Views: 0 Author: Site Editor Publish Time: 2026-02-27 Origin: Site
In injection molding, gas assist molding and insert molding are two fundamentally different specialized processes. But what if your product needs both—a hollow, lightweight structure and integrated metal components like threaded inserts or electrical contacts?
The good news: These technologies can be combined in a single mold, in one production cycle. This integrated approach creates products with both weight-saving hollow sections and durable metal-functional areas.
This comprehensive guide explains how gas assist and insert molding work together, the technical challenges, design principles, and when this combination makes sense for your application.
| Process | Advantages | Limitations |
|---|---|---|
| Gas Assist Molding | Hollow sections reduce weight; eliminates sink marks; lowers internal stress | Cannot integrate metal functional components |
| Insert Molding | Creates permanent bonds between plastic and metal; eliminates assembly steps | Parts are solid; thick sections prone to sink marks |
Combining these technologies enables:
Functional integration: Products with hollow lightweight structures and metal threads, contacts, or reinforcements
Process simplification: One molding cycle replaces multiple post-molding assembly operations
Design freedom: Place metal inserts precisely where needed, even in complex hollow parts
Cost reduction: Eliminates secondary operations, reduces material usage, lowers part weight
From a technical standpoint, these processes are compatible:
| Aspect | Gas Assist Requirements | Insert Requirements | Compatibility |
|---|---|---|---|
| Mold structure | Gas channels and gas pins needed | Insert positioning features needed | Can coexist in one mold |
| Molding cycle | Gas injected after plastic fill | Inserts placed before mold closes | Sequential, no conflict |
| Plastic state | Gas requires molten plastic | Inserts are encapsulated by molten plastic | Compatible |
| Material requirements | No special requirements | Must consider plastic-insert bonding | Can be unified |
While theoretically feasible, practical implementation must address:
Insert positioning during gas injection: High gas pressure can displace inserts if not properly secured
Gas channel layout: Must completely avoid insert areas to prevent gas breakthrough at the bonding interface
Wall thickness control: Insert areas need solid walls for strength; gas channels need hollow sections; transition zones require careful design
Gate location: Must consider both gas flow patterns and avoid direct impingement on inserts
According to patented technology, gas assist molding and insert molding can be successfully combined in one mold .
Mold Structure Schematic:
┌─────────────────────────────────────┐ │ Top Plate │ │ ┌─────────────────────────────┐ │ │ │ Injection Gate │ │ │ │ ↓ │ │ │ │ ┌─────────────────────┐ │ │ │ │ │ Part Cavity │ │ │ │ │ │ ┌──────────────┐ │ │ │ │ │ │ │ Insert Holder│←─────── Insert│ │ │ │ └──────────────┘ │ │ │ │ │ │ ↑ │ │ │ │ │ │ Gas Channel │ │ │ │ │ │ ↑ │ │ │ │ │ │ Gas Inlet │ │ │ │ │ └─────────────────────┘ │ │ │ └─────────────────────────────┘ │ │ Bottom Plate │ │ Ejector System │ └─────────────────────────────────────┘
Key Design Features :
Insert holder: Specially designed cavity area for precise insert placement and fixation
Gas inlet and channels: Located at the opposite end of the cavity from inserts
Runner and gate system: Ensures uniform filling while encapsulating inserts
Cold slug wells: Capture cool material at gas flow fronts
Research at Eindhoven University of Technology has explored two-component gas-assisted molding (2CGAIM) .
Principle:
First material injected (can contain inserts)
Second material injected
Gas introduced to create hollow sections
Advantages: Enables soft-hard combinations, different colors, and insert integration simultaneously
FCS Group has developed gas-assisted sandwich injection molding technology .
Features:
High-pressure nitrogen injected into sandwich-structured melt
Applicable to thin-wall 3C product housings
Improves moldability, reduces warpage, increases yield
For insert compatibility: Inserts can be positioned appropriately during molding for integrated production.
Core Principle: Gas channels must completely avoid insert areas
Correct Layout: ┌─────────────────────────────────────┐ │ Insert Area (Solid) │ │ ┌───┐ │ │ │ ● │ ← Insert │ │ └───┘ │ │ ↓ │ │ Transition Zone (Gradual Wall) │ │ ↓ │ │ Gas Channel (Hollow) ←→ Gas Inlet │ └─────────────────────────────────────┘ Incorrect Layout: ┌─────────────────────────────────────┐ │ Insert Area │ │ ┌───┐ │ │ │ ● │ │ │ └─┬─┘ │ │ ↓ │ │ Gas Channel ────→ Gas may penetrate │ │ insert interface │ └─────────────────────────────────────┘
Specific Requirements:
Distance between gas channel edge and insert area: ≥ 5mm
Insert area remains solid with wall thickness ≥ 1.5× insert diameter
Transition zones use gradual wall thickness changes over length ≥ 3× thickness difference
In gas assist molding, inserts face pressure from gas injection. Fixation methods must be robust:
| Fixation Method | Best For | Considerations |
|---|---|---|
| Mechanical clips | Larger inserts | Design elastic structures for easy removal |
| Vacuum suction | Flat inserts | Ensure suction force exceeds gas impact force |
| Magnetic holding | Ferromagnetic inserts | Simple and reliable, but magnetism may weaken at high temperatures |
| Interference fit pins | Precision inserts | High positioning accuracy, consider thermal expansion |
Patent Recommendation: Use specially designed insert holders to ensure positional accuracy during gas-assisted molding .
Gate Selection Principles:
Avoid direct impingement on inserts
Ensure melt fills insert areas first, then flows to gas channel regions
Consider multi-point gating for balanced filling
Gas Inlet Selection Principles :
Through-nozzle gas injection: Can use existing molds; gas channels must be interconnected
Through-mold gas injection (gas pins): Multiple entry points possible; gas channels need not be fully interconnected; leaves gas pin marks
For combined processes, through-mold injection is recommended because it allows:
Multiple gas entry points for flexible control
Avoidance of insert areas
Compatibility with hot runner systems
| Region | Wall Thickness Requirement | Notes |
|---|---|---|
| Insert zone | Solid, ≥1.5× insert diameter | Ensures bonding strength and pull-out resistance |
| Transition zone | Gradual change over length ≥3× thickness difference | Minimizes stress concentration |
| Gas channel zone | 3-8mm (resulting wall 2-3mm after hollowing) | Gas channel area |
Step 1: Insert Placement ──→ Step 2: Mold Close ──→ Step 3: Plastic Injection (Insert holder positions) (Mold closed) (Encapsulates inserts) Step 4: Gas Injection ──→ Step 5: Hold Pressure/Cool ──→ Step 6: Open/Eject (Creates hollow sections) (Gas pressure maintains) (Finished part)
| Parameter | Recommended Range | Control |
|---|---|---|
| Shot volume | 70-90% of cavity volume | Leave space for gas, but ensure complete insert encapsulation |
| Gas delay time | 0.5-3 seconds | Adjust based on wall thickness; ensure plastic remains molten |
| Gas pressure | 10-30 MPa | Adjust based on part size and wall thickness |
| Hold time | Until gate freezes | Gas pressure maintains, compensates shrinkage |
| Mold temperature | Material-dependent | Consider temperature control near inserts |
Why Preheating Matters:
Metal inserts conduct heat quickly, absorbing thermal energy from plastic
Temperature differences cause uneven shrinkage and internal stress
Affects bond strength
Recommended Temperature: Preheat inserts close to mold temperature (typically 80-120°C)
Product Features:
Thick-profile handle with hollow interior for weight reduction
Threaded metal inserts at both ends for installation
Solution:
Inserts placed at handle ends, secured with mechanical clips
Gas channel positioned in middle section, avoiding insert areas
Gates near inserts ensure insert encapsulation before gas flows to center
Result: One-shot production, no post-assembly, 30% weight reduction, strength meets requirements
Mack Molding Company developed dual gas-assist injection molding for large structural components .
Process Features:
Internal gas injection into rib structures forms channels
External gas between mold and part surface improves surface quality
Reinforcement inserts can be placed during molding
Application: Refrigerated panel for semi-trailer truck, 76 inches long, successfully integrated functional inserts
University of Paderborn developed the GITBlow process, combining gas-assisted molding with blow molding and studying integration with continuous fiber-reinforced thermoplastic sheets .
Key Technology:
Two gas injections: first creates hollow section, second expands
Final expansion stage bonds with molten reinforced sheets
Enables locally reinforced lightweight structures
Insights for Inserts: Inserts can bond with molten plastic at optimal timing for maximum strength.
| Aspect | Description |
|---|---|
| Functional integration | Hollow lightweight structures + metal inserts in one step |
| Process simplification | Eliminates post-molding assembly, saves labor and steps |
| Bond strength | Inserts fully encapsulated, more reliable than post-assembly |
| Design freedom | Place metal inserts anywhere in hollow products |
| Aspect | Description |
|---|---|
| Mold complexity | Requires both gas channels and insert positioning features; higher tooling cost |
| Process control difficulty | Must coordinate insert fixation, gas timing, and multiple parameters |
| Design restrictions | Insert areas must avoid gas channels; layout limited |
| Longer trial time | Multiple trial runs needed to optimize parameters |
| Insert preheating required | Additional equipment needed for temperature control |
| Product Characteristics | Suitable for Combined Process? | Reason |
|---|---|---|
| Hollow structure + needs metal threads | ✅ Excellent fit | Functional complement, one-shot production |
| Hollow structure + needs metal contacts | ✅ Suitable | Can integrate conductive functions |
| Hollow structure + multiple metal inserts | ⚠️ Evaluate | Many inserts may restrict gas channel layout |
| Very thin-wall hollow + inserts | ❌ Not suitable | Inserts require adequate wall thickness |
| Transparent parts + inserts | ❌ Not suitable | Gas channels may affect transparency |
| Question | Your Answer | Assessment |
|---|---|---|
| Does your product need weight reduction? | Yes/No | Yes → Gas assist valuable |
| Does it need metal functional components? | Yes/No | Yes → Insert molding valuable |
| Number of inserts ≤ 3? | Yes/No | Yes → Layout feasible |
| Are inserts concentrated in specific areas? | Yes/No | Yes → Can collectively avoid gas channels |
| Annual volume > 10,000 units? | Yes/No | Yes → Worth complex tooling investment |
If most answers are "Yes," the combined process is worth considering.
Gas assist and insert molding can be successfully combined in one process, creating integrated products with both hollow lightweight structures and durable metal inserts. Key success factors include:
Mold design: Use insert holders for precise positioning; strictly separate gas channels from insert areas
Insert fixation: Multiple methods (mechanical, vacuum, magnetic) to resist gas pressure
Gas channel layout: Completely avoid insert areas; design gradual wall thickness transitions
Process control: Precise shot volume, gas delay time, and pressure
Insert preheating: Minimize temperature differences for optimal bonding
While the combined process requires higher mold complexity and longer development time, for products needing both weight savings and metal functional integration, it offers the most elegant solution—simplifying downstream operations and improving product reliability.
