Introduction to HP-RTM Molding Process (First Half)

I. Overview of HP-RTM

HP-RTM is short for High Pressure Resin Transfer Molding, the full name is high pressure resin transfer molding process, HP-RTM molding process for short. It refers to the use of high pressure resin hedge mixed and injected into the pre-laid with fiber reinforced materials and pre-inserted vacuum closed mold, through the resin flow filling, impregnation, curing and demudding, to obtain the composite product molding process.

This process can achieve low cost, short cycle, large volume and high quality production. Compared with the traditional RTM injection pressure of 0.6 ~ 1.5 MPa (6 ~ 15 bar), HP-RTM is usually injected at a pressure of 1.0 ~ 6.0 MPa (10 ~ 60 bar) or even higher, and the resin can fill the mold cavity in a short time to complete the infiltration process of the preformed fiber body. And promote the bubble to discharge the resin, improve the surface molding quality of the product, the process can be shortened to less than 5 minutes.

Second, HP-RTM molding process characteristics

The HP-RTM molding process uses a mixing head to inject a low-viscosity resin into the mold, infiltrate the preformed fabric, and then quickly cure to form a high-strength composite part. The key technology lies in the two stages of resin injection and curing: first, the preformed carbon fiber braid is put into the mold cavity of the press, and then the liquid resin is injected under high pressure for curing. Due to the use of a new generation of rapid reaction chemical feedstock, the components of the feedstock formula are separated before mixing, and the multi-component feedstock is mixed when the carbon fiber pre-formed part needs to be injected with resin. The reaction time in the raw material mixing head is very short, so in the injection stage, the viscosity of the raw material begins to decrease rapidly, and the fluidity gradually decreases, which will lead to a sharp increase in the pressure in the mold (which is also the biggest feature of the process). The pressure in the mold is usually 5 to 12 MPa (50 to 120 bar), which is adjusted according to the actual process and parts.

HP-RTM molding process details flow chart

HP-RTM molding process advantages:

(1) Fast mold filling, good infiltrating effect, significantly reduce the bubble, reduce the porosity;

② The use of high-activity resin, shorten the production cycle, process stability and repeatability;

③ The use of internal release agents and self-cleaning systems, the surface quality of the parts is good, the thickness and shape deviation is small, can achieve low-cost, short cycle mass and high quality production.

HP-RTM process disadvantages are as follows:

① High requirements for resin systems, especially high-performance resin systems;

(2) The equipment system is complex and the manufacturing technology is difficult;

(3) High equipment investment and relatively high manufacturing costs;

④ the amount of resin wasted each time flushing the pipeline is large;

⑤ Fiber volume content and porosity are difficult to reach the indicators advertised by manufacturers.

HP-RTM specific process flow

1. Upstream process

1) Fiber open cutting

Firstly, the drum of the carbon fiber fabric is fixed on the rotation axis of the automatic cutting machine, and the pre-formed cutting pattern is input to the automatic cutting machine to optimize the arrangement of the cutting pattern; Unfold the carbon fiber fabric roll, start the cutting machine, and automatically cut the preformed body lay-up pattern, as shown in the figure. Using the suction cup of the mechanical arm, the cut fiber layer is picked up and transferred to the next process equipment.

2) Spray the predetermined agent

Transfer the cut fabric to the predetermined agent spraying equipment, and start the spraying equipment to spray the predetermined adhesive on the surface of the fiber fabric, and move the fiber fabric during spraying so as to evenly spray.

3) Localization and superposition of fiber layer

The carbon fiber fabric coated with the fiber presetting agent is transferred to the fabric stacking equipment, and the fiber fabric is positioned and stacked successively according to the designed fabric layering structure, and then laid flat on the fabric layering conveyor belt.

4) Fiber laying

The composite fiber fabric is transferred to the fiber preforming equipment by using the fabric superposition conveying equipment. When the fiber fabric is transferred, it is necessary to accurately control the moving speed and position of the conveyor belt to prevent the movement or dislocation of the fiber fabric during the laying process, which will affect the performance of the workpiece.

5) Fiber fabric predetermined type

The fiber fabric layer is evenly spread into the preforming die. First, the pressurized indenter in the center of the preforming body is pressed down to compress the fiber layer structure, and the pressurized indenter of the preforming die is successively pressed from the center to the outside, so as to reduce the crumpling of the fiber as much as possible when pressing, so as not to affect the performance of the product. Under the action of hot pressing of preforming die, the fiber preforming body is shaped.

6) Cutting of preform

The carbon fiber reinforced body after preheating and prepressing is transferred into the preform cutting mold and covered with the cutting mold. According to the cutting mold, the robot arm cuts the cutter along the edge of the mold to cut off the excess carbon fiber and obtain the fiber preform body corresponding to the size of the injection mold cavity.

This article is collected by China Composites Industry Association from the network, the article is not used for commercial purposes, only for the industry to communicate, please specified.