WO2002002296A1

WO2002002296A1 - Method for the production of a resin molded article having a metallic boss

Info

Publication number: WO2002002296A1
Application number: PCT/NL2001/000511
Authority: WO
Inventors: Hideki Yamaguchi; Johannes Gerardus Maria Nieuwkamp
Original assignee: Dsm N.V.
Priority date: 2000-07-06
Filing date: 2001-07-05
Publication date: 2002-01-10
Also published as: AU2001271140A1

Abstract

The invention relates to a method for the production of a multiple number of resin molded parts having a metallic boss, in which it is not necessary to subject the metallic boss to post-processing, and processed wastes containing a mixture of cutting pieces of metal and resin are not generated. This is achieved by using metallic bosses (1) which are previously processed into a final shape or a nearly final shape, arranging a multiple number of said metallic bosses (1) in line while maintaining a clearance portion (T), inserting the resulting structure in the inner face of a resin molding (21), integrally bonding the outer periphery of the metallic bosses (1) and the inner face of the resin (21) molding by heating to a temperature slightly above the melting temperature of the resin, and cutting and seaparating the product at the interval portions formed between the adjacent metallic bosses (1).

Description

METHOD FOR THE PRODUCTION OF A RESIN MOLDED ARTICLE HAVING A METALLIC BOSS

The present invention relates to a method for the production of a resin molded article having a metallic boss, and more particularly to an improvement in a production method for obtaining a multiple number of polyamide resin molded articles having a metallic boss.

Conventionally, as a method for the production of a resin molded article in which a resin molding is integrally formed on the outer periphery of a metallic boss, the following method has widely been used: a long-sized metallic boss is inserted in the inner side of a hollow cylindrical resin molding, followed by integrating the structure by heat fusion or the like, and the integrated product is then sliced in a disk shape having a given thickness to prepare a multiple number of intermediate materials having a metal boss inserted therein. Finally, in order to achieve a lightweight final product and to give a necessary shape to a side portion of the metallic boss, the side portion of the metallic boss of the intermediate material is individually subjected to a post-processing with a lathe or the like.

In the above conventional production method, extra steps are required because of the slicing operation for producing an intermediate material, a post-processing of the metallic boss, and the like, and a mixed waste of the metal and the resin is generated by the post-processing.

The present invention is to provide a method for the production of a multiple number of resin molded articles in which a resin molding is integrated with the outer periphery of a metallic boss, which solves the above problem. The invention resides in that several metallic bosses which are previously processed into a final shape or a nearly final shape are arranged in line as a multiple number of metallic bosses while maintaining a given clearance portion between them, inserting the resulting structure in the inner face of a hollow resin molding, integrally bonding the outer periphery of the metallic bosses and the inner face of the resin molding by heating to a temperature slightly above the melting temperature of the resin, and cutting and separating the product at the interval portions formed between the adjacent metallic bosses.

Preferred is a method, wherein a ring spacer is lien between a metallic boss and the adjacent metallic boss to maintain the clearance portion. The ring spacer is of a material that does not melt during the fusion process. Another preferred embodiment of the invention is a method wherein a projected portion for clearance is integrally molded with a side face of the metallic boss, maintaining a given clearance portion between the metal bosses.

Resins suitable for the present invention may be selected from high performance polymers with high thermal stability and good mechanical properties, such as polyesters, polyamides, fluoropolymers, polyketones (like PEEK, PEAK, PEKK), polyimides (like PAI), etc. Also, the coefficient of thermal expansion of the resin material should be close to the coefficient of thermal expansion of the metallic boss to preserve the integrity of the joined resin-metal body. The most preferred resins for use in production of worm gears are polyamides (like nylon 6, nylon 12, nylon 4,6) and polyacetals. In the preferred embodiment, a molded polyamide resin body (with inside diameter similar to the outside diameter of the metallic bosses) is pressed over the metallic boss- structure to produce a nylon coated metal product. Molded resin articles according to the present invention may be obtained from a wide variety of metals, such as steel, iron, brass, bronze or aluminum. Choice of a suitable metal for the metal bosses depends on the desired mechanical characteristics of the end product. For production of worm gears for automotive power steering systems requiring high load, energy and torque capacity, the preferred metal is steel.

In an embodiment of the invention, the metallic boss may be obtained by sintering of powder metal, i.e. by pressing powder metal and then heating the pressed metal. Various metals, such as steel, brass, aluminum or bronze may be used in the invention. The powder metal is placed into a die of a desired shape and compacted or pressed to form the unitary metallic boss of the desired configuration. The pressed metal particles are held together by inter- particle friction to form a "green-compact". The green compact is then placed into a furnace and heated to a temperature which is less than the melting temperature of the metal but which is sufficiently high to soften the metal particles and cause coalescing of the interfaces between the particles to unify the structure into a sintered metal matrix. The resulting structure is inherently porous. The metal body can be formed or sintered into a wide variety of final forms, from simple bars or rods to more complex irregular shapes depending on the end use of the final product. When the end product is a worm gear for a power steering system, the preferred powder metal is stainless steel powder.

In cases an improved adhesion between the molded resin body and the metallic bosses is needed, use can be made of a silane coupling agent, a primer or epoxy based adhesives, at the inferface.

A preferred method is a method, wherein the metallic boss- structure is directly inserted immediately after the hollow resin molding is molded, and followed by heat fusion.

It is of preference that the hollow resin molding has a cylindrical shape, as many of the final products require a cylindrical form.

The metallic bosses, which are previously processed into a final or nearly final shape, must have an identical or nearly identical outer diameter, in order to successfully mold the resin over all the metallic bosses. The metallic bosses are alined, so as to be able to cover all metallic bosses with the resin. A preferred mode is wherein the metallica bosses are alined via a shaft through a hole provided at the central part of the metallic bosses. After the molded resin body is pressed over the metallic bosses, the metallic bosses are heated, preferably by an induction coil, to a temperature slightly above the melting temperature of the resin, causing the resin surrounding the metallic bosses to melt. Generally, the temperature difference between the coil temperature and the melting temperature is not more than 50°C, more preferred not more than 25°C, and mostly preferred not more than 15°C. The molten resin flows to and fills the pores, voids, cavities and other irregularities on the surface of the metallic bosses. The joined body is then cooled to a temperature below the melting temperature of the resin, the resin solidifies and bonds adhesively and mechanically to the metallic bosses. In the case of metallic bosses, made via a powder sintering process, and due to the high porosity of the sintered powder metallic bosses, the bonding forces between the molded resin body and the metallic bosses are significantly stronger than the bonding forces in articles based on molded and knurled metallic bosses. This embodiment of the present invention allows the elimination steps of grit blasting of knurled metallic bosses, cleaning the metal surface, and using a silane coupling agent often necessary to achieve good bonding between the metallic bosses and the surrounding moulded resin body. The moulded resin article of the present invention is made by hot pressing a molded resin body to the outer circumference of a metallic boss structure and joining the parts together preferably using high frequency induction heating. The process for high frequency induction heating as such is known in the art. It generally uses a frequency of 0.5-200 kHz in a period of from 10-200 sec, this being dependant of the melting point of the resin in the molded resin body. The temperature to which the metallic boss is heated, is slightly above the melting temperature of the resin; in the case nylon-6 is used, said temperature is in the range of 240-260°C.

After the process in which the metal bosses and the resin molding are joint, the resulting product is cut and the individual coated metal bosses are separated, for instance by sawing at the internal portions formed between the adjacent metallic bosses.

The molded resin article with a metallic boss that has been obtained as described above, can be converted to a cogwheel part by sawtooth processing in the outer surface of the molded resin body, or it can be used as revolving articles such as wheels and rollers etc., and as construction members for tightening of industrial machinery and machine tools etc.

Particularly in the case that the molded resin body has been molded from a polyamide resin, it is suited as a raw material for machine parts for precision devices such as electronic machinery, because it can be used without oil supply. Because in the molded resin article with a metallic boss and the process for preparing such an article according to this invention, a metallic boss that has been preprocessed by forging etc., is used, metallic bosses with various forms of the side surfaces can be obtained in a simple way, and mass production with a good efficiency is possible without afterprocessing. Moreover, worrying about disposal of mixed processing waste of metal and resin scraps, that are produced by the afterprocessing as in the past, is not necessary.

The length of the resin molding is much greater than the thickness of each individual metallic boss. The man skilled in the art can easily determine the optional length of the resin molding, in order to be able to practically work the invention. The inner diameter of the resin molding is similar to the outside diameter of the metal bosses, and is preferably 0,4 - 3% smaller than said outside diameter. Because the production method of the resin molded part having the metallic boss of the present invention can use metallic bosses obtained by previously processing the metallic bosses by a lathe or the like, a multiple number of resin molded parts having a metallic boss having complicated various side portion shapes can simultaneously be produced with good efficiency. Further, if the method of the present invention is employed, there is no necessity to worry about disposal of processed wastes in which cut pieces of metal and resin, generated by the post-processing as in the conventional method, are mixed.

The production method of the present invention is explained in detail below in Figures 1-4.

Fig. 1 is a partially cut front view showing the embodiment that metallic bosses and spacer rings are alternately arranged on a shaft to fix them in a spit state. Fig. 2 is a partially cut front view showing the embodiment wherein a cylindrical resin molding is integrally bonded to the outer periphery of a metallic boss by heat fusion. Fig. 3 is a sectional view showing one embodiment wherein a resin molding having a metallic boss is obtained by the production process of the present invention, and Fig. 4 is a sectional view showing other embodiment of a resin molding having a metal boss obtained in the production process of the present invention. In Fig. 1, numeral 1 indicates a metallic boss, said metallic boss

1 being previously processed into a final shape or a nearly final shape by a lathe or the like.

The metallic boss has a hole 11 at the central portion, and surface uneven processing such as knurl processing or sandblast processing has been applied to the outer periphery. Further, slight bevel processing has been applied to corner portions of the outer periphery.

Numeral 3 indicates a spacer ring, and the spacer ring 3 is lien in order to maintain a given clearance portion between metallic boss 1 and the adjacent metallic boss 1 , thereby securing a cutting space T. The spacer ring 3 has a hole having the same diameter as that of the hole 11 of the metallic boss at the central portion thereof, and its outer diameter is much smaller than the outer diameter of the metallic boss 1. Further, its side shape is formed so as to be similar to the shape of the side face of the metallic boss 1 , and the thickness thereof is suitably about 1.5-3 mm. Numeral 4 is a shaft, and has an outer size which permits to penetrate the holes provided at the central portions of the metallic bosses 1 and the spacer rings 3. Screws, for example, are placed at both edges, thereby forming a structure such that nut 5 is screwed together to the shaft.

Nut 5 is screwed together to one edge of the shaft 4, the metallic bosses 1 and the spacer rings 3 are alternately fitted to the shaft 4, and the final edge of the shaft is screwed together with the nut 5.

Thus, the each metallic boss 1 is fixed in a spit state and lined up while maintaining a clearance T corresponding to the thickness of the spacer ring 3. In the case that knurl processing or the like is not previously applied to the outer periphery of the metallic boss 1 , the outer periphery of each metallic boss 1 may be subjected at once to knurl processing or the like at the stage of being fixed in the spit state.

In Fig. 2, numeral 21 indicates a long-sized cylindrical resin molding. The long-sized cylindrical resin molding 21 is a cast molded product comprising for instance a polyamide resin, and its inner diameter is formed so as to be smaller by its tightened part than the outer diameter of the metallic boss 1.

At a temperature (160-190°C), which is the remaining temperature immediately after the long-sized cylindrical resin molding 21 is molded, the metallic boss 1 in a spit state as shown in Fig. 1 is directly inserted, and after passing through appropriate annealing and aging steps, the outer periphery of the metallic boss 1 and the inner periphery of the long-sized cylindrical resin molding 21 are heat fused by, for example, high frequency heating, followed by cooling and solidifying, thereby preparing an intermediate material.

In the present invention, it is possible to employ the steps that after the long-sized cylindrical resin molding 21 is completely cooled, the inner face thereof is processed to a defined size, the molding is re-heated, the metal boss 1 in a spit state is inserted therein, followed by heat fusion, thereby integrally bonding the outer periphery of the metallic boss 1 and the inner periphery of the long-sized cylindrical resin molding 21.

In the intermediate material produced above, a clearance portion T is formed, in which a part of the inner periphery of the long-sized cylindrical resin molding 21 does not contact with the outer periphery of each metallic boss 1.

While rotating the intermediate material around the axial core of the shaft 4 as a center, the portion of the clearance portion T of the long-sized cylindrical resin molding 21 is cut at once using a rotating multi-blades tool from the outer periphery, so that each adjacent metallic boss is individually separated, and a multiple number of resin molded parts having the resin molding 2 integrated with the outer periphery of the metal boss 1 are simultaneously produced. Next, the nut 5 is removed from the shaft, and each resin molding having the metallic boss in it is taken out from the shaft 4. The resin molded parts are taken out from the shaft 4 and, if necessary, a fitting processing is applied, thereby obtaining a resin molded part having the resin molding 2 integrated with the outer periphery of the metallic boss

1 , as shown in Fig. 3.

Fig. 4 shows that a projected portion 12 for clearance is integrally provided to the side face of the metallic boss 1 , and in fixing the metal boss in a spit state, a given clearance portion is formed between the adjacent metallic bosses. The projection size of the projected portion 12 can be set to the same degree of the thickness as that of the spacer ring 3.

The cutting step is not a step of simultaneously cutting the metal and resin, as in the case in the convention method, but is a cutting step which cuts only resin material of the long-sized cylindrical resin molding 21. Therefore, the cutting and processing conditions can be set in conformity with the optimum conditions of the resin material. As a result, processing finish and productivity are very good. Further, in the method of the present invention, the cutting space T of the long-sized cylindrical resin molding 21 can be minimized, so that the amount of cutting wastes of the resin can be small. Explanation of the numerals in the Figures:

1 Metallic boss

11 Hole of metallic boss

12 Projected portion for clearance

2 Resin molding

21 Long-sized cylindrical resin molding

3 Spacer ring

4 Shaft

T Clearance between adjacent metallic bosses (cutting space)

Claims

1. A method for the production of a multiple number of resin molded articles in which a resin molding is integrated with the outer periphery of a metallic boss, wherein several metallic bosses which are previously processed into a final shape or a nearly final shape are arranged in line as a multiple number of metallic bosses while maintaining a given clearance portion between them, inserting the resulting structure in the inner face of a hollow resin molding, integrally bonding the outer periphery of the metallic bosses and the inner face of the resin molding by heating to a temperature slightly above the melting temperature of the resin, and cutting and separating the product at the interval portions formed between the adjacent metallic bosses.

2. Method according to claim 1 , wherein a ring spacer is lien between a metallic boss and the adjacent metallic boss to maintain the given clearance portion.

3. Method according to claim 1 , wherein a projected portion for clearance is integrally molded with a side face of the metallic boss.

4. Method according to anyone of claims 1 to 3, wherein the metallic boss structure is directly inserted immediately after the hollow resin molding is molded, followed by heat fusion.

5. Method according to anyone of claims 1 to 4, wherein the resin molding is a polyamide resin molding.

6. Method according to anyone of claims 1 to 5, wherein the resin molding has a cylindrical shape.

7. Method according to anyone of claims 1 to 6, wherein the metallic bosses are arranged in line via a shaft penetrated through a hole provided at the central part of the metallic bosses.