Main thickness of product: 1.5~2.0mm;
Product length: 327mm;
Product width: 216mm;
Product problem: Structural design itself is weak, and warpage value is large.

 

Figure 1: Flow - Heat Transfer - Plastic Properties

 

Figure 2: Flow - Heat Transfer - Fill Time vs. Temperature History for Each Gate

 

Figure 3: Product introduction

 

Figure 4: Introduction of product thickness

In addition to change of physical properties of plastic with molding, complex geometry of product itself, analysis difficulty of free surface flow of wavefront, complexity of filling process comes from mutual coupling between flow-heat transfer-plastic physical properties, that is, mutual influence of three mechanisms (Figure 1). Factors that affect filling process are discussed next:
● Plastics: viscosity and heat transfer properties.
● Product and mold design: meat thickness distribution, runner design, gate design.
● In terms of molding conditions: filling time, injection rate (flow rate curve), injection pressure (injection pressure curve), material temperature, mold temperature, etc.
● Function of runner and gate system of mold.
● Guide molten plastic from nozzle to cavity.
● Make molten plastic fill cavity smoothly and orderly.
● Gate should flow sufficiently before curing to prevent short shot dents.
● Fully transmit pressure to all parts of plastic parts to ensure effective pressure retention, so as to provide molding quality that conforms to external dimensions.

 

Figure 5: Three Gate Design

 

Figure 6: Four Gate Design

It can be seen from analysis results of computer mold test that configuration of gate positions and numbers of different designs will have different flow pressures and stresses, and pressure distribution at the end of filling, such as distribution areas of high pressure and low pressure, will also be different.

 

Figure 7: Pressure distribution 53~73MPa

 

Figure 8: Pressure distribution 46~63MPa

 

Figure 9: Stress distribution 5~7MPa

 

Figure 10: Stress distribution 1~2MPa

 

Figure 11: Flowing wavefront

 

Figure 12: Flowing wavefront

 

Figure 13: Flowing wavefront

 

Figure 14: Flowing wavefront

 

Figure 15: Warpage 7.6mm

 

Figure 16: Warpage 3.3mm
It can be seen from picture of pressure distribution that red area is high pressure area. If high pressure occurs, it is easy to cause deformation and stress will also increase accordingly. If you want to avoid inherent weak design structure of product and difference in flow area, it is necessary to select appropriate gate position and number of gates, observe and change plastic flow behavior in mold cavity. At the same time, gate is added for thicker area to achieve sufficient feeding, so as to adjust molding pressure of product and make it evenly distributed, so that product can achieve a better molding size.