JP5396901B2 - Mold and manufacturing method thereof - Google Patents

Description

  The present invention relates to a mold used for molding plastic parts and the like and a method for manufacturing the same, and more particularly to a mold suitably used for molding small plastic parts such as a connector in a wire harness and a method for manufacturing the same.

  In a wire harness for automobiles, a connector made of a small plastic part is used at a wire connecting portion. Such a wire harness connector is manufactured in a predetermined shape by injection-molding plastic into a predetermined mold.

  A mold used for forming a connector is generally formed into a predetermined shape by subjecting the surface of a metal base material to electrical discharge machining. However, in a die subjected to electric discharge machining, residual stress in the tensile direction remains on the die surface serving as a machined surface. The residual stress in the pulling direction has a problem of reducing the strength of the mold and shortening the mold life. Therefore, a method is known in which a residual stress in the compression direction is generated on the surface of the die subjected to electric discharge machining to improve the strength reduction of the die (for example, see Patent Documents 1 and 2).

  In the method described in Patent Document 1, the first step of completely removing the work-affected layer by injecting amorphous particles such as alumina onto the electric discharge machining surface, and spherical particles such as steel, ceramic, and glass beads are injected. And a second step of adjusting the surface roughness and applying a residual stress in the compression direction.

  In the method described in Patent Document 2, after applying impact plastic working to the mold surface, residual stress of 300 MPa or more and yield stress or less is added to the processed surface at a position of more than 0 MPa to 1000 MPa and a depth of 0.2 mm. Then, the part which performed the said process is removed in the range whose thickness is 0.3 mm-less than 1 mm by electrolytic polishing, emery paper polishing, wire discharge, etc.

JP-A 63-207563 JP 2008-73706 A

  However, if the method described in Patent Document 1 is applied to a wire harness mold and the work-affected layer is completely removed, there has been a problem that a change in the dimensions of the mold becomes large. The wire harness mold is a precision mold with small component dimensions, and if the work-affected layer is completely removed, the dimensional change before and after removal becomes too large. Further, in the method of Patent Document 1, the total processing time of the first step and the second step takes about 20 minutes, the processing time becomes long, and the processing cost increases.

  Further, if the method described in Patent Document 2 is applied to a wire harness mold, the surface is polished by 0.3 to 1 mm by electrolytic polishing or the like, so that the processing amount is large and the processing cost is increased. There was a problem. Further, it is considered that when the amount of processing of the mold increases, the processing accuracy of the mold is also adversely affected.

  The problem to be solved by the present invention is to solve the above-mentioned problems, and to provide a mold having good machining accuracy and low machining cost, and a method for manufacturing the same.

  In order to solve the above problems, the mold of the present invention is characterized in that a work-affected layer formed by electric discharge machining remains and the work-affected layer has residual stress in the compression direction. .

  The mold manufacturing method of the present invention includes an electric discharge machining process in which electric discharge machining is performed to form a predetermined mold shape, and a work-affected layer generated in the electric discharge machining process remains, and the work-affected layer has a compression direction. And a stress applying step for adding residual stress.

  Since the metal mold | die of this invention has the residual stress of a compression direction in the process-affected layer by electric discharge machining, the intensity | strength of a metal mold | die can be raised and the lifetime of a metal mold | die can be extended. Furthermore, since the mold dimension does not change greatly by not removing the work-affected layer, the precision of the mold dimension is good. In addition, since the work-affected layer is not removed, the mold does not warp. Furthermore, since the work-affected layer is not removed, the work can be performed in a short time, and the processing cost is not increased.

  The mold manufacturing method of the present invention includes an electric discharge machining process in which electric discharge machining is performed to form a predetermined mold shape, and a work-affected layer generated in the electric discharge machining process remains, and the work-affected layer has a compression direction. And a stress applying step for adding residual stress, so that a mold with good dimensional accuracy can be obtained with certainty. Furthermore, the processing time is short and the processing cost is low.

FIG. 1 is a cross-sectional view showing an example of a mold of the present invention. 2 (a) to 2 (c) are cross-sectional views showing respective steps of the mold manufacturing method of the present invention. FIG. 3A is a perspective view of a test piece used in the fatigue test, and FIG. 3B is an explanatory diagram of the fatigue test method. It is a graph which shows the fatigue test result of an Example and a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a mold of the present invention. As shown in FIG. 1, in the mold 1 of the present invention, the surface of a base material 2 is formed into a predetermined shape by electric discharge machining. Then, the work-affected layer 3 by electric discharge machining remains on the surface of the base material 2 without being removed. Further, the mold 1 applies a stress in the compression direction to the work-affected layer 3, and the work-affected layer 3 has a residual stress in the compression direction.

  The residual stress composed of stress in the compression direction of the work-affected layer 3 is added by injecting particles onto the work-affected layer 3 on the surface of the mold 1. The injection of the particles for applying the stress in the compression direction may be performed under injection conditions such as an injection pressure and an injection time that do not remove the work-affected layer 3 and change the mold size.

  Hereinafter, the manufacturing method of the metal mold | die of this invention is demonstrated. 2 (a) to 2 (c) are cross-sectional views showing respective steps of the mold manufacturing method of the present invention. In the mold manufacturing method of the present invention, first, as shown in FIG. 2A, a base material 2 is prepared, and an electric discharge machining process is performed in which electric discharge machining is performed on the surface of the base material 2. When the electric discharge machining process is performed, the surface of the base material 2 is formed in a predetermined mold shape as shown in FIG. Further, as shown in the figure, a work-affected layer 3 is formed on the surface of the base material 2 by electric discharge machining.

  As an electric discharge machining method for forming irregularities on the mold, a method using a known electric discharge machining apparatus or the like can be used. In addition, the base material 2 can be a metal material that is usually used in a molding die for small plastic parts such as a connector for a wire harness.

  Next, as shown in FIG. 2C, in the stress application step, particles are injected onto the work-affected layer 3 generated in the electric discharge machining step using the injection device 4 to apply a stress in the compression direction. At this time, the injection of particles is performed so as not to change the die size, and the stress in the compression direction is applied while the work-affected layer 3 remains without completely removing the work-affected layer 3. The spraying device 4 used for spraying particles can use a blasting device such as a blasting device.

  In the step of applying stress by the injection of particles, it is preferable that in the first injection step, angular irregular particles such as alumina are injected, and in the second injection step, spherical particles such as glass beads are injected. . In both the first injection process and the second injection process, the process-affected layer 3 is injected so as not to be completely removed. The amorphous particles used in the first injection step may be particles having a hardness higher than that of the mold base material. The amorphous particles may be other irregular particles other than alumina. The spherical particles used in the second injection step may be spherical particles having a hardness higher than that of the base metal of the mold, and particles such as steel and ceramic can be used in addition to glass beads.

  Thus, by adding stress to the two injection processes, the first injection process using irregular particles and the second injection process using spherical particles, there are the following advantages. First, in the first injection step, residual stress in the compression direction can be reliably applied to the work-affected layer 3 by injecting particles having irregular corners. Next, in the second injection step, the portion where the surface of the mold is roughened by the injection of angular irregular particles in the first injection step is polished and smoothed by the injection of spherical particles. Moreover, stress in the compression direction is further imparted to the work-affected layer 3 by the injection of spherical particles.

  An example of specific injection conditions in which the work-affected layer 3 is not removed in the first injection process and the second injection process is as follows. In the first injection step, it is preferable that the particle size of the irregular shaped particles is 20 to 40 μm. The pressure for injecting the irregular shaped particles is preferably 0.3 MPa or less, more preferably in the range of 0.1 to 0.2 MPa. In addition, the ejection time of the irregular particles is preferably 30 seconds or shorter, more preferably 20 seconds or shorter. Said injection conditions are a case where a processing distance is 50-150 mm.

  In the second injection step, the spherical particles preferably have a particle size in the range of 10 to 30 μm. The pressure for injecting the spherical particles is preferably 0.3 MPa or less, and more preferably in the range of 0.1 to 0.2 MPa. Further, the ejection time of the spherical particles is preferably 30 seconds or shorter, more preferably 20 seconds or shorter.

[Experimental example]
An experiment was conducted to verify the effect of applying stress in the compression direction by ejecting particles in two stages without removing the electric discharge machining layer. In the experiment, a test piece 5 having a shape shown in FIG. The test piece 5 formed an electric discharge machining portion 6 by performing electric discharge machining on a predetermined portion (a portion indicated by hatching in the drawing) of a plate-like steel plate having a thickness of 1.2 mm. Parts other than the electric discharge machining part 6 of the test piece 5 were formed by grinding. The test piece 5 is provided with fixing holes 7 for fixing to the fatigue tester. The electrical discharge machining part 6 of the test piece 5 is sprayed for less than about 10 seconds at an air pressure of 0.1 to 0.2 MPa and a distance of 50 to 150 mm using amorphous alumina particles having a particle diameter of 30 μm. Then, using a glass bead having a particle size of 20 μm, an air pressure of 0.1 to 0.2 MPa and a distance to the mold of 50 to 150 mm were sprayed for less than about 10 seconds to apply a stress in the compression direction. When the cross-sectional structure of the electric discharge machining portion 6 of the test piece 5 after the particle injection was observed with a microscope, it was confirmed that the work-affected layer remained on the surface.

  Further, a fatigue test of the test piece 5 was performed. For comparison, electric discharge machining was performed to form an electric discharge machining portion, but a test piece (only electric discharge machining) that did not add stress in the compression direction was also tested. The test results are shown in the graph of FIG. The fatigue test method is as follows.

  The fatigue test method was performed according to JIS Z 2275 “Flatness bending fatigue test method for metal flat plate”. As shown in FIG.3 (b), it attaches to the fixing | fixed part 9 of the test device 8 using the attachment hole 7 of the test piece 5, the upper part of the test piece 5 is supported by the support body 10 in the figure, and the repetition rate shall be 600 cpm. Bending stress was applied to the surface of the test piece 5 and the number of repetitions until failure was measured.

  As shown in the graph of FIG. 4, as a result of the fatigue test, the stress added in the compression direction (electric discharge machining + stress addition) has a larger number of repetitions than the electric discharge machining alone, and the strength Improvement was confirmed.

  The mold of the present invention is suitable for molding small, precise and small plastic parts having a side of about 10 mm or less, and particularly suitable for molding parts such as connectors for automobile wire harnesses.

1 Mold 2 Base material 3 Processed alteration layer 4 Injection device

Claims (4)

A mold used for molding a plastic for a connector for a wire harness , wherein a work-affected layer formed by electric discharge remains, and the work-affected layer has a residual stress in the compression direction ,
The mold according to claim 1, wherein the residual stress in the compression direction is added by injection of particles to the work-affected layer . A method of manufacturing a mold used for plastic molding of a connector for a wire harness , which includes an electric discharge machining process in which electric discharge machining is performed into a predetermined mold shape, and a work-affected layer generated in the electric discharge machining process remains. And a stress applying step of adding particles to the work-affected layer to inject a residual stress in the compression direction. 3. The method of manufacturing a mold according to claim 2 , wherein the stress applying step includes applying residual stress in the compression direction by injecting particles onto the electric discharge machining surface at a pressure of 0.3 MPa or less. The method of manufacturing a mold according to claim 2 or 3 , wherein the stress applying step includes a step of injecting irregularly shaped particles and a step of injecting spherical particles.

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