In Moldflow (mold flow analysis software), possibility of flash can be judged from following data and results:

 

When pressure in mold cavity is too high, plastic melt may be forced into mold fit gap, resulting in flash. In Moldflow analysis results, check pressure distribution. If a local high-pressure area appears near mold parting surface or at fitting of slider, insert, etc., this is a sign that flash may occur.
Specific viewing method
In "Pressure" result option of Moldflow analysis results, observe color distribution. Generally, red and orange areas represent higher pressures. If these high-pressure areas appear near parting surface or gap, special attention is needed. For example, in an injection molded plastic shell analysis, if a red high-pressure area appears at the edge of mold parting surface, this may mean that there is a risk of flash here.
Pressure distribution

 

Injection pressure is the only driving force for rubber to flow in mold cavity. During filling process (i.e., speed control stage), pressure is determined by resistance during filling process. During holding stage (i.e., pressure control stage), pressure is determined by set holding pressure.
Pressure distribution in cavity can intuitively reflect difficulty of filling each area of product, also reflect possible shrinkage differences in each area and internal stress distribution.

Speed and shape of melt front can also reflect possibility of flash. If speed of melt front is too fast, especially when it is close to mold parting surface or other mating parts, melt may break through mold gap to form flash. In addition, uneven advancement of melt front leads to excessive local melt pressure, which is also prone to flash.
Specific viewing method
In "Melt Front Time" result option of Moldflow, observe advancement of melt front. If melt front advances significantly faster in some areas than in other areas, and these areas are close to mold edge or mating, flash may occur. At the same time, check "Flow Wavefront" result to see if it has irregularities, such as wavy or turbulent flow wavefronts near parting surface, which also indicates risk of flash.

Insufficient clamping force will cause gaps in mold during injection molding process, causing plastic melt to overflow and form flash. Moldflow can estimate clamping force. If estimated clamping force exceeds actual clamping force of injection molding machine, or clamping force fluctuates greatly during injection molding process, flash may be generated.
Specific viewing method
In "Clamping Force" result option of Moldflow, view size and change curve of clamping force. If clamping force peak is close to or exceeds rated clamping force of injection molding machine, or clamping force curve fluctuates violently, this indicates that mold may have gaps during injection molding process and there is a risk of flash. For example, when analyzing injection molding of a large plastic product, it is found that clamping force peak exceeds capacity of injection molding machine, and it is necessary to consider adjusting injection molding process parameters or mold structure to avoid flash.
Influence of material injection pressure and clamping force
Different materials require different injection pressure and clamping force
Different materials have different viscosity ranges