Finish cutting of a plastic part during a blow molding cycle using a guillotine blade

A mold tool and cutting system are described for in-mold cutting of a molded article. The cutting system comprises a blade assembly for incorporation into the mold tool, defining at least in part a cavity for forming a molded article, the blade assembly including an extendable cutting blade and a wedge slide. The wedge slide is capable of rearward displacement to expose the cutting blade. During a molding process, the wedge slide is displaced fully forward so as to present a continuous molding profile with adjacent molding surfaces. Following the molding process, the wedge slide is displaced rearwardly so as to expose the cutting blade. The cutting blade is then extended into the cavity to cut a molded article contained therein.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing plastic blow-molded parts, and in particular to a method of in-mold finish cutting of the part during the blow-molding cycle.

BACKGROUND OF THE INVENTION

It is known and customary practice to subject molded articles, in particular blow molded articles to post-molding processing to remove flash and excess material. Post-mold processing such as trimming operations require additional time and resources, increasing overall labour requirements and consequently unit pricing on the molded article.

The incorporation of in-mold operations has the potential to decrease labour costs, and a shift to in-mold processing is evident in the plastics industry. Examples of in-mold operations in common use today are in-mold labelling, such as for the application of labels to consumer goods, and in-mold product assembly, such as for the assembly of articulating structures (i.e. medical syringes).

SUMMARY OF THE INVENTION

According to an aspect of an embodiment, provided is a cutting system for use in a mold tool. The cutting system comprises a blade assembly for incorporation into a mold tool defining at least in part a cavity for forming a molded article, the blade assembly including an extendable cutting blade and a wedge slide. The wedge slide is capable of rearward displacement to expose the cutting blade. During a molding process, the wedge slide is displaced fully forward so as to present a continuous molding profile with adjacent molding surfaces. Following the molding process, the wedge slide is displaced rearwardly so as to expose the cutting blade. The cutting blade is then extended into the cavity to cut a molded article contained therein.

According to another aspect of an embodiment, provided is a mold tool for forming a molded article. The mold tooling comprises a first mold half and a second mold half, the first and second mold halves jointly defining a cavity for forming the molded article. The mold tooling further comprises a cutting system including a blade assembly for incorporation into the first mold half. The blade assembly includes an extendable cutting blade and a wedge slide, the wedge slide being capable of rearward displacement to expose the cutting blade. During a molding process, the wedge slide is displaced fully forward so as to present a continuous molding profile with adjacent molding surfaces of the first mold half. Following the molding process, the wedge slide is displaced rearwardly so as to expose the cutting blade. The cutting blade is then extended into the cavity towards the second mold half to cut a molded article contained therein.

Specific embodiments of the present invention will now be described with reference to the Figures, wherein like reference numbers indicate identical or functionally similar elements. The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. A person skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the scope of the invention. Although the description and drawings of the embodiments hereof exemplify the technology in the form of a fluid conduit for automotive use, the invention may also be used in the manufacture of other automotive/non-automotive molded plastic structures such as air ducts, toys, etc. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

For the purposes of this description, the term ‘forward’ is defined as displacement towards the mold cavity, and the term ‘rearward’ is defined as displacement away from the mold cavity.

Generally, the present invention is an in-mold cutting system configured to trim molded plastic articles. The in-mold cutting system includes a cutting blade that extends through the molding cavity to effect the trimming action. To reduce flash in the finished molded product in the region of the cutting blade, the cutting blade is maintained behind a sliding wedge during the molding process. The sliding wedge forms a part of the molding surface, and is slidably retracted following the molding operation to expose the cutting blade. Stated differently, the sliding wedge operates as a door behind which the cutting blade is retaining during the molding stage of the cycle. On retraction of the sliding wedge (i.e. opening of the door), the cutting blade can then be extended through the molded product to effect the cut. To ensure the cutting blade fully extends through the molded product, the blade passes through the molding cavity and into a pocket provided opposite the cutting blade. To prevent the ingress of molten plastic into this pocket, a retractable plug is provided, thus presenting a continuous molding profile to the parison during the molding cycle.

The cutting system is well suited for use in blow molding environments, where the formed plastic product is generally in the form of a hollow article. In general, an exemplary blow molding process begins with the extrusion of a parison. The parison is then positioned and sealed within a suitable mold tool. The mold tool provides a cavity corresponding to the desired plastic product to be formed. The sealed parison is then inflated, generally using air, to urge the parison against the contours of the cavity. On sufficient cooling, the mold tool is opened, and the formed plastic product is removed, and subject to post-mold processing (e.g. de-flashing), if necessary. The present invention is intended to be incorporated into the blow molding process, by providing a cutting function within the mold tool. In this way, at least one cut can be performed prior to mold opening and ejection of the formed part.

Turning now toFIG. 1, shown is a portion of a mold tool10for use in a blow molding machine. Mold tool10generally includes a first mold half20, and a second mold half22that jointly define a mold cavity24for molding a desired plastic product. First mold half20is shown to include a first mold plate26, while second mold half22is shown to include a second mold plate28. Also shown is a cutting system30which includes a blade assembly32and a plug assembly34.

Referring now toFIG. 2, shown is a perspective exploded view of blade assembly32, configured to be incorporated into first mold half20of mold tool10. Blade assembly32generally includes a plurality of cutter inserts, in particular a first cutter insert36and a second cutter insert38, as well as a slide support block40. The assembly of these components (as best seen inFIG. 1) define channels for guiding a wedge slide42and a cutting blade44through forward/rearward displacement relative to cavity24. As specifically shown, wedge slide42is guided/supported by way of slide surfaces provided on slide support block40and first cutter insert36, while cutting blade44is guided/supported by way of slide surfaces provided on slide support block40and second cutter insert38. Second cutter insert38also provides a forward stop for wedge slide42, whereby sealing surface46of wedge slide42abuts against sealing surface48of second cutter insert38at the forward limit of displacement.

FIG. 3provides a perspective view of plug assembly34, configured to be incorporated into second mold half22of mold tool10. Plug assembly34generally includes a plurality of plug inserts, in particular a first plug insert50and a second plug insert52. The assembly of these components (as best seen inFIG. 1) define a channel for guiding a plug54through forward/rearward displacement relative to cavity24. As specifically shown, plug54is guided/supported by way of slide surfaces provided on first plug insert50, and second plug insert52.

Returning now toFIG. 1, cutting system30is shown in a first operational position, in which cutting blade44is fully retracted, and wedge slide42is positioned fully forward to effectively separate cutting blade44from molding cavity24. In this fully forward position, wedge slide42presents molding surface56, and forms a continuous molding profile of cavity24with adjacently located first cutter insert36and second cutter insert38. In this first operational position, plug54is also positioned fully forward to similarly form a continuous molding profile of cavity24with adjacently located first plug insert50and second plug insert52. In turn, these components of cutting system30for a continuous molding profile with the mold plates defining first and second mold halves20,22. By maintaining a continuous molding profile, that is by presenting a cavity surface without substantial voids or recesses attributable to the cutting assembly, a molded plastic product with reduced flash can be achieved. To further facilitate this, the tolerance between sealing surfaces, for example sealing surface46of wedge slide42and sealing surface48of second mold plate28are sufficiently small to prevent the ingress of plastic material therein during the blow molding cycle.

Referring now toFIG. 4, a second operational position is presented in which wedge slide42is displaced rearward, that is away from cavity24. This second condition occurs once the blow molding stage of the overall molding cycle is complete, and the molded plastic part has sufficiently cooled. The displacement of wedge slide42exposes cutting blade44to cavity24, through gap G created between wedge slide42and second mold plate28. Also shown is the rearward displacement of plug54, to expose recess58provided diametrically opposed to cutting blade44.

In a third and final operational position, as shown inFIG. 5, cutting blade44extends through cavity24sufficiently to enter recess58. Extension of cutting blade through cavity24has the effect of cutting/trimming the molded plastic article, while still within the mold tool. As a result, post-mold processing of the molded article is reduced, resulting in lower manufacturing costs and quicker overall manufacturing time. On completion of the cutting action, cutting blade44is retracted into the first position, and wedge slide42and plug54are displaced forward to the aforementioned first operational position, in preparation of the next molding cycle.

Presented inFIGS. 6 to 8is an alternate view of mold tool10, and serves to illustrate the same operational positions as those detailed above. Referring first toFIG. 6, shown is the initial first operational position in which cutting blade44is fully retracted, and wedge slide42is positioned fully forward. Plug54is also in the fully forward position, thus forming the continuous molding profile detailed above. In this arrangement, the mold tool is operably readied for the blow molding cycle. The second operational position is shown inFIG. 7, in which wedge slide42is displaced rearward to expose cutting blade44to molding cavity24. Also shown is the rearward displacement of plug54to expose recess58.FIG. 8illustrates the third operational position, in which cutting blade44extends through cavity24sufficiently to enter recess58.

As seen for example inFIG. 8, cutting blade44is configured as a guillotine-style blade having angled leading cutting edge60. The configuration of cutting edge60may vary depending on the application, but typical for this technology is the one-sided taper visible inFIGS. 1 and 2. As will be appreciated, the angle of the taper, as well as the implementation of other cutting edge styles (e.g. dual taper edge) may be dictated by the cutting performance desired, and the nature of the material being cut. In one embodiment, the blade is provided with 25° angled leading cutting edge60, and a taper of 12°.

While the cutting system described above includes both the blade assembly and the plug assembly, there may be instances where the cutting system includes only the blade assembly incorporated into the mold tool. Variations in the implementation/arrangement of the blade and plug assemblies will be a function of the molded article to be formed. It will be appreciated that such variants in the cutting system and resulting mold tool are intended to fall within the scope of the invention.