Sliding Core Mould Process
Moulds with sliding cores are used to create parts that have hollow cavities or sections. The hollow parts are reinforced with ribs or bosses created during the molding process that make them less prone to developing stress cracks. Sliding core moulds are expensive to make; however, their end products tend to be more stable and of a higher production quality. Sliding core moulds are also called composite injection moulds.
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Two-Stage Process
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The sliding core mould is composed of two halves that contain two or more interior cavities, or openings. During the initial injection stage, the molten plastic or metal is poured into the two halves of the mould. The mould is opened and a part of the mould called a sliding die moves one half of the part being made to a position where the surfaces of the two halves of the part will meet, which is called the "parting-line." Then the mold is shut. During the second injection stage, the "parting-line" is filled with molten metal or plastic. This joins the two halves together to create a single end product.
About Sliding Core Moulds
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The hollow areas of the mould are said to be "closed" when the sliding die is inserted into a cavity and "opened" when the sliding core is removed. Moulds made with holes that are parallel to the mould's "parting-line" have sliding cores that automatically retract from the part when the mould is opened. This type of sliding core mold is more complex and can add to the overall cost of its design and construction. When a mould is made and the hole does not go all the way through a part, or it has holes on more than one side of it, the mould is designed to hold one side of the part so that it is easier to remove.
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Sliding Core Mold Types
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There are three different types of sliding core moulds: a core-back mould, a rotating plate mould and an index mould. The core-back is a type of mould that has molten plastic or metal injected into it in the initial stage. The core-back is closed, meaning the sliding core is inserted into the mould and the initial injection is made. Then its sliding core is pulled out or removed and the second injection is made. The rotating plate method utilizes a two-station tool that rotates the mould in either a horizontal or vertical direction for the first and second stage injections. In the index method, the mould is physically moved while it is being made.
Uses
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Sliding core moulds are used to make products that have two or more integrated parts. These parts can be movable segments or parts that snap together and lock into place. Sliding core moulds are also used to create products made up of two or more different types of materials, such as different kinds of plastic polymers like a toothbrush that has a soft rubber hand grip.
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References
- Minnesota Rubber and Plastics: Designing Plastic Components
- Plastics Today: Sliding Dies for Molding Hollow Part
- Arburg: Composite Injection Moulding
- University of Maryland: Manufacturing of multi-material compliant mechanisms using multi-material molding
- Ticona Engineering Polymers: Manufacturing of multi-material compliant mechanisms using multi-material molding
Resources
- Photo Credit Plastic parts image by Dusi from Fotolia.com
