Threaded inserts for plastics’s common problems and solutions
Injection molded insert fasteners are a type of connecting element that permanently fixes metal or non-metal inserts into plastic parts through the injection molding process. They are widely used in plastic components that require high strength, removability or special functions. The following is a detailed description:
Definition of Threaded Inserts for plastics
– Insert fasteners: usually threaded sleeves, nuts, pins, etc. made of metal (such as copper, steel, aluminum alloy) or high-strength engineering plastics, embedded in the injection molded parts.
– Process combination: The molten plastic is wrapped around the insert through injection molding, and an integrated structure is formed after cooling.
Main uses of Threaded Inserts for plastics
– Enhance mechanical properties: provide areas of threaded connections, load-bearing or wear-resistant (such as screw holes, bearing positions).
– Simplify assembly: avoid secondary processing (such as tapping) and directly achieve threaded connections.
– Electrical connection: metal inserts are used for electrical conduction or grounding.
– Lightweight design: replace all-metal parts to reduce weight (such as automotive and aviation parts).
Typical application scenarios of threaded inserts for plastics:
– Electronic equipment housing (such as mobile phone screw posts)
– Automotive interior parts (seat adjustment knobs)
– Home appliances (washing machine barrel connectors)
– Medical devices (detachable disinfection parts)
Process steps of threaded inserts for plastics
- Insert pretreatment:
– Cleaning (degreasing, sandblasting) or heating (reducing thermal stress).
– Surface treatment (knurling, grooves) to enhance bonding.
- Insert positioning:
– Use mold positioning pins or clamps to fix the insert to prevent displacement.
- Injection molding:
– Place the insert in the mold cavity and inject molten plastic to wrap the insert.
- Cooling demolding:
– Control the cooling rate to avoid stress cracking.
Key considerations of threaded inserts for plastics
– Design phase:
– Inserts should have anti-rotation features (e.g. knurling, hexagonal edges).
– Plastic wall thickness should be uniform to avoid sink marks (usually ≥ 0.5 times the outer diameter of the insert).
– Material selection:
– The coefficient of thermal expansion (CTE) of the insert and plastic should be as close as possible (e.g. nylon with stainless steel).
– Heat-resistant inserts should be selected for high-temperature plastics (e.g. PEEK).
– Process control:
– Excessive injection pressure/temperature may cause insert displacement or plastic degradation.
– Rapid cooling may cause stress cracking at the bonding interface.
– Quality inspection:
– Check insert position accuracy (X-ray or CT scan).
– Pull-out test to verify bonding strength.
Common Problems and Solutions of Threaded inserts for plastics
– Loose inserts: Increase surface roughness or use ultrasonic embedding instead.
– Plastic cracking: Optimize cooling rate or choose plastic with better toughness (such as PC instead of ABS).
– Thread damage: Use protective sleeves or mold internal thread ejection design.
Through reasonable design, material selection and process control, injection molded insert fasteners can significantly improve product functionality and reliability, but it is necessary to balance cost and performance requirements.
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