Modflow solves molding defect standard indicators

Wall thickness of thermoplastic parts is generally 2~4mm. Wall thickness of plastic parts is related to process

If there are molding difficulties due to wall thickness, it can be solved by optimizing wall thickness. For example, increasing wall thickness along flow direction plays a role in guiding flow and ensuring that product is full.
In terms of mold structure, short shot problem can be solved by optimizing pouring position and quantity. For example, setting of gate should make melt flow along direction of reinforcing rib; gate should be away from area where wall thickness changes, etc.
Short shot judgment standard: gray at the end of flow

 

Car lamp products - Optimizing gate position to solve short shot problem

 

Flow mark judgment index:
1. Temperature distribution at the end of filling. If local temperature drops by 20 degrees, flow marks will appear.
2. Calculate acceleration based on this result. If acceleration is greater than 27, flow marks will appear.

 

Bumper - Flow Marks

 

During trial installation phase, a thin strip-shaped mark was found on main surface D1 of front bumper. After analysis, it was found that it was not a weld mark. Whether it was visually or by touching material, it felt that the area was not smooth, and paint could not cover it up. Features:
1. Slightly different glossiness
2. Surface curvature radius did not change smoothly
3. There was no fine seam in the center of strip-shaped mark
Bumper - moldflow judgment results of flow marks

 

Melt temperature isotherms at D1 are dense, indicating that melt temperature difference per unit distance there is large.
There are similar situations at D2 and D3.

 

Shear rate of both schemes is less than maximum shear rate of material, but shear rate of scheme 1 is smaller, and it is less likely to have surface defects such as impact marks.

1. Over-pressure maintenance caused by flow imbalance. Principle is to maintain pressure first in the places that are filled first, so two results of Fill time and Pressure can be used to determine whether there will be flash caused by over-pressure maintenance.
2. Pressure in cavity is greater than 80MPa.

 

Case: Fender - Optimize product design to solve flash problem

 

1. Volume shrinkage value >5%, or difference in volume shrinkage between adjacent positions exceeds 3%, which is prone to shrinkage marks.
2. Amount of dents >0.07mm, and weld line is obvious under natural light conditions.
Judge whether product structure and wall thickness design lead to obvious dents on product surface.

 

Product wall thickness design: When designing plastic parts, the wall thickness should be as uniform as possible, and the wall thickness should not differ too much. It should gradually decrease along material flow direction and transition smoothly. Ratio of two adjacent wall thicknesses should be less than 1.5~2.

 

Recommended values for wall thickness of some thermoplastic parts (mm)

Moldflow solves problem of shrinkage marks
Reinforcement rib design: Reinforcement ribs can effectively increase rigidity and strength of product. Reinforcement ribs can also serve as internal flow channels to help fill mold cavity. Reasonable reinforcement rib design can ensure functional requirements of product without causing surface dents.

 

Part wall thickness is T
Draft angle (d) is 0.5° -1.5
Reinforcement rib height (H) is less than 5T, usually 2.5T-3T
Reinforcement rib spacing is greater than 2T-3T
Chamfer radius (R) is 0.25-0.40T
Reinforcement rib thickness (W) is 0.4T-0.8T
Reinforcement rib structure diagram
Case: Optimizing product structure to solve sink marks

 

Maximum sink mark: reduced from 0.131mm to 0.068mm
Handle of rice cooker lid---Optimize product design to solve shrinkage problem

 

1. Weld line butt angle is <75 degrees
2. Wavefront temperature is 20 degrees lower than melting temperature
3. There is obvious air entrapment in weld line area

 

A standard design guide to avoid weld line problems has been established

 

As can be seen from figure above, when butt angle is 75 degrees, depth of weld line is exactly 2 microns. 2 microns is the boundary between visible and invisible weld lines, so 75 degrees is boundary between visible and invisible weld lines
Moldflow's weld line results describe butt angle of weld line. This butt angle is used to evaluate whether weld line is visible.
Glove box appearance parts
Product: Glove box appearance parts
Material: PA66+40%
Purpose: Influence of gate position on weld line

 

Glove box exterior parts

 

Battery shell - optimize product structure to solve weld line and injection molding machine problems

 

Product has weld lines. To achieve no weld lines, it must be formed with a high-speed molding machine. And scrap rate of this product produced with a high-speed molding machine is very high.

Indicators: Through moldflow analysis, air trap locations are predicted, especially at the end of flow, weld line location and stagnant flow location. When designing mold, exhaust at these locations should be strengthened.

 

Refrigerator fruit and vegetable cabinet--optimizing product structure to solve problem of idle air and welding lines

 

 

Scorch marks refer to combustion and degradation of plastics caused by failure to exhaust gas in cavity in time, which causes gas volume to compress and temperature to rise above maximum melting temperature of plastic.

 

Causes of burn marks
1. Air in cavity cannot be exhausted in time
2. Material degradation
Excessive melt temperature
Excessive screw speed
Improper flow channel system design
Indicators: In moldflow analysis results, trapped gas at flow end, weld line position and stagnant position must have an exhaust mechanism.

When product structure design is unreasonable, speed of two streams is inconsistent when they collide, which will cause molten material to flow back, that is, undercurrent effect occurs. At this time, weld line penetrates deep into product, weld line is obvious, and product strength is greatly weakened, causing product to break
Undercurrent problem indicators:
Average speed results check whether direction of arrow at confluence changes repeatedly when two streams merge.

 

Automobile air conditioning panel - Optimizing product design to solve cracking problem
Material: Bayblend KU1-1446, Bayer AG (PC+ABS)

 

Based on simulation analysis results, customer increased wall thickness of thin parts on both sides, making weld lines appear at larger cross-section, eliminating undercurrent effect and solving cracking problem at the front end of product.

Causes and solutions for warpage of plastic products:

Moldflow optimizes key indicators of cooling system

Vending machine cover plate - Optimize cold water circuit design to solve deformation problem
Main problem: Uneven cooling causes large deformation
Material: Lexan 500 (PC+10% GF), GE plastic (USA)
Product size: 207.8X29.5x47.8mm
Basic wall thickness: 1.9mm

 

Maximum deformation of product in Y direction: 0.98mm. Main reason for deformation is uneven cooling.
Optimize cooling water channel design to reduce mold temperature difference between front and rear molds

 

Connector--Optimize gate position to solve deformation problem

 

Material:LCP(liquid crystal polymer+30%GF)
Trade name: thermx LG431
Basic thickness:0.75~2.3mm
Manufacturer: Dupont Engineering Polymers
Material structure: Crystalline
Gate scheme and deformation results

 

Product model (printer parts)
Customer requirements
Due to assembly requirements, product side wall warpage tolerance must be controlled below 0.5mm
Product uses ABS+GF20% material to ensure strength

 

Analysis of main causes of warpage
Analysis results of causes of deformation

 

Optimize gate position

 

Comparison of fiber orientation

 

Automotive electronic cover - warping caused by corner effect

 

Original solution warping results

 

Optimization solution

 

Optimization scheme warpage results

 

Using Moldflow software, you can accurately predict filling time, holding time, cooling time, plus time of opening and closing mold, which is molding cycle.
Indicators for judging molding cycle:
1. Time to reach ejection temperature can be used to determine length of time it takes for product and runner to completely cool down
2. Frozen layer fraction can be used to accurately calculate molding cycle. Under normal circumstances, gate is completely cooled, holding pressure ends, product is completely cooled, and product can be ejected when flow cools more than 60%. This time plus time of opening and closing mold is molding cycle.
Case: Optimizing runner diameter to reduce molding cycle

 

Case: Comparison of results

Case: Headlight mirror - reduce runner diameter to reduce molding cycle

 

Reduce material loss and achieve acceptable runner/product volume ratio through runner optimization
Runner system adopts a high pressure gradient design, which saves runner material and also reduces ratio of runner system to cavity volume.

 

Combined mold, use reasonable injection pressure to fill each mold cavity at the same time

 

Optimize runner diameter to achieve flow balance

 

Moldflow has a powerful material library, which has collected characteristic parameters (thermal performance parameters, molding process parameters, viscosity and PVT data, etc.) of materials from more than 414 manufacturers and more than 8,479 material numbers.

 

Recommended Processing Parameters

 

These recommended process parameters can help mold test engineers effectively reduce mold test time