Difference between thermoforming and injection molding
Thermoforming and injection molding are two common methods used in the plastic industry. Their applications appear in many different fields. But do you know which method is more optimal than the other? And which one will help improve production efficiency? Bajaj Plast will answer these questions through the following article.
Thermoforming manufacturing process
Thermoforming is a manufacturing process performed by heating thin plastic sheets to a temperature just enough to make the plastic sheets pliable but not melted. These sheets of flexible plastic are stretched and shaped by using molds with specific shapes. The formed plastic is cooled and trimmed to obtain the finished product.
Thermoforming is divided into many different methods such as vacuum forming, pressure forming, mechanical forming, drape forming, matched mold forming, etc. But in general, they all go through the same steps.
A basic thermoforming process diagram
Thermoforming process steps
Heating Plastic Sheets
The plastic sheets are clamped and transported into the heating machine to heat to forming temperature. They are heated by hot air or an infrared heater.
The type of heating machine selected depends on the plastic material used and the desired heat. Temperature is one of the most important parameters in the thermoforming process to meet quality standards because it creates the required ductility and flexibility of the plastic sheets.
Forming Plastic Sheets
This process is accomplished by stretching the heated thermoplastic sheet over the mold surface of the desired shape of the finished product. There are two types of mold tools depending on the finished product geometry.
- Positive tool
The positive tool has a convex shape, and placing a flexible plastic sheet above that convex shape will create the final product. The outer surface of the positive mold gives the inner surface of the product.
Thermoforming with positive mold
- Negative tool
In contrast, the negative tool has a concave shape, and the inner surface of the negative mold generates the outer surface of the product.
Thermoforming with negative mold
Trimming formed sheets
- Negative tool
In contrast, the negative tool has a concave shape, and the inner surface of the negative mold generates the outer surface of the product.
Plastic thermoforming advantages and disadvantages
Advantages
Low cost: Thermoforming molds can easily be made from inexpensive materials such as silicone, fiberglass, etc., instead of expensive and laborious metal molds. This makes thermoforming capable of producing large parts at a cheaper cost than other plastic manufacturing methods.
Durability: The thermoforming method has a simple machining process but produces high-quality products that are resistant to external influences and durable over time.
Production time: Since thermoforming molds are made from materials that are easy to work with and do not require complicated machining, they can be put into production quickly.
Design: Thermoforming can create objects with large designs. This aspect is one of the main reasons why thermoforming has become such a popular method of plastic production, especially in automotive design.
Some applications of thermoforming process
Disadvantages
- Scrap: The finished product of the thermoforming method after being trimmed will create scrap plastic. Fortunately, this scrap plastic is all recycled in production.
- Geometric limitations: The thermoforming is limited by complex geometry. Usually, small parts and intricate details are not feasible with this method.
- Surface thickness: The part thickness may not be uniform across all surfaces of the finished product. Therefore, the temperature parameters need to be optimized during operation to ensure the best quality.
- The cost: cost per finished product can be higher than other methods.
An application of thermoforming process
Injection molding manufacturing process
Injection molding is a method of manufacturing plastic by injecting molten plastic at high pressure into a mold where it is shaped. The entire injection molding process only lasts from 10 seconds to 2 minutes. There are four main stages in an injection molding cycle: clamping, injection, cooling, and de-molding.
Injection molding process steps
Clamping
Before the material is injected into the mold, the two halves of the mold must be closed by a clamping device. Both mold halves must be held firmly while the material is injected.
Injection
The input material is put into the injection molding machine through a hopper. The plastic is then heated until completely melted. Next, the melted plastic is injected into the mold through a nozzle.
Cooling
The cooling process takes place using an air or water system. The plastic inside the mold begins to cool and harden to fix the desired shape.
Cooling
At this final stage, the mold is opened and the product is ejected from the mold. Then, the mold will clamp and prepare for the next cycle.
Plastic injection molding advantages and disadvantages
Advantages
- High efficiency: Thanks to the fast production cycle, this method can produce a large number of products per hour. The production speed depends on the complexity and size of the mold.
- Low labor costs: Plastic injection molding is an automated process, most of the process is done by machines and requires only one operator to manage.
- Low scrap rate: This is a plastic production method that produces very little scrap compared to the traditional manufacturing process. Scrap plastic, if any, is ground and recycled for future use.
- Good color control: The finished plastic product can be produced in any color by mixing the appropriate color masterbatches.
- Product consistency: Injection molding is a process with low tolerances and high precision in product dimensional specifications. This is a huge advantage in bulk production.
Injection molding application on small parts
Disadvantages
- Complex mold structure: Mold design plays a key role in determining the quality of the finished product. The mold must be strong and able to withstand the pressure during injection.
- High tooling costs: Since the mold must be made of metal and have high finishing, the initial cost of the manufacturing process is quite high.
- Long set-up time: Due to the meticulous requirements for the design and quality of the injection mold, it takes a long time to create the mold and successfully test it before being used in production.
- Design limitations: The injection molding technique is hard to meet the finished products with large weight and size. The larger the parts, the more difficult and expensive the manufacturing process.
Injection molding application on large parts
Injection molding manufacturing process
Mold | Thermoforming A single mold is created out of fiberglass, aluminum, wood, silicone,… | Injection molding A double-sided mold is created out of metal Flat thermoplastic sheets with a wide range of materials, colors, and thicknesses |
Input material | Flat thermoplastic sheets with a wide range of materials, colors, and thicknesses | Thermoplastic pellets in a wide variety of materials and colors |
Production | A flat plastic sheet is heated to a pliable temperature, then molded to the shape of a mold | Plastic granules are heated to a melted temperature, then injected into the mold |
Finishing | Products after molding need to go through the process of trimming out of the sheets to obtain the finished product | Products after de-molding are often painted or silk-screened to obtain the finished product |
Cost | The initial tooling cost is low, but per piece cost is high | The initial tooling cost is high, but per piece cost is low |
Size | Suitable for large parts without complex structure | Suitable for small and complicated parts |
Production volume | Suitable for projects with a small production quantity | Suitable for projects with bulk production volume |
| Type of Masterbatch | Purpose / Function | Used in Thermoforming | Used in Injection Moulding | Remarks / Typical Applications |
|---|---|---|---|---|
| White Masterbatch (TiO₂ based) | Provides opacity and whiteness | ✅ Yes | ✅ Yes | Used in PP, HIPS, PET sheets, containers, and molded parts |
| Black Masterbatch (Carbon Black based) | Provides color, UV protection, and opacity | ✅ Yes | ✅ Yes | Food trays, automotive parts, electrical components |
| Color Masterbatch | Adds desired color shades | ✅ Yes | ✅ Yes | Custom-colored thermoformed trays, caps, containers |
| UV Stabilizer Masterbatch | Protects against UV degradation | ✅ Yes | ✅ Yes | Outdoor packaging, automotive and garden products |
| Antistatic Masterbatch | Reduces static charge on plastic surface | ✅ Yes | ✅ Yes | Packaging trays, electronic parts, and appliance housings |
| Slip Additive Masterbatch | Reduces friction between surfaces | ✅ Yes | ✅ Yes | Aids in easy sheet release and product ejection |
| Antiblock Masterbatch | Prevents sticking of plastic films or sheets | ✅ Yes | ⚪ Limited | Used mainly in thermoformed sheet extrusion |
| Clarifying / Nucleating Masterbatch | Improves transparency and stiffness | ✅ Yes | ✅ Yes | Used in PP thermoformed cups and injection-molded containers |
| Antioxidant Masterbatch | Prevents polymer degradation during processing | ✅ Yes | ✅ Yes | Ensures long-term stability and prevents yellowing |
| Desiccant Masterbatch | Absorbs moisture from recycled polymer | ✅ Yes | ✅ Yes | Useful for recycled PP or HIPS sheets and molded items |
| Process Aid / Lubricant Masterbatch | Enhances surface finish and flow | ✅ Yes | ✅ Yes | Smooth glossy finish, reduced melt fracture |
| Impact Modifier Masterbatch | Improves toughness and impact resistance | ⚪ Limited | ✅ Yes | Especially in automotive parts and housings |
| Fragrance / Antimicrobial Masterbatch | Adds pleasant scent or prevents bacterial growth | ✅ Optional | ✅ Optional | Used in consumer goods, packaging, and household items |
About Bajaj Plast Pvt. Ltd.
Bajaj Plast Pvt. Ltd. is a leading manufacturer of high-quality masterbatch solutions, dedicated to innovation, sustainability, and excellence. With a strong focus on customer satisfaction and cutting-edge technology, we are committed to delivering superior products that meet the evolving needs of the polymer industry.
