One Article Explains RTM And Its Derivative Processes, So You Don’t Have to Confuse Them Anymore

 

The 23rd issue | High-performance Fiber and Composite Material RTM Molding Process Training Class

 

The RTM (Resin Transfer Molding) process is to inject a reactive low-viscosity resin into a closed mold under pressure injection or/and vacuum-assisted conditions to infiltrate dry fiber materials and remove gas at the same time. After the infiltration is completed, the resin is heated to undergo a cross-linking reaction to complete curing and obtain composite parts.

 

Many people engaged in the field of composite materials know these process principles and operation methods, but they are also confused about the RTM process and vacuum infusion, vacuum infusion, vacuum assistance and other terms. Today we will use an article to explain it clearly. After reading it, I believe everyone can have a more professional and clear judgment on what process they are using.

 

1. The feature of the RTM process (Resin Transfer Molding) is the closed mold, which adopts the method of matching the male and female molds. The process of infiltration, penetration and coating of the dry fiber by the liquid resin in the closed mold cavity. Developed from RTM, there are also LRTM (Light Resin Transfer Molding) and HP-RTM (High Pressure Resin Transfer Molding) according to the different pressure and flow rate of the injected resin.

 

HP-RTM came into being with the high demand for lightweight civilian equipment. The use of higher injection pressure and flow rate can greatly improve production efficiency and reduce production costs.

In addition, the impregnation quality of prefabricated parts is also improved under high pressure.

The disadvantage is that in order to cope with high injection pressure, the structural strength and rigidity of the mold must be improved accordingly to ensure that the mold does not deform under high injection pressure.

Usually, this type of mold will use a core-added composite material with steel pipe support, or an aluminum mold or steel mold processed by a CNC machine tool, which greatly increases the manufacturing cost and mold opening time.

 

 

(HP-RTM) LRTM is a low-cost manufacturing process developed in response to industry demand. In the fields of ships, medical treatment and certain developments, it does not require such high injection pressure and speed while ensuring the use effect, and the cost is controllable. Therefore, it has also been greatly developed in recent years.

 

Process Name	Mold Type	According to different injection pressure and speed	According to the different flexible mold expansion methods
RTM	Yin-yang mold	HP-RTM	Airbag assisted RTM (RARTM)
		L-RTM	Thermal expansion soft mold assisted RTM (TERTM)

 

2. Vacuum Assisted Forming Process

 

Vacuum Assisted Forming Process is a new type of low-cost forming technology for composite parts developed from RTM and obviously different from RTM. The most obvious difference is the use of a single-sided mold, on which a flexible vacuum bag film is used to cover and seal the fiber reinforcement material, and the vacuum negative pressure is used to remove the gas in the mold cavity, and the resin is driven to flow by the vacuum negative pressure to achieve the effect of resin impregnation on the fiber and its fabric.

 

VARTM (Vacuum Assisted RTM Forming Process), also known as VARI or VIP in some production, is a process that uses an open mold, and sets an exhaust port to evacuate the resin while injecting the resin, and uses vacuum to assist the resin flow to obtain better wettability and bubble removal ability. In specific implementation, the resin can be injected after the mold cavity is evacuated, or the resin can be injected only by relying on the negative pressure in the cavity after evacuation.

 

 

VARTM (vacuum assisted RTM molding process) , SCRIMP (resin infiltration molding process), also known as VIMP process, is an extension and development based on VARTM technology.

Its purpose is to solve the problems of driving pressure gradient and low permeability of preforms in vacuum infusion process. This process also uses a single-sided hard mold, lays reinforcing materials and various auxiliary materials on the mold surface, seals the edge of the cavity tightly with a vacuum bag, and then evacuates the cavity.

The direction of resin injection is controlled by a computer, first fully flows and penetrates in the length direction, and then flows and penetrates in the thickness direction, shortening the resin flow path, achieving fiber infiltration, and reducing the occurrence of defects.

 

 

SCRIMP (resin infiltration molding process) RIRM, resin injection cycle molding. Vacuum and pressure are combined to alternately inject resin into multiple molds to circulate the resin until the preform is fully saturated. CIRTM, Co-Injection RTM.

Co-injection RTM can inject several different resins, and can also use several preforms, and can use vacuum bags and molds with flexible surfaces. Co-injection resin systems should be able to be injected at a common process temperature (co-injection) and cured under the same curing conditions (co-curing).

The above are several commonly used RTM and vacuum-assisted molding technologies, and new process improvements are emerging in an endless stream.

For most people, there is no need to worry about what this process should be called in professional terms.

The above-mentioned processes with different names are actually connected, just a layer of window paper.

Once it is broken, it is found that the underlying logic of various processes is the same.

The reason why I want to list these processes is to avoid the embarrassment of being asked about the root cause.