Injection Molding vs. Thermoforming, What’s the Difference?

Thermoforming is a more specific method of plastic processing in which thermoplastic sheets are processed into a variety of cracked products.

Thermoforming is one of the methods of molding plastic products. Thermoforming is the process of forming a heated plastic sheet on the surface of a convex or concave mold.

The thermoplastic sheet or tube is heated until it is soft and then molded a second time under gas pressure, liquid pressure, or mechanical pressure using a suitable mold or fixture to form the plastic product.

Unlike injection molding, this is a one-sided plastic manufacturing process. Only one side of the plastic sheet is controlled by a mold or tool. Vacuum molding and pressure molding are both popular methods of thermoforming.

Injection molding vs. thermoforming advantages

Plastic injection molding offers several unique advantages of its own, including:

Detailed, highly engineered molds with multi-cavity mold options

Accurate, efficient handling of large numbers of small parts

Effective part count reduction

Efficient use of materials and low scrap rates

For projects requiring thousands or even millions of identical parts, plastic injection molding is ideal for high-volume orders and mass production.

Detailed tooling for complex parts

One of the main advantages of injection molding is the ability to create extremely complex components with exceptional detail. The high pressures used in the injection molding process allow for the production of complex parts and unusual geometries, as the material is firmly pressed into the smallest of tiny cavities.

The multi-cavity mold option allows further customization of the injection molding process to meet specific needs.

Extremely high precision and efficiency

Injection molding involves repeated runs using durable and reusable molds. Users can rely on the molds to provide highly accurate, repeatable results for years of mass production. This method is particularly useful for very small, complex, and intricate components that are very time-consuming or difficult to create using thermoforming, cutting, milling, and other manufacturing methods.

Lower Injection Molding Costs

Although injection molding is more expensive than thermoforming, the mold design and manufacturing process can be modified in a variety of ways to reduce overall production costs. Simplifying and streamlining the design can reduce some of the costs required to create a detailed mold. In addition, using material reduction methods such as undercutting and coring, or simply modifying the mold from a similar product, may provide the means to meet the needs of new projects in an affordable manner.

Efficient material use

Injection molding is a highly efficient process with very low scrap rates. The amount of material used for each component is precisely measured to ensure complete filling of the mold and ultimately little to no overflow or waste. Injection-molded products can be formed to scale and require little to no additional tooling after ejection from the mold.

Depending on the needs of the project, thermoforming can offer several distinct advantages, including:

Lower tooling costs compared to injection molding

Rapid product development and prototyping

Bright color and texture options

Extremely adaptable and easy to adjust

Thermoforming is ideal for small batches (250 to 3,000 parts per year)

Lower tooling costs

Tools used for thermoforming are less expensive than injection molding.

Molds used for thermoforming are typically made of inexpensive aluminum. In contrast, injection molds are typically composed of thicker aluminum, steel, or other heavier alloys to withstand higher pressures and be able to be continuously reused in larger production runs.

In addition, thermoforming uses only single-sided tools and not double-sided injection molds. This effectively halves the amount of material required for mold fabrication, thereby significantly reducing the upfront cost of thermoforming. However, the molds are less durable and cannot be used for mass or repeat production.

The size of the component plays an important role in the cost-effectiveness of thermoforming compared to injection molding. The larger the component, the greater the difference between the tooling costs. As part size increases, thermoforming becomes increasingly cost-effective.

Rapid Product Development and Prototyping

Thermoforming is much faster than injection molding for product development and prototype testing because of the ability to produce thermoforming molds quickly.

Injection molds are more time-consuming to process because the molds are double-sided and composed of harder materials (e.g., steel). In contrast, thermoformed molds are easier to design, fabricate and modify, making them ideal for development and testing. 

Multiple Texture and Vibrant Color Options

Thermoforming offers a variety of benefits for product design and branding. Vibrant colors can be added to thermoformed plastics, resulting in vivid, long-lasting coloring throughout the material.

In addition, thermoformed materials can be accepted for painting, screen printing, printing, decorating, and coating to provide unique designs, textures, and finishes that enhance the appearance and longevity of the product. 

Extremely adaptable and easy to adjust

Because thermoforming uses simple, one-sided molds made from highly moldable materials, thermoforming designs can be modified quickly and at a minimal cost.

Injection molding, on the other hand, requires double molds with heavier materials, which are more time-consuming and expensive for the tool.

Injection molding vs. thermoforming types

5 common injection molding processes

Blow molding injection molding process

Ideal for hollow objects, such as bottles.

The heated plastic block expands through the air. The air pushes the plastic into the mold to form the desired shape. After cooling, the product is ejected.

The blow molding process is designed to produce large volumes of one-piece hollow objects. Blow molding produces very uniformly, thin-walled containers in an economical manner.

Injection Molding Injection molding process

Suitable for high quality, high volume product manufacturing.

Injection molding is the most versatile of all molding technologies. Injection molding machines used in this process vary in size and are rated for settings based on tonnage or pressure.

Larger machines can injection mold automotive parts, while smaller machines can produce very precise plastic products. In addition, the injection molding process can use many types of plastic resins and additives, which increases the flexibility of designers and engineers.

Extrusion Injection Molding Process

Ideal for long hollow molding applications such as pipes, ducts, and straws.

Extrusion molding, also known as extrusion in plastics processing, uses hydraulic press pressure on the die itself in a non-rubber extruder process called press-out.

Extrusion molding is a processing method in which the material is thermoplasticized by the action of the extruder barrel and the screw while being pushed forward by the screw and continuously passed through the head to make various cross-sectional products or semi-products.

Compression injection molding process

Suitable for large parts, such as automotive parts.

Heated plastic material is placed in a heated mold and then compressed into a certain shape. The heating process, called curing, ensures that the product retains its integrity.

As with other molding methods, once the part is molded, it is removed from the mold. If a plastic sheet material is used, the material is trimmed in the mold before the product is removed.

This molding method is well suited for high-strength compounds such as thermoset resins as well as fiberglass and reinforced plastics. The excellent strength properties of the materials used in compression molding make it a valuable process for the automotive industry.

Rotational Injection Molding Process

Suitable for large, hollow, one-piece parts.

This process uses high temperatures and rotational motion to cover the inside of the mold and form the part. The constant rotation of the mold creates centrifugal forces, resulting in a uniform wall product.

Because it is ideal for large, hollow containers, it is not a fast-moving process. However, it is a very economical way to mold for specific applications and is cheaper than other types of molding.

Almost no material is wasted using this process, and excess material can often be reused, making it an economical, environmentally friendly manufacturing process.

What are the types of thermoforming?

Vacuum forming

There are dozens of thermoforming methods, and vacuum forming is one of the representative ones.

Vacuum forming is one of the representative methods. It uses a vacuum to make the heat-softened sheet cling to the surface of the mold and form it. This method is the simplest, but the pressure difference caused by vacuuming is not large.

It is only used for cracked products with a simple shape.

Air pressure thermoforming

This method uses compressed air or steam pressure to force the heated and softened sheet against the surface of the mold. Since the pressure difference is larger than that of vacuum forming, it can be used to crack more complicated-shaped cracked products.

Thermoforming to mold

The heat-softened sheet is placed between the paired negative and positive molds and molded by mechanical pressure. This method has higher molding pressure and can be used for cracking complex-shaped cracked products, but the mold cost is higher.

Plunger-assisted molding

The heated sheet is partially pre-stretched by a plunger or a positive mold and then formed by vacuum or air pressure.

Solid Phase Molding

The sheet is heated until the temperature does not exceed the melting point of the resin so that the material remains in a solid state. It is used for ABS resin, polypropylene, and high molecular weight high-density polyethylene. The rigidity and strength of the cracked parts are higher than those of general thermoformed products.

Two-sheet thermoforming

Two sheets are laminated together and the air is blown between them to make large hollow cracked parts.

It is a processing method to crack plastic products using thermoplastic sheets as raw materials. The sheet is cut to a certain size and shape, clamped to the frame of the mold, heated and softened, and then pressure is applied to make it cling to the molding surface of the mold to obtain a similar shape, and after cooling and shaping, and trimming, the cracked product is obtained. The thickness of the sheet used for molding is generally 1~2mm, and the thickness of the cracked product is always less than this value.

Injection molding vs. thermoforming materials

What are the materials used for injection molding?

The materials used for injection molding are ABS acrylonitrile-butadiene-styrene copolymer, PA6 polyamide 6 or nylon 6, PA66 polyamide 66 or nylon 66, PBT polybutylene terephthalate, PEI polyethyl ether, PMMA polymethyl methacrylate, etc.

What are the plastics used for thermoforming?

Plastics used for thermoforming are mainly PS, PVC, PE, PP, PET, and cellulose (such as nitrocellulose, cellulose acetate, etc.) plastics, but also for engineering plastics (such as ABS resin, PC).

Injection molding vs. thermoforming cost

Is thermoforming cheaper than injection molding?

The up-front cost of thermoforming is generally much less expensive than injection molding. Much of this is due to the cost of tooling used in thermoforming vs. injection molding.

The cost of tooling in thermoforming is much cheaper than the cost of injection molding. However, the cost of production per piece in injection molding can be less expensive than thermoforming.

Injection molding vs. thermoforming production

Applications for Injection Molded Products

Construction: Hand tools, fasteners, window and door locks, carpenters and handles, and other construction accessories

Aerospace: Turbine blades and housings, lenses, panels, and gears

Food and Beverage: Food-grade plastics for conveyors, filters, and processing systems; and food and beverage packaging

Medical and Pharmaceutical: Medical device components, diagnostic kits, x-ray components, and surgical preparation kits

Malls: Retail display equipment, such as partitions, hooks, and product stops

Applications that use thermoformed products

The lower cost, versatility, and adaptability of thermoforming make it ideal for many applications, including

Automotive: instrument panels, seat components, interior trim panels, bumpers, and air ducts

Aerospace: air ducts, seat components, interior panels, kitchen equipment, and window coverings

Structural: Equipment enclosures, toolboxes, interior, and exterior panels

Medical: Diagnostic and imaging equipment enclosures, bed and furniture components, auxiliary equipment, and walls and ceilings

Public transportation: interior and exterior panels, seat assemblies, instrument panels, and light fixtures

Office equipment: fax, printer, computer and copier enclosures, switchboards, walls and ceilings, and furniture

Is thermoforming better than injection molding?

While thermoforming is commonly used for large-scale designs and shorter production runs, injection molding tends to be a better choice for small, intricate parts and large production runs.

Which molding process is better?

For some industries and applications, both injection molding and thermoforming processes may be used for the manufacture of plastic parts. But many industries turn to a specific method based on the unique attributes of the project at hand. To determine which process is best for your plastic molding job, it’s important to carefully assess the unique characteristics and requirements of your project.