PROCESS FOR METAL FORMING

Abstract: A substantially water-free, liquid lubricant for metal forming, which comprises (a) a lubricating oil, and (b) at least one phosphoric acid monoester from the group repre­ sented by the general formula: RO--(OH)₂ wherein R is alkyl, alkylalkenyl or aryl, and optionally (c) at least one member of the group including fatty acids, fatty acid amides and metal soaps, can form a lubricating film with a good heat resistance and good lubricating properties by virtue of the heat generated by deformation and friction during the forming only by wetting the surface of a metallic workpiece (2) or a die (5) with the liquid lubricant, and can work effectively for prevention of galling. Parts or articles with a higher reduction of area and complicated shape can be readily formed. Furthermore, a film having a lubricating effect equivalent to that of the conventional phosphate coat­ ing film can be simply obtained with a great contribution to product cost reduction.

Description: BACKGROUND OF THE INVENTION This invention relates to a process for metal forming employing a substantially water-free liquid lubricant. A lubricant for metal forming must have a satisfactory lubricating ability up to an elevated temperature caused by deformation, friction, etc. and also to increasing new surface area of a workpiece created by the metal formation. The lubricants so far proposed for this purpose are water-soluble or water-insoluble liquid lubricants containing mineral oil or synthetic oil or their mixture as the major component and further containing a semi-solid lubricant such as metal soap, beef tallow, etc., a sulfur-based, chlorine-based, or phosphorus-based extreme pressure agent, or a solid lubricant such as graphite, molybdenum disulfide, etc. These lubricants can be used, without any problem, for the metal forming with low reduction of area, but in the case of high reduction of area which produces a higher temperature or a higher surface pressure, or in the case of forming products of complicated shapes, their load-carrying capacity, heat resistance, etc. are not satisfactory, resulting in galling. For the lubrication for larger plastic deformation, or forming products of complicated shapes, it has been so far proposed to plate a workpiece surface with a soft metal, such as copper, etc., or to coat a workpiece surface with a plastic resin film. A phosphate coating process comprising a series of such steps as defatting-water washing-acid pickling-phosphating-water washing-neutralization treatment-metal soap lubrication treatment-heat drying of a workpiece is also well known. These lubricating coating treatments all require a sufficient pretreatment and complicated coating steps, and thus require so many labors and costs and also have further problems of removing the coatings after the forming or of environmental pollution by the waste liquor liquid from the coating treatments after the forming. FR-A-2 289 601 discloses a process for cold and hot metal forming, respectively. Said process is characterized by the use of a lubricant which consists of a monocarboxylic tetraester of pentaerythritol, a phosphorus containing compound as well as a mineral oil. Apparently, the composition used in said process is an emulsion of oily components in an aqueous phase which additionally comprises an emulsifier. The amount of phosphorus compound in said composition is very low, i.e., restricted to the range of 0.1 to 1.1 parts per 100 parts of mineral oil. Such composition could not meet the requirements of liquid lubricants for metal forming under high pressure, for example to keep an excellent lubricating ability even under high reductions of area. Recently, lubricants containing phosphoric acid or its salts, boric acid or its salts, carbonates, nitrates, sulfates, or hydroxides of alkali metal, and laminar silicate, etc. have been proposed (Japanese Patent Application Kokai (Laid-open) No. 57-73089). However, since they consist of water-soluble glass powder of P₂O₅, B₂O₂ and M₂O (where M represents an alkali metal), and the laminar silicate, or their mixture and water, they fail to show lubrication at a low temperature forming (below about 300°C) such as cold forming, and thus cannot be used in the cold forming. Furthermore, an acidic lubricant for cold forming, which is prepared by reaction of a multivalent metal cation, orthophosphate, and alkyl alcohol or alkylaryl alcohol having 10 to 36 carbon atoms, and which has a water content of not more than 20% by weight has been proposed (Japanese Patent Publication Kokai (Laid-open) No. 47-15569), and liquid or paste lubricants further containing mineral oil, carboxylic acid, and alkylamine besides the said lubricant components, lubricants for cold forming, which comprises 30 to 94% by weight of a lubricant such as mineral oil, oleic acid, or oleylamine, 5 to 60% by weight of a reaction product of a multivalent metal cationic salt, polyphosphoric acid and an alcohol having 10 to 36 carbon atoms in a ratio of the metal cation : P₂O₅ : the alcohol = 1 : 3-60 : 14-150 by weight, and 0.5 to 10% by weight of water have been proposed (U.S. Patent No. 3,932,287). These lubricants show good results in drawing processing of pipes, etc., but fail to meet the requirements for forming steel workpieces with high reduction of area. SUMMARY OF THE INVENTION An object of the present invention is to provide a process for metal forming in a very simple manner in forming a lubricating film, using a substantially water-free, liquid lubricant for metal forming, which can keep an excellent lubricating ability even under high reductions of area which produces a higher temperature and a higher pressure, and can give a distinguished formability during the cold forming. According to a first aspect of the present invention a lubricating film having a good heat resistance and a good lubricating ability is formed on at least contact part between the surface of a die and the surface of a metallic workpiece such as a steel workpiece by virtue of the heat generated by deformation, or friction during the metal forming only by wetting the surface with a substantially water-free, liquid lubricant for metal forming, which comprises 100 parts by weight of a lubricating oil having a viscosity of 50 to 200 mm²/sec at 40°C and 2 to 30 parts by weight of at least one phosphoric acid monoester represented by the following general formula (I): wherein R is an alkyl group having 1 to 18 carbon atoms, an alkylalkenyl group or an aryl group, and then pressing the workpiece against the die, thereby carrying out metal forming while forming a lubricating film on the surface of the workpiece. According to a second aspect of the present invention, a lubricating film having a good heat resistance and a good lubricating ability is formed on at least the contact part between the surface of a die and the surface of a metallic workpiece by virtue of the heat generated by deformation or friction during the metal forming only by wetting the surface with a substantially water-free, liquid lubricant for-metal forming, which additionally comprises at least one of fatty acid, fatty acid amide, and metal soap. The lubricating oil for use in the process of the present invention is the ordinary, commercially available lubricating oil, including, for example, mineral oil, synthetic oil such as ester oil, ether oil, silicone oil and fluorinated oil, and their mixtures. It is preferable to select the viscosity of the lubricating oil in view of desired reduction of area, method for supplying the lubricating oil to a lubricating surface, etc. The phosphoric acid monoesters for use in the present invention include, for example, monomethyl phosphate, monoisopropyl phosphate, monobutyl phosphate, monooctyl phosphate, monoisodecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monooctadecyl phosphate, monooleyl phosphate, monophenyl phosphate, etc. The phosphoric acid monoesters can be used in the form of solution or suspension or dispersion in said lubricating oil. In the case of dispersion, it is preferable to add an emulsifying agent thereto. Preferable emulsifying agent includes polybutenylsuccinic acid imide or ester obtained by reaction of polybutenylsuccinic acid anhydride with an amine or alcohol, copolymers of polybutenylsuccinic acid ester and polymethacrylate or polyolefin, etc. By adding at least one of fatty acid, fatty acid amide and metal soap to the lubricating oil containing the phosphoric acid monoester, formation of a film of the phosphoric acid monoester can be promoted and the lubricating ability can be much improved, so that higher forming performance can be obtained. The fatty acid and fatty acid amide for use in the present invention are natural fatty acids, synthetic fatty acids and fatty acid amide prepared by condensation reaction of fatty acid and amine, and include, for example, butanoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, cis-9-cis-12-octadecadienoic acid, cis-9-cis-12-cis-15-octadecatrienoic acid, 9-decenoic acid, cis-9-octadecenoic acid, heptanoic acid, and their amides, for example, hexanamide, butanamide, octanamide, nonanamide, decanetriamide, undecanamide, dodecanamide, tridecanamide, myristylamide, palmitylamide, stearylamide, oleylamide, linolamide, etc. The metal soap for use in the present invention includes, for example, soap obtained by reaction of fatty acid having not more than 22 carbon atoms with a metal such as an alkali metal or nickel. In the case of the use of a liquid lubricant according to the first aspect of the process of the present invention which comprises employing (a) a lubricating oil and (b) a phosphoric acid monoester represented by the general formula (1), it is essential to use 2 to 30 parts by weight of the phosphoric acid monoester per 100 parts by weight of the lubricating oil. Below 2 parts by weight of the phosphoric acid monoester, formation of a lubricating film is deteriorated and a sufficient formability cannot be obtained, so that galling may sometimes occur, whereas above 30 parts by weight thereof, no better formability can be obtained and such excessive addition is not economical. In the case of the use of a liquid lubricant according to the second aspect of the process of the present invention, which comprises employing (a) a lubricating oil, (b) a phosphoric acid monoester represented by the general formula (1), and (c) at least one of fatty acid, fatty acid amide and metal soap, it is essential to use 2 to 30 parts by weight of the phosphoric acid monoester and preferred to use 1 to 20 parts by weight of at least one of fatty acid, fatty acid amide and metal soap per 100 parts by weight of the lubricating oil. Below 2 parts by weight of the phosphoric acid monoester and below 1 parts by weight of at least one of fatty acid, fatty acid amide and metal soap, a sufficient lubricating effect may not be sometimes obtained, whereas above 30 parts by weight of the former and above 20 parts by weight of the latter, no better formability can be obtained, and such excessive addition is not economically advantageous. In the case of the suspension and dispersion according to the present invention, an emulsifying agent can be used, where it is desirable to use 0.1 to 5 parts by weight of the emulsifying agent per 100 parts by weight of the lubricating oil. According to the present invention, a liquid lubricant comprises 100 parts by weight of a lubricating oil (viscosity: 50 to 200 mm²/sec at 40°C), 2 to 30 parts by weight of a phosphoric acid monoester such as monobutyl phosphate, preferably 1 to 10 parts by weight of fatty acid such as heptanoic acid, and optionally 1 to 5 parts by weight of an emulsifying agent such as polybutenylsuccinic acid ester. The lubricating film obtained from this liquid lubricant has a thickness of 3 µm or less, which is considerably smaller than the thickness of the conventional phosphate coating film, e.g. about 10 µm, though the formability of the present lubricating film is equivalent or superior to that of the conventional one, and particularly a more smooth forming surface can be obtained. The liquid lubricant can be put into service only by wetting the surface of a metallic workpiece or a die for metal forming with the present liquid lubricant according to the well known method, for example, by spraying, brushing, dipping, etc., followed by metal forming, or can be also used by heating either the present liquid lubricant or the metallic workpiece and dipping the metallic workpiece into the lubricant, thereby forming a lubricating film on the surface of metallic workpiece. For example, a metallic workpiece is dipped into the liquid lubricant heated to at least 50°C for 0.5 - 10 minutes, for example, 100°C for 0.5 minutes, whereby a lubricating film having a lubricating effect equivalent or superior to that of the conventional phosphate coating film and a high rust-proof effect on the metallic workpiece can be very readily formed. Thus, the present invention can considerably shorten the lubricating film-forming process. An antioxidant for preventing deterioration of the present liquid lubricant, a rust proof agent for preventing a metallic workpiece from rust, etc. can be added to the liquid lubricant, so far as they are not in ranges to deteriorate the desired lubricating effect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a workpiece used for evaluation of the properties of lubricants. Fig. 2 is a vertical cross-sectional view of an extrusion die used for evaluation of the properties of lubricants. Fig. 3 is a diagram showing relationship between the reduction of area or extrusion diameter and forming limit temperature (°C) according to Examples and Comparative Examples. Fig. 4 is a diagram showing relationship between the content of fatty acid and the forming limit temperature (°C). DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the present liquid lubricant for metal forming will be described in detail below, referring to Examples, which will not be limitative to the present invevtion. Examples 1 to 20 The present liquid lubricants having compositions shown in Table 1, where mineral oil (FBK150 R , trademark of a product made by Nippon Oil Company, Ltd., Japan) was used as a base oil, were applied to the surfaces of workpiece 2 , as shown in Fig. 1, chromium-molybdenum steel columns with a nose, 9.9 mm in diameter, 30 mm long and 90° at nose angle [SCM 415 as described in JIS (Japanese Industrial Standard G 4105: C: 0.03 - 0.18 wt.%, Si: 0.15 - 0.35 wt.%, Mn: 0.60 - 0.85 wt.%, P: under 0.030 wt.%, S: under 0.030 wt.% Cr: 0.90 - 1.20 wt.%, Mo: 0.15 - 0.30 wt.%, the balance being Fe)]. Then, the workpieces 2 were subjected to metal forming by forward extrusion with a hard metal die 5 with an extrusion angle of 120° and an extrusion diameter of 5 mm (reduction of area: 75%) and a punch 1 , as shown in Fig. 2, to evaluate the formability. The results of evaluation are shown in Table 2. The formability was evaluated as follows. A band heater 4 was provided around the die 5 to elevate the die temperature from the room temperature stagewise, for example, by 5 to 20°C for each stage, and 20 - 30 workpieces 2 of each Example, to which the liquid lubricants were applied, were subjected to metal forming, and maximum formable temperatures up to which no galling developed on the surfaces of workpieces after the metal forming were measured. A higher maximum formable temperature has a better formability of the lubricant. Forming load at the maximum formable temperature is obtained by recording an extrusion pressure at the forming by a strain gage. The conventional lubricants used for comparison with the liquid lubricants used in the process of the invention are as follows: Comparative Example 1 Commercially available oil for metal forming having the following composition was used: Comparative Example 2 Commercially available oil for metal forming similar to that of Comparative Example 1, which comprises a mixture of mineral oil and ester oil as a base oil, and fatty acid, oleic acid, and chlorinated hydrocarbon compound as additives was used. Comparative Example 3 The same workpieces used in Examples 1 to 20 were treated according to the well known phosphate coating consisting of the following steps: defatting → water washing → acid pickling → water washing → phosphating → water washing → neutralization → metal soap lubricating treatment → drying. Formabilities of the workpieces of Comparative Examples 1 to 3 were evaluated in the same manner as in Examples 1 to 20. The results of evaluation of Comparative Examples 1 and 2 are shown in Table 2. As is evident from the results of Table 2, all of the liquid lubricants had considerably improved formabilities, as compared with Comparative Examples. Forming loads were also smaller than that of Comparative Examples, and thus the coefficient of friction is low with a good lubricating effect. Examples 21 - 41 The liquid lubricants for metal forming were prepared by mixing polyol ester oil having a viscosity of 56 mm²/sec at 40°C with octanoic acid, heptanoic acid, octanamide and phosphoric acid monoester as shown in Table 3 by means of a high speed mixer. The liquid lubricants were applied to workpieces of chromium-molybdenum steel and the formability and forming load of the lubricants were measured by means of the same die as used in Example 1. The results are shown in Table 4. As is evident from the results of Table 4, the forming loads were smaller than those of Comparative Examples 1 and 2 shown in Table 2. Examples 42 - 59 The liquid lubricants for metal forming were parepared from compositions of mineral oil having a viscosity of 150 mm²/sec at 40°C, fatty acid, fatty acid amide and metal soap shown in Table 5. The lubricants were subjected to measurement of forming loads and formabilities under the same conditions as in Example 1. Results are shown in Table 6. As is evident from Table 6, the forming loads were smaller and the formabilities were better than those of Comparative Examples shown in Table 2. Examples 60 - 77 The lubricants having the same compo sition and the same mixing ratio as in Table 5 except that polyol ester oil having a viscosity of 56 mm²/sec at 40°C was used in place of the mineral oil was subjected to forming under the same conditions as in Example 1. The forming loads and formabilities are shown in Table 7. As is evident from the results of Table 7, substantially equal results to those of Examples 42 - 59 were obtained. Examples 78 - 88 The liquid lubricants containing mineral oil having a viscosity of 56 mm²/sec at 40°C (FBK-56, a product made by Nippon Oil Co., Ltd., Japan) and/or polyol ester oil having a viscosity of 56 mm² /sec at 40°C, shown in Table 8, were used as a lubricating film-treating agent for a metallic workpiece. The same workpieces as used in Example 1 and heated to 100°C were dipped in the present liquid lubricants to make lubricating film treatment. Then, the forming loads and formabilities of the lubricating films were evaluated by means of the same die (or tool) as used in Example 1. The results of evaluation are shown in Table 9. As is evident from Table 9, the formabilities of the lubricating films according to the liquid lubricants used according to the invention are equivalent to that of the conventional phosphate film, and the forming loads of the lubricating films are lower and the lubricating effects are better than those of the phosphate coating film. In Fig. 3, a diagram showing relationship between the reduction of area (%) or extrusion diameter (mm) on the abscissa and the forming limit temperature (°C) on the ordinate according to typical Examples of the present invention and Comparative Example is given, where the reduction of area (%) is given by the following formula: (D² - d²)/D² x 100 (%) D: diameter of workpiece before forming d : drawing (or extrusion) diameter, i.e. diameter of workpiece after forming (mm) As is evident from Fig. 3, the liquid lubricants used according to the invention have better formabilities than the conventional one. The formable limit temperatures were measured up to 280°C, but those which seem to have higher formable limit temperatures are indicated by the upward arrow mark ↑ on the curve. In Fig. 3, examples consisting only of mineral oil, of mineral oil and fatty acid and of mineral oil and metal soap are shown for comparison, which have considerably poor formabilities. Example 89 The liquid lubricants consisting of 100 parts by weight of mineral oil having a viscosity of 150 mm²/sec at 40°C, 1 to 30 parts by weight of monobutyl phosphate, 1 to 12 parts by weight of heptanoic acid, and 1 part by weight of polybutenylsuccinic acid ester as an emulsifying agent were prepared and their formabilities were evaluated in the same manner as in Example 1. The results are shown in Fig. 4. As is evident from Fig. 4, preferable ranges are 2 to 30 parts by weight of monobutyl phosphate and 1 to 10 parts by weight of heptanoic acid. As is obvious from the foregoing, the liquid lubricant used in the present process for metal forming can form a dense and heat-resistant lubricating film on the frictional surface of a workpiece or die by virtue of the heat generated during the forming owing to a synergistic effect of phosphoric acid monoester and fatty acid or aliphatic acid amide or metal soap as added to lubricating oil, and thus can be used in forming of parts with higher reduction of area or articles with more complicated shape than the conventional lubricant for the forming. The lubricating film formed by dipping a heated workpiece into the liquid lubricant or by dipping a workpiece into the heated liquid lubricant used according to the present invention has a formability equivalent to that obtained by phosphate film treatment. Furthermore, only one run of film treatment is enough in the process of the present invention, and thus the present invention can greatly contribute to simplification of the process and cost reduction.

Claims: A process for metal forming, characterized by applying a substantially water-free, liquid lubricant comprising 100 parts by weight of a lubricating oil having a viscosity of 50 to 200 mm²/sec at 40°C and 2 to 30 parts by weight of at least one phosphoric acid monoester represented by the following general formula: where R is an alkyl group having 1 to 18 carbon atoms, an alkylalkenyl group or an aryl group, to at least the contact part between the surface of a die and the surface of a metal workpiece, and then pressing the workpiece against the die, thereby carrying out metal forming while forming a lubricating film on the surface of the workpiece . A process according to claim 1, wherein said substantially water-free, liquid lubricant additionally comprises at least one of fatty acid, fatty acid amide and metal soap. A process according to one of claims 1 and 2, wherein the liquid lubricant is applied to the surface after heating at least one of the metallic workpiece, the die and the liquid lubricant, and then the metal forming step is carried out. A process according to one of claims 1 to 3, wherein the liquid lubricant is heated to at least 50°C for at least 0.5 minutes.

Inventors: KOMATSUZAKI, SHIGEKI, NAKANO, FUMIO, NARAHARA, TOSHIKAZU, TAKAMURA, TOMOE, UEMATSU, TAKAO
Applicants: HITACHI, LTD.
Application year: 1984
Main classification: C10M137
IPC codes: C10N30, C10N50, C10N40, C10N80, C10M137, C10M141