HK1189369B - Method for reinforcing welding tip and welding tip - Google Patents

Description

Method for reinforcing a welding tip and welding tip

Technical Field

The present invention relates to a method of reinforcing a welding tip and a welding tip reinforced by the method. More particularly, the present invention relates to a method of reinforcing a contact tip for forming a distribution point by a wire rod in arc welding and a nozzle for spraying plasma while surrounding the outer periphery of an electrode rod in plasma welding (the contact tip and the nozzle are collectively referred to as "tip" in the present invention), and a welding tip reinforced by the method.

Background

Since a high production speed is required, resistance welding (for example, spot welding and seam welding) is generally the mainstream welding method as a welding method used in a welding line in the automobile manufacturing industry and the like.

However, since reduction of fuel consumption is demanded in recent years, improvement of strength of a welded portion is demanded to reduce the weight of an automobile or the like. Therefore, in this regard, arc welding and plasma welding have been used in preference to resistance welding.

Further, the lack of power supply and the like in recent years have become one of the reasons for the shift to arc welding and plasma welding with lower energy consumption than resistance welding.

However, arc welding and plasma welding have low productivity due to the need for longer working time than resistance welding. Therefore, in order to adopt these welding methods instead of resistance welding, improvement in welding speed is required.

As an example of arc welding, MIG welding, which is a consumable welding method using an electrode rod as a filler metal, is now described. As shown in fig. 2, a gas nozzle 4 is provided at the tip of the welding torch for MIG welding, and an inert gas is introduced through the gas nozzle. Further, a contact tip 1 (11) as a welding tip is concentrically provided in the gas nozzle 4, and the electrode rod 5 as a filler metal is inserted into the contact tip 11 in a contact state, thereby allowing a current to flow to the electrode rod 5. Further, a passage of inert gas is formed between the outer periphery of the contact tip 11 and the inner periphery of the gas nozzle 4. Thus, continuous welding is performed by melting the electrode 5 and feeding the electrode 5 by the heat of the arc generated between the workpiece W and the electrode 5 inserted into the contact tip 11.

As shown in fig. 3, the tip of a welding torch for plasma welding is provided with an electrode 6 (e.g., a tungsten rod), a nozzle 12 provided on the outer periphery of the electrode 6, and a shield ring 7 covering the outer periphery of the nozzle 12. The arc (non-transferred arc) generated between the electrode rod 6 and the nozzle 12 or the arc (transferred arc) generated between the electrode rod 6 and the workpiece W causes the plasma gas introduced between the outer periphery of the electrode rod 6 and the inner periphery of the nozzle 12 to expand by the heat of the arc, so that the plasma gas is ejected at high speed through the nozzle hole 121 provided at the front end of the nozzle 12. A shielding gas is caused to flow between the outer periphery of the nozzle 12 and the inner periphery of the shield ring 7 to control the range of the plasma stream.

The welding tip 1 (11, 12) arranged as described above is worn due to its structure in sliding contact with the welding electrode 5 or in contact with plasma under high temperature conditions. Further, since the adhesion of the adhesion substance by sputtering or the like leads to a short life, the tip needs to be replaced.

Specifically, when the production speed is increased using these welding methods instead of resistance welding as described above, the welding tip 1 (11, 12) needs to be replaced over a short period of time.

Therefore, it is a common practice to introduce an expensive robot on a welding line to improve productivity through full automation in automobile production and the like. However, for example, replacing the welding tip 1 (11, 12) requires closing the welding line regularly and frequently (for example, every hour), and requires manual replacement work. These requirements of the replacement work are the cause of a significant reduction in productivity.

Further, since the tip 1 (11, 12) to be replaced is required to have high conductivity, copper, a copper alloy (e.g., chromium copper, ceramic-dispersed copper, or the like) is used as a raw material of the tip 1 (11, 12). Such a welding tip is expensive. If the frequency of replacement can be reduced, the production costs can be reduced.

Since ceramic-dispersed copper has excellent wear resistance and the like as compared with chromium copper, the use of ceramic-dispersed copper can reduce the replacement frequency. However, copper dispersed with ceramics costs 1.2 to 2 times as much as chrome copper and effects corresponding to the price difference cannot be obtained.

Accordingly, there is a need for a relatively simple and low cost tip that significantly improves the life of the tip.

In order to improve the wear resistance and the like of such a welding tip, the inventors of the present invention have proposed the following ideas: hard particles having a particle diameter of 40 to 300 μm and a hardness equal to or higher than the nozzle hardness are sprayed on the surface of a nozzle made of a nonferrous metal at a spray speed of 100m/s or more to raise the temperature in the vicinity of the nozzle surface to a recrystallization temperature or more, thereby miniaturizing the metal structure of the nozzle surface during annealing and recrystallization, and obtaining a nozzle having improved electrical conductivity and improved surface hardness (japanese patent publication (LOPI) H8-150483(JP8-150483 a)).

Further, regardless of the tip-related processing technique, in order to reinforce the surface of a sliding part of a cutting tool, a metal mold, a gear, a shaft, etc. to achieve improved wear resistance and higher surface hardness, the inventors of the present invention have also proposed the following ideas: tin powder having an average particle diameter of 10 μm to 100 μm and an oxide film formed on the surface thereof is sprayed on a product to be processed at a spraying pressure of 0.5MPa or more or at a spraying speed of 200m/s or more, thereby forming a tin oxide film having a thickness of 1 μm or less on the surface of the product to be processed (Japanese patent publication (LOPI)2009-270176(JP 2009-270176A)).

As described above, JP8-150483a has disclosed that particles having a particle diameter and a hardness equal to or higher than the nozzle hardness are sprayed onto the nozzle surface at a certain spraying speed to increase the surface hardness, thereby improving the wear resistance of the nozzle.

However, the tip obtained by the machining method described in JP8-150483a described above has a certain level of stability in hardness improvement, and the improvement in life of the tip obtained only by the machining method described in JP8-150483a is limited.

Therefore, it is desirable to reduce the frequency of replacement of the welding tip by further improving the life of the welding tip, thereby reducing the frequency of closing the welding line to further improve productivity.

The present invention is a continuation of the invention according to the above-mentioned JP8-150483a and aims to provide a long-lasting welding tip at low cost by a relatively simple method to meet the demand for a prolonged life in the above-mentioned market, which has further improved wear resistance and abrasion resistance as compared with a welding tip processed by the method according to the above-mentioned JP8-150483a, thereby meeting the demand for a prolonged life in the above-mentioned market.

As described in the above-mentioned JP2009-270176A, the inventors of the present invention have also proposed a method for improving wear resistance, in which tin powder having a certain average particle diameter on which a tin oxide film is formed is sprayed under certain spraying conditions onto a sliding portion of a product to be processed to form a tin oxide film, which is a hard substance of the surface of the sliding portion.

Therefore, when the tin oxide film is further formed by the method according to JP2009-270176A after surface strengthening according to the method of JP8-150483a, further improved surface hardness can be obtained by the synergistic effect of the two inventions.

However, the material of the film formed on the surface of the sliding portion by the method of JP2009-270176A described above is tin oxide, that is, "semiconductor", which is a substance having very high resistance to a conductive material such as copper as a tip base material under conditions of about room temperature (25 ℃).

Therefore, when such a tin oxide film is formed on a portion (for example, the inner peripheral surface of the tip) required to have high conductivity, the required characteristics may be lost. Therefore, the invention according to the above JP2009-270176A has a reason (obstacle factor) to prevent the application of the tin oxide film to a portion (for example, the inner peripheral surface of the welding tip) which is required to have conductivity.

Antimony-doped tin oxide (ATO), which is tin oxide to which a dopant such as antimony is added, is a substance exhibiting good conductivity, for example, used as a transparent electrode of a display panel. Therefore, when it is attempted to coat tin oxide on the inner peripheral surface of the tip without impairing the conductivity, a film can also be formed by tin oxide doped with antimony.

However, if an expensive antimony-doped tin oxide is used to form a film, the resulting tip is also expensive, making it out of price competitiveness in the market. Further, since antimony is a substance that imposes a large burden on the environment, it is preferable to limit the use of antimony if possible.

In view of the above, the inventors of the present invention have attempted to form a tin oxide film without adding impurities after spraying hard particles to the inner peripheral surface of the welding tip, although this is contrary to the above-described reason (hindrance factor).

As a result, even once the surface hardness is increased by jetting hard particles and then the tin oxide film is formed, the surface hardness is not increased any more. Therefore, the expected improved mechanical properties, such as further increase in surface hardness, as a synergistic effect of the combination of the above two inventions cannot be obtained.

On the other hand, although the reason is not known, the inner peripheral surface of the thus processed tip has desired conductivity by forming a semiconductor film without doping (adding impurities), and the inner peripheral surface is sufficiently durable to function as a tip. Moreover, the thus-processed tip generates less wear, although improved mechanical characteristics such as increased hardness are not obtained. Furthermore, the occurrence of welding defects is significantly reduced, which provides enhanced characteristics that are not foreseen from the combination of the above-mentioned conventional techniques.

Disclosure of Invention

The method for solving the above problems will be described below with reference to the reference numerals used in the detailed description of the preferred embodiments. The reference numerals are intended to clarify the relationship between the description of the claims and the description of the preferred embodiments for carrying out the present invention and are not necessarily indicative, and are not intended to be used in a limiting manner for understanding the technical scope of the present invention.

As described above, the present invention has been made in view of unexpected effects, and thus, the combination of the above two methods allows the semiconductor film to be formed without losing conductivity and improving wear resistance and the like, although no increase in hardness is observed.

A method for reinforcing a welding tip 1 (11, 12) of the present invention includes the steps of:

forming a surface reinforcing layer 2 by spraying metal powder particles having an average particle diameter of 40 to 150 μm and a hardness equal to or higher than that of a material of a welding tip 1 (11, 12) at a spraying speed of 100m/s or more at least on an inner peripheral surface of the welding tip 1 (11, 12) formed of any one of copper, a copper alloy, or copper in which ceramics are dispersed; and

a tin oxide semiconductor film 3 is formed on the surface reinforcing layer 2 by further spraying tin powder having an average particle diameter of 10 μm to 100 μm and having a tin oxide film formed thereon at a spraying speed of 200m/s or more onto the surface reinforcing layer 2 formed in the step of forming a surface reinforcing layer.

In the method for reinforcing a welding tip, the welding tip 1 to be processed may be provided for inert gas arc welding or CO₂A contact tip 11 at the tip of a torch for gas arc welding.

Also, in the method for reinforcing the tip, the tip 1 to be processed may be a nozzle 12 provided at the tip of a welding torch for plasma welding.

In the above-described step of forming the surface reinforcing layer, the surface reinforcing layer 2 to which the component reinforcement due to the diffusion and penetration of the components of the metal powder particles into the inner peripheral surface, the high hardness due to the miniaturization of the metal structure near the surface of the inner peripheral surface, and the compressive stress accompanying the plastic deformation due to the collision of the metal powder particles can be formed.

The welding tip 1 (11, 12) of the present invention includes:

a surface reinforcing layer 2 formed by spraying metal powder particles having an average particle diameter of 40 to 150 μm and a hardness equal to or higher than that of a material of the welding tip 1 (11, 12) onto at least an inner peripheral surface of the welding tip 1 (11, 12) formed of any one of copper, a copper alloy, or copper in which ceramics are dispersed at a spraying speed of 100m/s or higher; and

a tin oxide semiconductor film 3 formed on the surface reinforcing layer 2, the tin oxide semiconductor film 3 being formed by spraying tin powder having an average particle diameter of 10 μm to 100 μm and having a tin oxide film formed thereon onto the surface reinforcing layer 2 at a spraying speed of 200m/s or more.

The welding tip 1 may be a contact tip 11 having an inner peripheral surface in sliding contact with an outer peripheral surface of a welding rod and provided at a leading end of a welding torch for arc welding. Also, the tip 1 may be a nozzle 12 having an inner peripheral surface defining a space for introducing plasma gas and provided at a tip of a torch for plasma welding.

The components of the metal powder particles diffuse and penetrate into the surface reinforcing layer 2 and the surface reinforcing layer 2 has a miniaturized metal structure and compressive stress.

The above structure of the present invention provides the following outstanding effects to the welding tip having the surface reinforced by the method of the present invention.

Forming the surface reinforcing layer 2 and the semiconductor film 3 composed of tin oxide on the inner peripheral surface by the above method makes the life of the tip 7 to 8 times longer than that of an unprocessed tip, 2 to 3.5 times longer than that of a conventional tip having only the surface reinforcing layer formed thereon.

Since tin oxide formed as a film on the inner peripheral surface of the welding tip as described above is a semiconductor, it is anticipated that, with the welding tip 1 having the semiconductor film 3 composed of tin oxide formed on the inner peripheral surface by the method of the present invention, the decrease in the conductivity of the inner peripheral surface may cause a problem of power distribution of the electrode in the contact tip for arc welding, and a problem of plasma generation or the like in the nozzle for plasma welding, leading to welding defects or in some cases making welding itself impossible. However, when the tin oxide semiconductor film 3 is formed on the surface reinforcing layer 2 by the method of the present invention, it is observed that the welding tip 1 exhibits unexpected properties, for example, good conductivity even without any doping, although the principle is not clear.

Further, in the conventional copper welding tip, when the temperature rises due to heating during welding, the resistance increases in proportion to the rise in temperature. This accelerates wear of the welding tip and causes welding defects to frequently occur. However, in the welding tip having the surface reinforced by the method of the present invention, the increase in the temperature of the welding tip rather lowers the electric resistance of the inner peripheral surface, which produces the following effects: the generation of welding defects is significantly reduced and the wear rate is not increased.

In short, since the resistance in a semiconductor such as tin oxide is made smaller as the charge carrier density in the conduction band is larger, the charge carrier density is generally increased by increasing dopant atoms to supply free electrons to the conduction band or generate holes in the valence band, thereby reducing the resistance (improving conductivity). In such a semiconductor, it is considered that the charge carriers excited by heat account for a large part under high temperature conditions regardless of the amount of the dopant, and the resistance decreases exponentially with an increase in temperature,

furthermore, the tin oxide has an HV1650kg/mm²High hardness of 1630 c and a high melting point of 1630 c, which provides thermal resistance. Therefore, even when the semiconductor film 3 is brought into sliding contact with an electrode or the like under high temperature conditions, peeling or the like of the semiconductor film 3 is hardly caused.

As shown in fig. 4, when the temperature of tin oxide as a semiconductor is increased in the air, the amount of oxygen negatively charged and adsorbed on the surface of tin oxide increases. Further, the adsorbed oxygen captures electrons required for the tin oxide to conduct electricity to increase a potential depletion layer formed on the surface of the tin oxide, thereby raising a potential barrier to increase resistance.

However, when the welding tip of the present invention is used under a non-oxidizing environment, for example, when a contact tip of inert gas arc welding is used under a condition where an inert gas such as Ar is introduced, when CO is used under a condition where carbon dioxide or the like is introduced₂In the case of a contact tip for gas arc welding,and when the nozzle of plasma welding is used under the condition of introducing plasma gas such as argon, hydrogen, nitrogen, etc., the resistance can be prevented from increasing with the adsorption of negative charges of new oxygen, and it is considered that the decrease of the conductivity with the increase of the temperature can also be suppressed in this respect.

Drawings

The objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic cross-sectional view illustrating a welding tip of the present invention;

FIG. 2 is a schematic view illustrating a tip portion of a welding gun for gas-shielded arc welding (MIG welding);

FIG. 3 is a schematic view illustrating a forward end of a torch for plasma welding; and

fig. 4 is a schematic diagram illustrating a mechanism in which the resistance increases with oxygen adsorbed to the tin oxide film.

Detailed Description

Next, embodiments of the present invention will be described with reference to the drawings.

Outline of the manufacturing method

The method for reinforcing a welding tip of the present invention includes: a step of forming a surface reinforcing layer 2 in the vicinity of the inner peripheral surface of the welding tip by spraying metal powder particles having a hardness higher than that of the base material of the welding tip at least on the inner peripheral surface of the welding tip, and a step of forming a tin oxide semiconductor film 3 by further spraying tin powder particles having a tin oxide film formed thereon on the surface reinforcing layer 2.

Object to be processed

The welding tip to be processed in the present invention includes a contact tip 11 which is provided in the welding torch for arc welding shown in fig. 2 and forms a power distribution point by the electrode rod 5, and a nozzle 12 which is provided in the welding torch for plasma welding shown in fig. 3 and covers the outer periphery of the electrode rod 6.

Contact tips for arc welding include various types of contact tips according to the type of welding, for example, contact tips for submerged arc welding, contact tips for inert gas arc welding, and contact tips for CO₂A nozzle for gas arc welding, but the method of the present invention is applicable to any of these contact tips. Also, in the method of the present invention, the electrode itself as a contact tip for consumable welding (e.g., MIG welding) of filler metal and a contact tip for non-consumable welding (e.g., TIG welding) that hardly consumes the electrode itself can be used as objects to be processed.

Since the welding tip 1 (11, 12) for arc welding and plasma welding is required to have high conductivity, copper alloy, and ceramic-dispersed copper are used as materials, and any of these materials can be processed by the present invention.

Further, chromium copper, zirconium bronze, and the like are copper alloys commonly used for welding tips, and the present invention is applicable to any of these. Also, without being limited thereto, the present invention is also applicable to welding tips made of other copper alloys.

Processing equipment

In the step of forming the surface reinforcing layer and the step of forming the semiconductor film according to the present invention, commercially available air type blasting equipment applied to known blasting and shot blasting may be used.

As the air type blasting apparatus, various types of blasting apparatuses have been provided, for example, a gravity type (suction type) and a direct pressure type. In the processing method of the present invention, any blasting apparatus may be used as long as the blasting powder can be ejected by the compressed gas at a certain ejection speed, and the type of ejection is not particularly limited as long as an air type blasting apparatus is used.

Step of forming surface reinforcing layer

The step of forming the surface reinforcing layer is performed by: metal powder particles having a hardness equal to or greater than that of the base material of the welding tip are first sprayed at least on the inner peripheral surface, preferably on the inner and outer peripheral surfaces of the welding tip described above, to form the surface reinforcing layer 2 in the vicinity of the surface of the welding tip at the spraying position.

Examples of metal powder particles for spraying may include high speed steel and tungsten. In addition to these, various types of metal powder particles may be used as long as the metal powder particles are formed of a metal material having a hardness equal to or greater than that of the base material of the welding tip.

Further, by the collision of the metal powder particles sprayed at a high speed with the surface of the welding tip, a part of the composition of the metal powder particles may diffuse and permeate into the vicinity of the surface of the welding tip. Thus, for example, in order to strengthen and improve copper or a copper alloy as a base material of the welding tip, when other components are diffused and infiltrated therein, the component to be diffused and infiltrated may be included in the metal powder particles.

The metal powder particles for spraying have an average particle diameter of 40 to 150 μm, and are sprayed at a spraying speed of 100m/s or more.

The reason why the diameter of the metal powder particle is 40 μm to 150 μm is: a smaller particle diameter is required to obtain a higher ejection speed, to make the surface roughness of the processed surface uniform and to adjust the surface roughness to produce a contact surface that does not increase the electrical resistance. Further, the reason why the ejection speed is 100m/s or more is that: the spray velocity is a condition required to raise the temperature in the vicinity of the surface of the welding tip of copper or copper alloy having high heat dissipation to a desired temperature (for example, recrystallization temperature or higher) at the above particle diameter.

In this manner, when the metal powder particles are sprayed at least on the inner peripheral surface of the welding tip under the above-described conditions, heating and cooling are repeatedly performed by collision of the particles on the surface of the welding tip with the particles, thereby miniaturizing the structure in the vicinity of the surface of the collision portion. At the same time, compressive stress is applied to the impact portion, which is then reinforced.

A part of the components in the metal powder particles is diffused and infiltrated into the vicinity of the surface of the collision portion, thereby forming the surface reinforcing layer 2 in the vicinity of the surface of the welding tip as shown in an enlarged view in fig. 1.

The surface reinforcing layer 2 formed in this way obtains higher conductivity due to the miniaturization of the structure, as compared with the surface of the unprocessed inner peripheral surface of the welding tip.

Step of Forming semiconductor film

The step of forming the semiconductor film is performed by: tin powder is further sprayed on the surface reinforcing layer 2 formed by the above steps, thereby forming a semiconductor film 3 of tin oxide.

As the tin powder to be sprayed, a tin powder having a tin oxide film formed on the surface thereof is used, and this tin oxide is adhered, diffused and infiltrated to the inner peripheral surface of the welding tip to form the above-described semiconductor film 3.

The tin powder covered with such an oxide film can be obtained by, for example, manufacturing tin powder using a water mist method. In this water mist method, collision of molten tin with high-pressure water causes the molten tin to be instantaneously powdered and rapidly solidified, thereby obtaining powder. In the tin powder obtained by this method, the surface thereof is oxidized by quenching by collision with water, which results in a tin powder having a surface covered with an oxide film.

The average particle diameter of the tin powder to be used is from 10 μm to 100 μm, preferably from 20 μm to 50 μm. In order to form a film on the surface of a product to be processed by collision with tin powder, it is necessary to raise the temperature of tin powder by heating at the time of collision, and the temperature is raised in proportion to the collision speed of tin powder.

The tin powder having a particle diameter within the above range is easily carried by the air flow generated by the compressed gas used at the time of spraying, and the sprayed powder can be caused to collide with the surface of the product to be processed at high speed, thereby suitably forming a tin oxide film.

The shape of each particle of the sprayed powder to be used may be a sphere, a polygon or also a mixture of these shapes, and the shape of the particle is not particularly limited.

The tin powder is sprayed at a spray speed of 200m/s or more. The temperature increase generated when the tin powder collides with the surface of the product to be processed is proportional to the speed, and the tin powder is required to be sprayed at a high speed so that the tin powder is properly melted and adhered to the surface of the product to be processed.

Specifically, the tin powder used in the method of the present invention has an oxide film formed on the surface thereof. Further, the oxide film (tin oxide) has a higher melting point than tin (unoxidized), and therefore, it is necessary to eject tin powder at the above-described high ejection pressure and high ejection speed.

As described above, the tin powder having an oxide film formed on the surface and an average particle diameter of 10 μm to 100 μm, preferably 20 μm to 50 μm, is ejected at a relatively high speed of 200 m/sec or more and is caused to collide with the inner peripheral surface of the welding tip. Subsequently, the sprayed tin powder collides with the inner peripheral surface of the welding tip, and when the sprayed tin powder is rebounded, a part of the sprayed tin powder melts and adheres to or diffuses/permeates into and covers the inner peripheral surface to form a tin oxide film.

When the tin powder is sprayed at a high speed on the inner peripheral surface of the welding tip at the above-mentioned high spraying pressure or spraying speed, heat is generated in the tin powder by the speed change before and after the collision with the surface of the product to be processed. Since this heat is generated only in the portion where the tin powder collides and deforms, the temperature locally rises in the tin powder and in the vicinity of the inner peripheral surface of the tip with which the tin powder collides.

Since the temperature rises in proportion to the speed of the tin powder before the collision, the higher spraying speed of the sprayed tin powder raises the temperature of the tin powder and the temperature of the inner peripheral surface of the welding tip to higher temperatures. At this time, the tin powder is heated at the inner peripheral surface of the tip, whereby this increased temperature causes the temperature-increased portion of the tin powder to be oxidized. Meanwhile, it is considered that a part of the sprayed powder (including the oxide film formed on the surface of the tin powder) is melted by the elevated temperature and adhered to, diffused and infiltrated into the surface reinforcing layer formed on the inner peripheral surface of the welding tip, or covers the surface reinforcing layer formed on the inner peripheral surface of the welding tip, thereby forming the semiconductor film 3.

Tin as the metal is a soft metal having a Vickers hardness of about 5kg/mm². Tin oxide, which is an oxide of tin, is a substance having a high hardness, for example, a maximum Vickers hardness of about 1650kg/mm². The tin oxide film formed in this way had a hardness sufficient to form a film comparable to that of, for example, zirconium oxide (about HV1100 kg/mm)²) Alumina (about HV1800 kg/mm)²) Silicon carbide (about HV2200 kg/mm)²) And aluminum nitride (about HV1000 kg/mm)²) Such as ceramic, less susceptible to wear.

Further, the tin oxide film formed in this way is less likely to be peeled off or the like due to the sliding of the electrode or the like.

Also, tin has a low melting point of 232 ℃, but tin oxide has a high melting point of 1630 ℃. Therefore, even when used for a welding tip, the welding tip has thermal characteristics sufficient to withstand heating during welding.

Undoped tin oxide is a semiconductor having high resistance, but after the tin oxide semiconductor film 3 is formed on the surface reinforcing layer 2 by the above-described method, the inner peripheral surface of the welding tip exhibits good conductivity, although the principle and the like are unknown.

Further, in a welding tip which is not machined according to the present invention, the resistance increases with an increase in temperature, and the resistance thus increased causes a shortage of power supply to the electrode or an increase in power consumption. At the same time, the increased electrical resistance also generates heat, and the sliding contact of the welding tip with the electrode in this state results in a higher wear rate and a shorter life. This also leads to welding defects based on lack of power supply or poor contact. In the inner peripheral surface of the welding tip, on which the semiconductor film is formed by the surface strengthening processing according to the method of the present invention, the resistance of the semiconductor film 3 decreases with an increase in the temperature of the welding tip. Therefore, good electrical conductivity is maintained without reduction in power supply, increase in power consumption, further increase in temperature based on increase in resistance, or the like, even when the temperature of the tip is increased by heating during welding. Therefore, the welding tip is also hardly worn by contact with the electrode or plasma, and a welding defect is hardly generated.

Effects and the like

As described above, in the welding tip reinforced by the method of the present invention, the surface reinforcing layer 2 of high hardness is formed by spraying particles of the base material of the welding tip with hardness equal to or higher than that of the welding tip, and further the semiconductor film 3 having thermal change resistance and high hardness is formed on the surface reinforcing layer 2, whereby not only a decrease in conductivity expected from the formation of the semiconductor film 3 is not observed, but also good conductivity is exhibited without an increase in resistance even when the welding tip is heated to a higher temperature.

Therefore, in the tip subjected to the surface reinforcing process of the present invention, the surface hardness is not increased even if the above two processes are combined, but the expression of the electrical characteristics which cannot be predicted by the above two processes makes the life of the tip 7 to 8 times longer than that of the unprocessed tip and 2 to 3.5 times longer than that of the tip having only the surface reinforcing layer 2 formed thereon, and at the same time, the occurrence of welding defects is significantly reduced.

An example of the reinforcing process performed on the welding tip is described below. The results of evaluating the characteristics of the welding tip on which various processes are performed are shown below.

Example 1

The reinforcement method of the present invention was carried out on a contact tip (made of chromium copper, phi 1.2 mm) for arc welding under the following conditions.

(1) Surface reinforcing process

Metal powder was sprayed on the inner peripheral surface and the outer surface of the contact tip, respectively, under the following conditions.

TABLE 1

Condition for forming surface reinforcing layer on contact tip for arc welding

(2) Step of Forming semiconductor film

After the surface reinforcing processing was completed under the above conditions, tin powder was sprayed to the inner peripheral surface and the outer surface of the contact tip, respectively, under the following conditions.

TABLE 2

Conditions for forming semiconductor film on contact tip for arc welding

(3) Performance evaluation

Table 3 below shows the results of performance evaluation of the contact tip of the present invention (example 1 on which the surface reinforcing layer and the semiconductor film were formed under the above conditions), the unprocessed contact tip (comparative example 1), and the contact tip to which only the surface reinforcing process was performed (comparative example 2).

TABLE 3

Performance evaluation of contact tip for arc welding

(4) Results of the experiment

From the above results, it is understood that the surface hardness in comparative example 1 (unprocessed) is HV139kg/mm²While the surface hardness after the surface reinforcing step in comparative example 2 was HV181kg/mm²This shows that the diffusion of the metal component significantly improves hardness and stress, and increases the life (durability) by 4 times.

Therefore, in the contact tip of the present invention, to which the step of forming a semiconductor film was further performed, as compared with the contact tip subjected to the surface strengthening process, no improvement in hardness and pressure was observed with respect to the contact tip subjected only to the surface strengthening process (comparative example 2), but an increase in life (durability) was obtained, for example, 8 times longer than the unprocessed contact tip (comparative example 1) and 2 times longer than the contact tip subjected only to the surface strengthening process (comparative example 2).

The present inventors considered that the reason why the life (durability) of the contact tip of the present invention is improved even under the condition that no increased surface hardness or pressure is obtained as compared with the contact tip subjected to only the surface strengthening process (comparative example 2) is due to the effect of high conductivity of the semiconductor film at high temperature.

Further, since the conductivity is high at a high temperature in this manner, power consumption can be reduced, which is economical, and generation of welding defects due to poor power supply can be significantly reduced. Moreover, the nozzle having the semiconductor film formed thereon produces good wire sliding. Meanwhile, since the tin oxide semiconductor film has a high melting point and high hardness, peeling is difficult even in sliding contact with a welding rod at high temperature, and the above-mentioned excellent electrical properties can be continuously obtained over a long period of time.

Specifically, in this embodiment, the surface reinforcing layer and the tin oxide semiconductor film are also formed on the outer surface of the contact tip. Therefore, the slag hardly adheres to any position of the contact tip during welding, and when adhering, it can be easily removed, thereby preventing the life from being reduced due to the adhesion of the slag.

Example 2

The surface reinforcing processing of the present invention was performed on a nozzle (made of chromium copper, forged product, phi 2.5 mm) for plasma welding under the following conditions, and the characteristics of the processed nozzle were evaluated.

(1) Surface reinforcing process

Under the following conditions, metal powder was sprayed to the inner peripheral surface and the outer surface of the nozzle, respectively.

TABLE 4

Conditions for forming surface reinforcing layer on nozzle for plasma welding

(2) Step of Forming semiconductor film

After the surface reinforcing processing was completed under the above conditions, tin powder was sprayed to the inner peripheral surface and the outer surface of the nozzle under the following conditions, respectively.

TABLE 5

Conditions for forming semiconductor film on nozzle for plasma welding

(3) Performance evaluation

Table 6 below shows the results of performance evaluation performed on the nozzle of the present invention (example 2 on which the surface reinforcing layer and the semiconductor film were formed under the above-described conditions), the unprocessed nozzle (comparative example 3), and the nozzle to which only the surface reinforcing process was performed (comparative example 4).

TABLE 6

Performance evaluation of plasma welded nozzle

(4) Results of the experiment

Although the nozzle for plasma welding does not directly contact the electrode rod unlike the above-described contact tip for arc welding, plasma gas heated and expanded by arc heat between the outer periphery of the electrode rod and the inner periphery of the nozzle is collected through the nozzle hole and injected at a high speed. Therefore, the wear of the nozzle for plasma welding and the like directly affect the quality of welding.

The surface hardness of the nozzle (green product: comparative example 3) composed of chromium copper and made by forging was HV174kg/mm²While the hardness of the nozzle subjected to the surface strengthening processing (comparative example 4) was increased to HV196kg/mm². At the same time, a pressure increase is also observed, but the lifetime (durability) is increased only by a factor of 2.

On the other hand, with respect to the nozzle to which only the surface strengthening process was performed (comparative example 4), no improvement in hardness and stress was observed in the nozzle of the present invention on which the semiconductor film was further formed after the surface strengthening process (example 2), but an increase in lifetime (durability) was observed, for example, 7 times longer than that of the unprocessed product (comparative example 3) and 3.5 times longer than that of the surface strengthening product.

Even when compared with the case of using an unprocessed product (comparative example 3) or a surface-reinforced product (comparative example 4), it was confirmed that the generation of welding defects was significantly reduced.

In this method, although hardness and pressure are not changed before and after forming the semiconductor film, the nozzle life is increased and soldering defects in the nozzle are significantly reduced. Therefore, it is considered that these effects are obtained by the following facts: the formation of the tin oxide semiconductor film prevents a decrease in conductivity (to be exact, improves conductivity), even under high-temperature conditions.

Accordingly, the appended claims, in their broadest sense, do not refer to a machine that is configured in a particular manner. Rather, the broadest claims are intended to protect the core or spirit of the present breakthrough invention. The present invention is clearly new and useful. Moreover, the present invention as it is developed will not be obvious to one of ordinary skill in the art in view of the prior art as a whole.

Moreover, the invention is obviously an original invention from the innovative point of view. Thus, as a matter of law, the following claims are to be interpreted broadly to protect the core of the present invention.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

The description of the present invention has been completed so far.

Claims (8)

1. A method for reinforcing a welding tip, the method comprising the steps of:

forming a surface reinforcing layer by spraying metal powder particles at a spraying speed of 100m/s or more at least on an inner peripheral surface of a welding tip formed of any one of copper, a copper alloy, or copper dispersed with ceramic, the metal powder particles having an average particle diameter of 40 to 150 μm and a hardness equal to or higher than that of the material of the welding tip; and

forming a semiconductor film of tin oxide on the surface reinforcing layer by further spraying tin powder having an average particle diameter of 10 μm to 100 μm and having a tin oxide film formed thereon, the tin powder being manufactured using a water mist method, onto the surface reinforcing layer formed in the step of forming the surface reinforcing layer at a spraying speed of 200m/s or more.

2. The method of reinforcing a welding tip as defined in claim 1, wherein said welding tip is provided for inert gas arc welding or CO₂A contact tip at the tip of a torch for gas arc welding.

3. The method of reinforcing a welding tip as defined in claim 1, wherein the welding tip is a nozzle provided at a leading end of a welding torch for plasma welding.

4. The method of reinforcing a welding tip as defined in any one of claims 1 to 3, wherein in said step of forming a surface reinforcing layer, a surface reinforcing layer to which component reinforcement due to diffusion and penetration of components of metal powder particles into the inner peripheral surface, high hardness due to miniaturization of a metal structure near the surface of the inner peripheral surface, and compressive stress accompanying plastic deformation due to collision of metal powder particles are given is formed.

5. A welding tip, comprising:

a surface reinforcing layer formed by spraying metal powder particles at a spraying speed of 100m/s or more at least on an inner peripheral surface of a welding tip formed of any one of copper, a copper alloy, or ceramic-dispersed copper, the metal powder particles having an average particle diameter of 40 to 150 μm and a hardness equal to or higher than that of the material of the welding tip; and

a tin oxide semiconductor film formed on the surface reinforcing layer, the tin oxide semiconductor film being formed by spraying tin powder having an average particle diameter of 10 μm to 100 μm and having a tin oxide film formed thereon, the tin powder being manufactured using a water mist method, onto the surface reinforcing layer at a spraying speed of 200m/s or more.

6. The welding tip according to claim 5, wherein the welding tip is a contact tip having an inner peripheral surface that is in sliding contact with an outer peripheral surface of a welding wire and provided at a leading end of a welding torch for arc welding.

7. The welding tip according to claim 5, wherein the welding tip is a nozzle having an inner peripheral surface defining a space for introducing plasma gas and provided at a leading end of a torch for plasma welding.

8. The welding tip according to any one of claims 5 to 7, wherein a component of the metal powder particle diffuses and permeates into the surface reinforcing layer, and the surface reinforcing layer has a miniaturized metal structure and compressive stress.