3D printing and Injection molding are the two main technologies powering mass production of plastics parts. However, these two technologies have different use cases. For instance, 3D printing is a technology that is used to create parts by layering materials.
On the other hand, plastic injection molding capitalizes on the use of a mold filled with the molten polymer which is then cooled and hardens to make parts. Basically, injection molding and 3D printing are two competing innovations in the manufacturing sector.
Understanding the differences between these two plastic manufacturing processes is vital in promoting cost reduction, reducing lead times and ensuring quality end products. Read on to learn more about the differences between 3D printing and the injection molding process.
Overview of 3D Printing
3D printing is an additive manufacturing process that entails several technologies which can be used to make parts out of base materials. This manufacturing process is advanced and less expensive which has seen it has gained lots of traction amongst complex manufacturers.
3D Printing manufacturing (Image Source: Freepik)
The technology usually makes use of CAD (Computer-aided designs) to create desired products layer by layer and then fusing the layers to make the part. You can use both polymers and polymer composites in the 3D printing manufacturing process.
Types of 3D Printing Technologies
There are various 3D printing technologies that you can use in your project. These technologies include FD, SLA, and SLS.
1. FDM
Fused Deposition Modeling (FDM) is the most common and the oldest additive manufacturing method. One of its main advantages includes fast adjustment of filling the printed 3D models. This means that it is very easy to print a prototype only for checking the adjustment and finishing. The method has been widely used in creating architectural or model mock-ups
2. SLS
Selective Laser Sintering (SLS) involves merging polyamide particles with the use of a high-energy laser beam. This process starts with chamber filling with powdered material. Along with the progress of printing the working surface lowers and another layer of powder is added. It enables manufacturing of geometrically complex elements with high dimensional accuracy, compared to other 3D printing methods.
3. SLA
Stereolithography (SLA) is a precise 3D printing technology where the model material is cured with an UV laser beam in order to arrive at the final geometry. This technology is one of the most precise 3D printing technologies in the world. It enables recreation on the printed models of even the finest details.
Advantages of 3D Printing
- Customization – It allows for more complex designs.
- Complexity – Objects can be printed quickly depending on complexity.
- Setup times – Easy to setup and saves time by using a single step manufacturing process.
Limitations of 3D Printing
- Material restrictions – Selection of plastics and metals is not exhaustive.
- Strength – Layers can delaminate under stress due to the layer-by-layer production process.
- Scale – Cost per unit does not reduce significantly when scaled up for mass production
Overview of Injection Molding
Injection molding process is a manufacturing technique that is used by manufacturers across various industries to produce plastic parts. The process involves several stages whereby the material is prepared i.e., the plastic material pellets are well dried and fed into a hopper which is attached to the injection machine.
From the hopper into the heated barrel the plastic materials are melted and injected into the mold cavity. After the mold cavity is filled with the melted material under high pressure the cooling and solidification starts to produce the final part.
The mold is a key component in the injection molding process and directly impacts part quality, consistency, efficiency, reduced cycle time, flexibility and scalability. The mold design should be able to meet the desired geometry and complexity of the final parts.
Injection molds are a great way to mass-produce parts with detailed features. And thanks to use of extreme and excessively high pressure, the process tends to provide great details and design on all parts or products.
That said, several factors are crucial for the successful injection molding process. These include injection speed, melt temperature, injection pressure, cooling time, and packing pressure.
Each of these factors have an effect on product quality. Finding the ideal combination is key to getting optimal results.
Advantages of Injection Molding
- Efficiency at scale – Production output rate scales up and the cost per part significantly decreases with high volumes
- Material variety – There are various materials to choose from
- Part strength – Results in more durable and stronger parts due to utilization of high tensile strength materials
Disadvantages of Injection Molding
- Upfront costs – Initial cost of setting up the mold is high
- Design inflexibility – Once a mold design is created it makes changes to the design can be very costly
- Lead times – It can have longer cycle times which lead to longer lead times
Process and Time Efficiency
3D printing and injection molding are manufacturing processes used to produce parts but they differ in various key aspects as below.
1. Production speed
The production speed for 3D printing is generally slower compared to injection molding .3D printing is achieved using the additive process where an object is created by laying down successive layers of material until the final product is created. This can consume a lot of time depending on various factors such as part size and complexity.
In injection molding the production speed is relatively faster especially for large scale production. Once the mold is set up and the injection molding machine is in operation, parts are produced continuously and at a fast rate.
2. Set up Times
In 3d printing the setup period for production is relatively shorter compared to injection molding. Once the 3D model is created and the printer is calibrated, the setup process mainly involves loading printing materials and initiating the printing process.the setup time can vary under different factors such as material used, part complexity and the printer type.
Set up time for injection molding can be long due to various factors such as the mold design, creation and installation into the injection molding machine. The complexity of the mold design and material resources can lead to setup time varying.
3. Turnaround Times
In manufacturing this is the time a process takes to complete a certain task. Turnaround time in 3D printing can vary depending on several factors. Huge and complex parts can lead to a longer cycle time. For small batches of time the cycle time can range from a few hours to a few days.
Injection molding has longer turnaround times which are as a result of the setup process and lead time associated with mold creation. Turnaround times in injection molding can vary depending on mold complexity, production volume and material availability.
When project timelines are short and small batches are needed, 3D printing is the suitable choice. For medium to long-term projects that require large scale production, injection molding offers efficiency and cost effectiveness making it preferred for mass production. The choice between these two methods depend on project timelines, production volume and part quality.
Cost Implications
The analysis of upfront costs versus long term economies of scale is very important in determining the most cost effective manufacturing method.
1. Upfront Costs
In 3D printing the upfront costs are generally lower compared to injection molding. The initial investment involves buying a 3D printer and materials. The setup time of 3D printing is shorter and there is no need for mold designing and creation. The overall cost per part is higher, especially for large volume production.
Injection molding requires higher upfront costs due to the need for mold design, creation and installation of the mold into the injection molding machine. The cost of mold creation depends on complexity and size of the part. However the cost per part decreases for large production.
2. Long Term Economies of Scale
While 3D printing offers quick cycle time, it may not be cost effective for large scale production due to its low production speed and high cost per part. In the long run the cumulative cost of material outweighs the benefit of quick cycle time resulting in higher overall costs.
Injection molding is preferred in long term economies of scale. The cost per part decreases significantly in production of larger quantities outweighing the initial upfront cost. This process offers several advantages such as high speed production, consistent part quality and is highly cost effective for mass production.
The cost of 3D Printing vs. Injection Molding
We will use an SLS printed and injection molded PA+GF item as an example to compare the prices of 3D printing and injection molding. The item will have a standard deburr finish and measure 84.5 x 80.0 x 24.0 mm.
In this instance, the client would likely have to pay $3,000 right away to have a mold created. However, this could change according to the tool’s complexity, size, and manufacturing location.
Cost of 3D printing vs Cost of Injection molding (Image source: HLH )
The graph shows that because 3D printing doesn’t require expensive mold tooling up front, it’s a significantly more affordable option for smaller numbers. Nevertheless, injection molding starts to get more economical as you exceed 500 pieces.
Additive manufacturing is five times more expensive, with injection molding costing about $12,900 (or 99 cents each piece) at 10,000 pieces, compared to $70,000 (or $7 per piece) for 3D printing.
Quality and Material Considerations
Injection Molding provides access to various materials, including engineering-grade plastics. These materials offer specific properties such as high strength, heat resistance, chemical inertness, or electrical conductivity. Additionally, specialized materials like elastomers and thermosetting plastics are readily available for specific applications.
3D printing on the other hand offers a growing variety of materials, including plastics and composites which are more limited compared to injection molding. However, advancements in material development for 3D printing are continuously expanding the range of options and properties available.
The anisotropic properties of 3D printed parts can influence their overall strength and mechanical properties, resulting from layer-by-layer construction.
Material selection affects quality, strength and durability of parts in both 3D printing and Injection molding. With 3D printing, the material options are fewer and often more expensive while injection molding are more and are less expensive. However, mold development requires significant investment, making it unsuitable for low-volume production.
Design Flexibility and Complexity
If you prioritize rapid prototyping, then 3D printing may be the ideal solution. 3D printing provides design flexibility and quick prototyping capabilities. On the other hand, If you require tight tolerances or need a wide range of material options, injection molding may be the right option for your project.
Injection-molded parts feature a seamlessly poured single layer, ensuring a uniform and smooth surface finish. This smooth texture reduces friction when interacting with other objects, in contrast to the rougher finish of 3D printed parts.
3D printing does not require tooling that can cost a bunch. Consequently, it supports on-demand prototyping and production.
The lead times and setup times are shorter, and this form of additive manufacturing is cost-effective at lower part volumes. Importantly, 3D printing’s support for rapid, iterative prototyping can reduce project costs and timelines.
Compared to 3D printers, injection molding machines can produce more parts in less time. The tighter tolerances injection molding equipment can achieve, especially when steel molds are used, support greater part-to-part consistency.
Injection molding also supports the use of a wider selection of materials, including silicone rubber and thermoplastic elastomers. Designers can use the same polymer for prototyping and production, which facilitates testing and approvals.
Environmental Impact
Because extra plastic is frequently removed from the finished pieces during injection molding, there is normally more waste material produced. Nonetheless, the garbage is recyclable and reusable.
3D printing can be more material-efficient because it reduces waste and only uses the material required for the part. Nevertheless, failures or support structures are waste products of several 3D printing methods.
Widespread replacement of injection molding with 3D printing could notably increase or decrease greenhouse gas emissions on a global scale. These changes would probably be gradual. In terms of global resource depletion, 3D printing is unlikely to make significant changes even in the long term.
Sustainable Practices within 3D Printing and Injection Molding
3D printing, because of its additive nature, only uses the amount of material that is needed to create the product. The printing process is precise and efficient, ensuring that very little, if any, material is wasted.
On the other hand, injection molding can utilize eco-friendlier and non-toxic source materials. There is a growing list of more sustainable material for injection molding which include biodegradable or compostable plastics such as polybutylene adipate terephthalate (PBAT)
Choosing the Right Process for Your Project
The choice between 3D printing and injection molding often hinges on their applications, each suited to different production needs. While 3D printing excels in customization and complex designs, injection molding is the go-to for high-volume, cost-efficient production.
Additionally, selecting between injection molding and 3D printing involves considering factors such as production volume, cost, design complexity, material requirements, and time constraints.
Application Examples; 3D Printing Injection Molding
Usually, mass-producing a complex machine means manufacturing a million different parts. 3D-printing changes that as the technology makes intricate designs simple to produce. This has been a boon to the aeronautics, automotive and even the military industry. These days, the process of manufacturing jet and rocket engines, car parts and big weapons often involves 3D printed parts.
Whether it’s containers, shampoo bottles, cosmetic packaging, soap dispensers, or plastic kitchenware, there are a lot of everyday items that are mass-produced using injection molding. The flexibility of the process, i.e. the fact that most shapes can be manufactured to do the process, means that more complex designs for consumer items are not a problem.
Injection molding machine (Image Source: Pinterest)
Conclusion
When it comes to key differences, Injection molding is better for high volume production with minimal material wastage while 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. The choice between injection molding and 3D printing depends on specific project requirements.
Each technology has unique strengths and limitations, making each suitable for different applications. Understanding the strengths and limitations of each will guide you in making informed decisions, ensuring the optimal use of each method for its specific needs.
