JPH0411309B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of overlay welding to a predetermined workpiece (base material), and particularly to a method of overlay welding powder material using a plasma arc. An overlay welding method that improves the wear resistance, heat resistance, or corrosion resistance of the workpiece surface by welding a specified overlay material (filler metal) to the workpiece (base material) such as a valve or pipe. has been known for a long time. One such overlay welding method involves converting an arc (pilot arc) generated at the tip of an electrode in a plasma arc torch into a plasma arc using plasma gas supplied into the torch. The welding current supplied between the torch and a given workpiece causes the welding current to be transferred between the torch and the workpiece, and the welding current is applied to the workpiece within the plasma arc. There is a plasma build-up welding method in which a powder material is supplied, the powder material is melted and guided to the surface of the workpiece, and a predetermined build-up is performed. Since this plasma overlay welding method uses a powder material as the overlay material as described above, it is possible to easily select a wide range of materials for the overlay material, and compared to the case where a bar material is used, it is easier to select the material for the overlay material. It has been attracting attention in recent years because it has excellent features such as a faster melting rate and the ability to shorten welding time, and also because it is easy to fully automate the equipment. By the way, thick-wall welding involves melting and joining a build-up material to the surface of a workpiece, and at this time, the molten workpiece melts into the build-up material and dilutes the build-up material. The ratio of the penetration amount of the workpiece to the overlay material is expressed as a dilution rate (%). If these dilution rates are too low, there is a problem that the bonding strength between the overlay material and the workpiece is impaired, causing phenomena such as peeling.
On the other hand, if the temperature is too high, the structure of the overlay material will be damaged, making it impossible to obtain the desired properties such as heat resistance and wear resistance. It is desirable to take this into account and control it within a predetermined range (generally about several percent). For this reason, even in the above plasma overlay welding,
By appropriately setting the welding current, plasma gas amount, etc., a predetermined dilution rate can be obtained. On the other hand, this dilution rate is generally set based on the steady state of overlay welding, that is, the state where overlay welding has progressed to a certain extent and the workpiece (base material) has been sufficiently heated, so it is necessary to start overlay welding. In some cases, if the workpiece is not sufficiently heated, an appropriate dilution rate cannot be obtained. In order to solve this problem, the peak current value of the welding current is changed in two stages, and at the start of overlay welding, the peak current value is set relatively high and the workpiece is sufficiently heated. Welding methods have been proposed that provide an appropriate dilution ratio.
Note that the welding current is generally controlled in such a way that it gradually increases at the beginning of energization and gradually decreases when the energization is stopped, taking into account the supply status of powder materials, etc. The peak current value means the current value when the welding current is maintained at a constant value. However, even if plasma overlay welding is performed by changing the peak current value of the welding current in two stages as described above, it may be difficult to obtain a predetermined dilution rate over the entire overlay welding. In other words, especially when overlay welding is performed on a small workpiece, or when overlay welding is performed in multiple layers, heat builds up inside the workpiece and as the overlay welding progresses, There are cases where the dilution rate increases and exceeds the predetermined range. The present invention has been made against the background of the above circumstances, and its purpose is to provide a plasma overlay welding method that allows a predetermined dilution rate to be obtained throughout the overlay welding. It's about doing. In order to achieve this object, the present invention, in the plasma overlay welding method, changes the peak current value of the welding current in three or more stages, and decreases the peak current value as the overlay welding progresses. It was decided to supply it by doing so. Here, the number of stages in which the peak current value of the welding current is changed and the current value and time at each stage are as follows:
It will be set appropriately depending on the material and size of the workpiece, various types of overlay welding, etc. For example, when overlay welding is performed from one end of a workpiece to the other end, the escape of heat due to heat conduction within the workpiece is restricted, especially when overlay welding near the other end. It becomes easy to get stuck, the workpiece melts more than necessary, and the dilution rate increases. In addition, when the workpiece is a member that has a circumferential part on at least a part of it, such as a valve, and when overlay welding is performed in a circular manner in the circumferential direction along the circumferential part, overlay welding is particularly important. When you have completed one lap and reached the starting area,
The dilution rate increases due to the heat build-up mentioned above and the heating at the start. Therefore, in the above case, the peak current value is temporarily increased at the start part to heat the workpiece, and then at the intermediate part where the workpiece has been heated to some extent, the current value is slightly higher than at the start part. While the peak current value is set to be low, when the overlay welding progresses further and reaches the vicinity of the other end or the vicinity of the start part, the peak current value is further reduced. Incidentally, when performing overlay welding on the cap portion of an automobile valve, more suitable overlay welding can be performed if the current value and time at each stage are set so as to satisfy the following equation. T ₁ =0.002-0.13×T T ₂ =0.05-0.4×T T ₃ ≧0.4T T ₄ =0.07-0.35×T T ₅ =0.02-0.9×T W ₁ =0.05-0.94×W ₃ W ₃ <W ₂ ≦1.2W ₃ 0.9W ₃ ≦W ₄ ＜W ₃ W ₅ = 0.05 to 0.85×W ₃ However, each symbol in these formulas is: T: Total peak current supply time, T ₁ : Peak current value after welding current is applied T ₂ : Peak current supply time at the start part, T ₃ : Peak current supply time at the intermediate part, T ₄ : Peak current supply time near the start part, T ₅ : Welding current supply time at the overlapping part. Time to fall, W ₁ : Current value at the start of supply of welding current, W ₂ : Time T ₂
Current value at time T 3, W ₃ : Current value at time T ₃ ,
W ₄ : Current value at time T ₄ , T ₅ : Current value at the time of stopping the supply of welding current, respectively. In addition, in the above case, the middle part, that is, the time
In the T ₃ part, as overlay welding progresses, heat gradually builds up inside the workpiece and there is a risk that the dilution rate will increase, but in order to prevent this, the peak current value in this intermediate part is changed more finely. It is also possible to do so. On the other hand, when overlay welding is repeatedly performed on a predetermined portion of a workpiece, heat accumulates within the workpiece each time overlay welding is repeated, and the dilution rate increases.
Therefore, in such a case, first, the peak current value is temporarily increased in the starting part as in the above case, and then the peak current value is slightly lowered when the workpiece has been heated to a certain extent. At the same time, when the overlay welding returns to the starting point again, the peak current value is further lowered, and thereafter the peak current value is gradually lowered each time the overlay welding is repeated. In addition, in each case mentioned above, the oscillation rate,
In other words, the plasma arc torch and the workpiece,
If the overlay weld is made to have a predetermined width by reciprocating relative to the direction perpendicular to the welding direction, the increase in dilution rate due to heat buildup will become more pronounced, so take this into account when setting the peak It is necessary to set the number of stages in which the current value is changed and the current value and time in each stage. As described above, according to the plasma overlay welding method according to the present invention, it is possible to prevent overlay welding defects at the starting part, and to adjust the material and size of the workpiece, or to perform annular overlay welding on one circumferential part or multilayer overlay welding. Regardless of heat buildup in the workpiece due to the form of overlay welding, etc., overlay welding is performed with an excellent bead shape with a predetermined dilution rate throughout the overlay welding. You get it. Next, in order to clarify the present invention more specifically, one embodiment of the present invention will be described. First, FIG. 1 is an explanatory diagram of a plasma overlay welding apparatus in which the present invention can be suitably implemented, and 10 is the tip of a plasma arc torch (hereinafter referred to as a torch). The torch 10 has a tungsten electrode 12 at its center, and a torch inner tube 14 and a torch outer tube 16 are coaxially arranged outside the electrode 12 at a predetermined distance from each other. And between the electrode 12 and the torch inner cylinder 14,
Annular passages 18 and 20 are formed between the torch inner cylinder 14 and the torch outer cylinder 16, respectively. The passage 18 is connected to a plasma gas supply device 24 via a pipe 22, and a plasma gas such as angone gas is supplied thereto. Then, the plasma gas supplied into this passage 18 is ejected to the outside from a nozzle 30 provided at the tip of the torch inner cylinder 14. Further, the passage 20 is connected to a carrier gas supply device 34 via a pipe 32, and the pipe 32 is further connected to a carrier gas supply device 34.
A powder supply device 36 is connected to the middle part of the
A predetermined powder material is supplied from the powder supply device 36. That is, passage 20
A carrier gas containing a predetermined amount of powder material is supplied to the nozzle 3 provided at the tip of the torch outer cylinder 16.
8 and is ejected to the outside. In addition,
As the powder material, various filler powders such as Co-based, Ni-based, Fe-based, etc. can be used, and may be appropriately selected depending on the purpose of overlay welding, the material of the workpiece, etc. Further, as the carrier gas, an inert gas such as argon gas or helium gas is used. On the other hand, cooling water passages 40 and 42 are provided in the nozzles 30 and 38 of the torch inner cylinder 14 and the torch outer cylinder 16, respectively.
0 and 38. Furthermore, a shielding gas such as argon gas or helium gas is supplied to the tip of the torch outer cylinder 16 from a shielding gas supply device 44 via a pipe 46, and the shielding gas is supplied to the torch 1.
The welding area is shielded from the atmosphere by blowing out air in a substantially cylindrical direction in the axial direction of the Q A predetermined pilot current is supplied from a pilot power source 48, and a predetermined welding current is supplied from a main power source 50 between the electrode 12 and the workpiece (base material) to be overlay welded. Current Iw is supplied. Further, a high frequency oscillator 52 is inserted between the electrode 12 and the torch inner cylinder 14 in parallel with the pilot power source 48. Note that FIG. 1 shows a case where an automobile valve 54 is attached as a processing member, and this valve 54 is rotated around one axis at a predetermined speed, and is supplied with cooling water from a passage (not shown). It is fixed to a bucking 56 which is adapted to be held in place. Then, a predetermined surface hardening welding is applied to the welded portion 58 of the cap portion of the valve 54. Cap weld 58 of valve 54 in FIG.
The broken line shown in shows the overlay welded state. In order to perform overlay welding in the apparatus configured as described above, first, a pilot current is supplied from the pilot power supply 48 to create a pilot arc between the tip of the electrode 12 and the nozzle 30 of the torch inner cylinder 14. At the same time, plasma gas is supplied from the plasma gas supply device 24 into the annular passage 18. As a result, a plasma arc is formed at the tip of the electrode 12. Note that this plasma arc is generated in synchronization with the high frequency current supplied from the high frequency oscillator 52. Thereafter, a welding current Iw is supplied from the main power source 50 between the electrode 12 and the bulb 54, and the plasma arc formed at the tip of the electrode 12 is transferred to the bulb 54.
Move to 4. In this state, when a carrier gas containing a predetermined powder material is supplied from the carrier gas supply device 34 and the powder supply device 36 into the passage 20 and is ejected from the nozzle 38, the ejected powder material becomes a plasma arc. It is then melted and overlay welded to the cap weld portion 58 of the valve 54. At this time, shielding gas is blown out from the tip of the torch 10, so that the molten powder material and the welded portion 58 are not affected by oxygen in the air. As shown in FIG. 2a, the welding current Iw is set so that its peak current value is changed in three stages and decreases as overlay welding progresses. Therefore, at the stage when the valve 54 is not sufficiently heated at the start of overlay welding, that is, at the stage of time _T2 , the highest welding current is supplied and the welded portion of the valve 54 is
8 is quickly heated, and at a predetermined dilution rate, overlay welding with an excellent bead shape is performed. Also,
At the subsequent time _T3 , the melting current is lowered by the amount that the valve 54 is being heated, and overlay welding is performed at the same predetermined dilution rate. Then, the time when the overlay welding has progressed further and reached the vicinity of the start part.
At the _T4 stage, the welded area 58
Since the current value is further lowered as the temperature increases, the dilution rate of overlay welding is maintained within a predetermined range. Note that at time T ₁ in Fig. 2 a, the welding current
Iw is set to gradually increase because
This is to prevent deformation and deterioration of the valve 54 due to rapid heating, and to enable overlay welding to be performed at a predetermined dilution rate in accordance with the powder material supply situation shown in FIG. Furthermore, at time _T5 , the welding current Iw is also set to gradually decrease in response to the gradual decrease in the supply amount of powder material for crater treatment of the overlapping portion. . Incidentally, when welding Stellite #12 spherical powder material (-100 to +350 mesh) to an automotive valve 54 made of SUH36 material with a diameter of 36 mm, the welding speed was 5.9 mm/sec and the plasma gas was supplied. Each current value W ₁ to W ₅ of the welding current Iw under the conditions that the amount is 1.5/min, the supply rate of the carrier gas containing powder material is 6/min, the shielding gas supply rate is 25/min, and there is no Oresheet operation. time T ₁
Table 1 shows the results of measuring the beat shape of overlay welding and the penetration amount (dilution rate) of the base metal by changing _T5 . For comparison, welding current
A case where the peak current value of Iw is not changed and a case where it is changed in two stages will also be shown.

[Table] As is clear from Table 1, welding current
According to the overlay welding method according to the present invention in which the peak current value of Iw is changed in three stages, an excellent bead-shaped overlay can be obtained with a predetermined penetration amount over the entire overlay weld. If the change in peak current value is less than 2 steps, there may be insufficient penetration at the starting part of overlay welding at time T ₂ , or the amount of penetration may be insufficient at the start of overlay welding at time T ₃ .
The amount of penetration becomes excessive near the start point at time T ₄ in the middle part of the welding process, resulting in partial build-up welding defects. Furthermore, since the solidification rate of the overlay material changes as the temperature of the base material changes, the bead shape may be impaired. Above, an apparatus that can suitably carry out the present invention and an example of the case where the present invention is carried out using the apparatus have been described in detail, but the present invention is not limited in any way by these descriptions. Of course, the present invention may be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating an example of a plasma overlay welding apparatus that can suitably carry out the present invention. FIG. 2 is a diagram for explaining an example of the plasma build-up welding method according to the present invention, and is a time chart of welding current and powder material supplied corresponding to the welding current. 10: Plasma arc torch, 12: Electrode, 2
4: Plasma gas supply device, 36: Powder supply device, 50: Main power supply, 54: Automobile valve (processed member).

Claims (1)

[Claims] 1. An arc generated at the tip of an electrode in a plasma arc torch is made into a plasma arc by plasma gas supplied into the torch, and the plasma arc is connected between the torch and a predetermined workpiece. transfer the powder material from within the torch between the torch and the workpiece by a welding current supplied between the plasma arc and supply the powder material to be overlaid onto the workpiece into the plasma arc; In the welding method in which the powder material is melted and transferred to the surface of the workpiece to perform predetermined overlay, the peak current value of the welding current is varied in three or more steps, and the overlay welding A plasma build-up welding method characterized in that the peak current value is decreased and supplied as the process progresses. 2 The total time for supplying the peak current of the welding current is T, the time for gradually increasing the welding current until it reaches the peak current value after starting the supply of the welding current is _T1 , and the welding current is changed from the peak current value to The time during which the welding current is gradually lowered until the supply of the welding current is stopped is defined as _T5 , while the peak current value is changed in three stages, and the peak current supply time at each stage is defined as _T2, starting from the highest current value. , T ₃ , and T ₄ , each time T ₁ to T ₅ is calculated by the following formula with respect to the total time T: T ₁ =0.002 to 0.13×T T ₂ =0.05 to 0.4×T T ₃ ≧0.4 T T ₄ = 0.07 to 0.35 × T T ₅ = 0.02 to 0.9 × T and the current value at the time when the supply of the welding current is started is W ₁ , and the peak current value at times T ₂ , T ₃ , and T ₄ are respectively W ₂ , W ₃ , and W ₄ , and the current value when the supply of the welding current is stopped is W ₅ , and each current value W ₁ to W ₅ is calculated by the following formula: W ₁ =0.05 to 0.94 A patent characterized in that the overlay welding operation is performed such that ×W ₃ W ₃ <W ₂ ≦1.2W ₃ 0.9W ₃ ≦W ₄ <W ₃ W ₅ =0.05 to 0.85×W ₃ A plasma build-up welding method according to claim 1. 3. Claim 1 or 2, wherein the processed member is a member having a circumferential portion at least in part thereof, and the predetermined build-up is performed in the circumferential direction along the circumferential portion. Plasma build-up welding method described in section.