As molten resin travels through the nozzle, runners, gates, and into the cavity, it loses pressure along the way. That loss reflects how much resistance the system creates.
A Pressure Drop Study puts numbers to that resistance. It shows whether the mold, material, and machine are working together efficiently or forcing the process to compensate.
This step measures how much pressure is required to fill the mold at different injection speeds. It verifies whether the material is flowing within a stable viscosity range and whether the machine can support the process without strain.
It also highlights restrictions in the system, such as undersized runners or inefficient gates, that can affect balance and packing.
The study follows rheology and cavity balance. By this point, the optimal injection speed is already defined, and the mold has been confirmed to fill evenly.
With those variables controlled, attention shifts to how efficiently the system delivers material through that balanced flow path.
The goal is to understand how pressure changes with injection speed and whether those values stay within a practical operating range.
Most processes fall within a pressure drop range of roughly 1,500 to 3,000 psi, depending on the material. At the same time, the machine should have enough capacity left to maintain control during packing and gate seal.
If pressure demand is too high relative to machine limits, stability becomes harder to maintain.
The process starts at the optimized injection speed established during the rheology study. From there, short shots at about 90 to 95 percent fill are run across several speeds, typically four to six steps from low to high.
For each shot, peak injection pressure is recorded. These values are then plotted against injection speed to create a pressure drop curve.
If cavity pressure sensors are available, comparing nozzle pressure to cavity pressure gives a more precise view of where pressure is being lost.
Each run captures injection velocity, fill time, peak injection pressure, and part weight, while maintaining consistent melt temperature.
Visual checks ensure that part quality remains stable across all speeds, confirming that the data reflects true flow behavior rather than cosmetic variation.
A smooth, gradually decreasing slope usually indicates stable flow behavior. As injection speed increases, the material flows more easily, and pressure requirements drop in a predictable way.
A steep slope points to excessive resistance, often caused by restrictive runners or gates. A flattened curve can signal shear overheating or turbulent flow, while erratic data may indicate inconsistent material conditions or venting issues.
When pressure approaches the upper limits of the machine, it becomes clear that the process is operating too close to its capacity.
Pressure drop can often be traced to specific sections of the system.
The nozzle and sprue typically contribute a smaller portion, while runners account for the largest share of resistance. Gates also play a significant role, and cavity geometry adds the final portion.
Understanding where pressure is lost helps guide tool adjustments and improve overall efficiency.
This study also checks whether the press has enough available pressure to run the process reliably.
For example, if a process requires most of the machine’s available pressure just to fill the mold, there’s little room left for stable packing. A comfortable margin allows the process to absorb normal variation without losing control.
The study produces a pressure drop curve, raw data for each test condition, and a clear assessment of machine capability.
It also includes recommendations if adjustments are needed, whether that means modifying the tool or reevaluating the press.
With this information in place, the process moves forward with a clear understanding of how efficiently the system operates.
Pressure tells a detailed story about how a molding system performs. When the system flows efficiently, control improves across every stage, from filling to packing to cooling.
That efficiency carries forward into the next phase, where the full operating range of the process is defined and validated.