JP2002035885A - Estimation method of damage form of forging die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a technique for estimating a damage form generating in a forging die and a life of the forging die on the basis of the damage form of the forging die. SOLUTION: A data base outputting a damaged form generating in a forging die according to the combination condition of a mechanical load and a thermal load is constructed in advance by inputting the mechanical load and the thermal load acting on the forging die. After that, a mechanical load and a thermal load acting on the planning forging die are calculated. The calculated combination of loads is input in the data base and by inputting the calculated combination of loads and outputting a damaged form from the data base, a damage form generating in the forging die is estimated. The life of the forging die can be also estimated from the number of forging and the change of the damaged form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for predicting a damage form occurring in a forging die and further for predicting a life of the forging die.

[0002]

2. Description of the Related Art In forging, large force and high heat are applied to a forging die, and the forging die is easily damaged and its life is short.
For this purpose, a forging process is devised to adopt a forging process that extends the life of the mold as much as possible. However, at present, a technology for predicting the life of the forging die to a reliable degree has not been developed, and the forging process is determined by trial and error. In the world, technology that leads to technology for predicting the life of forging dies has been fragmentarily developed. For example, a conditional expression for predicting softening of steel due to tempering heating has been proposed (Iron and Steel, No. 10, 1980, Takeshi Inoue). However, this technique is only for prediction of temper softening of steel for machine structural use, and cannot predict the damage form and life. Although failure distribution forms have also been studied (Publications on Plastic Working Spring, Vol. 1, 1996, Shin-ichiro Fujikawa), failure forms cannot be predicted because damage factors cannot be specified. Research on the fracture theory of materials is also progressing (45th Lecture on Plastic Working 29, 1994, Miyahara et al.), But limited to fatigue fracture.
It is not sufficient for prediction of the damage form of the forging die and life prediction.
Japanese Patent Application Laid-Open No. 10-175037 discloses that a finite element method is applied to a forging die to calculate a plastic deformation stress and a maximum principal stress acting on the die, and a crack growth is calculated from the calculated plastic deformation stress amplitude and the maximum principal stress amplitude. This shows a technique of calculating the speed and calculating the number of processings until the calculated crack depth reaches a predetermined depth to calculate the life. However, the life of the mold is not only determined by the progress of cracks, but rather, in the case of a hot forging mold, the wear progresses and the life of the mold is more likely to occur. With the technology of calculating the crack depth and predicting the life, a reliable life can be calculated only in extremely limited cases.

When there are a plurality of forging process plans that can obtain the same forging result, the deformation process of the material, the hydrostatic pressure and the load applied to the forging die are calculated, and the calculation result is judged by a person to determine the life of the die. The forging process, which seems to be optimal from the point of view, is adopted.
However, knowledge of what is optimal is not actually obtained, and the optimal forging process is not always selected. It is still at the trial and error stage.

[0004]

Therefore, in the present invention,
Develop a technology that can predict the form of damage that occurs in forging dies. Furthermore, a technology for predicting the life of the forging die from the damage form of the forging die will be developed. The form of damage that occurs in the forging die is closely related to the life of the mold, and if the form of damage can be predicted, the validity of the forging process can be objectively evaluated. Alternatively, it is possible to evaluate whether the shape of the forged product is unreasonable.

[0005]

Means for Solving the Problems, Functions and Effects In the present invention, attention is paid to the fact that the loads acting on the forging die to determine the life are largely divided into mechanical loads and thermal loads. The mechanical load is an index for deforming or abrading the forging die, as represented by the stress acting on the die. The thermal load can be an index of the ease with which the forging die is deformed or worn, as represented by tempering of the forging die by repeatedly applying a high temperature to the forging die. The present invention relates to a "mechanical load-
Based on the analysis of the relationship between "thermal load-damage form generated in the forging die", it was found and confirmed that a clear relationship was obtained. The damage form that occurs in the forging die is "heat check, heat crack, streak marks, deformation, small wear,
Wear is large ". Here, when the damage form that occurs in the forging die under the combined state of the loads is classified based on the mechanical load and the thermal load acting on the forging die, the combined state of the load and the damage form correspond well. It was confirmed that. Therefore, once a database showing the relationship of "mechanical load-thermal load-damage form occurring in the forging die" is once constructed, thereafter, based on the mechanical load and the thermal load acting on the forging die, It is possible to predict the form of damage that occurs in the combined state of the loads.

In the first aspect of the present invention, a database is constructed in which a mechanical load and a thermal load acting on a forging die are inputted, and a damage form generated in the forging die in a combined state of the loads is output. . Then, a mechanical load and a thermal load acting on the planned forging die are calculated. The calculated combination of loads is input to the database, and the damage form generated in the forging die is predicted by outputting the damage form from the database.

[0007] According to this method, from the "mechanical load and thermal load acting on the forging die" which can be calculated and calculated, the form of damage generated in the forging die under the combined state of the loads is accurately predicted. can do. Knowing the damage form is extremely effective during the design or evaluation of the forging process, for example, heat check, if forging is completed while heat cracks occur, it turns out that the forging process is reasonable, On the other hand, it is immediately understood that when a large form of wear occurs, the forging process needs to be reviewed.

The cumulative frictional work is taken as the mechanical load,
Taking the yield strength ratio as the thermal load is particularly useful. In this case, the damage form is clearly classified in a two-dimensional plane in which the cumulative friction work is taken on one axis and the yield strength ratio is taken on the axis orthogonal to it, and is read from the cumulative friction work and the yield strength ratio. The damage form is extremely accurate and has few errors.

For the forging die used in the past, the database can be created by investigating the form of damage that has occurred in the forging die at that time for a combination of mechanical load and thermal load. In this way, there is no need to perform experiments or tests separately, and a reliable database suitable for the actual situation is constructed.

In a second aspect of the invention, the life is predicted by focusing on the damage form. In this embodiment, the mechanical load and the thermal load acting on the planned forging die are calculated for each forging process. Then, the combination of loads calculated for each number of times of forging is input to the database, and the number of times of forging until the damage form output from the database becomes a large wear form is calculated.

The number of workings calculated in this way is a number (corresponding to a minimum life) indicating that at least the number of workings indicates that forging is possible. The inventors' research has shown that the forging die is tempered and softened, and when a large mechanical load is applied thereto, the forging die begins to wear significantly and then reaches its life. Therefore,
When a combination of loads calculated for each forging process is input to the database, the damage mode output from the database can be forged without any problem except for the large wear mode, and when the number of processes increases, From the database, large wear forms began to be output, and it turned out that the service life was near at this point. In the present invention, the life is calculated using this knowledge. The life calculated here has a margin, and when this is used as an index to modify the forging process, a forging process that satisfies the given life can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The main features of the embodiments described below are listed first. (Mode 1) As the mechanical load, any one of the surface area expansion ratio, the slip distance, and the slip speed is adopted. (Form 2) The yield strength of the mold used for calculating the yield strength ratio adopted as the thermal load is determined by the activation energy required for the softening reaction, the value of λ calculated from the temperature and the duration, and the number of times of forging. It is calculated from the hardness information obtained by accumulating the effects of the high temperature and the duration applied each time. (Embodiment 3) The yield strength is calculated based on the high-temperature deformation resistance of various mold materials and the temperature of the forging die at the time of forging, which are experimentally obtained in advance. (Embodiment 4) The method according to claim 4 is applied to a forging die currently in use to predict the life. The method of the present invention is most effective when utilized in the preparation stage of a forging die, but it can also be applied to a currently used forging die to predict the remaining life.

[0013]

FIG. 1 shows the overall processing procedure of this embodiment. In step S1, the shape of the forged product is designed. Step S
In 2, a forging process is designed. In normal forging, a raw material is not forged at once and processed into a final shape, but as illustrated in FIG. 5, forged in a plurality of times and processed into a final shape. FIG. 5 shows a state in which the forging is performed twice to form the final shape. However, in practice, the forging may be performed to the final shape by performing many times of forging. The forging process referred to here is a chain of what shape is formed in each forging process to reach the final shape.

In step S6 of FIG. 1, geometric data such as a prototype, an intermediate shape, and a final shape of a material are created and input to the computer for numerical calculation by the computer. Step S8
Then, various data necessary for executing the coupled thermal-deformation analysis by the computer are input to the computer. For this, press D
/ B (hereinafter, D / B indicates a database) D1, workpiece deformation resistance D / B (D2), interface characteristic D / B (D
3) The thermophysical property value D / B (D4) is used.

In step S10, steps S6 and S8
A thermal-deformation coupled analysis is carried out using an electronic computer by using the data input in step (1). Here, the finite element method is basically executed. Details of this have already been published in a paper by the present inventors. For example, Akashi et al .: 1998 Spring Plastics Lecture (1998), 325-326, or Yano et al .: 4
It has been published nine times in the lecture on plasticity (1998), 91-92. As a result of this analysis, what part of the material is subjected to what kind of stress, what kind of temperature, and what kind of deformation will be analyzed. FIG. 6 illustrates an example of the analysis result, and analyzes a case where the material shown on the left is forged into the shape on the right.

Step S12 and subsequent steps in FIG. 1 are the parts that have been improved this time. In step S12, a monitoring position on the mold surface is designated. In the usual case, the position is specified because the shape of the forging die and the point where the most severe wear and end of the life of the die are known from the past experience. If the points cannot be narrowed down to a single point, the points that are likely to be specified are sequentially specified. When it is completely unknown, the monitoring position may be changed mechanically and regularly so as to cover all points of the forging die.

In step S14, the mechanical load acting on the monitoring position, here, the cumulative frictional work is calculated. Here, the friction work amount is a value obtained by multiplying a frictional force (μp, where μ is a friction coefficient, and p is a surface pressure) acting between a material and a forging die by a slip distance. What is integrated over the period is the cumulative frictional work. The cumulative friction work amount W is represented by ∫μpvdt. Here, v is a relative sliding speed. FIG. 7 exemplifies the cumulative frictional work that acts on the punch at all (9 in all) at the time of the finishing processing of FIG. 5. The horizontal axis indicates the elapsed time during one forging process, and the cumulative friction work increases with the elapse of the molding time. The value at the end of processing is the cumulative frictional work here.

In and after step S16 in FIG. 1, the thermal load acting on the forging die is calculated. In step S16, the temperature of the forging die is calculated. Here, hot forging is adopted, and the work is heated from the beginning. Further, the forging die is heated to a high temperature because it generates heat due to friction caused by forging. FIG. 8 shows a temperature change pattern generated everywhere in the punch during one processing. The left side of FIG. 9 shows a state in which the forging die is heated as the number of processing increases.
One peak corresponds to one forging process (hereinafter sometimes referred to as a shot). The forging die is heated by forging,
After the forging, the lubricant is sprayed and cooled. While this cycle is repeated, the mold temperature gradually rises, and heating and cooling are repeated within the same temperature range.

In step S18 of FIG. 1, the yield strength of the forging die softened by heat is calculated. At this time, D of the mold material λ value
/ B (D5) is used. λ is a value that is an index of the ease of softening, and is calculated by equation (92) in FIG. Here, Q is the activation energy required for the softening reaction specific to the material, and is measured for each steel type. T is the absolute temperature of the working temperature, and t is the duration. The value of λ increases with prolonged exposure to high temperatures. When the applied temperature is not uniform, it is possible to calculate the change in the value of λ by dividing by a short time period in which the temperature can be regarded as uniform and adopting equation (90). As a result, as shown on the right side of FIG. 9, the value of λ increases with time. The value of λ determines the hardness of the forging die. The hardness decreases as the value of λ increases. The Hv graph on the right of FIG. 9 illustrates this and shows the change in hardness of the forging die when exposed to the temperature change shown on the left of FIG. The degree of heat applied to the mold by the heat also changes depending on the stress acting on the mold. Therefore, equations (90) and (92)
It is more accurate to correct by adding the influence of stress to. FIG.
Is the hardness at room temperature. FIG.
It shows the relationship between temperature and hardness or yield strength, and the higher the temperature, the lower the yield strength. Therefore, in practice, the hardness at room temperature is obtained from the relationship on the right in FIG. 9, the curve corresponding to the hardness at room temperature in FIG. 10 is specified, and processing is performed from the specified curve and the processing temperature. Calculate the yield strength at the time. Thus, the yield strength at the processing temperature of the heated and softened forging die is calculated. From the yield strength σ _H , the yield shear stress of the forging die is calculated.

In step S20 of FIG. 1, the friction shear stress μp acting on the monitoring position where the yield strength has been calculated is calculated.
Is calculated. As described above, μ is the friction coefficient, and p is the surface pressure. In step S22, a yield strength ratio is calculated as a thermal load in this case. Here, the yield strength ratio is
It is a value obtained by dividing the yield strength σ _H by the friction shear stress μp.

The above processing can be applied to all forging dies whose shapes and working conditions are known. Therefore, by examining a forging die that has been used in the past and whose life has expired, it is possible to examine the relationship between the cumulative frictional work applied to the die and the yield strength ratio when the life has expired. The cumulative frictional work calculated in step S14 is substantially constant throughout the life of the forging die. On the other hand, the yield strength ratio calculated in step S22 decreases in hardness as the number of shots increases, as shown in FIG. 9, so that the yield strength ratio also decreases as the number of shots increases. FIG. 11 shows the tendency. Since the number of shots at the end of the life is known, the yield strength ratio at the end of the life is calculated. Also,
By examining the forging die, it is possible to examine the form of damage created when the life is over. A similar investigation is possible for the forging die in use, and the relationship between the cumulative frictional work, the yield strength ratio, and the damage mode at the time of the investigation can be examined.
The type currently in use obtained in this way, or
A large number of relationships of "cumulative friction work-yield strength ratio-damage form" are collected for the type with the end of life, and the horizontal axis shows the cumulative friction work and the vertical axis shows the yield strength ratio on a two-dimensional plane. FIG. 3 shows a plot of the damage mode.

Obviously, wear-heavy damage forms were observed in the lower right area, and they were exhausted.
The database of "mechanical load (cumulative frictional work) -thermal load (yield strength ratio) -damage form (damage area)" is shown in FIG.
As shown in simplified form in FIG. Here, the feature of each damage mode is shown in FIG. Here, the large abrasion and the small abrasion are classified according to the degree of abrasion, and can be clearly distinguished with the naked eye from FIG. The two-dimensional map is clear, plotting the damage form on a two-dimensional plane with the mechanical load (cumulative friction work) on one axis and the thermal load (yield strength ratio) on the other axis. It was confirmed that the forms were clearly classified by range.

Since this regularity was confirmed, "mechanical load (cumulative frictional work)-thermal load (yield strength ratio)-
It has been confirmed that the relationship of "damage form" is not only established for a specific forging die, but is generally established.

Therefore, even when a planned forging die for a designed forged product is analyzed, the step S in FIG.
At 24, using the mechanical load (cumulative friction work) calculated at step S14 and the thermal load (yield strength ratio) calculated at step S22 as keys, the "mechanical load (cumulative friction work)" shown in FIG. The damage form can be specified by searching the database of "work load) -thermal load (yield strength ratio) -damage form".

As described above, the mechanical load (cumulative friction work) does not change significantly with the number of shots. On the other hand, the thermal load (yield strength ratio) changes from large to small with the number of shots. Therefore, it usually changes as shown by the arrow on the map of FIG. Normally, what was not in the large wear mode at first is shifted to the large wear area as the number of shots increases. If the number of shots is small, the result of step S26 in FIG. 1 is NO. In this case, the damage mode at that time is displayed (step S28), the number of shots is increased by 1 (step S30), and the steps after step S18 are repeated to calculate the yield strength ratio (thermal load) of the next shot.
In the meantime, when the damage mode changes and the wear mode becomes large, step S26 becomes YES. Here, the number of times of processing (the number of shots) until the damage mode becomes a large wear mode is compared with a predetermined value.
The number of times of processing displayed here is the number of times of processing until the forging die begins to wear significantly, and is the number of times of forging at which the life of the forging die does not end at least up to this number. On the other hand, if the wear becomes large before reaching the target number of times, the forging process is modified in step S38 because the mold life does not reach the target number of times without any change. Modify the shape. FIG. 5 and FIG. 12 show the correction results of the forging process. Initially, the forging process was performed through the shape shown in (I). Therefore, as shown in FIG. 12, what was to be forged in the form of large wear was reviewed in the forging process, and the process of (II) was repeated. In response to the forging through the shape, it is possible to forge in the form of damage with streak marks, and it can be seen that the forging process can be modified to a reasonable forging process and a significant improvement in forging life can be expected. By doing so, the forging process or the shape of the forged product can be corrected to obtain the target forging die life.

In the above embodiment, the cumulative frictional work is employed as the mechanical load, but various parameters shown in FIG. 14 may be employed. FIG. 15 shows the surface area enlargement ratio during one shot. Even if the surface area enlargement ratio at the end of one shot is adopted, the damage form can be accurately predicted. In addition, it has been confirmed that a slip distance or a slip speed may be used as the mechanical load.

According to this embodiment, it is possible to utilize the result of prediction of the damage form and the mold life in the forging process and the preparation stage of the forging die, and it is possible to rationally determine whether or not correction is necessary. . Eventually, reasonable forging preparation work becomes possible.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an entire procedure performed in an embodiment of the present invention.

FIG. 2 Cumulative friction work−yield strength ratio−damage form D /
B shows how the cumulative frictional work-yield strength ratio is input to output the damage mode.

FIG. 3 shows “cumulative friction work−yield strength ratio−damage form” D / B obtained from a forging die used in the past.

FIG. 4 shows a form of damage that occurs in a forging die.

FIG. 5 shows two forging steps in comparison.

FIG. 6 shows a coupled thermal-deformation analysis of a workpiece during forging.

FIG. 7 shows how the cumulative frictional work is accumulated during one forging process.

FIG. 8 shows a temperature change occurring in a forging die during one forging process.

FIG. 9 shows how the hardness of the forging die is reduced by intermittent heating and cooling.

FIG. 10 illustrates the relationship between the temperature of a forging die and the yield strength.

FIG. 11 shows how the yield strength ratio changes with the number of times of forging.

FIG. 12 shows an example in which the form of damage that occurs is changed from a large form of wear to a streak-like form due to a change in the process.

FIG. 13 shows various types of damage generated in a forging die.

FIG. 14 illustrates various parameters that can be adopted as a mechanical load.

FIG. 15 shows how the surface area enlargement ratio changes during one forging process.

Continued on the front page (72) Inventor Yuji Yano 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Tadao Akashi 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Invention Person Yoshikazu Nogami 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Toshitaka Suzuki 1 Toyota Town Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yoshitaka Atsumi Toyota City, Aichi Prefecture 1 Toyota Town Inside Toyota Motor Co., Ltd. (72) Inventor Noritari Tsuchiya 41-cho, Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun Aichi Prefecture Inside Toyota Central R & D Laboratories Co., Ltd. (1) Inside the Toyota Central R & D Laboratories Co., Ltd. (72) Inventor Toshiaki Tanaka 41-Cho. Munehisa Nagakute, Aichi County, Aichi Prefecture Oaza Nagakute-shaped side street No. 41 land of 1 Co., Ltd. Toyota Central R & D Labs in the F-term (reference) 4E087 AA09 CB01 EC00 GA01

Claims (4)

[Claims] 1. A mechanical load and a thermal load acting on a forging die under planning are calculated, and a combination of the calculated loads is inputted by inputting the mechanical load and the thermal load acting on the forging die. A method of predicting a damage mode occurring in a forging die by inputting a damage mode occurring in a forging die in a combination state of the above and outputting the damage mode from the database. 2. The prediction method according to claim 1, wherein the mechanical load is a cumulative frictional work, and the thermal load is a yield strength ratio. 3. A database is created by examining a forging die used in the past for a combination of a mechanical load and a thermal load and examining a damage form generated in the forging die at that time. The prediction method according to claim 1 or 2, wherein 4. A mechanical load and a thermal load acting on a forging die being planned are calculated for each forging process, and a combination of loads calculated for each forging process is calculated as a mechanical load acting on the forging die. And thermal load, and input to the database to output the damage form that occurs in the forging die in the combined state of the loads, and the number of times of forging until the damage form output from the database becomes a large wear form How to predict the life of a forging die.