Automotive Injection Molding: Engineering Plastics To Make Car Parts

Cars nowadays have multiple plastic parts, and automotive injection molding refers to using the injection-molding process to manufacture car plastic components, such as intake manifolds and bumpers.

Let’s look at this process and the types of plastic materials used to make the various car parts using automotive injection molding.

What Is Injection Molding?

Injection molding is a plastic part manufacturing process that melts plastic pellets and utilizes high-pressure injection to create end products.

These end products are plastic car parts, such as exterior body panels, engine parts, and interior components.

Car plastic and rubber parts from a high-precision injection mold

The injection part of the process involves pushing the molten plastic at high pressure into a precision-machined mold.

When the plastic cools, it takes the shape of the mold. This manufacturing process enables OEM and aftermarket auto industry players to make complex parts cheaply and easily.

Types of Automotive Injection Molding

The typical injection molding processes used in the automotive industry include the following.

Thermoplastic Injection Molding

This process uses thermoplastic materials like ABS, nylon, and polypropylene to make plastic car parts.

It is more affordable, versatile, and has a shorter lead time than the other two, and these benefits make it the most common among the three.

Thermosetting Injection Molding

Thermosetting injection molding involves making car parts using thermosetting materials like polyester and epoxy.

Its advantages include high repeatability and precise dimensional tolerance.

Most automotive industry players use this process because the plastics don’t deform or melt at high temperatures.

Thermoplastic vs. thermosetting polymers

Elastomeric Injection Molding

This process deals with elastic materials like silicone and rubber, which have superb vibration-dampening and shock absorption properties.

And it has advantages like low production costs, versatility, and high production speed.

Benefits of Automotive Injection Molding

Injection molding is ideal for automotive parts because it brings about these benefits.

Cost Effectiveness

This process is attractive to the automobile industry because it lowers the cost of mass-producing car parts.

It is highly scalable, and prices become lower when producing more components. Additionally, the process wastes little material due to reusability.

High-Volume Production

Injection molding is highly repeatable because it uses molds to cool and form the parts. So you can make multiple identical parts with the same weight and design.

An industrial injection molding press for manufacturing conditioner parts

Weight Reduction

Plastics are significantly lighter than metal and fiber-reinforced composites.

So using them to make car parts reduces the vehicle’s weight, improving fuel economy and durability (by minimizing wear).

High Precision (Quality)

The precise repeatability ensures automotive plastic molding maintains consistent quality and meets strict standards.

Also, the process allows you to produce complex car parts that would be impossible or challenging when using other manufacturing processes.

Versatility

You can use automotive injection molding to create components for all types of vehicles.

The only challenging part is building the mold for injecting the molten plastic. But once you have it, you can create multiple copies.

A steel mold for a plastic product

Durability

Plastics are durable materials that can withstand extreme temperatures and corrosive substances without failure.

So they enhance the vehicle’s durability, which is why modern cars have plastic bumpers and side skirts.

Safety

Automotive plastic parts absorb collisions and can create a buffer zone to protect the driver and passengers inside from impact.

This protection begins with the plastic bumpers outside and concludes with the plastic steering wheel and dashboard inside.

Multiple Color Options

Adding a pigment to the plastic pellets before melting and mixing can alter the color of the plastic part.

This coloring process is more permanent than exterior painting, such as on metal.

Typical Plastics Used and the Parts They Make

Polypropylene

This thermoplastic polymer is a light synthetic fiber that resists most acids and alkalis.

It has a water absorption rate of less than 0.02%, a shrinkage of 1%-3.5%, and a suitable thickness of 1.5-2.5mm.

These properties make the material ideal for making column guard plates, bumpers, water tanks, door guard plates, instrument panels, and decorative plates.

A car bumper

Polyethylene

Polyethylene is a flexible, transparent thermoplastic with reliable water, base, and alkali resistance.

Its shrinkage rate is almost the same as that of polypropylene (1.5%-4%), and its injection molding fluidity is superb.

The material’s ideal operation thickness is 1.0-2.5mm.

Combining these properties make polyethylene suitable for molding parts like air ducts, vent pipes (left and right), foot vent assemblies (left and right), fuel tanks, and decorative covers for the front seats.

Polyvinyl Chloride

PVC is a brittle, high-strength thermoplastic material with multiple components, such as fillers, lubricants, stabilizers, processing aids, plasticizers, and pigments.

So it can have different mechanical properties depending on its ingredients.

But generally, the material is affordable, easy to process, and offers comprehensive mechanical properties.

So it is typical in various car parts, such as lining boards, steering wheels, instrument panels, and floors.

A car steering wheel

Polystyrene

Polystyrene is a sturdy and stiff synthetic resin made by polymerizing styrene monomers. Although rigid, this material is fragile.

So manufacturers usually co-polymerize and graft it with substances like HIPS (High-Impact Polystyrene) and butadiene.

The material’s shrinkage rate (0.4-0.7%) is relatively low, and its suitable thickness is broader than the rest (2-3mm).

And it can exist as a solid or foamed structure.

In vehicles, the material is suitable for making dashboard shells and thermal & sound insulation (in a foam structure) on the ceiling and door panels.

Acrylonitrile Butadiene Styrene

ABS has poor weather resistance, but it is affordable and has an elegant appearance.

So it is ideal for decorating car interiors when applied as surface treatment.

Vehicle manufacturers usually use it to make the shift handle, rear-view mirror frame, radiator grid body, rear spoiler assembly, armrest, decorative glitter, and license plate decoration plates.

A gear shift handle

Polyamide

Also known as nylon, PA is a highly water-absorbent material compared to other thermoplastics and is ideal for making parts like:

Oil and air filters
Headlight housings
Power steering & brake fluid tanks
Seat belts
Pump impellers

Poly(methyl methacrylate)

PMMA is also known as organic or acrylic glass because it offers excellent light transmission and resists aging outdoors because it is chemical and UV resistant.

Additionally, the transparent structure has high rigidity.

So it is ideal for making see-through automotive components on the exterior. These include door glasses, lighting signs, and lamp covers.

A tinted car door window glass

Polyformaldehyde

Polyformaldehyde or polyoxymethylene is an engineering thermoplastic for molding car parts requiring high stiffness.

These include door handles and pins, electrical switches, pinion electrical instruments, and impellers.

The plastic steel has a shrinkage rate of 2%-3.5% and a suitable wall thickness of 1.5-2.5mm.

Polycarbonate

This transparent thermoplastic is sturdy enough to resist fractures and impacts. Plus, it exhibits exceptional heat, creep, and cold resistance.

And when fused with fiberglass, the material can have better mechanical strength, lower shrinkage rates, and higher temperature resistance.

In vehicles, these properties are suitable for making wheel cover plates, wind frame covers, and rear bumper cushions.

Polyurethane

Polyurethane is a class of organic polymers that can be resinous, elastomeric, or fibrous.

These polymers are ideal for various applications, such as making soft foam for seats, door linings, window frames, instrument cluster anti-vibration cushions, headrests, and pillar trims.

Polyurethane form packaged in a spray can

Wrap Up

You can’t build a car without plastics, and injection molding simplifies the process of forming the plastic into various components.

But you need to understand the plastic properties to know which material is best for different areas in the vehicle. And we’ve listed these plastic types as a guide.