A Marriage of Necessity: Automotive Part Production and Plastic Injection Molding

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Karl Benz built the first automobile in 1886. It was not until the Second World War that the plastic industry boomed. This means that we used to make cars from metal, steel to be precise. It also suggests that cars used to be clunky and consume a lot of fuel. We started seeing cars with plastic adornments back in 1970. A decade later we had cars with plastic headlights, fenders, and numbers.

In the early 2000s, the production of plastic components for cars started peaking. Plastic is much lighter than steel. This led to the production of lightweight cars with excellent fuel efficiency. We were able to cut on costs seeing how steel was expensive. Plastic injection molding has remained dominant in the production of plastic car parts. This is because it is ideal for the mass production of similar parts.

Advantages of Plastic injection molding for the automotive industry

Plastic injection molding allows you to create parts and components with complex geometries. It additionally has a high part to part repeatability. Here are some advantages of using injection molding in automotive part production.


To start making your parts you will need to make a mold. Let’s say you need over a hundred thousand fenders for a specific brand of car. You will need fenders with the same dimensions. With a quality steel mold, you can produce countless parts of similar dimensions. Steel molds are expensive but durable. You will recover the incurred cost as production continues. Steel molds are ideal for the long-run production of similar parts.

Scale and costs

The process of making a mold can take several weeks especially if you are working with steel molds. Additionally, steel is rather expensive. This should not worry you. This is because you will recover your initial investment as you produce parts. After acquiring a mold the rest of the process is quite easy and fast. Machines do most of the work. Because machines do not get fatigued, your process can run all around the clock. You additionally have the option of going for low-end molds if you do not need a lot of parts. Low-end molds can come from aluminum which is available everywhere. Thanks to 3D printing we can now shorten the time needed to make molds.

Wide range of materials

Injection molding gives a wide range of materials to choose from. Not only for resins but also the mold. You can make molds from Steel, Aluminum, and Pre-hardened steel among others. For your resins, you can go with Polycarbonate plastic injection molding. Polycarbonates produce parts with superior impact strength. They are also light and durable. Nylon is another material used in plastic injection molding. Others are ABS, PMMA, and PE.

Plastics are much lighter than steel bumping up fuel efficiency in our cars.

High precision

If you have a quality mold with accurate dimensions, what could go wrong? The automotive industry calls for high precision and quality surface finishing. Injection molding will give you intricate parts that do not need post-processing. Injection molding is all about filling a cavity mold with a molten resin. With the correct parameters, you can rest assured of accuracy.

Color option

Unlike some production methods injection molding allows you to add dyes. You can add your dye while heating your resin. It eliminates the need for painting afterward. The advantage of this is the paint is not affected by abrasion.

Fast prototyping

The plastic market is a fast-paced sector. When it comes to prototyping, as a manufacturer, you have to be fast. When engineers in the automotive industry need prototypes, production should be fast. You need to get your prototype to the market fast for evaluation and feedback. Injection molding coupled with 3D printing is your answer to rapid prototyping. With a 3D printed and a CAD file, you can get your mold in less than 24hrs. Injection molding units run all around the clock.

Automotive Parts Produced through Plastic injection Molding

The demand for fuel-efficient and lightweight cars is growing. As a result, we have changed countless components in our cars from metal to plastic. We can not list all components but instead, let us look at the main ones.


The interior of the car is the most plastic-raided part of a car. From interior surfaces to dashboards, instrumental components, air vents, glove compartments among others. Surfaces made of plastic call for quality finishing. You can’t find different sizes of glove compartments for the same brand of car. Repeatability is key.


We witness the durability of plastic parts through the exterior of the car. Splash guards are perfect examples. Other parts of the exterior include; fenders, door panels, floor rails, and grilles.

Under the Hood

Over the years, we have created many plastic under the hood components. All have been in a bid to reduce weight to boost fuel efficiency. Materials like ABS, PET, and nylon are dominant in this sector. Cylinder head covers and oil pans are examples of injection molded components.

You can also find decorative adornments made from plastic injection molding.

Injection Molding Resins For Automotive Parts

The automotive industry calls for stringent safety measures during assembling. Any part used in assembling needs to have quality. Here are some materials used in injection molding and the parts they produce.

Acrylonitrile butadiene styrene (ABS)

We use ABS both in injection molding and 3D printing. It is weather-resistant and we use it to make dashboards and covers.


Possesses a high impact strength

Chemical resistant


Easy machining and thermoforming

 You can paint and glue ABS with ease

Has dimensional stability


We use this polymer to make bushes and bearings. It exhibits excellent chemical and abrasion resistance.

Polymethyl Methacrylate (PMMA)

 PMMA has the transparency of acrylic. This makes it an excellent and shatterproof alternative to glass. Manufacturers can use molded PMMA for headlights and internal screens


 Excellent clarity (transparent)

UV resistant


Hard and stiff

Polypropylene (PP)

Polypropylene is a water-resistant polymer. It exhibits good electrical resistance and chemical and UV resistance. Manufacturers can use it to make bumpers, battery covers, and cable insulation.



Has flexural strength

Has a low coefficient of friction

Resistant to moisture

Chemical resistant

Impact strength

Resistant to electricity

Polyurethane (PU)

Manufacturers use Polyurethane to make spongy and flexible components of a car. These are car settings, seals and gaskets, insulation panels, and suspension bushes. PU has high impact strength.

 Polyvinyl Chloride

It has good chemical resistance and durability.

Manufacturers use PVC to make interior panels, dashboards, and cable insulators

Automotive Plastic Trends

Here are some plastic trends for the automotive industry for 2021 and beyond

Light weighting for fuel efficiency

We have a projected increased rate from 37 miles per gallon to 51 miles per gallon by 2025. For this to happen, an average car should reduce its weight by 10%. Lightweight with plastic parts is the only choice we have. Enhanced technology will allow OEMs to produce more intricate automotive plastic components.

Increased demand for plastic components

Plastic has gained popularity in the automotive industry due to its versatility. We now have compounds with the same strength and durability as steel. This has seen a significant reduction in vehicle weight. As a result fuel efficiency is better. A recent report shows that there will be an increase in demand for plastic parts.

Enhanced Production methods will drive innovations

Take a look at fuel efficiency. It will be a selling point for manufacturers even if we delay the projected rate. Manufacturers will have to adopt new technology to cope with the changes. From thermal pressing to industrial 3D platforms. These are the changes we expect in the future.

Automotive injection molding defects

We all know that quality and accuracy can affect the reliability and safety of our cars. That is why plastic injected components need to perfect to the finest detail. Either way, you are likely to encounter some defects, and preventing them will save you a lot of costs. Imagine investing in a steel mold yet you do not get quality parts. Here are some defects you are likely to encounter and how to deal with them.

Short shot Molding

 Short shot molding is a result of plastic resin not filling up the cavity mold. This will result in parts without plastic on some sections. What causes short-shot molding?

 A faulty shot calibration, incorrect plasticizing capabilities, early hardening of a viscous resin. Trapped air can also cause short-shot molding.


 You can raise the injection pressure, speed, and temperature. You can also redesign your mold and add more air vents.


 It is how the molten resin travels around the mold. Lines appear as physical paths on parts and components. Flow lines are the results of disparities in flow speed, wall thickness, and low pressure. Weld lines show where different flow channels met in the mold. Wels lines are the result of inadequate bonding from different flow channels.


 Optimize your injection speed and pressure. You should also adjust your walls causing abrupt changes in directional flow. You should also introduce only one flow front.


We have two different types of mark; sink marks and burn marks

 Sink marks appear as small depressions on the surface of plastic parts. Burn marks are discolorations on the surface. Burn marks are the result of high mold temperature or overheating trapped hair. Sink marks are the result of incorrect cavity pressure and insufficient cooling.


For sink marks, you can increase holding time and pressure, lower mold temperature. This will allow more cooling and curing.

 For burn marks, you can reduce the injection speed, mold, and melt temperature. You should also look at your degassing system.

Those are some defects and how you can mitigate them.


 From steel vehicles to cars with plastic components. The automotive industry is growing fast. Plastic injection molding for the automotive industry has remained the dominant production method. For rapid prototyping, you can use 3D printing and injection molding. 3D printing allows you to create short-run molds in less than 24hrs. Injection molding machines can run all round the clock. For steel molds, we cannot deny they are expensive. But, you will recover your investment as you produce large volumes of parts. We now have plastic compounds with the same strength and versatility as steel. Light weighting for fuel efficiency is easier than ever. ABS, PMMA, Polyamide, and PVC are examples of plastics we use in injection molding. Repeatability in injection molding allows us to make large volumes of similar parts.

The future of the automotive industry is bright. We are expecting autonomous cars and cars with 10% less weight. Our viable option here is more plastic components for vehicles. We expect the demand for plastic parts to continue skyrocketing


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We will contact you within 1 working day, please pay attention to the email with the suffix “@cavitymold.com”. 

or email direct:jerry@cavitymold.com

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We will contact you within 1 working day, please pay attention to the email with the suffix “@cavitymold.com”. 

or email direct:jerry@cavitymold.com