Manufacture Process Insert Mould For Plastic Mould Injection

Insert molding is a specialized plastic injection molding process where pre-manufactured components (inserts) are embedded into a plastic part during the molding cycle resulting in a single integrated product. This is used across various industries to create strong, durable and often lighter parts with enhanced functionality and reduced assembly costs.

Here’s a breakdown of the process, design considerations and materials used in insert molding:

Insert Molding Process Steps

The insert molding process is similar to conventional injection molding but with the added step of inserting. The steps are:

1. Insert Preparation and Loading:

   • Manufacturing Inserts: If custom inserts are required (e.g. custom metal components), they are manufactured to precise specifications before the molding process begins. Common inserts are metal parts (brass, steel, stainless steel), pre-formed plastic components, ceramics or glass.

   • Loading Inserts into the Mold: The pre-manufactured inserts are placed into the mold cavity. This can be done:

     • Manually: Suitable for low volume production or prototypes, where operators place the inserts.

     • Automated (Robotic) Insertion: Ideal for high volume production, automated systems or robots place the inserts, ensuring consistency, efficiency and can withstand high temperatures.

2. Mold Clamping:

   • The two halves of the mold tool are closed and clamped together by the injection molding machine’s clamping unit. This creates a sealed cavity and can withstand the high pressures of plastic injection.

3. Plastic Injection:

   • Plastic granules (resin) are fed from a hopper into a heated barrel where a rotating screw melts the plastic.

   • Once melted, the plastic is injected under high pressure into the mold cavity, encapsulating the pre-placed inserts. Vents in the mold allow air to escape, preventing bubbles or defects.

4. Cooling and Solidification:

   • The molten plastic cools and solidifies around the inserts, conforming to the shape of the mold cavity and bonding to the inserts. The cooling time depends on the type of plastic, part wall thickness and mold design.

5. Mold Opening and Part Ejection:

   • Once the plastic has cooled and solidified, the mold opens. * Ejector pins or other mechanisms push the part out of the mold cavity. This step must be designed to not damage or deform the part.

6. Post-Processing (Optional):

   • After ejection, some parts may require:

     • Deburring/Trimming: Remove excess plastic (sprue or runners) or small burrs.

     • Surface Finishing: Printing, polishing or electroplating to enhance aesthetics or functionality.

     • Humidity Control/Heat Treatment: To stabilize dimensions, remove internal stress or improve physical properties.

Design of Insert Molding
The success of insert molding depends primarily on design. Some important factors are:

Material compatibility:

Insert material: It should be able to tolerate the temperature and pressure conditions in the molding process without deforming or getting destroyed. Examples are brass, steel, stainless steel, and engineered plastics.

Plastic resin: It should have a good bonding (either mechanical or chemical) relationship with the insert material. Common examples are thermoplastics such as nylons, polystyrenes, polyethylene; thermosets; elastomers.

Thermal expansion: Try to keep the difference in thermal expansion coefficients between the insert and the plastic material so that internal stress is kept at a minimum and therefore it does not crack or separate upon cooling and during use.

Insert design:

Geometry: Inserts should be round, or axially symmetrical, to allow uniform shrinkage and avoid stress concentration. Avoid sharp corners on inserts because then you would be creating stress concentration in the plastic.

Anchoring features: Add features such as knurling, undercuts (mechanical locks), or other textured surfaces on the insert to improve mechanical bonding with the plastic. This will enhance pull-out strength and resistance to rotation.
Size: Keep inserts generally small relative to the plastic component they are embedded in.
Placement: The right position is very important. Inserts must be placed in bosses or elevated areas with enough plastic around them so that they do not become loose or move. When multiple inserts are placed side by side, it helps prevent bending or damage.
Mold Design:

Cavity Design: The mold should be made in such a way that it holds the inserts properly during injection and cooling so that they do not move or become misaligned.

Gating and Venting: Choose gates at places that allows plastic to flow well around the inserts. Good venting is very important to stop air from getting trapped.
Draft Angles: Add suitable draft angles to make it easy to eject the molded part without harming the plastic or pushing out the insert.
Maintain uniform wall thickness around the insert to ensure that cooling is even and reduce the chances of warping or sink marks. It is recommended that a minimum plastic thickness be maintained around the insert. For example, at least one-sixth of the insert's diameter.

Insert Molding:

Vertical Injection Molding Machines: The vertical type is often preferred for insert molding as gravity assists in holding the inserts in position during the molding cycle.
Automation: In cases of huge volumes, efficiency can be significantly improved by automating the process of loading and unloading inserts with robots.

Plastic resins are widely used in various applications due to their versatility and recyclability.,Thermoplastics such as Nylon (Polyamide), Polystyrene, Polyethylene, Polypropylene, ABS (Acrylonitrile Butadiene Styrene), Polycarbonate, and TPU (Thermoplastic Polyurethane) are among the most commonly used types.,Thermoset plastics are utilized for applications requiring high heat resistance or specific chemical properties, while elastomers are preferred for flexible or soft-touch applications.,Insert materials include metals like Brass (common for threaded inserts), Steel (e.g., stainless steel for strength and corrosion resistance), Aluminum, as well as other materials such as pre-molded plastic components, ceramics, glass, and electronic components like wires, sensors, and contacts.,Insert molding is a highly effective manufacturing process that allows for the creation of complex, multi-material parts with enhanced properties.,This process is invaluable in a wide range of industries, including automotive, electronics, medical devices, and consumer goods.