Manufacturers utilize a range of techniques to overmold, seal, and protect cables and electrical connectors from environmental factors such as moisture, dust, debris, vibration, and strain. The two dominant overmolding methods are "low-pressure" and "high-pressure." Each method has its set of benefits and drawbacks, and the choice largely depends on the specific electrical assembly and its application.

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The Overmolding Process Demystified

Both high-pressure and low-pressure overmolding techniques follow a similar process. The process begins with the melting of adhesive thermoplastic polyamide materials in a large hopper. Subsequently, cable and connector components are placed in an enclosed mold. Molten material is then injected into the mold, encapsulating the cable and connector and resulting in a unified product.

Unpacking High-Pressure Overmolding

High-pressure overmolding, true to its name, involves injecting molten material into the mold at elevated temperatures (185-300+°C) and high pressures (approximately 25,000 PSI). The higher pressure enables faster injection times, allowing manufacturers to produce more overmolded cables efficiently. The material viscosity in high-pressure overmolding is similar to taffy (around 5 grams over 10 minutes).

Common Applications:

- PCB housings
- Plastic parts
- Medical devices
- Auto dashboards

Pros:

- Fast cycle times
- High efficiency
- Enhanced durability
- Ideal for large-volume orders

Cons:

- Higher melt temperatures and pressures may damage delicate electrical components.
- Material viscosity may shear off components.
- Faster fill rates can result in flaws or "molded-in stresses," uniformity issues, flow-front hesitation, and other quality, performance, and aesthetic problems.

Low-Pressure Overmolding: A Gentle Approach

Low-pressure overmolding involves injecting molten material into a mold cavity at lower temperatures (180-220°C) and pressures (around 100 PSI). This method is particularly suitable for delicate electrical equipment like sensors and PCBs, which are susceptible to damage when exposed to higher pressures and temperatures. Low-pressure overmolding uses low-viscosity polyamide resins, with a consistency akin to syrup (2,000–10,000 mPa·s (cP)), allowing effective filling of intricate and hard-to-reach cavities without additional pressure. Consequently, manufacturers can create thinner walls with minimal freeze-off.

Common Applications:

- PCBs
- Sensors
- Switches
- Batteries

Pros:

Contact us to discuss your requirements for low pressure overmolding materials. Our experienced sales team can help you identify the best options for your needs.

- Gentler on delicate electronics
- Greater consistency
- High precision for complex designs
- Better aesthetics
- Eliminates flow-front hesitation

Cons:

- Slower cycle times (relative to high-pressure molding)
- Less durability (compared to high-pressure molding)

General Advantages of Pressure Molding:

- Lower ownership costs
- Reduced material usage
- Smaller equipment and operational footprint
- Shorter cycle times per part
- Fewer manufacturing steps
- Environmentally friendly
- Higher quality outcomes
- Excellent resistance and protection

Nonetheless, injection molding remains the superior manufacturing technique for overmolding electrical cables and connectors when compared to alternatives like potting, which demand more resources, time, equipment, and steps to create a less durable product.

Insert Molding vs. Overmolding – What’s the Difference?

Unsure of the difference between insert molding and overmolding? Here is an explanation.

According to Thomas Net:

"Overmolding is an injection molding process that creates parts from two or more materials. It is sometimes referred to as 'in-mold assembly.' Overmolding is broadly categorized into two processes: insert molding and multiple-shot molding. Insert molding is typically used to add metal features to plastic parts, like threaded bosses, but it also describes coating any preformed object with plastic via injection molding. Multiple-shot molding creates plastic parts from multiple materials, such as polypropylene and silicone rubber, during a single molding process to enhance external characteristics like impact resistance and texture. This article delves into both processes, discussing when one might be chosen over the other.

Insert Molding
"Insert molding involves adding usually metal parts to injection molded parts during the molding process rather than post-molding, reducing post-molding manufacturing/assembly tasks. Inserts are placed manually or automatically onto mold cores integrated into the molds. Once the mold halves close, plastic pellets are melted in the injector barrel and injected into the mold, encapsulating the inserts in the plastic material. After the plastic solidifies, the parts are ejected with the inserts now embedded. Insert molding is a single-shot process. Inserts are often threaded nuts for later assembly, but they can also be bushings, sleeves, pins, blades, or even non-metallic parts. Standard inserts come from several manufacturers, many featuring knurled outer surfaces for better adhesion to the plastic.

"Insert molding also refers to overmolding an additional layer of plastic or rubber material onto an existing part. Here, the part is placed into a single-shot mold where the overmold material is injected around it. Single-shot overmolding uses a preformed substrate and a single-barrel injection molding machine to add another material layer to the product.

Double Shot Overmolding
"Plastic overmolding, also known as two-shot or multi-shot molding, adds materials like thermoplastic elastomer (TPE) to plastic substrates, improving aesthetics, handling, grip, impact resistance, and environmental resistance. This multi-shot process is performed by multi-barrel injection molding machines, wherein additional material is added shortly after the substrate forms to ensure strong bonds between the materials. Plastic overmolding eliminates steps in the manufacturing process while enhancing injection molded products.

"Depending on selected substrate and overmold materials, bonds may be achieved chemically or mechanically (using undercuts, for example). Various charts detail the compatibility of different substrate and overmold materials for chemical adhesion. Often, mechanical bonding supplements any chemical bonding. Common substrate materials include polycarbonate, ABS, HDPE, and nylon. Overmold materials comprise thermoplastic polyurethane (TPU), styrene-ethylene/butylene-styrene copolymer (SEBS), thermoplastic rubber (TPR), thermoplastic vulcanite (TPV), and others.

Applications
"Insert molding is commonly used to produce connectors, electronic sockets, and more, in addition to parts assembled with threaded fasteners. It provides soft grips on tools like screwdrivers and surgical instruments.

"Multi-shot overmolding has numerous applications in high-volume personal products like toothbrushes and disposable razors and high-value items such as medical instruments, where it enhances grip, cleanability, and moisture protection. Delicate electronic circuits can be overmolded using a two-step process that first encapsulates the circuit in low-melt-temp resin before adding a higher-temperature protective shell. Automobile manufacturers use overmolding to reduce additional assembly steps requiring adhesives. A typical use is a plastic engine part with an overmolded elastomer seal.

"Many injection molding companies provide both insert molding and two-shot overmolding. Given the cost of specialized multi-shot machinery, two-shot overmolding is typically employed for high-volume production where high capital costs are offset by reduced labor expenses. Generally, multi-shot molding is economically viable at volumes of 250,000+ parts per year. Sometimes, two-shot molding is the only method to achieve an acceptable bond between different materials.

"A common misconception in overmolding soft grips is attributing final product softness solely to the overmold material. The thickness of the applied layer significantly impacts feel, as too thin a layer will allow the harder substrate to affect the softness perceived from the top coat.

"Overmolding is complex, with numerous variables and the potential to replicate errors across countless injection-molded copies. Consulting companies that provide overmolding services in the early design stages can help avoid various pitfalls that could hinder successful part creation.

"When designing for overmolded parts, several guidelines apply: Overmold edges should not feather but end abruptly and at full thickness against a stop or indentation. Surface texture on the overmold aids in mold release, provides a softer feel, and conceals molding process flaws. Ample draft angles also help with mold release. Mold designers need to give careful attention to gate and vent design."

Summary
"This article provided an overview of the differences between insert molding and multi-shot overmolding. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to find potential suppliers or view details on specific products."

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