This article will be discussing automotive plastic injection molding from various aspects, including its history, advantages, applications, alternative solutions, and materials. Swipe down and read on!
In the early days of the automotive industry, cars were made almost entirely of metal, which meant they were clunky and extremely heavy. However, the industry became advanced and the plastics market erupted in the 1940s and 50s. Therefore, automotive manufacturers began to experiment with plastic car parts in their production.
In the 1970s, manufacturers rolled out the first cars with plastic decorative elements. Later in the 80s, they also introduced more functional parts like plastic headlights, bumpers, and fenders.
In the early 2000s, automotive manufacturers unveiled the first plastic structural components for cars, which had the advantage of being more lightweight than their metal counterparts, unlocking improved fuel efficiency and cheaper production. Today, injection molding is now a dominant production method for manufacturing plastic car parts in the automotive industry.
Injection molding is an established production process in which automotive mould manufacturers inject molten plastic materials into a mold cavity. The melted plastic then cools and hardens, and the manufacturers extract the finished part. Though the mold design process is critical and challenging (a poorly designed mold can result in defects), injection molding itself is a reliable method for producing solid plastic parts with a high-quality finish.
Here are a few reasons why the process is beneficial for automotive plastic parts production:
In the automotive industry, repeatability—or the ability to consistently produce identical parts—is crucial. Because automotive plastic injection molding typically relies on robust metal molds, the final molded automotive parts produced using the mold are practically identical. Some factors come into play with injection molding, but injection molding is a highly repeatable process if the mold has a good design and finishing.
2. Scale and Cost
The injection mold-making process can be an expensive process due to the cost of the mold. However, it remains a highly scalable process whose overall cost decreases as the manufacturer makes more parts. For mass production applications, injection molding is thus beneficial to the manufacturer. For anything less than mass production, however, injection molding tooling costs may curb the cost efficiency of the process.
3. Material Availability
A significant benefit of using injection molding for automotive production is the wide range of rigid, flexible, and rubber plastics the process is compatible with. Manufacturers use a wide range of different polymers for various applications in the automotive industry, including ABS, polypropylene, acrylic, acetal, nylon, polycarbonate, and more.
4. High Precision and Surface Finish
Injection molding is ideal for producing plastic parts with relatively simple geometries and results in high surface finish quality. Manufacturers have many finish options when producing parts, including various surface textures—such as glossy, rough, or matte—which they apply directly to the automotive exterior mould rather than the molded part. However, different plastic materials also influence the final surface finish.
5. Color Options
In automotive plastic injection molding, it is easy to modify the colors of molded automotive parts to fit the vehicle’s color scheme. Unlike other processes, injection molding allows you to mix dyes with the raw material pellets before manufacturing begins. This produces solid, consistent coloration without the need for painting or tinting after the molding is complete.
6. Fast Prototypes with Rapid Tooling
Although automotive manufacturers widely use injection molding for mass production of auto parts, they also use it as a prototyping tool. By creating fast, low-cost aluminum molds with rapid tooling — usually by additive manufacturing or CNC machining — automotive mold manufacturers can turn around short runs of prototype molded car components much faster than traditional (steel) tooling.
For the past two decades or so, many under-the-hood components that manufacturers formerly made from metal have been transitioned to plastic. For these applications, robust polymers such as ABS, Nylon, and PET are common. However, manufacturers now make parts such as cylinder head covers and oil pans using injection molding. This method offers lower weights and costs compared to metal parts.
Injection molding is an established process for many exterior automotive components, including fenders, grilles, bumpers, door panels, floor rails, light housings, and more. Splash guards are a fine example for demonstrating the durability of injection molded parts. In addition, the components, which protect the car from road debris and minimize splashing, are often made from rubber or other durable and flexible materials.
In many cases, molded plastics serve as an alternative to metals. Formerly, manufacturers make items like brackets, trunk lids, seatbelt modules, and air-bag containers exclusively from metal. Nowadays, injection molding is the preferred production method for these plastics.
On the other hand, manufacturers can sometimes replace molded plastic parts with 3D-printed plastic car parts. This happens especially in prototyping, where there is less need for extreme durability or a smooth surface finish. Many moldable plastics can serve as FDM 3D printer filaments or as SLS 3D printer powders for nylons. Some specialist and high-temp 3D printers can also print reinforced composites for high-strength parts.
At RapidDirect, we offer professional injection molding services, delivering mass-produced plastic car parts to clients in the automotive and other industries. Our services include thermoplastic injection molding, over-molding, insert molding, and mold making. In the latter case, our experts work with clients to produce high-quality molds for prototyping or large production runs.
We also work with a wide range of plastic injection materials, including strong, heat resistant, and rigid thermoplastics; flexible, fast curing thermoplastics; and durable, high-temperature rubber plastics. Our professional automotive plastic injection molding services enable our automotive clients to obtain high-quality molded automotive parts that meet their application requirements.
Rapid Tooling processes are developing and proving to be a reliable method to compete with subtractive techniques for tool making. This paper investigates large volume production of components produced from Selective Laser Melting (SLM) fabricated injection moulding tool inserts. To date, other researchers have focused primarily on investigating the use of additive manufacturing technology for injection moulding for low-volume component production rather than high volume production. In this study, SLM technology has been used to fabricate four Stainless Steel 316L tool inserts of a similar geometry for an after-market automotive spare part. The SLM tool inserts have been evaluated to analyse the maximum number of successful injections and quality of performance. Microstructure inspection and chemical composition analysis have been investigated. Performance tests were conducted for the four tool inserts before and after injection moulding in the context of hardness testing and dimensional accuracy. For the first reported time, 150,000 injected products were successfully produced from the four SLM tool inserts. Tool inserts performance was monitored under actual operating conditions considering high-level demands. In the scope of this research, SLM proved to be a dependable manufacturing technique for most part geometries and an effective alternative to subtractive manufacturing for high-volume injection moulding tools for the aftermarket automotive sector.
At this point of the process, we’ve released our designs to our vendor and molds build has started. The time we have now could vary from 3–4 weeks to 20 weeks or more, depending on the household mould and part. During this time, there are two things we should do:
Time control. It is quite common that the container mould maker will send a bi-weekly report with detailed progress regarding the mold manufacturing. You may want to look only that the first trial, T1, is as promised, but you may also want to monitor the progress to predict delays. For that, you may need a professional who has a deep understanding of the steps of mold manufacturing.
Regroup and start preparing for T1. We have the time to look back into our plans and check if we covered all bases, if we defined all we wanted to, and if we covered operation issues such as raw materials for the testing, as well as double checking that the mold maker has the latest part drawings, etc.
I’ll explain how I see the difference between T0 and T1.
The first stage before injection of the plastic that will form into parts is to see that the mold works. This is what I call T0. This is the first time the mold maker mounts the mold on the injection machine and sees that the moving elements move well, that the plastic melt flows well, that the cooling performs, and more. Just like every car manufacturer will have a “dry run” of the car before it is driven out of the assembly hanger, the mold maker should ensure this machine performs its basic functions before handing samples for examining.
If the mold performs well in T0, then this test can be called T1 because we have samples. However, T1 samples might not (or, in some predefined cases, should not) be within the final dimensions; the surface finish is not final; and we may have visual marks, flashes, and mismatches. That being said, the samples are a milestone with two main aspects: one is that the mold maker delivered a mold — a tool, a machine — that can produce the parts we had up until now only as a CAD file, 2D drawings, and models. The other is that the developer gets the queue to initiate the final stage of the product development, what we call the “T1 to T-final” (the well-known Tf) phase, which is the “money time” of our project.
To clarify, this stage is not a chair mould process validation (installation qualification, operational qualification, performance qualification). This is the stage in which we aim to achieve a verified, stable part that will qualify our definitions. Once we get that, we may initiate mold performance validation.
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