Today, injection molding is recognized as one of the most favored and widely used manufacturing processes for plastics. This is because it enables you to achieve efficient and cost-effective production of plastic parts rapidly.
These manufactured parts are also identical, which is why injection molding is used in the automotive sector, where the parts need to be reliable and of superior quality.
In this article, we will explain the reasons why injection molding is used in the production of automotive parts, as well as outline the parts that are commonly made using this process.
We will also discuss the alternatives you have instead of injection molding and the various plastics that can be used in the process.
Automotive Plastic Injection Molding: The History
When the automotive industry took off towards the start of the 19th century, most of the vehicles were made completely of metals. This made them heavy, causing manufacturers to look for alternative materials to produce their parts.
Then after World War II, the growth of industries and the development of plastics took place, which enabled the manufacturers to use them as substitutes for metal parts in their vehicles.
The latter half of the 1950s saw the use of plastics to make car roofs, elbow rests, and the cabins of trucks. This was followed by the development of polypropylene in the 1960s, which offered a lightweight, recyclable option for use in vehicles.
Injection molding was used to make parts such as cooling fans and hydraulic fluid tanks, and so the use of plastics in the automotive industry grew.
Further technological and material advancements in the 1970s led to the important development of the plastic bumper, which drastically reduced the weight of vehicles.
Renowned manufacturers of the time, including BMW, Renault, and Volkswagen used their research to discover further uses for plastic to gain a competitive advantage.
They aimed to come up with plastics that had better mechanical and chemical properties such as corrosion resistance and impact absorption. Resultantly, new applications such as plastic fuel tanks, fenders, bumpers, headlights, oil collectors, and spoilers emerged in the decades that followed.
After the turn of the millennium, the automotive industry experienced an increase in the use of plastics to make structural parts of cars. This significantly reduced their weight and thus enabled fuel savings and a cheaper product when compared to cars with metal structures.
Today, using plastics in the automotive industry has become common, and with current trends indicating a greater focus on the recyclability of plastics to ensure environmental protection, you can expect new types and uses of plastic to arise in the future.
Advantages of Injection Molding for Automotive Applications
1. Repeatability
With cars being made at a mass scale, manufacturers often look for methods to produce a large number of identical parts without changing any initial conditions.
You may also know this concept as repeatability, which is one of the several advantages that come with plastic injection molding. This is achieved by using the same mold to produce thousands of similar parts with high tolerances.
2. Scale and Cost
Questions are often asked regarding the costs incurred in an injection molding process. That is because of the relatively high initial cost of designing and preparing the mold. You may also know this as the tooling cost.
As you produce more parts, economies of scale enable you to achieve a reduction in the overall production costs. Automotive manufacturers can produce thousands of car parts at a time using injection molding.
For low-volume production, however, you may need to carry out a cost-benefit analysis to determine whether the process is profitable or not.
3. Material Availability
Another reason why the use of plastic injection molding is so widespread in the automotive industry is the wide variety of different plastics easily available in the market.
Since the process can be used with plastics having different physical and chemical properties, it is heavily favored as different car parts require different characteristics.
The plastics currently being used include ABS, polyamide/nylon, PMMA, polypropylene, polyurethane, PVC, and reinforced composites. These will be discussed in a later section.
4. High Precision and Surface Finish
Automotive manufacturers have the choice of choosing their required part roughness from a dozen surface textures. These are broadly categorized into four categories, which include glossy, semi-glossy, matte, and textured finishes.
This is accomplished by applying the chosen surface directly onto the mold than on the molded part. Moreover, the surface finish chosen also depends on the application of the molded part and the type of plastic used to make it.
5. Color Options
Injection molding also allows the manufacturer to choose the color of the molded parts according to the requirements. If you want blue fenders, you can easily obtain them by mixing blue dyes with the plastic pellets before the material enters the mold.
This eliminates further processes such as painting or tinting to obtain the desired color once the part has been molded, saving time and costs.
6. Fast Prototypes With Rapid Tooling
Even though injection molding is usually used to fulfill high-volume orders, you can also use it for prototyping. Manufacturers sometimes use rapid tooling methods, such as additive manufacturing or CNC machining, to produce inexpensive aluminum molds quickly.
When compared with steel tooling, these molds can produce prototypes of car parts in a shorter time.
Production Applications for Automotive Injection Molding
You can classify parts made by plastic injection molding into three types depending on where they are found in a car.
Parts can be present under the car’s hood (bonnet if you are from the UK); they can be fixed on the car’s outer structure; and they can be observed while sitting inside the car.
Here, we take a look at a few examples of plastic parts belonging to each of these three categories:
1. Components Under-the-hood
Under-the-hood components refer to those car parts that you see when you open your car’s hood. These parts include the engine and other systems which help with the car’s operations.
Ever since plastics replaced metals for making such parts, manufacturers have needed them to be robust as well as lightweight, so plastics like ABS, PET, and nylon are used to manufacture them via injection molding. Such components include oil pans and electrical kits.
2. Exterior Components
These are automotive parts you normally find on the outer body of your car. Since they are more exposed to the elements than other parts, they need to be durable as well as lightweight. Grilles, mudguards, headlights, sensor holders, door panels, and bumpers are all examples of such parts.
3. Interior Components
Components found inside the car such as door handles, center consoles, roof lining, and glove compartments are also made from plastic injection molding.
Alternatives to Injection Molding for Low-cost Automotive Prototypes
As mentioned before, parts that were once made from metal, such as brackets and airbag containers, are now being produced from plastics through injection molding.
However, you don’t always have to make these components using injection molding. Additive manufacturing, or 3-D printing as you may call it, can also be used to produce such parts.
This technique is often used for prototyping applications, where there is less emphasis on the part’s robustness and finish as compared to when you mass-produce these parts.
You may be interested in knowing that several of the plastics used in injection molding can also be used in fused deposition modeling (FDM) and selective laser sintering (SLS) 3-D printing.
Furthermore, some special printers are capable of using reinforced composites to make parts with superior strength.
This provides another useful alternative for automotive manufacturers when deciding the method with which to make their parts as 3-D printing proves cheaper than injection molding for low-volume production. This is because there are no tooling costs associated with this method as the part is directly manufactured from the design.
In addition to prototypes, you can also make ready-to-use products using 3-D printing. Parts such as valves and bumpers can be made using SLS 3-D printing. Other 3-D printing techniques such as selective laser melting (SLM) and electron beam melting (EBM) may also be used in place of plastic injection molding to make automotive parts in the future.
Injection Molding Materials for Automotive Parts
Here, we list a few plastics that are usually used in the injection molding of automotive parts are outlined below:
1. Acrylonitrile Butadiene Styrene (ABS)
It is known to be resilient against weather conditions and is used to make dashboards and covers.
2. Polyamide (PA) or Nylon
Owing to its strong resistance to wear and chemicals, it can be used in bushings and bearings.
3. Poly(Methyl Methacrylate) (PMMA)
Having a transparent appearance due to the presence of acrylic in its structure, PMMA proves to be an outstanding replacement for glass. It can also be colored using dyes if required.
It is not fragile like glass and, therefore, is used to make f