JPH02218520A - Manufacturing of high strength bolt - Google Patents

Abstract

PURPOSE:To obtain a serration bolt capable of withstanding the increasing output and revolution of an engine by peening the serrated section of the serration bolt with shots each of which is Hv700 to 900 in hardness and 0.18 to 3.3 in a ratio of a grain size (d) to a fillet R, for a specified time. CONSTITUTION:Peening is, of course effective for improving fatigue strength even with shots each of which is less than Hv700 in hardness, shots with the thickness value equal to or more than Hv700 are however actually desirable. The use of the shots with the hardness value of Hv900 is sufficiently effective since the use of the shots with the harness value equal to or more than Hv900 results in the markedly shortened life of shot grains, the use of the hardness value less than Hv900 is appropriate. As for the shot size, grains with 50mu to 200mu in diameter can be used and are affected by relation with the radius of a fillet R section. Let the shot size be (d), and let the fillet radius be (R), it is desirable that d/R is 0.18 to 3.3. As for shot peening time, time less than 30 seconds by the use of the hardness value of Hv800 is insufficient to keep residual compression stress which is considered effective to improve fatigue strength in bending, time equal to or more than 90 seconds however saturates residual compression stress increasingly on the contrary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a high-strength bolt by performing a shot peening process on the serrations of the bolt.

(Conventional technology) An example of a serration bolt is shown in FIG.

In the figure, 1 is the head, 2Fi is the lower part of the neck, 3Fi is the silane part, and 4 is the screw part.

The serration portion 5 has several spiral grooves formed therein.

This serration bolt is used by press-fitting the serration portion into a bolt hole of a connecting rod body of an engine.

Traditionally, serration bolts are manufactured by cold forging the head, lower part of the neck, and shaft (other than the morley part and the thread line), then cold rolling the serrations and the thread.
This was then quenched and tempered to produce a finished product.

(Problems to be Solved by the Invention) Recent engines tend to have high output and high rotation speed, such as turbo engines and supercharged engines.

Along with this, the load stress applied to engine connecting rod bolts (serration bolts) has also become severe.

Therefore, the reality is that conventional serration bolts tend to have insufficient bending fatigue strength.

As a countermeasure to this problem, we are using high-quality materials for the serration bolts and considering the shape of the serration grooves from a technical perspective, but in terms of stability and reliability, this is still a definitive measure. The reality is that it is difficult to say so.

It is also possible to use a connecting rod of a higher rank, but this is not a special solution as it increases the weight and reduces fuel efficiency.

As described above, the current situation is that there is an urgent need to develop large-range bolts that can be used with high-output, high-speed engines.

The present invention has been made in view of the above circumstances, and provides a method for manufacturing a serration bolt that can be used in high-output, high-speed engines without changing the material, size, or shape of the serration grooves of conventional serration bolts. This is what we intend to provide.

(Means for Solving Problem 11) In order to solve the above problems, the present invention provides that the serration portion of a serration bolt that has been quenched and tempered has a shitat grain hardness Hv of 700 to 900 and a shitat grain. It is characterized in that shot peening is performed by projecting shot grains whose diameter d is CL18 to CL55 with respect to the minimum radius RK of the serration portion and the value of d/R is CL18 to CL55.

(Function) Compressive residual stress is generated during shot peening on the serrations of the quenched and tempered nine-serration bolt.

By using shot grains whose diameter d is the minimum radius R of the fillet and the value of d/R is Q, 18 to 3, and whose hardness Hv is 700 to 900, the entire area of the serration part can be Compressive residual stresses are generated that are guaranteed over a period of time.

(Example) An example of the present invention will be described in detail below. The inventor believes that the conventional manufacturing of serration bolts involves machining by cold forging and cold rolling, followed by quenching and tempering.
It was predicted that tensile residual stress would occur on the surface of the completed serration bolt, and it was determined that the low bending fatigue strength was due to this tensile residual stress.

Therefore, by applying shot peening to the large rayon bolt after quenching and tempering, compressive residual stress was generated on the surface of the serration bolt, and an experiment was conducted to determine the bending fatigue strength.

The specifications of the experiment are as follows.

In Figure 1, the outer diameter of the serration part is 8 m and the upper limit tolerance is α.
010Illl lower limit tolerance α015, valley diameter 7.2 wx
A serration bolt with a groove pitch of 1.5 strokes, a mountain width (18 m, a radius of α5 from the peak to the valley, a groove (mountain) twist angle of 60° and a number of threads of 8, and a total length of lIr of 149 mm) was used.

Further, as shown in FIGS. 2 and 5, the serration bolt was divided on the center line and the R of the fillet portion was measured. As a result, R=α17, [LO7a.

α18 fog, (L27 stage was obtained.

Todoroki bolts are processed using JISSCM440H as the material.
(CCr-Mo steel), cold forged, cold rolled K,
Quenching and tempering were performed so that the internal hardness was approximately Hv550.

The fatigue test was conducted using a hydraulic camera to simulate the failure mode of an actual engine, with connecting rod bolts installed.

The repetition rate at this time was 2000 cpm, and the number of repetitions was 101 to 1010.

The specifications of the Shikit Beening are that a direct pressure air blast machine is used, the nozzle diameter is Id 5 m, the injection pressure is 5 Ke 7 cm'', the injection distance is about 15 mm, and the injection time is about 60 seconds.

In the experiment shown in Figure 4, the hardness of shot grains was HvaooO
This study examined how the sheet grain size affects the relationship between the bending load Kf (change in bending stress) applied to the serration bolt at that time and the repeated load.

The results of this test revealed that it is more advantageous to perform shot peening using small shot particles.

The experiment shown in FIG. 5 was conducted to determine how the grain size and hardness of shot grains affect the fatigue limit of a bolt.

This experiment showed that the particle size of the shot grains was small and the hardness was H.
It has been found that a larger v is more advantageous.

FIG. 6 is an experimental result of the relationship between the residual stress value of the serration bolt and the shot projection time using shot grains having a hardness of 1 (y 800).

In this experiment, it was found that the residual stress value did not increase any further after about 90 seconds, and the residual stress was saturated, regardless of the grain size of the shot grains.

In this experiment, the residual stress value was measured at fillet 8
Since it was not possible to measure the grooves of the serrations, the measurements were taken at the grooves of the serrations.

This experiment in Figure 6 and the previously mentioned Figures 4 and 5
When comparing the experiment shown in the figure, in the previous experiment, the smaller the particle size, the more advantageous it was, whereas in the experiment shown in Figure 6, the residual stress value was larger with the larger particle size, and the previous experiment On the contrary, the larger the particle size, the more advantageous it becomes.

What can be concluded from this is that a larger grain size is advantageous for areas where the shot grains collide with a flat surface, and a larger grain size is advantageous for areas with sharper areas such as the 8th part of the fillet. The smaller the value, the more advantageous it is.

Therefore, when considering the bending fatigue strength of the entire serrated bolt, it can be said that there is a predetermined relationship between K, the grain size of the shot grains, and the fillet R of the serrations.

In this experiment, the minimum value of fillet H is [L071s
Since this part is the most difficult part to perform the shot beaning process, considering this as a standard, the value of d/R in relation to the grain size d of the shot grains is 1L7 to 2.9.
becomes.

And the fillet R at the end of the serration cut is a
06, d/R is α83-55.

Also, from Fig. 5, the ratio of the curve of the serration bolt without sit, when the fatigue strength is 1, is 1.
Since it is sufficient to have a particle size of 2 or more, particles with a particle size of 200 μm also satisfy this condition. From this, the particle size is 50μ to 200μ.
Valid within the range of

Therefore, in the range of α06wx-α27 of fillet R, d
The range from the minimum value to the maximum value of /R is [118 to 55
become.

Next, when looking at the hardness of shot grains, as shown in Figure 5, at a shot time of 60 seconds, )(v800
and) iv900 both satisfy the ratio 1.2 even when the particle size is 200μ. For Hv 700, the maximum particle size is 150μ with a shot time of 60 seconds, but if the shot time is extended, the ratio of 1.2 can be satisfied even with a particle size of 200μ.

Next, regarding the shot time, experimental results for HV800 are shown in FIG.

In this experiment, when the shot time was 50 seconds, the residual stress value was in the process of increasing rapidly, and reached a saturated state after 90 seconds.

The following conclusions can be drawn from the above experimental results.

First, regarding the hardness of the shot grains, even if the hardness is less than Hv700, it is of course effective in improving the fatigue strength, but in order to obtain the desired effect, the shot projection time must be increased. However, when productivity is considered in consideration of other processing steps such as cold forging and cold rolling, it is not a good idea to lengthen the time. Therefore, v700 or higher is suitable in practice.

In addition, a sufficiently good effect can be obtained with a hardness of Hv900, and a hardness of Hv900 or less is suitable since a hardness of Hv90 (3 or more will significantly reduce the life of the shot grains).

Therefore, the shot grain hardness is Hv700 or higher (V900 or lower is the most suitable hardness).

Next, regarding the particle size of the cylindrical grains, it is possible to use 50 to 200 microns, and it is influenced by the relationship with the radius of the fillet 8 portion.

As a result of the experiment, the grain size of the shot grain is d, and the radius of the fret is R.
In this case, the appropriate value of d/R is 11L18 to 53.

Next, regarding shot projection time, hardness Hvso.

According to the experimental results, the compressive residual stress, which is beneficial for improving bending fatigue strength, is still insufficient if the time is less than 50 seconds.
If the time is 0 seconds or more, the compressive residual stress will become saturated and break.

Moreover, if the shot projection time is long, the serration seal part will wear out, and the machining tolerance for press-fitting the serration seal bolt into the connecting rod body hole cannot be maintained, resulting in a shin condition.

Further, as can be seen from FIG. 5 (shot projection time 60 seconds), the shot projection time can be determined by the selected combination of the particle size and hardness of the shot grains.

For example, under the conditions of hardness Hv7oo and particle size 100μ, a shot projection time of 60 seconds is sufficient.

According to an experiment with the average hardness Hvaoo, it is appropriate that the shot projection time be 50 seconds or more and 90 seconds or less.

(Effects of the Invention) As detailed above, according to the present invention, the hardness of the shimito grains in the serration part of the serration 3 port which is quenched and tempered after cold forging and cold rolling is
, Particle size d was applied to the fillet R (L18 to 55) for a predetermined period of time by jet blasting and pressure was applied to perform the sheet beaning process, so that a predetermined compressive residual stress was generated in the entire 17th part of the fillet. be able to.

As a result, the ratio when the bending fatigue limit of a serration bolt without a shim is 1 can be increased to t2 or more without changing the material of the serration bolt, the shape of the serration, or the dimensions of the serration bolt. We were able to obtain a Ceresi bolt that can be used with high-output, high-speed engines.

Further, as long as the conditions for the above-mentioned cut peening process are met, the desired bending fatigue strength can be obtained, resulting in an excellent effect of high reliability.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an example of a serrated bolt;
The figure is a vertical cross-sectional view of the celery 91 port used in the experiment divided along the center line, Figure 3 is a partially enlarged view of the mole 91 part in Figure 2, and Figure 4 is the hardness of the shot grains Hv 8.
Q O, The curve applied to the bolt is a diagram showing the results of an experiment on the effect of the shot grain size on the load under the condition that the shot projection time is 60 seconds. Diagram 6 showing the results of an experiment on the influence of shot grain size and hardness on bending fatigue strength under various conditions.
The figure is a diagram showing the results of an experiment on the influence of shot projection time and shot grain size on the residual stress value on the surface example of a serration groove using shot grain hardness Hvsoo. 1...Head, 2...Lower neck, 3-Sereshiwan part,
4...Threaded part. Figure 2 Figure 3 (and 2 others) Figure 4 Figure 2 (μ) Figure 6

Claims (1)

[Claims] The serration part of the serration bolt that has undergone quenching and tempering treatment has a shot grain hardness of Hv700 to 900, a shot grain diameter d, and a value of d/R of 0.18 to 3.3 with respect to the minimum fillet radius R of the serration part. A method for manufacturing a high-strength bolt, characterized by performing shot peening by projecting shot grains for a predetermined period of time.