JP6874803B2 - Gnawing resistance evaluation method - Google Patents

Description

The present invention relates to a method for evaluating the galling resistance of a die for evaluating the durability of the surface of a press molding die against galling.

Press molding using a press device and a press die is mainly used for processing a metal plate such as an automobile part. At that time, the mold galling phenomenon may occur and the mold may be damaged depending on the conditions such as the molding material, the material and shape of the press die, the presence or absence of a coating on the surface of the die, and the lubrication state at the time of press molding. Then, by continuing press molding with the damaged mold, the molding material is damaged, which leads to deterioration of product quality.
In recent years, automobile bodies _{have been required to improve collision safety and reduce CO 2} emissions by reducing the weight of the vehicle bodies. In order to meet these demands, automobile bodies such as automobile skeleton parts have high material strength. High-tensile materials are often applied.

However, when the material strength of the metal plate to be processed increases, a high contact surface pressure is generated between the material to be processed (metal plate) and the mold during molding, and in that state, sliding with the mold is accompanied. However, since the material to be processed is molded, galling is likely to occur on the surface of the mold. Therefore, it is necessary to replace and maintain the mold very frequently, and measures against galling have been an issue of applying high-tensile steel to the automobile body.
In order to solve these problems, the friction coefficient between the work material and the mold is reduced by forming a film on the surface of the mold, and galling is suppressed. Mold surface coatings include DLC (Diamond Like Carbon) method, PVD (Physical Vapor Deposition) method, and CVD (Chemical Vapor Deposition) method, and many manufacturers have developed various types of surface coatings. Has been done. Therefore, a method for evaluating the galling resistance is required to select a coating having excellent galling resistance (also referred to as mold galling resistance) of the mold from among the coatings formed on the surface of the mold.

As a method for evaluating the galling resistance of a mold, for example, the evaluation method described in Non-Patent Document 1 has been proposed. All of the mold galling evaluation methods proposed in Non-Patent Document 1 are methods in which a force is applied in the direction perpendicular to the surface of the work material to evaluate under lubricating conditions such as rust preventive oil, kerosene, and Japanese working oil. ..
There is also a galling resistance evaluation method described in Patent Document 1. In Patent Document 1, a metal plate is formed by using a press machine and using a punch block having three or more recesses on the outer circumference and a die block having a fitting portion to be fitted with a predetermined clearance in parallel view in the pressing direction. Mold. At this time, in Patent Document 1, the metal plate is made to slide to evaluate the galling resistance.
Further, in Patent Document 2, in a state where a metal plate is sandwiched between test blocks corresponding to a press die from above and below, sliding is repeated, and the sliding surface of the test block after the test is observed to determine the number of times of sliding. The galling resistance is evaluated from the transition of the adhesion occurrence situation with the increase.

Thin Steel Sheet Molding Technology Study Group [ed.], "Press Molding Difficulty Handbook-4th Edition-", Nikkan Kogyo Shimbun, February 20, 2017, p. 452-453

Japanese Unexamined Patent Publication No. 2010-167437 Japanese Unexamined Patent Publication No. 2006-255741

However, since the mold galling evaluation method proposed in Non-Patent Document 1 is a method of evaluating under lubricating conditions such as rust preventive oil, kerosene, and Japanese working oil, a mold having a coating on the surface is evaluated. In that case, there is a high possibility that galling does not occur in the mold.
Further, in the evaluation method proposed in Patent Document 1, the clearance between the die block and the punch block is easily changed due to the displacement of the die block and the punch block, and the clearance acts in the direction perpendicular to the surface of the work piece during sliding. The force to do is also liable to fluctuate. Therefore, the method of Patent Document 1 has low reproducibility, and it is not possible to obtain a quantitative evaluation value such as a dynamic friction coefficient during sliding. Further, when a work material having a low ductility such as a high-tensile material is molded by a die block and a punch block, the work material may be cracked during molding, and when evaluating the galling resistance of the mold. Can be an inhibitory factor in.

Further, in the evaluation method proposed in Patent Document 2, depending on the test conditions, there is a possibility that an enormous number of repeated slidings may be required until it is determined that the adhesive has adhered to the sliding surface and the mold galling has occurred. There is. Further, in order to evaluate the galling resistance, it is necessary to observe all the sliding surfaces tested, which may increase the time and effort required for the evaluation.

The present invention has been made focusing on the above-mentioned problems, and an object of the present invention is to provide a method for more accurately evaluating the durability of the surface of a press molding die against galling.

The present inventor has diligently studied a method for easily evaluating the durability (galling resistance) of the surface of a press molding die with respect to galling with high reproducibility. As a result, the front and back flat portions of the sliding plate whose sliding surface has been degreased are sandwiched between a pair of dies whose surface has a flat surface and which has been coated. By observing the dynamic friction coefficient and the surface condition of the die when the material to be slid is repeatedly pulled out at a speed slower than the sliding speed assumed in press molding while a constant load is applied in the direction perpendicular to the surface. , We obtained the finding that it is possible to evaluate the galling resistance of the mold. In particular, the sliding surface of the plate to be slid is degreased, and the sliding speed is slower than the sliding speed assumed in press molding, so that the galling resistance of the die can be evaluated more accurately and more easily. I got the knowledge that it can be done.
The present invention has been made based on such findings.

Then, in order to solve the problem, one aspect of the present invention relates to a metal plate having a tensile strength of 1180 MPa or more in a pair of molds having an evaluation surface made of a flat surface on which a film is formed facing each other. This is a galling resistance evaluation method for evaluating galling resistance, in which the metal plate that has been degreased is placed on the facing evaluation surfaces of the pair of molds from the plate thickness direction, and the surface pressure between the evaluation surface and the metal plate. The metal plate is in-plane at a sliding speed slower than the processing speed at the time of press molding in a state where the metal plate is sandwiched with a constant load such that the value exceeds 0 MPa and the tensile strength of the metal plate is 10% or less. The galling resistance is evaluated from the magnitude relationship of the value of the dynamic friction coefficient between the evaluation surface and the metal plate when the metal plate is repeatedly slid in the direction a plurality of times and slid until the total sliding distance becomes 500 mm or more. However, when the evaluation of a plurality of evaluation surfaces is performed and the difference between the above dynamic friction coefficients of the two evaluation surfaces is within ± 0.02, each evaluation is performed instead of the magnitude relationship of the dynamic friction coefficient values. The gist is to evaluate the relative galling resistance between the above two evaluation surfaces based on the surface condition after the surface test.

According to the aspect of the present invention, it is possible to easily evaluate the durability (galling resistance) of the surface of the press molding die against galling with high reproducibility.

It is a schematic diagram which shows the structural example of the test apparatus which carries out the galling resistance evaluation test. It is a perspective view which shows an example of the tip part shape of a mold. It is a figure which shows an example of the planar shape of the sliding plate. It is a flowchart which shows the processing example of the galling resistance evaluation method. It is a figure which shows the relationship between the dynamic friction coefficient and stroke at the time of sliding once. It is a figure which shows the relationship between the dynamic friction coefficient and stroke at the time of repeated sliding. It is a figure of the result of observing the surface state of the mold surface at the time of repeated sliding. It is a figure which shows the observation range with a laser microscope. It is a figure which shows the relationship between the dynamic friction coefficient and stroke at the time of repeated sliding in an Example. It is a figure which shows the average friction coefficient of the mold of each film treatment. It is a figure which shows the result of the average friction coefficient of a mold when the sliding plate to which oil is attached is used. It is a figure of the result of observing the surface state of the mold surface at the time of repeated sliding.

Next, an embodiment of the present invention will be described with reference to the drawings.
<Test equipment>
Here, in the following description, a galling resistance evaluation method of the mold 1 when a test apparatus having the configuration shown in FIG. 1 is used will be described.
As shown in FIG. 1, the test device includes a pair of dies 1, a sliding plate 3 made of a metal plate, a pressing device 4, and a drawing device 7.

<Mold 1>
The pair of molds 1 are arranged inside the highly rigid mold frame 2. In this embodiment, a case where a pair of molds 1 are arranged vertically facing each other will be illustrated. However, the facing directions of the pair of molds 1 are not limited to the top and bottom. For example, the pair of dies 1 may be arranged so as to face each other in the left-right direction, and the sliding plate 3 may be slid in the vertical direction or the horizontal direction.
The upper mold 1A is detachably fixed to the mold frame 2.
The lower mold 1B is arranged to face the upper mold 1A from below. The lower portion of the lower mold 1B is detachably connected to the movable portion of the pressing device 4. The lower mold 1B can be moved up and down by the pressing device 4.

The pair of molds 1 have an evaluation surface composed of facing flat surfaces 1a. That is, the lower surface of the upper mold 1A and the upper surface of the lower mold 1B each have a flat surface 1a, and the sliding plate 3 can be sandwiched between the pair of flat surfaces 1a from above and below with a predetermined load. ing.
FIG. 2 shows an example of the mold shape at each tip of the pair of molds 1. As shown in FIG. 2, the tip surfaces of the molds 1A and 1B are a central flat surface 1a (evaluation surface) extending in a direction intersecting the sliding direction and left and right formed on the left and right sides of the flat surface 1a. It is composed of a fillet portion 1b of. In this example, a case where the flat surface 1a extends in a direction orthogonal to the sliding direction is illustrated. The pair of flat surfaces 1a is a region that can come into contact with the sliding plate 3, and for example, the central portion of the pair of flat surfaces 1a in the longitudinal direction is a region that comes into contact with the sliding plate 3.

The dimensions shown in FIG. 2 are examples. The width of the flat surface 1a, the lengths of the molds 1A and 1B, and the like may be changed according to the size and the like of the sliding plate 3 to be used. In this example, the fillet portion 1b is set to have a radius of about 3 mm. If the radius of the fillet portion 1b is extremely small or at a right angle, the sliding plate 3 may be excessively caught during sliding, and the dynamic friction coefficient may not be evaluated appropriately. Therefore, the fillet may not be evaluated properly. It is desirable that the radius of the portion 1b is 3 mm or more.
Each flat surface 1a, which is both the upper and lower evaluation surfaces, is coated to form a coating.

<Sliding plate 3>
The sliding plate 3 is composed of a flat metal plate. In the evaluation test of the present embodiment, press deformation such as bending molding does not occur, so that the metal plate constituting the sliding plate 3 does not have to be the same metal plate as the metal plate used for the pressed parts. Considering the degree of freedom of the pull-out load F, a high-strength metal plate such as a high-strength steel plate is preferable. The metal plate does not have to be a steel plate, and may be a plate material such as an aluminum alloy.
Here, the inventor uses a rolled steel sheet as a material to be rolled, and withstands the case where the rolling direction and the sliding direction of the test are configured to be the same direction and the case where the rolled steel sheet is configured to be orthogonal to each other. It was confirmed whether the evaluation of galling property would be affected. As a result of confirmation, there was no particular difference if the pull-out load F was 10% or less of the tensile strength of the sliding plate 3.
Here, oil such as rust preventive oil generally adheres to the surface of rolled steel sheets and the like.

On the other hand, the sliding plate 3 of the present embodiment is subjected to an organic solvent such as alcohol, acetone, or toluene before being used for the test (before being sandwiched between the pair of molds 1) on the surface of the sliding plate 3. It is used for evaluation tests after degreasing rust preventive oil, cleaning oil, etc. adhering to.
FIG. 3 shows an example of the shape of the test piece of the sliding plate 3. The shape of the test piece is basically preferably a strip shape, but if there is no problem in mounting on the test device and the test piece has a length L that can secure a sufficient sliding distance, the sliding surface (sliding direction). There are no restrictions on the plate shape except that the width in the direction orthogonal to) is a constant width W.

<Pressing device 4>
The pressing device 4 of the present embodiment is composed of a pressing hydraulic cylinder device whose axis is directed in the vertical direction. The pressing device 4 is not limited to the hydraulic cylinder device, and is not particularly limited as long as it is a device capable of advancing and retreating one mold 1 and generating a pressing load P.
In the case of a pressing hydraulic cylinder device, the pressing load P generated by the pressing hydraulic cylinder device can be obtained by using the hydraulic pressure of the hydraulic cylinder device or the load cell. In this embodiment, it is assumed that the measurement is performed by a load cell.
By driving the pressing device 4, the sliding plate 3 is sandwiched between the pair of dies 1 from above and below, so that a load can be applied in the direction perpendicular to the surface of the sliding plate 3.

<Pulling device 7>
The pull-out device 7 of the present embodiment includes a pull-out hydraulic cylinder device 5 and a chuck 6 provided at the tip of a piston portion of the pull-out hydraulic cylinder device 5.
The chuck 6 is a device that connects the sliding plate 3 to the piston portion of the pull-out hydraulic cylinder device 5 by sandwiching the sliding plate 3 from above and below.
The pull-out hydraulic cylinder device 5 is a device that pulls the sliding plate 3 in the sliding direction.
By using the pull-out hydraulic cylinder device 5 or the load cell, the pull-out load F of the sliding plate 3 can be obtained.

<Displacement meter 8>
The displacement meter 8 is a device that measures the sliding distance of the sliding plate 3.
The displacement meter 8 measures the sliding distance of the sliding plate 3 by measuring the stroke amount of the piston portion of the pull-out hydraulic cylinder device 5, for example.
Then, when the sliding distance measured by the displacement meter 8 reaches a preset set stroke amount, the drawing by the pull-out hydraulic cylinder device 5 is stopped.
The set stroke amount is, for example, 100 mm.

<Evaluation test method>
As shown in FIG. 1, the test apparatus arranges a pair of molds 1 to be evaluated vertically opposed to each other inside a highly rigid mold frame 2. At this time, the lower mold 1B is fixed to the pressing device 4 including the pressing hydraulic cylinder device.
By arranging the sliding plate 3 with the plate thickness facing up and down between the pair of dies 1 and driving the pressing device 4, the lower die 1B is raised and covered by the upper and lower dies 1. The sliding plate 3 is sandwiched from above and below by the set pressing load P. As a result, a load is applied to the sliding plate 3 in the direction perpendicular to the surface of the sliding plate 3.
Here, prior to the evaluation test, it is advisable to press the pressure-sensitive paper with the pair of upper and lower dies 1 to confirm whether or not the flat surfaces 1a of the upper and lower dies 1A and 1B hit uniformly. At this time, if the flat surfaces 1a of the upper and lower molds 1A and 1B are not uniformly in contact with each other, the inclination of the flat surface 1a of the mold 1 is adjusted by using a shim plate or the like.

The area where the sliding plate 3 is loaded from the upper and lower molds 1 is a value obtained by multiplying the width W of the sliding plate 3 by the width of the flat surface 1a of the mold. It is desirable that the surface pressure applied to the sliding plate 3 is larger than 0 MPa and is 10% or less of the tensile strength of the sliding plate 3. If it is 10% or less of the tensile strength of the sliding plate 3, the elongation generated in the sliding plate 3 falls within an allowable range. When a metal plate having a tensile strength of 1500 Mpa is used, the pressing load P is 150 Mpa or less.
The pull-out speed, that is, the sliding speed is preferably slower than the press speed at the time of press molding. The sliding speed is, for example, 150 mm / min or more and 300 mm / min or less.

The chuck 6 grips the end portion of the sliding plate 3 in the longitudinal direction before and after the pinching due to the raising of the lower mold 1B. As a result, the sliding plate 3 is connected to the pull-out hydraulic cylinder device 5. The direction of advance / retreat of the piston portion of the pull-out hydraulic cylinder device 5 is set to be in-plane along the longitudinal direction of the sliding plate 3. That is, the shaft of the piston portion and the longitudinal direction of the sliding plate 3 are set to coincide with each other. In FIG. 1, the pull-out hydraulic cylinder device 5 can slide and move in the longitudinal direction of the sliding plate 3, and the sliding plate 3 is pulled out from right to left. It is configured to slide.
Here, the load generated by the pressing device 4 and the pull-out hydraulic cylinder device 5 is acquired by, for example, a load cell at a predetermined sampling cycle. Further, the moving distance of the sliding plate 3 pulled out by the pull-out hydraulic cylinder device 5 is acquired by the contact type or non-contact type displacement meter 8.

After setting as described above, the pull-out hydraulic cylinder device 5 is operated to pull out the sliding plate 3 from the mold 1 in the in-plane direction (longitudinal direction in this embodiment) of the sliding plate 3. At this time, the data of the pressing load P, the pulling load F, and the moving distance of the sliding plate 3 are acquired by the load cell and the displacement meter 8 at predetermined sampling cycles, respectively.
Here, the dynamic friction coefficient μ acting on one side (upper surface or lower surface) of the sliding plate 3 at the time of pulling out can be calculated by “μ = F / 2P”, where P is the pressing load and F is the pulling load. ..

The pressing load P and the pulling load F are each acquired at a predetermined sampling cycle, and are taken as the average value of the acquired values acquired at the time of sliding. Here, since the values are unstable at the start of sliding, the pressing load P and the pulling load F are set from, for example, an intermediate position of the sliding stroke (for example, a position of 1/2) to immediately before the end of the sliding stroke. It is preferable to use the average value between.
After the above test, the galling resistance of the evaluation surface, that is, the galling resistance of the mold 1 (mold galling resistance), depends on at least one of the obtained dynamic friction coefficient and the surface state of the flat surface 1a which is the evaluation surface after the test. To evaluate.

As a general rule, evaluation is based on the coefficient of dynamic friction. In this case, it is determined that the smaller the coefficient of dynamic friction is, the higher the galling resistance of the mold 1 is (first evaluation). The first evaluation may be an absolute evaluation based on the value of the coefficient of dynamic friction.
However, in the evaluation between a plurality of evaluation surfaces, if the difference between the dynamic friction coefficients of the two evaluation surfaces is within ± 0.02, the surface condition of the evaluation surfaces after the test is replaced with the evaluation based on the magnitude of the dynamic friction coefficients. It is determined that the evaluation surface having less adhesion of the sliding plate 3 to the evaluation surface or less wear on the evaluation surface has better galling resistance (second evaluation). ).

The evaluation is performed by, for example, acquiring the value of the dynamic friction coefficient and the surface condition by conducting a test with the mold 1 as a reference in advance, using it as the evaluation reference data, and comparing it with the evaluation reference data.
Or, if there are multiple coatings to be compared, perform the above test with the mold 1 provided with each coating, compare the dynamic friction coefficient and surface condition, and compare the relative coatings among the plurality of coatings. The galling resistance of the mold 1 is determined. In this case, it is preferable to carry out the test under the same conditions except for the coating film.

Next, an example of the processing of the above-mentioned galling resistance evaluation method will be described with reference to FIG.
A pair of molds having an evaluation surface on which a coating is formed are attached to the above testing machine (step S10). After that, the flatness of the evaluation surface of the mold is confirmed by sandwiching a pressure-sensitive paper or the like (step S20).
After that, the sliding test is repeated until the total sliding distance becomes 500 mm or more, and the coefficient of dynamic friction between the evaluation surface of the mold and the sliding plate 3 is obtained (step S30).
Before performing this sliding test, the surface of the plate to be slid 3 is degreased.

In addition, the following conditions are set as the conditions for the sliding test.
Pressing surface pressure P: 0 MPa <P ≦ 10% of the tensile strength of the metal plate constituting the sliding plate 3
-Sliding speed: slower than press working-Sliding distance: 500 mm or more in total In addition, a sliding test according to steps S10 to S20 may be performed on a plurality of dies, or the coating formed on the same flat surface may be changed. Or (change the evaluation side) and carry out multiple times.
Further, the sliding test according to steps S10 to S20 may be performed a plurality of times on the evaluation surface under the same conditions. In this case, the obtained average value of the plurality of dynamic friction coefficients is used for the evaluation.

After the above test, the evaluation surface is evaluated.
In the first evaluation (step S50), the evaluation is performed using the acquired value of the dynamic friction coefficient. In the first evaluation based on the dynamic friction coefficient, it is determined that the smaller the dynamic friction coefficient, the higher the galling resistance of the mold 1.
However, it is determined whether or not the difference between the dynamic friction coefficients of the two evaluation surfaces is within ± 0.02 (step S40), and when it is determined that the difference is within ± 0.02, a difference is observed in the dynamic friction coefficients. It is determined that there is no evaluation surface (step S60), and the galling resistance is evaluated by the second evaluation (step S70).

In the second evaluation, when the evaluation is made in the surface state of the flat surface 1a after the test, it is determined by the change in the roughness of the surface. It is determined that the larger the height of the unevenness of the surface after sliding, that is, the rougher the surface shape after sliding is, the lower the galling resistance of the mold 1. Here, the minute powder generated by rubbing the sliding plate 3 by sliding temporarily adheres to the surface of the flat surface 1a, so that only that portion becomes convex. Further, when the powder is removed, if the galling resistance is poor, a part of the coating film may be removed together with the removal of the powder to form a recess.
The evaluation of the surface condition after the test in the second evaluation is not limited to the sensitivity evaluation by observing the roughness, and the surface roughness is measured by a roughness meter to determine the degree of roughness and the roughness. The galling resistance may be evaluated by the change.

The relationship between the dynamic friction coefficient and the stroke amount (sliding distance) obtained by performing the above-mentioned evaluation test using the die 1 which has been subjected to two coating treatments having the same properties and the sliding plate 3 having the same properties. Is shown in FIG.
In FIG. 5, the film treatment B shows a lower dynamic friction coefficient than the film treatment A, and it can be seen that the film treatment B is superior in mold galling resistance. Here, when evaluating by the value of the dynamic friction coefficient, for example, the set stroke amount may be set to 100 mm, and the average values of the dynamic friction coefficients acquired at 50 mm or more and less than 100 mm may be compared with each other.

Further, when it is desired to evaluate the mold galling resistance according to the number of times the mold 1 is used, the sliding plate 3 is slid in the in-plane direction with the sliding plate 3 sandwiched between the pair of molds 1 described above. It is preferable to repeat the step of making the die a plurality of times and acquire at least one of the coefficient of dynamic friction for each step (each time of sliding) or the surface state after sliding on the evaluation surface to evaluate the galling resistance.
Further, when the step of sliding the sliding plate 3 in the in-plane direction while sandwiching the sliding plate 3 which is a metal plate that has been degreased by a pair of dies 1 is repeated a plurality of times, the total sliding is performed. It is preferable to set the moving distance to be 500 mm or more. By setting the total sliding distance to 500 mm or more, it is possible to more reliably evaluate the galling resistance. There is no particular upper limit on the total sliding distance, but it is, for example, 1000 mm or less.

FIG. 6 shows the relationship between the dynamic friction coefficient and the stroke amount obtained from the repeated flat plate pull-out sliding test using the sliding plate 3 and the die 1 which has been subjected to the coating treatment as in FIG. In this example, the test was carried out by replacing the sliding plate 3 with a new sliding plate 3 each time. Further, it is a result that the sliding distance at one time is 100 mm and the number of repetitions is 20 times. In the case of FIG. 6, even in the repeated flat plate pull-out sliding test, it can be determined that the surface coating B has a lower friction coefficient than the surface coating A and is excellent in mold galling resistance.

In the results shown in FIG. 6, the coefficient of kinetic friction is almost constant throughout the total stroke, and the coefficient of kinetic friction is stable. Therefore, it is possible to determine the superiority or inferiority of the mold galling resistance from the magnitude relation of the average value of the dynamic friction coefficient over the total stroke. The average value of the dynamic friction coefficient in this case is a value obtained by obtaining the average value in each step and further taking the average value of the average values in each step.
On the other hand, it is assumed that the coefficient of dynamic friction gradually increases, decreases, and fluctuates throughout the total stroke and is not stable. In that case, the mold galling resistance is inferior when the dynamic friction coefficient of the maximum stroke deviates by 50% or more from the stroke in which the average value of the dynamic friction coefficient of each process is the minimum among the total strokes. It is determined that it is. It should be noted that the mold galling resistance is higher when the coefficient of dynamic friction is stable throughout the total stroke.

Next, in each coating treatment, out of a total of 20 slidings (processes) in the test obtained in FIG. 6, before sliding, after sliding once, after sliding 10 times, and sliding 20 times. The surface of the mold 1 later was observed with a laser microscope. FIG. 7 shows the state of the height of the unevenness on the flat surface. At this time, the range of the mold 1 observed with the laser microscope is schematically shown in FIG. In FIG. 8, reference numeral S is a sliding region, and reference numeral K is a range in which the surface state is observed. That is, the state of the surface roughness of the sliding plate 3 at the center position in the width direction was evaluated. It is estimated that the center position of the sliding plate 3 in the width direction is the most stable.
Here, the surface condition was observed by observing the unevenness of the surface of the mold 1 with a laser microscope, but the surface of the mold 1 was observed using an observation device such as a scanning electron microscope (SEM) or an electron probe microanalyzer (EPMA). The superiority or inferiority of the mold galling resistance may be determined.

In the surface observation results of the mold 1 subjected to the coating treatments A and B shown in FIG. 7, the surface of the mold 1 of the coating treatment A has a convex portion, that is, a metal plate having a sliding plate 3 on the surface. Fine powder is stuck. On the other hand, it can be seen that the surface of the mold 1 of the coating treatment B is almost flat over the total stroke, and the fine powder of the sliding plate 3 is not adhered.
Normally, fine powder of a metal plate, which is a sliding plate 3, tends to adhere to the surface of a mold having low mold galling resistance. The small pieces of the metal plate adhered to the mold surface repeatedly slide to peel off from the mold surface and re-adhere repeatedly. Therefore, the mold galling resistance is determined not only from the surface condition of the mold 1 after the final test of the repeated sliding test but also from the history of the surface condition of the mold 1 measured throughout the initial to middle to late stages of the repeated sliding test. Is desirable.

As described above, from the value of the dynamic friction coefficient obtained from the one-time or repeated sliding test using the mold 1 subjected to various coating treatments and the observation result of the surface state of the mold 1 after the sliding test. Comprehensively judging, it can be evaluated that the coating treatment B is superior to the coating treatment A in the mold galling resistance.
Here, in the present embodiment, the metal plate to be the sliding plate 3 is degreased in advance. As will be described later, when a metal plate not subjected to the degreasing treatment is used, the difference in the dynamic friction coefficient becomes smaller than that in the case of the degreasing treatment, and the evaluation accuracy deteriorates. Therefore, in the present embodiment, the metal plate to be the sliding plate 3 is degreased in advance to improve the evaluation accuracy.

Next, an example based on this embodiment will be described.
The mold 1 to be evaluated uses SKD11, which is a steel for cold molds, as a base material. The surface of the flat surface 1a was subjected to four types of coating treatments, C, D, E, and F. The shape of the mold 1 is the same as that shown in FIG. 2, and a sliding test was performed using the test apparatus having the configuration shown in FIG. The metal plate to be the sliding plate 3 was a 1320 MPa class cold-rolled steel plate, and a plate thickness of 1.6 mm was used.
The surface of the metal plate was degreased with acetone. For comparison, a sliding plate 3 coated with Preton R352L, which is a general cleaning oil, was also separately prepared and evaluated after the degreasing treatment.

The die 1 coated with the coatings C to F was pressed against the sliding plate 3 from above and below, and the pressing hydraulic cylinder device was operated so that a surface pressure of 20 MPa was applied. Then, the pull-out hydraulic cylinder device 5 was operated so that the sliding distance was 100 mm and the sliding speed was 200 mm / min, and the step of pulling out the sliding plate 3 was carried out 20 times repeatedly. If the sliding speed is low, the coefficient of kinetic friction increases, so it becomes easier to determine the mold galling resistance. In this test, the speed was set to 200 mm / min, which is slower than the press stroke speed. The test may be performed at a lower speed than this, but since the test time becomes long, about 200 mm / min is preferable.

FIG. 9 shows the relationship between the pull-out stroke of the degreased sliding plate 3 and the coefficient of dynamic friction in the die 1 obtained at this time. Further, FIG. 10 shows an average value (average friction coefficient) of the dynamic friction coefficient in each coating treatment at this time.
Further, FIG. 11 shows an average value (average friction coefficient) of the dynamic friction coefficient in the sliding test of the first step using the sliding plate 3 coated with Preton R352L.
Further, the range K shown in FIG. 8 on the surface of the mold after each sliding using the metal plate in the degreased state was observed with a laser microscope. The state of the unevenness of the observed surface is shown in FIG.

<Evaluation result>
As can be seen from FIG. 9, in the coating treatments C to F using the degreased metal plate, the dynamic friction coefficient was stable in all the coating treatments throughout the total stroke. Therefore, it was evaluated by the average value (average friction coefficient) of the dynamic friction coefficient in the total stroke.
As can be seen from FIG. 10 showing the average friction coefficient in each coating treatment, the coating treatment F has the lowest dynamic friction coefficient in the average value of the dynamic friction coefficient of the degreased plate 3 in each coating treatment, and the coating treatment C. Has the highest coefficient of dynamic friction. Further, in the first evaluation based on the present invention, it can be evaluated that the coating treatment F has the highest galling resistance and the coating treatment C has the lowest galling resistance at this point.
Further, since the coating treatments D and E show approximately the same approximate average friction coefficient, it is difficult to evaluate the galling resistance based on the magnitude relationship of the dynamic friction coefficient. Since the average value of the dynamic friction coefficients of the film treatment D and the film treatment E is 0.349, which is within ± 0.02 from the average value, the galling resistance is evaluated by the second evaluation.

Next, from the results of surface observation of the mold 1 after each sliding shown in FIG. 12, the surface shape of the coating treatments C to F is a convex portion, that is, a sliding surface in the coating treatment C having the highest average friction coefficient. Since traces of the moving plate 3 adhering to the surface of the mold were confirmed, it was evaluated that the mold galling resistance was the worst. Further, in the coating treatment F having the lowest average friction coefficient, the mold surface was almost flat, and no damage such as adhesion of the sliding plate 3 or wear of the coating was confirmed, so that the mold galling resistance was the best. Can be evaluated. In this way, it can be seen that the galling resistance can be evaluated from the evaluation of only the surface condition.

On the other hand, with respect to the mold surfaces of the coating treatments D and E, for which it was difficult to determine the galling resistance by the first evaluation, adhesion or wear of the sliding plate 3 could not be confirmed on the surface by the coating treatment D. In the coating treatment E, adhesion of the sliding plate 3 is observed. As described above, when it is difficult to determine the galling resistance by the first evaluation, it can be seen that the second evaluation, which evaluates the surface condition of the evaluation surface after the test, can evaluate it accurately.

By comprehensively judging the above results, it is evaluated that the coating treatment F has the best mold galling resistance, and then the coating treatment D and the coating treatment E have the worst mold galling resistance. Can be done.
On the other hand, as shown in FIG. 11, when the sliding test was performed under the condition that Preton R352L was applied, the average value of the dynamic friction coefficient after sliding was found to be the average of the dynamic friction coefficient even if the type of coating treatment changed. The value is in the range of approximately 0.10 to 0.11. That is, it is not possible to accurately evaluate the performance difference in the galling resistance of the mold due to the difference in the coating treatment. Therefore, by performing a sliding evaluation after degreasing the sliding plate 3, even if a film is formed on the mold surface, the galling resistance can be evaluated with high accuracy.

1 Die 1A Upper mold 1B Lower mold 1a Flat surface 1b Fillet part 2 Mold frame 3 Sliding plate 4 Pushing device 5 Pull-out hydraulic cylinder device 6 Chuck 7 Pull-out device 8 Displacement meter

Claims (1)

This is a galling resistance evaluation method for evaluating the galling resistance of the evaluation surface with respect to a metal plate having a tensile strength of 1180 MPa or more in a pair of molds having the evaluation surfaces of flat surfaces on which a film is formed facing each other.
On the facing evaluation surfaces of the pair of dies, the surface pressure between the evaluation surface and the metal plate exceeds 0 MPa from the thickness direction of the degreased metal plate, and the tensile strength of the metal plate The metal plate is repeatedly slid in the in-plane direction a plurality of times at a sliding speed slower than the processing speed at the time of press molding in a state of being sandwiched with a constant load of 10% or less, and the total sliding is performed. The galling resistance was evaluated from the magnitude relationship of the value of the dynamic friction coefficient between the evaluation surface and the metal plate when the metal plate was slid until the distance was 500 mm or more.
When the evaluation of a plurality of evaluation surfaces is performed and the difference between the dynamic friction coefficients of the two evaluation surfaces is within ± 0.02, instead of the magnitude relationship of the dynamic friction coefficient values, the evaluation surfaces of each evaluation surface are evaluated. A galling resistance evaluation method, characterized in that the relative galling resistance between the two evaluation surfaces is evaluated according to the surface condition after the test.

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