Recycling from Insert Moulded Parts: The Challenge from Waste to Resource Recovery

1. Introduction

In recent years, insert molding has been widely used in molded products—particularly automotive parts—to enhance product functionality. However, insert-molded products containing metal parts have faced a major challenge: even when waste is generated due to in-process defects or scrap shots, it is difficult to reuse them. In particular, the integration of metal and resin has made the labor and cost of separation significant barriers to recycling.

In this article, we will introduce the technical initiatives undertaken by Sanko Gosei Co., Ltd. regarding the “recycling of insert-molded products” and discuss their effectiveness and future potential.

2. Background of Theme Selection

This project originated from the increase in insert-molded products and the corresponding rise in resin waste. While reducing process defects to near zero is ideal, complete elimination is difficult in actual production settings, resulting in a certain amount of scrap.

Therefore, from the perspectives of reducing environmental impact and achieving the SDGs, the theme of “removing metal inserts in a form suitable for use as recycled material and recycling them” was established.

3. Target Product and Challenges

The target for development was an automotive part produced at a rate of 1 million units per month.

The part features an aluminum insert embedded in PBT-GF30% (manufactured by Toray). This insert has a retaining tab, making it physically difficult to remove from the resin.

4. Trial and Error in Removing the Insert

The following approaches were considered as removal methods:

　Method 1: Drilling

Although this is a simple method for drilling holes with a drill press, it took too long to remove the holes and wasn't practical.

　Method 2: Removal by Physical Impact

A method involving embedding a screw and striking it with a hammer. However, this method carried a high risk of component damage or fragmentation, and safety concerns for workers remained.

Method 3: Ultrasonic Cutting and Thermal Separation

In collaboration with an external organization, we tested thermal cutting using an ultrasonic knife, cylindrical tools, and perforated tools. Although we achieved some success, challenges remained, including flying metal fragments, difficulties in securing the workpiece, and inconsistent machining results.

5. The Key to the Solution: Insert Removal via High-Frequency Induction Heating

The method ultimately adopted as an effective solution was insert removal using high-frequency induction heating. This method operates on the same principle as an induction cooktop: it selectively heats only the metal portion of the insert to loosen its bond with the resin, thereby separating the two.

This technique made it possible to remove the inserts without damaging them and to preserve the resin in a condition suitable for reuse as recycled material.

6. Benefits and Future Applications of Recycling

The benefits resulting from the introduction of this technology are as follows:

Annual cost savings of 9.6 million yen by reusing 2,000 kg of PBT waste material per month

This technology can also be applied to products with PA6 (Zytel) inserts, with projected annual savings of 2.4 million yen

This technology is expected to be applicable to a wide range of products that combine thermoplastic resins with metal inserts

7. Future Challenges and Outlook

Future challenges for this technology include:

Developing flexible jigs to accommodate multiple products using a single machine

Expanding the range of insert materials and shapes compatible with high-frequency heating

Moving forward, we will continue to apply this technology to other products while aiming to establish a circular production system within the factory.