Injection molding plays a significant role in the manufacture of parts and products for a wide range of industries, including automotive, electronics, and medical. The process involves the injection of molten plastic into custom molds to produce solid pieces in large volumes.

In particular, the automotive industry regularly makes use of the injection molding process due to its consistency and reliability. It serves as an ideal method of mass producing high-quality plastic automotive parts that are lighter and comparably durable to metal parts produced through conventional means.

Applications of Plastic Injection Molding in the Automotive Industry

In the automotive industry, the plastic injection molding process is used to manufacture a wide range of parts, including:

  • Panel components such as lenses, bezels, knobs, assemblies, door handles and handle components, housings, and sunroof parts
  • Under-the-hood components such as oil pans, fans and fan shrouds, HVAC kinematics, and radiator end tanks
  • Exterior components such as fenders, grilles, bumpers, door panels, floor rails, light housings, skid plates, and wheel trims
  • Interior components such as air vents, glove compartments, door handles, dashboard faceplates, and instrumentation parts

How to Choose the Right Material for Automotive Injection Molding Operations

Industrial organizations, such as the National Highway Traffic Safety Administration (NHTSA), outline the requirements for materials used in automotive construction and assembly operations. These requirements may refer to various characteristics of potential materials, such as safety and crash performance, fuel efficiency, weather resistance, retention of physical properties in relation to temperature extremes, and compatibility with mechanical fasteners.

When selecting a material for an injection molding operation, there are several factors to keep in mind, including:

  • Tensile Strength
  • Flexural Modulus of Elasticity (FME)
  • Izod Impact
  • Heat Deflection Temperature (HDT)
  • Water Absorption

Common Plastics Used in Automotive Injection Molding Operations

There are five main types of plastics commonly used in automotive injection molding operations:

Acrylonitrile Butadiene Styrene (ABS)

ABS is easy to mold and colorfast. It provides a glossy, high-quality surface finish and demonstrates excellent toughness, strength, impact, and temperature resistance. Additional material characteristics include:

  • Tensile Strength: 4,100 psi
  • FME: 304,000 psi
  • Izod Impact: 7.7 ft × lbs./in.
  • HDT: 200º F @ 66 psi/177º F @ 264 psi
  • Water Absorption: 0.3% in 24 hour immersion
  • Applications: automotive body parts, wheel covers, and dashboards

Acetal

Acetal—also referred to as polyoxymethylene (POM), polyacetal, or polyformaldehyde—is a stiff and dimensionally stable thermoplastic that exhibits considerable toughness, good heat distortion, low moisture absorption, and excellent wear, creep, and chemical solvent resistance. Additional material characteristics include:

  • Tensile Strength: 10,000 psi
  • FME: 420,000 psi
  • Izod Impact: 1.5 ft × lbs./in.
  • HDT: 336º F @ 66 psi/237º F @ 264 psi
  • Water Absorption: 0.25% in 24 hour immersion
  • Applications: fuel systems, interior and exterior trims, and small gears

Polypropylene (PP)

Due to its versatility, polypropylene (PP) is sometimes called the “steel” of plastics. Although flammable and vulnerable to UV wear, PP offers chemical and fatigue resistance, elasticity and toughness, insulation properties, and transmissivity. It is also easily customized through the introduction of special additives or alteration of its manufacturing process. Additional material characteristics include:

  • Tensile Strength: 5,400 psi
  • FME: 225,000 psi
  • Izod Impact: 1.2 ft × lbs./in.
  • HDT: 210º F @ 66 psi/—
  • Water Absorption: slight
  • Applications: automotive bumpers, cable insulation, carpet fibers, chemical tanks, and gas cans

High-Impact Polystyrene (HIPS)

Good impact resistance, superior machinability, dimensional stability, excellent aesthetic qualities, and high customizability make high-impact polystyrene (HIPS) a viable choice for a wide range of automotive components. Its cost-efficiency and accommodation of printing, gluing, bonding, and decorating operations similarly contribute to its popularity in automotive injection molding operations. Additional material characteristics include:

  • Tensile Strength: 3,500 psi
  • FME: 310,000 psi
  • Izod Impact: 2.8 ft × lbs./in.
  • HDT: —/196º F @ 264 psi
  • Water Absorption: —
  • Applications: buttons, equipment housings, car fittings, and display bases

Low-Density Polyethylene (LDPE)

Low-density polyethylene (LDPE) is the most flexible variation of polyethylene, offering high-level moisture resistance, high-impact strength, good chemical resistance, and translucence. It is a low-cost material option for weatherproof components and is easy to process. However, it does not accommodate bonding and does not hold up well in harsh weather or high-temperature applications. Additional material characteristics include:

  • Tensile Strength: 1,400 psi
  • FME: 30,000 psi
  • Izod Impact: no break
  • HDT: 122º F @ 66 psi/—
  • Water Absorption: 0.1% in 24 hour immersion
  • Applications: car bodies (glass reinforced) and electrical insulation

Custom Plastic Materials

In addition to the plastics mentioned above, automotive industry professionals also employ a variety of other materials in injection molding operations. For highly specialized applications, they may invest in a custom plastic formulation tailored to their exact needs.

Advantages and Disadvantages of Automotive Injection Molding

When used for the manufacture of automotive parts and products, injection molding offers several advantages, including:

  • Cost-effectiveness (especially for high-volume production)
  • Process repeatability and product consistency
  • Operator and user safety
  • Lightweight alternative to metal components

However, there are also a few disadvantages associated with the process. For example, it may carry higher upfront costs for tooling, and any redesigns may require additional time and money.

Automotive Injection Molding Solutions From D&M Plastics

At D&M Plastics, we overcome the challenges of injection molding by assisting in the design and manufacture of molds that will produce high-precision, geometrically complex molded parts in high volumes. Our injection molding capabilities include cleanroom molding, overmolding, insert molding, and in-mold labeling. We can produce multi-component parts with Class A surfaces, complex geometries, undercuts, and thin walls and easily uphold tolerances as small as ±0.001 inches.

By partnering with us for their injection molding needs, automotive industry customers benefit from our:

  • Rigorous materials management program with special attention to humidity, material density, and mix ratios
  • Bi-hourly internal inspections that ensure parts meet precise function, strength, durability, and color specifications
  • Adherence to ISO 9001 and ISO 13485 standards

Our best-in-class engineering and manufacturing capabilities have earned us a reputation as a trusted partner for customers across a wide range of industries, including automotive, consumer, medical, and electrical. For additional information on our injection molding capabilities and how we serve the automotive industry, contact us or request a quote today.