WO2002020243A1

WO2002020243A1 - Method and apparatus for determining variation in a molding process

Info

Publication number: WO2002020243A1
Application number: PCT/US2001/028251
Authority: WO
Inventors: Roger R. Budnick
Original assignee: Patent Holding Company
Priority date: 2000-09-08
Filing date: 2001-09-10
Publication date: 2002-03-14
Also published as: AU2001290714A1

Abstract

A method and apparatus for determining whether a molding process variation has occurred is disclosed. An indicating device includes first (38) and second (40) body portions that are movable relative to each other and define a hollow chamber, the hollow chamber (44) communicating with an article defining cavity (16) of the mold. A plurality of indicia (48) are formed in at least one of the body portions (38, 40) that are visible when the body portions are separated from each other. The hollow chamber (44) is sized so that for each first iteration of a molding process for a given batch of a moldable material, an amount of the moldable material flows into the hollow chamber (44) and covers a particular number of indicia. Molding process variations are determined is subsequent iterations of the molding process by determining whether the moldable material has covered a number of indicia (48) other than the particular number of indicia (48).

Description

METHOD AND APPARATUS FOR DETERMINING VARIATION IN A MOLDING PROCESS

Field of the Invention The present invention generally relates to various types of molding processes and, more particularly, to a method and apparatus for determining whether a molding process variation has occurred.

Background of the Invention There are numerous types of molding processes that currently are in use today. Examples of such molding processes include die casting, injection molding, compression molding, reaction injection molding, sheet molding, and blow molding. Such molding processes are utilized to manufacture a variety of articles. An air bag cover for use in an automotive application is an example of an article that is manufactured by an injection molding process. U.S. Patent No. 5,776,522 discloses an apparatus for making an air bag cover having a hidden tear seam. A molten thermoplastic material is injected into a mold cavity of a mold that has a shape defining the air bag cover. An insert having a shape defining a tear seam is inserted into the mold cavity before the thermoplastic material completely solidifies. The resulting air bag cover is then cooled to a temperature beneath the softening point of the molten resin. U.S.

Patent Nos. 5,868,988 and 6,050,594 are related to U.S. Patent No. 5,776,522 and disclose various aspects of air bag cover technology. U.S. Patent Nos. 5,776,522, 5,868,988, and 6,050,594 are incorporated by reference into this application as if fully set forth herein. An air bag cover typically is manufactured to have a predetermined tear strength. Proper tear strength is an important characteristic for an air bag cover because the air bag cover must be formed to tear at the appropriate time in an air bag deployment cycle so that the air bag is properly deployed. When an air bag cover is manufactured by a molding process such as injection molding, various factors must be taken into account in order for the air bag cover to be formed with the requisite tear strength. Such factors include pressure, temperature, and the volume of the article defining cavity of the mold. A variation in any one of these parameters during the injection molding process may cause the air bag cover to be unsatisfactory in a number of different ways. For example, an injection molding process variation may cause the air bag cover to be aesthetically unacceptable or may cause the air bag cover to have an improper tear strength. Typically, an operator monitors the injection molding manufacturing equipment and performs a visual inspection to determine whether a molding process variation has occurred. Such inspections typically are performed on a relatively large batch of air bag covers. If any of the air bag covers are unsatisfactory, then the entire product run usually is discarded. Such visual inspection techniques generally are suitable for their intended purposes. However, utilization of such techniques may not afford the ability to spot defects that are not visually apparent to the naked eye. Also, due to cost and time constraints, such techniques are not useful for inspection of each air bag cover as it is manufactured.

Summary of the Invention

It is desirable to provide an improved method and apparatus for determining whether a molding process variation has occurred. According to an aspect of the present invention, an indicating device includes first and second body portions that are utilized in conjunction with the first and second mold halves of a mold, the body portions defining a hollow chamber. The hollow chamber communicates with an article defining cavity of the mold. A plurality of indicia are formed in at least one of the body portions that are visible at least in an open position of the mold. The hollow chamber is sized so that for each first iteration of a molding process for a given batch of a moldable material, an amount of the moldable material flows into the hollow chamber and covers a particular number of indicia. Molding process variations are determined in subsequent iterations of the molding process by determining whether the moldable material has covered a number of indicia other than the particular number of indicia covered in the first iteration of the process.

Providing such a method and system has a number of distinct advantages. First, labor costs associated with manufacturing articles by a molding process are decreased because after a person skilled in the art of the molding process determines the number of indicia that are covered by a moldable material in a first iteration of the molding process for a given batch of a moldable material, persons not skilled in the art of the molding process may be utilized to monitor each subsequent iteration of the molding process. Second, material costs are reduced because monitoring of each iteration of a molding process allows the molding process to be stopped immediately after a molding process variation has been determined.

Other features and advantages of the invention will become apparent from the description that follows.

Description of the Drawings Fig. 1 is a view, partially broken away and in cross-section, of an indicating device of the present invention and a mold with which the indicating device may be utilized;

Fig. 2A is cross-section of the indicating device shown in Fig. 1 taken along lines 2A-2A; and

Fig. 2B is a cross-section of the indicating device shown in Fig. 2 A taken along lines 2B-2B.

Detailed Description of the Invention Referring to Fig. 1, a mold is illustrated generally indicated at 10 that may be used in a gas-assisted injection molding system. The mold 10 includes a first mold half 12 and a second mold half 14. The first and second mold halves 12 and 14, respectively, are movable relative to each other between an open position and a closed position as shown in Fig. 1. The first and second mold halves 12 and 14, respectively, define an article-defining cavity 16. The second mold half 14 includes a gas passageway 18 that extends from an exterior surface (not shown) of the second mold half 14 to an inner interior surface 20 of the second mold half 14 in fluid communication with the article defining cavity 16.

The second or stationary mold half 14 includes a sprue 22 for communicating thermoplastic material to a runner 24 that, in turn, communicates with the article-defining cavity 16 via a gate 26. A thermoplastic flow path is defined by the sprue 22, the runner 24 and the gate 26. Article ejector pins 28 are extendable through the first or movable mold half 12 to eject a completed part. The mold includes a gas pin assembly, generally indicated at 30. Reference is made to U.S. Patent No. 6,053,720 for further details of the gas pin assembly 30. The content of U.S. Patent No. 6,053,720 is incorporated by reference into this application as if fully set forth herein.

Referring to Fig. 1, an indicating device 32 is shown that communicates with the article defining cavity 16 via a runner 34. Alternatively, indicating device 32 may communicate with runner 24 via runner 34. A vent 36 is provided in the indicating device 32 so that any air that is displaced by the introduction of a moldable material into the indicating device 32 during an iteration of a molding process is vented to atmosphere.

Indicating device 32 includes first and second body portions 38 and 40 that are detachably coupled to the first and second mold halves 12 and 14 by conventional attachment techniques such as a welding operation or by a screw and bolt connection. Alternatively, the first and second body portions may be integrally formed as a portion of the first and second mold halves 12 and 14. In the latter case, the body portions 38 and 40 may be machined directly into the mold halves 12 and 14. Referring to Fig. 2A, a sectional view of the indicating device 32 is shown taken along lines 2A-2A in Fig. 1. Fig. 2B is a sectional view of the indicating device 32 taken along lines 2B-2B of Fig. 2A. A gate 42 allows a moldable material to flow from the runner 34 to the hollow chamber 44, a lower portion of which is shown in Figs. 2A and 2B. A plurality of generally equally spaced divisions or scribe lines 46 are formed in the second body portion 40. A plurality of indicia 48 are formed in an inclined surface 50 (Fig. 2B) defined in the second body portion 40. Indicia 48 are visible at least in an open position of the mold 10. In the illustrated embodiment of the invention, nine scribe lines 46 and ten indicia 48 are utilized. The indicia 48 are formed in second body portion 40 in mirror image format so that the flash that is created by the introduction of a moldable material into the hollow chamber 44 during an iteration of a molding process is imprinted with a plurality of the indicia. It should be understood that a change in any variable relating to the particular molding process utilized changes the number of indicia that are covered by the moldable material. In this case, images corresponding to the indicia 48 are formed in the flash that are easily read by an operator. Alternatively, the indicia 48 may be formed in second body portion 40 in a readable, non-mirror image format so that an operator may read the number of the indicia 48 that are not covered by a moldable material. The gate 42 and the hollow chamber 44 are sized so that during each iteration of a molding process, at least some moldable material flows into the hollow chamber 44 to cover a number of the indicia 48, and no moldable material flows out of the vent 36. Referring to Fig. 2B, gate 42 is generally parallel to a longitudinal axis of the indicating device 32. Inclined surface 50 is formed at a predetermined angle with respect to the longitudinal axis. Overall, the indicating device 32 is sized to minimize the flash created in the hollow chamber 44 and to allow indicia 48 to be easily read by an operator.

The indicating device 32 is utilized to determine whether a molding process variation has occurred as discussed in greater detail hereafter. It should be understood that the indicating device 32 may be utilized in connection with any molding process such as die casting, injection molding, compression molding, reaction injection molding, sheet molding, and blow molding.

In operation, the first and second body portions 38 and 40 are mounted to the first and second mold halves 12 and 14. A moldable material such as a thermoplastic resin is inserted into the article defining cavity 16, for example through sprue 22, during a first iteration of the molding process for a given batch of a moldable material. This causes at least some of the moldable material to flow into the hollow chamber 44 and cover a number of the indicia 48. The particular number of indicia 48 that are covered by the moldable material is recorded by an operator typically skilled in the art of the particular molding process that is being utilized at the time.

The operator may then monitor each iteration of the molding process, or may instruct another who may be unskilled, as to the number of indicia 48 that should be covered by a moldable material during each subsequent iteration of the molding process. Should the operator or worker determine that a number of indicia 48 other than the predetermined number has been covered, that other number provides a signal or indication that a molding process variation has occurred. Upon such signal or indication, the cause of the variation may be investigated. While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is considered as illustrative and not restrictive in character, it being understood that all changes and modification that come within the spirit of the invention are desired to be protected.

Claims

What is claimed is:

1. An indicating device for providing a visual indication of a molding process variation with respect to a given batch of a moldable material portions of which are utilized in iterations of a molding process to form an article during each successive iteration of the molding process, said indicating device to be utilized in conjunction with a mold having a first mold half and a second mold half that are movable relative to each other between an open position and a closed position, the mold halves defining an article defining cavity in the closed position of the mold, the article defining cavity being adapted to receive a portion of the moldable material during each iteration of the molding process, said indicating device comprising: first and second body portions that are movable with respect to each other and define a hollow chamber, said hollow chamber being adapted to be placed in communication with the article defining cavity in the closed position of the mold so that the insertion of a moldable material into the article defining cavity during an iteration of the molding process causes at least some moldable material to flow into said hollow chamber; a plurality of indicia formed in at least one of said first and second body portions that are visible when said first and second body portions are separated from each other; and said hollow chamber being sized so that for each first iteration of the molding process for a given batch of moldable material, an amount of the moldable material flows into said hollow chamber to cover a particular number of said indicia, wherein a molding process variation is determined in subsequent iterations of the molding process by determining whether the moldable material has covered a number of indicia other than said particular number of indicia.

2. The indicating device of claim 1 wherein said hollow chamber includes a vent that allows air that is displaced by the moldable material that is inserted into said hollow chamber during an iteration of the molding process to be vented to atmosphere.

3. The indicating device of claim 1 wherein the moldable material comprises a thermoplastic material.

4. The indicating device of claim 1 wherein the article to be formed by the molding process comprises an air bag cover.

5. The indicating device of claim 1 wherein the molding process is selected from a group consisting of: die casting, injection molding, compression molding, reaction injection molding, sheet molding, and blow molding.

6. The indicating device of claim 1 wherein said first and second body portions are to be integrally formed as a portion of the first and second mold halves, respectively.

7. The indicating device of claim 6 wherein said first and second body portions are to be machined in the first and second mold halves, respectively.

8. The indicating device of claim 1 wherein said first and second body portions are to be detachably coupled to the first and second mold halves, respectively.

9. A method of determining whether a molding process variation has occurred, said method comprising the steps of: providing an indicating device in conjunction with a mold having a first mold half and a second mold half that are movable relative to each other between an open position and a closed position, said mold halves defining an article defining cavity in a closed position of said mold, said indicating device comprising first and second body portions that are movable relative to each other and define a hollow chamber, said hollow chamber being placed in communication with said article defining cavity in the closed position of said mold, a plurality of indicia being formed in at least one of said first and second body portions that are visible when said first and second body portions are separated from each other; inserting a moldable material into said article defining cavity during a first iteration of said molding process for a given batch of a moldable material to cause at least some of said moldable material to flow into said hollow chamber; determining the number of said indicia that are visible after the moldable material has flowed into said hollow chamber during said first iteration of said molding process; and determining whether a molding process variation has occurred during subsequent iterations of said molding process by determining whether the number of visible indicia that are not covered by said moldable material during said subsequent iterations of said molding process is different than the number of visible indicia during said first iteration of said molding process.

10. The method of claim 9 wherein said hollow chamber includes a vent that allows air that is displaced by said moldable material during an iteration of said molding process to be vented to atmosphere.

11. The method of claim 9 wherein said moldable material comprises a thermoplastic material.

12. The method of claim 9 wherein the article to be formed by said molding process comprises an air bag cover.

13. The method of claim 9 wherein said molding process is selected from a group consisting of: die casting, injection molding, compression molding, reaction injection molding, sheet molding, and blow molding.

14. The method of claim 9 wherein said first and second body portions / are integrally formed as a portion of said first and second mold halves, respectively.

15. The method of claim 14 wherein said first and second body portions are machined in said first and second mold halves, respectively.

16. The method of claim 9 wherein said first and second body portions are detachably coupled to said first and second mold halves, respectively.