Plastic molding is an essential manufacturing process across the automotive industry. Dozens of plastic components in modern vehicles get produced using molded plastics. Understanding what is automotive plastic molding provides insight into a vital fabrication method for car parts.

This guide covers the basics of automotive plastic molds, common materials and applications, the injection molding process, benefits over other methods, design considerations and future trends shaping automotive plastic molding.

What Are Automotive Plastic Molds?

Automotive plastic molds are custom metal tools specially designed to produce plastic parts for vehicles. They are made from tool steel or aluminum alloys and machined to form a specific mold cavity.

In plastic injection molding, the automotive injection mould tool comprises two halves - the core side and the cavity side. When closed together, these form the complete mold cavity that gives shape to the melted plastic material.

The core side usually forms any interior features of the part such as holes, threads or overhangs. The cavity side shapes the exterior form. Automotive molds have extensive cooling channels to improve cycle times and quality.

In addition to core pins, ejector pins, gates, runners and cooling lines, automotive molds contain other critical components:

• Sliders allow side pulls and undercuts through moving components within the mold.
• Rotating stacks enable multi-angle ejection for complex geometries.
• Hot tip gates localize flow front heat to minimize defects.
• Venting evacuates trapped air through micro-sized vents.

The initial mold design process and tooling must account for crucial factors like plastic flow, fill time, clamp tonnage and cooling. Proper mold design helps ensure production of high quality automotive plastic parts.

Common Automotive Plastic Materials

Various plastic materials apply to automotive parts production through injection molding:

• Polypropylene (PP): Highly versatile polymer used for bumpers, interior trims, battery cases, ducting. Heat and chemical resistant.
• Acrylonitrile Butadiene Styrene (ABS): Amorphous thermoplastic noted for strength and rigidity. Used in instrument panels, mirror housings, grilles and other interior/exterior components.
• Polyurethane (PU): Known for abrasion resistance and durability. Used for seats, armrests, instrument panels and trim parts.
• Polyvinyl Chloride (PVC): Budget friendly option for window trims, wire harnesses, upholstery. More temperature sensitive.
• Polycarbonate (PC): High-impact resistance ideal for headlights, meter clusters, lenses. Optical clarity and heat resistance.
• Nylon: Excellent chemical resistance. Used for fuel tanks, gearbox components, air intake manifolds.
• Polyethylene (PE): Lowest density of injection molding plastics. Used for flexible bumper covers, interior panels.

The rising use of plastic materials over metals allows vehicles to reduce weight and improve fuel efficiency. Plastics also provide styling, aerodynamic and corrosion resistance benefits.

Major Automotive Plastic Applications

Many vehicle components get manufactured from plastic resins using injection molds:

• Exterior body panels - Door panels, bumpers, spoilers, mirrors, grilles
• Lighting systems - Headlight lenses, lamp housings, reflectors
• Interior trims - Dashboards, armrests, door handles, knobs, switches
• Fluid handling - Coolant tanks, washer fluid reservoirs, fuel tanks
• Under the hood - Air intake manifolds, battery cases, connectors, ducting
• Structural components - Load floors, cross car beams, chassis parts
• Wheels - Plastic wheel covers, trims and decorative inserts

By combining plastics with reinforcing fibers, plastic composites enable lightweight structural parts as well. Carbon fiber reinforced plastics continue displacing metals in racing and high-end vehicles.

China remains the top location for automotive plastic and composite parts production. Many global OEMs rely on Chinese manufacturing for cost-effective high volume molding.

Injection Molding Process for Automotive Parts

Injection molding is the predominant method for high volume production of automotive plastic parts. The steps in the injection molding process include:

• Clamping - The mold halves close and the injection molding machine clamps with enough force to resist injection pressures.
• Filling - Molten plastic gets injected into the mold cavity through the sprue, runners and gates. It quickly fills the cavity geometry.
• Packing - Added pressure gets applied to pack more material into the mold and reduce shrinkage.
• Cooling - Cooling channels circulate water to solidify the molten plastic inside the mold. This takes 40-90 seconds.
• Ejecting - Pins push the finished part out of the opened mold. The mold closes and the cycle repeats.

Compared to other forming methods, injection molding provides extremely high production rates. Automotive manufacturers can produce hundreds of high quality plastic parts per hour using a single mold tool. This makes injection molding ideal for large volume production.

Benefits of Injection Molded Automotive Parts

• Accuracy and repeatability - Injection molds produce near net shape parts within tight tolerances.
• Production efficiency - Complex parts get mass produced with speed and precision.
• Design freedom - Ability to produce complex or intricate shapes not possible with other methods.
• Material versatility - Wide range of automotive grade plastics to choose from.
• Quality surface finishes - Glossy class A finishes achieved right out of the mold.
• Lightweighting - Replacing metals with plastics reduces vehicle weight and boosts fuel economy.
• Part consolidation - Multi-material molds combine hard/soft plastics in one component.
• Cost-effectiveness - High volumes lower cost per part through mold reuse.

Design Considerations for Automotive Plastic Molds

Several factors must get considered during design of an automotive plastic injection mold:

• Dimensional accuracy - Parts must conform precisely to CAD models with tight tolerances.
• Wall thickness - Varying wall thickness can lead to defects like sinks and warpage.
• Ribs and gussets - Strategic structural ribs or gussets prevent warping.
• Draft angles - angled surfaces ensure proper part ejection from the mold.
• Radii and fillets - Generous internal radii increase moldability and appearance.
• Surface finish - Materials and mold polishing is key for smooth, glossy finishes.
• Weld lines - Changing flow paths create weak spots along weld lines.
• Ejection system - Proper placement of ejector pins avoids part damage during ejection.

Detailed mold flow analysis optimizes these parameters before tooling production begins. Simulations help predict and prevent defects.

Future Trends in Automotive Plastic Molding

Several emerging trends will shape automotive plastic molding in the future:

• Lightweighting - Continuing replacement of metal parts with plastic for increased fuel efficiency.
• Advanced plastics - Wider use of high performance polymers like PEEK, PEI, LCP.
• Composite materials - Increasing use of plastics reinforced with carbon fibers or glass fibers.
• Multi-component molding - Combining hard and soft plastics into single parts with overmolding.
• In-mold coatings - Primers/coatings applied during the molding process rather than after.
• 3D printing applications - Using 3D printed tooling for low volume production applications.
• Simulation and automation - Digital mold design workflows and Industry 4.0 integration.

As automotive manufacturing evolves, plastic injection molding and molded plastics will remain essential processes and materials for vehicle components. OEMs continue seeking lightweight, cost-effective means of producing high quality plastic parts via innovative mold designs.

Conclusion

From exterior panels to under-hood components, automotive injection molding companies produces millions of essential parts each year. Injection molding offers unparalleled efficiency at high production volumes. However, the tooling design process must optimize manufacturability and part quality. When executed properly, automotive plastic molding provides exceptional accuracy, repeatability, design freedom and cost savings versus other fabrication methods.