JPH0780009B2 - Method and device for preventing self-excited vibration of mandrel - Google Patents

Description

The present invention relates to a self-excited vibration of a mandrel, which can surely eliminate self-excited vibration generated in a mandrel in a cold drawing process of a metal tube in a short time. Prevention method and device.

(Prior art) Cold drawing of metal materials is aimed at reducing the outer diameter of metal pipes, such as seamless steel pipes or welded steel pipes, making the surface beautiful, and improving dimensional accuracy. This is a kind of cold working to be performed, in which the metal pipe manufactured by hot working is pulled out in order from the front through the hole of the tool (die) to reduce the cross-sectional area or change the shape once or more, usually. It is a processing method repeated several times,
It is a means for imparting predetermined dimensions, strength, etc., and processing into products such as boiler tubes, steel pipes for machine structures, and the like.

FIG. 4 shows an example of a pipe producing apparatus by the cold drawing method. The cylindrical plug 2 attached to the other end of the mandrel 1 having one end fixed is installed inside the hole of the die 3,
A metal tube 4 having an outer diameter larger than the hole diameter of the die 3 is pulled by a carriage to pass through the die hole,
A product 5 having a desired cross-sectional shape is obtained. At this time, lubricating oil is dropped on the outer surface and the inner surface of the metal tube 4 to reduce the frictional force generated between the plug 2 and the metal tube 4 to improve the workability.

By the way, in such a cold drawing method for a metal tube, when the rate of change of the frictional force with respect to the relative speed between the plug 2 and the inner surface of the metal tube 4 is a negative value, that is, the plug 2 and the metal tube 4 When the inner surface of the plug is not sufficiently lubricated, the plug 2 vibrates. That is, the frictional force between the plug 2 and the inner surface of the metal tube 4 is a value determined by the relative speed of the two, and for example, when the relative speed of the plug 2 and the metal tube 4 is 0 (adhesion, that is, sticking). (In the state), the plug is pulled in because the frictional force is large, and when it is pulled in to a certain degree, it becomes a slipping state (slip state), the relative speed between the two increases and the frictional force decreases, so this vibration gradually grows and becomes large. Become. Generally, such vibration is called a stick-slip phenomenon.

FIG. 5 is a graph showing the relationship between the sliding speed of the plug and the frictional force between the plug and the inner surface of the metal tube. The graph shown in FIG. 5 is created from the data obtained when the steel pipe is used as the metal pipe and the drawing process is performed by the apparatus shown in FIG. In the section -A or -A 'in Fig. 5, the frictional force between the plug and the inner surface of the drawn pipe decreases (or increases) as the sliding speed of the plug increases (or decreases) (negative resistance and It is considered that when the sliding speed of the plug changes between A'-A, the energy of frictional force is received to cause self-excited vibration.

Therefore, in order to analytically express the stick-slip phenomenon, the pipe manufacturing apparatus shown in FIG.
The figure shows approximately using a vibration model. In FIG. 6, the equation of motion for the plug 2 is M + C + kx = f (1), and from the relationship between the sliding speed of the plug and the frictional force between the plug and the inner surface of the metal pipe in the section A′-A shown in FIG. , F = −α (V −) + β (where α> 0, β> 0) ...
(2) However, k: spring constant of mandrel c: damping coefficient of mandrel M: equivalent mass of mandrel and plug f: frictional force between plug and metal tube x: displacement of plug can be approximated.

Therefore, from equations (1) and (2), M + C + kx = −α (V −) + β Therefore, M + (C−α) + kx = −αV + β Here, by using the characteristic equation obtained from the left side of the above equation, The conditions that cause self-excited vibration are However, since this constant α is mainly determined by the lubrication state between the plug and the metal pipe, α may satisfy the condition shown in the equation (3) during processing, Self-excited vibration is generated.

When such vibration occurs, not only the surface quality of the drawn material is deteriorated, but also the wear of the tool is accelerated, and eventually the equipment is damaged.

Therefore, when this vibration occurs during processing, a "method of reducing the drawing speed to adjust the processing speed so that the vibration does not occur and weakening the vibration" (Japanese Patent Laid-Open No. 50-128665) has been widely used in the past. . If the vibration does not converge even if the machining speed is reduced, a measure to reduce the machining rate to change the schedule so that vibration does not occur, or change the lubricant used during machining to a higher-grade lubricant Measures were being taken.

Further, as a proposal for reducing the vibration of the plug, "a method of vibrating the plug by ultrasonic waves to improve friction characteristics to prevent vibration of the plug" (Japanese Patent Laid-Open Nos. 51-116157 and 51-116157). 12
No. 6368) is known.

(Problems to be Solved by the Invention) However, these methods cannot prevent the vibration generated in the plug during the drawing process without lowering the productivity. That is, all of the methods disclosed in Japanese Patent Laid-Open No. 50-128665 reduce the drawing efficiency. That is, when the processing speed is decreased, the processing efficiency is naturally decreased, and when the processing degree is decreased, the number of steps until the final dimension is finished increases. Therefore, the processing efficiency is decreased by any method.

In addition, the measure to change the lubricant to a higher-grade one is not only a supplementary measure, but also requires extra man-hours and cost when changing. Therefore, if such a measure is used, the productivity of the drawing process is significantly reduced and the vibration generated in the plug 2 cannot be basically prevented.

Further, in the methods disclosed in Japanese Patent Laid-Open Nos. 51-116157 and 51-126338, expensive and large-scale equipment is required to generate ultrasonic waves and apply the ultrasonic waves to the plug. Cannot be adopted.

Also, magazines (TUBE INTERNATIONAL, March 1986, p.39)
~ P.43) discloses a method of fixing a mandrel through a hydrostatic thrust bearing and utilizing the damping effect of the hydrostatic thrust bearing to reduce the vibration of the mandrel and the plug. However, since it is difficult to adjust the spring constant and the damping coefficient of the thrust bearing by this method, the vibration generated in the plug 2 during the drawing process could not be removed.

Here, an object of the present invention is to provide a self-excited vibration preventing method and device for a mandrel, which can surely eliminate self-excited vibration generated in a mandrel in a short time in cold drawing of a metal tube. Yes, and more specifically,
A method for preventing self-excited vibration of a mandrel, which can surely eliminate self-excited vibration generated in the mandrel in a short time even when the constant α in the equation (2) is a value satisfying the equation, and To provide a device.

(Means for Solving the Problems) As a result of various studies for solving the above problems, the present inventor did not directly fix the mandrel, but installed the mandrel via a fluid pressure cylinder, thereby Knowing that it is possible to completely prevent the vibration that occurs in the plug, we have previously described in Japanese Patent Application Laid-Open No. 2-99216 (Japanese Patent Application No. 63-251351), "The other end of a cored bar with one end fixed. The plug attached to is installed inside the hole of the die, and a product having a cross section corresponding to the hole diameter is obtained by passing through the hole of the die while pulling a metal pipe having an outer diameter larger than the hole diameter of the die. In the method of drawing metal pipes, the core metal is installed movably in the drawing direction via the fluid pressure cylinder, and the piston creates a fluid layer in the cylinder during processing. The method of drawing a metal tube is characterized by performing the processing while maintaining the state of being supported through. ”

FIG. 7 schematically shows the apparatus used in this proposal and approximately shows it by using a vibration model. This device is obtained by adding a mass, a spring and a damper system to the device whose vibration model is shown in FIG. As shown in FIG. 7, the mass, the motion equation relating to the mandrel of the device fitted with a spring and a damper to the rear end of the _{mandrel, M + C (- P)} + K (x-x P) = f ...... (4)
M _{P p} + C _P ( _P −) + K _P (x _P −x) = 0 (5)
However, Mp: Equivalent mass of piston Cp: Equivalent damping coefficient of piston Kp: Equivalent spring rigidity of piston xp: Displacement of piston, and the frictional force f is f = −α (V− ) + Β (where α> 0, β> 0) (2) ′.

Here, in equations (4), (5) and (2) ', since M, K, C and α are known values, the mandrel is self-excited if Mp is determined to be an appropriate value. No vibration
The values of Kp and Cp can be determined. For example, M =
38.37kg, K = 7.02 × 10 ⁶ N / m, C = 5.08 × 10 ³ N ・ S / m, M
Fig. 8 shows an example of calculating the stability condition of the plug when p = 10 kg and α = 7000 N · S / m. As is clear from FIG. 8, the spring constant Kp of the added spring and damper is
By limiting (N / m) and the viscosity coefficient Cp (NS / m) to the values in the shaded area in FIG. 8, it becomes possible to prevent self-excited vibration occurring in the plug.

However, according to the subsequent studies by the present inventors, the means proposed by this Japanese Patent Application No. 63-251351 is certainly a method capable of preventing self-excited vibration generated in the mandrel. As shown in Fig. 8, there is a wide allowable range for the spring constant Kp, but only a very narrow allowable range (7.0 × 10 ^{3 to} 1.2 × 10 ⁵ N · S / m) for the viscosity coefficient Cp. I knew it wasn't. In addition, there is also a problem that the stability condition (hatched portion) of the plug shown in FIG. 8 changes depending on the contact condition between the plug and the inner surface of the metal pipe, that is, the value of α in the expression (2). It was difficult to obtain the stable condition of the plug.

Therefore, as a result of further studies by the present inventors, in order to solve the problem of the method proposed by Japanese Patent Application No. 63-251351, the desired viscosity coefficient Cp and spring constant Kp are obtained. It was found that it is effective and necessary to realize a mechanism in which the viscosity coefficient Cp can be adjusted to some extent. Then, after further study, the present invention was completed.

Here, the gist of the present invention is a method for preventing self-excited vibration of a mandrel in cold drawing of a metal pipe, in which the mandrel has its rear end to adjust the resistance at the time of oil inflow and outflow. It is installed via a hydraulic cylinder that has a servo valve, and a device that generates a spring force in the expansion and contraction direction of the hydraulic cylinder is installed in the hydraulic cylinder. Through the valve, the difference between the oil pressure on the cylinder side and the oil pressure on the anti-cylinder side, that is,
This is a method for preventing self-excited vibration of a mandrel, which is characterized in that adjustment is made so as to be proportional to the square root of the absolute value of the differential pressure between inflow and outflow of the servo valve.

Further, from another aspect, there is provided an automatic vibration preventing device for a mandrel in cold drawing of a metal tube, which includes (i) a plug attached to the tip of the mandrel and provided inside the hole of the die, ii) A hydraulic cylinder provided between the rear end of the mandrel and the fixed part, which has a servo valve for adjusting the resistance when the oil flows in and out, and (iii) a spring force in the expansion and contraction direction of the hydraulic cylinder. And a device for adjusting the opening degree of the spool valve of the servo valve, (iv) a self-excited vibration preventing device for a mandrel.

(Operation) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view showing a self-excited vibration preventing device for a mandrel according to the present invention. In FIG. 1, the plug 2 installed inside the hole of a die (not shown) is installed on the tip side of the mandrel 1.

The rear end side of the mandrel 1 is installed in a hydraulic cylinder 6 having a servo valve 7 for adjusting its hydraulic pressure. The type and size of the servo valve 7 are not limited in any way, but it is preferable to use an electrohydraulic servo valve from the viewpoint of responsiveness, maintainability, and cost. Further, the hydraulic cylinder 6 does not need to be limited at all.

Further, the hydraulic cylinder 6 is provided with a device 11 for generating a spring force in its expansion / contraction direction. This is because, as described above, the device according to the present invention is provided with a predetermined spring constant Kp to absorb and eliminate self-excited vibration generated in the mandrel 1. In the embodiment shown in FIG. 1, as such a device, a coil spring 11 is provided inside the hydraulic cylinder 6, but the invention is not particularly limited to this mode, and for example, as shown in the embodiments described later. Alternatively, it may be realized by using an accumulator (11 'in FIG. 2). The "spring force generating device 11" is installed so that the spring force can be generated in the expansion / contraction direction of the hydraulic cylinder 6 (the direction of the arrow in FIG. 1). However, it is not strictly necessary to generate the spring force in parallel with the expansion / contraction direction of the hydraulic cylinder 6, and the hydraulic cylinder 6 may be installed so as to have a damping capability.

In FIG. 1, 10 and 10 'are hydraulic pressure gauges capable of detecting the differential pressure (differential pressure between the cylinder side hydraulic pressure and the anti-cylinder side hydraulic pressure) generated in the servo valve,
Reference numeral 8 is an amplifier for outputting the signal from the arithmetic unit 9 to the servo valve. Reference numeral 9 is an optimum value for the servo valve 7, as will be described later, due to the difference between the two hydraulic pressure values detected by the hydraulic pressure gauges 10 and 10 '. It is an arithmetic unit that calculates the opening of the spool valve and changes the opening of the spool valve according to the calculated value.
In addition, in order to obtain the optimum opening degree of the spool valve in the servo valve 7 from the above-mentioned two hydraulic pressure values, the equation (10) described later may be used for the calculation.

Further, as is well known, the spool valve provided in the servo valve 7 is a spool that slides in the sleeve.
By reciprocating with the stroke formed by the sleeve, the opening is 0 to 100% (the opening at the end of two strokes is 100%, and the opening at the intermediate position of the stroke is 0%). %)), So that it can be continuously changed in the range of
By outputting the spool valve opening obtained by the expression (10) described later to the servo valve via, for example, a servo amplifier, the opening as the calculated value can be constantly maintained.

Next, the operation of the device according to the present invention will be described.

Now, if the piston displacement is Δx _P and the hydraulic pressure on the servo valve 7 side changes by Δp between time t and time (t + Δt), let the piston cross-sectional area be A and ignore the oil compressibility. , The volume ΔV of oil passing through the servo valve 7 and the flow rate Δq of oil are ΔV = A · Δx _P (6) Becomes

On the other hand, from the flow characteristics of the servo valve 7, Ksv is a constant, Xs
Is the spool valve opening of the servo valve, Is represented.

If the viscosity coefficient is Cp, the viscous force Δfp applied to the piston is Therefore, according to equations (6) to (9), Is guided.

That is, in the apparatus according to the present invention shown in FIG. 1, the pressure gauge 10 measures the pressure in each of the cylinder and the servo valve which gives ΔP in the equation (10), and the arithmetic unit 9 gives the equation (10). The opening Xs of the spool valve is calculated, and the opening Xs of the spool valve obtained by the above calculation is adjusted to the actual opening of the spool valve of the servo valve 7. Specifically, the spool of the servo valve can be continuously changed from -100 to + 100% with respect to the input range of the servo amplifier of ± 10V. In this way, by adjusting the opening degree of the spool valve of the servo valve 7, the magnitude of resistance when the oil in the hydraulic cylinder 6 passes through the servo valve 7 is set to the magnitude of the moving speed of the piston as much as possible. This is to achieve a value as close as possible to the desired viscosity coefficient Cp in proportion.

Further, according to such means, a relatively simple device can be obtained without requiring signals that are not easy to measure such as the above-mentioned plug displacement and plug speed, and a great effect from a practical point of view. is there.

In addition, when actually using this device, the servo valve 7
It is not possible with the current technology to completely eliminate the delay in the operation of the hydraulic pressure detector, the delay in the operation of the oil pressure detecting device, and the like, so it is not easy to finally obtain a desired constant viscosity coefficient Cp. However, in practice, select a servo valve 7 that has a cutoff frequency that is somewhat larger than the self-excited vibration frequency (for example, a servo valve that has a cutoff frequency of about 100 Hz for several 10 Hz self-excited vibration). Then, there is no problem from the viewpoint of eliminating self-excited vibration.

Further, the effects of the present invention will be clarified more quantitatively by using Examples, but this is only for exemplifying the present invention, and the present invention should not be construed to be limited thereto.

Example A self-excited vibration preventing device for a mandrel having the structure shown in FIG. 2 was prepared. In FIG. 2, the mandrel 1
The rear end portion is installed on the piston of the hydraulic cylinder 6. Further, a servo valve 7 and an accumulator 11 'for adjusting the hydraulic pressure in the hydraulic cylinder 6 are provided. Therefore, the pressure difference between the pressure in the cylinder and the gas pressure of the accumulator is taken, but in this case,
The inside of the cylinder corresponds to the cylinder side pressure of the servo valve, and the gas pressure of the accumulator corresponds to the counter cylinder side pressure of the servo valve. Further, in this embodiment, the accumulator 11 'is used as a "device for generating a spring force in the expansion / contraction direction of the hydraulic cylinder" instead of the spring 11 in the device shown in FIG. As described above, when the accumulator 11 'is used, the spring force is generated by the adiabatic compression of the gas that is previously sealed in the accumulator 11' at a predetermined pressure.

The configuration other than the above is the same as that of the apparatus shown in FIG. 1, and the reference numerals in the figure are the same as those in FIG. 1, so further explanation is omitted. In the embodiment shown in FIG. 2, the hydraulic gauge 10 is provided independently of the hydraulic cylinder 6 and the accumulator 11 ', but it is different from the embodiment shown in FIG. 1 in the essential function. Absent. Moreover, the calculation in the sequencer was performed by the following formula.

However, U: Servo amplifier input A: Piston cross-sectional area Cp: Target viscosity coefficient Ksv: Servo valve flow coefficient Using the self-excited vibration suppressor of the mandrel according to the present invention shown in FIG. Fig. 3 shows the results of suppressing self-excited vibration during drawing of a seamless steel pipe with a thickness of 7.8 mm.

FIG. 3 is a graph showing how the vibration speed of the plug during processing changed before and after the activation of the device according to the present invention. As is clear from Fig. 3, after starting
It can be seen that the self-excited vibration of the plug was eliminated in 0.5 seconds.

(Effects of the Invention) According to the present invention, it is possible to completely prevent vibration generated in a plug installed through a core metal inside a die hole during drawing of a metal tube by using an apparatus having a simple structure and inexpensive. It has become possible. Therefore, (i) the drawing process can be performed with a high degree of processing, and the process can be shortened.

(Ii) It can be processed at a high drawing speed, and productivity is improved.

(Iii) Can be processed with a low-grade lubricant or lubrication method,
Cost reduction can be achieved.

(Iv) Since the load generated in the tool can be absorbed, damage to the tool can be prevented, and cost reduction and productivity improvement can be achieved.

(V) It is possible to prevent the surface pattern of the material pipe from being generated due to vibration,
Since dimensional accuracy can be improved, product quality and yield are improved.

(Vi) Even if the plug and the inner surface of the metal pipe are not very well lubricated, a stable drawing process can be performed by adjusting the oil flow resistance in the servo valve by changing the opening of the spool valve. It becomes possible.

The effect was obtained. The practical significance of the present invention having such effects is extremely remarkable.

[Brief description of drawings]

1 is a schematic explanatory view showing an embodiment of a self-excited vibration preventing device for a mandrel according to the present invention; FIG. 2 is a schematic view showing another embodiment of a self-excited vibration preventing device for a mandrel according to the present invention. Explanatory drawing; FIG. 3 is a graph showing the self-excited vibration control effect of the device shown in FIG. 2; FIG. 4 is a schematic explanatory view showing a conventional drawing processing device; FIG. 5 is shown in FIG. A graph showing the relationship between the sliding speed of the plug and the frictional force between the plug and the inner surface of the metal tube during processing of the device; Fig. 6 is a schematic representation of the device shown in Fig. 4 schematically using a vibration model. FIG. 7 is a schematic explanatory view schematically showing an apparatus for carrying out the method proposed in Japanese Patent Application No. 63-251351, which is approximately shown by using a vibration model; and FIG. In the device shown in FIG. 7, the self-excited vibration of the mandrel can be stably suppressed. 7 is a graph showing a range of the spring constant Kp and a viscosity coefficient Cp. 1: Mandrel, 2: Plug 3: Die, 4: Metal tube 5: Product, 6: Hydraulic cylinder 7: Servo valve, 8: Servo amplifier 9: Calculator, 10: Pressure gauge 11: Spring, 11 ′: Accum Lator

Claims (2)

[Claims] 1. A method for preventing self-excited vibration of a mandrel in cold drawing of a metal pipe, the hydraulic cylinder having a servo valve for adjusting resistance at the time of oil inflow and outflow at the rear end of the mandrel. Installed on the hydraulic cylinder, a device for generating a spring force in the expansion and contraction direction of the hydraulic cylinder is installed on the hydraulic cylinder, and during the drawing process, the opening of the spool valve of the servo valve is changed to the cylinder via the servo valve. Self-excited vibration prevention method for mandrel, characterized by adjusting the viscosity coefficient to be within a predetermined range by adjusting it so as to be proportional to the square root of the absolute value of the difference between the hydraulic pressure on the side of the cylinder and the hydraulic pressure on the side of the opposite cylinder. . 2. A device for preventing self-excited vibration of a mandrel in cold drawing of a metal tube, comprising: (i) a plug attached to the tip of the mandrel and provided inside a hole of a die; and (ii) A hydraulic cylinder having a servo valve provided between the rear end of the mandrel and the fixed portion, for adjusting resistance at the time of oil inflow and outflow, and (iii) generating a spring force in the expansion and contraction direction of the hydraulic cylinder. A device for preventing self-excited vibration of a mandrel, comprising: a device for tightening; and (iv) a device for adjusting the opening of the spool valve of the servo valve.