JP3785015B2 - Mold lubrication method in hot forging of sintered alloys. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold lubrication method for hot forging a sintered alloy material, and is an effective method for producing a machine part made of a sintered aluminum alloy having a high density.
[0002]
[Prior art]
One method of manufacturing machine parts is to combine powder metallurgy and forging. That is, the material design necessary for the function of the product is first performed by powder metallurgy to create a material having an approximate shape, and then hot forging is performed in order to reduce the pores in the material and obtain the required strength.
At the time of hot forging, since the surface of the material and the tool is in a high temperature and high pressure state and the material is likely to adhere to the cavity surface of the mold, it is necessary to reduce the frictional shear coefficient. For that purpose, a lubricant is applied to the inner surface of the mold. Mold lubrication is essential, especially when dealing with light alloy sintered materials. For the application of the lubricant, a spray is often used because it can be applied uniformly and is easy to automate.
As the lubricant, graphite, which is a solid lubricant having an excellent film forming function and having a low friction coefficient up to about 500 ° C., is most often used. In particular, it is said that a lubricant containing graphite as a solid lubricant is excellent for lubrication in aluminum forging. As the lubricant, a lubricant dispersed in a fluid dispersion medium so as not to precipitate solid lubricant particles such as graphite is used. Dispersion media include oily, aqueous and emulsion types.
[0003]
Among these lubricants, an oil-based lubricant in which solid lubricant particles are dispersed using oil as a dispersion medium has an advantage that film formation proceeds rapidly in a wide range of mold temperatures. That is, when the lubricating component comes into contact with the high-temperature mold, the mold inner surface is wetted, and the surface tension of the oil sufficiently spreads to the application surface to uniformly disperse the solid lubricant particles. Lubricating with a cushioning effect, and because the oil is adsorbed to the solid lubricant particles, the lubrication function of the particles is exhibited more effectively, especially in the temperature range of hot forging of aluminum alloys. It is said to show lubricity. On the other hand, oil-based lubricants have a problem in that combustion oil smoke is generated and is easily ignited.
[0004]
Water-based lubricants in which solid lubricant particles such as graphite are dispersed are those in which water is a main component as a dispersion medium, and a dispersant, a viscosity modifier or the like is added to improve the dispersibility of the solid lubricant particles. . In the case of an aqueous lubricant, since the water evaporates, the solid lubricant particles are almost lubricated with a dry film. In addition, since the water-based lubricant has a great cooling effect on the mold, there is little concern that the mold is locally softened and deformed.
In any lubricant, when the mold temperature is high, a phenomenon of repelling liquid occurs on the inner surface of the mold, and the coating thickness tends to be uneven, and the frictional shear coefficient may increase. If the temperature is maintained at a relatively low temperature by the cooling effect, a uniform lubricating coating film can be formed. Furthermore, water-based lubricants are safer in terms of ignition and the like than oil-based lubricants.
[0005]
Emulsion lubricants in which solid lubricant particles such as graphite are dispersed have both the lubricity of oil-based lubricants and the clean and safe advantages of water-based lubricants. Although the dispersion medium contains water as a main component, since the lubricating oil is emulsified, the film attached to the inner surface of the mold exhibits characteristics similar to those of an oil-based lubricant. However, the cooling effect is inferior to that of the aqueous lubricant. On the other hand, since supercooling can be prevented more than water-based lubricants, in some cases, it may be an alternative to oil-based lubricants.
[0006]
The conditions for using the lubricant in the hot forging are appropriately determined by experience since the relationship between the dilution ratio, the coating amount, the mold temperature, etc. and the lubrication performance are not formulated. If the sintered alloy material is a light metal such as aluminum or magnesium and the mold temperature is relatively low, use a water-based lubricant, and if the mold temperature is relatively high, such as precision forging, oil lubrication It is considered preferable to use an agent. In the case of processing an iron-based sintered alloy material, an aqueous lubricant is mainly used.
[0007]
[Problems to be solved by the invention]
When spraying a lubricant in which solid lubricant particles as described above are dispersed on the inner surface of a mold heated to a temperature of about 200 to 400 ° C., generally, the higher the temperature, the worse the wetting of the inner surface of the mold. Therefore, an oil-based lubricant is preferable when relatively uniform coating is performed over a wide temperature range to produce a forging defect that is difficult to occur.
However, oil-based lubricants smoke or ignite in a short time after spraying, so a large-scale device is required as a countermeasure. In addition, some of the oil in the pores of the sintered alloy material may cause material defects on the forged surface, and it may be difficult to remove the dirt of the lubricant, which may be troublesome to handle. Therefore, it is preferable to avoid use. Furthermore, the applied lubricant is deposited at the corners of the mold cavity during repeated forging, and the forged workpiece is thinned, etc., which requires removal of deposits and reduces productivity. There are also problems.
[0008]
If the lubricant in which the solid lubricant particles are dispersed is water-based or emulsion-based, the problem of smoke generation and ignition is improved, but when the mold temperature is relatively high, the wettability of the lubricant to the mold inner surface is poor. The lubricating coating becomes non-uniform and the lubricating effect is reduced. Further, the deposition of the lubricant in the mold cavity is the same as in the case of the oil-based lubricant described above.
[0009]
For example, in the case of a sintered aluminum alloy, the thermal conductivity is better than that of an iron alloy, so that it is necessary to heat a mold when performing hot forging. Increasing the forging temperature has the advantage of lowering the forging pressure to achieve the required deformation amount, but the lubricant coating is not good because the wetness of the lubricant to the mold heated to a high temperature is inferior to that at a low temperature. This is not preferable because it becomes uniform and damage to the mold occurs.
For this reason, means for forging before the temperature of the material drops significantly using a device with a high pressurization speed such as a friction press as a means for heating the mold to a relatively low temperature and making the required amount of forging deformation. Is used. Even in such a case, when applying a water-based or emulsion-based lubricant, a punch that is galvanized by the repeated hot forging several times and that is fitted to the die of the die. This causes problems such as the need to clean the mold because the lubricant in which the solid lubricant particles are dispersed accumulates on the corners of the mold cavity.
An object of this invention is to provide the lubrication method which can be continuously forged by the hot forging of comparatively low temperature against the background of the above conventional subjects.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, when the liquid lubricant is sprayed on the inner surface of the heated mold, and then hot forging is performed by introducing a material of the heated sintered alloy, the liquid lubricant is used. (1) a step of spraying an emulsion lubricant containing no solid lubricant particles, and (2) a step of spraying an aqueous lubricant in which solid lubricant particles are dispersed in water one or more times thereafter. As the solid lubricant particles, graphite, molybdenum disulfide, tungsten disulfide, graphite fluoride, or the like can be used.
The emulsion lubricant sprayed in the above (1) contains 0.5 to 30% by mass of oil (preferably an oil containing at least one selected from the group consisting of sulfur-based, phosphorus-based and chlorine-based extreme pressure additives). Suitable results are obtained when the aqueous lubricant to be sprayed and then sprayed contains 1-25% by weight of graphite as solid lubricating particles. Such a lubrication method is particularly suitable when the sintered alloy material is an aluminum alloy.
Examples of the sulfur-based extreme pressure additive include sulfurized fats and oils, sulfurized olefins, sulfide mineral oil, dialkyl disulfide, dialkyl polysulfide and the like. Examples of the phosphorus extreme pressure additive include phosphate ester (salt), phosphite (salt), thiophosphate (salt), and phosphine. Moreover, chlorinated paraffin etc. can be used as a chlorine-type extreme pressure additive.
[0011]
As described above, continuous forging can be performed by spray-coating the emulsion lubricant and the aqueous lubricant. The reason for this is not clear, but is thought to be as follows.
When a conventional aqueous lubricant in which solid lubricant particles are dispersed or an O / W emulsion lubricant in which solid lubricant particles are dispersed is sprayed on a mold heated to a temperature of about 250 ° C., the former is highly viscous. Since it does not contain oil, mist can be made finer when spraying. A fine mist can form a uniform coating film inside the cavity even in a complicated mold. Moreover, the inner surface of the mold is cooled by the vaporization of water, so that wetting of the mold is improved and a thin and uniform coating film can be formed. This coating film adheres to the above-mentioned aqueous lubricant with an organic compound such as carboxymethylcellulose (CMC) or water glass (sodium silicate) added to adjust the viscosity and improve the dispersibility of the solid lubricant particles. Since it acts as an agent, it has good adhesion to the inner surface of the mold. On the other hand, when forging light metals such as aluminum, lubrication is insufficient with only a dry coating film of a solid lubricant, and it is necessary to perform a large amount of spraying to make up for it. As a result, the lubricant is easily deposited in the mold cavity.
[0012]
In the case of the latter O / W emulsion lubricant, water is boiled and vaporized in the initial stage to reduce moisture, and after forming a solid lubricant and oil coating film, the oil is vaporized in the process. Wetting is improved. However, a portion where the concentration of the solid lubricant is high and a portion where the concentration is low, and a water-based one cannot make the mist fine, resulting in uneven portions in the thickness of the formed coating film. In addition, since the adhesion of the film is poorer than that of the aqueous lubricant, the formed film is easily peeled when the material is charged. For the above reasons, it is considered that a sufficient lubricating effect cannot be obtained despite the fact that the lubricating effect of oil is added. In addition, if the heated material is introduced into the mold and pressurized with the oil remaining, the lubricating film of oil and solid lubricant remains viscous, so the lubricating film penetrates into the pores of the material. Then, there is also a concern that the vicinity of the forged body surface is fouled and causes surface defects.
[0013]
On the other hand, according to the lubrication method of the present invention, the emulsion surface (not including solid lubricant particles) is first sprayed to evaporate water and cool the inner surface of the mold, so that the mold surface is wetted. Is improved, and the oil becomes thinly covering the inner surface of the mold. The vaporized water fills the mold cavity and plays a role in suppressing oil evaporation. When an aqueous lubricant in which solid lubricant particles are dispersed is subsequently sprayed, it is considered that a solid lubricant coating film is formed on the oil film surface by evaporation of water and drying.
The lubricating film formed by this method is composed of two layers, an oil layer and a solid lubricant layer, which are uniformly and completely formed in order from the inner surface of the mold. Since the adhesion of the coating is also good, the lubricant hardly enters the pores of the material. In addition, the oil present on the inner surface side of the mold provides a good lubricating effect and good releasability, so that the friction between the mold and the work is reduced, and mold galling does not occur. Further, the solid lubricant does not remain attached to the mold cavity, and as a result, it is considered that continuous forging is possible.
[0014]
When forming a lubricating film in which the inner surface of the mold is coated with an oil layer and a solid lubricant film is formed thereon, for example, first, only oil or an oil-based lubricant is sprayed, and then an aqueous lubricant Even when sprayed, since the oil sprayed first is sprayed directly on the heated mold, the temperature drop of the mold is relatively small, so that wetting is insufficient and the coating becomes uneven. Moreover, since the space of the mold cavity is also in a high temperature state, it becomes a state where it is likely to emit smoke in a short time, and the desired coating film cannot be formed even if spraying of the aqueous lubricant is performed thereafter.
Further, in the method of reversing the procedure and first spraying the aqueous lubricant in which the solid lubricant particles are dispersed and then spraying the emulsion lubricant, the viscosity of water is adjusted to the aqueous lubricant and the solid lubricant is used. An organic compound such as carboxymethylcellulose (CMC) added to improve the dispersibility of the particles or an inorganic compound such as water glass (sodium silicate) acts as an adhesive, so that the solid lubricant is easily deposited on the inner surface of the mold. Become.
[0015]
An emulsion lubricant is an emulsion of water and oil. The oil may be a lubricating oil such as a mineral oil or a synthetic oil, but an oil containing at least one of the extreme pressure additives is preferable because it has excellent lubricating properties under high temperature and pressure.
The amount of water and oil is determined by the amount of water that generates an appropriate amount of steam necessary for cooling the inner surface of the mold in one spray and the mold surface temperature cooled by the water. It is necessary to satisfy the amount of oil necessary for uniform application, and an O / W emulsion lubricant having an oil content in the range of 0.5 to 30% by mass is suitable. If the oil content is low, a large amount of emulsion must be sprayed to supply the required amount of oil, and the mold is cooled because of the relatively high water content, and it takes a long time to evaporate the water. On the other hand, if the amount of oil is too much, the amount of spraying can be reduced, but the application is likely to be uneven and the amount of water is small, so that it is close to the state where only oil is applied. In addition, about several percent of emulsifier is added.
[0016]
The aqueous lubricant in which solid lubricant particles are dispersed is obtained by dispersing solid lubricant particles in water. It is necessary that the concentration of the solid lubricant is as high as possible, the solid lubricant particles are difficult to settle, and do not block the nozzle of the spraying device. In order to adjust the viscosity of water and improve the dispersibility of the solid lubricant particles, an organic compound such as carboxymethyl cellulose (CMC) or an inorganic compound such as water glass (sodium silicate) is added in an amount of about 0.1 to 5% by mass. The solid lubricant contained in the aqueous lubricant is suitably 1 to 25% by mass.
A lubricant liquid with a small solid lubricant content can make mist fine and has good sprayability, so that a thin and uniform film can be formed. What is necessary is just to spray once or several times according to the quantity of the solid lubricant required for a metal mold | die. In the case of a lubricant solution with an extremely low solid lubricant content, a large amount of the lubricant solution is sprayed, resulting in a lower mold temperature than necessary and a long time for evaporation of moisture. It is not preferable.
On the other hand, when the concentration of the solid lubricant is high, the spray amount may be small. However, when the concentration is too high, the spray nozzle is easily blocked, and continuous forging work becomes difficult.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to examples.
【Example】
(Manufacture of sintered body)
The sintered body for hot forging is made of an aluminum alloy, and the shape is a connecting rod having bearing holes at both ends of the rod. This was created by the following method.
First, mixed powder of 38% by mass of pure Al powder, 20% by mass of Si-Al alloy powder: 57% by mass, 4% by mass of Ni-Cu alloy powder: 4% by mass, and 50% by mass of Mg-Al alloy powder: 1% by mass is prepared. did. The total composition is calculated as follows: Si: 11.4% by mass, Cu: 3.84% by mass, Mg: 0.5% by mass, Ni: 0.16% by mass, and Al: balance.
The mixed powder was compacted into the shape of a connecting rod, and the compact was heated in a non-oxidizing gas to a temperature of 400 ° C. to dewax the molding lubricant, and then sintered at a temperature of 540 ° C. The sintered body has a density ratio of 80% and is formed smaller than the cavity of the forging die.
[0018]
(Forging equipment)
As a forging device, a friction press is used with a die comprising a die forming a cavity, a lower punch, a core rod, and an upper punch, and a heating means and a temperature control means are attached to the die. Along with the press machine, two sets of lubricant spray nozzles that move forward from the mold cavity in synchronism with the operation of the press machine and withdraw from the mold area are installed, and the lubricant is fed from the reserve tank, respectively. Means for introducing compressed air, means for introducing compressed air, and means for controlling operation. Further, a non-oxidizing gas atmosphere furnace for heating the sintered body material to a predetermined temperature and a material supply device for transferring and inserting the heated material into the mold cavity are provided.
The mold is kept at a temperature of 250 ° C. In addition, the spray nozzle is installed so that the spray liquid spreads through the cavity.
Using the lubricants shown below, hot forging of the sintered body material was continuously performed. A pressure at which the density ratio of the forged body was 100% and forging burrs were generated was applied.
[0019]
<Comparative Example 1>
As a forging lubricant, a graphite dispersed oil lubricant (made by Hitachi Powdered Metallurgy Co., Ltd., trade name: HITAZOL GO-102) having a graphite content of 10% by mass was used.
Since smoke was generated immediately after spraying the lubricant, it was necessary to leave it for several minutes after spray application, or to burn the generated gas with a burner or the like. Further, when several pieces were continuously forged, scraping residues of lubricant and raw material were accumulated at the corners on the lower punch side, and thinning was observed at the corners of the forged body. Further, when the cross section of the surface of the forged body in contact with the punch was observed, there was evidence of oil and graphite entering the pores.
[0020]
<Comparative example 2>
As a forging lubricant, a graphite-dispersed aqueous lubricant having a graphite content of 17% by mass (trade name: Hitachi GA-361, manufactured by Hitachi Powdered Metals Co., Ltd.) was used.
In this case, when the forging was repeated several times, galling occurred on the side surface of the forged body, resulting in poor lower punch operation. When the lower punch surface was observed after spraying, the mist was spread over the entire surface. It seems that the lubricating film of graphite only lacked lubricity.
[0021]
<Comparative Example 3>
As a forging lubricant, an O / W emulsion lubricant having a sulfurized oil content of 20% by mass (manufactured by Hitachi Powdered Metallurgy Co., Ltd., trade name: HITAZOL WA-337PH) was used.
In this case, both galling and mold operation were worse than the former. This is thought to be due to lubrication using only a small amount of oil.
[0022]
<Comparative Example 4>
As the forging lubricant, a graphite-dispersed aqueous lubricant was first sprayed, and the O / W emulsion lubricant was applied after about 1 second. Die operation and release of the forged body were good, but if forging was performed continuously, scraping residue of lubricant and material accumulated in the corner on the lower punch side, and there was a lack of thickness in the corner of the forged body. Admitted.
[0023]
<Example 1>
First, the O / W emulsion lubricant was sprayed as a forging lubricant, and after about 1 second, a graphite-dispersed aqueous lubricant was applied. The mold operation and release of the forged body were good, and forging could be continued continuously. When the lower punched surface after spraying was observed, it was found that it was coated with graphite with a small gap.
[0024]
As described above, the example in which the material is a sintered aluminum alloy and the solid lubricant is graphite has been described. However, the optimal lubrication method described above is to first spray and apply water and oil in the form of an emulsion to the inner surface of the mold. By forming an oil film and then spray-coating an aqueous solid lubricant solution to provide a solid lubricant film, the friction between the mold and the forged body is reduced. That is, the solid lubricant does not adhere to and accumulate on the mold, and the pores of the forging material are rarely impregnated with the lubricant, so that continuous forging is possible. Therefore, by adjusting the spray amount in accordance with the mold temperature, the size of the die cavity, etc., it can be applied to other sintered light alloys and iron-based sintered alloy materials.
[0025]
【The invention's effect】
According to the hot forging lubrication method of the present invention, since the maintenance work of the forging work can be reduced, the production efficiency can be improved, and a forged body having no surface defects and excellent in appearance can be stably provided. .

Claims (4)

In the case of performing hot forging by introducing a heated sintered alloy material after spraying a liquid lubricant on the heated inner surface of the mold, the spray of the liquid lubricant is (1) free of solid lubricant particles A step of spraying an emulsion lubricant, and (2) a step of spraying an aqueous lubricant in which solid lubricant particles are dispersed in water once or a plurality of times. Mold lubrication method in forging. The emulsion lubricant not containing the solid lubricant particles is an O / W emulsion containing 0.5 to 30% by mass of oil, and the aqueous lubricant contains 1 to 25% by mass of graphite particles as solid lubricant particles. The die lubrication method in the hot forging of the sintered alloy according to claim 1, wherein the die is lubricated.   The oil in the O / W emulsion lubricant contains at least one additive selected from the group consisting of sulfur-based, phosphorus-based and chlorine-based extreme pressure additives. Mold lubrication method in hot forging of sintered alloy.   The die lubrication method in hot forging of a sintered alloy according to any one of claims 1 to 3, wherein a material of the sintered alloy is an aluminum alloy.