JP3959637B2 - Weld line generation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-precision gear suitable as a paper feed drive gear in a printer such as a copying machine, a facsimile machine, a computer, and a word processor, and more specifically, it has excellent precision and strength for obtaining high speed and high image quality. The present invention relates to a method of forming a precision gear that requires dimensional stability and wear resistance by injection molding of a fiber reinforced thermoplastic material.
[0002]
[Prior art]
As shown in FIG. 5, conventionally, an injection-molded gear T is molded by injecting a plastic material from a multi-point gate G that opens on a web W surface provided with a concave portion V for stealing meat. In this case, in a thermoplastic having an orientation reinforced with glass fibers, carbon fibers, or other additives, weld lines L are generated radially in the direction in which the materials merge between adjacent gates. In the line L, the radial orientation H of the filled fibers as shown in the figure is seen.
[0003]
Accordingly, during cooling, the weld line L direction in which the fibers are oriented hardly contracts. On the other hand, in the region F in the radial direction from the gate sandwiched between the weld lines L, the flow perpendicular to the flow front indicated by S is normal. Since the mixed fibers are oriented in the circumferential direction, large shrinkage in the radial direction appears in this portion. An arrow R is a vector illustration of the contractile force distributed unevenly around the circumference.
[0004]
The outer shape of the gear is deformed due to the change in shrinkage due to the locationally biased orientation non-uniformity in the web W, and the gear T shown in FIG. When the “test” is performed, as shown in the graph of FIG. 6, a significant deviation in the center distance in the weld line L direction is detected. Symbols a to i indicate correspondences with the meshing positions of the gears in the biased pattern by the “meshing test”. According to this biased figure, the difference between the peak and the valley showing the maximum bias is about 15 μm, and the influence of the non-uniformity of the shrinkage becomes noticeable as the peak and valley bias.
[0005]
[Problems to be solved by the invention]
However, with the remarkable improvement in the resolution of the print head in printers and the like in recent years, even higher accuracy is required for paper feeding. In order to manufacture a metal gear with high accuracy, advanced mechanical technology is required for hobbing, tooth surface polishing, and the like, which is not only suitable for mass production but also extremely expensive. Therefore, this problem must be overcome with plastic molded gears in order to improve productivity and provide products at low cost.
[0006]
Accordingly, the present invention suppresses the amount of shrinkage that occurs in the radial region from the gate by equalizing the fiber orientation by generating a large number of weld lines in the injection molding of high-precision gears using fiber-reinforced thermoplastic material. Accordingly, it is an object of the present invention to improve the meshing accuracy of the gear by preventing the gear shape from being deformed and the accuracy from being reduced.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a method for generating a weld line in injection molding using a fiber reinforced thermoplastic material according to the present invention includes a gate provided with a plurality of fiber reinforced thermoplastic materials at equal intervals on a circumference. The fiber-reinforced thermoplastic material that has flowed into the mold from the adjacent gates is merged between the two gates, the mixed fibers are oriented by this merge, and a weld line is formed radially to inject. When molding, by a cylindrical obstacle provided on the outer circumference in the radial direction of each gate on the circumference concentric with the circumference formed by the plurality of gates, apart from the weld line based on the gate, Forming a weld line based on the cylindrical obstacle between adjacent weld lines based on the gate; It is an feature.
According to the present invention, the number of weld lines can be increased without increasing the number of gates. That is, even when the number of gates is physically limited due to dimensional constraints, the number of weld lines can be increased .
Specifically, in a high-precision gear injection molding method using a fiber-reinforced thermoplastic material, a precise circular gear tooth mold engraved on the outer periphery, a main cylinder that determines the central axis of the gear, and the tooth An injection molded gear mold cavity is defined by a web portion intermediate between the mold and the cylinder.
[0008]
In this mold, gates are provided at equal intervals at a plurality of locations on the circumference of the web concentric with the cylinder in the web portion in the vicinity of the center cylinder. Therefore, a plurality of small cylinders having a required diameter are planted in the mold cavity at equal intervals on concentric circles outside the gates, with the central axis and the axis parallel to each other.
[0009]
The high-precision gear of the present invention manufactured by the above-mentioned mold is a high-precision circular gear made of a fiber-reinforced thermoplastic material by injection molding in which teeth are engraved on the outer periphery, and the gear has a central axis thereof. In the intermediate web portion between the main spindle cylinder to be determined and the dentition, generally on a substantially concentric circle outside the position corresponding to the gates of injection molds provided at equal intervals at a plurality of locations on the circumference concentric with the cylinder, etc. Through holes having a required diameter are provided at intervals.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
As a thermoplastic material as a base material, polypropylene (PP), polyethylene sulfide (PPS), polyacetal (polyoxymethylene: POM), polybutylene terephthalate (PBT), modified polyphenylene oxide (PPO), polycarbonate (PC), polyamide (Nylon 6.6) is suitable for use, and polythioether sulfone (PTES) is particularly excellent in dimensional stability, heat resistance, and rigidity.
[0011]
Glass fiber and / or carbon fiber is added to the reinforcing filler to be mixed at a ratio of 20 to 50% by weight. Preferably, about 15 to 30% by weight of glass beads having an average diameter of several μ to 40 μ are mixed.
[0012]
As described above, the fiber-containing plastic material that has flowed out from the adjacent gates merges between the two gates, and the mixed fibers are oriented to form a weld line radially. In the region separated from the weld line, the fiber orientation is in the circumferential direction, and the shrinkage tends to increase according to the separation distance.
[0013]
Therefore, it is conceivable to increase the number of weld lines by increasing the number of gates to reduce the region having a large amount of shrinkage and to equalize the fiber orientation with a radial arrangement. However, the increase in the number of gates is physically limited due to dimensional constraints. On the other hand, it has been found that the generation of the weld line is possible even if a cylindrical obstacle is provided in the middle of the flow of the fiber-containing plastic material.
[0014]
The gist of the present invention is to equalize the directionality of the fibers of the forming material in the circumferential direction by increasing the number of weld lines in the gear web. Therefore, instead of adding gates, for example, as shown in FIG. 1, a weld line is generated on the circumference of a concentric circle 19 where a radius line 18 from the gate 12 toward the outer periphery 16 of the gear 14 intersects in the mold cavity 10. A plurality of small cylinders 20 having the same effect as described above were implanted in parallel with the axis 22 of the gear 14. A manifold 23 branches the gate 12 into eight locations.
[0015]
Thus, in addition to the eight weld lines 24 formed by the eight gates 12, eight weld lines 25 formed by the eight small cylinders 20 are generated, and the total number of the weld lines 24, 25 is doubled to sixteen. Normally, the nozzle inner diameter of the gate 12 is φ0.5 to 2.0 mm, and the outer diameter φd of the small cylinder 20 may be a dimension that can withstand the flow pressure of the fiber-containing plastic material. Depending on the required strength, the number of small cylinders to be implanted, the arrangement and the like, the dimensions can be set appropriately.
[0016]
The weld lines 25 are increased by the number of arrangements of the small cylinders 20, and the shrinkage region (region between adjacent weld lines) 26 can be decreased accordingly. As shown in another example in FIG. 2, the small cylinder 20 is further expanded at 16 locations on the outer concentric circumference 27 at equal intervals, 16 weld lines 28 are added, and the number of weld lines is reduced to 32. Can be doubled. Along with this, the fiber orientation toward the outer periphery is equalized over the entire surface of the gear web, and the contraction region 26 between adjacent weld lines is reduced, so that the contraction occurs almost uniformly over the entire circumference of the gear. become. In FIG. 2, the same reference numerals are used for the same parts as in FIG.
[0017]
【Example】
3 shows the number of teeth (N.T.) = 160, module (m) = 0.5, pitch circle diameter (P.C.D.) formed based on the high-precision gear injection molding method according to the present invention. ) = Φ80 mm gear 30, 32 is a trace of eight gate positions provided at equal intervals on the circumference of the concentric circle 33, and 34 is equally spaced at eight positions on the concentric circle 35 outside the concentric circle 33 on which the gates 32 are arranged. These are through-holes generated by small cylinders arranged in a row. Eight portions of the small cylinder are provided on the same radial line as the gate position. Reference numeral 36 denotes 16 weld lines generated by such a mold configuration. Reference numeral 37 denotes a main hollow cylinder that determines the central axis of the gear 30.
[0018]
As shown in the graph of FIG. 4, the fluctuation range is within 10 μm as a result of the “JGMA standard for the gear 30” based on the JGMA standard. The deviation tendency due to the non-uniform shrinkage is Not noticeable. Reference signs A to I indicate correspondences with the meshing positions of the gears in the biased pattern by the “meshing test”.
[0019]
According to JGMA 116-02 (meshing accuracy of spur gears and helical gears), the allowable value of the total meshing error of both tooth surfaces of small module gears with a module of 0.2 to 0.6 is the highest precision grade. In the grade 0, which is the notation, a gear having a pitch circle diameter of more than 50 mm and not more than 100 mm is 20 μm, so the conditions for the meshing accuracy are sufficiently satisfied. The same result can be obtained when molding a non-reinforcing (without mixing reinforcing fibers) thermoplastic resin that has a tendency to crystallize, that is, easily oriented during molding.
[0020]
As described above, according to the high-precision gear injection molding method according to the present invention, the orientation of the molding material is made uniform and the shrinkage is uneven by a simple method of implanting a small cylinder in the gear mold cavity. This eliminates the deformation of the gear caused by this, so that JGMA standard 0 accuracy can be achieved for fiber-reinforced thermoplastic injection molded gears, and mass production of such high-precision gears with excellent strength and durability can be achieved. It becomes possible.
[Brief description of the drawings]
FIG. 1A is a plan view of a gear mold manufactured by a high-precision gear injection molding method according to the present invention, and FIG. 1B is a cross-sectional view taken along line 1b-1b of FIG.
FIG. 2 is a plan view showing another arrangement of small cylinders in a gear mold by the high-precision gear injection molding method according to the present invention.
FIG. 3 is a plan view of a gear produced by a high precision gear injection molding method according to the present invention.
4 is a graph showing how the center distance varies in the gear meshing test shown in FIG. 3; FIG.
5A is a plan view and FIG. 5B is a cross-sectional view of a conventional plastic gear mold.
6 is a graph showing how the center distance fluctuates in the gear meshing test shown in FIG. 5; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Mold cavity 12 Gate 14 Gear 16 Outer periphery 18 Radial line 19 Concentric circle 20 Small cylinder 22 Axis 24, 25, 36 Weld line 26 Contraction area 27 Concentric circle 30 Gear 32 Gate trace 34 Small hole 35 (by small cylinder) Concentric circles

Claims (1)

The fiber-reinforced thermoplastic plastic material from the gate provided plural positions at equal intervals on the circumference drained into the mold, the adjacent said fiber-reinforced thermoplastic plastic material is flowing out of the gate in the middle of the both gates At the time of injection molding by forming a weld line radially by orienting the mixed fibers by this merge,
Based on the gate, separately from the weld line based on the gate, by a cylindrical obstacle provided on a circumference concentric with the circumference formed by the plurality of gates and at an outer position in the radial direction of each gate. between adjacent weld lines, the method of generating the weld lines in an injection molding with a fiber-reinforced thermoplastic plastic material, characterized in that to form a weld line based on the cylindrical obstacles.

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