JP2015054346A - Cold press die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a press die that is used to apply cold press working to a high-strength steel plate and that is excellent not only in galling resistance but also in maintainability.SOLUTION: A coat made of zinc or a zinc alloy is imparted to a surface of a die 1.

Description

  The present invention relates to a press die used for cold-pressing a high-tensile steel plate (high ten), and more particularly, to a press die having excellent galling resistance and excellent maintenance properties.

  By using a high-tensile steel plate (high tensile) having a high tensile strength, the exterior of an automobile or the like can be thinned and the weight of the vehicle body can be reduced. Such steel sheets are often hot dip galvanized on the surface from the viewpoint of rust prevention as the exterior of the vehicle body, and are widely distributed as “hot dip galvanized steel sheets”. On the other hand, press working is often used for forming, but because the tensile strength is high, the press pressure is also high, control of uniform elongation to prevent cracking, shape fixing control to suppress spring back, press gold There are many problems in machining, such as dimensional control due to early wear of the mold.

  For example, in Patent Document 1, by adjusting the composition of each component of C, Mn, N, Ti, and Nb and further controlling the structure, it is possible to combine excellent ductility and bendability with high strength and press workability. An alloy hot-dip galvanized steel sheet is disclosed. Here, an alloyed hot-dip galvanized steel sheet is described in which a hot-dip galvanized steel sheet is heated, Fe is diffused from the steel sheet into the Zn-plated layer, and a plated layer made of a Zn—Fe alloy is provided. In press working, when the plating layer contains a soft alloy phase (ζ phase) with a relatively low Fe content, plating peeling (flaking) or press cracking of the steel sheet may occur due to adhesion between the plating layer and the mold surface. On the other hand, when the plating layer contains a hard alloy phase (Γ, Γ1, δ1c phase) having a high Fe content, powdering (powdering) of the plating layer is likely to occur.

Also, for example, in Patent Document 2, a hard coating having a three-layer structure of a TiN layer, a Ti (C _x N _1-x ) layer having a gradient of C and N concentration, and a TiC layer is applied to the mold surface by the PVD method. A press die for pressing a high-strength steel plate is disclosed. In general, such press dies have a CVD method or the like so as to increase wear resistance and prevent galling during press processing (scratches on the die surface caused by contact between the die and the workpiece). A hard film made of ceramics such as TiC or TiCN is formed by the PVD method. Here, in the film formation by the CVD method, the processing temperature is high, and the distortion and thermal deformation of the mold base material become problems, and in the TiC film formed by the PVD method, the adhesion force is insufficient and it is easy to peel off and the durability is problematic. It also describes that a TiCN film having better adhesion than a TiC film is easily worn due to low slipperiness.

  By the way, even when a hard coating is applied to the mold surface in order to ensure galling resistance while suppressing wear of the press mold, the hard coating gradually wears with the press work, and eventually "galling" occurs. Will occur. In such a case, the press mold can be repaired by reforming the hard coating.

  For example, Patent Document 3 describes the repair of a press die provided with a hard coating on multiple layers. When a first coating having a large thickness is formed on the surface of the press mold, a second coating having a thickness smaller than that of the first coating is formed thereon, and the second coating is worn and the first coating is exposed. Only the worn part of the second coating or the second coating is removed, and the second coating is formed again to repair the press die.

JP 2008-255442 A JP 2008-207219 A JP 2009-166096 A

  When the hard coating is a multilayer coating as in Patent Document 3, it is possible to repair the press mold by re-forming only the coating near the worn surface, but the adhesion between the multilayer coatings. Inferior to soundness. Further, in the multilayer coating as in Patent Document 2, only the coating in the vicinity of the surface of the press die does not contribute to galling resistance at the time of press working, but it is applied to the entire multilayer coating. . Even if only the film near the worn surface is re-formed, the initial galling resistance cannot be reproduced. In view of the above, generally, it is desired to repair a press die that once removes all the multilayer coatings and forms a similar multilayer coating again.

  In addition, since the multilayer coating is a hard coating, mechanical removal is difficult, and in the case of a hard coating made of a chemically relatively stable ceramic, chemical removal is also difficult. That is, the maintainability of the mold for repairing the removal and reforming of the film is not good.

  The present invention has been made in view of the situation as described above, and an object of the present invention is to provide a press die having excellent galling resistance and excellent maintainability.

  As described above, in a press mold having a hard coating such as that used for cold pressing of a high-strength steel sheet, for example, a hard coating made of ceramics, in the repair, the mechanical or chemical of the hard coating is performed. A lot of labor is required for removal and reforming. In particular, when a multi-layered hard coating is applied, it is necessary to remove all the hard coatings once and re-form them in order to ensure the soundness of the coating, resulting in a very high cost. On the other hand, the present inventor has found that galling resistance can be improved only by applying a metal film made of zinc or zinc alloy, which is an inexpensive element and has a relatively low melting point, to the press die. In a press die provided with such a coating, it is easy to mechanically or chemically remove the metal coating, and it is relatively easy to re-form, and is excellent in maintainability.

  That is, the press die used for cold pressing the high-tensile steel plate according to the present invention is characterized in that a coating made of zinc or a zinc alloy is provided on the die surface.

  According to this invention, high galling resistance at the time of press working by the lubricating action of a coating made of zinc or a zinc alloy can be provided. Furthermore, the use of a metal film having a low melting point with a relatively inexpensive element facilitates a series of repairing steps in which the metal film is removed and re-formed, thereby providing high maintainability.

  In the above-described invention, the zinc alloy may be a Zn-Fe alloy. According to this invention, the film can be firmly adhered, and the anti-galling property due to the lubricating action during press working can be imparted satisfactorily and stably.

  In the above-described invention, the Zn—Fe alloy may be an alloy containing 5 to 25 mass% Fe in Zn. According to this invention, it is possible to provide good and stable anti-galling due to the lubricating action during press working and to provide high maintenance by a metal film having a relatively low melting point.

  In the above-described invention, the coating film may have a thickness of 5 μm or more. According to this invention, the early depletion of the lubricating action due to the peeling of the coating can be prevented, and the anti-galling property due to the lubricating action during press working can be imparted with good and stability.

It is a side view of the principal part of the press apparatus about a bending iron test. It is a figure which shows the result of a bending ironing test.

  The “bending ironing test” for evaluating the anti-galling property of the press die for cold press working as an example of the present invention and a comparative example will be described below. First, the test method will be described.

  As shown in FIG. 1, the bending and ironing test apparatus 10 is an apparatus for bending and ironing a steel sheet, and is opposed to a prismatic punch 1, a die 2 located below the punch 1, and an end surface A of the die 2. And back die 3 to be included. The punch 1 can be lowered along the end surface A of the die 2 from a position further above the upper surface B of the die 2, and the back die 3 is punched 1 so as to maintain the clearance W with the end surface A of the die 2. Is restricted from moving in the horizontal direction.

  For the punch 1, die 2 and back die 3, SKD11, which is defined as JIS G4404 alloy tool steel, is tempered to 60 HRC. As will be described later, except for a part of the comparative example, at least the surface of the punch 1 facing the end surface A of the die 2 is coated. In FIG. 2, it showed about the film of the punch 1 of Examples 1-9 and Comparative Examples 1-3. In Example 1, a single-layer metal film made of zinc is provided. In Examples 2 to 9, a single-layer metal film made of a Zn—Fe alloy (zinc alloy) having a predetermined component composition is provided.

  In Example 1, the surface of the steel material after processing is degreased, and a metal coating made of pure zinc is provided by a hot dip galvanizing method in which the steel is immersed in a hot dip galvanizing bath at 440 to 460 ° C. and air cooled. On the other hand, in Examples 2-9, the metal film which consists of zinc alloys is given by PVD process. In the PVD process, the coating time is 150 minutes, the coating temperature is 450 to 500 ° C., the bias voltage is 100 V, the atmospheric gas is Ar, the gas pressure is 0.5 Pa, and the arc current is 100 V.

  In Comparative Example 1, no film is provided, and in Comparative Examples 2 and 3, a film made of a single layer of nitride of TiN and TiCN is provided by the same PVD treatment as described above.

  Referring to FIG. 1 again, a 780 MPa class high-tensile steel plate not subjected to a surface treatment with a plate thickness T = 1.6 mm was used as the steel plate 4 as a workpiece for bending and ironing.

  In the bending and ironing process, the steel plate 4 is placed on the upper surface B of the die 2, the end 4 a is arranged so as to slightly protrude from the die 2, and the punch 1 is lowered. The end 4 a of the steel plate 4 is pushed downward by the punch 1 and bent along the end surface A of the die 2. Here, no lubricant is used. Further, the clearance W from the end surface A of the die 2 to the punch 1 is adjusted to 10% of the plate thickness T of the steel plate 4 by the back die 3, and the steel plate 4 is subjected to ironing as well as bending. Such bending and ironing was continuously performed by a progressive press at a speed of 50 shots / minute.

  Each time 100 shots of bending and ironing were performed, it was observed whether the surface of the steel plate 4 was galling, and the number of shots that produced this “galling” was defined as “lifetime” regarding the galling resistance of the coating film of the punch 1. About such life. The results are summarized in FIG.

  Next, the results of the above-described bending and ironing test of the steel sheet and the galling resistance of the mold will be described.

  As shown in FIG. 2, in the punch 1 to which the coating film of Comparative Example 1 was not applied, the mold was galled after about the first about 10 shots, and the bending and ironing process could not be continued. On the other hand, in the punch 1 to which the metal film made of zinc or zinc alloy of Examples 1 to 9 was applied, no scratches were observed even after passing at least 100 shots, compared with Comparative Example 1 in which no film was applied. The usefulness of the metal coating made of zinc or a zinc alloy in galling resistance was confirmed.

  Further, in Examples 7 to 9 in which the metal coating was made of a zinc alloy, the lifetime for galling resistance was increased from 100 shots to 2300 shots as the thickness of the metal coating was increased to 1, 5 and 15 μm. . That is, it is considered that the metal coating made of zinc or zinc alloy gradually peels off every shot of the bending and ironing process and reduces the film thickness, and the peeled piece provides a lubricating action with the steel plate 4. If the film thickness of the metal coating is thin, the lubricating action is lost earlier. Although it does not specifically limit about the film thickness of a metal film, It is preferable that it is larger from a viewpoint which gives an above-mentioned lubrication effect | action in the range which does not impair adhesiveness. On the other hand, in Examples 7-9, since the lifetime about the galling resistance of a metal mold | die is greatly extended by the film thickness of at least 5 micrometers or more, it is preferable to set it as 5 micrometers or more.

  By the way, in Examples 1 and 2, which were metal coatings made of zinc and a zinc alloy, respectively, the lifetime for galling resistance was the same, but the film thickness was small in the latter. This is because, by adding Fe to zinc and alloying, the metal coating can be more firmly adhered to the base material of the punch 1, and sufficient lubrication even if the amount of peeling for each shot of bending and ironing is reduced That you can give. Thereby, good and stable galling resistance can be imparted.

  Comparing Examples 3 to 5 with a metal film made of a zinc alloy, if the Fe content is increased to 5, 10 and 25% by mass, respectively, the lifetime for galling resistance becomes 1700, 2000 and 1500 shots, respectively. It became the largest at 10% by mass. All of these have a longer life against galling resistance than Comparative Examples 2 and 3, which are hard coatings made of nitride.

  Similarly, when Examples 2 and 6 having zinc alloy films having different Fe contents were compared, the life of galling resistance of Example 6 was shorter than that of Example 2 although the film thickness was the same. This is because when the Fe content is increased to a predetermined value or more, about 30% by mass of Example 6 above, the peeling piece generated at every shot as described above adheres to the steel plate 4, and the coating wears quickly, I think that the lubricating action will be depleted earlier.

  From the above, considering the results of Example 1 together, the Fe content is preferably in the range of 5 to 25% by mass, more preferably 5 to 10% by mass, with respect to Zn.

  As described above, the galling resistance of the mold is not limited to this, but only by applying a metal coating made of zinc or a zinc alloy to a press mold for cold pressing by hot dip galvanizing or PVD. Can be improved. Compared with the conventional nitride film, the metal film made of zinc or zinc alloy in this example is a relatively soft film, so it is easy to remove mechanically. Removal is easy. Further, such a metal film is made of a metal element having a low melting point and can be easily re-formed. In addition, since the metal film gradually decreases in film thickness for each shot as described above, the dimensional accuracy in the thickness direction is not strictly required. Moreover, it may be a single layer and is easier to re-form than a multilayer coating. That is, a press die provided with such a coating is excellent in maintainability. In addition to such excellent maintainability, such a metal film is made of an inexpensive metal element and is inexpensive. Therefore, as in Example 7, even if the life against galling resistance as in Comparative Examples 2 and 3 cannot be obtained, the coating can be re-formed easily and inexpensively, so that the total cost can be reduced.

  As mentioned above, although the Example by this invention and the modification based on this were demonstrated, this invention is not necessarily limited to this, A person skilled in the art will deviate from the main point of this invention, or the attached claim. Various alternative embodiments and modifications could be found without doing so. For example, high-speed steel such as SKH51 or super hard material mainly composed of tungsten carbide can be used for the press die.

1 Punch 2 Die 3 Back die 4 Steel plate

Claims (4)

  A cold pressing die used for cold pressing a high-tensile steel plate, wherein a coating made of zinc or a zinc alloy is provided on the surface of the die.   The cold press die according to claim 1, wherein the zinc alloy is a Zn-Fe alloy.   The cold press die according to claim 2, wherein the Zn-Fe alloy is an alloy containing 5 to 25 mass% of Fe in Zn. 4. The cold press die according to claim 1, wherein the coating has a thickness of 5 [mu] m or more.

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