DE102006026819A1 - Plasticizing and injection device for micro injection molding - Google Patents

Abstract

The plasticizing and injecting device for the production of micromechanical component or small medical parts by micro injection molding, comprises rotationally driven plasticizing screw revolvably arranged in a storage (8) with which the plasticizing cylinder is connected in torque-proof manner. The plasticizing cylinder has an extension piece formed as injecting piston at its front end. A linear and rotating drive (1) is arranged for the plasticizing screw. The rear end of the screw and shaft drive of the drives are connected with one another over a coupling. The plasticizing and injecting device for the production of micromechanical component or small medical parts by micro injection molding, comprises rotationally driven plasticizing screw revolvably arranged in a storage (8) with which the plasticizing cylinder is connected in torque-proof manner. The plasticizing cylinder has an extension piece formed as injecting piston at its front end. A linear and rotating drive (1) is arranged for the plasticizing screw. The rear end of the screw and shaft drive of the drives are connected with one another over a coupling. Axial and radial bearings are arranged in the area of the coupling. The storage has a housing (3) in which the axial and radial bearings are arranged. The plasticizing screw is nonrelocatably arranged in the storage. The plasticizing cylinder is firmly connected with the housing. A backflow stop is arranged downstream of the screw. The front end of the plasticizing screw is formed as a valve body that is sealed with the interior wall of the cylinder. Mechanical, hydraulic and/or pneumatic prestressing means are arranged between the cylinder and the housing. The cylinder is prestressed from the storage deflection, so that the valve body of the screw forms a durable column with the interior wall of the cylinder during the dosing process and is pressed with its front end against the cylinder during the injecting process. The plasticizing cylinder is arranged to the storage, so that the cylinder is separated from the valve body during the dosing process through pump pressure by which the molten mass is conveyed into the cylinder. After termination of the dosing process, the plasticizing cylinder adjoins with its valve body at the interior wall of the cylinder and proceeds forward by the linear drive of the screw. The screw and the interior of the cylinder are conically formed. Adjusting screws are intended for adjusting the die gap between the screw and the interior wall of the cylinder. The outside diameter of the screw pitch continuously decreases and the diameter of the screw core remains constant over a section of the plasticizing screw in conveying direction. Two subsequently turned hollow shaft motors (4, 5) are intended as linear and rotatable drives. The injecting device is arranged on a stand by the linear drive at a nozzle disk or a form tool of molding machine. The cylinder and the housing are firmly connected with the stand. An independent claim is included for an injection molding machine.

Description

The The invention relates to a plasticizing and injecting device for micro injection molding according to the preamble of claim 1.

It there is an increasing demand for molded parts with very small dimensions, For example, micromechanical components or medical small parts. For such Micro parts is the shot weight often at about 1 g and below. Typically and within the meaning of the present Application should be understood by micro injection molding of the field of injection molding in which the shot weight (Sum of molding weight and gate weight) less than one gram at plastic melt amounts.

For the production of such micro-parts plasticizing and injection devices in various configurations are known (Johannaber, "Kunststoffmaschinenführer", 4.A., 2004, pages 227 to 233; DE19714149C2 . DE19724346C2 . DE10243683A1 . EP0999029B1 ). The known screws have a very small screw diameter of typically 12 mm to 18 mm. In principle, plasticizing screws should offer a combination of high mechanical strength, good metrological resolution of the spray path and low material residence times.

at residence-time-critical molding compounds, such as e.g. Bioresorbable polymers have screws with a diameter of more than 14mm too high Screw channel volume. usual Measures to reduce the auger channel volume, such as auger widening and pitch increase, rich for a significant reduction in the residence time is not enough. With snails a diameter of less than 14mm must, for reasons of strength (torque) made of expensive special materials and show at usual Granules clearly feed problems, resulting in dosing time fluctuations and thus to fluctuations in the residence time and in the cycle time leads. To avoid these problems must be special and costly Microgranules are used.

Out The field of micro-extrusion is the use of conical screws known (Symposium "Micro tube extrusion for the Medical " November 10, 2005, Marienbert Fortress, Würzburg, Chapter A, "Fundamentals the microextrusion "by Dipl.-Ing Eberhard Grünschloß, picture 29b). Here, the conical screw as in single screw extruders usual in a plasticizing cylinder arranged in the axial direction stationary and operated continuously.

From the DE 19925578 A1 For example, a plasticizing and injecting apparatus for micro injection molding is known, in which a plasticizing screw is rotationally driven in a plasticizing cylinder and where a melted line emanates from the front end of the plasticizing cylinder and opens into the antechamber of an injection cylinder in which an injection piston is moved axially back and forth can. The plasticizing screw is acted upon by a spring in the conveying direction of the melt with a sealing force to press the valve body designed as the front end of the plasticizing against the inner wall of the plasticizing when the dosing is completed and the injection piston is moved forward. In this way it should be prevented that melt is forced back out of the injection cylinder into the plasticizing cylinder. The front end of the plasticizing screw takes over the function of a backflow in this case. Such Rückströmsperre is also from the DE 1917975 A known where instead of springs hydraulic means are provided for generating the sealing force. A disadvantage of these known plasticizing and injection devices is that the melt which finally reaches the injection cylinder is first driven out of the latter and enters the mold; So there is no so-called "first in - first out".

When the closest The prior art is a plasticizing and injection device according to Fig. 159 on page 232 in Johannaber, "Kunststoffmaschinenführer", 4.A., 2004, pages 227 to 233, viewed. This is a plasticizing and injection device for the micro Injection molding known in which in a plasticizing a rotatably driven Plasticizing screw is provided, wherein the plasticizing cylinder has an extension piece formed as an injection piston at its front end, in a trained as injection cylinder nozzle body axially back and forth is movable. In the melt line from the worm entrance into the injection cylinder is a ball check valve as Rückströmsperre arranged.

outgoing It is the object of the invention to provide a plastifying and injection device for the micro injection molding to specify that works with only one drive and nevertheless the "First In - First Out "principle guaranteed.

The solution effected by a plasticizing and injection device according to claim 1. Advantageous embodiments and further developments can be found in the subclaims.

The fact that only the worm is moved, and the linear movement of the plasticizing screw is transmitted via the storage on the non-rotatably connected to this storage plasticizing, with a drive both the Plastifi zieren (metering) and the injection done, with very precise movements can be performed. In addition, the "first in - first out" principle is adhered to.

If one allows a slight axial movement between the cylinder and screw can the front end of the screw serve as a backflow preventer, with the front End as a valve body is formed, which can seal with the inner wall of the cylinder. The cylinder can be biased away from the storage or towards storage.

The The worm can also be conical. This allows the passage depth in the catchment area of the screw are chosen so low that standard granules can trickle easily and be fed into the screw threads. Furthermore can over the conical shape of the ridge outside diameter of the core diameter so large in the catchment area, that even with standard materials for the screw no problems with the mechanical strength of the screw occur when this gets very small. about the cone of the Schneckenaussendurchmessers and the course depth course of the The auger can then reduce the auger channel volume so much be processed so that also zeitzeitzeitkritische plastics easily can be. The residence time can also optionally further reduced thereby be that the snail feeds is operated, for example using a gravimetric dosing for the Supply of plastic granules.

By the axial displaceability of the screw relative to the plasticizing cylinder can the game between the Schneckenaussen- and the cylinder inside diameter be suitably adjusted to shear-sensitive materials with process the "right" gap to be able to, because need these materials experience shows a bigger game, about the shear over to reduce the screw web. So with the same snail can Shear-insensitive materials as well as shear-sensitive materials are processed. A screw change is not required. Furthermore can over the variably adjustable gap the homogeneity of the melt can be adjusted (about the Shear rate).

By using an electromechanical drive, for example according to the DE 4344335 , the disclosure of which is hereby expressly incorporated, very precise movements during dosing and injection can be performed, which is especially in micro-injection molding advantage.

The housing of the drive and the injection cylinder can be mounted on a common frame, so that there is a rigid connection between these components and only the screw and the cylinder during dosing and injection between these components are reciprocated. Injection cylinder, plasticizing cylinder with screw, and drive are coaxial cascaded on a common axis, the injection axis. If an electromechanical drive according to DE 4344335 is provided, the axes of the hollow shaft motors are also on the spray axis. The entire plasticizing and injection device can be easily removed as a structural unit of the injection molding machine, for example for maintenance purposes.

following the invention based on embodiments and below Reference to the figures closer explained become.

It show in a very schematic representation:

1 first embodiment with spring bias of the cylinder away from the screw during the metering phase;

2 first embodiment with spring bias of the cylinder away from the screw during the injection phase;

3 second embodiment with Ferdervorspannung of the cylinder on the screw during the dosing phase;

4 second embodiment with Ferdervorspannung of the cylinder on the screw back during the injection phase;

5 third embodiment with hydraulic adjustment of the gap width at the screw tip (in the open position during the metering phase);

6 third embodiment with hydraulic adjustment of the gap width at the screw tip (in the closed position during the injection phase);

7 conical screw (dosing phase);

8th conical screw (injection phase);

8a Detail from the 8th ;

9 fourth embodiment with Rückströmsperre;

10 Use as injection module;

11 Details of the storage of Plasti fizierschnecke.

According to 1 is in a rotary and linear drive 1 in a housing 3 a drive shaft 2 arranged. Furthermore, a first 4 and a second hollow shaft motor 5 in the case 3 attached. The drive shaft 2 is with a motion spindle 6 firmly connected, in a spindle nut 7 is guided. It is a ball screw drive. The spindle nut 7 forms the hollow shaft of the first hollow shaft motor 4 and is by means of a storage 8th supported directly in the motor housing. In one with axial grooves 9 provided recess 10 the movement spindle 6 protrudes a drive pin 11 also with axial grooves 12 is provided and thus with the movement spindle 6 rotatably but axially displaceable coupled. The drive pin 11 is with the hollow shaft 13 of the second hollow shaft motor 5 firmly connected to the drive pin 11 with the release of an annulus 14 surrounds. The hollow shaft 13 is by means of a storage 15 supported directly in the motor housing. The hollow shaft motors 4 and 5 are transverse flux motors with cylindrical magnets 16 and 17 , each on both sides of windings 18 and 19 are surrounded. Alternatively, other embodiments of hollow shaft motors can be provided.

The drive shaft 2 is about a clutch 20 with the plasticizing screw 21 connected. The clutch disc 21 is in one in a housing 26 secured storage 22 on both sides by means of thrust bearings 23 and 24 rotatable but axially fixed relative to the bearing, supported. Furthermore, it is a radial bearing 25 at the edge of the clutch disc 21 intended. The plasticizing cylinder 27 is rotatable with the housing 26 connected, but axially by a small stroke relative to the housing 26 displaced. By means of spring elements 28 , For example Tellefederpaketen, is the plasticizing 27 from the case 26 kept biased away, so that between the as a valve body 29 trained front end of the plasticizing screw 21 and the inner wall of the plasticizing cylinder in this area a gap 33 is formed. The front end of the plasticizing cylinder 27 goes into an extension piece, as an injection piston 30 in an injection cylinder 31 by means of the drive 1 can be moved back and forth. The injection piston 30 has a melt channel communicating with the screw antechamber 32 ,

During the dosing process, the second hollow shaft motor rotates 5 the drive shaft 2 over the drive pin 11 with the required plasticizing speed. The first hollow shaft motor 4 rotates at approximately the same speed as the second hollow shaft motor 5 , The speed difference results in the return speed of the drive shaft 2 and thus the unit of plasticizing screw 21 , Storage 22 , Casing 26 and plasticizing cylinder 27 , The melt generated during dosing can through the gap 33 and the melt channel 32 into the injection chamber 34 of the injection cylinder 31 stream. During the dosing and thus the filling of the injection chamber with the required shot volume or shot weight, the unit of drive shaft 2 , Plasticizing screw 21 , Storage 22 , Casing 26 and plasticizing cylinder 27 move backwards (in the figure to the right). The plate horse packages 28 hold the plasticizing cylinder 27 at a distance to the plasticizing screw 21 ,

The 2 shows the situation during injection. The first hollow shaft motor 4 turns the spindle nut 7 and the drive shaft 2 is moved axially (in the figure to the left). The second hollow shaft motor 5 remains stationary. During this movement, the entire unit is made of plasticizing screw 21 , Storage 22 , Casing 26 and plasticizing cylinder 27 proceeding to the left, being in the injection chamber 34 a pressure is built up. After a short time, a pressure is built up in front of the injection piston, which leads to the disc springs 28 be compressed and as a result the plasticizing screw 21 relative to the plasticizing cylinder 27 is moved forward. As a result, then comes the valve body 29 to stop with the inner wall of the plasticizing cylinder and the gap 33 is sealed. In the further method of the drive shaft 2 forward (in the figure to the left) is the melt from the injection cylinder 31 displaced in a mold, not shown here, wherein the dense seat between the screw and cylinder backflow of melt is prevented in the screw flights.

Instead of the bias described here, the plasticizing cylinder 27 also on the case 26 to be biased towards 3 and 4 ), ie the plasticizing cylinder is held attracted to the housing. In this case, the valve body is at the beginning of the dosing process 29 on stop with the inner wall of the plasticizing cylinder. Only through the forward fed melt is a pressure between plasticizing screw 21 and plasticizing cylinder 27 constructed, which causes the plasticizing screw 21 from the inner wall of the plasticizing cylinder 27 is lifted and a small gap 33 adjusted, by the melt in the melt channel 32 and from there into the injection chamber 34 can flow. This is in the 3 illustrated by the arrows there and for the melt flow through the left-pointing arrows and for moving the screw through the arrows pointing to the right. As soon as the delivery pressure decreases and falls below a lower threshold, the plasticizing cylinder becomes 27 from the springs 28 on the case 26 and thus pulled relative to the plasticizing out, whereupon the gap 33 disappears again and the valve body 29 provides a seal, as indicated by the arrows pointing to the right in the figure. This is the case, for example, at the end of the dosing process. The operation of the two hollow shaft motors 4 and 5 takes place as in the example above. In contrast to the embodiment described above, the plasticizing screw is located 21 with her valve body 29 at the beginning of the injection process, close to the inner wall of the plasticizing cylinder 27 at. With the beginning of the injection process, therefore, the entire unit of plasticizing screw is immediately 21 , Storage 22 , Casing 26 and plasticizing cylinder 27 move to the left and the melt from the injection cylinder 31 displaced in the mold, not shown here. A backflow of melt into the screw flights can not take place.

Instead of the springs, other biasing means may be provided, such as hydraulic and / or pneumatic cylinders 35 (please refer 5 and 6 ). These have the added benefit of being active a certain width of the gap 33 can adjust. In addition, in the case of a bias away from the housing, so when setting an open gap 33 during dosing, at the end of dosing the gap 33 already closed and sealed by means of Hyraulik- and / or pneumatic cylinder, before with the hollow shaft motor 4 and the spindle nut 7 the drive shaft 2 is moved axially forward to execute the injection stroke.

The screw can also be conical (see 7 . 8th and 8a ). The conical snail 40 has a cylindrical or conical screw core 41 and a conical tapered in the conveying direction helical web 42 on. The volume of the screw channel can be determined via the cone of the external diameter of the screw and the course of the channel depth G 43 from the filling opening 44 be reduced to the weft tip in the desired manner. In addition, the flight depth G in the region of the filling opening 44 be chosen so large that standard granules can trickle easily and be retracted. The plasticizing cylinder 27 has a from the filling opening 44 conically tapered cylinder wall in the conveying direction 45 , wherein the cone of the cylinder inner wall corresponds to the cone of the screw. By means of a Tellefederpaket 28 performed adjusting screw 46 can the shear gap 47 between the Schneckenaussen- and the cylinder inner diameter, ie the gap DELTA between the top of the screw flight 42 and the inner wall 45 of the plasticizing cylinder. Like in detail the 8a it can be seen, is the set screw 46 as a threaded bolt 59 formed by a flange of the plasticizing 27 and the plate spring package 28 passed through and into a threaded blind bore 60 in the bearing housing 26 is turned on and off. The desired position of the threaded bolt 59 in the blind hole 60 can with a lock nut 61 on the bearing housing 26 be fixed. Due to the force of the plate spring packages, the plasticizing cylinder 27 from the bearing housing 26 away on strike to the head 62 of the threaded bolt 59 pressed and biased in this direction. The plate spring package 28 So holds the plasticizing cylinder 27 under bias at a distance from the housing 26 and from the snail 40 , where the maximum distance is determined by the position of the threaded bolt 59 in the blind hole 60 is determined. During the dosing process thus a constant shear gap 47 maintained. The injection takes place in the same manner as in the first embodiment, ie by means of the linear and rotary drive 1 becomes the drive shaft 2 axially (in the figure to the left) shifted. During this movement, the entire unit of conical plasticizing screw 40 , Storage 22 , Casing 26 and plasticizing cylinder 27 proceeding to the left, being in the injection chamber 34 a pressure is built up. After a short time, a pressure is built up in front of the injection piston, which leads to the disc springs in the sequence 28 compressed and the conical plasticizing screw 40 relative to the plasticizing cylinder 27 is moved forward. This is the threaded bolt 59 through the flange of the plasticizing cylinder in the 8a moved to the left and the head 62 lifted off the flange. As a result, then comes the valve body 29 on stop with the inner wall 45 of the plasticizing cylinder, the gap 33 is sealed and the shear gap 47 disappears, ie he goes to zero. In the further method of the drive shaft 2 forward (in the figure to the left) is the melt from the injection space 34 displaced in a mold, not shown here, wherein the dense seat between the screw and cylinder backflow of melt is prevented in the screw flights.

According to the 9 The plasticizing and injection device can also be equipped with a non-return valve, for example a ball check valve 36 be equipped, in which case no relative movement between the plasticizing cylinder and the screw is required to prevent during injection of a backflow of melt into the screw threads. The plasticizing cylinder 27 So it is rigid with the case 26 storage 22 connected. The drive shaft 2 is like in the embodiments described above with a linear and rotary drive 1 coupled, for example, in the 1 and 2 closer drive described with series-connected hollow shaft motors.

The plasticizing and injection device according to the invention can (see 10 ) on a Ge Vice 37 be mounted, with a front support and fastener 38 and a rear support and fastening element 39 are provided. The injection cylinder 31 is on the front support and fastener 38 attached and the rotary and linear drive 1 on the rear support and fastening element 39 ie there is a rigid connection between the injection cylinder 31 and the drive 1 , Between these two is the unit of plasticizing and screw and storage 22 , The frame 37 is slidable on a machine bed 48 supported, for example on wheels 49 , and can by means of a displacement cylinder 50 to the nozzle plate 51 moved to a known injection molding machine and moved away from this. With this configuration it is ensured that the entire plasticizing and injection device can be easily removed as a structural unit of the injection molding machine, for example for maintenance purposes.

An example of a concrete execution of the storage 22 is in the 11 shown. In the case 26 , consisting of the two housing parts 26a and 26b , are the drive shaft 2 and the snail 21 verkuppelt each other, for example in the shaft shoulder 52 , A double-sided axial deep groove ball bearing 58 absorbs the axial load while a cylindrical roller bearing 53 absorbs the radial load. Several bearing washers 54 , Pass rings 57 and a locknut 55 ensure a secure fit of the entire storage. seals 56 prevent leakage of lubricating oil. The power flow in the bearing is shown as a thick curve. The power is transmitted via shaft shoulder, fitting rings, axial deep groove ball bearings and cylindrical roller bearings.

1

Linear- and rotary drive

2

drive shaft

3

casing

4

first Hollow shaft motor

5

second Hollow shaft motor

6

movement spindle

7

spindle nut

8th

camp

9

axial grooves

10

recess

11

drive journal

12

axial grooves

13

hollow shaft

14

annulus

15

camp

16

magnet

17

magnet

18

winding

19

winding

20

clutch

21

clutch disc

22

storage

23

thrust

24

thrust

25

radial bearings

26

casing

26a

first housing part

26b

second housing part

27

plasticizing

28

Adjusting springs

29

valve body

30

Injection piston

31

Injection cylinder

32

melt channel

33

gap

34

Injection room

35

hydraulic or pneumatic cylinder

36

Ball check valve

37

frame

38

Front Carrying and fastening element

39

rear Carrying and fastening element

40

conical slug

41

screw core

42

flighting

43

screw channel

44

fill opening

45

conical cylinder wall

46

screw

47

shear gap

48

machine bed

49

roll

50

displacement cylinder

51

nozzle plate

52

shaft shoulder

53

Cylindrical roller bearings

54

bearing washers

55

locknut

56

seals

57

pass rings

58

Thrust ball bearings

59

threade

60

blind hole

61

locknut

62

head of the threaded bolt

Claims (17)

Plasticizing and injection device for micro injection molding, comprising a plasticizing screw rotatably drivable in a plasticizing cylinder, wherein the plasticizing cylinder has at its front end an extension designed as an injection piston which is axially movable back and forth in an injection cylinder, characterized in that a storage is provided, in which the plasticizing screw is rotatably mounted, that the plasticizing cylinder is rotatably connected to the storage, and that a linear and rotary drive is provided for the plasticizing screw. Device according to claim 1, characterized in that that the rear end of the plasticizing screw and the drive shaft of the linear and rotary drive over a coupling are drivingly connected to each other, and that axial bearings and radial bearings are provided in the region of the coupling. Device according to claim 2, characterized in that that a clutch disc is provided that on both sides the clutch disc thrust bearing and in the edge region of the clutch disc a Radial bearing is provided. Device according to one of claims 1 to 3, characterized that the storage is a housing has, are arranged in the axial and / or radial bearings. Device according to one of claims 1 to 4, characterized that the plasticizing screw in the storage axially immovable is stored, that the plasticizing cylinder firmly connected to the storage is, especially with the housing storage, and that downstream the plasticizing screw a backflow is provided. Device according to one of Claims 1 to 4, characterized that the front end of the plasticizing screw designed as a valve body is that can seal with the inner wall of the plasticizing, and that between the plasticizing cylinder and the housing of the Storage mechanical and / or hydraulic and / or pneumatic Biasing means are provided. Device according to claim 6, characterized in that that the plasticizing cylinder is biased away from the storage, so that the valve body the plasticizing screw during the metering process a permanent gap with the inner wall of the Plasticizing cylinder forms and during the injection process the plasticizing screw first be pressed with its front end against the plasticizing cylinder can and subsequently both together by means of the linear drive of the Move the plasticizing screw in the injection cylinder to the front can be. Device according to claim 6, characterized in that that the plasticizing cylinder is biased toward storage, so that the plasticizing cylinder of the valve body of the plasticizing screw during the Metering process lifted by the delivery pressure so that melt can be fed into the injection cylinder can, and after the dosing process, the plasticizing screw with her valve body abuts against the inner wall of the plasticizing and both together by means the linear drive of the plasticizing screw in the injection cylinder can be moved forward. Device according to one of claims 1 to 8, characterized that the plasticizing screw and the inside of the plasticizing cylinder are conical. Device according to claim 9, characterized in that that one or more screws for adjusting the gap width DELTA between the plasticizing screw and the inner wall of the plasticizing cylinder are provided. Device according to one of claims 9 or 10, characterized that over at least a portion of the plasticizing screw in the conveying direction the outer diameter of the screw flights and the diameter of the Remove the worm core continuously. Device according to one of claims 9 or 10, characterized that over at least a portion of the plasticizing screw in the conveying direction the outer diameter of the screw flights decreases continuously and the diameter of the screw core remains constant. Device according to one of claims 1 to 12, characterized that as linear and rotary drive two in series Hollow shaft motors are provided, wherein the one hollow shaft motor as a linear drive and the other hollow shaft motor as a rotary drive serve. Device according to one of claims 1 to 13, characterized that the plasticizing and injection device on a rack is arranged, which by means of a linear drive to a nozzle plate or moved up a mold of an injection molding machine and can be moved away from this. Device according to claim 14, characterized in that that the injection cylinder and the housing of the drive of the plasticizing screw firmly connected to the frame. injection molding machine with a plasticizing and injection device according to one of previous claims, with a closing unit, and a mold, wherein the plasticizing and injection device displaceable on a machine bed of the injection molding machine abestützt is and zoom by means of a linear drive to the mold and from can be moved this way. Injection molding machine according to claim 16, characterized in that the injection cylinder of the plasticizing and injection device and the hous se of the drive of the plasticizing screw are firmly connected to a frame which is slidably supported on the machine bed and can be moved by means of the linear drive.