RTM/HP-RTM Fabrication Method for CFRP

Contents

Introduction
Overview
CFRP Characteristics
CFRP Manufacturing Methods
RTM & HP-RTM Fabrication Methods
Summary

Introduction

The term carbon fiber has become high-use jargon in recent years. While most people know it is a lightweight and strong substitute material for metal, frequently used in commercial planes and automobiles, that’s usually the extent of information we have. So, what else is there to know about this material?

Overview

Modern carbon fiber technology (material) originated in Japan and is now widely employed combination with a polymer plastic matrix to create composite materials known as carbon fiber reinforced plastics (composite material). In this section, we’ll take a deeper look into RTM and HP-RTM, one of the many techniques used in CFRP molding.

CFRP Characteristics

CFRP is distinguished by “lightweight, strong, and non-corrosive” characteristics. Read more here in our previous articles.

A Lighter and More Durable Material—CFRP

CFRP’s Potential

CFRP Manufacturing Methods

Although CFRP has various advantages, what manufacturing methods are utilized?

In this section, we will focus on two key topics: 1) Autoclave Molding as the leading molding technique, and 2) Prepregs, the core CFRP material used in Autoclave Molding.

Carbon & CFRP Autoclave Molding?

Prepregs: What are CFRP Prepregs?

RTM & HP-RTM Fabrication Methods

RTM Method

RTM stands for Resin Transfer Molding and refers resin injection molding. Unlike the autoclave molding whereby the carbon fiber base material is pre-impregnated with resin, with RTM we first arrange and shape the fiber base material (preform) inside an integrated male and female mold in accordance with the product design. After setting, we impregnate the base material with a resin mixed with a primary and hardening agent and then cure the product.

The major difference is that autoclave molding is suited to small-lot productions and large-scale thin-walled structures that start with prototyping, while RTM requires a metal die and offers a reasonable degree of product stability, making it ideal for medium lot production. Accommodating last minute changes to the plate thickness or complex shapes is limited, since the product is formed within a male/female mold.

HP-RTM Method

HP-RTM (High Pressure Resin Transfer Molding) refers to high pressure resin injection molding.

The HP-RTM process is achieved with a dedicated press, resin injector, mixing head for collision mixing of the primary and hardening agents, and a mold that can accommodate the mixing head. This technology was utilized in the frame and chassis of the BMW i3 electric vehicle and with the development of high-speed curing resin allows for product mold removal in only 3-minutes. The curing efficiency solves extended curing times (4 to 6 hours) of conventional autoclave molding, which was one of the key disadvantages. *At the time, this advancement made huge waves in the industry. The HP-RTM method delivers significant cost efficiency compared to prepreg sheets due to the elimination of specialized facilities and control

Advantages

High quality, high cycle times (Current developments in improved resin allow for product mold removal in 1–1.5 minutes.)
Suitable for medium- to high-volume production; material handling robot enabled automation.

Disadvantages

High equipment/facilities and mold costs.
Requires expert intuition and skill to determine the molding conditions.
Since resin is impregnated into the fiber base material in the X/Y/Z directions under high pressure, the fiber base material tends to meander. Devising ways to expel the fine air pockets (voids) inside the matrix and exert the unique strength characteristics of CFRP requires specialized skill and ingenuity. Currently various molding methods are being developed for varying matrix materials/forms and molding conditions. These include the “Gap-RTM method,” in which the mold is not completely closed, but left slightly open while the resin is injected to reduce defects and enable molding at low pressure, and “WCM-RTM (Wet Compression Molding),” whereby mixed resin is applied to the base material before it is placed into the mold.

Summary

This issue discussed one of the many CFRP molding methods; RTM and HP-RTM. Molding method selection requires careful consideration of product features, materials, form, size and production lot size to ensure that the optimal method is adopted. Achieving this during the product design stage is a challenging task.

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DMG森精機 - VS1000/40/2050
X軸：2,050mm（ストローク）／ Y軸：1,000mm ／ Z軸：600mm ／テーブル作業面：2,250×1,000mm

ASHIDA MFG Co., Ltd.
Autoclave Oven 2
Size : Ø1,150x1,000mm / Operating temperature : at normal temperature - 400℃ / Design pressure : 2.0Mpa (maximum working pressure) / Vacuum system : back suction system / Vacuum units : 5

ASHIDA MFG Co., Ltd.
Autoclave Oven 3
Size : Ø3,000x6,000mm / Operating temperature : at normal temperature - 200℃ / Distribution accuracy : ±2.5℃less / Heating rate : 4.0℃/min. (empty furnace) / Cooling rate : 4.0℃/min. (empty furnace) / Design pressure : 0.99Mpa (maximum working pressure) / Working pressure : 0.7Mpa less (if no specification from the manufacuturer 0.3Mpa around) / Pressure accuracy : ±0.02Mpa（for pressure setting of ０ - 0.99Mpa/cm²） / Boost pressure accuracy : 0 - 0.03Mpa/min / Pressure source : compressed air (regular use) / Vacuum system : back suction system / Vacuum units : 10

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Oven
Size : W1,000xH1,000xD1,000mm / Temperature range : Environmental Temperature +20 - 300℃ / Temperature elevation capability : Environmental Temperature (20 - 40℃) - 300℃ / 45min less / Vacuum system : back suction system / Vacuum units : 10

ESPEC CORP.
Temperature & Humidity Chamber

INSTRON
Static Universal Testing Machine 5985

Oven
Size : W7,000xH3,000xD2,000mm / Temperature range : Environmental Temperature +20 - 300℃ (Max) / Temperature elevation capability : Environmental Temperature (20 - 40℃) - 300℃ / 60min less / Vacuum system : back suction system / Vacuum units : 10

NEO
X axis : 4,000mm (stroke) / Y axis : 2,000mm / Z axis : 1,200mm / C axis : 0° - ±270° / B axis : 0° - ±110° / Table working place : 4,000x2,000mm

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Painting booth
Various painting, and clear finish is done in dedicated painting booth

Adhesion, Finishing, Coating Room
Finishing process, such as trimming, drilling, and bonding, surface treatment of the molded product type and is done in a private booth

Toshiba Matrixeye EX (Ultrasonic flaw detector)
Matrix-Arrey : 32

AMETEK CREAFORM Metra
SCAN750 Elite (3D scan)

Olympus Corp.
Inverted Microscopes

Oven
Size : W450xH450xD450mm / Temperature range : Environmental Temperature +20 - 650℃ / Temperature elevation capability : Environmental Temperature+50 - 650℃/120min less

Cutting Plotter Table working place : W1,500xL3,500mm

SHIMA SEIKI MFG., LTD
Cutting Plotter

KUKA
Robot

Krauss Maffei
Epoxy resin injection machine Resin 60L ／ Hardener 25L

Krauss Maffei
630t Press machine Height total 5,200mm ／ Length max 1,500mm ／ Width max 1,200mm ／ Whole cycle time per component part 240sec

DMG森精機 - NV5000B/40
X軸：1,020mm（ストローク）／ Y軸：510mm ／ Z軸：510mm ／テーブル作業面：1,320×600mm

Big sized clean room
JIS B 9920 cleanliness class maximum concentration (Pcs/m³） / Class 5 : 100,000m³ / Capacity : m² (16,000x16,000mm) 760m² (16,000x16,000x3,000mm) / Temperature and humidity condition : Temperature : 23℃±3℃, Humidity 65% less / Ambient conditions : Temperature 35℃ during summer, Humidity 70% less / Ambient conditions : Temperature 35℃ during summer, Humidity 70% less / Temperature -5℃ during winter, Humidity 40% less