Abstract:
A method of forming a part with a solid urethane elastomer skin is provided, wherein the mold is moved by a mold manipulation tool to present differently oriented surfaces of the mold in a horizontal orientation when the urethane elastomer is sprayed on each of the differently oriented surfaces. A multi-axis robot is provided with a spray head that sprays the urethane elastomer onto a mold surface. A mold manipulator moves the mold that has a plurality of differently oriented mold surfaces so that the surface to be sprayed is held in a horizontal orientation as they are coated with the urethane elastomer and for a predetermined time period after spray coating until the urethane elastomer sets up.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 60/330,157 filed Oct. 16, 2001, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for applying spray urethane to form a skin layer of a part in a mold. 
     2. Background Art 
     Solid urethane elastomer material is used as part of a process for forming parts in a mold. The solid urethane elastomer is a two-part composition that is mixed at the spray head before applying the material to a mold. The urethane elastomer is formulated to set-up relatively quickly. For example, the urethane elastomer is sprayed from the spray head as a liquid and begins to set-up in about 10 to 15 seconds after it contacts the mold. In about two minutes, the urethane elastomer is cohesive and its surface is tack-free. Even with this relatively rapid set-up, when the urethane elastomer is sprayed on a vertical surface, the elastomer forms drips or runs on the vertical surface and may accumulate in liquid pools where a vertical surface meets a horizontal surface. It is also difficult to obtain a surface coating having relatively uniform thickness if the urethane elastomer is sprayed on a vertical surface because gravity causes the material to flow. On a horizontal surface, the urethane elastomer is easily applied to form a uniform thickness after it contacts the horizontal surface. 
     Examples of automotive parts that may include a urethane elastomer skin include instrument panels, inner door panels, consoles, glove box doors, steering wheel covers, body pillar covers, and the like. An example of a process for forming automotive parts having a urethane elastomer skin is provided below. In an in-mold painting process utilizing an aromatic urethane, the process would begin by applying paint to a mold release agent in the mold for the part. After painting, the aromatic or aliphatic urethane elastomer is sprayed onto the paint layer to form a wall having a thickness of approximately {fraction (1/16)} to ⅛ inch. However, if the part has surfaces that are not substantially horizontal, but are vertical or sloped, the urethane elastomer will form drips and pools and have areas of reduced thickness. After the urethane elastomer has solidified, an injection molded part may be inserted into the mold on top of the urethane elastomer skin. The injection molded part provides reinforcement ribs, frames for installation of components such as air bags or instruments, and fastener receptacles. Foam is then injected into the mold to fill the mold and secure the injected molded part to the urethane elastomer skin. The part may then be removed from the mold and trimmed. 
     Recent developments in the manufacture of vehicles include incorporation of a plurality of air bags in the vehicle interior. Parts such as inner trim panels for doors, instrument panels and steering wheel covers that may be formed by the above-described process must be formed with more uniform wall thickness to meet part specifications for air bag covers. 
     There is a need for a method and apparatus for forming complexly shaped parts with a solid urethane elastomer skin having a relatively uniform wall thickness. There is also a need for a method and apparatus for making parts with a solid urethane elastomer skin that eliminates drips, runs and pools of urethane elastomer material on the part while assuring adequate coverage of a relatively uniform wall thickness on the part. By eliminating waste and reducing the amount of material required to form the urethane elastomer skin on a part, considerable savings can be achieved. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an apparatus for forming a part and a method of forming a part with a solid urethane elastomer skin is provided, wherein the mold is moved by a mold manipulation tool to present differently oriented surfaces of the mold in a horizontal orientation when the urethane elastomer is sprayed on each of the differently oriented surfaces. 
     According to another aspect of the invention, an automated system is provided for forming a solid urethane elastomer skin for a part, wherein a multi-axis robot is provided with a spray head that sprays the urethane elastomer onto a mold that is secured to a mechanism that moves the mold. The mold has a plurality of differently oriented mold surfaces that must be coated with the urethane elastomer. The mold may be moved by several different mechanisms, including hydraulic or pneumatic cylinder actuators or for more complex mold movement the mold could be moved by a multi-axis robot. 
     According to another aspect of the invention, movement of the spray head by a multi-axis robot and movement of the mold are coordinated by a computer process control system so that the portion of the mold to which the spray head is directed is held in a substantially horizontal orientation whenever the spray head is spraying the urethane elastomer on that portion of the mold. The apparatus for moving the mold is also preferably programmed to only move the mold after the urethane elastomer has been provided with enough time to initially set-up so that runs, drips and pools of elastomeric material are not formed. 
     These and other aspects of the present invention will be better understood in view of the attached drawings and in light of the following detailed description of an embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a urethane elastomer spray application booth; 
         FIG. 2  is a side elevation view of a urethane elastomer spray application booth showing the mold in a tilted position; 
         FIG. 3  is a side elevation view of a spray applicator robot, part mold, and mold manipulator; 
         FIG. 4  is a top plan view of the spray applicator robot, part mold and mold manipulator; 
         FIG. 5  is an enlarged side elevation view of the part mold and mold manipulator; 
         FIG. 6  is a diagrammatic perspective view of a spray applicator robot and mold showing the mold being held to present a substantially horizontal surface to be sprayed; 
         FIG. 7A  is a cross-sectional view taken along line A—A in  FIG. 6 ; 
         FIG. 7B  is a cross-sectional view taken along line A—A in  FIG. 6  showing the mold surface as the mold would be rotated to present a generally horizontal application surface; 
         FIG. 8  is a cross-sectional perspective view showing a spray urethane application tool applying urethane elastomer to a mold that is not provided with the mold manipulator of the present invention that illustrates the problems encountered by such systems. 
         FIG. 9  is a plan view of a robot spray applicator and mold manipulator; 
         FIG. 10  is a front elevation view of the mold manipulator; and 
         FIG. 11  is a rear plan view of a production line including mold carriers and the urethane elastomer application station. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1 and 2  a urethane spray application booth is generally indicated by reference  10 . A multi axis robot  12  is provided within the booth  10 . The multi axis robot  12  may also be referred to herein as a spray applicator robot. A mold manipulator, generally indicated by reference  14 , is used to move a mold  16  that is used form parts in a molding process. The mold  16  is carried into and out of the booth  10  by a carrier  18 . A heater  20  is provided in the spray booth to heat the mold to the desired temperature to cure urethane elastomer. A metering unit  22  is used to meter two different components of the urethane elastomer composition that react and cure to form a urethane skin in the mold  16 . The booth  10  is provided with an exhaust system  24  that filters and exhausts air from the booth  10 . 
     The robot  12  carries a spray head  26  on the end of a robot arm  28 . The spray head  26  is used to spray the urethane elastomer and may also be provided with a in-mold paint spray nozzle. The robot  12  is mounted on a base  30 . 
     Referring now to  FIGS. 3 and 4 , the robot  12  and mold manipulator  14  are shown in greater detail. The robot  12  is mounted on the base  30  with the robot arm  28  extending toward the mold  16 . The mold is shown in  FIG. 3  in a horizontal orientation as it would be when transported into the spray booth by the carrier  18 . A counterweight  32  is provided to counter balance the weight of a platform  34 , a platen  36 , and mold  16  as they are tilted by a tilting link  38 . The tilting link  38  is driven by means of a ball screw drive  40  that is connected to the tilting link by means of a carriage  42 . The tilting link  38  is connected to a bracket  44  that is secured to the bottom of the platform  34 . Platform  34  pivots on a platform pivot  46  that allows the mold  16  to be pivoted from 0 to 90 degrees allowing the mold to be manipulated so that it presents a substantial horizontal surface onto which the spray head  26  directs urethane elastomer. By the term “substantially horizontal” it is meant that the surface is at an angle of inclination of less than 30 degrees relative to horizontal. 
     Referring more specifically to  FIG. 5 , with continuing reference to  FIGS. 3 through 4 , the mold manipulator  14  is shown in greater detail. The mold  16  is secured to the platen  36  on which the mold  16  is carried into the spray booth  10 . The platen is precisely located by means of a plurality of shot pin assemblies  48  that are secured to the platform  34  and each engage one of a plurality of shot pin receptacles  50  in the platen  36  when the mold  16  is moved on the platen  36  into the booth  10 . 
     As shown in  FIGS. 3 and 4 , grabbers  52  are provided on opposite ends of the platform  34  to secure the platen  36  and mold  16  to platform  34  as the mold  16  is tilted by the mold manipulator  14 . The grabbers  52  are actuated by means of pneumatic cylinders  54  but could also be operated by means of hydraulic cylinders. The ball screw drive  41  includes a motor  41  that drives the ball screw drive  40  to move the carriage  42 , tilting link  38  and platform  34 . As shown in  FIG. 5 , the platform  34  is in its horizontal orientation and the carriage  42  is in its lowered position. As shown in phantom lines in  FIG. 5 , the platform may be tilted by moving the carriage to the left as shown in  FIG. 5  thereby raising the bracket  44  and platform  34 . 
     Referring now to  FIG. 6 , the robot  12  and mold  16  are shown diagrammatically. The mold  16  includes a mold surface  56  toward which a spray  58  is directed by the spray head  26 . The spray head  26  is secured to the end of the robot arm  28  that forms part of the robot  12 . 
     Referring now to  FIG. 7A , the robot arm  28  is shown with the spray head  26  directing the spray  58  downwardly onto the horizontal portion of the mold surface  56 . Referring now to  FIG. 7B , the mold is shown rotated (clockwise as shown) by the mold manipulator so that a further portion of the mold surface  56  shown in  FIG. 7A  is now arranged in a generally horizontal orientation so that the spray  58  may be directed on that now horizontal portion of the mold surface  56 . In a similar manner, the mold manipulator rotates the mold such that the respective further mold surfaces  56  are presented generally horizontally so that the spray  58  may accordingly be directed on that now horizontal portion of the mold surface  56 . This reduces drips and runs. 
     Referring now to  FIG. 8 , a prior art system is shown operating on the same part shown in  FIGS. 7A and 7B  with the spray  58  being directed toward a vertical target surface portion  62  of the mold surface  56 . When the spray  58  is directed toward the vertical target surface  62  drips/runs  64  form on the lower portion of the vertical target surface. A pool (not shown) of urethane elastomer may accumulate in the lower part of the mold  16  creating an unwanted buildup of urethane elastomer in that area. 
     Referring now to  FIG. 9  the multi axis robot  12  is shown with a mold manipulator  14  in a top plan view. The carrier  18  extends from a loading station  70  through the urethane spray application booth  10  and to a exit station  72 . 
     Referring now to  FIG. 10 , the mold manipulator  14  is shown in a front elevation view. The mold manipulator includes a platen  36  that is secured to the platform  34  by means of the shot pin assemblies  48  and grabbers  52 . The ball screw drive  40  is connected to the carriage  42  that drives the tilting links  38 . The tilting links  38  are connected to a bracket  44  that is secured to the platform  34 . As the ball screw drive  40  is moved toward and away from the robot  12  the platform  34  and platen  36  are pivoted about the platform pivot  46 . The grabbers  52  are moved by pneumatic cylinders  54  to secure the platen  36  to the platform  34  as shown on the left side of FIG.  10  and release the platen  36  as shown on the right side of FIG.  10 . Cylinders  54  are extended to lock the grabbers  52  onto the platen  36 . Cylinders  54  are retracted to release the platen  36 . When the mold  16 , platen  36 , and platform  34  are tilted both of the grabbers  54  are in the position shown on the left side of FIG.  10 . When the mold  16  and platen  36  are indexed through the booth  10  the grabbers  52  are retracted to the position on the right side of FIG.  10 . 
     Referring now to  FIG. 11 , the spray booth  10  is shown in conjunction with the loading station  70  and exit station  72 . The mold manipulator  14  is shown below the urethane spray application booth  10 . Also shown in  FIG. 11  is the filter inlet for the exhaust system  24  of the booth  10 . 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.