Patent Application
20060128573
1. Field of the Invention
This invention relates to lubricants used in metal forming processes and, in particular, to lubricants used in hydroforming processes.
2. Background Art
Processes in which metal parts are manipulated or formed typically require lubricants to reduce equipment wear. These processes include such operations as bending, swaging, roll-tapping, drawing, and hydroforming. Hydroforming is a particularly important process in which a relatively complex metal part is fabricated.
There are two types of hydroforming processes. One is used to form parts from sheet metal and the other is used to form parts from metal tubes. Many tube hydroforming applications are currently utilized by the automotive industry.
In a tube hydroforming process, a workpiece tube is placed in a tool cavity. The geometry of the die cavity corresponds to the external geometry of the produced part. The tool cavity is closed by the ram movement of a press. At the same time, the tube ends are loaded by two punches moving along the tube axis, and an aqueous fluid is pumped into the tube. As the internal pressure of this pressure-side aqueous fluid is increased, the tube expands until the expanding tube wall contacts the inner surface of the die, and the part is formed.
There are three types of lubricants involved in the tube hydroforming process: a bending lubricant, the pressure-side aqueous fluid mentioned above, and a die-side lubricant that is used between the workpiece tube and the die. The bending lubricant is used on the inside of the tube to bend the tube into a desired shape just prior to mounting the tube in the hydroforming tool cavity. The pressure-side fluid is the aqueous hydraulic fluid used to transmit the pressure to the inside of the tube. Although little lubricity is required of the pressure-side fluid, other properties, such as corrosion protection, high pressure stability, and the ability to reject the bending and die-side lubricants, are important to the performance. The die-side lubricant is the primary forming fluid in high-pressure hydroforming. It provides the lubricity between the workpiece and the die.
The demands on the die-side lubricant vary widely. Some light duty applications require little of the die-side lubricant. In the case of lower pressure applications, the pressure-side fluid may also be used simultaneously to transmit pressure inside the tube and to provide die-side lubrication. As the complexity of the application increases, the importance of the die-side lubricant increases. Furthermore, the die-side lubricants' compatibility with the pressure-side lubricant and the removal of the die-side lubricant from the newly formed part are important considerations.
The present invention discloses a liquid film die-side hydroforming lubricant that comprises an oil and a surfactant. The liquid film die-side lubricant is typically already a liquid when applied to the workpiece tube. Preferably, the liquid film die-side lubricant has lubrication properties that are not substantially damaged by contact with the pressure-side fluid which usually contains water. Furthermore, the liquid film die-side lubricant preferably has high viscosity.
In accordance with another aspect of the present invention, a solid film die-side hydroforming lubricant is disclosed. The solid film die-side lubricant comprises a wax such that the stress value within the die-side lubricant is at least 540 kPa at 0.75 sec after a compressive stress is imposed. Preferably, the solid film die-side lubricant is a liquid when applied to the workpiece tube. The applied liquid then either dries or cures into a solid lubricating film. The solid film die-side lubricant has lubrication properties that are not substantially damaged by contact with the pressure-side fluid, which usually contains water. Furthermore, the liquid film die-side lubricant preferably has high viscosity. When the die-side lubricant of the present embodiment is a solid at the time of emplacement, the die-side lubricant preferably has high hardness and optionally a high elasticity. The solid film lubricant also optionally includes a wetting agent to improve the ability of the composition to wet metallic surfaces.
Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventor.
For purposes of the present invention, the resistance of a lubricant to damage to its lubrication properties by pressure-side fluid is most conveniently measured by measuring the coefficient of friction of two metal surfaces, lubricated with the die-side lubricant to be measured, in a sliding friction test at a pressure from 65 to 400 bars and in a twist compression test at a pressure from 675 to 2500 bars. A die-side lubricant to be tested is first placed on one surface of a substrate of the same type of metal as is to be hydroformed in the same manner as if the substrate were to be hydroformed, but the substrate in this instance has a shape suitable for the intended method of measurement of coefficient of friction. After the coefficient of friction has been measured, the die-side lubricant layer is sprinkled or otherwise gently wet with the intended pressure-side fluid for hydroforming or a surrogate for this pressure-side fluid, plain deionized or tap water often being an effective surrogate. A volume of the pressure-side fluid or surrogate therefor that is not more than about twice the volume of the wetted die-side lubricant film itself should be used, and no substantial mechanical force such as would result from high pressure spraying should be used. After a minute or two of contact between the lubricant layer and the pressure-side fluid or surrogate therefor, any remaining aqueous liquid is allowed to drain away under the influence of natural gravity, and the coefficient of friction of the substrate bearing the thus-drained die-side lubricant film is again measured. The die-side lubricant has sufficient pressure-side fluid-resistance for the purposes of this invention when the coefficient of friction measured with the thus wetted and drained die-side lubricant film does not exceed the coefficient of friction measured under the same conditions with the originally emplaced and unwetted die-side lubricant film by an amount that is preferably more than about 50 percent of the value of the coefficient of friction for the originally emplaced and unwetted die-side lubricant film, more preferably more than about 30 percent of the value of the coefficient of friction for the originally emplaced and unwetted die-side lubricant film, and most preferably more than about 1.0 percent of the value of the coefficient of friction for the originally emplaced and unwetted die-side lubricant film. In particularly favorable instances, the coefficient of friction is reduced by contact with the pressure-side fluid or surrogate therefor. All of the measurements involved in this determination of the pressure-side fluid resistance of a lubricant should be made at the intended temperature of the hydroforming process itself, or, if the latter is unknown, at a normal ambient human comfort temperature (between 18 and 23° C.).
In one embodiment of the present invention, a liquid film die-side hydroforming lubricant is disclosed. The liquid film die-side lubricant is typically already a liquid when applied to the workpiece tube. The liquid film die-side lubricant has lubrication properties that are not substantially damaged by contact with the pressure-side fluid as defined above. Furthermore, the liquid film die-side hydroforming lubricant includes an oil that has a kinematic viscosity measured at 40° C., that is at least, with increasing preference in the order given, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0. 17.5, or 20 stokes. Suitable commercially available oils include vegetable oils, blown (alternatively called “oxidized”) vegetable oils, polymers of vegetable oils, animal oils, and blown animal oils along with typical petroleum oils. Specific examples include blown canola oil, blown fish oil, canola oil, blown rapeseed oil, and naphthenic oil.
The liquid film die-side hydroforming lubricant (“liquid film composition”) of the present invention optionally further include a surfactant. The surfactant improves the cleaning properties of the lubricant, i.e., the ease of removing residual lubricant. Although any surfactant may be utilized, preferably non-ionic surfactants are used. The surfactant also preferably improves the lubricity of the liquid film when wetted. Though not restricting the improvement of lubricity to any particular mechanism, the surfactant appears to form an emulsified layer when wetted that enhances lubricity. However, the amount of surfactant is not so much that the liquid film is deteriorated during emulsification. The surfactant is preferably present in an amount of 0.1% to 10% of the total weight of the liquid film composition, more preferably in an amount of 1.0% to 5% of the total weight of the liquid film composition, and most preferably in an amount of about 2.5% of the total weight of the liquid film composition. Preferred surfactants include vegetable oil ethoxylates, ethoxylates of alkyl alcohols, ethoxylates of acetylenic diols, block copolymers of ethylene and propylene oxides, ethoxylates of alkyl carboxylates such as typical fatty acids, alkyl polyglycosides, and mixtures thereof. Examples include but are not limited to Chemal DA-6, Chemal DA-9, Chemal LA-4, Chemax CO-5, Chemax CO-16, Chemax CO-25, Chemax CO-30, Chemax CO-36, Chemax CO-40, Chemax CO-80, and Chemax CO-200/50 commercially available from Chemax, Inc. located in Greenville, S.C. Suitable surfactants also include but are not limited to Surfynol 440 commercially available from Air Products, TOMAH E-14-5 (poly (5) oxyethylene isodecyloxypropylamine) and TOMAH E-14-2 commercially available from Tomah Products Inc. located in Milton, Wis.; NINOL 11CM (a modified coconut diethanolamide surfactant sold by Stepan, Inc.) TRITON X-100 (octylphenol ethylene oxide condensate; Octoxynol-9) commercially available from Union Carbide; and APG 325 CS (decyl polyglucoside) commercially available from Cognis Corporation located in Cincinnati, Ohio. Other suitable non-ionic surfactants include block surfactants containing polyoxypropylene hydrophobe(s) and polyoxyethylene hydrophile(s). In order to properly function, the surfactant must be soluble or dispersible in the lubricant. The blocks may be homopolymeric or copolymeric, for example copolymers derived from oxyalkylating with mixtures of ethylene oxide and propylene oxide. Such surfactants are available from numerous sources, including the Pluronic®, Tetronic®, and Pluronic® R polyether surfactants from BASF Corporation.
In another embodiment of the present invention, a solid film die-side hydroforming lubricant (“solid film composition”) is disclosed. Typically, the solid film lubricant will be applied to a surface as a liquid which is subsequently dried and cured. The resultant solid lubricant of the present invention preferably has a hardness as measured at 23-26° C. by the American Society for Testing and Materials (“ASTM”) Procedure Number D-5 that is not more than, with increasing preference in the order given, 50, 40, 30, 20, 15, 13, 11, 9, 7, 5, or 3. The solid film lubricant of the present invention includes solid lubricants that are characterized by one or more of the following properties when subjected to a compressive stress within the range from 1.50 to 2.00 percent over a time interval of 0.20 to 0.30 seconds at 23-26° C.:
The solid film die-side hydroforming lubricant of the present invention optionally further includes a surfactant. Although any surfactant may be utilized, preferably non-ionic surfactants are used. The surfactant also preferably improves the lubricity of the solid film when wetted. The surfactant is preferably present in an amount of 0.05% to 10% of the total weight of the solid film composition, more preferably in an amount of 0.1% to 5% of the total weight of the solid film composition, and most preferably in an amount of about 1% of the total weight of the solid film composition. Preferred surfactants include vegetable oil ethoxylates, ethoxylates of alkyl alcohols, ethoxylates of acetylenic diols, block copolymers of ethylene and propylene oxides, ethoxylates of alkyl carboxylates such as typical fatty acids, alkyl polyglycosides, and mixtures thereof. Suitable surfactants also include but are not limited to Surfynol 440 commercially available from Air Products, TOMAH E-14-5 (poly (5) oxyethylene isodecyloxypropylamine) and TOMAH E-14-2 commercially available from Tomah Products Inc. located in Milton, Wis.; NINOL 11CM (a modified coconut diethanolamide surfactant sold by Stepan, Inc.) TRITON X-100 (octylphenol ethylene oxide condensate; Octoxynol-9) commercially available from Union Carbide; and APG 325 CS (decyl polyglucoside) commercially available from Cognis Corporation located in Cincinnati, Ohio. Other suitable non-ionic surfactants include block surfactants containing polyoxypropylene hydrophobe(s) and polyoxyethylene hydrophile(s). The blocks may be homopolymeric or copolymeric, for example copolymers derived from oxyalkylating with mixtures of ethylene oxide and propylene oxide. Such surfactants are available from numerous sources, including the Pluronic®, Tetronic®, and Pluronic® R polyether surfactants from BASF Corporation.
The solid film die-side lubricant optionally comprises a wetting agent. Utilization of such agents improves the ability of the dry film composition (which is a liquid when applied) to wet metals such as the various steel alloys (stainless steel, hot rolled steel, and cold rolled steel), aluminum alloys, titanium, and copper. It will be recognized by those skilled in the art, that many wetting agents are surfactants and many surfactants are wetting agents. Accordingly, a subset of the surfactants listed above will also function as wetting agents. Suitable wetting agents include, but are not limited to, nonionic fluorosurfactants, anionic fluorosurfactants, ethoxylated tetramethyldecynediols, acetylenic glycol-based surfactants, dialkylsulfosuccinates, and mixtures thereof. Suitable ethoxylated tetramethyldecynediols include members of the Surfynol 400 series such as Surfynol 440 and 420 commercially available from Air Products. An exemplary acetylenic glycol-based surfactant is Dynol 604 commercially available from Air Products. Suitable dialkylsulfosuccinates include dioctylsulfosuccinates. The preferred wetting agent is a fluorosurfactant which includes both nonionic fluorosurfactants and an anionic fluorosurfactants. Most preferably the wetting agent is a nonionic fluorosurfactant. Suitable nonionic fluorosurfactants include fluoroaliphatic ethoxylates and related derivatives. Specifically, Clariant Fluowet OTN and DuPont Zonyl FSN 100 are nonionic surfactants that performed well. Fluowet OTN is a proprietary fluoroaliphatic ethoxylate commercially available from Clariant. Zonyl FSN 100 is a Telomer B monoether with polyethylene glycol which is a 1:1 mixture of poly(oxy-1,2-ethandiyl), α-hydro-Ω-hydroxy-ether with α-fluoro-Ω-(2-hydroxyethyl)poly(difluoromethylene). Suitable anionic fluorosurfactants include fluoroalkylsulfonates and carboxylates with a range of counter ions that include potassium, sodium, and amines. Preferably, the fluorosurfactant is present in an amount of about 0.1% to 1.0% by weight of the dry film composition. More preferably, the fluorosurfactant is present in an amount of about 0.1% to 0.5% by weight of the dry film composition.
The solid film die-side lubricant also optionally includes a corrosion inhibitor and/or a defoamer. Suitable defoamers include neo-decanoic acid. Suitable corrosion inhibitors include soaps or salts of carboxylic acids or organo-sulfonates. Agents capable of adjusting the pH of the lubricant may also be included, such as, for example, amines (e.g., alkanolamines).
Regardless of whether the die-side lubricant is solid or liquid at the time of emplacement or whether the die-side lubricant has an aqueous-based liquid after being emplaced, the coefficient of sliding friction between two metal surfaces with a layer between them of a die-side lubricant to be used in a process according to the invention preferably is not more than about 0.3 to 0.5, more preferably is not more than about 0.1 to 0.3, and most preferably is not more than about 0.04 to 0.1.
Furthermore, the die-side lubricant is preferably capable of being readily cleaned from the hydroformed object after hydroforming is complete, preferably with an aqueous-based cleaner. Preferably, the die-side lubricant is capable of being cleaned at a temperature not higher than 55° C., more preferably a temperature not higher than 40° C., and most preferably at a temperature not higher than 28° C. This preference is not inconsistent with the need for pressure-side fluid resistance of the die-side lubricant as described above. Typical aqueous based cleaners are either more acidic or more alkaline than most aqueous pressure-side fluids used in hydroforming. Furthermore, even if the cleaners are neutral, they usually contain other cleaning-promoting ingredients such as detersive surfactants that are not present in typical pressure-side fluids for hydroforming.
The die-side lubricant is also preferably easy to separate from the pressure-side fluid should the lubricant become contaminated by the pressure-side fluid. Accordingly, self-segregation of the die-side lubricant into a separate phase that can be skimmed or drained off from a reservoir of pressure-side fluid is highly desirable.
Finally, the lubricant is preferably easy to apply to the surface to be lubricated, without producing any hazard such as flammable, toxic, or noxious fumes, without requiring any equipment more complicated than simple spray, immersion, and/or roll coating, and without requiring any special drying equipment. For example, if a die-side lubricant that is a solid when emplaced ready for use can be applied from a latex and allowed to dry in the ambient air without producing any fire hazard or unpleasant odor, there is a substantial practical advantage and therefore a preference for it over a solid die-side lubricant that must be melted to be applied and then quickly cooled to avoid having the melted die-side lubricant run off the substrate being hydroformed.
In another embodiment of the present invention, a process for hydroforming a tube of a ductile solid material is provided. The process comprises the following steps:
Only a relatively thin layer of the die-side lubricant is needed for satisfactory lubrication. More particularly, the average thickness of the die-side lubricant layer formed before hydroforming begins preferably is in the range 0.2 to 200 microns, more preferable in the range 1.0 to 100 microns, and most preferably about 15 microns. Uniformity of the die-side lubricant is not critical. The films may even be discontinuous ball-like lumps and aggregates evenly distributed over the surface of the part.
Preferred lubricants for use according to the invention can be readily removed from surfaces of metal ductile tubes, after hydroforming is completed, by conventional alkaline cleaners.
Except for use of the characteristic lubricant for this invention as described above, the process conditions for a hydroforming process according to the invention are normally the same as those already in use in the art. A process according to the invention is particularly advantageous in “high pressure” hydroforming, in which the hydraulic pressure in step (V) of the process as described above is at least 340 bars and independently is particularly advantageous in hydroforming cold rolled steel, but is suitable for hydroforming any other ductile solid as well. Hydroforming with these lubes is successful with hot-rolled steel, cold-rolled steel, and aluminum, both 5000 and 6000 series alloys.
The invention may be further appreciated by consideration of the following examples and comparison examples. In all of the tests below, the metal substrate was type ADKQ 95 hot-rolled steel, which is one of the most commonly hydroformed substrates.
Cornerfill Test
The cornerfill test is designed to test the properties required by a die-side hyroforming lubricant in the expansion zone of a hydroforming process. In these tests, the exterior surface of a welded cylindrical steel tube was coated with test die-side lubricant and then mounted in a die with a square cross-section that was within one millimeter of touching the exterior cross-section of the cylindrical steel tube at the center of all four walls of the square die, with no weld line at or near one of these centers of the die walls. The lubricant-coated exterior of the steel tube was then sprayed lightly with water before the die was closed. The interior of the steel tube was then filled with a volume of a water-based pressure side fluid, and the pressure in the tube was then increased until the tube burst. Sensors detected the pressure at various stages of expansion, the maximum pressure before the tube burst, and the maximum expansion of the tube. The burst tube was then removed from the die, and the tube burst location was noted. Then the dimensions of the burst tube were measured and the true thickness strain was calculated for seven locations: the four corners and the centers of the three walls of the square cross-section into which the tube had expanded that did not include the original welded area. Three of the properties measured in this type of test are generally considered relevant to performance in actual hydroforming. A higher burst pressure is better than a lower one; a low standard deviation of the true thickness strain is better than a higher one; and a burst near the center of the tube is better than a burst in any other part of the tube.
Twist Compression Test
A twist compression test is designated to test the properties required by a die-side hydroforming lubricant in transition zones near the edges of expansion zones in hydroforming. In these tests, an annular tool was rotated under pressure over a flat plate of steel on which the test lubricant had been emplaced. The pressure applied on the lubricated plate in one set of tests was 10,000 psi and in another was 15,000 psi. These pressures are typical of commercial hydroforming of hot rolled steel tubes. A plot of the coefficient of friction as a function of time was generated. The results are reported at 1, 2, and 3 revolutions. The test was first conducted dry for each lubricant and then twice after the lubricant had been sprayed lightly with water. Only the average of the latter two of these measurements is reported below. The tests were also performed on lubricants sprayed with Novacool 9034, a pressure-side fluid commercially available from Henkel Corporation, Madison Heights, Mich. The lower the coefficient of friction in these tests, the better performance the lubricant usually gives in the transition zone.
Sliding Friction Test
The sliding friction test measures the properties of the die-side lubricant that are important in the “end-feeding zone” of a hydroforming process. In this end-feeding zone, the tube being hydroformed does not substantially expand or contract its eternal cross-section, although its walls may thin or thicken. Instead, part of the tube moves laterally along the die to allow for expansion in another part of the die. This end-feeding is very important in the production of some part designs by hydroforming. The procedure used for this type of test for which values are reported here is described in American Society for Testing and Materials (“ASTM”) Procedure 4173-82, using a compressive pressure between the sliding workpieces of 69 bars (1000 psi). (This is officially an “obsolete” ASTM test method, but it is still useful for measuring the coefficient of friction in sliding friction.) The lower the coefficient of friction in sliding friction, the better is the lubricant in the end-feeding zone.
Solid Film Lubricants
Examples 1-4 provides examples of the solid film lubricants of the present invention.
The monoethanolamine reduces the staining by the wax by the slightly acidic carnuba wax by raising the pH. Finally, the sodium benzoate is a corrosion inhibitor. The carnuba wax is characterized with a hardness of about 1 (ASTM-D-5), a particle size of about 0.15 microns, and a melting point of about 85° C.
The microcrystalline wax is a mixture of two waxes of hardness 5 and 13 using ASTM D-5 and with melting points centered around 68 and 101 degrees C. Furthermore, the microcrystalline wax has a particle size of about 0.18 microns.
The Fischer-Tropsch wax is characterized with a hardness of about 1 (ASTM-D-5), a particle size of about 0.6 microns, and a melting point of about 98° C.
The neodecanoic acid functions as both a corrosion inhibitor and defoamer. The Fischer-Tropsch wax is characterized as set forth above for example 3.
The results of the twist compression measurements for the lubricants in examples 1-3 are summarized in Tables 1 and 2.
The coefficient of friction (COF) was determined by the sliding friction test for various wetted and unwetted waxes. The results are summarized in Table 3. Surprisingly, the COF is reduced when the waxes are wetted.
Liquid Film Lubricants
Examples 5-8 provide examples of the liquid film compositions of the present invention.
In view of the tackiness of blown canola oil, the ethoxylated castor oil is water miscible and makes it easier to wash the composition in example 5. The ethoxylated castor oil in provided in such an amount that the washability of the formulation improved but lubricity of the formulation is only minimally degraded. Small amounts of the ethoxylated castor oil actually improve lubricity. Example 5 has a burst pressure of about 10,510 psi; a twist compression coefficient of friction at 10,000 psi of about 0.06; a twist compression coefficient of friction at 15,000 psi of about 0.05; and a sliding coefficient of about 0.065.
Tables 4 and 5 summarize the twist compression results for the composition described by example 5.
Example 8 has a burst pressure of about 10,510 psi; a twist compression coefficient of friction at 10,000 psi of about 0.06; a twist compression coefficient of friction at 15,000 psi of about 0.05; and a sliding coefficient of about 0.065
The coefficient of friction (COF) was determined for mixtures of blown canola oil and various surfactant. The COF was measure both for neat (unwetted) and wetted mixtures. Table 6 summarizes the results. The coefficient of friction is surprisingly reduced in each case when wetted. Chemal DA-6 is the surfactant ethoxylated decyl alcohol with 6 moles of ethoxylation for each mole of alcohol, Chemal DA-9 is the surfactant ethoxylated decyl alcohol with 9 moles of ethoxylation for each mole of alcohol, Chemal LA-4 is the surfactant ethoxylated lauryl alcohol with 4 moles of ethoxylation for each mole of alcohol, Chemax CO-5 is the surfactant ethoxylated castor glyceride with 5 moles of ethoxylation for each mole of castor glyceride; Chemax CO-16 is the surfactant ethoxylated castor glyceride with 16 moles of ethoxylation for each mole of castor glyceride; and Chemax CO-80 is the surfactant ethoxylated castor glyceride with 80 moles of ethoxylation for each mole of castor glyceride.
The COF was determined for neat (unwetted) and wetted mixtures of blown canola oil and the surfactant Chemax CO-40. Table 7 summarizes the COF for varying amounts of Chemax CO-40 in blown canola oil, Z2, viscosity. Chemax is an ethoxylated caster glyceride with 40 moles of ethoxylation for each mole of caster glyceride. Again, the wetted mixtures have lower COF than the neat mixture.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10/339,523 | Jan 2003 | US | national |
This application is a continuation-in-part of U.S. application Ser. No. 09/957,911 filed Sep. 21, 2001 which, in turn, claims the benefit of U.S. Provisional Application Ser. No. 60/234,833, filed Sep. 22, 2000.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US03/41577 | 12/30/2003 | WO | 1/17/2006 |
