3D printing and injection moulding are both techniques for producing plastic parts and components, but each manufacturing process has its own advantages and can be used together as complementary manufacturing methods.
3D printing technology is an additive printing process that creates objects by building up layers of material, while plastic injection moulding uses a mold that is filled with molten material that cools and hardens to produce parts and components.
Injection moulding and 3D printing can both be used for protoyping, but there are some key differences between the processes.
The Key Differences
- Injection moulding is better for high volume production with minimal material wastage
- 3D printing is a slower process, but is faster to set up and allows for frequent design changes as well as being better for complex designs
3D printing (also known as additive manufacturing) offers fast turnaround times of 1-2 week, making it ideal for rapid prototyping and for designs with frequent changes. This process is also able to produce relatively small plastic parts and components as well as being ideal for complex or intricate designs. It is, however, best suited to print parts for low production runs of 100 parts or fewer, as it can be costly in terms of time and money for larger runs.
- 3D printing has a low entry cost. A desktop 3D printer and supply of materials is cheaper than injection moulding equipment. The proliferation of open-source software and hardware can also provide ongoing support at little or no cost
- Easy to make design changes. Since it is an additive process, 3D printing allows you to make design changes even during production, saving time and money on a run of components that may have a flaw. Being able to pause mid process and make design changes means that you do not need to start the entire production run from the start. 3D printing is also good for quick prototypes as there is little set-up required ahead of production
- Good for intricate designs. Because it produces parts layer-by-layer, 3D printing is perfect for producing complex or intricate designs with detailed infrastructures
- Despite the set-up being relatively fast, 3D printing is a slow production method. The CAD-based, detail oriented process limits how many parts can be produced at once, with most printers only capable of building one or two items at a time
- 3D printing is unable to produce larger items as the process is limited by the size of the printing area. The design becomes increasingly unstable if parts hang off the edge of the printing area, so while large scale 3D printing is possible, it is not the best use of this process
- Rough finish. The finish of 3D printed parts is rough due to the layers being additively built, no matter how fine the detail is. As a result, post-build smoothing is required should you need a smooth finish
Injection moulding has long turnaround times to prepare for the creation of parts (5-7 weeks even for simple parts), which means it is not well suited to frequent design changes. However, despite the long turnaround times this process is ideal for producing parts in high volumes (1,000+ parts per run). The mold tool is also fine for producing large or small components of any complexity.
- Able to mass produce a high volume of parts. Injection moulding can use a high number of molds at once, meaning that it is more cost-effective for producing a large number of objects
- Enhanced strength of objects. Injection molded parts are created using a single layer of poured material, eliminating any fissures or other areas of weakness. This process also works for dense materials, such as concrete, that would need to be diluted or modified for 3D printing
- Minimal wastage. Because injection moulding involves pouring material into a mold, it uses exactly the amount of material required for the design. This means this manufacturing method is ideal for mass producing objects cost-effectively
- Limited design capabilities. The use of a mold means there are design limitations placed upon this production method. Right angles in the design can make it difficult to remove an object from the mod without it breaking. Injection moulding is also not well suited to creating precise and delicate designs that can stand on their own
- Difficult to correct mistakes or change designs. Because of the long set-up times associated with injection moulding it is difficult and expensive to rectify any mistakes in the design. The mold needs to be completely remade to change designs or fix problems, while any objects produced would need to be scrapped
- Expensive entry costs. Injection moulding machines are expensive, often costing upwards of six figures. Designed for industry, these systems are not really for hobby use as there is the cost of making molds, materials and design prototyping to take account of in addition to the original machine cost
3D Printing is best suited to:
- Small batch production, including prototyping
- Intricate designs with gaps or holes in the middle
- Design changes, even during production
Injection moulding is best suited to:
- Large batch production as you can create multiple identical objects simultaneously
- Strong, solid designs that are based on one continuous form
- Smooth finishes for parts that move against other objects. The ease of creating smooth parts means that there is reduced friction as compared to the rougher finish associated with 3D printed parts
Will 3D Printing Replace Injection Moulding?
3D printing and injection moulding are often seen as competing technologies, but each has their own set of benefits and suitable uses.
While 3D printing has become more widely used in recent years, injection moulding is still used for the manufacture of the majority of plastic parts for industry. This is due to the ease with which costs and quality can be controlled while also allowing for mass production.
However, because of the cost and time consuming nature of injection moulding tooling design, 3D printing is generally seen as a better process for prototyping. The medical industry is just one area where 3D printing has been embraced for the production of custom items such as artificial heart valves, dental products or prosthetics.
Rather than seeing 3D printing as a potential replacement for injection moulding, the two technologies should be seen as complementary processes that can be used together depending upon requirements. By using the processes together, it is possible to shorten pre-production cycles before moving onto large batch production.
Both processes have their benefits and drawbacks and so they should be considered as complementary rather than competing technologies. 3D printing is better for small batch, complex parts that may require frequent design changes or customisation. Injection moulding, on the other hand, is better for large volume production of less complex parts that have successfully completed the design stage.
TWI can support you with all aspects of design and manufacture related to injection moulding and 3D printing, whether that is technical support, technology acquisition, product and process development or manufacturing and production support.
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