Injection Moulding vs Thermoforming: Which is best for your product?
Injection moulding and thermoforming (also called vacuum forming) are the two main processes for producing plastic moulded parts. Injection moulding involves heating plastic pellets and injecting the resulting liquid into metal moulds, before cooling and releasing the plastic part. Whereas thermoforming involves heating a plastic sheet and stretching it over or into a mould’s surface using a vacuum and atmospheric air pressure.
Injection moulding vs thermoforming – which process to choose?
There are a number of key differences between injection moulding and thermoforming that will dictate which process is best suited for your application:
| Consideration | Injection Moulding | Thermoforming |
| Volume | Extremely high-volume production | High volume production (ranging from one-off to thousands) |
| Finish | Finished parts produced | Secondary finishing processes may be required and can be combined with sub-assembly on site to further refine and adapt the finished parts |
| Part size | Small, intricate, complex parts with narrow size tolerances | A full range of small, medium, and large parts with precise geometries and extremely high tolerances are achievable |
| Material | A selection of materials are available | A large range of materials are available in a variation of colours |
| Lead times | Long-lead times | Short-lead times |
| Cost | Cost-effective for extremely high-production runs | Cost-effective across a wider range of batch quantities |
| Tooling | High initial tool cost, and tooling is unable to be modified easily | Lower tooling cost and can be readily modified. Also good for prototyping as soft tooling is available |
In conclusion, thermoforming is suited to a broad range of production applications. This is because thermoforming can be utilised to produce parts in a variety of sizes, which can then be further adapted through sub-assembly finishing. Moreover, thermoforming allows for shorter lead times when compared with injection moulding and is a cost-effective solution across multiple batch quantities. Finally, thermoforming results in lower tooling costs, with these tools also having the capacity to be modified throughout the production process.
The thermoforming process
Tool design and creation
Tool creation can be achieved with different production methods and materials depending on the specifications of the project. Tools are either positive (plastic is pulled over the mould) or negative (plastic is sucked into the mould using a vacuum). Tools can be made from the following materials:
- Wood – Used for experimental or short runs
- Resin/model board – More resistant, smooth, non-porous surface, and keeps its shape
- Aluminium – Can be machined into more specific dimensions and used for longer production runs
Tool production
Once a design is finalised, the tools themselves need to be produced in line with the customer’s CAD data and drawings. Prior to use, these tool designs are sent to the customer for final approval.
Manufacture
In thermoforming, the materials are loaded onto the moulding machine, where they are heated until they reach the optimum temperature to be formed. A vacuum is then applied to pull the plastic over the tool while the edges of the sheet are held in place by a clamp frame. Once the material has cooled to the required temperature it then dismoulds.
As mentioned in the table above, thermoformed plastics can be further refined with secondary finishing, such as where the part is trimmed, as well as adding details like cutouts, holes, and sub-assemblies.
Sustainability of plastics
We now know that the revolution in plastic has been both a benefit and a detriment to our world. The versatility of plastic, its ability to be moulded into almost any shape and its durability have meant endless functions and unlimited possibilities – from kids’ toys, containers and wrapping, to computers, car parts, building materials and more. However, the advantages of plastic are also its disadvantages – its durability means an unnaturally long life, with some plastics taking up to a thousand years to decompose, and its ubiquity in modern (often disposable) culture have meant an increasing build-up with damaging effects on animals and the environment.
With rising concern and focus on the proliferation of plastics, those in the industry are working hard to lessen its impact. At Cox Wokingham, we pride ourselves on the fact that all of our excess materials are gathered and fully recycled – this means that none of our byproducts find their way to a landfill site. The use of recycled material helps the planet, helps companies hit their environmental targets, and can also help bring down the cost of certain projects, where virgin material cannot meet the same pricepoint as re-granulated plastics.
