Integral frame structures and manufacturing method

Abstract

A method allows production of integral frame structures having at least three structural portions separated circumferentially about a central axis and at least one hollow region radially inward thereof. Each of plural mold sections fits between structural potions, and a portion of the mold interior includes a wedge shaped portion which allows the mold sections to slide past the structural portions when molding is complete.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a manufacturing method and article produced thereby, and more particularly to a method of manufacturing a three-dimensional structure having hollow portions and structures produced in accordance with the method.

In order to produce an integrally molded product, various molding techniques have been conventionally employed. Blow molding offers one way in which a hollow product is produced. In accordance with such approach, a “bubble” of plastic is expanded into a shaped mold cavity, thereby assuming a hollow form corresponding to the interior topography of the cavity walls. While effective for producing structures having a relatively thin wall, such as bottles and the like, blow molding cannot be used to produce structures having substantial thickness. The process is further limited to the extent that if openings in the hollow structure were desired, such as provided to form an open frame structure, an additional fabrication step would be required.

Rotational molding (roto-molding), a process which involves rotation of a mold to deposit molding material on an interior of a mold has been used to produce various hollow structures, but is also limited with regard to what materials can be used in the molding process, and generally involves relatively long cycle times. As with blow molding, finishing of the molded articles, particularly those with openings defining a frame structure, generally requires additional steps after molding.

Notwithstanding the above approaches, it has remained difficult heretofore to produce a structure having hollow inner portions which is integrally molded as a single part, particularly utilizing injection and compression molding techniques.

It would therefore be desirable to provide a method of molding structures having hollow interior portions which is applicable to injection molded and compression molding processes.

Accordingly, it is an object of the invention to provide a molding method for hollow articles of integral unitary structure which overcomes the drawbacks of the prior art, and which is applicable to injection and compression molding techniques.

It is a further object of the invention to provide an article of unitary structure which includes a hollow portion inward of a portion of the structure comprising the article.

SUMMARY OF THE INVENTION

In accordance with these and other objects of the invention, there is provided a method which permits the molding of three-dimensional articles which include at least one hollow region disposed radially inward of structure comprising the article.

Briefly stated, the method includes providing a mold for producing an article having at least three structural portions separated circumferentially from one another about a central axis of the article, the mold having a number of mold sections corresponding to the number of structural portions to be produced thereby. The article further includes at least one hollow region radially inward of at least one of the structural portions, the hollow region being formed during molding of the article by engagement of respective mold sections which serve to form the particular structural portion(s) having the hollow region inward thereof. The shape of the mold cavity corresponding to the structural portion associated with the hollow region allows the corresponding mold sections to be withdrawn after molding is complete, by permitting clearance, of that portion of each of the mold sections which mutually engages with the other to form the hollow region, past the structural portion which is radially outward of the hollow region, and which would otherwise impede movement of the mold section outwardly of the article. This is accomplished by providing a portion of the mold interior (and hence the article produced thereby), with a wedge portion having a wedge-shaped profile which faces radially inward towards the hollow region. Such wedge-shaped profile of the wedge portion is provided with an angle no larger than an angle described between the axes along which the respective mold sections are withdrawn after molding of the article, thereby allowing the structure of the mold which forms the hollow region of the article to slide past the structural portion of the article disposed radially outward thereof.

The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of an article having four circumferentially-spaced structural portions disposed radially outward of an inner hollow region which can be produced by the method according to the invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional schematic view of a mold for use in carrying out the method in accordance with the invention for producing the article example of FIG. 1;

FIG. 4 is a cross-sectional schematic view of a mold for use in carrying out the method in accordance with the invention for producing an article having a structural form roughly analogous with that of FIGS. 1 and 2, but having three rather than four structural portions disposed outwardly of a hollow inner region;

FIG. 5 is another example of an article which can be produced by the method in accordance with the invention; and

FIG. 6 is a perspective view of yet another example of an article which can be produced by the method in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, an example of an article which can be produced according to the method of the invention is generally designated 10. Article 10 includes four circumferentially-spaced structural portions 11, and a hollow region 12 inward thereof. Structural portions 11 in the depicted example each meet at common poles aligned with a central axis A_L, however, the inventive method is not, by any means, limited to such arrangement. Each of the structural portions 11 includes a wedge portion 13 having a wedge-shaped profile which faces radially inward towards the hollow region 12. The purpose of this wedge portion 13, which lies at the heart of the invention, will be explained in detail below, with reference to description of the molding process used to form the depicted example of FIGS. 1 and 2, as well as a vast array of other structural articles which include hollow portions inward of solid structural portions of the article.

Turning now to FIG. 3, a mold for producing the example of FIGS. 1 and 2, generally designated 20, is depicted for illustrative purposes only, and it will be understood that the principles employed with respect thereto can be applied by analogy to any other mold used to produce any other article of different configuration and shape. Mold 20 includes four mold sections 20a, 20b, 20c, 20d, corresponding in number to the number of structural portions 11 of article 10. Each of the mold sections 20a, 20b, 20c, 20d mutually engages an adjacent one thereof and adjacent pairs include cavity portions 21 which collectively define a mold cavity portion for producing a corresponding structural portion 11 of article 10.

The mold sections 20a, 20b, 20c, 20d are moved inwardly and outwardly along respective molding axes A₁, A₂, A₃, A₄ during mold cycling. As seen in the depicted example of FIG. 3, portions 22 of the mold sections 20a, 20b, 20c, 20d inward of the cavity portions 21 mutually engage during molding to prevent flow of molding material therebetween for formation of the hollow region 12. When molding is complete, the mold sections 20a, 20b, 20c, 20d are moved outwardly along molding axes A₁, A₂, A₃, A₄ to release the article 10 form the mold 20. Cavity portions 21 each includes a wall 23 which, collectively with another wall 23 of a cavity portion 21 of an adjacent one of the mold sections 20a, 20b, 20c, 20d, corresponds to the wedge-shaped profile 13 of the structural portion 11 of the article 10. As shown, the walls 23 of adjacent ones of cavity portions 21 are advantageously arranged at an angle to one another which is less than or approximately equal to an angle between the respective ones of the molding axes A₁, A₂, A₃, A₄. This permits the portions 22 of the mold sections used to form the hollow region 12 to be withdrawn past the structural portion 11 of the formed article 10 to allow removal of the article 10 from the mold 20.

It is noted that when the article 10 is molded from a resilient material which demonstrates some “give,” the angle between the walls 23 of adjacent ones of cavity portions 21 may be a little larger than the respective ones of the molding axes A₁, A₂, A₃, A₄, since the structural portions will yield even though presenting an undercut. It is further noted that, although shown as defined by planar intersections, the wedge portions 13 can comprise curved surfaces as long as there is sufficient clearance to remove the mold sections 20a, 20b, 20c, 20d past the structural portions 11.

Turning now to FIG. 4, another mold, designated 30, is directed to production of an article 10′ which includes three structural portions 11′. In the depicted example, for simplicity of disclosure, the structural portions 11′ of article 10′ are circumferentially spaced by equal angular intervals. Each of the mold sections 30a, 30b, 30c move along respective molding axes A′₁, A′₂, A′₃ which are arranged at an angle θ₁ to one another, where θ₁ is equal to 120°. Therefore, in accordance with the invention, each of the structural portions 11′ is provided with a wedge portion 13′ presenting a wedge-shaped profile describing an angle θ₂ which is less than or approximately equal to θ₁ (assuming the material of the structural portion can not be appreciably compressed).

While the aforementioned and described articles have a generally spherical shape, the invention is not limited to such configurations. For example, the article of FIG. 5, designated 40, can be produced by the method in accordance with the invention, provided the structural portions 11″ are provided with wedge portions 13″.

The invention is also suitable for use in producing more complex structures, as shown for example in FIG. 6, and which employs the principles described above, i.e., the provision of wedge portions on the various structural portions radially outward of a hollow region.

Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

1. A method of molding an article having a hollow region inward of a structural portion of the article, comprising: providing a mold including at least three mold sections each movable in a direction along a respective molding axis, the mold sections including cavity portions for molding structural portions of the article and engaging portions inward of the cavity portions which mutually engage during molding to prevent flow of molding material therebetween for formation of the hollow region, the cavity portions each includes a wall which, collectively with another wall of a cavity portion of an adjacent one of the mold sections corresponds to a wedge portion of the structural portion of the article, the walls of adjacent ones of the cavity portions being arranged at an angle to one another which is less than or approximately equal to an angle between respective ones of the molding axes; moving the mold sections together along the molding axes to mold the article; and moving the mold sections apart along the molding axes to remove the article from the mold.

2. An article having a hollow region inward of a structural portion of the article, comprising: a body having a structural portion radially outward of the hollow portion, said structural portion including a wedge portion having a wedge-shaped profile facing inwardly towards the hollow portion.