Companies use a low-volume approach to test products in the market before high volume production or if the demand is small. Low volume options include injection molding, CNC milling, and 3D printing. Each low-volume manufacturing method has pros and cons and is best implemented for specific applications.
Low Volume Manufacturing Method 1: Injection Molding
Injection molding is used for high-volume manufacturing of products or parts. With high setup and tooling costs, it is not a common production method for low-volume products unless there are plans to increase volume or the product has high price points like medical devices.
Low volume injection molding uses low-cost materials for tooling, such as aluminum or reinforced plastics, that also have limited lifespans. High volume injection molding tools are more expensive and made of steel molds that can support production over millions of units. Low volume molds don’t last as long as their steel-built counterparts.
If you plan to increase production volume in the near future, low volume production methods may not be the best option. However, with high tooling costs used in large volume manufacturing and long lead time to create tools or retool i.e., months, alternative production methods may be better to get products to market quickly, efficiently, and with lower cost or MOQs. For most companies, CNC milling and 3D printing provide better alternatives because they eliminate most of the pre-production work and time.
| Injection Molding | |
|---|---|
| Pros | • Low volume injection molds can be used to test the product and tool. |
Cons | • High tooling prices. • Making tools can take weeks to months. • May require product redesigns that increase pre-production time. • Aluminum / plastic / glass-filled plastic tools don’t last long MOQs |
Low Volume Manufacturing Method 2: CNC Milling
CNC milling is a subtractive manufacturing process that uses rotary cutters to remove material from the source material. Compared to low-volume injection molding, CNC machines can create products at a far quicker pace and lower upfront cost as there are fewer tooling costs. In CNC milling, production begins once the CAD file is converted to the CNC program and the machine is set up for production.
Depending on the complexity of the part, CNC milling machines can produce products or parts in a few hours. Large CNC models can produce parts up to 2000 x 800 x 1000 mm ( 78 in x 32′ in x 40 in). CNC tools enable high repeatability, with high-end models featuring tolerances within 0.13mm (+/- .005 in) for metal parts and +/- 0.25mm (+/- .010 in) for plastic parts (i.e., CNC machines can achieve a dimensional tolerance of +/- 0.13mm (0.005 in) of dimension). However, CNC milling has some drawbacks.
CNC prep times are far shorter than injection molding, but it can still take hours to days. Sometimes a part requires a specialized tool that a machine shop orders before production begins. With the evolution of more advanced computerized CNC milling machines, only very skilled machinists can operate them – visualizing and designing the machining process, selecting the correct tools and sequences for the job, and writing the program on top of making adjustments and performing testing. The subtractive approach used by CNC machines is also inherently wasteful.
| CNC Milling | |
|---|---|
| Pros | • Faster turnaround and lower cost than injection molding. • Can accommodate large sizes. • High repeatability/high accuracy. |
| Cons | • Machine prep times. • Requires a skilled machinist in all steps. • May require specialized tools. • High material waste. |
Low Volume Manufacturing Method 3: 3D Printing
]Building products by adding material from the ground up, 3D printing is an additive manufacturing technique. Like CNC milling, 3D printing uses CAD files to directly produce the product. Additionally, 3D printing does not need tooling and is much easier to use than a CNC milling machine. Companies can utilize 3D printers for low-volume production runs by using in-house 3D printers or a smart factory with 3D printing services.
In both scenarios, the 3D printing process begins with a designer creating a CAD file of the product. 3D printers support more complex designs, such as non-accessible voids or internal geometries. With greater flexibility, designers can consolidate multiple components or sub-parts that are necessary for injection molding or CNC milling. Reducing parts streamlines assembly for more efficient production and a sturdier structure.
After the CAD file is created, it is translated into a .STL file (Standard Tessellation Language) and sent to the in-house machine or a smart factory. The 3D printing software takes the .STL file and slices the model into layers for printing. The 3D printing process can take a few minutes to several hours, depending on the part’s size, design, and the printing technology to produce the part. The production process itself is faster than CNC milling, as 3D printing does not require the manual repositioning of parts and fixtures, and with advanced 3D printers, require little to no post-processing. 3D printing is an additive process and wastes much less material than subtractive methods. With good designs, there is minimal waste from the support structures.
The highest-priced and precision CNC machines offer only slightly better tolerance than 3D printers, measured between thousandths of an inch. For most applications, 3D printing is the optimal choice, and the technology will continue to evolve and improve resolution and tolerance.
| 3D Printing | |
|---|---|
Pros | • No tooling. • Low material waste. • Supports more complex designs. • Enables part consolidation of parts for stronger models and fewer assembly steps. • Faster speeds and higher output capacity than CNC. • Greater flexibility – change design and reprint. • Less human labor/intervention. |
| Cons | • Size can be an issue for very large parts. • The higher tolerance capabilities of CNC milling may be required for specific products. |
Choose the Low Volume Manufacturing Method That’s Right For You
The three low-volume manufacturing methods each have scenarios where they’re the best choice. Low volume injection molding can benefit companies looking for near-term expansion into high volume production. CNC milling offers very tight tolerances and can meet larger size requirements. 3D printing enables products to get from design to market the fastest, greater design freedom, and more sustainable manufacturing.
Companies can also take a hybrid approach to selecting a manufacturing method to reduce cost and or time. 3D printing machines can be used to print injection molding tools for testing or for low volume manufacturing – depending on the injection molding material and the heat and wear tolerance of the 3D printed tool. With greater speed, companies can try multiple iterations of the tool in a short amount of time. Once the tool design is finalized, it can be made of more expensive materials, such as aluminum or steel, using the 3D printed one as a template.
Modernizing manufacturing with technology innovations can make it easier to produce products and for companies to be more competitive in an increasingly challenging global market.
To learn more about the pros and cons of different low-volume manufacturing methods, visit our contact page or call (650) 336-0888.
