Selection Principles of Supporting Molds for Chinese Plastic Mold Insert Molding Process

Insert molding combines prefabricated metal, ceramic and fiber inserts with plastic in one injection molding step. This integrated manufacturing technology has achieved mature technical iteration and large-scale application within China’s plastic mold industry. Unlike conventional injection molds, insert molding molds must simultaneously balance plastic melt fluidity, insert positioning stability, clamping force uniformity and the bonding strength of finished products. Improper mold selection will trigger frequent defects including insert shifting, plastic delamination and dimensional tolerance failure, raising overall production costs and reject ratios. Based on on-site manufacturing experience from domestic mold manufacturers, this article sorts out complete supporting mold selection standards for Chinese plastic mold insert molding process across five core dimensions: insert structure, plastic raw material, monthly output, precision standards, as well as temperature control and exhaust systems. The guidelines cover sample trial runs, small-batch custom production and standardized mass manufacturing scenarios.

Mold Structure Selection Based on Insert Structural Characteristics

Two mainstream mold structures are widely used in Chinese insert molding production lines, each matching distinct insert shapes and precision requirements.

Simple single-side fixed molds suit regular sheet-shaped or cylindrical inserts with evenly distributed plastic wrapping thickness. This mold type features simplified internal positioning parts, allowing workers to place inserts quickly. Its low processing and maintenance cost makes it ideal for general household appliance components without strict coaxiality requirements.

Bidirectional clamping composite molds target irregular inserts such as bent, eccentric and multi-hole metal terminals widely used in automotive and precision electronics. Both upper and lower molds are equipped with synchronous clamping positioning components to lock inserts firmly during melt injection. This structure counteracts impact from high-speed plastic flow and drastically cuts defective parts caused by insert deformation and dislocation. For electronic components requiring verticality and coaxiality tolerance within 0.05 mm, bidirectional clamping composite molds are the primary reliable option adopted by domestic factories.

Mold Steel Selection According to Plastic Material Properties

Chinese plastic mold manufacturers judge mold steel types mainly by plastic abrasion resistance, corrosion risk and forming temperature.

P20 pre-hardened steel serves as the standard choice for general plastics such as ABS, PP, PE and common modified nylon. Its moderate hardness simplifies cavity polishing and machining, fitting medium-low speed production of less than 800 cycles per day. With prominent cost performance, it is widely applied for new product sampling and short-term small-batch orders among domestic small and medium mold factories.

718H hardened steel is customized for glass fiber reinforced engineering plastics with fiber content over 10%, including PA, PBT and PC. The material delivers excellent anti-scouring and wear resistance, preventing long-term fiber friction from scratching cavity surfaces and generating product burrs. Molds made of 718H steel can reach a service life of 300,000 molding cycles, perfectly matching long-term mass production projects for domestic auto component manufacturers.

S136 anti-rust stainless steel is exclusively used for corrosive flame-retardant plastics like flame-retardant PVC and halogen-containing flame-retardant PC. High-temperature melt of these materials releases corrosive substances that easily rust mold cavities and metal inserts. Featuring oxidation and corrosion resistance, S136 steel sustains stable insert fitting accuracy during continuous long-hour production, a necessary configuration for insert molds producing flame-retardant electrical components.

Cavity Quantity Configuration Matching Monthly Production Capacity

Domestic insert molding projects classify molds into single-cavity dedicated molds and multi-cavity balanced molds based on order volume, with clear capacity matching rules.

Single-cavity dedicated insert molds apply to monthly output below 10,000 pieces, mainly for new product structural verification, performance testing and custom small-batch manufacturing. Each independent cavity comes with exclusive insert positioning tooling that allows separate fine-tuning, helping factories keep reject rates under control during trial production. The compact mold body fits small horizontal injection molding machines and shortens model switching debugging time, satisfying flexible sampling demands of many new energy and electronic R&D enterprises in China.

Multi-cavity balanced insert molds are designed for standardized insert plastic parts with monthly output exceeding 50,000 pieces for automated assembly lines. A balanced runner design guarantees consistent melt flow velocity and injection pressure in every cavity, so inserts in all cavities bear uniform impact force without unbalanced displacement. Compatible with unified standardized insert positioning tooling, the molds support synchronous insert loading by manual workers or automated manipulators, greatly boosting hourly production efficiency. They represent the mainstream mold configuration for large-scale plastic molding factories in China’s coastal industrial zones.

Auxiliary Positioning Structure Selection for Different Precision Demands

Insert position tolerance divides Chinese insert mold positioning systems into pin positioning and magnetic clamping positioning.

Fixed pin positioning molds match ordinary structural parts with insert position tolerance above 0.2 mm, without sealing or high-precision assembly demands. The combination of cylindrical positioning pins and prefabricated insert holes delivers simple machining, easy replacement of damaged positioning accessories in daily maintenance and low overall mold manufacturing cost. It accounts for the majority of molds used for low-precision civil plastic products.

Magnetic clamping positioning molds target high-precision military and automotive electronic parts with strict anti-floating and anti-offset standards. Permanent magnet modules are embedded inside mold bases to bidirectionally adsorb and fix metal inserts before and after mold closing. Magnetic force offsets instantaneous thrust generated by melt injection, fundamentally eliminating common precision molding defects such as insert floating and misalignment.

Temperature Control and Exhaust System Matching Based on Product Wall Thickness

The thickness of plastic wrapping inserts determines cooling water channel layout and exhaust groove design for domestic insert molds.

Thin-wall insert products adopt straight-through temperature control molds with cooling channels arranged close to insert wrapping areas. Even mold temperature distribution reduces internal stress of plastic products, avoiding cracking and delamination at bonding joints between plastic and metal inserts, and raising the yield of thin-wall electronic terminal parts.

Thick-wall insert products require split dedicated exhaust molds with multi-section embedded exhaust grooves on parting surfaces. This structure rapidly expels air trapped inside cavities during melt filling, stopping air bubbles from forming around wrapped inserts. Sufficient exhaust greatly enhances bonding adhesion between plastic and metal inserts, lowering risks of separation and detachment during long-term product service.

In conclusion, supporting mold matching for Chinese plastic mold insert molding process cannot rely on a single judgment factor. Production engineers need comprehensive evaluation covering insert shape, plastic abrasion and corrosion characteristics, monthly order capacity, dimensional tolerance and product wall thickness, to select targeted mold structures, steel grades, cavity counts, positioning assemblies and temperature exhaust setups. Scientific mold selection balances manufacturing cost and long-term production stability, maximizes the technical strengths of integrated Chinese plastic mold insert molding technology, and helps domestic manufacturers achieve high-efficiency, low-defect mass production of insert molding finished goods.