MXPA06011913A - Electronic power assist steering worm gears - Google Patents

Abstract

Composite worm gears having little residual stress are prepared by forming a tube of synthetic resin by extrusion, compression molding, or centrifugal processing, and fixing the tube thus produced or rings cut therefrom onto a boss or core, preferably of metal. The process allows high performance high molecular weight thermoplastics to be employed.

Description

NON-END SCREW GEAR AUXILIARY DIRECTED BY ELECTRONIC ENERGY FIELD OF THE INVENTION The invention relates to a process for the production of worm gears, hybrids, plastics and clutch parts using clutch projections made of synthetic materials, especially thermoplastic materials.

Background of the Invention < In electronic power steering (EPS) systems many different types of worm gear / worm gear sets are used. For reasons of noise reduction, the lower coefficient of friction and the reduction of wear, one of the components or the clutch portion of that component is normally made of thermoplastic, synthetic material, preferably the worm gear. Two technologies are currently used to produce worm gear sets. Such a worm gear may consist of a fused nylon ring of a PA6 or PA6 / PA 12 mixture, which is pressed into or melted on a mainly metallic hub (metal hub) and then fused together by heating inductively. The disadvantage of the above-mentioned process is that the nylon ring is only useful at a temperature of up to approximately 80 ° C. However, if the product, for example, a worm gear, is to be used in the engine compartment of an automobile or in another environment in which higher temperatures are possible, such a product should not be used. Another type of worm gear is produced by injection molding of a filled or unfilled filler, generally based on polyamide (PA) 6, 6.6, 4.6, 12 PPA, or mixtures thereof; and also polyphenylene sulfide (PPS); polyamide-imide (PAI); and polyetheretherketone (PEEK); they are fixed directly (by over-mold) to a cube, usually one that has a metal structure. In both cases, one or more heat treatments are required to reduce the stresses in the products and / or obtain the required dimensional stability of the final product. The disadvantage of the aforementioned process is that the injection molding process leads to a product, i.e., a worm gear, which is not resistant to tension to the extent required by the application, as mentioned above. Many of these processes and products have been described in the prior art, for example, JP-A-2002/172703 for a "re resin mold having a metal bucket and its manufacturing method", JP-A-2002/079581 for a method of manufacturing resin-molded article having metal bucket ", JP-A-2002/370290 for a" method for fixing metal bucket to thermoplastic resin molding "and JP-A-2003/1 18006 for a "Resin-molded item that has metal cube and manufacturing method thereof. "DE-A-101 27 224 discloses the production of a worm gear by a process of molding a thermoplastic in a metal core, however, this process includes all the disadvantages of the prior art A similar disclosure is included in JP-A-2002 / 248649. It would be desirable to provide a process for the manufacture of worm gears, which do not share the deficiencies of the previously discussed processes.

Brief Description of the Invention An object of the invention is to provide a production process for worm gear parts comprising fewer stages and / or having higher quality. These and other objects are provided by a process in which tubes made by extrusion technology are used. According to a first aspect of the invention, the object of the invention is solved by a process for forming an article comprising a cube, preferably a metal cube or comprising metal, and an external part of synthetic resin (102), preferably an outer part of thermoplastic resin, the outer part surrounding a periphery of the metal cube, this process comprising the steps of: (a) extrusion, compression molding or centrifugal processing of the tubes, optionally followed by machining, up to the required dimensions , (b) cutting the tubes in an appropriate length and (c) securing a ring produced by step (b) in the Cube. As a main result of the invention, the process leads to products with a lower internal stress level and better dimensional stability; greater resistance to wear due to the higher molecular weights that can be used compared to injection molding; and lower production expense. According to another aspect of the invention, an object of the invention is solved by a process for forming an article that preferably comprises a metal bucket or a bucket containing metal, and an external part of synthetic resin, preferably an external part of thermoplastic resin, circumscribing the external part to the metal cube, this mode comprising the steps of: (a) extrusion, compression molding, or centrifugal processing of tubes in the required dimensions, optionally aided by machining steps, (b) fixing of tubes produced by step (a) in a pre-formed core; and (c) cutting rings from the tubes fixed in a preformed core at a suitable length.

Brief Description of the Drawings FIG. 1 illustrates an embodiment of the invention wherein an extruded resin material is cut and then combined with metal rings, and FIG. 2 illustrates a further embodiment of the invention wherein the extruded resin material is directly combined with a metal rod and then cut.

Detailed Description of the Preferred Processes Both of the above-mentioned embodiments allow the production of tubes in a wide variety of materials and formulations thereof, including, but not limited to, fillers, lubricants, copolymers , reinforcing fibers, etc. Preferred materials include the aforementioned PA-based materials, POM, PPA, PPO, PPS, PEEK, PAEK and PEKK, PAI and LCP. Also, co-extrusion of more than one material or formulation is possible in order to obtain optimum properties in relation to the function of the particular stratum, for example, the clutch stratum and the stratum which facilitates attachment to the core. Centrifugal extrusion and molding make it possible to use materials with higher thermal capacities in order to meet more demanding applications than those that can be achieved with nylon 6 or monomer 12 nylon. Additional details, characteristics and advantages of the objects of the invention they are obtained from the description of the relevant drawings wherein, for example, two methods according to the present invention are explained. An application of the products produced by the inventive process refers to worm clutches for EPS systems. Such screw clutches are considered a "safe part" in the automotive industry. The manufacturers of EPS systems thus require materials and products without Internal deformations in order to help prevent fracture during use. The processes described herein for the production of tubes from thermoplastic materials (extrusion, compression molding and centrifugal processing) provide all products with a very low voltage level, thus fulfilling the aforementioned needs of the automotive industry. Especially when compared to injection molded products, the inventive processes exhibit significant advantages by offering much higher safety levels. There is a tendency in the automotive industry to place EPS systems "under the arrow" (hood), near the engine. Consequently, all components of an EPS system are exposed to higher temperatures, which are typically above 120 ° C. As a consequence, standard polyamides are not useful in such applications due to their physical and thermal properties. For the same reason, the fusion of tubes made of Polyamide 6 is not an option either, so that the injection molding of thermoplastic materials resistant to temperature is the only alternative. The present invention offers another option with the significant advantage of lower stress level compared to injection molding. This includes the possibility to select from a wide variety of thermoplastic materials resistant to temperature. Another innovative aspect of the present invention is the fact that one can directly influence the properties of the tube thermoplastic by adjusting the process parameters. In particular, the need for increased hardness can be met by the use of resins with high molecular weight, which is often not possible in injection molding processes due to a higher melting temperature and melt viscosity. A first embodiment according to the present invention is described in more detail by means of FIG. 1. The process of producing screws / worm gears of the invention starts with the extrusion of tubes 101 in the required dimensions. From these tubes, the rings 102 are cut to the appropriate length (process 1 10), if machining is required to size, cleaned by a solvent if necessary and pressed (process 11) into a core 103. These cores are preferably metal cubes made by a process of machining, sintering, forging, and / or metal injection molding, including bleaching, and cutting into corresponding rings. According to a preferred embodiment of the invention, the process of pressing the ring on the hub is facilitated by the use of residual heat from the extrusion process. However, according to an alternative embodiment, additional heat may be used for step 1 1 1. After pressing ring 102 into hub 103, the device is cooled (process 1 12). By secondary melting (process 1 13), the product is fixed to cube 103. This secondary melting is preferably carried out by means of induction coils 200 around the preformed rings. Depending of the material used and the required dimensions, a hardening cycle (not shown in Fig. 1) can be used. In a final machining process 14, the product is separated into composite discs, if it is not already in this form, which can then be cut to a gear. It is preferable that the inner diameter of the plastic ring is somewhat smaller than the outer diameter of the metal hub. The process according to this modality can be used for all the materials currently used, as well as those mentioned above. Additional advantages occur in case of semi-crystalline / amorphous materials. When extruding at low temperatures and maintaining the inner surface of the extruded tube below the Tg of the polymer in rapid cooling combination after extrusion, the material inside will remain amorphous (first layer). After cutting the rings and preheating at temperatures just above the Tg, the amorphous stratum will allow the ring to be easily pressed onto the tube and with low stress formation. During melting, the material will heat up to allow crystallization of the first amorphous phase. The use of this process leads to products with considerably lower stress levels and better wear properties than comparable products, manufactured through injection molding. In addition, the safety of the application increases, as in the injection molding process, the problem of hole formation due to shrinkage of the material during cooling is a problem very well-known. However, hollow formation is totally absent in an extrusion process. The hub can be made by any suitable process and can be supplied in pre-cut lengths or as a continuous or substantially continuous product. The surface is preferably "textured" to facilitate firm coupling with the outer part of resin. Various kinds of texturing may be employed, such as the use of a surface submerged in sand, a threaded or grooved surface, etc. A knurled surface, preferably one with a diamond pattern, is preferably used. The cube is preferably made of metal, all or in part. However, non-metallic cubes can also be useful in some applications. In general, the material of the cube will have greater resistance properties than the "exterior" that will be cut or machined in the gear. Examples of suitable thermoplastic materials include, without limitation, the above identified polymers, as well as thermoset polymers such as epoxy resins, bismaleimide resins, polyurethane resins and the like. The cube material will generally have a physical property profile different from the outside of the gear, due to the different requirements of these respective portions of the hub and in general will have greater hardness and temperature resistance, that is, when a thermoplastic will have a higher melting temperature than the gear layer. For resistance requirements improved, such non-metallic bucket materials can be reinforced fiber, for example, with glass, carbon or aramid fibers or the like. The thermoplastic or thermosetting cube materials may also contain metal particles so that the induction heating can still be used for melting a thermoplastic exterior to the core. In a similar manner, a hybrid cube can be prepared by filling a metal tube with the cube material. The tube, after its pressure on the outside of the gear, can be heated easily by induction to melt the tube and the exterior as a whole. In the modality according to Fig. 2, the tubes 1 01 are extruded continuously or semi-continuously (process 120) or are centrifugally molded in a preformed core 1 05, resulting in an intermediate product 121. By melting 1 13, the extrusion product is fixed to the core 105 according to the previous embodiment, by means of induction coils 200 around the pre-formed product. In a final machining process 122, the product is finished by cutting and bleaching. The process of the invention includes several alternatives that can be described as follows: "Cable extrusion" In this process the material is extruded continuously or semi-continuously into a preformed core. The core is either formed into ingots (Fig. 1) or "endless" (Fig. 2). "in line" The heat of the extrusion is used to press the rings in the tubes "in line". "Offline" The tube and rings are cooled and assembled "off line". The skilled technician can select a process depending largely on the shape of the cube and the tolerances and performance criteria required as ordered by the customer and will thus select the most appropriate process according to these limits. EXAMPLES The following is provided as examples of the subject EPS invention by putting into practice: Example 1 UHWM rod deposit (ultra high molecular weight polyethylene) was fused to a carbon steel core (SAE 1 17) by the use of 1 KHz of induction unit. The procedure was the following: 1. The extruded UHMW rod was machined into a tubular geometry, the ID being machined in a dimension that was 2% less than the outer diameter of the steel graft (core). The appropriate dimensions were 3"OD x 2" ID x 6"length (7.6 cm x 5.1 cm x 15.2 cm) 2. The UHMW tube was heated to 65 ° C in an oven for 30 minutes in order to help the tension on the steel graft. 3. The steel graft having a knurled outer diameter (12 knurling of primitive diamond) was pressed into the heated UHMW tube by the use of a small pneumatic press. 4. The assembly was cooled to room temperature. 5. The assembly was placed inside an induction coil and heated by induction so that the steel surface reached a temperature above the melting point of the EHMW. The exact time and surface temperature were selected by observation of a melt bed that is formed at the steel-polymer interface. In this case, the selected energy level and time resulted in a cycle time of 30 seconds and a steel surface temperature of 135 ° C. 6. The assembly was cooled to room temperature. 7. Lengths of 6 inches (15.2 cm) were cut into shorter pieces. Example 2 The UHWM rod deposit was melted into an aluminum core by the use of a 1 KHz induction unit. The procedure was as follows: 1. The extruded UHMW rod was machined into a tubular geometry, the ID being machined in a dimension that was 2% less than the outer diameter of the aluminum (core) graft. The appropriate dimensions were 3"OD x 2" ID x 6"length (7.6 cm x 5.1 cm x 15.2 cm). 2. The UHMW tube was heated to 65 ° C in an oven for 30 minutes with the purpose to help the tension on the aluminum graft. 3. The aluminum graft having a knurled outer diameter (12 knurling of primitive diamond) was pressed into the heated UHMW tube by the use of a small pneumatic press. 4. The assembly was cooled to room temperature. 5. The assembly was placed inside an induction coil and heated by induction so that the steel surface reached a temperature above the melting point of the EHMW. The exact time and surface temperature were selected by observation of a melt bed that is formed at the aluminum-polymer interface. In this case, the energy level and the selected time resulted in a cycle time of 2 minutes and an aluminum surface temperature of 135 ° C. 6. The assembly was cooled to room temperature. 7. Lengths of 6 inches (15.2 cm) were cut into shorter pieces. Example 3 The PAI Torlon tube tank was fused with a carbon steel core (SAE 1 17) using a 1 KHz induction unit. The procedure was the following: 1. The extruded PAI Torlon rod was machined in a tubular geometry, machining the ID in a dimension that was 1% smaller than the external diameter of the steel graft. The approximate dimensions were 2.5"OD x 2" ID x 6"length (6.4 cm x 5.1 cm x 15.2 cm) 2. The Torlon PAI tube was heated up to 200 ° C in an oven for 45 minutes in order to help the tension on the steel graft 3. The steel graft that had a knurled outer diameter (12 knurling of primitive diamond) was pressed into the PAI Torlon tube heated by the use of a small pneumatic press 4. The assembly was cooled to room temperature 5. The assembly was placed inside an induction coil and heated by induction so that the steel surface reached a temperature above the glass transition temperature of the Torlon PAI (285 ° C) The exact time and temperature of the surface were selected by observing a melting bed that is formed at the steel-polymer interface.In this case, the selected energy level and time resulted in a cycle time. of 40 seconds s and a steel surface temperature of 315 ° C. 6. The assembly was cooled to room temperature. 7. Lengths of 6 inches (15.2 cm) were cut into shorter pieces. Example 4 The plate deposit PA4.6 Stanyl was fused with a graft formed of powder-metal by the use of a 1 KHz induction unit. The procedure was as follows: 1. The extruded Stanyl PA4.6 plate was machined into an annular geometry, the ID being machined in a dimension that was 2% less than the outer diameter of the steel graft p / m. Suitable dimensions were 4,625"OD x 2.75" ID x 1"length (1 1 .8 cm x 7.0 cm x 2.5 cm) 2. Stanyl 4.6 rings were heated to 150 ° C in an oven for 30 minutes in order to help stress on steel grafts p / m 3. Steel grafts that had a knurled outer diameter (12 knurling of primitive diamond) were pressed into the Stanyl PA 4.6 rings heated by using a small pneumatic press The knurled outer surface was treated with a silane mixture to promote the adhesion of the plastic phase to the steel graft 4. The assemblies were cooled to room temperature 5. The assemblies were placed inside an induction coil and they were heated by induction so that the steel surface reached a temperature above the melting point of Stanyl PA 4.6.The exact time and surface temperature were selected by observation of a melting bed that formed in the steel-polymer interface. In this case, the energy level (50 kW) and the selected time resulted in a cycle time of 15 seconds and a surface temperature of the steel of 329 ° C. 6. The assemblies were cooled to room temperature. It is expected that in a complete production process, the external part of resin will be extruded in a tube having the desired internal and external diameters in order to avoid or reduce the machining processes. However, the use of rod deposit and sheet deposit as in the Examples illustrates the flexibility of the process, particularly in "one-off" products or short production runs that become the separate extrusion of unique external profiles less economic

Claims (18)

1. CLAIMING IS 1. A process for forming a composite gear part (1 04), which comprises a hub, preferably a metal or metal-containing hub (103) and an outer part of synthetic resin (1 02), preferably an outer part of resin thermoplastic, said outer portion comprising said hub (103) in a circumferentially adjacent manner, said process comprising the steps of: (a) extrusion, compression molding or centrifugal processing of a tube (01) in the required dimensions, (b) cutting rings (1 02) from said tubes in a suitable length (c) fixing said ring (102) produced by step (b) around said hub (103).
2. 2. The process according to claim 1, characterized in that the residual heat of the extrusion process is used for step (c).
3. 3. The process according to claim 1 or 2, characterized in that the additional added heat is used for step (c).
4. 4. The process according to any of claims 1 to 3, characterized in that a tempering cycle (d) is added.
5. The process according to any of claims 1 to 3, characterized in that said cube is a metal cube or that it contains metal.
6. 6. A process for the formation of a gear part compound comprising a cube, preferably a metal or metal-containing cube, and an external part of synthetic resin, preferably an outer part of thermoplastic resin, said outer part comprising said cube in a circumferentially adjacent manner, said process comprising the steps of (a) extrusion, compression molding or centrifugal processing of a tube (01) in the required dimensions, (b) fixing said tube produced by the step (s) in a pre-formed core (1 05), and (c) cutting rings (1 04) comprising a length of said tubes (01) and a length of said preformed core (1 05).
7. 7. The process according to any of claims 1 to 6, characterized in that said material (01) is extruded continuously or semi-continuously.
8. The process according to claim 6 or 7, characterized in that said core (1 05) is endless.
9. 9. The process according to any of claims 6-8, characterized in that said core is a metal core or a core containing metal.
10. The process according to any of claims 1-5, characterized in that said cube has a textured surface. eleven .
11. The process according to claim 10, characterized in that said textured surface is a knurled surface.
12. 12. The process according to any of claims 6 to 9, characterized in that said core has a textured surface.
13. The process according to claim 12, characterized in that said textured surface is a knurled surface.
14. The process according to any of claims 1 to 13, characterized in that said tube is produced by co-extrusion of at least two thermoplastics in concentric layers.
15. 15. The process according to any of claims 1 to 14, characterized in that it further comprises induction heating of the gear part after fixing in step c) at a temperature above the melting temperature of the thermoplastic.
16. 16. The process according to any of claims 1 - 15, characterized in that the tube is semi-crystalline or crystallizable amorphous thermoplastic and is extruded in such a way that the inner diameter of the tube remains amorphous, further comprising heating the tube before the tube. fixing step (c) just above the Tg of the thermoplastic, followed by additional heating after fixing to crystallize the thermoplastic.
17. The process according to any of claims 1 to 16, characterized in that said tube has an internal diameter that is smaller than the outer diameter of the hub or core prior to said fixing step (c).
18. 18. An endless screw gear or worm / worm gear combination, characterized in that a worm gear part is produced in accordance with any of claims 1 to 17, and the outer part of the synthetic resin is machined in a worm gear.