The Application Of LFT (Long Fiber Thermoplastic) Composite Materials in Compression Molding Dies
Jan 16, 2026
LFT, as a type of high-performance composite material, has a core advantage in that the fiber length is typically maintained at over 5 millimeters. Compared with short-fiber reinforced materials and thermosetting materials, it offers superior mechanical properties, recyclability, and molding flexibility. The compression molding process, with its characteristics of closed mold operation, precisely controllable pressure, and strong stability in batch production, has become the core carrier for the large-scale application of LFT materials. The collaborative adaptation of the two has formed mature application systems in multiple fields such as automobiles, new energy, and home appliances, providing core support for the lightweight and green upgrading of products.
I. The Foundation of Compatibility between LFT Materials and Compression Molding Process
The efficient compatibility between LFT and compression molding tools stems from the deep alignment of material properties and process principles. At the material level, LFT primarily uses polypropylene (PP) and polyamide (PA) as the mainstream matrix resins, combined with reinforcing fibers such as glass fiber and carbon fiber, and processed into long, strip, or block-shaped preforms through a dedicated impregnation process. These preforms exhibit excellent fluidity when heated, allowing them to fully fill the mold cavity under the pressure of the compression molding process. Moreover, the fiber length loss is within a controllable range - the compression molding process can maintain the average fiber length in the final product at 4-20 millimeters, significantly outperforming injection molding in this regard. This effectively maximizes the reinforcing effect of long fibers, thereby significantly enhancing the impact resistance, creep resistance, and heat resistance of the products.
At the technological level, LFT molding mainly consists of two technical routes: LFT-G (granule molding) and LFT-D (online direct molding), both of which can be efficiently adapted to molding dies. Among them, LFT-G uses granules with a length of 12-25 millimeters as raw materials, with granules around 25 millimeters being more suitable for compression molding. After heating, plasticizing, and pressurizing in the mold, the fiber length of the product can be stably maintained at 3.2-6.4 millimeters. LFT-D, on the other hand, integrates online compounding, fiber impregnation, extrusion of preforms, and molding into a single process, eliminating the semi-finished product processing stage. The fiber length can be flexibly adjusted to 10-50 millimeters, and the fiber content, resin formula, and additive ratio can be precisely adjusted according to the specific requirements of the mold product. It can meet the molding requirements of complex-structured molds, and the molding cycle can be shortened to within 60 seconds, significantly enhancing the efficiency of large-scale production.
Compared with traditional materials such as metals, SMC (Sheet Molding Compound), and GMT (Glass Fiber Mat Reinforced Thermoplastic), LFT (Long Fiber Thermoplastic) compression molded products have significant advantages in the balance of cost and performance: compared with metals, the investment in molds and processing equipment is lower, the weight reduction effect of the products can reach more than 30%, and the overall strength of the components is high, which can reduce subsequent assembly processes; compared with SMC, the LFT compression molding process is odorless and non-toxic, the scraps can be recycled and reused, the molding speed is several times faster, and the strength and impact toughness of the products are better; compared with GMT, the LFT raw material has better fluidity, can adapt to more complex mold cavities, and the material cost is lower, while the core performance is basically the same.
II. Core Design Points of LFT Compression Molding Dies
The flowability characteristics of LFT materials and the requirement for fiber retention impose specific demands on the structural design, temperature control, and exhaust system of compression molding dies. The rationality of the design directly affects the quality of the products and the stability of production.
1. Mold Structural Design
The cavity design must fully adapt to the flow pattern of LFT preforms, adopting a gradient runner structure to avoid sharp corners and narrow slots that can cause fiber agglomeration or breakage. At the same time, the gate location and number should be optimized based on the complexity of the product to ensure uniform filling of the cavity. For LFT-D processes, the cavity size of the mold must precisely match the specifications of the online extruded preforms to reduce material waste from cutting and increase material utilization to over 95%. Additionally, the parting surface of the mold should be designed with high-precision sealing to prevent melt overflow during heating, ensuring dimensional accuracy of the products, especially for components in the automotive industry and battery pack parts where tolerance control is strict.
2. Temperature and Pressure Control Design
The mold should be equipped with a zoned temperature control system, setting appropriate temperature parameters based on the characteristics of the LFT matrix resin: the compression molding temperature for PP-based LFT is typically controlled at 180-220°C, while for PA-based LFT, due to higher heat resistance requirements, the temperature should be increased to 200-240°C to ensure complete plasticization of the preform and prevent thermal damage to the fibers. In terms of pressure control, the mold must be capable of withstanding a basic extrusion pressure of 4-6 MPa and a compression molding pressure of 5-15 MPa. The pressure loading rate should be precisely controlled through a hydraulic system to prevent fiber breakage due to excessive pressure while ensuring product density, keeping the production defect rate below 1%.
3. Exhaust and Demolding Design
During LFT compression molding, a small amount of volatile substances are produced, and residual air remains in the cavity. Therefore, the mold should have exhaust channels at critical locations such as the parting surface and the end of the runner, with precise control over the width and depth of the channels to facilitate the rapid escape of air and volatiles while preventing melt leakage. The demolding system should adopt a multi-point uniform ejection structure to avoid uneven force on the product during ejection, which could cause deformation or fiber peeling. Additionally, anti-sticking treatment can be applied to the mold cavity surface to improve demolding smoothness and reduce the workload of subsequent trimming processes.
Automotive front frame
III. Core Application Scenarios of LFT in Compression Molding Dies
1. Automotive Industry: The Main Solution for Lightweight Structural Components
The automotive industry is the most mature application field of LFT compression molding technology. Driven by the trend of lightweighting and ELV environmental regulations, LFT compression molded products have widely replaced metals and thermosetting materials for the mass production of structural and semi-structural components. In components such as front-end modules, bumper beams, and instrument panel frames, LFT-G compression molded products dominate due to their cost advantages and molding stability. For example, the front-end frame of the Volkswagen Golf V is made using LFT-D compression molding, balancing structural strength and lightweighting requirements.
In the field of new energy vehicles, LFT molding is a core supporting technology. The end plates of the battery pack of NIO ET5 adopt long glass fiber reinforced PA6 LFT material, which is formed through LFT-D in-line molding molds. The fiber length retention reaches 35mm, and the tensile strength can reach 180MPa. The molding cycle only takes 90 seconds, reducing the weight by 35% compared to traditional aluminum alloy end plates. At the same time, it has excellent insulation performance, effectively avoiding the risk of battery short circuit. The longitudinal beams of the chassis and the protective plates of the battery pack, etc., achieve the unification of anti-stone impact, corrosion resistance and lightweight through the optimization of the molding mold structure, with a service life of up to 10 years or 200,000 kilometers. In addition, the seat frame, spare tire compartment and other parts adopt LFT molding technology, which can achieve the integrated molding of complex structures through molds, reducing the number of parts and lowering assembly costs.
2. Household Appliance Industry: Upgrading Path of High-Performance Components
In the household appliance field, LFT molding technology is mainly used to solve the problems of insufficient strength and limited service life of traditional materials, especially for components of washing machines and air conditioners that have load-bearing and vibration requirements. A well-known washing machine manufacturer uses LFT-G PP-LGF 50% material to mold the drum component through a molding mold. By optimizing the mold temperature and pressure parameters, the mechanical properties of the product are improved by 30% to 40%, significantly enhancing the wear resistance and vibration resistance of the component. Currently, more than 2,000 tons of materials have been applied in batches. In addition, LFT molded products are used for outdoor air conditioner brackets, refrigerator load-bearing structural parts, etc., which can reduce weight while improving weather resistance and service life, meeting the usage requirements of outdoor and complex working conditions.
3. Other Fields: Scenario-based Expansion Applications
In the field of construction machinery, LFT molded products are used for protective plates, operation platforms, etc. Through mold optimization, a structure design that is resistant to impact and corrosion is achieved. Compared with metal parts, they are lighter and have lower costs. In the construction field, LFT molded products are utilized for their weather resistance and insulation properties, and are formed into decorative panels, load-bearing brackets, etc. through special molds, suitable for long-term outdoor use scenarios. In the new energy field, LFT molding technology is also used for photovoltaic brackets, energy storage equipment shells, etc., achieving the unification of lightweight and insulation performance, in line with the development trend of green energy.
LFT New Energy Vehicle Battery Tray
IV. Core Advantages and Technical Challenges of LFT Molding Applications
1. Core Application Advantages
In addition to the performance and cost advantages mentioned earlier, LFT molding applications also have significant environmental value and batch production advantages. Thermoplastic LFT materials can be recycled, and production waste and scrapped products can be re-used for molding after being crushed and granulated, with a retention rate of mechanical properties of over 85%, in line with the circular economy development policy. The closed mold forming characteristics of LFT molding molds have no VOC emissions, effectively improving the production environment. At the same time, the molding cycle is shortened by more than 60% compared to hand lay-up processes, with a low defect rate, fully meeting the requirements of large-scale mass production. In addition, LFT material formulas have high flexibility, and through the collaborative optimization of molds and material formulas, customized product functions can be achieved, such as adding flame retardants, UV stabilizers, etc., to meet the special needs of different scenarios.
2. Existing Technical Challenges
Although LFT molding applications have become relatively mature, they still face some technical bottlenecks: First, it is difficult to control the uniformity of fiber distribution. Improper design of the mold flow channel can lead to fiber agglomeration or uneven orientation, affecting the consistency of product performance. Second, the molding of complex structure products is difficult. For deep cavity and thin-walled parts, it is necessary to precisely control the mold temperature field and pressure field to avoid insufficient filling of the blank or excessive fiber breakage. Third, the cost adaptability of molds is insufficient. High-precision LFT-D molding molds have a high initial investment, which has a certain impact on the economic efficiency of small and medium batch production.
LFT tray
V. Application Trends and Development Directions In the future, the application of LFT in compression molding molds will be iteratively upgraded around three major directions: "high performance, high efficiency, and low cost".
At the material level, the composite application of carbon fiber reinforced LFT and high-performance resin matrix will be gradually promoted. Combined with the design of dedicated compression molding molds, the specific strength of the products will be further enhanced, and the application will be expanded to high-end fields such as aerospace. At the process level, the LFT-D technology will continue to be optimized. Through the intelligent interaction between the mold and the online extrusion system, the real-time and precise control of molding parameters can be achieved, shortening the molding cycle and improving the fiber retention rate. At the mold level, the application of integrated molds, rapid mold changing technology, and simulation-optimized design will become increasingly widespread. Through simulation to predict the flow trajectory of the blank and the distribution state of the fibers, the mold structure can be optimized in advance, reducing the cost and cycle of mold trials.
Meanwhile, with the continuous tightening of environmental protection policies and the upgrading of lightweight demands in various industries, LFT molding technology will accelerate its application in emerging fields such as rail transit components and medical equipment shells. The collaborative innovation of molds and materials will become the core driving force to break through application boundaries, promoting the transformation of LFT molding applications from "substitute" technology to "leading" technology.
