Patent Application
20060186575
This invention relates to improvements in molds, and more particularly to improvements in molds used to make parts comprised of more than one material.
Multi-material molds are used to make parts having more than one material, parts with one material having more than one color, or both more than one material and color. It has been known to make such parts using a multi-station mold. In a two-station mold, a first material is shot into a mold cavity at a first station. The part is attached to one mold half and then moved to a second station where a second material is shot into a mold cavity. Once the molten material has hardened, the part is ejected from the mold and the process repeated.
Two station multi-material molds have found use in various applications, including, for example, automotive lighting such as covers for headlights, brakelights, turn signal lights, etc. Such lighting applications may also have so-called optical components, where the parts have optical properties in addition to being comprised of multiple materials. These optical components are normally formed from an electroform of optical surfaces in the mold. A wide variety of optical mold surfaces are known, including reflective surfaces, retroreflective surfaces, pillow, flute, fresnel and other optical surfaces. More specifically, the electroform is made as an array of pins set as a mold matrix. The resulting matrix is used to make an electroform block (i.e, the optical surface) through an electroplating process. This electroform is subsequently used as an insert tool (generally formed integral with one half of a mold) used in injection molding to make optical and reflective light assemblies. Optic or reflex pins are set in the mold surface to create a plurality of reflective prisms for emitting an array of light from a specified part of the light assembly.
In known two station molds, optical surfaces have been required at both stations. This has been accomplished by having the optical surfaces present on the mold half which moves between stations. Representative examples of these kinds of molds are made by Hallmark Technologies, Inc. of Windsor, Ontario Canada. With these designs, the optical surfaces are positioned on the movable half of the mold. The first material is shot at the first station, the mold half with the optical surface is rotated to a second station, and the second material is shot at the second station. Simultaneously, the first material is shot for a second part at the first station. The part formed at the second station is ejected, and the process repeated until as many parts are made as needed.
Electroforming optical surfaces is relatively expensive and the process of making such surfaces is time consuming. Also, for known multimaterial molds, core pulls and lifters (for undercuts) are required at both stations. It would be desirable to provide a multi-material mold which reduces the amount of electroformed surfaces required on a mold and to provide a mold which reduces the need for core pulls and lifters.
In accordance with a first aspect, a multi-material mold comprises a core half having a first station and a second station, a slide, and a cavity half movable with respect to the core half between a first closed position wherein the at least one slide cooperates with the first station of the core half and the cavity half to define a first mold cavity adapted to form a portion of a part, and a second closed position wherein the portion of the part cooperates with the second station of the core half and the cavity half to define a second mold cavity. The slide is slidable between an extended position adapted to hold the portion of the part formed in the first mold cavity to the cavity half, and a retracted position adapted to permit the part to exit the mold. In accordance with another aspect, optical surfaces can be placed on the core half. A method of making an injection molded part using the mold as described is also disclosed.
From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology of molding. Particularly significant in this regard is the potential the invention affords for providing a high quality, low cost mold for making multi-material parts. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the mold as disclosed here will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to enhance visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation illustrated in the drawings.
It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the mold disclosed here. The following detailed discussion of various alternative and preferred features and embodiments will illustrate the general principles of the invention with reference to a mold particularly suitable for use in making multi-material parts having optics such those found on headlamp covers or lens. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure.
Referring now to the drawings,
Advantageously, the second station 15 of the core half 12 is a mirror image of the first station 13 in terms of position of optical surfaces. That is, in accordance with a highly advantageous feature, no optical surfaces are present at the non-mating surface 94 which corresponds to the surface 91 on the first station 13. Optical surfaces, core pulls and lifters may be used at surface 93, but they are not necessary in this design. Mating surface 93 cooperates with the first surface 86 of cavity half and the first portion 29 of the part 99 to help define a second mold cavity 17 (seen in
Ejector pins 32 (shown in
After the injection molding material (e.g. a polycarbonate resin) has been injection molded into the first mold cavity and the portion 29 formed is allowed to cool, the cavity half 14 is separated from the core half 12 and the portion 29 stays with the cavity half. The cavity half is then rotated about 180 degrees to the second station. As shown in
Once the mold is closed at the second station, horn pins 60 or other similar devices may be used to urge the slides 40 away from portion 29 to a retracted position (See
The lifter 23 (shown in
In operation, the mold 10 is closed by clamping the cavity half 14 against the core half 12 at first station 13 with latch mechanism 59. The optical surfaces are on the fixed, core half 12 of the mold 10. The slides 40 are in the extended position, cooperating with surface 86 of the cavity half and surface 91 of the core half to define the first mold cavity 16. The slides are held in place by a plunger 77. In fact, the slides 40 preferably have nowhere to move at the first station 13. A molten material is injected into the first mold cavity 16. The gate location for the introduction of molten material will be readily apparent to those skilled in the art given the benefit of this disclosure. Electroforms 50, 51 forming one or more optical surfaces 18, 21 may be provided on the core half 12 at part or all of the first surface 91 that defines part of the first mold cavity 16. A second surface 92 of the core half is not part of the first mold cavity. The molten material is allowed to cure, forming a portion 29 of a part 99 to be made. Optionally the portion 29 may have an undercut 28 and the core pull 25 mounted on the core half 12 may be retracted prior to movement of the cavity half. A lifter 23 may be also used. Pin 31 mounted on the ejector plate 56 can retract and move the lifter 23 out of engagement with the part prior to rotation of the cavity half 14 to the second station. As shown in the drawings, both a core pull 25 and a lifter 23 may be used with the same part, depending on the desired aspects of the part.
After any core pull and lifters have been accounted for, the mold 10 is opened. Ejector pins 32 whose movement is coordinated with the opening of the mold urge the portion 29 of the part against the cavity half 14, and the slides 40 captivate the portion 29, helping to secure the portion to the cavity half as the cavity half rotates 180 degrees to the second closed position. The mold 10 is closed and the portion 29 is now at the second station 15. The act of closing the mold (moving the cavity half to the second closed position) urges cylinder 52 and ejector pins 30 back to their original position. Once the mold is closed, a second mold cavity 17 is formed. Second mold cavity is defined by previously formed portion 29, cooperating with first surface 86 of the cavity half and mating surface 93 of the core half to define the second mold cavity 16. The slides 40 do not define the second mold cavity. Now that they have served their task, the slides 40 are retracted by engagement of horn pins 60. The second material is shot into the second mold cavity 16, forming the second portion 69 of part 99. Once the material has cooled sufficiently, the mold is opened. This time, due to the geometry of the part and the lack of slides, the part 99 adheres to the core half 12 instead of the cavity half 14. Ejector pins 30 urge the part 99 out of the mold.
Advantageously, no duplicative electroform is required at the second station. Any electroform is required only if the second portion 69 requires optical components and even then, the electroform would not be required at the first station. Several variations in design will be readily apparent to those skilled in the art given the benefit of this disclosure. For example, more than two materials may be used, and additional stations supplied on each mold half as needed.
From the foregoing disclosure and detailed description of certain preferred embodiments, it will be apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
