A Case Study in Complex Assembly – Silicone, Plastic, Metal & Finishing

Project Overview – Customizing 9 Components and assembly with Tight Tolerances

A US‑based DIY jewelry brand approached us with an ambitious necklace design comprising 9 distinct parts, of which 7 required full customization (only the forcep and PP packaging box were off‑the‑shelf). They provided 2D engineering drawings for each custom component and required complete assembly before shipment.

The parts included:

• 2 silicone rings
• 2 silicone magnet sleeves
• 1 plastic connector (PP + PA composite)
• 1 decorative metal plate (high‑gloss finish)
• 1 custom spring gate carabiner
• 1 existing forcep
• 1 standard PP box

Challenge

The core difficulty lay not in any single part, but in the synchronisation of three fundamentally different materials—each with its own processing constraints—and their final integration into a durable, wearable chain that meets tensile strength and user‑comfort criteria.

Our Engineered Solutions – Material by Material

🔹 Silicone Components – Hardness Tuning & Magnetic Integration

The product contains four silicone parts with distinct hardness requirements. We tackled two critical issues:

• Silicone rings (softness & stretch) – Through iterative hardness testing, we balanced wear comfort with tensile strength, ensuring the rings remain flexible yet robust enough for daily use.
• Silicone magnet sleeves (over‑molding with magnets) – The key challenge was preserving magnetic strength during the over‑molding process, while achieving a tight, permanent bond without damaging the magnet. Our solution:
• Evaluated multiple adhesives and structural adjustments;
• Selected a high‑viscosity, specialty glue that bonds securely;
• Redesigned the magnet‑enclosure geometry to increase contact surface while keeping the magnet visible (aesthetic requirement), so that the magnetic force remains uncompromised.

🔹 Plastic Connector – Over‑Molding PP with PA (Tiny Dimensions)

The connector is a small‑sized over‑molded part combining polypropylene (PP) and nylon (PA)—two materials with vastly different shrinkage and flow characteristics. This made process control extremely challenging.

Our approach:

• Designed custom precision fixtures to hold the minuscule base part during over‑molding, preventing any shift;
• Fine‑tuned injection parameters to guarantee consistent dimensional accuracy and positional alignment across every production batch;
• Achieved a structurally sound bond without flash or deformation, even at such a small scale.

🔹 Metal Decorative Plate – High‑Gloss Finish & Magnetic Performance

The metal plate must be visually brilliant (glossy) and simultaneously highly responsive to magnetic attraction—since it interacts with the magnet‑embedded silicone sleeves. Material selection and surface treatment were decisive.

• We compared DT4C (pure iron) and SPCC (cold‑rolled steel).
• DT4C offers excellent magnetic properties but is costlier and more challenging for surface preparation.
• SPCC, after stamping and high‑gloss painting, delivered the required shine while maintaining sufficient magnetic strength—at a lower material cost.
• We also implemented strict pre‑treatment quality control to ensure paint adhesion and consistent magnetic performance after coating.

Full Assembly & Performance Validation – Pull Strength & Durability

All 7 custom parts, together with the standard pliers and spring, are assembled into a complete necklace chain. We conducted rigorous pull‑force and tensile tests throughout development and pilot production to verify:

• The overall chain strength under daily wear conditions;
• The retention force of magnetic connections;
• The resistance to separation or breakage at stress points.

Every assembly passed our quality gates, guaranteeing a reliable, comfortable, and visually appealing final product.

Outcome – A Seamless Sourcing Success

This project vividly demonstrates our capability as a full‑service sourcing partner that can:

• Manage multiple material streams (silicone, engineering plastics, ferrous metals) under one roof;
• Solve complex over‑molding and insert‑molding challenges with custom tooling and fixturing;
• Optimise material costs without sacrificing performance or aesthetics;
• Deliver fully assembled, ready‑to‑sell products with documented quality assurance.

By entrusting us with this multifaceted development, the client received a high‑quality, market‑ready necklace within their timeline—and a proven partner for future multi‑material innovations.

Need help developing a similar product? Explore our product design, product sourcing and mass manufacturing services, or contact IFBrand Sourcing to discuss your project.