Technical Field of the Invention

The present invention relates to a molding system including a molding core with fluid channels, and a fluid-aided molding method.

Background of the Invention

Injection molding of polymeric articles with complex geometries such as undercut zones is being performed and developed for several decades. The complexity of such geometries require complicated systems and methods, which result in high process and investment costs, added with inevitable further costs due to high defect ratios in final products.

Undercut geometries can be obtained using memorial cores. But memorial cores are not suitable for defect-free obtainment of sharp-edged undercut geometries in molded articles. At removal of the memorial core, such articles are exposed of high amount of stress, which easily causes damage on the molded article. Defect-free removal of the memorial core from the polymeric article is hardly achieved only by maintaining a high temperature at the polymeric article, which solution requires longer molding cycle times.

Also collapsible cores are used in obtainment of undercut geometries. Collapsible cores are complex structures as described in US 2015/115 502, comprising a higher number of movable interrelated mechanical parts. Due to its complex structure, manufacturing of a collapsible core is difficult and thus expensive. Its complex geometry reduces the convenience of obtainment of cooling fluid lines in the collapsible core. The high number of movable mechanical parts causes simultaneous wearing out of the core at plurality of zones thereof. Additionally such wearing out induces formation of burrs on the movable parts, which decreases the performance of the collapsible core, especially in terms of fluid tightness if the molded polymeric article is a gasket.

The technical field of injection molding is still seeking basic and effective cores for obtainment of undercut geometries in polymeric articles.

Objects of the Invention

Primary object of the present invention is to overcome the abovementioned shortcomings of the prior art.

Another object of the present invention is obtainment of a molding core providing fluid-aided molding of polymeric items with undercut zones.

Another object of present invention is obtainment of a molding core providing homogeneous and rapid cooling to a molded item.

Yet another object of the present invention is to provide a simple, rapid and cost- effective molding method for obtainment of polymeric items with undercut zones.

Summary of the Invention

The present invention proposes a core for use in molding of a polymeric article having an undercut zone, said molding core comprising a channel having an inlet and one or more outlet(s) for, in operation, provision of pressurized fluid towards a polymeric material to be molded surrounding the core, such that the fluid flows through the channel and exits the core through the outlet(s) and pushes polymeric material to be molded away from the core. The present invention further proposes a shift for cooperating with the core, slidably and telescopically engageable therewith; and a mold comprising a guide configured to guide and limit the sliding motion of the shift on the core; the mold further comprising an expansion cavity defined by a support surface distantly surrounding the outlet(s) and by an outer surface portion of the shift, such that at a first position, the expansion cavity is a closed volume between the support surface and said outer surface portion of the shift. The present invention further proposes a method for obtainment of polymeric articles having an undercut zone. Brief Description of the Figure

The figures, whose brief explanation is herewith provided, is solely intended for providing a better understanding of the present invention and is as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description.

Figure 1 shows (a) an exemplary perspective view of a core according to the present invention, and (b) an embodiment of the core with inner fluid lines visualized.

Figure 2 shows (a) an exemplary side view of a core according to the present invention, and (b) an embodiment of the core with inner fluid lines visualized.

Figure 3 shows exemplary longitudinal sections showing engagement of a core and a shift according to the present invention (a) at the first position, and (b) at the second position.

Figure 4 shows an exemplary side view of a combined pair of molding systems according to the present invention, wherein two molding systems are arranged in series.

Figure 5 shows an exemplary side view of another combined pair of molding systems according to the present invention, wherein two molding systems are arranged in parallel.

Detailed Description of the Invention

Referring now the figures outlined before, the present invention proposes a molding system for use in molding of a polymeric article having an undercut zone. The present invention further proposes a mold and a fluid-aided molding method.

The core according to the present invention as exemplified in Fig. 1(a) and Fig. 2(a), comprises a channel (2) having an inlet (21) and one or more outlet(s) (22). When pressurized fluid is provided towards a polymeric material to be molded surrounding the core (1), the fluid flows through the channel (2) and exits the core (1) through the outlet(s) (22) and pushes the polymeric material to be molded away from the core (1). Thus an undercut zone on the polymeric material can be easily formed. The fluid may also facilitate cooling of the polymeric material, thus quicker formation of the polymeric article can be enabled.

The channel (2) preferably comprises a main line (20) and a plurality of branches (21) which are preferably narrower than the main line (20), and each of which has its own outlet (22) on a distal end thereof with respect to the main line (20). In operation, each branch (21) conducts fluid from the main line (20) out of the core (1) through a respective outlet (22) towards polymeric material surrounding the core.

In a preferred embodiment of the core (1) according to the present invention, the branches (21) are radially positioned around the main line (20), and the respective outlets (22) are evenly distributed around the core (1), such that in operation, polymeric material to be molded is radially and evenly pushed away from the core (1) and thus a circular undercut zone is obtained at the polymeric material to be molded around the outlets (22).

As exemplified in Fig. 1(b) and Fig. 2(b), the core according to the present invention preferably further comprises a cooling line (3) having a cooling fluid inlet (31) and cooling fluid outlet (32), configured for receiving a cooling fluid into the core (1) through the cooling fluid inlet (31), circulating the cooling fluid inside the core (1) throughout the cooling line (3), and letting the cooling fluid out through the cooling fluid outlet (32). A part of the cooling line (3) is preferably positioned in vicinity of the outlet(s) (22), such that in operation, heat from the polymeric material to be molded is at least partly transferred to the cooling fluid. Thus, conformal cooling of both mold and polymeric material to be molded is provided for rapid formation of the polymeric article.

The present invention further proposes a shift (3) which is slidably and telescopically engageable with the core. The shift (3) has a cavity (31) for receiving molten polymeric material (70), wherein at a first position exemplified in Fig. 3(a), the shift (3) covers the outlet(s) (22) and the cavity (31) surrounds the outlet(s) (22). At a second position obtainable by telescopically sliding of the shift (3) on the core (1) as exemplified in Fig. 3 (b), the outlet(s) (22) are opened for pressurized fluid exit, or exposed to the surroundings of the shift (3). In operation, at the first position, the cavity (31) receives molten polymeric material and the shift (3) prevents contact between polymeric material to be molded and fluid from the outlet(s) (22) by preventing fluid release from the outlet(s) (22). At the second position, the outlet(s) (22) are uncovered (i.e. exposed) and polymeric material to be molded is partly extracted from the cavity (31), such that the polymeric material is available to be exposed to the fluid released from the outlet(s) (22).

The present invention further proposes a mold (4) comprising a guide (41) configured to guide and limit the sliding motion of the shift (3) on the core (1). The mold (4) further comprises an expansion cavity (42) defined by a support surface (43) distantly surrounding the outlet(s) (22) and by an outer surface portion of the shift (3). At the first position, the expansion cavity (42) is a closed volume between the support surface (43) and said outer surface portion of the shift (3). In operation, at the first position of the shift (3), the expansion cavity (42) is unavailable for the polymeric material to be molded; and at the second position, an extracted portion of the polymeric material to be molded expands until abutting the support surface (43) upon being pushed by fluid released from the outlet(s) (22).

The mold preferably further comprises a reciprocating and mechanical locking piston connected to pins engageable with respective holes on the shift (3) for delimiting the sliding motion thereof.

Molding system according to the present invention may comprise a plurality of abovementioned interrelated parts (core, shift and mold), configured in series as exemplified in Fig. 4, or in parallel as exemplified in Fig. 5. With such congifurations, same compressor, liquid pump, piston etc can be arranged to serve each mold. In this case, investment and operational costs are minimized and high production rates of molded polymeric articles can be easily achieved with low cost. The present invention further proposes a molding method for obtainment of a molded polymeric article having an undercut zone. The method comprises the following steps:

a) engagement of a core and a shift slidably and telescopically surrounding the core, the core comprising a channel having an inlet and one or more outlet(s) for fluid flow, and the shift having a cavity for receiving molten polymeric material, such that the shift covers the outlet(s) and the cavity surrounds the outlet(s);

b) placing the core and shift into a mold comprising a guide configured to guide and limit the sliding motion of the slide on the core; the mold further comprising an expansion cavity defined by a support surface distantly surrounding the outlet(s) and by an outer surface portion of the shift, such that the expansion cavity is a closed volume between the support surface and said outer surface portion of the shift;

c) provision of polymeric material to be molded such that the cavity of the shift is at least partly filled with polymeric material;

d) sliding the shift to a second position wherein the outlet(s) are opened, and polymeric material is at least partly extracted from the cavity of the shift such that the polymeric material is faced with the opening(s); and provision of a pressurized fluid through the outlet(s) such that the polymeric material gets exposed to the pressurized fluid, and pushed towards the support surface.

The method preferably further comprises heat transfer from the polymeric material to a cooling fluid being circulated through the core.

For minimizing process costs and maximizing the labor safety, the pressurized fluid used in shaping of polymeric articles is preferably air, and the cooling fluid is preferably water. Hence, an aircore is provided for use in injection molding of polymeric articles with complicated geometries. With the core, molding system and method according to the present invention, undercut zones on polymeric articles are obtained with the aid of pressurized fluids, without being pushed by movable solid parts of the molding system. This provides high production quality with decreased defect ratios and costs in the molded final product.

The following objects are achieved by the present invention:

- overcoming the abovementioned shortcomings of the prior art,

provision of:

- a molding core providing fluid-aided molding of polymeric items with undercut zones,

- a molding core providing homogeneous and rapid cooling to a molded item,

- a simple, rapid and cost-effective molding method for obtainment of polymeric items with undercut zones.