Small series, pre-series, pilot series of plastic parts

For the mass production of plastic components, injection molding is almost always the most economical method. For certain objects (e.g., eyeglass frames), milling is often used as well. Vacuum forming/thermoforming is also a commonly used method for packaging/blister packaging.
In the case of small series (quantities up to a few thousand), the situation looks somewhat different. Additive manufacturing methods have gained a lot of ground on traditional methods in this area in recent years. With the Multi Jet Fusion process (HP), the limits of what is possible have been pushed even further in this area.
In this article, we want to take a closer look at the most important methods for the pre- and zero-series production of plastic objects and show the advantages and disadvantages as well as the application possibilities of the individual technologies. Due to the complexity and variety of the respective components and methods, this can naturally only be a rough overview, which does not cover all details and methods.
For the sake of clarity, we have not included laser cutting and punching in the comparison, as these methods can also be an economic option for some objects/projects.

For the small series production of plastic objects, three 3D printing methods are suitable: Multi Jet Fusion (standard and full-color); laser sintering; and FDM/FFF.

HP’s Multi Jet Fusion 3D printing process is a new method that has only been on the market since 2017. Similar to laser sintering, it uses PA 12 (‘Polyamide 12’ or ‘Nylon 12’) as the material. The main advantages of Jet Fusion over laser sintering are significantly higher production speed, greater accuracy, and increased stability of the 3D-printed objects. In terms of mechanical strength, Jet Fusion objects are comparable to those produced by injection molding with PA 12. Geometries similar to those achievable with laser sintering are possible with Jet Fusion, but thinner wall thicknesses can be achieved. The main disadvantage currently is that the maximum size of objects is 380 mm, and the base color is always gray, although it can later be colored with dark colors (usually black). Since 2019, it has been possible to print in full color using the Multi Jet Fusion process. The parts produced with this method are minimally less stable but otherwise equivalent to standard parts.
Nevertheless, the process is considered the new standard in additive manufacturing for small series production of plastic components with quantities in the low thousands.

Laser sintering primarily uses polyamide 12 (Nylon 12) as the material. The material is often supplemented with additives (glass beads, aluminum powder, or short fibers). The major advantages of PA 12 are its durability, biocompatibility, and high stability. These properties make PA 12 a popular material used in many industries.

With laser sintering, you can produce virtually any geometric complexity (no support structures required), allowing parts to be optimized for their intended function. The only limitations are the need to maintain certain minimum wall thicknesses (∼ 1 mm). Compared to FDM, laser sintering has a high production speed. Machine build volumes can also be used much more efficiently, enabling a large number of parts to be produced per production cycle. However, cycle times are quite long, meaning the process is less suitable for mass production. Additionally, material costs are high because only a small portion of the material powder can be recycled (approximately 50 – 60%).
The main applications of laser-sintered parts are housings/casing parts or mechanically stressed components.

In Fused Deposition Modeling (FDM), the plastic (thermoplastic) is in the form of wire (filament). The filament is melted and deposited onto the build platform. The process is relatively slow and produces surfaces of medium quality (good surfaces only achievable with elaborate post-processing methods). Due to its high stability and the popularity of the thermoplastics used (e.g., ABS, polycarbonate, polyamide 6, polyetherimide), it is in high demand. The heat resistance and high impact resistance of the materials, in particular, make the 3D printing process popular with users in the automotive and aerospace industries.

The greatest advantage of additive manufacturing is that no tools/molds or other fixtures are needed to produce the objects. Therefore, the implementation speed of your project is much higher than with machining processes or plastic injection molding. If the surface quality and available materials are acceptable for the particular product, then additive manufacturing (especially Jet Fusion) is a fast and cost-effective solution for your prototypes or small series.

The costs in additive manufacturing consist of the following 3 components:

In vacuum casting, there are mainly two cost factors:

Vacuum casting is particularly suitable for the production of pre-series parts that are later to be produced by injection molding (vacuum casting enables surface qualities similar to injection molding). Other methods are better suited for the production of functional components (additive manufacturing, injection molding, machining processes).

Machining technologies (e.g., turning, milling) are highly complex but also offer users many production possibilities. The rotary tools used to extract the desired objects from the material block/plate are among the best the industry has to offer. However, when working with plastics, these tools can also cause problems as the resulting temperatures can damage the workpieces.

For machining processes, the following factors have been identified as cost drivers:

Machining processes are suitable for prototypes or for quantities below those for which injection molding would be economical. This is particularly true when only small tolerances are desired or very good surface finishes are needed. Especially for compact shapes or objects with low geometric complexity, machining is an economical option.

Injection molding is a relatively old (since about 1850) and well-developed process for mass production. In this process, heated, liquid plastic is injected into a mold. There, it cools down until it solidifies again. The finished object is then ejected from the mold. This process offers a huge range of applications. The most famous objects manufactured using this process are the famous LEGO bricks. But also the garbage containers in front of your house are manufactured using this process.
The crucial aspect of injection molding is the creation of the mold. The quality of the mold determines the cycle time (time from injection to ejection of the object), accuracy, surface quality, and many other parameters. Therefore, a large part of the development work is invested in creating the mold.

In injection molding, the creation of the mold is the biggest cost driver. For very large objects with high quality requirements, six-figure amounts are possible. For small, simple objects of lower quality and for batch sizes of < 5,000 pieces, you can expect costs starting from approximately EUR 2,500. Typical tools for producing several thousand pieces typically cost (for ‘normal’ components) around EUR 15,000 – 25,000.

Injection molding is suitable for the production of plastic objects of any kind in high to very high quantities.

A plastic sheet is heated and sucked/pressed onto a mold using vacuum/underpressure. The plastic sheet now takes on the contour of the mold and solidifies in this position. The molds for this process are usually much cheaper to produce than for injection molding. However, there are some limitations in component geometry. Only objects that can be formed from a plastic sheet can be manufactured (usually cups/blister packaging).

The shape of the object also has a major impact on the costs in deep drawing. However, the mold/tool is less expensive than in the injection molding process. Material consumption is also a cost factor, especially since relatively large amounts of material are cut off depending on the shape of the object (especially at the edge). Labor costs for post-processing of the objects are not crucial for series production in deep drawing.

Deep drawing is most commonly used in the production of packaging materials (blister) and simple disposable items like drinking cups. However, form components are also manufactured using this method in the automotive industry.

On the way from prototype to finished mass-produced product, all sorts of uncertainties can arise. For mass-produced goods, a zero or pilot series is recommended. This allows you to test the product/production well before transitioning to mass production (usually injection molding). For lower quantities (several hundred to a few thousand) and especially for small/medium-sized objects, additive manufacturing offers a fast and flexible alternative to traditional manufacturing methods. Another advantage of 3D printing processes is the significant simplification of design work and the production process.