When designing a new part, a critical component of this process is determining the best processing method. While there are variety of plastic molding processes to consider, thermoforming and injection molding are two of the most popular methods used in the molding of plastic parts. However, there are a variety of factors to consider such as cost per part, tooling cost, design, and aesthetics, all of which are ultimately affected by the processing method used.
Below are a few key differences between these two popular plastics processing methods:
Tooling Comparison
Arguably the most important component of any plastic molding process is tooling. The tooling is the vessel through which your plastic part comes to life, and a problem with the tooling can delay the entire project.
Tooling for a thermoformed part is a far less complicated process than for an injection molded part. A thermoforming tool is a single sided mold made out of aluminum with either a vacuum or plug assist to help form the plastic sheet into a formed part. This single sided tool is a cost-effective option for producing parts with less complex geometry. For pressure forming, the typical lead time for a is 0-8 weeks, with the first production taking place around 2 weeks after that. Thermoforming molds are typically made from aluminum, which contributes to their lower cost and faster turnaround compared to injection molds.
An injection molding tool requires a double-sided 3D mold created out of steel, aluminum or beryllium-copper alloy. Injection molds often contain many cavities, allowing for the simultaneous production of multiple parts and increasing efficiency for high-volume orders. For a new injection molding tool the time to production is around 16-20 weeks - 12-16 weeks for design and machining and an additional four weeks until first production.
Another important consideration when it comes to tooling is cost - injection molding tools are much more expensive! However, despite the increased tooling cost for injection molding, what you spend on tooling cost can be made up for by your cost per part - if you produce enough parts that is! Generally the break even point for an injection molding tool is around 2,000 – 5,000 parts per year depending on the complexity of the formed part – so production volume is an important component to consider. The higher initial costs associated with injection molds can be offset by lower per-part costs at scale.
Materials and Production
Another key difference between these two processes is the medium in which the raw material is received and the method used for forming.
The thermoforming process requires flat dimensional sheet or roll stock—commonly referred to as flat sheet—that is heated until pliable and then sucked by a vacuum or pushed by a plug assist into the mold. The plastic sheet then takes the form of the tooling, giving you your finished part. Vacuum forming is a common thermoforming technique where a heated plastic sheet is shaped over a mold using vacuum pressure. Sheet or roll stock can be purchased by a custom plastic sheet extrusion company like Impact Plastics, or for larger proprietary projects, inline equipment can be used. In an inline process the plastic sheet is fed directly from the sheet extrusion line into the forming equipment. Large thermoformed products, such as vehicle dashboards, are often manufactured using this method due to its efficiency for big components.
The process of injection molding requires a thermoplastic pellet or resin which is heated into a liquid state and injected into the mold where it then cools and solidifies. Plastic pellets are the raw material used in injection molding, which are melted into molten material before being injected into the mold. The injection molding machine plays a key role in melting and injecting the plastic into the mold. Resins can be purchased directly from producers or through brokers.
Both processes use a variety of plastic materials; for example, polyethylene and polycarbonate are common in both, but thermoforming materials are often selected for their flexibility and cost advantages.
Aesthetics and Functionality of the Finished Part
And last but not least – aesthetics and performance. From an aesthetic perspective, the thermoforming process offers more options. Plastic sheet or roll stock can be purchased in a variety of custom colors, finishes and textures. Decorative films, embossed texture, and crystal caps can be incorporated into the extrusion process, resulting in an appealing and very cost effective finished part. This process also offers the ability to create large, heavy-gauge parts, such as wheelbarrows, that are not possible or cost effective for injection molding. Once the part is formed it is then trimmed on the machine and is ready for use. The final pieces may undergo additional trimming, painting, or coating to achieve the desired appearance and functionality.
A custom finish on an injection molded part generally requires the part to be painted, silk screened or specialty coated. Since the part is molded from liquid resin no finishes can be applied until after the molded part is complete - unlike in forming, where a finish can be applied directly to the sheet during the extrusion process. However, despite this drawback, injection molding tools offer the opportunity for much a much more complex and intricate part - so for small and complex items with large volume runs, injection molding is the correct solution. Injection molded parts are widely used in industries requiring high precision and consistency. Injection molded plastic parts are ideal for projects that demand intricate shapes and high-volume production. The injection molding process is especially advantageous for producing small parts with detailed features.
Generally the break even point for an injection molding tool is around 2,000 – 5,000 parts per year depending on the complexity of the formed part – so production volume is an important component to consider. Plastic injection molding is a preferred method for manufacturing high-quality, consistent products at scale.
Thermoforming is best suited for large, heavy-gauge parts, while injection molding is ideal for small, complex, high-volume parts. The shape of the final product is determined by the forming process, with thermoforming best suited for simpler shapes and injection molding for more complex geometries.
The application of finishes and the choice of manufacturing process depend on the project's requirements, including cost, complexity, and production volume.
Each process has its own advantages: thermoforming offers speed and flexibility for large parts, while injection molding provides precision and efficiency for small, complex components. Both thermoforming and injection molding processes are used to manufacture a wide range of products, each with unique benefits depending on the application.
Thermoformed products are produced quickly and cost-effectively, making them ideal for prototypes and smaller production runs.
Custom finishes can be applied to meet specific needs, and the manufactured parts may require additional post-processing to meet specific industry standards.
When determining which processing method to select for your next project cost, aesthetics and functionality of the finished part will all help determine which method is ultimately selected. For more information on materials or to receive a referral for a thermoforming partner, contact out team!
Introduction to Plastic Processing
Plastic processing is a fundamental aspect of modern manufacturing, enabling the creation of a vast array of plastic parts used in industries ranging from automotive to consumer goods. Selecting the right plastic manufacturing process is crucial for ensuring that the final product meets the desired specifications, budget, and production timeline. Among the various manufacturing processes available, injection molding and thermoforming stand out as two of the most widely used methods. Each process offers unique advantages and is suited to different types of projects, depending on factors such as part complexity, production volume, and the specific application. Understanding the differences between injection molding and thermoforming is essential for making informed decisions that will impact the success of your plastic manufacturing project.
Plastic Processing Techniques
There are several plastic processing techniques available to manufacturers, each tailored to different production needs and end-use requirements. Two of the most prominent methods are thermoforming and injection molding. Thermoforming involves heating a plastic sheet until it becomes flexible, then shaping it over a mold to produce the desired part. This process is particularly effective for creating large, simple shapes from flat sheets of plastic. In contrast, injection molding utilizes molten plastic, which is injected under high pressure into a mold cavity to form the final product. This method excels at producing complex, detailed plastic parts in high volumes. The choice between these processes depends on factors such as the complexity of the part, the required production volume, and overall cost considerations. By understanding how each process shapes and produces plastic parts, manufacturers can select the most suitable method for their needs.
Injection Molding
Injection molding is a highly efficient plastic manufacturing process designed for producing precise, intricate parts in large quantities. The injection molding process begins with thermoplastic pellets, which are melted into molten plastic and then injected under high pressure into a double sided mold cavity, typically made from durable materials like steel or beryllium copper alloy. This high-pressure environment allows for the creation of complex geometries and fine details that are difficult to achieve with other manufacturing processes. Injection molding is particularly well-suited for high volume production runs, where the initial investment in tooling is offset by the low cost per part over large quantities. While the process is ideal for manufacturing small, intricate parts, it may not be the most cost-effective choice for parts with large surface areas or for smaller production runs. Nevertheless, injection molding remains a cornerstone of plastic manufacturing, delivering consistent, high-quality results for a wide range of applications.
Comparison of Methods
When evaluating thermoforming and injection molding, it’s important to consider several key factors that influence the overall efficiency and cost-effectiveness of the plastic manufacturing process. Tooling costs are a major consideration: thermoforming typically offers lower tooling costs and shorter lead times, making it an attractive option for smaller production quantities and projects with tight deadlines. In contrast, injection molding requires a higher initial investment in tooling, but becomes more cost effective for high volume production runs due to the lower cost per part. The complexity of the part also plays a significant role—thermoforming is best suited for large, simple shapes, while injection molding excels at producing intricate parts with detailed features. Lead times, production volume, and the specific application should all be weighed when choosing between these two processes. By understanding the differences between thermoforming and injection molding, manufacturers can select the most appropriate and cost-effective method to produce high-quality plastic parts tailored to their project’s requirements.