Automotive Plastic Parts: Types, Materials and Manufacturing

Plastics account for approximately 10% to 15% of the total vehicle weight in passenger vehicles, and this proportion continues to grow. A single vehicle utilizes over 13 main types of plastic materials to manufacture thousands of different plastic auto components, such as body panels, interior trim parts, air intake system and bumper. This article will provide an overview of the main plastic parts used in automobiles.

Plastic Parts in A Car

Plastic parts are extensively used in modern passenger vehicles across various key areas, including interior and exterior trims, powertrain systems, and functional components, such as instrument panels and headlamp lenses. To fully appreciate the diversity of these applications and their contribution to vehicle lightweighting, we should examine their locations and the roles they play.

Instrument Panel

The instrument panel is one of the most critical functional components and structurally the most complex system within the vehicle interior. It works in conjunction with the seats and airbags to safeguard occupants, thus imposing high requirements on its styling, haptic quality (texture/feel), comfort, and occupant protection features. The instrument panel main body can be categorized into hard instrument panels and soft instrument panels based on the surface texture.

Automotive dashboards are predominantly plastic, varying primarily in rigidity. The soft type is polyurethane (PU), which is relatively light and offers superior safety (energy absorption) and sound absorption characteristics. The hard type is polypropylene (PP), which is comparatively lower in price. High-end vehicle interiors typically opt for polyurethane.

Instrument Cluster Hood

The instrument cluster hood is manufactured through injection molding using materials such as ABS, ABS/PC, and Reinforced PP. ABS and ABS/PC struggle to meet stringent heat resistance requirements and are more expensive than Reinforced PP, but they are easier to surface treat (allowing for painting, chrome plating, etc.) to meet specific styling demands. Reinforced PP can satisfy thermal resistance requirements but is challenging to customize with specialized surface treatments. Material selection involves balancing actual performance requirements against cost.

Center Console Panel

The center console Panel is in the central area of the IP and directly influences the instrument panel’s overall visual effect. OEMs frequently change the styling or surface treatment of the CCP to achieve the effects of minor model updates or variations. It requires excellent capability for customized surface treatment. Due to the need for frequent maintenance of electronic or HVAC components, it must be easy to install and disassemble, requiring a certain degree of strength and toughness. In the design process, the CCP typically uses ABS or ABS/PC, with finishes like painting, chrome plating.

Glove Compartment/Box

The glove compartment primarily serves to store items and protect the occupant’s knees. Its appearance must be consistent with the IP, sometimes requiring additional exterior treatment. The inner and outer panels of the glove box are generally injection molded using modified PP or PC/ABS. Luxury vehicles often employ a flocking process inside to prevent stored items from rattling and generating noise while driving. Glove box accessories such as handles, pivot pins, latches, and clips are often made of Polyoxymethylene (POM), which resists repeated impact and wear.

Air Vent Assembly

The air vent assembly is composed of front and rear guide vanes, the vent housing/body, damper flaps, and a rotary switch. Automotive air conditioning vents are frequently adjusted and exposed to alternating cold and hot airflow. This necessitates materials with high heat resistance, impact resistance, flexibility (toughness), and dimensional stability. Recommended materials are often PA6 or ABS/PC for the blades/vanes, ABS or PP+T (Talc-filled PP) for the vent housing, PP+T for the damper flap structure with EPDM as the sealing ring, and wear-resistant materials like POM or TPO for the rotary switch assembly.

Door Trim Panel System

The door trim panel is mainly divided into the main body (substrate), insert panel, armrest, decorative trim strip, map pocket, and speaker grille. The main body acts as the skeleton for the entire door panel, supporting all functional and decorative components, requiring sufficient strength and rigidity to maintain its shape and prevent deformation. The commonly used material is Polypropylene (PP). The insert panel material is consistent with the main body. Due to comfort requirements, the armrest generally adopts a three-layer structure: skeleton, foam layer, and outer skin. The decorative trim strips, considering the overall styling effect, require surface treatment and mostly use ABS. The materials for the map pocket and speaker grille are consistent with the main body.

Bumper

The bumper system, consisting of the front and rear bumpers, uses the largest volume of plastic material in automotive exterior parts, accounting for approximately 42% of the total plastic consumption in a vehicle. The bumper is a safety component designed to absorb the immense energy generated during a collision, minimizing personal injury to occupants. Therefore, the bumper must pass a series of relevant tests and regulations regarding exterior protrusions and crash performance. For instance, the bumper must be able to return to its original shape after a collision at 9 km/h and must possess resistance to stone chipping. Material selection for the bumper must thoroughly consider properties such as durability, hardness, and strength. Furthermore, the material must exhibit characteristics such as energy absorption, deformation resistance, and good moldability. Hence, the choice of material is crucial for realizing its intended function.

The front and rear bumpers are typically manufactured using Polypropylene (PP) material. On one hand, this choice facilitates processing and lowers costs, while ensuring the bumper has sufficient elasticity and buffering/energy-absorbing capacity, providing effective protection against bodily harm to occupants. On the other hand, it reduces the high mass associated with metal bumpers, contributing to vehicle lightweighting.

Headlamp Lens

The headlamp lens is required to maintain the headlamp’s brightness over extended use without degradation and to protect the light source. This demands a plastic with excellent moldability, high transparency, and sufficient surface hardness. Therefore, high-performance optical plastics such as Polycarbonate (PC) are the material of choice for the headlamp lens, thanks to their high strength, UV resistance, toughness, and excellent light transmission properties.

Air Intake Grille

Many vehicle grilles feature chrome plating, lending a strong metallic feel, but they are, in fact, also plastic. The primary functions of the air intake grille are to cool the engine and manage airflow at the front of the vehicle, which imposes high requirements on the material’s moldability. ABS is a commonly used material for the grille due to its high impact resistance, ease of molding, and suitability for electroplating.

Types of Plastics Used in Automotive

These materials can primarily be categorized into Commodity Plastics and Engineering Plastics, and their unique properties dictate their specific applications in interior and exterior trims, powertrain systems, and structural components. The following section will detail the physical properties, processing characteristics, and key advantages of nine crucial polymers, including Polyethylene (PE), Polypropylene (PP), Polyamide (PA), and Polycarbonate (PC), showcasing the precise utilization of materials science in modern automobiles.

Polyethylene (PE)

It is a crystalline plastic formed by the polymerization of ethylene. It exhibits good melt flow properties. Low-Density Polyethylene (LDPE) is produced by the high-pressure method, with a lower crystallinity of 45%–65%. It features good flexibility, elongation at break, impact strength, and transparency. High-Density Polyethylene (HDPE) is produced by the low-pressure method, with a high crystallinity of 85%–95%. It possesses higher mechanical strength and higher service temperature, making it suitable for blow molding, injection molding, and extrusion of various bottles, basins, barrels, sheets, pipes, and profiles.

Polypropylene (PP)

It is a crystalline polymer with low density and good heat resistance. Its properties are similar to PE, but it has a high molding shrinkage rate, good melt flowability, and outstanding anti-fatigue performance. The resulting products have good mechanical properties, high rigidity, and surface hardness, notably featuring excellent resistance to bending fatigue. It can withstand hundreds of thousands of folding and bending cycles without failure, making it highly suitable for hinges. Its long-term service temperature can reach 120°C, and up to 150°C when not subjected to external force. It has low water absorption and outstanding chemical resistance, being able to withstand acids, bases, salts, and many polar organic solvents below 80°C.

Polyvinyl Chloride (PVC)

Various additives can be incorporated into PVC resin to produce plastic products with diverse properties. PVC exhibits amorphous polymer characteristics; its melt has poor thermal stability, a narrow processing temperature range, and can be corrosive to molds. At low temperatures, PVC tends to become stiff and brittle. Flexible PVC is commonly used in automotive design as sealing and decorative materials.
Polystyrene (PS)It is a colorless and transparent plastic. PS is an amorphous polymer with good melt flowability and is not easily decomposed, offering good injection molding processability. Its mechanical properties are generally average, and its impact resistance is poor. It is prone to fracture upon dropping or heavy impact. Plastic parts should have uniform wall thickness, rounded corners at connecting surfaces, and should avoid the design of inserts. Excessive residual stress in the plastic parts can lead to stress whitening and cracking. PS has a large coefficient of thermal expansion. Alternating expansion and contraction forces can cause cracking in the connection bases of the plastic parts.

ABS (Acrylonitrile Butadiene Styrene)

It is an amorphous plastic copolymerized from styrene, butadiene, and acrylonitrile. ABS generally has better toughness than High Impact Polystyrene (HIPS) and good overall mechanical properties. It has moderate melt flowability and is easy to injection mold. It exhibits low molding shrinkage, resulting in stable product dimensions. Its service temperature ranges from -40°C to 100°C. It has good chemical stability, excellent printability, dyeability, adhesion, and good electroplating properties, along with satisfactory acoustic characteristics, making it suitable for audio equipment housings. ABS is frequently used to manufacture various automotive accessories and structural bodies, such as handles, lamp covers, automobile dashboards, radiator grilles, and decorative parts treated with surface processes like electroplating.

Polymethyl Methacrylate (PMMA)

It is a highly transparent amorphous plastic, commonly known as Acrylic. Acrylic has poor surface hardness, making it easily scratched by hard objects. Environmental stress cracking is another weakness of PMMA.

Polyamide (PA)

It is a multi-variety crystalline polymer, commonly known as Nylon. It is tough, wear-resistant, and fatigue-resistant, but it is highly moisture-absorbent. It has a high melting point and a narrow melting temperature range. The material must be thoroughly dried before injection. Due to low melt viscosity, stringing and flash are common during injection molding. The mold temperature influences the crystallinity. Plastic parts have a high and fluctuating molding shrinkage rate, and the dimensions of molded products can be unstable due to moisture absorption and other factors. PA6 offers good elasticity and high impact strength, but greater water absorption. PA66 provides high strength and good wear resistance.

Polycarbonate (PC)

It is an amorphous polymer with outstanding impact strength and creep resistance, as well as good resistance to cold and heat. PC has excellent mechanical and electrical insulation properties, and good transparency. Molded products have a relatively small shrinkage rate, resulting in high dimensional accuracy. It is the second-highest production volume engineering plastic after PA. PC’s impact strength is 2–3 times that of PMMA, and its creep is about 10% of PMMA. PC can be used long-term in the range of -100°C to 300°C, has a thermal decomposition temperature >310°C, and its flammability rating is self-extinguishing. At room temperature, it resists dilute acids and is relatively stable towards alcohols, oils, and salts, with the exception of formaldehyde.

Polyoxymethylene (POM)

It is a highly crystalline polymer with excellent physical and mechanical properties. It is wear-resistant, water-resistant, corrosion-resistant, and possesses good dimensional stability. It has moderate melt flowability, a narrow material melting temperature range, is highly heat-sensitive, and prone to decomposition. Reinforcement with glass fiber can reduce the molding shrinkage rate. Prolonged exposure to the atmosphere accelerates aging. Its long-term service temperature is -40°C to 100°C. It exhibits high rigidity, high hardness, and high elastic modulus, combined with good impact strength. Its specific strength and specific stiffness are close to those of metal materials, and it has a low friction coefficient and wear volume, along with excellent self-lubricating properties.

How Getzshape Can Help

Getzshape is your essential manufacturing partner in producing lightweight plastic car components. By leveraging our certified network and advanced equipment, Getzshape can handle the complex CNC machining, injection molding required for plastic auto components, ensuring your instrument panel system, headlamp lens, bumpers and body panels meet the lightweighting necessary to achieve next-generation vehicle performance and efficiency goals.