Injection Molding Mold Parts: Core, Insert, Lifter and Slide introduction

Injection molding is a widely used manufacturing process that involves injecting molten plastic or other materials into a mold cavity under pressure to create a desired shape. The mold itself is a critical component in this process, and it consists of several intricate parts that work together to ensure accurate and efficient production.

In this article, we will delve into the key mold parts: the core, insert, lifter, and slide, explaining their functions, design considerations, and significance in the injection molding process.

Introduction to Injection Molding Mold Parts

Core

The core is a central component of the injection mold that forms the internal cavity or shape of the plastic part. It is typically positioned inside the mold cavity, facing the cavity block (also known as the cavity side), which forms the outer shape of the part. The core must be designed with precision to ensure accurate dimensions and tolerances of the internal features, such as holes, threads, and undercuts.

For more information, please read: Mold Core In Injection Molding

Insert

Inserts are replaceable components within the mold that allow for the customization of the part being produced. They can be designed to create specific features, such as threads, grooves, or complex geometries, that would be challenging to achieve with a solid core alone. The use of inserts not only enhances design flexibility but also extends the life of the mold, as worn or damaged inserts can be replaced without needing to manufacture an entirely new mold.

Lifter

A lifter, also known as an ejector pin or pin ejector, is a small, rod-like component used to eject the molded plastic part from the mold after it has cooled and solidified. Lifters are installed in the mold base and push against the underside of the part, forcing it out of the mold cavity. Lifters typically operate on a sliding mechanism, which is activated during the ejection phase of the molding cycle.

For more information, please read: Injection Mold Lifter Design

Slide

A slide is a specialized mold component used to form undercuts or side-action features in the plastic part. A slide moves laterally within the mold, allowing for the formation of features that cannot be easily pulled straight out of the mold. Slides are particularly useful for creating handles, snaps, or other protruding elements on the part. They are typically mounted on guide pins to ensure smooth operation and accurate positioning. The design of the slide must be carefully considered, as it must withstand the forces generated during injection while also providing a reliable path for part ejection.

For more information, please read: Injection Mold Slide Design

Design Considerations for Injection Molding Mold Parts

1. General Range: The wall thickness in injection-molded plastic parts usually ranges from 0.03 to 0.19 inches (0.76 to 4.83 mm).
2. Thickness Variation: If non-uniform walls are required, the change in thickness should be 15% of the nominal wall and transition gradually.
3. Minimum Radius Requirement: Interior 2.5 mm minimum radius at the 100 mm ball contacting area. Exterior 1 mm minimum radius at the seat belt passing through opening.
4. Corners: Inside corner radii should be 50% of wall thickness, while outside corner radii should be 150% of wall thickness.
5. Ribs or Bosses: Radii at the base of ribs or bosses should be at least 0.25 mm.
6. Rib Height: For ribs over 15 mm in height, use inserts to aid venting. Ribs less than 15 mm in height should have a draft angle greater than 0.5°.
7. Appearance Parts: Non-grained or shallow (0.04 mm depth) A surface: 40% max of wall thickness. Heavy grained A surface: 50% max of wall thickness.
8. Structural Parts: 80% max of wall thickness if sink marks are acceptable.
9. Rib Height: For ribs height more than 15mm, use an insert to help venting.
10. Draft Angle: The draft of ribs height less than 15mm should be bigger than 0.5°.
11. Gate Location: Choose the gate location carefully to minimize flow lines, sink marks, and other defects.
12. Gate Type: Select the appropriate gate type (e.g., sprue gate, edge gate, subgate) based on part geometry and material.
13. Ejection Pins: Use the minimum number of ejection pins necessary to support the part, and ensure they are properly positioned to avoid leaving marks on the part surface.
14. Parting Line: Design the parting line to minimize its visibility and impact on the part’s appearance and function.
15. Undercuts: Avoid undercuts if possible, as they can complicate mold design and increase manufacturing costs. If necessary, use sliding cores or other mechanisms to eject parts with undercuts.
16. Material Selection:  Factor in governmental and private standards for properties such as heat resistance, flammability, and electrical and mechanical capabilities. Approval bodies include Underwriters Laboratories, NSF International, Canadian Standards Association, U.S. Food and Drug Administration, and U.S. Department of Agriculture.

For more information, please read: Injection Molding Design Guide

Conclusion

The core, insert, lifter, and slide are essential components of the injection molding process, each playing a crucial role in producing high-quality plastic parts. Understanding the design considerations and functional requirements of these mold parts is essential for ensuring the success of any injection molding project. With precise design and execution, these components can enable the efficient and cost-effective production of complex plastic parts with excellent dimensional accuracy and surface finish.

Fuquan Chen

This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.