METHOD OF PRODUCING COMPONENT PARTS OF PRINT HEAD FOR WIRE IMPACT TYPE DOT PRINTER

Abstract: Component parts of a magnetic circuit for an impact dot head, wherein the number of parts is reduced and the magnetic efficiency is high, and a method of producing thereof. Out of a plurality of members (a base frame (2) and a core (5)) constituting the component parts of a magnetic circuit of a print head, at least one member is produced in such a manner that a binder is added to metallic powder of a magnetic material and kneaded, and thereafter, injection-molded, combined with another molded member after the binder is removed, and then sintered.

Description: Technical Field The present invention relates to a method of molding a magnetic circuit component which constitutes a printing head for a wire impact type dot printer. Background Arts A printing head for a wire impact type dot printer is, as illustrated in FIG. 8, typically composed of: a nose frame a; a core block b fixed to a rear face thereof; a spring holder c provided in a central circular hole of the core block b; a yoke d mounted on the core block b; a multiplicity of printing levers ℓ positioned and held on the yoke d; and a presser plate f which covers the printing levers. Among these components, for instance, the core block b for constituting a magnetic circuit is constructed by joining a multiplicity of sub-cores b2 each formed of a material such as Permendur having a large saturated magnetic flux density in a soft iron base frame b1. The printing lever ℓ is constructed by joining a lever ℓ2 and a fulcrum pin ℓ3 to a plunger ℓ1 formed of Permendur. It requires a considerable number of steps to integrally joining these components. Besides, particularly in the core block b, a slight gap is invariably formed between the base frame and the core irrespective of the way of joining these members. This causes a magnetic loss. A backlash tends to be produced between the lever l 2 and the fulcrum pin l 3 of the printing lever l . There arise inconveniences in which wire motions become unstable, and adverse influences are exerted on the respondency. Japanese Patent Application No. JP-A-56-131906 suggests that the structure of a magnetically operated actuator can be made more solid by forming the armature and bearing part of the actuator monolithically and sintering them. A paper entitled Fe-50 % Co Sintered Alloy for Magnetic Circuit Yoke, published in the Fujitsu Scientific and Technical Journal, vol 24, no. 3, September 1988, Kawasaki, Japan, describes an improved method of fabricating components from the Fe-50%Co "Permendur" alloy by powder sintering. It is an object of the present invention, which has been devised in the light of the foregoing problems, to provide a new wire impact type dot head component in which a plurality of members are made integral by sintering. Accordingly, it is another object of the present invention to provide a method of molding a new head component, by which a plurality of members are easily surely made integral. To accomplish these objections, according to the invention there is provided a method of molding a magnetic circuit component of a printing head for a wire impact type dot printer, comprising the steps of: molding at least one member constituting a part of a magnetic circuit component for a printing head which is configured as a joint body comprising a plurality of integral members by use of metallic powder; effecting integral sintering by joining said one member to another previously molded member in said process; and subsequently sintering said one member. Preferably, the molding process is an injection molding process. Therefore, according to the present invention, at least one member among the plurality of members constituting the magnetic circuit component for a printing head is molded by use of the metallic powder by injection molding and subsequently sintered, in this process, the foregoing member is joined to another member previously molded, thus effecting integral sintering. Hence, the plurality of members can be joined integrally and easily without a particular working accuracy of the joint portion, it is possible to remarkably reduce the number of assembling steps and the number of parts as well. An inter-member gap is eliminated, whereby the magnetic circuit component with almost no magnetic loss can be constructed. Further, it is possible to mold the component in which an expensive material exhibiting a high permeability is applied to only the parts required. Thus, the printing head can be constructed at still lower costs. FIGS. 1 through 6 are perspective views and step charts showing integral joining steps of a printing head component; FIG. 7 is a perspective view showing the integral joining steps of the printing head component; and FIG. 8 is a view illustrating one example of a printing head for a wire impact type dot printer. Best Mode for Carrying out the Invention An illustrative embodiment of the present invention wilt hereinafter be described in detail. Referring to FIGS. 1 and 2, there is shown a molding method of a core block for configuring a magnetic circuit. Formation of one base frame 2 involves the steps of adding 5 - 60% by volume of an organic binder to powder of magnetic substance, having a particle diameter of 3 - 25 Mm, of pure iron Fe or 3% silicon steel Fe- Si and kneading these substances. Under an injection pressure of 300 - 3000 kgf/cm 2 by an injection molding machine, the kneaded substances are molded into a base frame prototype formed with a central circular hole 3 and a multiplicity of core fitting holes 4... which encompass the hole 3 in an inner bottom face. Pin gates are employed as those required for the injection molding, resulting in a reduction in the remainder of gates. The base frame 2 formed by the injection molding is joined simply by the binder. The base frame 2 exhibits a high workability and is therefore capable of easily removing the gate remainder. The runner is pulverized and kneaded, whereby it is reusable for injection molding. The base frame 2 can be therefore inexpensive. Next, de-binder processing is effected in an inert gas or in vacuum for 2 - 60 hrs at 300°C - 700°C after being held for 1 - 3 hrs at, e.g., 50°C - 200°C. The binder composed of an organic substance is removed from the base frame 2. The other core 5 is formed in the following manner. Kneaded with the binder in the same manner with as the above-mentioned is powder of Permendur (Fe-Co- V alloy) having a large saturated magnetic flux density or 3% silicon steel Fe-Si having a large permeability or a nickel alloy Fe-Ni. The kneaded substances are injection-molded into a core prototype provided with fitting protrusions 6 on its lower face. Then, it undergoes de-binder processing. Subsequently, the fitting protrusions 6 of the core prototype are fitted in the fitting holes 4 of the base frame prototype, thereby joining the two prototypes. More specifically, the base frame fitting hole 4 is formed in a substantially rectangular parallelopiped shape. The configuration of the core fitting protrusion 6 is substantially the same as the substantially rectangular parallelopiped. Positions of the base frame 2 and the core 5 are thereby easily determined. Besides, a stepped portion 6a of the core protrusion 6 impinges on a bottom part 4a of the base frame, thereby easily determining the position. A method which uses a jig illustrated in FIG. 7 is also available. A jig 17 is formed with a groove 17a assuming a configuration corresponding to the core 5. The core 5 is inserted in this groove 17a. A depth of the groove 17a is so set that the stepped portion 6a of the protrusion 6 of the core 5 is higher than an upper face 17b of the jig. The core 5 is set in the jig 17. The fitting protrusion 6 of the core 5 is formed in, e.g., a substantially cylindrical shape, and the hole 4 of the base frame 2 assumes a configuration corresponding to the protrusion 6. The protrusions 6 are press-fitted in the holes 4, whereby the two members are joined. The joined body is sintered in vacuum or in an atmosphere of inert gas. Molding is performed in this manner, interfaces between the base frame 2 and the cores 5 are welded. The base frame 2 and the cores 5 are integrally joined without any gap. A core block 1 with almost no magnetic loss is thereby obtained. The following are test results of an input energy, an output energy and an energy efficiency ( output energy input energy x 100) by use of the core block molded by the above-mentioned method and a conventional core block in which the cores are joined with a bonding agent. Input Energy Output Energy Energy Efficiency Core Block by the Present Method 4.3mj 0.4mj 9.3% Conventional Method 6.3mj 0.4mj 6.3% It can be found out from these results that the core block molded based on the method of the present invention exhibits a less magnetic loss and a higher energy efficiency than in the prior art. FIGS. 3 and 4 show a method of molding a printing lever 7. A lever piece 9 is previously molded by press working from a plate material of pure iron Fe or 3% silicon steel Fe-Si or stainless steel each having a high strength. A fulcrum pin 10 is also previously molded by cutting work from a wire rod composed of carbon steel and the like. These members are molded integrally with a prototype of a plunger 8 by an insert method in the process of injection-molding the plunger prototype with a molding die while kneading an organic binder with powder of a high saturated magnetic flux density alloy or a high permeability alloy such as Permendur Fe-Co-V and the like. Subsequently, these members undergo de-binder processing and sintered in vacuum or in an atmosphere of inert gas. The following is an explanation of another method. The binder is kneaded with powder of the high saturated magnetic flux density alloy or the high permeability alloy such as Permendur Fe-Co-V and the like. The plunger 8 is formed by injection molding. After effecting de-binder processing, the printing lever piece 9 is joined to the fulcrum pin 10. These members are sintered in vacuum or in the atmosphere of inert gas. Molding is performed in the manner discussed above, and it is possible to obtain the printing lever 7 showing a high energy efficiency, using an expensive material with a high permeability for the plunger 8 alone. Besides, the lever piece 9 and the fulcrum pin 10 are accurately firmly made integral with a predetermined portion of the plunger 8. Thus, the operation thereof can be stabilized. Turning to FIGS. 5 and 6, there is shown a method of molding a yoke 11. A disk-like yoke 12 are formed with a multiplicity of radial grooves 13... and fulcrum pin insertion recesses 14.... A dish-like yoke 15 is formed with a multiplicity of radial grooves 16... The yokes 12 and 15 are molded by injection molding from a raw material obtained by kneading the binder with powder of pure iron Fe, or silicon steel Fe-Si or Permendur (Fe-Co-V alloy) as a magnetic material. Those yokes are subjected to debinder processing. Subsequently, the prototypes of the yokes 12, 15 are superposed to align the radial grooves 13, 16 with each other and sintered in vacuum or in the atmosphere of inert gas. Molding is carried out in this manner, whereby the two yokes which could not be formed integrally so far can be integrally molded into a single yoke 11. Left in the portion where the binder existed in this yoke are minute voids smaller than fine powder particles. It is because sintering is effected after injection-molding the fine powder with the binder. It is feasible to configure the yoke 11 capable of permitting the printing lever 7 to smoothly surely operate as a porous yoke exhibiting a less magnetic loss and self-lubricity because of a lubricating oil impregnating in those voids, Note that the present invention has been described by exemplifying the component applied to a typical suction type wire impact dot head. In addition to this, the present invention is, however, applicable to yokes used for store energy type dot heads using permanent magnets. Namely, though the illustration is omitted, a permanent magnet is formed beforehand of a material such as samarium cobalt or neodymium. The yokes are previously molded by sintering or press working by use of a material such as pure iron Fe or silicon steel Fe-Si. These members are made integral with the base frame by an outsert method in the process of injection-molding the base frame prototype by kneading the binder with powder of a ferromagnetic substance such as silicon steel Fe-Si or Permendur Fe-Co-V. After undergoing de-binder processing, those members are sintered. As a result, the yokes for constituting the magnetic circuit can be molded to reduce the magnetic loss to the greatest possible degree. Industrial Applicability The present invention is employed for the impact dot head of a dot printer and is applicable to all kinds of dot impact printers which will be spread from now onwards. The present invention largely contributes to an improvement of performance and a cost-down thereof.

Claims: A method of molding a magnetic circuit component of a printing head for a wire impact type dot printer, comprising the steps of: molding at least one member constituting a part of a magnetic circuit component for a printing head which is configured as a joint body comprising a plurality of integral members by use of metallic powder; effecting integral sintering by joining said one member to another previously molded member in said process; and subsequently sintering said one member. A method as set out in claim 1, wherein said molding is injection molding. A method as set out in claim 1, wherein said metallic powder is a material exhibiting a high permeability or a high saturated magnetic flux density. A method as set out in claim 1, further comprising the steps of: kneading a binder with fine powder of a magnetic material; injection-molding said kneaded substances; performing a de-binder process to remove said binder at a high temperature; and effecting integral sintering by joining said one member to another member previously molded. A method as set out in claim 3, wherein said plurality of members are a core (5) and a base frame (2).

Inventors: KOIKE KIYOFUMI, TANAKA MINORU, KOIKE, KIYOFUMI, 3-5, OWA 3-CHOME, TANAKA, MINORU, TANAKA, MINORU, 3-5, OWA 3-CHOME
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1991
Main classification: B41J2
IPC codes: B41J2, B22F7, B22F3