Injection molding is the workhorse of modern manufacturing, turning plastic pellets into everything from tiny electronic components to large automotive parts. For engineers and product designers, understanding this process isn’t just about knowing the steps—it’s about mastering the details that separate a good part from a great one. Let’s break down the injection molding workflow, key parameters, and how to optimize for high-performance materials like PA6+30GF (BASF Ultramid B3EG6).
The Core Injection Molding Workflow: 6 Key Steps
At its heart, injection molding is a deceptively simple process: melt, inject, cool, repeat. But each step demands precision to avoid costly defects.
1. Material Preparation & Drying
Many engineering plastics (like PA6/Nylon) are hygroscopic, meaning they absorb moisture from the air. If not properly dried, this moisture turns to steam during heating, causing defects like silver streaks or bubbles in the final part.
Action: For PA6+30GF, dry at 80°C for 4+ hours until moisture content is below 0.05%.
2. Plasticization (Melting)
The plastic granules are fed into a heated barrel, where a rotating screw shears and melts them into a uniform, viscous melt. The temperature profile of the barrel is critical—too hot and the material degrades; too cold and it won’t flow properly.
Example: PA6+30GF typically requires a barrel temperature of 260–280°C.
3. Clamping
The two halves of the mold close, and a powerful clamping force is applied. This force must be sufficient to counteract the pressure of the molten plastic being injected, preventing the mold from opening and creating flash (excess plastic at the part edges).
4. Injection & Packing
Injection: The screw moves forward, forcing the melt into the mold cavity at high pressure (80–200 MPa) and speed.
Packing (Holding): After filling, pressure is maintained to compensate for the material’s shrinkage as it cools. This step is crucial for preventing sink marks and ensuring dimensional accuracy.
5. Cooling
The mold is cooled, typically with circulating water, to solidify the plastic. The cooling time is a major factor in the overall cycle time and directly impacts the part’s crystallinity and internal stress. For PA6+30GF, a mold temperature of 80–100°C helps achieve optimal crystallization and stability.
6. Ejection
Once the part is rigid enough, the mold opens, and ejector pins push the finished part out of the cavity.
Key Process Parameters: The Levers of Quality
Every decision in injection molding revolves around a set of critical parameters. Here’s how they impact your part:
表格
Parameter
Role
Typical Range for PA6+30GF
Barrel Temperature
Controls melt flow and stability
260–280°C
Mold Temperature
Influences crystallinity, surface finish, and cooling
80–100°C
Injection Pressure
Overcomes flow resistance to fill the cavity
80–150 MPa
Holding Pressure
Compensates for shrinkage
50–80% of injection pressure
Cooling Time
Ensures part rigidity before ejection
10–30 seconds (depends on wall thickness)
Optimizing for PA6+30GF (BASF Ultramid B3EG6)
PA6 reinforced with 30% glass fiber is a popular choice for structural parts like our Holder Backplate because of its exceptional strength-to-weight ratio. However, it presents unique challenges:
Fiber Distribution: To avoid "fiber bloom" (visible fibers on the surface), use a moderate-to-high injection speed to ensure the fibers are evenly distributed within the melt.
Shrinkage Control: Glass fiber reduces overall shrinkage, but it can cause anisotropic shrinkage (different rates in different directions). This is why proper packing and mold temperature control are non-negotiable.
Wear and Tear: Glass fiber is abrasive. Molds used for PA6+30GF must be made from hardened steel to resist premature wear.
Common Defects & Troubleshooting
Even with the best setup, defects happen. Here’s how to diagnose and fix the most common issues:
Sink Marks: Caused by insufficient packing or thick, uncooled sections. Fix: Increase holding pressure/time or add ribs to the design.
Warpage: The result of uneven cooling or differential shrinkage. Fix: Balance the cooling system and consider post-molding annealing.
Flash: Occurs when the mold isn’t clamped tightly enough or the material is too fluid. Fix: Increase clamping force or lower the barrel temperature.
Final Thoughts
Injection molding is both an art and a science. By mastering the core process and tailoring your approach to the material, you can produce high-quality, consistent parts that meet the most demanding specifications. Whether you’re molding a simple bracket or a complex structural component like our PA6+30GF Holder Backplate, the principles remain the same: control, precision, and a deep understanding of the material.
Yixun is the China first generation mold maker, specialize in mold and moulding, provide one-stop plastic manufacturing service, feature in building medical and healthcare device tooling.
