Mold flow analysis (MFA) is an analysis method that uses simulation technology to simulate flow, pressure holding, and cooling process of plastic melt in mold cavity to predict possible defects (such as shrinkage, warping, weld marks, etc.) of parts after molding.

 

As key components for appearance and safety of automobiles, car lamps are usually composed of following parts:
Lampshade: (transparent parts, high light transmittance and surface finish are required)
Lamp housing, bracket, etc.: (structural parts, high strength and dimensional stability are required)
Reflector, thick wall, etc.: (optical parts, precise optical pattern surfaces are required)

 

Molding difficulties:
Appearance parts, transparent parts (such as lampshades) are prone to weld marks, air marks, and shrinkage, which affect light transmittance and appearance;
Complex structures (such as multiple curved surfaces, thin-walled or thick-walled transition areas) are prone to uneven filling and warping;
Optical parts have extremely high requirements for dimensional accuracy (such as optical pattern surface tolerance) and need to control shrinkage consistency.

1. Filling analysis
Goal: Simulate flow process of plastic melt in mold to determine whether there are problems such as short shot (insufficient filling), retention, and jet flow.
Analysis points: Filling time distribution: ensure that melt fills cavity evenly to avoid local too fast or too slow;
Pressure distribution: optimize gate position, reduce filling pressure, and reduce mold wear;
Flow front temperature: prevent melt from solidifying prematurely due to low temperature, or degrading due to high temperature.

 

2. Holding pressure analysis
Goal: Optimize holding pressure and time, reduce product shrinkage and concavity, and improve density uniformity.
Analysis points: Holding pressure curve: determine the best holding pressure attenuation mode (such as segmented holding);
Volume shrinkage: predict shrinkage difference in different areas of product, especially thick wall area (such as lamp housing mounting column).

 

Generally speaking, it is normal if product surface is within 0.3mm, but shrinkage mark is related to pressure holding, and it may also appear if pressure holding is not good.
3. Cooling analysis
Goal: Optimize cooling water channel design, shorten molding cycle, reduce product warping and residual stress.
Key points of analysis
Cooling time: ensure that product is cooled to ejection temperature (usually lower than glass transition temperature);
Temperature distribution: avoid local overheating or overcooling caused by uneven cooling, which affects optical performance (such as stress spots inside lampshade).
4. Warpage analysis
Goal: Predict deformation trend of product after molding, optimize mold design and process parameters.
Key points of analysis
Uneven shrinkage: caused by material crystallization, cooling differences or insufficient pressure holding;
Molecular orientation: Orientation of polymer chains in transparent parts will cause optical anisotropy, affecting uniformity of light transmission.

 

5. Special structure analysis
Multi-material molding
For example, for two-color injection molding of lampshades, interface compatibility and filling balance of two materials need to be analyzed;
Optical surface: Optimize gate position through mold flow analysis to avoid weld marks appearing in optical functional area of thick walls or lenses.

Mold design optimization: Determine the best gate position (such as fan-shaped gates for transparent parts to reduce weld marks);
Optimize runner system (such as using hot runners to reduce material waste and improve melt temperature consistency).
Process parameter optimization
Recommend parameters such as molding temperature, injection speed, and holding pressure to reduce number of mold trials;
Predict risks under extreme process conditions (such as high temperature causing yellowing of lampshades).
Prediction of quality problems
Identify potential defects (such as shrinkage holes in reflectors) in design stage to avoid batch scrapping during mass production;
Assist DFM (design for manufacturability) to adjust product structure (such as adding positioning ribs and optimizing wall thickness).

 

There may be wire crawling on the back of product pattern. Pay attention to controlling mold temperature, material temperature and flow speed, etc.

Model preparation: Import 3D model of headlight parts and divide mesh (surface mesh or 3D solid mesh);
Material selection: Call material database (such as DSM's optical grade PMMA, BASF's PC/ABS), and input rheological parameters;
Process setting: Define mold temperature, melt temperature, injection speed, holding curve, etc.;
Simulation calculation: Run filling, holding, cooling and other modules to generate an analysis report;

Filling time cloud map: Uniform color indicates filling balance, and local dark areas may be short-shot risk points;
Pressure distribution: Maximum pressure should be lower than mold pressure limit (usually ≤150 MPa). If it is too high, runner needs to be optimized or number of gates needs to be increased;
Temperature distribution: Temperature difference at flow front should be less than 10℃ to avoid local overheating and degradation;
Warp deformation: Compare with tolerance requirements. If tolerance exceeds tolerance, holding pressure needs to be adjusted or product structure needs to be modified (such as increasing wall thickness).
Conclusion and risk warning: For example, "weld mark cannot be completely eliminated, and it is recommended to focus on testing in subsequent mold trials."