The present invention relates to the injection molding of plastic products, particularly thin walled plastic products.
The manufacture of plastic products and components by injection molding techniques is common today. Plastic products and plastic components constitute a major part of numerous consumer products in common use, including houseware products, components for vehicles, sports and leisure products, and the like. The large size of many components, however, as well as complex exterior configurations, often causes difficulties in the injection molding process. Common problems include warpage, shrinkage, non-uniform color, sink marks, and knit line issues.
Also, in efforts to reduce material costs and increase production, particularly relative to plastic products which are made in large quantities, efforts have been made to reduce the wall thicknesses wherever possible. Thinner walls result in the use of less plastic material which can result in significant savings. Material costs are often the largest part of the cost of plastic injection molded parts and components. Also, the thinner the plastic parts, the faster the cooling time and thus the faster the cycle time. This results in increased production over a given time period, also resulting in decreased manufacturing costs.
The efforts to reduce the thickness of walls and other portions of plastic injection molded components, however, have often not been satisfactory. One or more of the common problems mentioned above often result from these attempts. Thus, there is a need for improved manufacturing and processing techniques in the plastic injection molding field for producing parts and components which have thin wall sections, as well as a need for an improved process and system for creating thinner wall sections on existing plastic products.
It is an object of the present invention to provide an improved process and system for the manufacture of plastic injection molded parts and components. It is another object of the present invention to provide a commercially acceptable plastic injection molded manufacturing process and system which can produce products or portions of products which have thinner walls.
It is a further object of the present invention to provide an improved plastic injection molding process and system which reduces the expense of existing processes and systems. It is an additional object of the present invention to provide a plastic injection molding process and system which has improved efficiency and economy.
It is a still further object of the present invention to provide a plastic injection molding process and system which creates thin-walled parts and components without experiencing the common problems which typically affect such processes and systems.
These objects are achieved by the present invention which overcomes the problems commonly experienced with present systems and processes which attempt to manufacture plastic injection molded parts with thin wall sections. In accordance with a preferred embodiment of the invention, a mold is provided with a cavity in the size and shape of the final product. A moveable plunger or piston member is provided in one of the mold halves and operated to narrow the plastic part at substantial portions of its area. Preferably, the molded product has a thinner wall portion over 70-75% or more of its total surface area.
In alternate embodiments, two or more piston members could be provided which could form thin areas in separate or contiguous areas. In addition, opposed piston members in both halves of the mold could be provided.
The present invention has particular use in providing thin wall sections or portions of plastic injection molding products. The manufacture of plastic parts and components is in common use today and significant savings can be created, particularly in large volume production, if the walls or portions of the products can be made thinner, thus utilizing less plastic material and decreasing the cycle time. The cost of the plastic material is often one of the largest costs, if not the largest cost, in the production of plastic parts and components. For example, a savings and material cost on the order of 10 cents per part relative to parts which are produced on the order of several hundred thousand a year could result in a savings of over a million dollars a year alone, simply by reducing the thickness of one or more portions of the parts.
One preferred use of the present invention is in the production of plastic interior door panels for automobiles and other vehicles. A schematic diagram of an interior door panel of that type is shown schematically in
Also, the preferred plastic material for producing interior door panels today is polypropylene. The present invention thus has particular use with the manufacture of plastic parts and components from that material. However, it is also to be understood that the present invention is not limited to the use of polypropylene, but can be used with all types and kinds of plastic materials which are in use today.
In the door panel 10 shown in
Also, the thin wall area 12, as shown in
Using present techniques for attempting to reduce the portions of plastic products to make wall sections or portions on the order of 2.5 millimeters thickness or less, the processes typically cause significant stress in the parts making them commercially unacceptable for large scale production. Also, these attempts have created color issues in the manufactured parts, with the color not being uniform throughout. Further, the knit lines where the injected plastic flows meet within the mold cavity have not been of sufficient commercial quality. Areas in which knit lines are often unacceptable with present commercial products are indicated by the reference letter A in
With use of the present invention, the plastic parts and components are also lighter in weight, making them easier to handle, both manually and automatically, in the production process. Also, portions of the thinner areas 12 in the door panel can be covered with carpeting or other decorative trim and components.
Two of the steps in the process according to a preferred embodiment of the present invention are shown in
As shown in
The location for the injection of the plastic material into the mold cavity is typically a matter of choice to the molder or mold maker. For example, the plastic material could also be injected into the mold cavity through sprue areas 50A and/or 50B from sources 52A and/or 52B, respectively, as shown in phantom lines in
Once the requisite quantity of plastic material has been injected into the mold cavity, or substantially injected into the mold cavity, the piston or plunger member 30 is moved to the position as shown in
Movement of the plunger member 30 to the position shown in
It is to be understood that the degree of movement of the plunger/piston member 30 in
Another embodiment illustrating use of the present invention is shown in
Although the embodiments shown herein utilize a plunger or piston member to form the thin wall sections, it is also possible within the scope of the invention to use other mechanisms for accomplishing that same result, such as a molding press.
It is also possible to vary the speed of the movement of the plunger/piston member in the mold. The speed of the movement of the plunger/piston member can be dependent upon many factors, including the type of plastic material utilized, the time delay between injection of the plastic material and movement of the piston member, and the resultant commercial quality of the resultant parts or components. The speed of the plunger/piston member can be determined on a case-by-case basis.
Thereafter, the plastic material forming the molded part is allowed to cool and solidify sufficiently in order for the part to be ejected from the mold cavity. This is shown in Box 88. Thereafter, the mold is opened and the part is ejected 90. The ejection is typically aided by the use of one or more ejector pins (not shown). Subsequently, the mold is closed and the cycle is repeated.
In alternate embodiments, two or more plunger members could be provided in the mold. The plunger or piston members could be positioned in the mold in order to provide thinner wall sections at separated or contiguous areas. Plunger or piston members could also be positioned in both mold halves which could provide thinner wall sections in separate areas or in the same area opposed to one another. Any combinations of plunger or piston members in the same and/or opposed mold halves could be provided.
Examples of some of these alternate embodiments are shown in
In
While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms, processes and procedures which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the methods and apparatus described without departing from the spirit and scope of the invention as defined by the appended claims.