JPS5838265B2 - Hot coining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot coining method, and more specifically, to a high precision hot coining method.

As is well known, the hot coining method is a method in which a material such as a blank or billet is placed in a sealed mold and the top and bottom surfaces are hot pressed with a die to obtain a product with the desired shape. It has been widely adopted in the field of metal processing, taking advantage of the fact that a desired shape can be obtained with higher productivity compared to other methods.

By the way, if you want a product in which only a part of the material is deformed by hot coining, instead of heating only the part locally, heat the entire material before placing it in the die to improve its plastic deformability. It has been adopted to reduce the internal strain that causes cracking by increasing the

Instead of this method, a local heating method in which only the processed area is heated with high frequency has also been adopted with the same intention.

However, when these methods are used, when the workpiece material has a complicated shape, the temperature distribution and processing pressure distribution become uneven during cooling after hot coining, resulting in complex cooling distortion, and the material In the case of thermal transformation, transformation strain is added to cooling strain, and in either case, the result is that the coined part is distorted by strain other than the coined part, making it difficult to achieve high accuracy.

Therefore, for products that require high precision, we either abandon the application of hot processing methods such as the coining method and adopt other mechanical methods, or even if we adopt the hot coining method. Heat treatment must be carried out in order to remove material distortion that will cause undesirable distortion later in the state of the material before hot coining, or to remove cooling distortion or transformation strain in the product state after hot coining. I had to.

However, this approach significantly reduces productivity,
In addition, for materials that require heat treatment at high temperatures, for long periods of time, and in a special atmosphere, or for materials that are difficult to machine, the cost of machining or heat treatment may exceed the cost of hot coining, which is extremely inconvenient.

Furthermore, the heat treatment method has the problem of reducing the quality of the material or product, and there are many problems in terms of the physical properties required of these materials.

The present invention prevents the distortion caused by hot coining and the resulting precision defects by a means completely different from the conventional heat treatment method, and eliminates the need for the conventional machining method. The purpose is to provide a hot coining method that ensures accuracy.

The most significant feature of the hot coining method according to the present invention is that coining is repeated two or more times using the same die and under substantially the same pressure and temperature conditions.

On the other hand, in the conventional method, coining was performed once, and it was ideal to obtain a product with a predetermined precision, but this was not possible due to distortion before and after coining, so heat treatment or machining methods were adopted. I was there.

However, as a result of careful investigation and research by the inventor of the present invention into the strain behavior associated with hot coining, it has been found that the strain generated by the first (previous) hot coining is alleviated by the second (next) hot coining. The present invention was completed by discovering the following.

The configuration of the present invention will be described in more detail below.

In the method of the present invention, the reason why the same die is used is to avoid a drop in efficiency due to exchanging the die, and if there is a dimensional difference between the front and rear dies, new processing distortion will occur due to this, making it impossible to achieve the intended purpose. This is because it will no longer be possible.

Next, the reason why the applied pressure was made substantially the same and the temperature was also made substantially the same is that these conditions are optimal for removing strain, and there is also a certain width, for example, ±100 for the applied pressure.
This is because a width of ±50°C is allowed for kg and temperature.

Between the previous coining and the next coining, air cooling (cooling) is performed from the coining temperature in the previous question to approximately room temperature l, and heating for the next hot coining, for example, high-frequency heating only on the part desired to be coined, is performed. Perform hot coining.

According to the above method, there is no need for machining, heat treatment, etc., and high-precision hot coining of about 0.02 to 0.03 is achieved, so the present invention has great industrial significance.

Examples of the present invention will be described below.

Example 1 The test piece shown in Figure 1 was set as a shape in which cooling strain would be likely to occur to a large extent due to non-uniform temperature distribution and shape effects when cooling from the heating temperature due to local heating to room temperature 1. was manufactured using the precision casting method.

Next, after locally heating part A to approximately 1000'C using high frequency,
Using SKD61 as a coining pin, an attempt was made to coin from the shape of section A shown enlarged in FIG. 2 to the target dimensions shown in FIG. 3.

F in FIG. 2 indicates the coining direction.

Table 1 shows the coining test piece number, the number of test pieces, and the number of coinings.

The "number of coinings" refers to the number of times each test piece was hot coined as described above, cooled to approximately room temperature, heated again using the same procedure, and coined using the same coining machine.

The sample specimens were {high-frequency heated one by one} and immediately loaded into a coining machine, and the maximum load (3 tons), which was set in advance as a load that would not cause cracks in the specimen, was applied each time.

In addition to SCSI8 described above, high chromium cast iron was selected as a material that causes transformation strain in addition to cooling strain, and hot coining was performed using the same procedure.

The results of measuring the roundness of part A are shown in the following table.

As is clear from Table 2, hot coining By repeating this process, the roundness can be improved.

The effect of the second application is particularly remarkable, and the roundness is improved regardless of the material used.

The reason why roundness improves through repeated hot coining is that the distortion that occurs during cooling after the previous hot coining is restored by local heating during the next hot coining ( In other words, with cooling strain remaining),
This is thought to be because the cooling distortion from the previous time is corrected in order to perform the next hot coining.

However, as long as heating is performed before coining by local heating, there will be heat distortion in the test specimen, and therefore, the cooling distortion from the previous time will not be alleviated by mere local heating, but if the coining is performed under the same or almost the same conditions as the previous time. It is believed that the coining deformation caused by the previous cooling removes or alleviates the distortion caused by the previous cooling so as not to leave any distortion that would impair accuracy later.

Of course, some cooling distortion occurs due to cooling after the next hot coining, but it is judged from the results in Table 2 that the cooling distortion is significantly reduced.

According to the method of the present invention explained above, it has been found that a predetermined precision shape of the product can be ensured only by hot coining, regardless of the material of the product, and without causing thermal defects in areas other than the hot coining area, which improves mass production. This makes it possible to secure significant cost reductions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view and a front view of a test piece, FIG. 2 is an enlarged view of a hot coining section, and FIG. 3 is a diagram showing a target shape after hot coining. A...Coinink club.

Claims (1)

[Scope of Claims] 1. A hot coining method characterized by hot coining a portion to be coined two or more times using the same die under substantially the same pressure and temperature conditions. 2. The hot coining method according to claim 1, wherein the area to be coined is locally heated by high frequency.