JPH05161979A - Ceramic guide pin for resistance welding machine - Google Patents

Abstract

PURPOSE:To prevent the defective welding of a nut, the breaking of a guide pin, etc., as much as possible since the nut is easily put on the guide pin and can be accurately put thereon without inclination. CONSTITUTION:The curved surface is formed so that the radius of curvature of the guide pin tip guide surface 5 for guiding the nut 6 is changed smoothly from a curved surface inlet part 3 to the nut seat part position 4 so that the tangent of an angle alpha formed between the axis 2 of the guide pin 1 and the tangent of the curved surface inlet part 3 and the tangent of an angle beta formed between the axis 2 and the tangent of the curved surface at the nut seat part position 4 are regulated to 0.04-0.15 and >=0.2, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a guide pin for a resistance welding machine for welding small articles such as nuts to a vehicle body, a panel or the like of an automobile.

[0002]

2. Description of the Related Art Spot welding by a resistance welding machine is generally performed as a method for attaching small articles such as nuts to the body of an automobile. A guide pin having a shape as shown in FIG. 4 is used for positioning in this spot welding. During spot welding, after the nut is fitted into the tip of the guide pin protruding from the center of the cylindrical electrode, the nut and panel (body) are pressed by the upper and lower electrodes while still fitted into the guide pin. Welded. As this guide pin, a metal guide pin is usually used, but in recent years wear resistance,
A ceramic guide pin having excellent insulation and heat resistance has been proposed.

Since metal guide pins have a lower hardness than ceramic guide pins, wear and deformation occur during nut insertion and guidance, and electrolytic corrosion wear and melting damage due to spatter also add to the guide pin surface of the guide pin. It will be in a rough state. With a metal guide pin, the roughened state deteriorates, the insertion and guidance of the nut cannot be performed smoothly, and if the frequency of occurrence of welding failure of the nut increases rapidly, the function as a guide pin cannot be achieved and the life ends.

For this reason, in the conventional metal guide pin, the shape of the guide surface is designed to focus on the nut insertion and the guide in order to cover the nut insertion and the guide failure due to the roughness of the guide surface. The design was disadvantageous in terms of structural strength. However, in the case of a metal guide pin, since it has a high degree of toughness and has sufficient margin in terms of impact strength, it is almost always the case that the guide part at the tip of the guide pin breaks and reaches the end of its life unless it is subjected to extreme impact. In most cases, the life was shortened due to a sharp increase in welding defects due to surface roughness before breakage. Since the ceramic guide pin is a material with high hardness, high elasticity, high insulation, and high heat resistance, there is almost no evidence of wear, deformation at the time of nut insertion, guiding, electrolytic corrosion wear due to spatter, and melting loss. Compared with this, the life is remarkably improved, the frequency of defective welding of nuts is reduced, and it is effective in improving productivity.

[0005]

Such a ceramic guide pin is superior in durability to a metal guide pin, but it is difficult for a nut to enter depending on the shape of the tip guide portion or the surface roughness thereof. It has been found that the nut is tilted and the ceramic guide pin is broken when the nut is tilted, or the work collides from the side of the ceramic guide pin and the tip end is broken. The reason why the tip of the tip is often broken in the ceramic guide pin, which is not often seen in the conventional metal guide pins, is that the conventional ceramic guide pins have the toughness and impact resistance deteriorated compared to the metal. This is because the shape design of the metal guide pin, which focuses on the nut insertion and guide functions, was applied to the ceramic guide pin as it was.

As a result of further studies, it was found that the durability of the ceramic guide pin depends on the shape of the tip guide portion, and further on the smoothness or smoothness of the surface thereof. The surface roughness referred to here is the surface roughness when the guide pin guide surface is measured in the axial direction, that is, in the direction in which the nut shifts. As a result of earnest studies based on the above findings, the present inventor has found that the curved surface of the guide portion at the tip of the guide pin has an appropriate shape, and the surface of the guide portion has an appropriate gentleness, whereby the ceramic guide pin is broken. The inventors have found that the above can be prevented and have reached the present invention.

That is, since the conventional metal guide pin and ceramic guide pin are insufficient in the nut insertion and the guide function on the surface of the guide portion, the shape design of the guide portion causes
Although it compensated for the lack of the function, it was disadvantageous for the ceramic guide pin because it deteriorated the structural strength characteristics. However, the present inventor has found that by ensuring the surface of the guide pin guide portion with an appropriate gentleness, the nut insertion and guide functions are dramatically improved, and further, the nut insertion, guide function and structural strength characteristics are improved. The inventors have found that by designing the shape of the guide portion in consideration of the balance between the two, it is possible to prevent breakage without impairing the nut insertion and guide performance in actual use.

[0008]

That is, according to the present invention, in a guide pin for a resistance welding machine, the tangent of the angle formed by the guide pin axis and the tangent line at the curved surface inlet is 0.
04-0.15, the radius of curvature of the guide pin tip guide surface that guides the nut is such that the tangent of the angle between the guide pin axis and the tangent of the curved surface at the nut seat position is 0.2 or more. There is provided a ceramic guide pin for a resistance welding machine, characterized in that a curved surface is formed so as to smoothly change from the position to the nut seat position.

In the present invention, the guide pin tip is formed so that the radius of curvature from the curved inlet to the nut seat position on the guide surface of the guide pin tip guiding the nut is in the range of 30 mm to 100 mm. A ceramic guide pin for a resistance welding machine is provided. In the present invention, when the surface shape of the nut guide surface is viewed microscopically, it is preferable that the upper part of the protrusion of the outwardly projecting portion has a gently curved surface so that the nut slides well. Further, conventionally, a structure has also been proposed in which a hole is made inside the ceramic guide pin and a metal pin is inserted to reinforce it, but with this structure, the manufacturing cost of the guide pin increases significantly, and it cannot be practically used in the production process. .. The present invention provides a ceramic guide pin that can be mass-produced at low cost within a practically usable range.

[0010]

In the ceramic guide pin of the present invention, the radius of curvature of the guide surface at the tip of the guide pin for guiding the nut is formed so as to smoothly change from the curved surface inlet portion to the nut seat portion position. This makes it easier to insert the nut into the guide pin, and since it can be inserted accurately without inclination, it is possible to prevent welding failure of the nut and breakage of the guide pin as much as possible. In addition, as shown in FIG. 3, when the surface shape of the upper portion of the convex portion protruding outward of the guide surface at the tip of the guide pin is formed into a gently curved surface, the surface roughness is less than a predetermined value (its center line depth Rp Is 3 μm or less), the slip characteristics of the nut are good, and the above effects can be further improved.

In the ceramic guide pin of the present invention, it is necessary that the tangent of the angle formed by the guide pin axis and the tangent line at the curved inlet is in the range of 0.04 to 0.15. If the tangent is less than 0.04, the tip of the guide pin is likely to break, and if it exceeds 0.15, the nut is difficult to insert. Further, it is necessary that the tangent of the angle formed by the guide pin axis and the tangent to the curved surface at the nut seat position is in the range of 0.2 or more. When the tangent is less than 0.2, the nut easily tilts, and it becomes difficult for the nut to sit stably on the guide portion.

Further, according to the present invention, the guide pin tip end portion may be formed so that the radius of curvature from the curved inlet portion to the nut seat portion position on the guide pin tip guide surface for guiding the nut is in the range of 30 mm to 100 mm. preferable.
If the radius of curvature is less than 30 mm, the tip of the guide pin is easily broken, and if the radius of curvature exceeds 100 mm, it is difficult for the nut to enter. The ceramic guide pin of the present invention can be manufactured by producing a molded body of a size obtained by multiplying the product size by the firing index, sintering the molded body, and then subjecting it to barrel polishing.

[0013]

EXAMPLES The present invention will now be described in more detail with reference to the illustrated examples, but the present invention is not limited to these examples. (Example 1) At least 1 ton / cm of Si ₃ N ₄ granulated powder added with a sintering aid such as yttria or magnesia
By ^more than one pressure to a rubber press molding into a cylindrical shape, the guide pins predetermined shape shown in FIG. 4 in anticipation of sintering shrinkage (M6
(For use)) with a lathe, and the surface is finished with sandpaper until there are no processing marks, especially on the guide surface, and after removing the binder, firing is performed at 1700 ° C. in a nitrogen atmosphere.

Next, 50 pieces of the predetermined guide pin-shaped sintered bodies were placed in a 7.5 liter hexagonal columnar steel container,
Alumina ball media of φ3 mm to φ5 mm is further added until the volume of the container reaches 60 vol%, and water is further added to make it 80 vol%. Then, a small amount of a surfactant is added and the container is closed, and then set on a Tipton centrifugal barrel polishing machine. and, rotated over 10 minutes at a rotation speed of 150-200 rpm, performs surface barrel treatment of the guide pins, Si ₃ N
₄ barrel processing guide pins were manufactured.

An example of the case where a nut is inserted into the obtained guide pin is shown in FIG. Ceramic guide pin 1 in Figure 1
The angle α between the axis 2 and the tangent to the curved inlet 3 is 5 ° 15 ', the angle β between the axis 2 and the tangent to the curved surface at the nut seat position 4 is 12 ° 46', and the guide pin tip is The guide pin tip guide surface 5 was formed so that the radius of curvature forming the guide surface 5 was 46.8 mm. In addition, as shown in FIG. 3, the surface shape of the guide pin tip guide surface 5 was a gently curved surface at the upper part of the convex portion protruding outward. Using this ceramic guide pin 1, nut welding was performed 10,000 times, and the number of occurrences of nut jamming at the guide tip portion, the number of occurrences of tilt welding failure of the nut, and the occurrence of breakage at the guide tip portion were examined. Here, the degree of breakage at the tip of the guide was examined by intentionally making the work easier to collide with the tip of the guide pin. The results are shown in Table 1.

(Examples 2-3, Comparative Examples 1-2) Example 1
A ceramic guide pin different from that of Example 1 only in the radius of curvature of the guide surface at the tip of the guide pin as shown in Table 1 was manufactured by a method similar to. That is, the axis 2 of the ceramic guide pin 1
Table 1 shows the angle α formed by the tangent line of the curved surface inlet portion 3, the angle β formed by the axis 2 and the tangent line of the curved surface at the nut seat position 4, and the radius of curvature forming the guide pin tip guide surface 5. The guide pin tip guide surface 5 was formed by changing it. Using this ceramic guide pin 1, nut welding was carried out in the same manner as in Example 1, and the number of occurrences of nut catching at the guide tip portion was examined. The results are shown in Table 1.

As is clear from the results shown in Table 1, Example 1
It can be seen that the guide pins Nos. 3 to 3 are superior to the Comparative Examples 1 to 2 in the sliding characteristics of the nut and the breakage occurrence rate. The tip guide surfaces of the ceramic guide pins according to Example 1 and Comparative Examples 1 and 2 are shown in FIG. Further, FIG. 5 shows the relationship between the tangent of the tangent angle to the radius of curvature at the position of the curved inlet portion and the nut seat portion on the guide surface of the guide pin tip that guides the nut.

[0018]

[Table 1]

[0019]

As described above, according to the ceramic guide pin of the present invention, the radius of curvature of the guide surface at the tip of the guide pin for guiding the nut is curved so as to smoothly change from the curved surface inlet portion to the nut seat portion position. By forming the nut, the nut can be easily inserted into the guide pin and can be accurately inserted without inclination, so that welding failure of the nut, breakage of the guide pin, etc. can be prevented as much as possible.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example in which a nut is inserted into a guide pin according to a first embodiment.

FIG. 2 is a schematic cross-sectional view showing a tip guide surface of ceramic guide pins according to Example 1 and Comparative Examples 1 and 2.

FIG. 3 is a graph showing an example of a surface roughness curve of a ceramic guide pin.

FIG. 4 is a side view showing an example of the shape of a guide pin.

FIG. 5 is a graph showing a relationship of a tangent of a tangent line angle to a radius of curvature at a curved surface inlet portion and a nut seat portion position.

[Explanation of symbols]

 1 Ceramic guide pin 2 Ceramic guide pin axis 3 Guide pin tip guide surface curved inlet 4 Nut seat position 5 Guide pin tip guide surface 6 Nut

[Procedure amendment]

[Submission date] February 25, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

Claims (3)

[Claims] 1. A guide pin for a resistance welding machine, wherein a tangent of an angle formed by the guide pin axis and a tangent at a curved surface inlet portion is 0.04 to 0.15, and the curved surface at a position of the guide pin axis and the nut seat portion. The tangent of the angle with the tangent of is 0.2
As described above, the ceramic guide for a resistance welding machine is characterized in that the curved surface is formed so that the radius of curvature of the guide surface at the tip of the guide pin for guiding the nut smoothly changes from the curved surface inlet portion to the nut seat portion position. pin. 2. A guide pin tip portion for guiding a nut, wherein the guide pin tip portion is formed so that a radius of curvature from a curved surface inlet portion to a nut seat portion position is in a range of 30 mm to 100 mm. Ceramic guide pin for welding machine. 3. The guide pin tip end surface of the guide surface, when viewed microscopically, the convex upper portion of the outwardly protruding portion has a gentle curved surface shape. Ceramic guide pin for resistance welding machine.