Do you need a few high-quality plastic parts but are worried about the high cost of injection molds and tooling? If so, there are several alternatives to injection molding that can deliver the same quality and precision.
Alternative plastic manufacturing processes, such as thermoforming, 3D printing, blow molding, and CNC machining, are even affordable for prototyping and small batches. They are flexible for complex designs, customization, and repetitive iterations.
This article will discuss seven injection molding alternatives and how you can choose the best one for your project.
Plastic Injection Molding and Its Alternatives
Injection molding is an advanced and precise process for manufacturing plastic parts, popular for mass production. This technology shapes thermoplastic materials by melting and injecting them into a mold with an exact negative geometry of the intended part. The molten plastic flows inside the cavity and solidifies before ejecting from the mold.
Manufacturers typically use either an aluminum mold or a steel mold, depending on the type of plastic and the number of production cycles required.
Injection molding applications are widespread, including automotive, electronics, aerospace, medical, consumer products, and research & development industries. But as said earlier, it is expensive for small volumes due to the high per-part tooling cost.
Instead of injection molding plastic parts, you can opt for the following alternatives.
- Blow Molding
- Thermoforming Process
- Rotational Molding
- Vacuum Casting
- 3D Printing
- CNC Machining
- 3D Print Molds
Let’s overview these techniques in a table and discuss them further in detail.
| Process | What is it? | Materials | Cost | Complexity | Best for |
| Blow Molding | It expands a heated plastic tube in a mold to form hollow parts. | HDPE, PET, PP, PVC | Relatively higher | Moderate | Bottles, tanks, containers |
| Thermoforming | Thermoforming of plastic sheet by placing plastic over a mould using pressure/vacuum. | ABS, PS, PVC, PETG | Low tooling cost | Low to Medium | Large thin-walled panels, trays |
| Rotational Molding | A heated mold rotates with resin powder to form hollow parts. | PE, PP, Nylon | Medium | Low | Large hollow parts |
| Vacuum Casting | It uses silicone moulds to cast the parts. | PU, epoxy resins | Low | Low | Prototype or short-run parts |
| 3D Printing | A 3D printer builds parts layer by layer from CAD data. | PLA, ABS, Nylon, Resin, Metal | Low to Medium | High | Complex prototypes and low-volume parts |
| CNC Machining | A CNC machine tool subtracts material from a solid block using cutting tools. | Metals, plastics | Low for small runs | High | Precision prototypes, functional parts |
| 3D-Printed Molds | It involves creating molds using 3D printing for short-run moulding. | Resin, metal powders | Low to Medium | Medium | Short-run injection or testing molds |
Blow Molding
and pressurized air. This process is ideal for containers, tanks, bottles, fluid reservoirs, custom tubes, and packaging items.
Although it does not have extensive capabilities like the standard injection molding technique, blow molding excels in producing thin-walled & hollow components across various industries.
There are three different types of blow molding:
Extrusion Blow Molding
This is the most common form of blow molding. First, a hollow tube, called parison, is made by extruding the molten plastic and placed inside the heated mold cavity. Then, compressed air inflates the parison, forming the desired shape.
Extrusion blow molding is suitable for simple and large-sized products requiring reasonably good strength. For example, fuel tanks, watering cans, and lightweight toys.
Injection Blow Molding
This technique is a combination of injection and blow molding, where the initial tube is formed by injection molding and transferred to the blow molding die. You can only use it for materials that do not harden in a short time, like PTE, polycarbonate, and polypropylene.
Injection blow molding has the capability of making complex tubular structures. For example, cosmetic containers, pharmaceutical bottles, and threaded caps.
Injection Stretch Molding
The only difference from injection blow molding is the use of a stretching rod inside the preform before applying pressurized air. The stretching is beneficial for creating polygonal geometries with high detail and accuracy.
Thermoforming Process
The thermoforming process involves heating and stretching a plastic sheet over a mold, followed by cutting or trimming of edges to exact the shape. It is an affordable low volume injection molding alternative for the production of plastic items.
Vacuum or mechanical forces pull the heated sheet against the mold surface. So, the sheet stretches and captures the shape details. You can thermoform a wide range of plastic materials, including polypropylene, polystyrene, PET, PVC, and HDPE.
This method has extensive applications in automotive, defense, medical, and consumer industries. Some notable examples are a car’s fender & dashboard, medical equipment, computer parts, and food trays.
Rotational Molding
Rotational molding is one of the best injection molding alternatives for producing hollow and tubular parts. For example, storage tanks, trash cans, and components for chemical processing equipment.
The process involves placing the material powder inside a roto mold and rotating it while applying heat simultaneously. The heat melts the material powder, and rotational motion forces it to stick to the mold surface. Then, the mold cools while rotating and solidifies the sticky plastic layer, capturing the shape.
You can compare this method with blow molding, but it is a simpler and inexpensive injection molding technique, even for large production volumes.
Vacuum Casting
Vacuum casting, also known as silicone casting, utilizes silicone molds to produce small batches of rubber and plastic parts, typically comprising up to 20 identical items. First, a replica of the desired shape (or pattern) is created using 3D printing, casting, or CNC machining. Then, pouring liquid silicone around this pattern and ejecting it after solidification creates a mold for casting.
This method significantly reduces mold and tooling costs, making it an ideal choice for small run injection molding projects. It also offers high design flexibility and customization benefits.
You can use this alternative for rapid prototyping of plastic parts, especially when you need to test the functional model in a short time.
3D Printing
It is an advanced and fast manufacturing process that builds designed 3D shapes by adding successive material layers with high details and accuracy. 3D printing can produce complex geometries with intricate internal features, outperforming the injection molding capabilities.
Moreover, techniques like stereolithography (SLA), fused deposition modelling (FDM), and Selective Laser Sintering (SLS) are available for plastic 3D printing.
Utilize 3D printing as an alternative to injection molding when you require complex and consolidated assemblies, as well as faster iterations for product development. For prototyping, it is almost five times faster than the regular plastic molding processes.
CNC Machining
This is another alternative plastic manufacturing process that eliminates the need for molds and other costly tooling. Machining involves shaping plastic workpieces into the desired shape using computer-controlled tools via known as G & M codes. Based on the capabilities of CNC equipment, the cutting tools can move across various axes to remove the material from the plastic workpiece.
Multi-axis CNC mills and lathes can perform a range of machining operations, including turning, profile milling, drilling, threading, and grooving. Consequently, these operations maintain a tight accuracy of ±0.0254, or even lower. However, there are limitations in wall thickness and material choices.
3D Print Molds
One of the key disadvantages of injection molding is the high upfront cost for mold making & tooling, which is unjustifiable for small volumes. Therefore, 3D printed molds are the most effective alternatives to traditional metal molds, enabling low cost injection molding. Additionally, 3D printing can make a complex mold cavity with internal channels, grooves, undercuts, and sharp edges.
They perform plastic molding processes with tight tolerances. Unlike other types of injection molds, they are reusable for up to 100 production cycles.
How to Choose the Right Alternative to Injection Molding?
Selecting an affordable alternative to injection molding for plastic parts manufacturing necessitates consideration of various factors. You must define the part’s complexity, tooling cost, lead time, and texture, as these decide whether alternatives can deliver high-quality parts in small volumes at an affordable cost or not.
Let’s look at the common factors to consider in brief.
Material Type
Consider the required part material as it not only affects the properties but also the compatibility with alternative processes. Some methods, such as thermoforming and vacuum casting, are not suitable for molding certain thermoplastics and elastomers.
Mechanical Strength
Methods like 3D printing might not produce parts with high strength and stiffness. Therefore, determine the required strength, impact resistance, dimensional stability, and creep resistance for optimal performance, and analyze which alternative is most suitable for these requirements.
Tolerances and Finish
Each plastic manufacturing method has distinct capabilities of precision and surface finish. CNC machining can provide high accuracy and a smooth finish, whereas 3D printed parts might struggle with tight tolerances and leave layer marks on the surface.
Design Complexity
Does your part/mold design feature complex elements such as internal channels, deep cavities, and irregular contours? If so, 3D printing can be a great alternative. Otherwise, choose thermoforming, casting, or machining. Consequently, choose rotational or blow molding for hollow tubular designs.
Iteration Flexibility
If you are looking for product testing and validation, also consider the iteration flexibility of alternative methods. CNC machining and 3D printing are more flexible for design changes, whereas thermoforming, rotation molding, and casting are relatively expensive and slower due to the need for mold rework.
Conclusion
As we have discussed, there are various alternatives to injection molding for your short run project. You can choose the right method and produce the plastic parts without investing significantly in metal die tooling. It allows you to convert your design into a functional part/product at an affordable cost. Meanwhile, you must consider factors like design specification, material type, iteration flexibility, and others.
Furthermore, it is equally important to choose an expert and reliable manufacturer like RapidDirect for precise and high-quality plastic parts. We not only provide injection molding service, but also its alternatives.
Our plastic molding facility has advanced equipment and quality control instruments to ensure industry standards. Subsequently, our latest updates on Teamspace collaboration provide real-time updates, avoiding any misunderstandings.
FAQs
Injection molding, compression molding, thermoforming, blow molding, and extrusion are among the most widely used plastic manufacturing processes.
3D printing is a cheaper alternative to injection molding for low volumes. However, the exact costing depends on the type of part being made and the material used.
Yes, 3D printing can be the best alternative for short run plastic molding. However, if you require strength, a good finish, and material flexibility, CNC machining or vacuum casting may be better alternatives.
