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Long fibre reinforced thermoplastic 101

Join Date: 2022-05-21

As early as the 1980s, European and American countries put forward the concept of LFT. However, due to the relative backwardness of the fiber impregnation technology and the injection molding, compression molding process and production equipment of long fiber pellets at that time, and the research and application of short fiber reinforcement, filling and other modification technologies of thermoplastics at that time Great progress has led to slow progress in the research of LFT technology. In the mid-1990s, automobile lightweight became the development trend of new types of automobiles, which made people once again turn their attention to LFT research and development.

LFT, long fiber reinforced thermoplastic material, is compared with ordinary fiber reinforced thermoplastic materials, under normal circumstances, the fiber length in fiber reinforced thermoplastic materials is less than 1 mm, while in LFT, The length of the fiber is generally greater than 2 mm. The current processing technology has been able to keep the fiber length in the LFT above 5 mm. LFT (Long fibre reinforced thermoplastic) uses PP the most as the matrix resin, followed by PA, and some resins such as PBT, PPS, SAN, etc. are also used. The long fiber is impregnated with a special resin system through a special mold to obtain a long strip fully infiltrated by the resin, and then cut into the required length as required. Depending on the end use, the finished product can be strips, strips, boards with a certain width, or even rods, which can be directly used to replace thermosetting products. There are many applications of LFT in automobiles, and the main advantage is the flexibility that materials can be compounded in it.

Three LFT Types

There are three main types of LFT: D-LFT, LFT-G and LFT-PP. Each has its own advantages and disadvantages. LFT-D is the most commonly used type of compression molding for composite parts. D-LFT is a relatively new process with a short development time. Polyolefins have long been the mainstay of D-LFT composites, but styrenic thermoplastics are replacing these materials. This new process is a key part of the development of direct long-fiber thermoplastic composites and is being extended to exterior body panels.

Advantages of LFT

LFTThe manufacturing process of the LFT sheet is very similar to the SMC (sheet molding material) in the thermosetting composite glass fiber reinforced plastic. The same is made by pressing a sheet in a mold. LFT is a hard sheet that is heated and softened and then cold-pressed in a mold, while SMC is a cold-pressed soft sheet that is placed in the mold and hot-pressed. Compared with SMC sheet, LFT sheet has the following advantages in technical performance:

  • 1. It is harmless and tasteless, which can improve the working environment.
  • 2. Light weight, density is only 1~1.2g/cm3.
  • 3. Leftovers and waste products can be recycled to minimize waste.
  • 4. The strength is higher than that of SMC, and the impact resistance is particularly outstanding.
  • 5. Corrosion resistance and better electrical performance.

LFT compression molding

The compression molding process is an important step in the manufacture of lightweight composites, which allows the production of LFT articles of complex shapes with high precision. Compression molding can produce products with 5 to 20 mm long fibers. Using UD tape and D-LFT together also produces parts with better print-through and dispersion. The use of D-LFT in automotive engine bays allows parts to have higher heat and wear resistance. This process is relatively inexpensive than the metal impact forming process. It offers excellent economy and performance even in small batches. LFT compression molding process involves a press that presses material into a mold cavity and cures the semi-finished product. Quickly shut down the press to prevent the raw material from solidifying in the LFT mold. During this process, molten material flows from the center to the edges of the semi-finished product. This allows a high degree of geometric freedom.

Advantages of LFT Compression Molding

While injection molding is a common option, it can cause severe fiber breakage in the LFT. Fiber length determines the impact properties of LFT. Advantages of LFT compression molding include low cost and excellent design flexibility, enabling the molding of complex parts and oversized flat items.

LFT compression molding is more cost effective than injection molding. The process has high efficiency and is suitable for mass production. Because parts are loaded manually, LFT molding reduces the number of steps required to produce each part. It also eliminates the need to clean the mold after each molding cycle. The process is also much faster than injection molding. Additionally, it is highly flexible, enabling molded parts to be shaped into complex shapes with minimal effort. It is commonly used to make plastic parts for electronic and automotive applications.

The benefits of LFT compression molding go beyond cost-effectiveness. It is an excellent solution for producing complex parts. It can be combined with B-face geometry to improve part durability. The shrinkage of LFT parts is extremely low or even zero. The use of thickeners in the raw material makes it suitable for thermoforming and avoids significant fiber orientation distortion.

However, LFT compression molding has its drawbacks, including poor final product consistency and flash. Also, it doesn't work with some part types.

bus compression tooling

MDC has been always committed to manufacturing high quality compression tools. For this purpose, we purchased 4000T press and five axis high speed machining center and other advanced equipment. MDC works with leading companies in the industry to help them develop and manufacture molds. LFT moulding can be used to form automotive parts.

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