United States Patent [19J
`Nakatsuka
`
`[54] STATOR WITH MOLDED ENCASEMENT
`FOR SMALL MOTORS AND
`MANUFACTURING PROCESS THEREFOR
`
`[75]
`
`Inventor: Ginzoh Nakatsuka, Ueda, Japan
`
`[73] Assignee: Alon Co., Ltd, Nagano-ken, Japan
`
`[21] Appl. No.: 09/318,229
`
`[22]
`
`Filed:
`
`May 25, 1999
`
`[62]
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Related U.S. Application Data
`
`Division of application No. 08/848,371, Apr. 30, 1997.
`
`Int. Cl.7 ....................................................... H02K 1/00
`U.S. Cl. ............................ 310/216; 310/43; 310/179;
`310/258; 310/259; 29/596; 29/598
`Field of Search .............................. 310/216, 43, 179,
`310/258, 259; 29/596, 598
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,710,437
`4,825,114
`5,124,607
`5,214,839
`5,350,960
`5,382,859
`5,490,319
`
`1/1973 Kipple et al. ............................. 29/596
`4/1989 Ohtsuka et al.
`.......................... 310/90
`6/1992 Rieber et al. ........................... 310/214
`6/1993 Rieber et al. ............................. 29/596
`.. .... ... ... ... ... .... ... ... ... 310/194
`9 /1994 Kiri et al.
`1/1995 Huang et al. ........................... 310/216
`2/1996 Nakamura et al. ....................... 29/596
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US006075304A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,075,304
`Jun.13,2000
`
`Primary Examiner-Nestor Ramirez
`Assistant Examiner-Thanh Lam
`Attorney, Agent, or Firm-Jordan and Hamburg LLP
`ABSTRACT
`
`[57]
`
`A stator has a lamination stack with a first electrically
`insulating layer and coil guides formed of high flow ther(cid:173)
`moplastic synthetic resin simultaneously insert-molded
`thereon. A coil is wound onto the stack and over the
`electrically insulating layer and the coil guides, and a second
`electrically insulating layer is molded over the coil to encase
`the coil. The second electrically insulating layer is formed of
`the high flow thermoplastic synthetic resin by injection
`molding. The method for producing the stator includes
`inserting the lamination stack into a first molding tool
`installed on an injection molding machine and injection
`molding onto the lamination stack the first insulation layer
`and the coil winding guides wherein the first insulation layer
`coats at least top and bottom surfaces and surfaces of slots
`of the lamination stack with thin resin skin insulation. The
`coil is then wound using insulated thin copper wire. The
`lamination stack is inserted into a second molding tool,
`having a gate disposed at a location where injected resin will
`not directly hit the coil, and the second insulator layer is then
`injection molded on the coil using the high flow thermo(cid:173)
`plastic synthetic resin injected at a filling pressure about 20
`to 60% lower than a standard value for the high flow
`thermoplastic synthetic resin and at an injection speed more
`than twice as high as a standard injection speed for the high
`flow thermoplastic synthetic resin.
`
`21 Claims, 2 Drawing Sheets
`
`2
`
`Mitsuba - 1006
`Page 1 of 8
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`

`

`U.S. Patent
`FIG. 1
`
`Jun.13,2000
`
`Sheet 1 of 2
`
`6,075,304
`
`A 4""",
`f
`
`2
`
`FIG. 2
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`1
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`7
`::; ___ 5
`
`FIG. 3
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`7
`1~2
`5
`
`FIG .4
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`Mitsuba - 1006
`Page 2 of 8
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`Jun.13,2000
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`Sheet 2 of 2
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`6,075,304
`
`U.S. Patent
`FIG. 5
`
`• ~,
`
`5
`
`3
`
`\ /J
`
`C
`2
`
`7
`~5
`
`FIG. 6
`
`12
`
`C
`-J
`
`8
`
`FIG. 7
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`12
`
`10
`
`9
`
`10
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`Mitsuba - 1006
`Page 3 of 8
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`

`

`1
`STATOR WITH MOLDED ENCASEMENT
`FOR SMALL MOTORS AND
`MANUFACTURING PROCESS THEREFOR
`
`6,075,304
`
`10
`
`2
`The manufacturing process is also complicated because
`the winding guide is affixed after the coating is applied.
`There is a method disclosed by published Japanese patents
`#63-3636 and #63-3637 which uses a steel lamination with
`thermoplastic synthetic resin pre-adhered on outer face
`surfaces of the two outer most steal plate laminations. After
`lamination of the steel plates, the synthetic resin is heated to
`deform and flow to coat edges of the laminations to provide
`insulation. However, a sufficient amount of synthetic resin
`on the steel plate laminations must be provided to permit the
`requisite amount of deformation and coating using such a
`method. Accordingly, the resin coating must be relatively
`thick to permit a sufficient flow to the center of the lami(cid:173)
`nations for complete coverage with synthetic resin.
`Furthermore, it is rather difficult to coat the whole stack with
`15 uniform thickness.
`Methods to enclose wound wire with synthetic resin have
`been suggested. When enclosing windings with synthetic
`resin, it is important not to damage the insulation of the wire
`by heat or pressure, and not to disturb the wound coil. In
`general, enclosing with synthetic resin is performed with
`thermosetting resin under low temperature (less than 120°
`C.) and low pressure. Bulk molding compound (BMC) is
`mainly used as resin material. The resin temperature is low,
`but the manufacturing cycle takes several minutes using
`such a method.
`Some methods using injection molding have also been
`suggested for enclosing wound wire with synthetic resin.
`Published Japanese patent #61-10949 discloses inserting
`coiled wire into a molding tool for injection molding, setting
`30 the tooling temperature at a 120---150° C., using polyphe(cid:173)
`nylenesulfide (PPS) resin with 20-40 wt % inorganic filler,
`and setting the resin temperature at 300---350° C. and injec(cid:173)
`tion pressure at 800-1000 kg/cm2 in the process of coating
`the wound wire. This enables molding with relatively short
`35 cycle by using thermoplastic resin for enclosing wound wire
`since conventionally used thermosetting epoxy resin
`requires a longer molding cycle which results in low pro(cid:173)
`ductivity. Since this method applies high pressure to inject
`molten resin at high temperature, it may be acceptable for
`40 applications where the diameter of wire is large enough and
`insulating coating of coil is thick enough to withstand the
`process. In applications involving coil wire of smaller diam(cid:173)
`eter and a thin insulating coating of the coil wire, the wound
`coil is susceptible to being disturbed and the insulation
`45 coating of wire is prone to damaged. Thus, this method is not
`practical in such applications.
`Published Japanese patent #3-70441 discloses a stack
`having multiple slots to be wound. The stack of the rotor
`with a rectifier and an outer surface of wound wire are
`50 enclosed by injection molding with insulating encapsulating
`material (polyacetal with glass fiber). The resin injecting
`position is located at an opposite surface of the rectifier and
`parallel with the axis of the rotor. Injection is performed in
`two stages. In the first stage an injection pressure of is 220
`55 kg/cm2 is used and in the second stage a pressure of 50
`kg/cm2 is used. However, the method relates to the rotor, not
`the stator, and differs from the object of the present inven(cid:173)
`tion. The technical point of the published patent is to specify
`the direction of resin injection to prevent disturbance of
`60 wound wire and minimize molding defects such as wrinkles
`and sink marks. The resin injection time is reduced to 2.5
`seconds. Even with this shortened time, as the insulation
`coating of the winding of the stator for the small-sized
`precision motor is so thin, the wire is prone to damaged by
`65 the high temperature of molten resin. Also, as the initial
`injection pressure of 220 kg/cm2 is high, the wound coil is
`prone to being disturbed by the effect of injected resin.
`
`This is a division, of application Ser. No. 08/848,371, 5
`filed Apr. 30, 1997.
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a stator having a molded
`casing and, more particularly, to a stator for small motors
`having a first molded layer on a stack and a second molded
`layer enclosing a coil and portions of the first molded layer.
`The stator has applications in small motors such as spindle
`motors or servo motors, which are used in hard disk drives,
`wherein thin insulation is required.
`The ever increasing demand for hard disk drives with
`greater storage capacity has resulted in increasingly strict
`requirements for cleanliness of the driving unit. Motors have
`been found to be a source of particles, gas, organic
`substances, and ionic substances. Thus, spindle motors used 20
`in hard disk drives must not produce contaminants during
`operation. It has been found that particles are generated from
`the stator or the wound windings of the rotor coil due to
`abrasion. Improvement in the functioning of hard disk drives
`is achieved by enclosures for containing particles and gases 25
`generated by the coil and stack of the motor stator of the hard
`disk driving unit. Even trace foreign particles can adhere
`onto the magnetic head or hard disk and cause noise or a
`head crash. Therefore, it is necessary to prevent particles or
`gasses from being generated by the-motor.
`Various kinds of small or thin motors are applied in
`various fields, and the demand for further reduction in size
`is increasing. At the same time, simplification of the manu(cid:173)
`facturing process for such motors and improvements in
`reliability are required. Motor characteristics such as starting
`torque and power are improved when an insulator on the
`stack of the stator is thinner because more coil can be wound
`on the stator. Furthermore, a thinner insulation results in
`better thermal transfer characteristics allowing improved
`dissipation of heat generated by the motor. Finally, it is also
`necessary to protect against vibration, noise caused by
`electric current pulses and to increase durability of the hard
`disk unit.
`In the conventional methods used to manufacture stators,
`multiple plates of punched thin thickness steel are inter(cid:173)
`locked to produce a lamination stack. The stack is then
`coated with insulation after an anti-corrosion treatment.
`Following the coating, a coil is wound after a winding guide
`is affixed. However, due to laminating the punched thin
`steel, the outer surface and slot being exposed is not be
`completely planar, thus resulting in recesses and projections.
`A major issue for using an insertmolding process is the
`variation in the thickness of the laminated stack. Therefore,
`in order to perform insertmolding, screening of the thickness
`and adjustment of the core in the molding tool is required.
`The adjustment of the core in the molding tool further causes
`the formation of flash which requires deburring. Thus, the
`screening, the adjustment and the deburring add further
`costs to the production process.
`A coating of 50-80 micron thickness is necessary to
`provide insulation on such rough surface. Prior to coating,
`costs are further increased by the requirement for a pre(cid:173)
`treatment of shotblasting or tumbling to effect deburring.
`Despite such steps, the coating is often left with pinholes
`which deteriorate the insulation or edges are left uncovered
`by the coating which results in low yields.
`
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`6,075,304
`
`3
`Finally, published Japanese patent #6-327208 discloses an
`assembly of a stator block of an axial gap type DC brushless
`motor provided with multiple stator blocks having stacks of
`columnar soft magnetic material with coils wound between
`a set of permanent magnets affixed to the rotor. The coils are 5
`fixed by a resin having a major filler with a heat conductivity
`of more than 10 (w/m·k). The resin to be used is either
`thermoplastic and thermosetting resin, but the thermosetting
`resin is mainly described. Molding methods discussed
`include injection molding, which is not disclosed in detail, 10
`a potting method for liquid thermosetting resin, a transfer
`molding method for powder thermosetting resin, and a
`casting method, the particular method depending on the
`configuration. An epoxy resin containing a filler of improved
`heat conductivity, such as aluminum oxide or aluminum 15
`nitride, is also discussed but no reference to the flow
`character of such a resin is made.
`
`4
`The present invention also provides a manufacturing
`method comprising the steps of punching steel plate into a
`desired shape to form a requisite number of laminations for
`a lamination stack, interlocking the laminations together to
`form the lamination stack, inserting the lamination stack into
`a molding tool installed on an injection molding machine,
`undermolding the lamination stack with a high flow ther(cid:173)
`moplastic synthetic resin having desired insulation charac(cid:173)
`teristics to coat at least top and bottom surfaces and slots of
`the lamination stack with a thin resin skin for insulation
`while simultaneously forming with the resin a hook member
`as a coil winding guide on a top surface of the stack, winding
`a coil of insulated thin copper wire using the hook member
`as a guide, overmolding the stator with the coil wound upon
`it by injection molding using the high flow thermoplastic
`synthetic resin used for undermolding at a filling pressure
`20-60% lower than a standard value of the injection
`machine to be used and an injection speed at least twice as
`high as a standard injection speed using a molding tool
`20 having a gate disposed at a position where injected resin will
`not hit directly the wound coil of the stator.
`According to a feature of the invention, there is further
`provided method for producing a stator with a lamination
`stack comprising: inserting the lamination stack into a first
`25 molding tool installed on an injection molding machine;
`injection molding onto the lamination stack a first insulation
`layer and coil winding guides formed of a high flow ther(cid:173)
`moplastic synthetic resin which is an electrical insulator, the
`first insulation layer coating at least top and bottom surfaces
`30 and surfaces of slots of the lamination stack with thin resin
`skin insulation and the coil winding guides being simulta(cid:173)
`neously formed integral with the first insulation layer on the
`top surface of the lamination stack; winding a coil of
`insulated thin copper wire over the first insulation layer and
`35 the winding guides; inserting the lamination stack with the
`coil into a second molding tool having a gate disposed at a
`location where injected resin will not directly hit the coil;
`and injection molding a second insulator layer on the coil
`using the high flow thermoplastic synthetic resin injected at
`40 a filling pressure about 20 to 60% lower than a standard
`value for the high flow thermoplastic synthetic resin and at
`an injection speed more than twice as high as a standard
`injection speed for the high flow thermoplastic synthetic
`resm.
`The present invention further includes the second molding
`tool including a pressure adjusting means for maintaining
`injection pressure within the range of the filling pressure.
`The pressure adjusting means in one embodiment of the
`invention comprises spring biased pins communicating with
`50 an interior of the second molding tool which are displaced
`by the filling pressure to maintain the filling pressure within
`a desired range.
`The above, and other objects, features and advantages of
`the present invention will become apparent from the fol-
`55 lowing description read in conjunction with the accompa(cid:173)
`nying drawings, in which like reference numerals designate
`the same elements.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, it is an object of the invention to provide a
`stator with a molded encasement and a method for produc(cid:173)
`tion thereof which overcomes the drawbacks of the prior art.
`Accordingly, it is an object of the present invention to
`provide a stack produced with insulation for encasing the
`stack applied using a simplified manufacturing process
`which reduces defects and wherein the insulator and wind(cid:173)
`ing guides are simultaneously formed, and resistance and
`inductance is improved. Wound wire is enclosed with syn(cid:173)
`thetic resin to prevent contaminants from spreading from the
`stator or abrasion of the wound wire of the rotor, and reduce
`vibration and noise generated by electric current pulses.
`Briefly stated, the present invention provides a stator
`having a lamination stack with a first electrically insulating
`layer and coil guides both formed of high flow thermoplastic
`synthetic resin simultaneously insert-molded thereon. A coil
`is wound onto the stack and over the electrically insulating
`layer and the coil guides, and a second electrically insulating
`layer is molded over the coil to encase the coil. The second
`electrically insulating layer is formed of the high flow
`thermoplastic synthetic resin by injection molding. The
`method for producing the stator includes inserting the lami(cid:173)
`nation stack into a first molding tool installed on an injection
`molding machine and injection molding onto the lamination
`stack the first insulation layer and the coil winding guides 45
`wherein the first insulation layer coats at least top and
`bottom surfaces and surfaces of slots of the lamination stack
`with thin resin skin insulation. The coil is then wound using
`insulated thin copper wire. The lamination stack is then
`inserted into a second molding tool, having a gate disposed
`at a location where injected resin will not directly hit the
`coil, and the second insulator layer is injection molded on
`the coil using the high flow thermoplastic synthetic resin
`injected at a filling pressure about 20 to 60% lower than a
`standard value for the high flow thermoplastic synthetic
`resin and at an injection speed more than twice as high as a
`standard injection speed for the high flow thermoplastic
`synthetic resin.
`In accordance with these and other objects of the
`invention, there is provided an overmolded stator for small- 60
`sized motor having a stack which is insert-molded to form
`a first insulator layer of insulating high flow thermoplastic
`resin on the stack, coil windings wound on the stack over the
`first insulating layer, and a second insulating layer over(cid:173)
`molded on the coil windings by injection molding using the 65
`same type of thermoplastic resin used for the first insulating
`layer.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows a plane view of an embodiment of the
`present invention having a lamination stack with an insulator
`insertmolded;
`FIG. 2 shows the front view of the lamination stack with
`the insulator insertmolded of FIG. 1 with a winding guide is
`partially omitted;
`FIG. 3 shows the cross section along line A-A of FIG.
`
`1;
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`6,075,304
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`5
`FIG. 4 shows the cross section along line B-B of FIG.
`
`1;
`
`FIG. 5 shows the front view of a lamination stack of
`another embodiment of the present invention having the
`insulator insertmolded wherein the illustration of a winding
`guide is partially omitted;
`FIG. 6 shows a plan view of the overmolded stator of the
`present invention; and
`FIG. 7 shows the enlarged cross section along line C-C
`of FIG. 6.
`
`DETAILED DESCRIPTION OF IBE
`INVENTION
`Referring to FIGS. 1 to 5, there is shown an embodiment
`of a product and method of the present invention wherein a
`lamination stack 1 is produced for use as a stator in a spindle
`motor for use in a hard disk unit. The lamination stack 1 is
`formed from multiple thin steel laminations stacked and lock
`together. The lamination stack 1 is inserted into a first
`molding tool of an injection molding machine, and an
`insulator 2 is undermolded onto the lamination stack using
`a high flow thermoplastic resin material. The undermolded
`insulator 2 forms a first insulating layer, which also called an
`undermold and is preferably less than 0.2 mm in thickness.
`The insulator 2 is molded to cover both top and bottom
`surfaces 3 of the lamination stack 1, slots 4, and an outer
`surface 5. Furthermore, the insulator 2 is optionally under(cid:173)
`molded to cover the whole surface of the lamination stack 1
`including an inner surface 6 collectively formed by ends of
`radially extended pole portions provided in the form of teeth
`9, and which defines an opening where the rotor is inserted.
`Winding guides 7 are formed on the surface 3 from the same
`resin as the insulator 2 during the undermolding. The
`insulator 2 preferably covers the whole surface at a thickness
`of less than 0.2 mm, including the inner surface 6.
`Optionally, depending on the usage, the whole surface
`excluding the outer surface 5 is covered.
`Referring to FIG. 5, the insulator 2 is molded using the
`first molding tool to cover both the top and bottom surfaces
`3 of the lamination stack 1 and slot 4, and the winding guide
`is formed on the surface 3 of the insulator 2. Thin thickness
`insert molding (less than 0.2 mm thickness) combined with
`simultaneous formation of the winding guide 7 and the
`insulation 2, and the configuration of the winding guide 7 are
`epochal aspects of the present invention. The configuration 45
`of the winding guide 7 is not necessarily of a hook shape
`such as "I'" as shown, but may be simply a straight member
`projecting perpendicularly from or on a slant from the top
`surface 3.
`The synthetic resin used to mold the insulator 2 is
`preferably a high flow thermoplastic material having elec(cid:173)
`trical insulating characteristic. Examples of such a resin
`include nylon 66, PET resin, LCP resin, or PPS resin. The
`terminology "high flow" as used herein defines a resin of
`having a melted viscosity of less than 7xl03 poise at a shear
`rate (shear speed) of 102 (1/second), and less than 3xl03
`poise of melted viscosity at the shear rate of 103 (1/second),
`when the resin is molten at the necessary temperature for
`molding.
`Referring to FIGS. 6 and 7, the manufacturing method of
`the present invention is described below with relation to the
`above described overmolded lamination stator 1. The insu(cid:173)
`lator 2 is identified as "the undermold 8" in the following
`explanation. Teeth 9, of the lamination stack 1 with the
`undermold 8, have coil wire wound thereon to form a
`winding 10. The construction of the winding 10 is accom(cid:173)
`plished using known winding techniques.
`
`10
`
`6
`The undermolded lamination stack 1 with the windings 10
`formed thereon are inserted in a second molding tool. In the
`second molding tool a gate is disposed at a position where
`injected resin does not directly hit the windings 10 of the
`5 stator 11. The same type of high flow thermoplastic resin as
`is used for the above mentioned insulator 2 is then injection
`molded over the stator 11 to form an overmold 12 so that the
`windings 10 are enclosed in a coating of the resin. The
`overmold 12 prevents exposure of the windings 10 to the
`outside environment, for example, the interior of a hard disk
`drive unit.
`During injection molding of the overmold 12, depending
`on the configuration of the product to be molded and the
`resin material to be used, the peak filling pressure of the
`15 resin is preferably 20-60% lower than the normally used
`filling pressure, and the injection speed is preferably higher
`than the normal speed by more than two times. In general,
`injection molding is done with a peak filling pressure
`normally between 70 kg/cm2 and 150 kg/cm2
`. Where a
`20 normal peak filling pressure is 70 kg/cm 2 (against material
`and product) during normal molding, the present invention
`preferably uses a peak filling pressure between 15 kg/cm 2
`and 40 kg/cm2
`. Where the peak filling pressure during
`normal molding is 150 kg/cm2
`, the peak filling pressure in
`25 the present invention is preferably between 30 kg/cm2 and
`90 kg/cm2
`.
`For use in formation of the overmold 12, spring operated
`movable pins for pressure adjustment are provided commu(cid:173)
`nicating with a cavity of the molding tool. When the resin
`30 injection pressure is applied, the pins are depressed by the
`resin pressure and function as dampers to reduce rapid
`pressure increase in the molding tool to ensure that the
`windings 10 will not be disturbed by the resin injection
`pressure. This pressure adjustable system is effective when
`35 the resin peak filling pressure is high.
`The injection speed is preferably more than twice the
`injection speed used in a normal injection molding process.
`For example, an embodiment of the present invention pref(cid:173)
`erably uses an injection speed of more than 270 mm/sec
`40 which is more than twice of the standard injection speed of
`135 mm/sec. Injection molding machines are available
`which are capable of injection speeds of up to 1000 mm/sec.
`When the injection speed is increased twice, the injection
`filling time will be minimized by half.
`In an embodiment of the present invention the coil wire
`for the windings 10 is, for example, a copper wire having a
`diameter of 0.13 mm with insulation of coated polyurethane
`(155° C. of heat resistance temperature) of which a coating
`thickness is 0.01 mm. With the above conditions (filling
`50 pressure and injection speed), damage to the coating mate(cid:173)
`rial of even this kind of coil wire is prevented. The tem(cid:173)
`perature of the molding tool is preferably between 30° C.
`and 80° C., and more preferably less than 50° C., since too
`high a temperature of the molding tool may cause deflection
`55 of the undermold 8 and heat to be conducted to the windings
`10 should be minimized. Also, by locating the gate at a
`position where the injected resin will not directly hit the coil
`wire 10, disturbance of the wound coil is prevented. In an
`embodiment of the present invention, a gate is preferably
`60 located inside of the slots 4 and between coils wound on the
`teeth 9 such that resin is injected in a direction perpendicular
`to an axis of the stator 11. It is desirable to increase the
`number of the gates to complete injection molding in a
`shorter time, but this should be decided depending on the
`65 size of the stator or the number of poles. The high flow
`thermoplastic resin to be used in the overmold 12 is to be the
`same type of resin used in the undermold 8 to promote
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`6,075,304
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`20
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`7
`appropriate coordination of resin. The molding temperature
`of the resin is preferably 300° C. Using this kind of high heat
`resistance resin for overmolding, a high durability motor is
`producible.
`As is stated above, the overmolded stator prevents dis-
`bursement of contaminants from windings during motor
`operation and reduces vibration and noise generated by
`electric current pulse.
`In accordance with the manufacturing method for the
`overmolded stator, the overmolded stator can be easily 10
`manufactured by injection molding without damaging the
`wound coil, and small-sized and high performance spindle
`motors are thus producible.
`Having described preferred embodiments of the invention
`with reference to the accompanying drawings, it is to be 15
`understood that the invention is not limited to those precise
`embodiments, and that various changes and modifications
`may be effected therein by one skilled in the art without
`departing from the scope or spirit of the invention as defined
`in the appended claims.
`What is claimed is:
`1. A stator, comprising:
`a lamination stack including a top surface, a bottom
`surface and an outer surface, said lamination stack
`further including radially extended pole portions, 25
`opposed surfaces of adjacent ones of said pole portions
`defining slots therebetween, ends of said pole portions
`collectively presenting an inner surface defining an
`opening for receiving a rotor said inner surface facing
`the rotor when same is received within the opening;
`a first electrically insulating layer of high flow thermo(cid:173)
`plastic synthetic resin insert-molded on said lamination
`stack and covering at least a portion of each of said top,
`bottom and opposed surfaces;
`a coil wound onto said lamination stack and over said first
`electrically insulating layer; and
`a second electrically insulating layer molded over said
`coil to encase said coil, said second electrically insu(cid:173)
`lating layer being formed by injection molding and 40
`being comprised of said high flow thermoplastic syn(cid:173)
`thetic resin used for said first electrically insulating
`layer.
`2. The stator according to claim 1, further comprising coil
`winding guides formed of said high flow thermoplastic
`synthetic resin insert-molded integrally with said first elec(cid:173)
`trically insulating layer.
`3. The stator according to claim 1, wherein said first
`electrically insulating layer has a thickness of less than about
`0.2mm.
`4. The stator according to claim 1, wherein said first
`electrically insulating layer further covers at least a portion
`of at least one of said inner and outer surfaces.
`5. A stator for precision motors, comprising:
`a lamination stack;
`a first insulation layer injection molded onto said lami(cid:173)
`nation stack and coil winding guides formed simulta(cid:173)
`neously with the first insulation layer on a top side of
`said lamination stack, said first insulation layer and said
`coil winding guides being formed of a high flow 60
`thermoplastic synthetic resin which is an electrical
`insulator, said first insulation layer coating at least top
`and bottom surfaces and surfaces of slots of said
`lamination stack in the form of a thin resin skin
`insulation;
`a coil of insulated thin copper wire wound over said first
`insulation layer and said winding guides; and
`
`8
`a second insulator layer injection molded on said coil
`using said high flow thermoplastic synthetic resin used
`for said first insulation layer and said coil winding
`guides to encase said coil and inhibit exposure of said
`coil to an outside environment.
`6. The stator according to claim 5, wherein said first
`insulation layer has a thickness of less than about 0.2 mm.
`7. The stator according to claim 5, wherein said copper
`wire has a diameter of no greater than about 0.13 mm.
`8. A method for producing a stator with a lamination
`stack, comprising:
`inserting the lamination stack into a first molding tool
`installed on an injection molding machine;
`injection molding onto said lamination stack a first insu(cid:173)
`lation layer, which is a thin resin skin, and coil winding
`guides, each being formed of a high flow thermoplastic
`synthetic resin which is an electrical insulator, said first
`insulation layer coating at least top and bottom surfaces
`and surfaces of slots of said lamination stack and said
`coil winding guides being formed integral with said
`first insulation layer on said top surface of said lami(cid:173)
`nation stack;
`winding a coil of insulated thin copper wire over said first
`insulation layer and said winding guides;
`inserting said lamination stack with said coil into a second
`molding tool having an interior cavity for accepting
`said lamination stack and a gate communicating with
`said interior cavity and disposed at a location where
`injected resin will not directly hit said coil; and
`injection molding a second insulator layer on said coil
`using said high flow thermoplastic synthetic resin
`injected at a peak filling pressure in a range about 20 to
`60% lower than a standard value for said high flow
`thermoplastic synthetic resin and at an injection speed
`more than twice as high as a standard injection speed
`for said high flow thermoplastic synthetic resin.
`9. The manufacturing method of claim 8, wherein said
`second molding tool includes a pressure adjusting means for
`maintaining injection pressure within the range of said peak
`filling pressure.
`10. The manufacturing method of claim 9, wherein said
`pressure adjusting means includes spring biased pins sup(cid:173)
`ported in holes communicating with said interior cavity of
`said second molding tool such that filling pressure displaces
`said spring biased pins away from said interior cavity to
`45 maintain said injection pressure.
`11. The method according to claim 8, wherein a tempera(cid:173)
`ture of said second molding tool is between about 30° and
`about 80° C.
`12. The method according to claim 8, wherein a tempera(cid:173)
`so ture of said second molding tool is less than about 50° C.
`13. The method according to claim 8, wherein a molding
`temperature of said high flow thermoplastic synthetic resin
`is about 300° C.
`14. The method according to claim 8, wherein said peak
`55 filling pressure in said step of injection molding a second
`insulator layer on said coil is between about 15 kg/cm2 and
`about 40 kg/cm2
`.
`15. A method for producing a stator with a lamination
`stack, co