LFT-D

LFT-D is the abbreviation of Long Fiber Reinforce Thermoplastic In Direct Processing. This paper describes the process, product characteristics and applications of LFT-D technology for compression molding of long fiber reinforced thermoplastics.

Compared to GMT and LFT-G, which rely on semi-finished sheets or pellets, LFT-D is produced directly from polymer masterbatches and glass fibers on a daily basis, eliminating the intermediate process of sheeting or pelletizing. This reduces costs and makes it easier and more practical to select raw materials for the product.

Polymer pellets can be quickly adjusted and converted to meet product requirements and adverse conditions that occur during production. The fibers used for reinforcement can be varied in terms of formulation content and length according to the mechanical properties required. For some special physical properties and some special characteristics, such as thermal stability, flame retardancy, heat aging resistance, coloring, water absorption resistance, etc., the final product performance can be improved by directly adding other modification additives. The LFT-D process will result in a unique material formulation that can be adapted to the performance requirements of most parts for different product requirements.

The LFT-D process

The typical LFT-D process is that polymer pellets and additives are fed into a dosing and feeding unit, which is initially programmed to ensure that the designed ratio of material is fed. The proportionally dosed feedstock is plasticized and mixed in a twin-screw extruder, where the molten polymer is passed through a film die to form a waterfall-like polymer film.

Glass fibers are introduced to the top of the polymer film through a specially designed yarn frame, preheated and dispersed, and then merge with the film into a second stage twin-screw extruder where the glass fibers are impregnated, cut and mixed to form a continuous block.

The cutting tool at the front end of the twin-screw glass fiber plastic mixing extruder cuts the block to meet the molding area of the product, and the conveyor belt transports it to the appropriate location, and then sends it into the mold for low-temperature molding, the whole process generally takes 30-50 seconds, which has great processing cost advantages compared to GMT molding.

LFT-D performance characteristics

• light weight and high strength. the density of LFT is about 1.1g/cm3, only 1/5 to 1/7 of steel, tensile strength 50-120 MPa, bending strength 90-120 MPa.
• thermal properties. General plastic temperature of 50 ~ 100 ℃, the use of glass fiber reinforced, can be increased to more than 100 ℃, some special LFT use temperature can even be increased to more than 200 ℃; coefficient of linear expansion than the unreinforced plastic is 25% to 50% lower, the thermal conductivity of 0.3 ~ 0.36 W / (m / K), and thermosetting composites are very similar;.
• Chemical corrosion resistance. This characteristic is mainly determined by the performance of the matrix material. There are many types of thermoplastic resins, and each resin has its own anti-corrosion characteristics; therefore, the matrix resin can be preferably selected according to the environment and media conditions of LFT use.
• good dielectric properties. lft does not reflect radio waves and has good microwave transmission properties. The addition of conductive materials to LFT can improve its conductive properties and prevent the generation of static electricity.

LFT-D economic advantages

• The direct production mode of raw materials greatly reduces the cost of final products and avoids the higher procurement and related logistics and storage costs of semi-finished products.
• As the raw materials required for production are directly procured, the rapid change of raw materials can compensate for the long lead time and high management costs associated with the procurement of raw materials for semi-finished products, indirectly reducing production costs.
• Low raw material usage during processing - low start-up consumption, solving the problem of raw material loss.
• Immediate compression molding using the residual temperature of the plasticized material, eliminating the energy loss caused by secondary heating of semi-finished sheets, and the production process is all controlled by the program and the production line runs automatically, significantly reducing overall energy consumption.
• The thermoplastic LFT material is recyclable plastic, and the LFT production line can process recycled material online, which is environmentally friendly and brings excellent economic benefits at the same time.
• A large number of manual operations are reduced, and labor costs are reduced considerably.

LFT-D technical advantages

• Formulation adjustment is more flexible and diverse, only need to make corresponding adjustment to the LFT-D production line equipment, you can use PP, PA6, PET, ABS, PC and other different polymer pellets, and for the special requirements of different products can quickly adjust the ratio of raw materials on site.
• Glass fiber as an important component in composite products to ensure mechanical properties, the continuous adjustable molding technology will greatly optimize the performance of the products.
• The final product retains more than 20mm of glass fiber length, solving the problem of low mechanical strength caused by too short glass fiber length.
• Excellent mixing process, which can ensure full mixing of glass fiber and plastic and uniform fiber distribution even in the ribbed part.
• Superior flowability, which greatly improves the surface quality of the product.
• The high automation of LFT-D equipment ensures the quality stability of the products.

LFT-D application scope

At present, the main application area of LFT-D production technology is still automotive manufacturing. At present, the parts with more mature applications include bumper bracket, instrument panel skeleton, seat skeleton, underbody guard, interior trim parts bracket, wheel cover, battery tray, grocery box cover, rear liftback door, spare tire box, etc.

For example, underbody shield, which needs to meet the requirements of sound absorption, heat insulation, corrosion prevention, high rigidity, high impact strength, etc.. Initially, the manufacturing materials evolved from steel and aluminum to GMT, and now MDC has a lower cost and more flexible molding method, LFT-D technology. In addition, MDC Mould has started to use LWRT, a lightweight, high-strength thermoplastic with highly expanded fibers, which is less tough than traditional GMT but has high specific stiffness and excellent sound absorption properties.

Over the decades, LFT-D has evolved into a leading-edge production model, slowly moving from simple products to complex, functional products in the automotive sector, and LFT is beginning to replace some traditional processes in many areas outside of automotive manufacturing.

MDC offers automotive lightweighting solutions, contact us today for LFT-D molding solutions.