KR20040078812A - Manufacturing method of cemented carbide cutting tool inserts by powder injection molding - Google Patents

Abstract

PURPOSE: A manufacturing method of cemented carbide cutting tool inserts by powder injection molding is provided to greatly reduce manufacturing cost by simplifying process compared with an existing powder metallurgy process when manufacturing WC-Co based cemented carbide inserts by powder injection molding. CONSTITUTION: The method comprises a process of preparing a feed stock for injection by mixing raw material powder consisted of cemented carbide, cobalt and added compounds including TaC, TiC and Cr3C2 with polymer binder; a process of obtaining powder compact by injecting the feed stock into dies at high pressure; a process of removing the polymer binder from the obtained powder compact by solvent extraction and pyrolysis; and a process of sintering the debinded compact under the vacuum state, wherein the raw material powder is in the average particle diameter range of 0.5 to 5 μm, wherein a filling ratio of raw material powder to the polymer binder is 45 to 57 vol.%, wherein temperature of solvent is 30 to 35 deg.C, and extraction time is 6 hours or more during the solvent extraction process, wherein the manufacturing method further comprises a process of drying the compact powder impregnated with ethyl alcohol in the atmosphere after dipping the compact powder into ethyl alcohol for 30 minutes or more after the solvent extraction process, wherein the pyrolysis process is performed at an atmosphere of a mixed gas containing 30 to 70 vol.% of hydrogen and nitrogen gas in the temperature range of 400 to 500 deg.C, and wherein the sintering process is performed at temperature of 1,380 to 1,480 deg.C in the vacuum degree range of 10¬-1 to 10¬-2 torr.

Description

Manufacturing method of cemented carbide cutting tool inserts by powder injection molding}

The present invention relates to a method for producing a cemented carbide cutting tool insert by a powder injection molding method and to providing an improved method for manufacturing an insert as a cutting tool.

According to the present invention, when the cemented carbide insert (WC-Co-based), which is widely used as a cutting tool, has high drag force, hardness, and abrasion resistance at a high temperature, is manufactured by powder injection molding. It is related with the manufacturing method of the carbide cutting tool insert which can simplify the manufacturing cost and greatly reduce the manufacturing cost.

The insert of the carbide cutting tool (WC-Co), which is widely used as a cutting tool because of its excellent mechanical properties both at home and abroad, is a representative hard-working material. To date, powder metallurgy (P / M) technology It has been known as a product that can be manufactured only by.

However, the conventional manufacturing method by powder metallurgy not only has the disadvantage of producing a product having a relatively simple shape since the molding operation to form the product is simply performed by uniaxial press.

Before and after making the final sintered product, machining of roughing, grinding, turning, etc., 3-4 steps must be performed 5-7 times, resulting in a large increase in manufacturing cost due to excessive material and processing costs.

On the other hand, the recent powder injection molding technology can produce large quantities of complex and precise three-dimensional parts in real shape with little post-processing, which can greatly reduce manufacturing costs, especially cemented carbide, titanium, and polymer alloys. It is attracting much attention as a new manufacturing technology for hard-working precision parts.

In general, the powder injection molding process is a process for preparing a mixture of a fine powder (average particle diameter of 20 µm or less) and a polymer binder (mainly a thermoplastic binder) and an injection molding process for injection molding a mixture into a mold mounted on an injection molding machine. and,

It consists of a binder removal process for removing the binder from the injection molded product and a process for sintering the degreasing body at a high temperature to obtain desired physical properties and dimensions.

However, existing powder injection molding related patents are related to the manufacturing method of iron-based and stainless parts (Korean Patent 345877, Republic of Korea Patent Publication 0042176), or simply to adjust the components of the binder to improve the strength and injection properties of the injection molding Most of the methods (Korean Patents 149240, 216874, 361741, etc.) are hardly found, and examples of directly manufacturing carbide cutting tool inserts using powder injection molding are difficult to find.

This is because the particles of the powder used in the manufacture of cemented carbide tools are much finer than the powder particles (average particle diameter of 20 μm or less) used in the manufacturing method of the above iron and stainless steel products (average particle diameter of 0.5-5 μm), The main difficulty is the technical difficulty of the manufacturing method due to the very high physical properties such as the force of bending, hardness, compressive strength.

The present invention has been made in view of the above-mentioned conventional problems, and the object thereof is to apply a powder injection molding technique, a degreasing and decarburization technique, and a sintering technique to significantly reduce the processing cost when manufacturing the actual shape of the carbide cutting tool insert which is a representative hard workable material. By providing a method that can be produced at low cost.

1 is a table showing the solvent extraction rate and the appearance change of the molded body according to the solvent extraction conditions and the air drying method when the solvent is extracted with hexane as the powder injection molding,

FIG. 2 is a graph showing changes in the carbon content of the degreasing body and the presence of a harmful phase after sintering according to the gas atmosphere change in the furnace during pyrolysis degreasing and presintering of the powder injection molding;

Figure 3 is a table comparing the physical properties of the insert prepared according to the method of manufacturing a cemented carbide cutting tool insert by the powder injection molding method of the present invention and the insert prepared by the conventional powder metallurgy method,

Figure 4 is a graph showing the density change of the mixture according to the filling rate in the manufacturing method of the carbide cutting tool insert by the powder injection molding method of the present invention,

Figure 5a is a photograph of the appearance of the carbide cutting tool insert injection molded by the powder injection molding method,

Figure 5b is a photograph showing the appearance of the molded body when not immersed in alcohol during air drying after solvent extraction of the injection molded product,

Figure 5c is a photograph showing the appearance of the degreasing body completely removed the binder by the solvent extraction process and pyrolysis method,

Figure 5d is a photograph showing the appearance of the carbide cutting tool insert after the final sintering process.

In the present invention, a feed stock for injection is prepared by mixing a raw material powder composed of cemented carbide (WC) powder, cobalt powder and, if necessary, an additive compound (TaC, TiC Cr ₃ C _2, etc.) with a polymer binder,

The present invention provides a method for producing a cemented carbide cutting insert comprising forming the feedstock by high-pressure injection molding into a mold, removing the polymer binder from the obtained molded body by using solvent extraction and pyrolysis, and vacuum-sintering the obtained degreasing body at a high temperature.

Here, the raw material powder is characterized by using a purity of 99.9% or more and an average particle diameter of 5㎛ or less in order to impart physical properties as a cutting tool.

In addition, when the raw material powder is composed only of cemented carbide and cobalt, the use of the cutting tool is preferable to cut cast iron, nonferrous alloy, stainless steel (200-300 series) discontinuously, and the raw powder is cemented carbide. And when 0.5-10 wt.% Of a compound (at least one compound of TaC, TiC, Cr ₃ C ₂ ) is added to the cobalt powder, the cutting tool is mostly used for carbon steel, alloy steel, stainless steel (400-500 series), and the like. It is desirable for cutting continuously.

The additive compound has an effect of increasing machinability and tool life through grain refinement and suppression of thermal deformation.

In addition, the feedstock filling rate compared to the binder in the production of the feedstock is 45-57vol% and solvent extraction is carried out for 6 hours at 30-35 ℃ by immersing the injection body in the hexane solution 90% paraffin wax and stearic acid in the binder Remove it.

This removal of the binder upon thermal decomposition, the gas to be used for the strict control of carbon content is characterized by using a compound gas of nitrogen gas (containing 30-70% by volume) of hydrogen gas, and the vacuum degree of vacuum sintering is 10 ^- It is preferable to perform about 60-120 minutes in the range of ¹ -10 ^-2 torr and the temperature of 1380-1480 degreeC.

Specific manufacturing processes and features of the method of manufacturing the carbide cutting tool insert by the powder injection molding method of the present invention together with the accompanying drawings will be described in detail with reference to the following examples.

1 is a diagram showing the solvent extraction rate and the appearance change of the molded body according to the solvent extraction conditions and the air drying method when the solvent is extracted with hexane as a solvent, Figure 2 is a thermal decomposition degreasing and pre-sintering process of the powder injection molding Table showing the change in carbon content of the degreasing body and the presence of a harmful phase after sintering according to the change in the gas atmosphere in the furnace, FIG. 3 is an insert manufactured according to the method for producing a cemented carbide cutting tool insert by the powder injection molding method of the present invention. 4 is a graph comparing the physical properties of inserts prepared by conventional powder metallurgy, FIG. 4 is a graph showing the density change of the mixture according to the filling rate in the method of preparing the carbide cutting tool insert by the powder injection molding method of the present invention. 5a is a photograph of the appearance of the carbide cutting tool insert injection molded by the powder injection molding method, Figure 5b is the atmosphere after extraction of the solvent of the injection molding Figure 5c is a picture showing the appearance of the molded body when not immersed in alcohol during drying, Figure 5c is a picture showing the appearance of the degreasing body completely removed the binder by the solvent extraction process and pyrolysis method, Figure 5d is a carbide cutting after the final sintering process Photo shows the appearance of the tool insert.

Example 1

First, for powder injection molding, cemented carbide powder having a purity of 99.9% or more with an average particle diameter of 0.8 μm, 91wt.% And an average particle diameter of 3 μm, and 6wt% and 3wt% of the cobalt powder and TaC powder of the above purity, ) And 50 wt% of each was mixed with nitrogen and ball milled for 48 hours.

The injection powder is mixed by mixing a polymer binder such as paraffin wax, polyethylene, stearic acid, and the like in the mixed powder for 1 hour at 140-180 ° C. in a pressure kneader, That is, a feed stock (Feed stock) was prepared.

In this feedstock, the volume ratio (powder loading: solid loading) of the raw material powder to the binder was 45-57 vol.%. The reason for limiting the filling rate of the powder is that if the filling rate is lower than 45%, the amount of the binder is excessive and separation of the raw material powder and the binder occurs during injection molding, and stress is concentrated in the injection molding to degrease and sinter. It is very likely that a defect will occur in the process.

On the other hand, when the powder filling rate exceeds 57%, the injection molding itself is difficult due to the lack of fluidity of the mixture, and even if the injection molding is performed, the amount of the binder is insufficient. .

Figure 4 compares the measured density change of the mixture according to the powder filling rate compared to the binder of the mixture with the theoretical density value.

The density of the mixture was calculated by measuring the volume and weight of the molded body obtained by manufacturing a rectangular specimen of 5.0x5x45mm (TxWxL) size in the powder filling rate range.

As shown in FIG. 4, as the powder filling rate increases, the density value of the mixture increases in a tendency almost the same as the theoretical density, and the density value of the mixture rapidly decreases based on 57%.

The closer the density value of the measured mixture is to the theoretical density value, the better the ejectability and the less porosity and defects in the injection molding. Therefore, the powder filling rate in the present invention is 45-57vol.% Is appropriate, more preferably 50-55vol.%.

Example 2

Insert injection molded product of a healthy appearance as shown in Figure 5a by injecting the feedstock prepared by the above method in the injection mold of the mold temperature 30-40 degrees ℃, injection pressure 60-100bar, injection time 2-10sec Was prepared.

The molded product was immersed in a hexane solution and subjected to solvent extraction at 30-35 ° C. for at least 6 hours to remove more than 90% of paraffin wax and stearic acid in the binder.

Table 1 shows the solvent extraction rate and the appearance change of the molded body according to the solvent extraction conditions and the air drying method when the solvent is extracted using the hexane as the solvent.

Here, the solvent extraction rate (%) means the percentage of the binder weight dissolved in hexane when the weight of paraffin wax and stearic acid added as a binder is 100.

And, the reason for limiting the solvent extraction conditions as described above is that when the temperature of the hexane used as the solvent, as shown in the table of Figure 1 is more than 35 ℃ binder removal reaction rate before the appropriate extraction passage is formed inside the injection molding It is so fast that stress concentrates inside the injection molding causing cracks.

In addition, if the solvent temperature is lower than 30 ℃ cracks do not occur, but the process cost increases because it takes a long time to extract the solvent. Therefore, the solvent extraction of the injection molded body is most preferably carried out for 6 hours or more at a hexane solution temperature of 30-35 ℃.

In addition, in the case of extracting the binder at a faster time (relative to alcohol or thinner) using hexane as a solvent, as shown in the table of FIG. After immersion in ethyl alcohol for 30 minutes or more to dilute hexane remaining in and outside the molded body with ethyl alcohol, air drying is performed to prevent cracking inside and outside the molded body.

If the molded product, which has no solvent extraction, is dried in the air without being immersed in ethyl alcohol, the hexane remaining in the inside and the outside of the molded product is rapidly vaporized and volatilized. It is not possible to obtain a good solvent extraction molded body to cause cracks.

Example 3

Pyrolysis of a small amount of paraffin wax, stearic acid, and main binder polyethylene in a solvent-extracted molded body using hydrogen (containing 30-70 vol.%) + Nitrogen complex gas at 400-500 ° C. for 4-6 hours It was completely removed by thermal decomposition, and pre-sintering (900 ° C., 2 hours) was performed simultaneously, which gave some rigidity for easy handling of the degreasing body (molded body in which the binder was completely removed).

5C is a photograph showing the sound appearance of the insert after pyrolysis degreasing and presintering as described above.

As described above, the reason for limiting the content of hydrogen gas in the composite gas is that strict carbon within ± 0.05 wt% of the theoretical carbon amount (5.76 wt% in the embodiment) of the initial raw material powder during pyrolysis degreasing and presintering. For carbon control.

For example, when carbonization occurs in the degreasing body during pyrolysis degreasing and presintering, free carbon, which is a harmful phase, is generated in the product during the subsequent sintering process.

On the contrary, when decarburization occurs, carbon is deficient, which causes undesirable η (W ₃ Co ₃ C) phase, which causes fatal deterioration of product properties and lifespan.

Therefore, the change of carbon content of the degreasing body and the presence of the harmful phase after sintering according to the gas atmosphere change in the furnace during pyrolysis degreasing and presintering were investigated and the results are shown as a table of FIG. 2.

When pure nitrogen is used during pyrolysis degreasing as shown in the table of FIG. 2, about 0.5 wt% or more of the carbon is generated in the degreasing body, and when sintered, a large amount of free carbon is generated in the sintered body, and thus the density of the sintered body is increased. It can be seen that the theoretical density (14.92 g / cm ³ ) is significantly lower.

When pure nitrogen is used, the reason for the carbonization is that the hydrocarbon group (C-H), the main component of the binder, remains incompletely decomposed and vaporized.

On the contrary, when only hydrogen gas is used, not only carbon in the binder is removed, but also carbon in the raw material powder itself decarburizes to produce η (W ₃ Co ₃ C) phase, which is a sintered oil phase, and thus does not reach theoretical density.

Since cemented carbide is basically liquid phase sintered, the density of sintered body should be at least 99% of theoretical density to ensure the required mechanical properties and lifespan. In this case, carbon control becomes impossible and a product of good physical properties cannot be obtained.

However, the use of hydrogen-nitrogen composite gas containing 30-70 vol.% Of hydrogen gas not only enables strict carbon control of ± 0.03 wt.% Or less, but also produces no sintered body after sintering. You can do it.

Therefore, in the present invention, the pyrolysis degreasing and presintering of the molded body is carried out using a hydrogen + nitrogen composite gas containing 30-70 vol.% Of hydrogen gas (more preferably 40-60 vol.% Of hydrogen gas) for strict carbon control. It is characterized by using.

Example 4

Sintering treatment was finally performed to give strength and rigidity to the degreasing body prepared as in Examples 1, 2 and 3 above.

Sintering was performed at 1380-1480 ° C. for 60-120 minutes in the range of vacuum degree of 10 ⁻¹ −10 ⁻² torr. The reason for limiting the sintering conditions as described above is that when the degree of vacuum becomes less than 10 ^-2 torr during sintering, it is difficult to maintain the shape due to severe oxidation reaction of the degreasing body.

In addition, since the cobalt in the cemented carbide is evaporated when the vacuum degree is 10 ^-2 torr or more, a good sintered body cannot be obtained due to the change in the alloy composition.

In addition, when the temperature is high and the sintering time is long, oversintering and grain growth occur, thereby deteriorating physical properties. Figure 5d shows the sound appearance of the final insert after the sintering process as described above.

Table 3 compares the properties of the insert prepared according to the present invention and the insert prepared by the conventional powder metallurgy method.

The tensile test was performed separately from the test specimen. The test specimen was ASTM B406-76 standard, 5.0x6.25x19mm (TxWxL).

As shown in the table above, the physical properties of the inserts manufactured by the powder injection molding method have at least the same physical properties as those of the products manufactured by the conventional powder metallurgy method (ASM metals handbook, 9th ed. Vol. 7, 782p). Can be seen.

In addition, as a result of measuring the dimensions of the main parts (4.3 mm ± 0.05) and the center circle (4.1 φ ± 0.05 mm), which are the main parts of the insert product manufactured by the present invention, all the tolerances within the required tolerance ± 0.05 mm were satisfied. So basically does not require post-processing,

If necessary, the cutting edge and thickness of the insert can be finished once within the tolerance range, thereby improving surface roughness and controlling the size more precisely.

The production method of cemented carbide cutting tool insert according to the powder injection molding method of the present invention having the above configuration can not only manufacture cemented carbide cutting tool insert of high function and precision shape at a lower price than the conventional powder metallurgy process, but also There is a desirable effect that can be used to produce solid shapes of workable precision parts.

Claims (7)

Raw material powder consisting of cemented carbide, cobalt, and additive compounds (TaC, TiC Cr ₃ C _2, etc.) is mixed with a polymer binder to prepare feedstock for injection; High pressure injection of the feedstock into a mold to obtain a molded body; Removing the polymer binder from the obtained molded body by solvent extraction and pyrolysis; A method of manufacturing a cemented carbide cutting tool (WC-Co-based) insert by a powder injection molding method comprising the step of vacuum sintering the obtained degreasing body. The method of claim 1, Carbide cutting tool (WC-Co-based) insert manufacturing method according to the powder injection molding method characterized in that the average particle diameter of the raw material powder is within the range of 0.5-5 ㎛. The method of claim 1, A method for producing a cemented carbide cutting insert by a powder injection molding method characterized in that the filling ratio of the raw material powder is 45-57 vol.% Relative to the polymer binder. The method of claim 1, In the solvent extraction step, the temperature of the solvent 30-35 ℃, extraction time is 6 hours or more method for producing a cemented carbide cutting insert by the injection molding method. The method of claim 1, Method for producing a cemented carbide cutting insert according to the powder injection molding method characterized in that after the solvent extraction step, the molded product is immersed in ethyl alcohol for 30 minutes or more to air. The method of claim 1, The pyrolysis process is a method of producing a cemented carbide cutting insert by a powder injection molding method characterized in that the use of an atmosphere of hydrogen + nitrogen composite gas containing 30 to 70 vol.% Hydrogen in the pyrolysis temperature range 400-500 ℃. The method of claim 1, The sintering process is a method of producing a cemented carbide cutting tool insert by powder injection molding, characterized in that the sintering at a sintering temperature of 1380-1480 ℃ in the range of vacuum degree 10 ^-1 -10 ^-2 torr.