Insert Molding VS Overmolding: Select the Right Manufacturing Process

Insert molding and overmolding are two widely used plastic injection molding processes to combine different materials together to manufacture high quality product parts. However, it’s essential for manufacturers to understand the distinctions between these two methods to maximize product success and profitability. 

What is Insert Molding?

Insert Molding is a plastic injection molding process. In this process, a pre-formed component known as insert is put into the molded plastic and it becomes a unified part of the final product.

Technical Details for Insert Molding Process

What is Overmolding

Overmolding process is a multi-step plastic injection molding process. In this process, you will make a pre-formed component known as substrate and put it in a mold. After that you will inject overmold material, usually a softer thermoplastic or elastomer over the substrate.

Technical Details for Overmolding Process

Similarities between Insert Molding and Overmolding

Multi-Material Integration

Both insert molding and overmolding process allow melit-material integration to manufacture plastic product parts. 

In insert molding, metal insert is integrated into plastics like polycarbonate, ABS, or nylon. In overmolding, soft materials like thermoplastic elastomers (TPE), silicone are applied around the substrate. 

Improve Product Functionality

By injecting metal or ceramic, insert molding can improve the stiffness, wear resistance or increase mechanical strength by up to 30-50% of product parts. 

By applying a material layer on the substrate, the overmolding process can improve the improve grip, sealing capabilities or increase metal bond strength exceeding 30 MPa. 

Injection Molding Basis

Both insert molding and overmolding depend on injection molding technology. The injection molding base processes require high pressure ranging from 5,000 psi to 30,000 psi depending on the selected molding method to ensure proper part formation.. 

Reduced Assembly Steps

Both of the methods can reduce assembly steps as they combine multiple materials in a single process. This eliminates the need of any secondary operations like fastening, welding, or adhesive bonding and saves 20-50% of your assembly time. 

Complex Design Capabilities

Both insert molding and overmolding processes can create product parts with complicated shapes and designs. The dimensional tolerance varies from ±0.001 inches to ±0.005 inches depending on the part size, design complexity and choosen molding process. 

Difference Between Insert Molding and Overmolding

Process Sequence

Insert Molding: In insert molding, you will place the pre-formed insert within the mold cavity and to fix the insert in one place with locate features like pins, undercuts, or snap-fit mechanisms. Then, inject the molten plastics around the insert. 

Overmolding: Overmolding process requires two steps to complete. First, conduct the molding process to create a substrate. In the second step, put the substrate into a mold cavity and inject material over the substrate.

Material Selection

Insert Molding: Materials like steel, brass, aluminum are used to produce the insert. And the molten plastic is typically made from high-performance engineering thermoplastics like nylon, or polycarbonate (PC) to enhance thermal resistance and stiffness. 

Overmolding: Substrate is normally made from rigid plastics like ABS, PP, PC or metal to improve the structural integrity. And the overmold is typically made from a soft, flexible thermoplastic material like TPE, silicone, or TPU to improve sealing properties, grip and flexibility. 

Material Compatibility and Bonding

Insert Molding: Insert molding creates mechanical bonding between the materials. To improve the bond and create physical lock between material features like grooves, holes, or knurls added in the insert. 

Overmolding: Overmolding injection processes mainly create chemical  bonds between substrate and overmold material. However, mechanical interlocking can work as a supplementary mechanism between materials. 

Applications

Insert Molding: Insert molding mainly used to create parts that require high electrical conductivity, strength, structural integrity, wear and thermal resistance. Some of the common uses of insert molding is in creating medical devices, mechanical connectors and electrical housings.

Overmolding: Overmolding process is mainly used to improve aesthetic, sealing, grip and soft finish in product parts. Some of the common use of overmolding is in creating consumer products, automotive parts like trim components, medical devices like wearable electronics. 

Design Flexibility

Insert Molding: Insert molding design flexibility is limited because of  geometry and size of the premade insert. As insert’s features and dimensions are rigid, it’s not perfect for creating multi-layer surfaces designs.

Overmolding: Overmolding is more suitable for complex geometries as it allows more flexibility. In this process, you can apply overmold material over the substrate in different ways that allows you to create multi-material combinations and also add decorative elements.

Injection Pressure and Temperature

Insert Molding: Insert molding requires higher injection pressure typically ranging from 15,000 to 30,000 psi to ensure proper molten plastic flows around the insert. The temperature will be also high typically ranging from 200°C and 300°C depending on the materials.

Overmolding: Overmolding requires lower temperature typically ranging from 8,000 to 20,000 psi to prevent obstructions from applying secondary material. The temperature will also be low typically ranging from 180°C and 230°C to protect substrate from any damage. 

How to Select the Right One

Here are the some criteria you can analyze before selecting between Insert molding and overmolding:

Design Consideration

Insert Molding: If your product needs more structural integrity and metal insert for structural and complex geometry, insert molding will be the right choice. 

Overmolding: If your product needs a soft-touch surface, multi-material combination or multi-layer, then the overmolding process will be the right choice.

Production Volume and Cost Consideration

Insert Molding: The initial cost is high for insert molding because of its complex mold design and insert placement. Insert design is more suitable for high volume production to offset tooling cost and cycling time. 

Overmolding: The initial tooling cost is lower in the overmolding process but the cost of material can vary depending on the application. Overmolding process is more suitable for low to medium volume production.

Product Part Performance

Insert Molding: If your product needs high mechanical load, durability and mechanical strength then insert molding perfect as premade insert increases mechanical performance. 

Overmolding: But if you need additional functionality in your product part like impact resistance, waterproofing or absorption then overmolding will be the best choice.

Thermal and Electrical Properties

Insert Molding: Insert molding process is suitable for product parts that require high thermal and electrical properties like heat sink, electrical connectors. 

Overmolding: Overmolding process is suitable for product parts that need electrical insulation or thermal shielding like consumer electronics, medical devices.

Bottom Line

Insert molding and Overmolding processes both have their unique advantages and challenges. However, as a manufacturer you must select the injection molding process that is most suitable to your product requirements, budget, production volume and manufacturing strategy. 

Tuling’s Insert Molding and Overmolding Services

Tuling offers both insert molding and overmolding services for producing product parts to meet your specific needs. Our expert team can help you to select the right process. Contact us to discuss your project requirements.