Injection molding is a common process for plastic part manufacturing but with heavy investments in Steel molds and injection machines. So, when just a one-off part or small batches of parts are needed, traditional injection molding becomes not cost-effective. However, manufacturers find a good solution to solve this issue that using a low-volume injection molding process. Today, KUSLA, as a low-volume injection molding supplier, will share with you a complete guide to this process to help you understand what is it and how it works.
What Is Injection Molding?
Injection molding is a production method of plastic parts that enables manufacturers to produce parts in large quantities with uniform quality. In this process, pressurized molten plastic is injected into a steel tooling, allowing for rapid cooling and ejection of the part. After ejection, the tooling opens and closes, and the process repeats.
What is Low-Volume Injection Molding?
Low-volume injection molding refers to producing small batches (typically less than 10000 pieces) of plastic parts by injection molding process. With lower-grade mold steel and simplified mold design, low-volume injection molding is being considered as prototype injection molding to make parts for testing purposes and Short-run productions.
When To Use Low-Volume Plastic Injection Molding?
Rapid prototyping
In some cases, Engineers need only one or a few plastic prototypes to make the function test. The first idea may be CNC machining or 3D Printing, but there will be constraints for these two processes that the material properties can not be the same exactly as mass production. So, injection molding prototyping is perfect for this case, using the same materials and injection molding process as mass production but with rapid tooling.
On-Demand Manufacturing
On-demand manufacturing is an excellent way for manufacturers to control the cost of molded plastic parts according to the market needs. Low-volume injection molding could perfectly match the needs of the market, No matter just 100 pieces or 10000 pieces. In addition, even if you need more volumes over 1000 Pieces, you can make another rapid tooling to continue the production.
Benefits Of Low-Volume Injection Molding
Enhanced Quality
Low-volume injection molding uses the same materials as mass production which could ensure the performance of plastic parts and achieve the quality level of final production.
Faster lead time
low-volume injection molding uses rapid mold which means you can save a lot of tooling making time. Traditional tooling takes months but rapid tooling only takes weeks.
Cost efficiency:
When the quantity is over 100, the piece price will be lower with low volume injection molding technique, because the injection process is quick and easy. Compared with CNC machining and 3D printing, it takes less time and saves the total cost.
Easy design change:
The rapid tooling used for low-volume injection molding is easy to modify at a low cost. this means you can modify all the issues you identified on the rapid mold before the mass production tooling kick-off.
3 Types Of Rapid Tooling for Low-volume Injection Molding
3D Printed tooling
Stereolithography (SLA) 3D printing can be used to make a plastic cavity and core of the tooling with a high temperature resistant plastic material. this mold can be used for that kind of low melting point plastic injection.
Aluminum Tooling
Aluminum Tooling is another good choice for low-volume injection molding because Aluminum is an easy machinable metal, which can save time in manufacturing the tooling. Aluminum tooling usually produces plats parts of less than 1000 pieces because aluminum is not so strong enough to resist the impact of too many times injections.
Soft Steel tooling
Soft steel Tooling does not mean the steel used for mold is soft. this only compares with the hard tooling used for mass production. Two primary types of soft steel tooling used for low-volume injection molding are P20 and NAK80. Soft steel is harder than aluminum which has a better lifespan which means it can used for producing more parts and up to 10000 pieces.
A Comparison table of the three methods above is below, and you will see which one is suitable for your project.
| 3D printed | Machined aluminum | Machined soft steel | |
| Tooling cost | <$100 | $1,000 – $5,000 | $2,000 – $10,000 |
| Lead time to final parts | 1-3 days | 2-3 weeks | 3-4 weeks |
| Ideal production volume | <500 | 500 – 10,00 | 1,000-10000 |
How to Make the Tooling Rapidly?
Rapid tooling is produced quickly and cost-effectively, but do you know how? here we explain how it works below:
Split Machine the core of the tooling
To achieve a fast lead time for the tooling, split the core of the mold and machine them at the same time to save the total manufacturing time. Although this will leave lines on the part, it can be designed in an area without any function.
Simplify the lifter and slider structure
Due to the low volume of parts, the lifter and slide structure can be simplified as much as you can without considering automation and lifespan. sometimes, we can consider manual operation.
Simplify cooling system design
Using a straight-through cooling system can simplify the tooling structure and speed up the tooling manufacturing cycle for low-volume manufacturing.
Simplify tooling Surface treatment
Due to the short light span of mold for low-volume injection molding, there is no need to make complex surface treatments like the mass production tooling.
Use a standard tooling frame and hot runner system
when designing the tooling, consider using the standard tooling frame and hot runner system which is already been used in other projects. this could save much the cost of rapid tooling.
Low-Volume vs. High-Volume Plastic Injection Molding
There are several differences between low-volume and high-volume injection molding processes. below are the main points we summarized.
Tooling materials
low-volume injection molding uses rapid tooling also called soft tooling with aluminum or soft steel material, High-volume injection molding uses hard steel to make the tooling.
lifespan
Low-volume injection molding works for a volume less than 10,000 pieces, however, high-volume works for more than 10 times volumes than low-volume injection molding.
Precision
Due to the hard steel tooling and more robust tooling structure, high-volume injection can get a better precision of parts than low-volume injection molding.
Leadtime of tooling making
Making the tooling for low-volume injection molding only takes from 2-4 weeks, but making the tooling for high-volume injection molding will take 12 weeks to 16 weeks. this can allow low-volume injection molding to get the parts much earlier than high-volume.
Cycle time of parts injection
Due to the automation of high-volume injection molding, it can inject parts more quickly than low-volume injection molding which reduces the cycle time of parts making and leads to a lower part piece price.
Design TIPS FOR INJECTION MOLDING PARTS
Select The Right Material
The first step for low-volume injection molding is to choose the materials for your product. this is because the material you use for injection molding will affect the materials of the tooling you can use. high melting point materials require high strength and high-temperature resistance tooling materials such as Aluminum and Steel. so, you need to evaluate the functions of your product and choose those materials easy to inject.
Refine A Part’s Finish
A common mistake in plastic injection molding is demanding a smoother surface finish than necessary, potentially impacting product functionality. this is increasing the complexity of making the rapid tooling. if necessary, consider hand polish to use on the injected parts.
Consider Multi-Cavity tooling
Using Multi-Cavity tooling can reduce a lot your production time for small volumes. this is easy to understand that once producing, you can get more parts.
Make Draft For Easy Part Ejection
Even rapid tooling sometimes does not require draft angles on a product, but, if possible, apply draft angles in the design, this will reduce issues during injection molding.
Adjust Wall Thickness In Both Directions
Wall thickness is important in plastic parts production. walls should follow the standards to avoid shrinkage and wrap during the injection molding process. They recommend thickness of plastic is from 1.5mm to 3mm.
Address Weak Corners With Radii
Aluminum mold machining uses end mills, which may not work for sharp internal corners. so, make a Radii to improve the part strength and also easy for tooling making.
Alternatives For Low-Volume Injection Molding
When you need to make plastic parts with low volume, there are several alternatives you can consider as below：
Urethane casting
Urethane casting uses silicone mold to cast plastic parts, it can create plastic parts faster than low-volume injection molding. although one silicone mold only works for 25 pieces, it will be a good alternative when the volume is less than 100 pieces.
To get a more detailed comparison of urethane casting vs. injection molding, please click the link.
3D Printing
3D printing can create plastic parts very quickly with resin materials and higher piece cost than low-volume injection molding, So when you do not care about the material properties and budget of your project, you may consider 3D printing plastic parts as a good solution.
Thermoforming
When we make plastic parts like plastic trays, injection molding could work, but also thermoforming can work. it uses vacuum conditions to create pressure to form the plastic trays, this solution will get a lower piece price due to machines and mold is simpler than that of low-volume injection molding.
Conclusions
Low-volume injection is not a complex process, but you need a professional supplier with equipment and experience to work for you to finish the job. And some injection molding suppliers only work for high-volume projects for bigger sales, However, KUSLA’s Low-volume injection molding service can work for you to produce plastic parts in quantities from 1 to 10,000 pieces.
FAQ
What is the minimum quantity for Low-Volume Injection Molding?
The minimum quantity is only one piece for rapid prototyping. and 1000 pieces for a short-run production.
How much does a rapid mold cost?
A small and simple single-cavity plastic low-volume injection tooling usually costs between $1,000 and $5,000. Very large or complex tooling may cost as much as $30,000 or more.
