Controlling an injection moulding machine having a mould and at least two injection units

The present invention relates to an auxiliary injection unit for moulds for moulding articles of at least two parts from plastics material as disclosed in the preamble of appended claim 1.

Nowadays, it is known for articles of plastics material to be manufactured by moulding at least two components, having different characteristics, according to the following method.

The main component, distinguished by its greater volume or weight, is injection-moulded first, in a prepared main mould, by means of machines, such as a press, provided for injecting the plastics material.

Meanwhile, an auxiliary unit, or injector can be wired into an appropriate connection, ready to mould a second component in a separate injection step.

Up to now, the said auxiliary unit requires electric and/or electrodynamic signals from the said press in order to operate.

This involves a considerable disadvantage in that the said presses must be electrically connected to the said injector, meaning that an operator is obliged to work on the press to modify the electrical circuit.

It is therefore necessary to employ a qualified technician with a good knowledge of the structure of the press.

Another disadvantage lies in the waste of time caused by the said electrical interconnection operation, a waste of time which involves an unnecessary and economically damaging immobilisation of the press.

EP-A-0 805 870 describes a moulding assembly including a mould for moulding articles of plastic material made of a single injection unit, wherein the mould comprises movable parts operable to adapt the mould cavity for injection by the injection unit, which movable parts are connected to a control unit which is operable to control the injection unit.

US-A-4 335 068 describes a mould defining a moulding space divided into two subspaces which are defined by retractable partitioned walls and including two injection units for the separate injection of the plastics material into said two sub-spaces.

The main purpose of the present invention is therefore to solve the technical problems described above, eliminating the disadvantages described with reference to the prior art and thus provide an auxiliary injection unit which operates independently of the type of press used.

In the context of the above task, another important object is to provide a unit which achieves the main purpose simply and rapidly, without any need for frequent adjustments.

Last but not least, the unit must be structurally simple and relatively inexpensive to manufacture.

The main purpose and the other referred to are achieved, along with other which will become apparent later, by providing an auxiliary injection unit for a mould for moulding articles of plastics material according to the features disclosed in the characterising part of appended claim 1.

Preferred embodiments are disclosed in the appended dependent claims.

Further characteristics and advantages of the invention will become apparent from the detailed description of one embodiment thereof, illustrated purely by way of non-limitative example in the appended drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 is a three-quarters view of the unit of the invention connected to a mould;</li><li>Figure 2 is a block diagram of the electrical connections relating to the microswitches used;</li><li>Figure 3 is a three-quarters view of the overall structure: including a press, a mould and the invention;</li><li>Figure 4 is a section, taken on a first section plane, of the mould containing the microswitches after the first component has been injected;</li><li>Figure 5 is a section, taken on another section plane, of the unit of the invention connected to the mould after the injection of the second component.</li></ul>

With reference to the aforesaid drawings, a mould is indicated 1 for the injection-moulding in plastics material of a first component 2, having an auxiliary unit, indicated 3, connected thereto for the separate injection of a second component 4.

Three detectors are arranged in the said mould 1, three microswitches, for example.

A first detector, indicated 5, is associated with the forward movement of a blade assembly indicated 6.

The said blade assembly 6 comprises a mechanism for managing the geometry of the mould, in particular in the area indicated 7, between the injection of the first component 2 and the injection of the second component 4.

In particular, it is in this area 7 that contact occurs between a first path 8, for the said first component 2, and a second path 9, for the second component 4.

The forward movement of the said blade assembly 6 interrupts the connection between the said first path 8 and the said second path 9, so that the said first component 2 only has access to the area of the mould 1 involved with it.

When the said blade assembly 6 is advanced, the first detector 5 is activated, permitting a press, indicated 10, to inject the said first component 2 (see Figure 4).

A T-shape arm, indicated 11, is provided to synchronise the movement of the blade assembly 6 with the activation or non-activation of a second detector 12, in such a way that when the blade assembly 6 is withdrawn, as shown in Figure 5, the said second detector 12 is activated in its closed position following the opening of the said first detector 5.

In this way, the said second detector 12 closes its respective circuit when the said blade assembly 6 is withdrawn, enabling the second path 9 to communicate with the said first path 8 and permitting the activation of the auxiliary unit 3.

A third detector 15 is arranged at the point where the plug, indicated 14, meets the die, indicated 13, of the said mould 1.

The said third detector 15 is activated when the two parts of the said mould 1, the plug 14 and the die 13, close together, thereby permitting operation of both the press and the auxiliary unit.

The said first, second and third detectors are connected, as illustrated in the diagram of Figure 2, to a sixteen-pin connector, indicated 16, arranged on the external surface of the mould 1, and are part of three independent circuits, as shown in Figure 2.

These circuits may be identified by the reference numbers of each pin (contact) in the following way: the first detector 5 closes the circuit between the pins indicated 10' and 16', permitting injection by the said press 10; the second detector 12 closes the circuit between the pins 11' and 16', permitting injection by the auxiliary unit 3; the third detector 15 closes the circuit between the pins 12' and 16' when the mould is closed, while it closes the circuit between the pins 13' and 16 when the mould is open.

The said auxiliary unit 3 can be connected to the said connector 16 by means of a cable, indicated 17, through a sixteen-pin connector indicated 18.

Operation is therefore as follows: with reference to the appended drawings, the moulding operation begins with the mould 1 closed and thus with the circuit closed between the pins 12' and 16', associated with the third detector 15, and with the blade assembly 6 advanced and the first detector 5 closed.

In this way, the second detector 12 remains open since the second component 4 is injected only once injection of the first component 2 has been completed.

Once the press 10 has been started to inject the first component 2, at the end of this step the blade assembly 6 is withdrawn, thus altering the area 7 of the press 1 so that the second path 9 is in communication with the first component 2, which during the preceding step occupied the path 8.

As a result of this withdrawal, the T-shape arm 11, which is securely fixed to the blade assembly 6, opens the first detector 5 and closes the second detector 12.

This closes the circuit between the pins 11' and 16', signalling consent for the auxiliary unit 3 to inject the second component 4.

The mould is then opened in order to extract the workpiece, thus activating the third detector 15 which closes the circuit between the pins 13' and 16', giving to the auxiliary unit 3 a signal for resetting the cycle.

It can thus be appreciated that the invention has achieved its object and aims, by providing an auxiliary injection unit which is controlled directly by the movement of the parts of the mould during the moulding steps, with no need for intervention on the press.

The materials used and the dimensions of individual components of the unit of the invention can of course be adapted to the specific requirements of each case.