JPH07214307A - Method for remelting treatment of metallic surface - Google Patents

Abstract

PURPOSE:To provide an efficient method for remelting treatment in which a dimensional accuracy is maintained, generation of blow holes is suppressed, and also an inexpensive TIG arc is used, in the case of treatment a width dimension more than the diameter of the arc generating a high density heat energy. CONSTITUTION:In regard to a method in which a surface layer is remelted by applying TIG arc on the metallic surface and in which the surface layer is modified by a subsequent rapid solidification. The TIG arc is moved 10 through a synthesized periodic motion between the advancing direction 9 of the treatment and the direction parallel with the metallic surface but different from the advancing direction of the treatment; a treatment is performed for a width dimension more than the diameter of the arc; and also it is efficiently carried out to maintain a dimensional accuracy and to suppress the generation of blow holes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remelting treatment method for locally modifying a part of a metal surface layer such as an aluminum alloy casting.

[0002]

2. Description of the Related Art A member having a complicated shape such as a cylinder head is usually formed by casting. However, since the cast product contains internal defects such as porosity and has a coarse structure, a product with high fatigue strength cannot be obtained as compared with a forged or press-formed product. In order to improve the fatigue strength of casting products, while reducing internal defects,
It suffices to refine the crystal grains. And, in order to make the crystal grains fine, it is sufficient to increase the cooling rate during solidification, but if the cooling rate is increased, not only the moldability of the casting such as the flow of molten metal and the molten metal is hindered, but also the internal The defect may be frozen and remain inside.

In the production of an aluminum alloy cylinder head, after it is once formed by casting, the portion where fatigue strength is particularly required is irradiated with high-density heating energy such as TIG arc, laser beam, electron beam or plasma arc. A method for locally modifying the surface layer by re-melting it and then rapidly solidifying it is disclosed in JP-A-61-161.
It is proposed in Japanese Patent No. 193733. This local surface modification method is called "remelting treatment" or "remelting treatment".

In JP-A-61-193773, a necessary portion of an aluminum alloy cylinder head for an internal combustion engine is irradiated with high-density heating energy and remelted so that it exists inside the portion. It is described that mechanical defects are improved by extruding structural defects such as micropores to the outside and refining metal crystal grains by rapid cooling.

[0005] TIG arc melting is usually used for the remelting process because the equipment is inexpensive and there are few blowholes during melting. But TIG
The remelting process by arc melting has a problem of poor dimensional accuracy, and particularly for parts having a complicated shape such as a cylinder head, the size is constrained by the valve seat and the water jacket, and thus high accuracy is required.

FIG. 7 shows the condition of dimensional restraint in the cylinder head. FIG. 7A is an explanatory view showing the surface condition of the valve portion of the cylinder head, and the remelt processing unit 3
1 indicates that there is a dimensional constraint indicated by an arrow that requires high accuracy in the intermediate portion between the exhaust valve seat 32 and the intake valve seat 33. FIG. 7B is an explanatory view showing a cross section of a portion of the cylinder head where the water jacket is present. The remelt processing section 31 has a wall thickness of the cylinder head determined by the shape of the hollow water jacket section 34 in the portion indicated by the arrow. Reference numeral 35 indicates that there is a dimensional constraint in the depth direction.

In order to improve the dimensional accuracy by TIG arc melting, it is necessary to increase the density of the energy rays of the heat source used, that is, the applied heat energy is not wasted and is used for melting. Just do it. The arc diameter that is normally used is 5 to 8 mm, and it is possible to increase the arc diameter to perform remelting treatment with a width larger than that, but it is difficult to obtain high dimensional accuracy.

FIG. 8 shows the high and low density of the energy rays of the heat source used, and the situation of the melting portion corresponding thereto. In FIG. 8A, the curve 36 showing the energy distribution shows a state in which the arc diameter of the heat source is small and the density of energy rays is high, and the shape of the fusion zone 38 obtained by this is shown in FIG. 8A (b). This figure shows a state in which thermal energy is not wasted due to heat dissipation from this shape and the dimensional accuracy is maintained. In FIG. 8B (a), the curve 37 showing the energy distribution shows a state where the arc diameter of the heat source is large and the density of energy rays is low, and the melting portion 39 obtained by this is shown.
8B shows the shape of FIG. 8B. From this shape, heat energy is often wasted due to heat dissipation, and it becomes difficult to maintain dimensional accuracy.

Laser sources, electron beams and the like are examples of heat sources having a high energy ray density. TIG is 10 ⁴ to 1
0 ⁵ W / cm ² , whereas the laser beam is 10
^The electron beam has an energy ray density of ⁷ W / cm ² or more and 10 ⁶ W / cm ² or more. However, these heat sources are not only expensive for the apparatus, but also may generate a large amount of blow holes depending on the components of the target component to be remelted. Since blowholes have a great influence on hot cracking, they should not be generated as much as possible, but they remain a very difficult problem at present.

Further, there is a pulse melting method as a means for improving the dimensional accuracy by TIG melting. In the pulse melting method, the input current to the torch which becomes the melting energy is made into a pulse shape with a constant cycle, and the peak current of the pulse flows. When the base current flows, the torch is moved while cooling the melting point of the part when it is in the middle, and when the base current is flowing, the spot-like melting pools that are periodically formed are overlapped. Is the way.

FIG. 9 is an explanatory diagram of the pulse melting method. FIG. 9A shows a pulse-shaped waveform 4 of the input current applied to the torch.
0, indicating that the peak current and the base current are alternately applied to the torch. FIG. 9B shows the surface and cross-section of the component that has been remelted by the pulse melting method. The melting bead 41a is a moving process of the torch, and the melting pools corresponding to the peak current of the current waveform 40 are superposed. The cross-section 41b is formed and shows a melted shape, but the boundary 41c between the molten layer and the unmelted base material of the component is wavy.

According to this method, the melting is instantaneous, so that the efficiency is high and the dimensional accuracy can be improved. However, the following problems occur. The boundary between the molten layer and the unmelted base material of the part is wavy. Normal TIG because the penetration is shallow even at peak current
A large power supply that can carry a larger current is required. Generates a harsh noise. The width of the molten bead is narrow. There is a method of increasing the frequency of the pulse as a countermeasure against the wavy boundary with the base material, but the penetration becomes shallower, the width of the molten bead becomes narrower, and more noise is generated. Further, if the frequency is increased too much, sufficient cooling cannot be performed, so that it is not spot-like melting, but almost the same as continuous normal TIG welding. As a measure against the shallow penetration, a method of lowering the moving speed of the torch without increasing the current can be considered, but not only the melting time becomes longer, but the thermal efficiency as the original purpose is lowered and the processing time is also increased.

[0013]

In a remelting method for applying a high-density thermal energy to a metal surface while moving it to remelt the surface and locally modify the surface layer by subsequent rapid solidification, When processing a dimension larger than the width of the arc that produces high-density heat energy, the dimensional accuracy is maintained, the generation of blowholes is suppressed, and the expensive laser beam, electron beam, or TIG pulse melting method of the apparatus is used. It is an object of the present invention to provide an efficient remelt processing method that uses an inexpensive TIG arc without using the.

[0014]

DISCLOSURE OF THE INVENTION The present invention provides a metal surface with T
In a method of applying an IG arc to remelt the surface layer and subsequently modifying the surface layer by rapid solidification, TI
When the G arc is moved, the arc is moved by a combined movement of a periodic movement parallel to the metal surface and in a direction different from the process proceeding direction and a motion in the process proceeding direction,
This is a method for remelting a metal surface in which a width dimension equal to or larger than the arc diameter is treated.

[0015]

[Function] The arc diameter is small relative to the area to be subjected to the remelting process, and an inexpensive TIG arc can be used. The heat radiation is small, the dimensional accuracy is maintained, and the melting and cooling are fast, so that the crystal grain of the metal structure is made fine. Is promoted and the effect of the remelt treatment is increased. Further, since the molten pool is agitated by the synthetic motion performed by the arc, harmful internal blowholes in the remelt processing portion are floated and removed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustration of a first embodiment for carrying out the remelting process according to the present invention. 1A shows a TIG torch 1
2 shows a situation in which the robot 3 is used for the above movement to perform the remelt processing on the work 2. TIG on the tip of the robot arm
The torch 1 is installed, and one of the outputs of the power source 8 for melting energy is connected to the TIG torch 1 to generate an arc, and the other is connected to the earth 4 connection of the work 2. TIG torch 1
The robot controlled by the robot control device 7 performs the remelt processing while drawing the track taught to the work 2.

The robot digitizes the locus to the teaching point input in advance, and the digitized coordinates (x,
y, z), the voltage of the sine wave generated by the AC oscillator 5 is output in analog here, and after being digitally converted by the arithmetic unit 6 (such as a personal computer),
It is input to the robot controller 7 as an offset amount Δx in the x-axis direction, and the coordinates to be drawn by the robot are (x + Δ
x, y, z). FIG. 1B is an explanatory diagram of conversion into the offset amount Δx input to the control device 7,
(A) is a voltage waveform generated by the AC oscillator 5, (b) and (c) are offset amounts Δx of the voltage waveform by the arithmetic unit 6.
Indicates the status of conversion to. As described above, the locus of the robot arm tip, that is, the locus of the TIG torch 1 is zigzag from the straight line from the starting point a to the ending point b shown in 9 of FIG. Change into something.

In the present invention, the AC oscillator can be built in the robot controller, or the robot outputs analog data that can be arbitrarily set to an external arithmetic unit (personal computer, etc.) to obtain this numerical value. By controlling the oscillator settings (voltage amplitude, frequency, duty) with
It becomes possible to perform the remelt treatment while changing the width of the zigzag in one molten bead in various ways.

Next, a specific example will be described. AC2B
Re-melting treatment with a TIG torch was performed between the lower surface valve seats of the cylinder head formed by casting the material by the method according to the present invention. The processing locus at this time is shown in FIG.
Start the arc of the TIG torch at the point a and cut the offset input signal from the oscillator in order to stabilize the arc up to the point b. Is changed to a zigzag locus 10, and after reaching the point c, the offset input signal from the oscillator is stopped again, the locus of the TIG torch is returned to the state before the signal input, and the processing up to the point d is performed. .
In the section of the zigzag locus, the vibration amplitude of the TIG torch is 2.5 mm, the frequency is 2 Hz, and the duty is 50.
%. Also, the current in the operating section of the TIG torch is 3
50 → 430 → 300 (A), voltage is 44.5 → 45 →
At 45 (V), the speed was changed to 8 → 7 → 11 (m / min) in each of three stages, and the remelting treatment was performed to obtain good results. In the present invention, the movement of the arc becomes faster due to the trajectory drawn, and therefore the repetition of melting and cooling also becomes faster, and it is possible to improve the dimensional accuracy of the molten portion by not adding extra heat to the molten pool. Becomes In the conventional linear TIG remelting process, the dimensional accuracy of width is ± 4 mm and the dimensional accuracy of depth is ± 3 mm, whereas according to the present invention, both width and depth are within ± 1 mm. I was able to.

Although the first embodiment has been described as a structure in which the movement of the locus required for the TIG torch is caused by an electric signal, the same operation can be performed also by a mechanical structure. This is shown in FIG.

In FIG. 3, the torch 1 held by a suitable cam follower and a moving device (not shown) can be moved on the surface of the cam 11 to draw the torch trajectory 10 along the surface of the cam.

In FIG. 4, a pair of meshing pinions 12 and gears 13 are used, a TIG torch 1 is installed in the vicinity of the tooth teeth of the gears, and movement is performed by holding an appropriate gear train and rotating drive and moving device (not shown). If it is performed, the trajectory shown in 10 can be drawn on the torch.

FIG. 5 shows a cam 15 that rotates about a shaft 16 and a follower bar 1 that abuts on the cam 15 and moves in parallel.
The TIG torch 1 is slidably provided on the torch 4. If the holding and movement of these are performed by an appropriate device (not shown), the trajectory shown by 10 can be drawn on the torch.

Since the TIG arc is a flow of electricity, it is possible to vibrate the arc by the magnetic field generated by the electromagnet. FIG. 6 is an explanatory diagram of this.
In FIG. 6A, 17 is the electrode of the TIG arc, the arc is emitted in the direction perpendicular to the paper surface, 19 is the coil of the electromagnet, and the magnetic field lines in the direction indicated by 20a are generated by the current applied to this. Due to the influence of the magnetic field generated by the magnetic field lines, the arc, which is the flow of electricity from the electrodes, is deflected as shown at 18a. FIG. 6B shows a state in which the direction of the current applied to the coil of the electromagnet is opposite to that of FIG. 6A.
8b is also deflected in the opposite direction with respect to the electrodes. Therefore, by applying an electric current to the coil and controlling its direction and holding and moving both the coil and the TIG torch with an appropriate device (not shown), a desired locus can be drawn on the arc of the TIG torch.

[0025]

INDUSTRIAL APPLICABILITY The present invention, in the remelting treatment for locally modifying the surface layer, maintains the dimensional accuracy and suppresses the generation of blowholes when the width dimension of the arc diameter or more is processed. Moreover, it can be efficiently performed by using an arc of a cheap TIG torch.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory view of the trajectory of the torch according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a shape of a processing unit.

FIG. 8 is an explanatory diagram of an energy distribution of an arc and a fusion zone.

FIG. 9 is an explanatory view of a current waveform and a fusion zone in a conventional technique.

[Explanation of symbols]

1 TIG Torch 2 Work 3 Robot
4 ground 5 AC oscillator 6 arithmetic unit 7 robot controller 8 power source for melting energy

Claims (1)

[Claims] 1. A method of applying a TIG arc to a metal surface to remelt the surface layer and subsequently modifying the surface layer by rapid solidification, wherein the TIG arc is moved in parallel with the metal surface when the TIG arc is moved. A metal surface characterized in that the arc is moved by a combined motion of a periodic motion in a direction different from the process progressing direction and a motion in the process progressing direction, and a width dimension greater than the diameter of the arc is processed. Remelting method.