The manufacturing industry is currently undergoing a significant transformation. This dynamic market necessitates the rapid introduction of products with small volumes. Simultaneously, designers, engineers, and manufacturers must guarantee product quality. One solution of manufacturing that addresses customer requirements is low-volume injection molding and On-demand Manufacturing.
This production technique permits the production of similar plastic components with consistent features and attributes. Manufacturers are presently embracing new operational approaches to gain an edge in evolving markets. This comprehensive guide provides a detailed overview of low-volume injection molding.
What is Injection Molding?
Injection molding is a production method that enables manufacturers to produce parts in large quantities with uniform attributes and qualities. In this process, pressurized molten plastic is injected into a sturdy metal mold, allowing for rapid cooling and ejection of the part. After ejection, the press re-closes, and the process repeats.
What is Low-Volume Injection Molding?
Low-volume injection molding refers to the production of small batches (typically less than 1000 pieces) of plastic parts. This process, similar to the low-volume production of metal or wood, generally uses smaller machines suitable for plastic prototyping purposes. These low-volume items usually serve as prototypes or functional components, like those found in medical devices or automotive parts.
What Is Low Volume Plastic Injection Molding Used For?
Low-volume plastic injection molding is a critical step in product engineering design development, particularly during rapid prototyping and functional testing stages. it fulfills the role of producing end-use parts for limited production runs, including applications within companies like Apple and Tesla.
Low-Volume Plastic Parts Production
When it comes to low-volume production of plastic parts, the method is most appropriate when the part quantity is relatively small and unlikely to significantly increase. The specific threshold that distinguishes low-volume from high-volume injection molding may vary but it is generally understood to include quantities ranging from several hundred to tens of thousands of parts.
Bridge Production
Additionally, low-volume injection molding can function as a bridge between initial prototyping and full-scale production, facilitating the creation of pre-production prototypes. These prototypes are typically generated in batches of up to 1000 parts to ensure an adequate supply for testing or market research purposes. Importantly, this approach can be cost-effective in identifying issues that necessitate adjustments to more expensive tooling or alterations to injection molding machine parameters.
Advantages of Low-Volume Injection Molding
As implied by its name, low-volume injection molding is most suitable for applications needing small parts. In many instances, it stands as the primary and practical choice for prototyping or short-run production. Low-volume injection molding presents multiple advantages compared to alternative manufacturing techniques:
- Faster lead times: As it utilizes existing molds, low-volume injection molding eliminates the need to wait for tooling creation. This leads to significant reductions in lead times, especially for prototypes.
- Cost efficiency: Typically, low-volume injection molding proves to be more economically viable than other methods like CNC machining or 3D printing, particularly when extensive quantities are unnecessary.
- Enhanced design adaptability: Low-volume injection molding permits modifications to the part’s design without incurring substantial tooling expenses. This makes it an excellent option for prototyping or manufacturing small batches of parts with varying designs.
Tooling for Low-Volume Injection Molding
3D Printing Polymer tooling
Stereolithography (SLA) 3D printing technology serves as an excellent option for molding. It boasts a smooth surface finish and high precision, transferring these qualities to the final part and aiding in demolding. Stereolithography-produced 3D prints are chemically bonded, ensuring full density and isotropy, resulting in functional molds of a quality not achievable with fused deposition modeling (FDM) 3D printing.
Aluminum tooling
Aluminum molds demand less machining time than steel molds, making them a more efficient choice. Moreover, due to aluminum’s excellent heat transfer properties, it can heat and cool quickly. This translates to shorter lead times during mold fabrication and faster cycle times during injection molding, offering certain advantages.
However, aluminum molds have notable drawbacks. Their softer nature compared to steel leads to quicker wear and fewer shots. The softer aluminum cannot withstand the high clamping pressures exerted by larger injection molding machines, limiting their use for large or complex parts requiring multiple side actions.
Soft and Semi-Hardened Steel Tooling
Two primary types of soft and semi-hardened steel tooling are employed for low-volume injection molding: P20 and NAK80. Another grade, 718H, is also used, boasting a slight hardness advantage over P20 but sharing similar pros and cons.
P20 steel is harder than aluminum and exhibits a tooling lifespan of five to ten times longer. It doesn’t require heat treatment, can be welded easily, and can be machined more rapidly than harder steel grades. Tooling lead times may range from one to two weeks, although they still exceed those of aluminum molds.
NAK80, a semi-hardened tool steel, offers an extended tooling life compared to P20 steel but comes at a higher cost and typically requires 25% more machining time. NAK80 polishes effectively, making it a suitable choice for optically clear and high-gloss parts.
| Mold | 3D printed polymer | Machined aluminum | Machined soft steel |
| Mold cost | <$100 | $2,000 – $5,000 | $10,000 – $30,000 |
| Lead time to final parts | 1-3 days | 2-3 weeks | 3-5 weeks |
| Ideal production volume | <500 | 500 – 10,00 | 1,000-10000 |
| Applications | Rapid prototyping Custom injection molding Short-run injection molding | Short-run injection molding | Short-run injection molding |
Design Tips For Low-Volume Injection Molding Parts
Select the Right Material for Your Injection Molded Part
Numerous commercial-grade plastic materials are available for manufacturing. The initial step in designing for low-volume injection molding involves material selection. Thermoplastic resins offer various options, including additives, fillers, and colors.
Characteristics such as strength, thermal and chemical resistance, durability, and others will differ based on the chosen material. Material flexibility affects the need for drafts. Consider the intended application and potential exposure level before material selection.
Refine a Part’s Finish
A common mistake in plastic injection molding is opting for a smoother surface finish than necessary, potentially impacting product functionality. Exceptionally smooth finishes necessitate hand-polishing of mold cavity surfaces, elevating manufacturing costs and lead times. A more cost-effective finish includes as-milled surfaces with visible tool marks or options like 600-grit stone or bead-blasted textured finishes. The chosen finish should align with the part’s function.
Consider Multi-Cavity Molds
If producing multiple identical parts simultaneously is desired, multi-cavity molds prove beneficial. They accommodate two or more designs with minor variations, enabling swift testing of different product iterations. These molds are also cost-effective for larger quantities beyond initial samples.
Incorporate Draft for Easy Part Ejection
Generously incline injection molded parts to create components with tapered edges, facilitating smooth release from the mold.
Adjust Wall Thickness in Both Directions
Wall thickness plays a pivotal role in plastic parts production. Walls should adhere to recommended thickness ranges for specific plastic families to avoid defects like sink marks and warping. A rule of thumb is to maintain a consistent wall thickness between 0.04 to 0.14 inches throughout the part.
Address Weak Corners with Radii
Aluminum mold machining employs end mills, which can be problematic for sharp internal corners. Such corners often induce stress and compromise part integrity. To enhance product strength and moldability, opt for vertexes or rounded edges (radii) in plastic part design.
Alternatives to Low-Volume Injection Molding
Low-volume injection molding isn’t always the most suitable choice for lower-volume production. While low-volume injection molds are less expensive than high-volume ones, any kind of tooling demands an investment. These four manufacturing methods offer substitutes for plastic injection molding.
- CNC Machining: In cases of lower part volumes, CNC machining is occasionally preferred over injection molding. However, more intricate parts necessitate multi-axis CNC machines. Despite being highly automated, CNC machines still can’t match the speed of plastic injection molding.
- 3D Printing: 3D printers can produce parts with intricate geometries, including those impossible with other manufacturing methods. However, the production rate is relatively slow. Consequently, though 3D printing is frequently used for prototyping, it may not be capable of swiftly producing parts for low-volume production.
- Urethane Casting: Urethane casting can yield sturdy components resembling injection molded parts but without a substantial tooling investment. However, the manual nature of this process significantly drives up costs, and urethane materials can be more expensive than thermoplastics.
- Thermoforming: Vacuum forming, a form of plastic thermoforming, suits thinner parts with simpler designs. Nevertheless, production rates are sluggish, and material choices are limited compared to injection molding.
KUSLA Supports Low-Volume Injection Molding
Regardless of part volume, it’s important to get a design for manufacturing (DFM) assistance as soon as possible during the design process. When you request a quote, you’ll get DFM feedback in a few days that can help to ensure the success of your injection molding project. KUSLA will guide you through the entire process and help you find the right tooling solution for your project.
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The manufacturing industry is currently undergoing a significant transformation. This dynamic market necessitates the rapid introduction of products with small volumes. Simultaneously, designers, engineers, and manufacturers must guarantee product quality. One solution of manufacturing that addresses customer requirements is low-volume injection molding and On-demand Manufacturing.
This production technique permits the production of similar plastic components with consistent features and attributes. Manufacturers are presently embracing new operational approaches to gain an edge in evolving markets. This comprehensive guide provides a detailed overview of low-volume injection molding.
What is Injection Molding?
Injection molding is a production method that enables manufacturers to produce parts in large quantities with uniform attributes and qualities. In this process, pressurized molten plastic is injected into a sturdy metal mold, allowing for rapid cooling and ejection of the part. After ejection, the press re-closes, and the process repeats.
What is Low-Volume Injection Molding?
Low-volume injection molding refers to the production of small batches (typically less than 1000 pieces) of plastic parts. This process, similar to the low-volume production of metal or wood, generally uses smaller machines suitable for plastic prototyping purposes. These low-volume items usually serve as prototypes or functional components, like those found in medical devices or automotive parts.
What Is Low Volume Plastic Injection Molding Used For?
Low-volume plastic injection molding is a critical step in product engineering design development, particularly during rapid prototyping and functional testing stages. it fulfills the role of producing end-use parts for limited production runs, including applications within companies like Apple and Tesla.
Low-Volume Plastic Parts Production
When it comes to low-volume production of plastic parts, the method is most appropriate when the part quantity is relatively small and unlikely to significantly increase. The specific threshold that distinguishes low-volume from high-volume injection molding may vary but it is generally understood to include quantities ranging from several hundred to tens of thousands of parts.
Bridge Production
Additionally, low-volume injection molding can function as a bridge between initial prototyping and full-scale production, facilitating the creation of pre-production prototypes. These prototypes are typically generated in batches of up to 1000 parts to ensure an adequate supply for testing or market research purposes. Importantly, this approach can be cost-effective in identifying issues that necessitate adjustments to more expensive tooling or alterations to injection molding machine parameters.
Advantages of Low-Volume Injection Molding
As implied by its name, low-volume injection molding is most suitable for applications needing small parts. In many instances, it stands as the primary and practical choice for prototyping or short-run production. Low-volume injection molding presents multiple advantages compared to alternative manufacturing techniques:
- Faster lead times: As it utilizes existing molds, low-volume injection molding eliminates the need to wait for tooling creation. This leads to significant reductions in lead times, especially for prototypes.
- Cost efficiency: Typically, low-volume injection molding proves to be more economically viable than other methods like CNC machining or 3D printing, particularly when extensive quantities are unnecessary.
- Enhanced design adaptability: Low-volume injection molding permits modifications to the part’s design without incurring substantial tooling expenses. This makes it an excellent option for prototyping or manufacturing small batches of parts with varying designs.
Tooling for Low-Volume Injection Molding
3D Printing Polymer tooling
Stereolithography (SLA) 3D printing technology serves as an excellent option for molding. It boasts a smooth surface finish and high precision, transferring these qualities to the final part and aiding in demolding. Stereolithography-produced 3D prints are chemically bonded, ensuring full density and isotropy, resulting in functional molds of a quality not achievable with fused deposition modeling (FDM) 3D printing.
Aluminum tooling
Aluminum molds demand less machining time than steel molds, making them a more efficient choice. Moreover, due to aluminum’s excellent heat transfer properties, it can heat and cool quickly. This translates to shorter lead times during mold fabrication and faster cycle times during injection molding, offering certain advantages.
However, aluminum molds have notable drawbacks. Their softer nature compared to steel leads to quicker wear and fewer shots. The softer aluminum cannot withstand the high clamping pressures exerted by larger injection molding machines, limiting their use for large or complex parts requiring multiple side actions.
Soft and Semi-Hardened Steel Tooling
Two primary types of soft and semi-hardened steel tooling are employed for low-volume injection molding: P20 and NAK80. Another grade, 718H, is also used, boasting a slight hardness advantage over P20 but sharing similar pros and cons.
P20 steel is harder than aluminum and exhibits a tooling lifespan of five to ten times longer. It doesn’t require heat treatment, can be welded easily, and can be machined more rapidly than harder steel grades. Tooling lead times may range from one to two weeks, although they still exceed those of aluminum molds.
NAK80, a semi-hardened tool steel, offers an extended tooling life compared to P20 steel but comes at a higher cost and typically requires 25% more machining time. NAK80 polishes effectively, making it a suitable choice for optically clear and high-gloss parts.
| Mold | 3D printed polymer | Machined aluminum | Machined soft steel |
| Mold cost | <$100 | $2,000 – $5,000 | $10,000 – $30,000 |
| Lead time to final parts | 1-3 days | 2-3 weeks | 3-5 weeks |
| Ideal production volume | <500 | 500 – 10,00 | 1,000-10000 |
| Applications | Rapid prototyping Custom injection molding Short-run injection molding | Short-run injection molding | Short-run injection molding |
Design Tips For Low-Volume Injection Molding Parts
Select the Right Material for Your Injection Molded Part
Numerous commercial-grade plastic materials are available for manufacturing. The initial step in designing for low-volume injection molding involves material selection. Thermoplastic resins offer various options, including additives, fillers, and colors.
Characteristics such as strength, thermal and chemical resistance, durability, and others will differ based on the chosen material. Material flexibility affects the need for drafts. Consider the intended application and potential exposure level before material selection.
Refine a Part’s Finish
A common mistake in plastic injection molding is opting for a smoother surface finish than necessary, potentially impacting product functionality. Exceptionally smooth finishes necessitate hand-polishing of mold cavity surfaces, elevating manufacturing costs and lead times. A more cost-effective finish includes as-milled surfaces with visible tool marks or options like 600-grit stone or bead-blasted textured finishes. The chosen finish should align with the part’s function.
Consider Multi-Cavity Molds
If producing multiple identical parts simultaneously is desired, multi-cavity molds prove beneficial. They accommodate two or more designs with minor variations, enabling swift testing of different product iterations. These molds are also cost-effective for larger quantities beyond initial samples.
Incorporate Draft for Easy Part Ejection
Generously incline injection molded parts to create components with tapered edges, facilitating smooth release from the mold.
Adjust Wall Thickness in Both Directions
Wall thickness plays a pivotal role in plastic parts production. Walls should adhere to recommended thickness ranges for specific plastic families to avoid defects like sink marks and warping. A rule of thumb is to maintain a consistent wall thickness between 0.04 to 0.14 inches throughout the part.
Address Weak Corners with Radii
Aluminum mold machining employs end mills, which can be problematic for sharp internal corners. Such corners often induce stress and compromise part integrity. To enhance product strength and moldability, opt for vertexes or rounded edges (radii) in plastic part design.
Alternatives to Low-Volume Injection Molding
Low-volume injection molding isn’t always the most suitable choice for lower-volume production. While low-volume injection molds are less expensive than high-volume ones, any kind of tooling demands an investment. These four manufacturing methods offer substitutes for plastic injection molding.
- CNC Machining: In cases of lower part volumes, CNC machining is occasionally preferred over injection molding. However, more intricate parts necessitate multi-axis CNC machines. Despite being highly automated, CNC machines still can’t match the speed of plastic injection molding.
- 3D Printing: 3D printers can produce parts with intricate geometries, including those impossible with other manufacturing methods. However, the production rate is relatively slow. Consequently, though 3D printing is frequently used for prototyping, it may not be capable of swiftly producing parts for low-volume production.
- Urethane Casting: Urethane casting can yield sturdy components resembling injection molded parts but without a substantial tooling investment. However, the manual nature of this process significantly drives up costs, and urethane materials can be more expensive than thermoplastics.
- Thermoforming: Vacuum forming, a form of plastic thermoforming, suits thinner parts with simpler designs. Nevertheless, production rates are sluggish, and material choices are limited compared to injection molding.
KUSLA Supports Low-Volume Injection Molding
Regardless of part volume, it’s important to get a design for manufacturing (DFM) assistance as soon as possible during the design process. When you request a quote, you’ll get DFM feedback in a few days that can help to ensure the success of your injection molding project. KUSLA will guide you through the entire process and help you find the right tooling solution for your project.
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