Aligning device for vertical injection molding machine

Details Aligning device for vertical injection molding machine Aligning device for vertical injection molding machine

2002-04-17

2003-09-09

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Female mold and charger to supply fluent stock under...

With means to cause relative movement between mold and charger

C425S576000, C425S589000

Reexamination Certificate

active

06616441

ABSTRACT:

This invention relates generally to injection molding machines and more particularly to an aligning device for a table used on injection molding machines having vertically oriented clamp systems.
BACKGROUND
“Vertical” injection molding machines consist of an injection unit mounted either with a horizontal or vertical orientation and a clamp system oriented vertically to hold the two mold halves together under force sufficient to resist the pressure exerted by the molten plastic. Orientation of the clamp system vertically allows for operational ease as compared with horizontal clamp systems for certain applications including, but not limited to, insert molding and cable connectors.
Vertical injection molding machines can be equipped with a rotating table mounted to rest on the stationary platen. A plurality of lower mold halves are mounted on the table at set positions or stations. The table rotates a set amount to bring a lower mold half into alignment with an upper mold half mounted on the vertically movable platen. The upper mold half mates with the lower mold half, molding material is injected, packed, and the movable platen withdrawn upward. The lower mold half with the molded part therein is now indexed or rotated to another station. At the same time, a “fresh” lower mold half also mounted to the table and previously positioned at some station on the table where it is made ready for molding, is rotated into molding relationship with the upper mold half.
At least two stations are provided in the rotating table, i.e., an injection station and an ejection station. By performing ejection away from the injection station, it may be possible for certain molding applications to reduce cycle time as contrasted to the traditional horizontal injection molding machine which must eject the molded part from the mold cavity. While time is spent indexing the part, that time can be spent in cooling the part which must occur no matter which machine is used before ejection can happen. Usually, the table is equipped with two, three or more stations and the additional stations typically involve stations that set inserts. Thus, a three station table will typically have a separate insert station which occurs after ejection and prior to injection.
All stations are typically automated. At the ejector station, ejector pins, typically positioned beneath the table, dislodge the molded part from the lower mold half and a robotic arm typically transfers the part from mold half to some other station in the plant. Similarly, robotic arms subsequently set inserts into the now empty lower mold half at the insert station. Because of the vertical positioning of the lower mold half with exposed upward cavity, there is an orientation advantage enjoyed by the vertical injection molding machine making it receptive to molding parts requiring a number of intricately placed inserts.
It is to be appreciated that the vertically oriented clamp system with stationary platen fixed to ground lends itself well to high tonnage moldings having relatively heavy mold halves. In addition, advances in molding technology have improved the quality of molded parts produced today and require that the mold halves be precisely aligned. Alignment is conventionally assured by guide pins from one of the mold halves received in guide pin holes in the other mold half. Tolerances between guide pins and guide pin holes are therefore reduced to assure precise alignment of the mating mold halves required (among other things) for precision molding. At the same time, heavy mold parts in a vertical injection mold machine can excessively wear the guide pins if the bottom mold half is not rotated into accurate alignment with the upper, vertically movable mold half.
The problem to which the invention is directed may best be understood by reference to the schematic prior art arrangement depicted in FIG.
1
.
FIG. 1
shows an upper mold half
1
with guide pins
2
which will vertically descend into mating relationship with a lower mold half
3
mounted on rotatable table
4
by guide pins
2
nesting into guide pin holes
5
. Table
4
is also shown in top view between the vertically displaced upper mold half
2
and lower mold half
3
. In the top view, the lower mold half at the injection station is designated
3
A, at the ejection station
3
B, and at the insert station
3
C.
Typically, table
4
is rotated about its center by a drive (not shown). A limit or proximity switch is manually set to be actuated when the table rotates to its next successive position. That is when lower mold half
3
C rotates to the injection station (shown occupied by lower mold half
3
A in FIG.
1
), the switch is actuated and the drive stops. For a number of reasons, the switch cannot precisely position the lower mold half at the injection station to assure alignment of guide pins
2
.
The prior art has recognized this and has provided an aligning mechanism for the table. This aligning mechanism conceptually comprises a locating hole
6
in table
4
and a power driven locating pin
7
. Specifically, one power driven locating pin
7
is provided and table
4
has at each station a locating hole designated
6
A,
6
B, and
6
C in the plan view. When the switch is actuated to stop table rotation, final alignment results by the tapered locating pin
7
fitting into locating hole
6
. This causes a slight rotational movement of table
4
and brings lower mold half
3
into better alignment with upper mold half
1
as locating pin
7
is forced upwardly into locating hole
6
than the alignment possible using only a manually set switch. The system described works and has produced acceptable molded parts for years.
For precision molding with good guide pin life, the prior art system is not acceptable. Table
4
is a large diameter and sophisticated jigs and fixtures are used to drill locating holes
6
. Size of locating holes
6
and, more importantly, position of locating holes
6
, can be held to tolerances of ±0.003″. The cumulative effect of hole tolerance in the table can account for 0.010″ to 0.012″ variation in hole position which is not acceptable. It is to be also recognized that there are variations in other manufacturing tolerances that also contribute to random positioning of the locating holes in the table. For example, variations in the spindle (about which the table rotates) and variations in the gear drive arrangement also account for variations in the position of the locating holes in the table. The cumulative effect of all the tolerances, as well as slippage in the drives, reduce the diametrical size of the locating pin to a dimension not acceptable for the heavy mold, high precision moldings desired to be produced for certain molding applications.
The effect of positional variation in the locating holes is illustrated diagrammatically in exaggerated form by the overlay of locating holes
6
A,
6
B,
6
C shown in the upper right hand corner of FIG.
1
. Assume table
4
can be stopped at a precise rotational angle so that no variation in rotation occurs when the table is indexed. Locating hole
6
A will occupy the position shown by the solid circle, locating hole
6
B will occupy the position shown by the dash circle and locating hole
6
C will occupy the position shown by the dot-dash circle. Common area for all three locating holes is shown by cross-hatching and is a reduction in the effective size of locating hole
6
. This means that the locating pin can only be the diameter of the reduced locating hole size if the locating pin is to extend through all three locating holes. Reducing the diameter of the locating pin, even in the range of 0.01041, will not provide the desired accurate positioning of the lower mold half relative to the upper, vertically movable mold half.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to overcome the alignment problem discussed above resulting in a reduction of guide pin wear and/or precision molding for certain molding applications.
This object along with other feature

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