DE8806805U1 - Injection molding tool for producing plastic parts with large wall thickness differences on injection molding machines - Google Patents

Description

'« Applicant: · ^: '' ^! ·· ^! ■ 5Ö82^Me ^: iM. ^: erzhagen 1

Rüdiger Potthoff Grotmicke 7

Injection molding tool for producing plastic injection molded parts, large, wall thickness differences on injection molding machines.

The field of application is the production of plastic injection-molded parts on conventional plastic injection machines with an injection molding tool.

The purpose of the invention is to make it possible to manufacture dimensionally accurate plastic injection molded parts with very different wall thicknesses and extremely thin, film-like wall thicknesses with a high dimensional tolerance of less than 0.5 - °'° » as is required today in medical treatment and in chemistry.

When producing plastic injection molded parts with very different wall thicknesses, difficulties arise in injection molding machines due to the uneven flow and cooling of the liquid plastic in the mold cavities. This leads to porous areas and breakouts in the case of particularly film-like wall thicknesses of less than 0.5 mm. Increasing the holding pressure or re-embossing during the cooling time in the tool only partially reduces this problem. The holding pressure does not always have a full effect in the removed mold cavities and re-embossing during the cooling time crushes or cuts into the fiber flow of the plastic. These disadvantages are particularly noticeable in plastic injection molded parts with strong transitions into film-like walls and high wall thickness dimensional accuracy.

With the present invention, these disadvantages are avoided by intervening in the liquid flow process of the injection process of an injection molding machine shortly before the cooling time with a corresponding increase in holding pressure at the sensitive workpiece points in the injection molding tool.

•—2—&igr;

The injection molding tool provided for in our invention narrows the cavity to a precise size by pushing the cavity walls forward and displaces the still liquid, penetrated solder into the surrounding cavity without cutting through the flow fibers and avoids local hardening through a homogeneous flow of the plastic. The internal material stresses at the transitions between thicknesses are reduced to a minimum. This gives the plastic part a higher fatigue strength and a precise diameter at the indented points.

2a distinctive plastic injection molded part and a matching injection molding tool are described below and shown in Fig. 1 and 2:

Fig. 1 - Sleeve as a plastic injection-molded part with strong wall thicknesses and high tolerances on the thin wall thickness.

Fig. 2 - Longitudinal section through a plastic injection molding device for part 1 .

Fig. 2 shows the longitudinal section of an injection molding tool clamped in the working position on an injection molding machine, with the injection side on the right and the closing side on the left of the parting line 2.
It is a multiple injection molding tool.

On the closing side, the core forming bolt 3 is permanently installed with the contact face 23 and is enclosed by the ejector bush 4. On the injection side, the core guide bolt 7 with the contact face 24 is clamped in the movable plates 8 and 16. The dimension X is the critical dimension, which is determined by the distance between the two contact faces 23 and 24. This dimension X can be changed by moving the wedge piece 14 up to the stop surface 27. The roller guide bar 10 transfers the longitudinal movement of the wedge piece 14 into a transverse movement offset by 90 and via the wedge piece 9, the plates 8+16

t · · &igr; Il · ·

on the core guide bolt 7, which influences the dimensional distance X with the contact surface 24. The disc springs 18 always ensure a pressure contact without play. The possible stroke is determined by the distance Y in which the plates 8 and 16 as well as the wedge piece 9 can move in the center of the spray axis p^. The connecting block 15 is controlled and moved either hydraulically or mechanically in the axial direction by the working cycle of the spraying machine.

How it works: The injection molding tool is clamped in a normal injection molding machine with the connecting bars 5 and 12 - as shown in the closed state. The wedge piece 14 is in the lowest position so that the distance X is the greatest. When the plastic is injected from the injection molding machine via the sprue channels 26 into the mold cavity of the plastic injection molded part 1, the enlarged mold space at X also flows fully. Before the injection cycle is finished, the drive (e.g. hydraulic cylinder) of the connecting bolt 15 has received a command from the injection cycle to advance it to the contact surface 27 of the stop screw 11. This causes the core guide bolt 7 to be moved to the left and reaches the set dimension X. In doing so, it presses the still liquid plastic surplus back into the remaining mold cavity and the dimension X and the tightness of the plastic film are guaranteed in the subsequent cooling process.

The advantage of this injection molding tool is the ability to produce highly precise injection molded parts with tolerances of - 0.01 mm for medical devices and the chemical industry with extremely small wall thicknesses on normal injection molding machines.

List of reference symbols

1.) Striking plastic injection molded part la.)Plastic film 2.) Parting line 3·) Core mold bolt 4.) Ejector sleeve

5.) Connection plate to the closing side of the injection molding machine

6.) Guide plate

7.) Core guide bolt

8.) Plate

9.) Wedge piece

10.) Roller guide rail

11.) Stop screws

12.) Connection plate to the spray side of the spray machine

13.) Guide rail

14.) Wedge piece

&igr; 15.) Connecting bolt

16.) Plate

17.) Disc spring guide pin

Y ) Distance

!X ) Critical dimension

18.) Disc springs

19.) Mold carrier plate

20.) Form plate

21.) Inclined surface

22.) Ejector plate

23.) Stop face

24.) Anschiags s t i rnf1a che

25.) Spray center

26.) Sprue channel

27.) Stop surface

28.) Adjustment scale

Claims (6)

Protection claims 1.) Injection molding tool for producing plastic parts, characterized in that it has a variable mold cavity wall part on the core guide bolt 7 for each mold cavity, which changes the dimension X by moving the wedge piece 14 in the longitudinal direction simultaneously in the mold cavities arranged in the mold carrier plate 19 via a controllable wedge gear consisting of the wedge pieces 9 and 14 with the connecting bolt 15 during the injection process. 2.) Injection molding tool for producing plastic parts according to claim 1, characterized in that the drive for moving the connecting bolt 15 in the longitudinal direction is derived mechanically or hydraulically from the injection molding machine or is carried out as an external drive. 3.) Injection molding tool for the production of plastic parts according to claims 1+2, characterized in that in order to achieve a low-impact movement of the wedge piece with a small angle of inclination of the surface 21 to the parting plane, smooth guide rails 13 or roller guide rails are provided. 4.) Injection molding tool for producing plastic parts according to claims 1-3, characterized in that the disc springs 18 keep all movable parts 7, 8, 9, 10, 13, 14 and 16 in frictional engagement with one another without play. 5.) Injection molding tool for producing plastic parts according to claims 1-4, characterized in that the end stop of the wedge piece 14 can be adjusted by adjusting the stop screw 11 with the stop surface 27, the dimension X. 6.) Injection molding tool for producing plastic parts according to claims 1-5, characterized in that the stop screw II has an adjustment scale 28