Patent Application
20070077379
The present invention relates to injection molded members which can be used as structural members in a vehicle body or the like. More specifically, the present invention relates to long glass fiber reinforced thermoplastic members which include hollow chambers formed via water-assist injection molding and can be used as structural members.
Injection molding of various members used in vehicle bodies and the like is well known. Typically, members are formed from thermoplastic material via injection molding and such members can include single-walled open and/or planar members, such as interior trim pieces, liners for liftgates or tailgates, roof rails, etc.
For single-walled open members or planar members which must bear larger loads, such as running boards, etc., the thermoplastic material is often reinforced with material such as glass fibers, which are added to the thermoplastic melt from which the member is to be molded from.
However, generally such single-walled open members or planar members cannot bear structural loads, even when reinforced with glass fibers in the conventional manner. If such single-walled open members or planar members are required to bear structural loads, for example to support other components attached to them or to support their own attachment to a vehicle, metal inserts to carry the loads must be formed in the molded part or separate reinforcements such as metal plate gussets must be provided.
It is also known to produce hollow members, such as roof rails or the like, using known gas-assist injection molding techniques. While hollow members can provide increased rigidity or other structural load carrying capabilities, it has proven difficult to employ gas-assist injection molding techniques with thermoplastic melts containing reinforcing glass fibers. Members produced with such technology have suffered from irregular wall thickness which often precludes their use as structural members. Further the strength of the fiber-reinforced thermoplastic materials is insufficient for carrying structural loads due to insufficient fiber length and/or poor bonding between the thermoplastic and the fibers.
More recently, water-assist injection molding has been developed. Water assist injection molding is similar to gas assist injection molding with water replacing the gas which is injected into the molten plastic shot in the mold to form one or more hollow cavities within the finished molded part. The greater pressures which can be achieved with water, compared to gas, and the fact that water is incompressible, result in much better wall thickness uniformity than can be achieved with gas assist technologies.
Accordingly, none of the known technologies for injection molding can produce, at a reasonable cost, injection molded members with load carrying capabilities permitting the finished members to be used as structural members.
It is an object of the present invention to provide a novel method of manufacturing members from fiber reinforced thermoplastic, via injection molding, which obviates or mitigates at least one disadvantage of the prior art.
According to a first aspect of the present invention, there is provided a method of molding a member capable of carrying light structural loads, comprising the steps of: (i) extruding a shot of a molten thermoplastic material into a mold, the thermoplastic material being reinforced with relatively long length reinforcement fibers; (ii) injecting water into the shot of melt in the mold to form at least one hollow chamber therein, the chamber serving to stiffen the finished structural member; (iii) removing the structural member from the mold and draining the water from the at least one chamber.
Preferably, the thermoplastic material is selected from a group comprising polypropylene, Nylon, PET, ABS, TPO and thermoplastic polyurethane. Also preferably, the reinforcement fibers are selected from a group comprising glass, Aramid, carbon and natural fibers.
The present invention provides a method of forming members of fiber reinforced thermoplastic members via molding, the members including at least one hollow chamber, formed by water injection into the melt in the mold, to stiffen the finished member.
Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
a, 1b and 1c show three stages in a conventional water-assist injection molding process;
a through 1c show a water-assist injection molding process in accordance with the present invention. As shown, a mold 10 includes a cavity 14 for a structural member 34 to be molded. In
The shot 18 of fiber reinforced thermoplastic material may be prepared using an extruder with the method and system described in a co-pending U.S. provisional application entitled, Method and System of Compounding Fiber Reinforcing Thermoplastic, to Schrempf, Armstrong and Ranjit, filed on Mar. 3, 2005 and assigned to the assignee of the present invention and the contents of this Schrempf et al. provisional application are incorporated herein by reference.
With the method and system of the Schrempf et al., a melt can be obtained wherein the average length of the glass fibers in the melt produced are 100% longer, or greater, than the length obtained in other processes. The long glass fibers will have a minimum length of 4 mm up to a maximum length of approximately 50 mm. However, fibers having a length range of 35 mm and up provide the best or most ideal melt; fibers 20-34 mm in length yield a better quality melt; and fibers 5-19 mm in length provide a good quality melt. Depending on the particular application the quality of melt may be more important than in other types of applications. Other reinforcement fibers which can be employed with the present invention include aramid, carbon and natural fibers, such as hemp. The typical material composition of the fiber reinforced thermoplastic material will be approximately 40%; however, it is conceivable for the material composition to range from substantially 0% to 50%. The addition of the fiber material yields a fiber reinforced injection molded member capable of carrying light structural loads. The molded member will also exhibit a certain degree of flexibility. In particular the modulus of flexibility of the fiber material is in the range of 500-1000 Kpsi but preferably in the 700-900 Kpsi range. This property adds to the durability and versatility of the molded member. In addition to the fiber material the shot 18 also has thermoplastic material. Preferably, the thermoplastic material is selected from a group comprising polypropylene, Nylon, PET, ABS, TPO and thermoplastic polyurethane.
Due to the increased viscosity of the enhanced-length fiber-reinforced thermoplastic melt which results from the longer fiber length, the injection of water depicted in
The structural member 34 that is produced from the process described above will have several unique features and can take many forms. The structural member 34 is a flexible body formed of the fiber reinforced polymeric material. As indicated above the fiber content of the flexible body will range from substantially 0% to 50%. Furthermore, the flexible body will have a modulus of flexibility ranging from 500 1000 kpsi. As indicated above a hollow cavity is formed through the flexible body and as described below will serve many functions. As stated the structural member 34 will take many forms and can be used to form both interior and exterior components. While the situational member is designed to handle light loads, it can be modified to handle heavier loads my placing metal supports within the hollow cavity which will increase the integrity of the structural member. The rest of this section will now focus on some of the specific embodiments of structural members that can be formed using the molding process described above.
As shown in
If desired, metal inserts can be loaded into the mold when molding tailgate 100 to provide reinforcement for attachment points wherein high stress is expected such as for hinges and/or latches. As will be apparent, tailgate 100 can act as a light duty structural member, bearing hinge loads, body loads and also being able to support some cargo load when in the open (down) position.
As it is formed from enhanced-length fiber-reinforced thermoplastic and includes stiffening chambers 204 and 208, liftgate 200 can bear light structural loads and liftgate 200 need not include any metal load bearing members to carry these structural loads. Additionally the stiffening chambers 204 and 208 can be used for wiring purposes, speaker mounts or other components.
As shown in
As should now be apparent, the present invention allows the molding of large members and/or members which are be capable of carrying at least light structural loads such as are experienced by body panels and closures. The members are preferably molded from enhanced-length fiber-reinforced thermoplastic and include one or more hollow features, or chambers, which serve to stiffen the resulting molded member. The chambers are preferably created via the injection of water into the shot of thermoplastic in the mold, in a manner similar to conventional water-assist injection molding techniques.
The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.
