powder volume ratio in the injection molding raw material and the injection molding pressure, and Figure 7 is the graph showing the relationship between the density ratio of the powder compact after dewaxing and before sintering. A graph showing the relationship between the density ratio of the sintered product, Figure 8 is a graph showing the HIP processing conditions set in this example, and Figure 9 is when the density ratio of the sintered product and the strength of the ingot material are taken as 100%. It is a graph showing the relationship between impact strength ratio and impact strength ratio. In the drawing, 1 is a blade wheel, 2 is a shaft hole, 3 is a boss part, 4
is a wing base, 5 is an injection molded product, 6 is a powder molded product, 7
10 is a sintered product, 10 is an injection molded product in the mold, 11 is a runner, 12 is a gate between the runner and the injection molded product, 13 is a movable plate, 14 is a cooling water hole for cooling the mold, 15 is a Movable mold, 16 is a fixed mold, 17 is an ejector, 18 is a main ram, 19 is a movable plate, 20 is a sprue, 21 is a nozzle, 22 is a heating cylinder, 23 is a band heater, 24 is a plasticized raw material, 26 is a high-pressure container, 27 is a seal for inert gas as a pressure medium, 28 is a heat insulating layer, 29 is a heating element,
30 is an arrow explaining how gas pressure acts hydrostatically, 31 is a sintered product to be subjected to HIP treatment, l is the length of the blade, and t is the thickness of the blade.

Claims (1)

[Claims] 1 Add a thermoplastic material and a molding aid to metal powder with an average particle size of 2 μm to 10 μm, mix and knead while heating to obtain a raw material for injection molding, and use this raw material for injection molding to create a machine. An injection molded product as a component is obtained, and the thermoplastic material and molding aid contained in this injection molded product are dewaxed by heating the thermoplastic material and molding aid above their melting point and applying pressure, and a powder molded product is obtained when dewaxing is completed. The raw material is metal powder, which is characterized by suppressing the porosity to less than 20%, sintering it while heating in vacuum or atmospheric gas, and then hot isostatically pressing it into a high-density product. Processing method for machine components.