Injection Molding for Small Parts | Complete Manufacturing Process

The small-part injection molding technique is used to produce small, high-quality parts. This process can add all the little features that are in the part and make a complete product. The operator prepares the molten material, which is then actually injected into the cavity of the mold.

But why is small-part injection molding important? Basically, it is essential to meet today’s increasing miniaturized and performance-driven market.

The key aspects of small-part injection molding are mentioned below; you will learn these in this article.

• Voordelen
• Ontwerpoverwegingen
• Toepassing
• DIY Injection Molding, etc

What is Small Part Injection Molding?

Small-part injection molding is a manufacturing process for plastic components. You can sum up this process in 5 steps:

1.  Gereedschap: A specialized mold is designed and created to produce the desired small part.
2. Materiaalkeuze: The desired plastic material is selected and prepared for injection.
3. Injectie: Molten plastic is injected into the mold cavity under high pressure.
4. Koeling: The plastic cools down and solidifies within the mold.
5. Uitwerpen: The mold is opened, and the cooled. You will eject the formed part.

Key Mold Components:

• Adapter Plate for Movable Side: This is here to help align the material and support the mold halves, usually when you open and close the mold.
• Spacer Block: These blocks mostly give enough space between mold plates. That is important to get uniform flow and consistency in parts.
• Adapter Plate for Fixed Side: These are the plates in the machine that stabilize the stationary mold sections.
• Kern en holte: There are two halves: one is a cavity and another is a core. They define the inside and outer geometries of the part.
• Locating Ring: The product is between the core and mold, where the rings support the mold by aligning it with the injection nozzle.
• Sprue and Runner: Pressurize the plasticized material into the mold cavity.
• Ejector Pin and Plate: It helps remove the solidified part from the mold.

Size Limits and Considerations

Just about any new small product is going to feature a thickness as minimal as approx. 1.4 t with a radius (as the image shows) at corners accordingly optimized for stress reduction.

Some type of plastic enclosure or other custom small plastic parts can be designed focusing on smooth transition with internal r = 06t and external r = 0.6+t. These dimensions of thickness ensure strength and durability.

But when doing product development, sharp internal or external edges cause stress concentrations. The worst corner designs weaken the part.

Het spuitgietproces

Generally, the technology of injection molding that is used for several small-size parts includes the following steps:

1. Material Melting: First, the chosen thermoplastic is placed into the injection unit. The screw rotates the material throughout the heating process, sourcing via a heater.
2. Injectie: The liquified material is charged or poured into the injection part, where the valve sprue and runner force toward the mold cavity.
3. Koeling: The internal cooling channels of mold move away the heat into the surroundings and let the part be solidified.
4. Uitwerpen: Lastly, the operators remove the molded part from the ejector mechanism. The ejector pin and plate here drive this mechanism, allowing safe removal.

The remaining components of the machine, like the clapping unit, tie bar motor and back flow cylinder, respectively, coordinate in giving you accuracy and precision.

Micro Injection Molding Challenges

Micro injection molding is very hard. Parts are very small, less than 1mm. Material flow is hard to control. Cooling tiny parts quickly is difficult. Removing parts from mold without damage is hard.

Why is it hard?

Small parts need precise control. Material flow must be perfect. Cooling systems must be fast. Demolding must be gentle.

Techniques for Micro Injection Molding

Special molds are made. Micro injection units are used. Material flow is controlled. Cooling systems are advanced. Vacuum-assisted demolding is used.

Benefits of Micro Injection Molding

Micro injection molding has many benefits. Parts are very accurate. Complex designs are possible. Material waste is low. Production rates are high.

Small Part Injection Molding Materials

You will find many types of material that are used to make small parts via injection molding. In some cases, engineering-grade plastics are selected as they provide falling features to the parts.

• Chemische bestendigheid: If the parts are going to be exposed to chemicals, you need to be aware of their performance. Then, you can choose polypropylene (PP) material.
• Flexural Strength: Nylon 6/6 offers good protection to fragile parts or those that may bend under load.
• Durometer: if you want to make your part durable and tough, then ABS is suitable. But, it is prone to scratches in some projects.
• Yield Strength: Some heavy-duty parts need to be built with superior strength and performance so you can go ahead with the PEEK option.

Materials Comparison for Injection molding Small Parts

Advantages of Small Part Injection Molding

Betaalbaarheid

Mostly small-part injection molding requires relatively low labor costs for production because this process gives economical high production output rates.

Full automation in the process aids in low-volume production and large ones. However, 3D printing technology is generally the technology that you use for rapid injection molding to produce plastic prototypes.

You may find the initial cost of tooling amortized over continued and large production volumes. That is a way to reduce the per-unit cost. Another benefit of this process is that it generates virtually no waste, reducing material usage.

High Precision and Accuracy

The molding method quite commonly offers precision in parts with close tolerance and high repeat tolerance. Using automation in the process completely changes the way of ordinary production as it enables stringent specification options for parts.

Advanced machines and tooling can meet the need for little to no finishing of parts. That must be effective for reducing cost and production time.

Tolerances in Small-part Injection Molding

Complex Shapes and Geometries

With spuitgieten, you can literally create just about any shape or part that your mind can imagine.

This is a very forgiving technology without many design limitations. That incorporates undercut ribs and detailed geometry. You can generate versatility in both functional and aesthetic ways in a wide range of materials.

Repeatability and Consistency

Most importantly, injection molding allows a repeatable process that strictly practices identical parts with high quality and accurate size. When designing your enclosure, this high degree of consistency minimizes the errors. It assures you reliability, especially across large production runs.

Small Parts Design Guideline for Injection Molding

Draft Angles

With proper knowledge of draft angles, you can make the ejection of parts easy. Vertical walls of parts often cause stickiness. In these cases, several defects occur and increased wear on mold.

The troubleshooting tip for this issue is to incorporate draft angles of at least 1 to 2 degrees for plastic material. This will work and does not need much ejection force.

Wall Thicknesses

Find yourself with a design that can be uniform in wall thickness. This factor very much caters to consistent material flow and also reduces internal stress. For instance, as the attached diagram shows some thickness illustrations:

• Too thin: It might disrupt the flow, failing it to fill properly and producing weak parts.
• Too thick: Thicker walls need more cooling power; otherwise, they can warp.
• Correct Thickness: It can be an absolute balance of strength and cooling efficiency if the internal radius R1 and external radius R2 = R1 + t.

Undercuts and Other Design Features

Designs involving undercuts and complex shapes can never be easy for beginners. However, with sliding cores or side action, it can be simplified. That moves perpendicular to the mold opening directions in order to get intricate geometries just perfect.

Gate Locations and Runner Systems

Focus on positioning the gates appropriately to avoid weld lines, air traps, or uneven fillings. As we are discussing small-part production, so you can choose pin gates or submarine gates. These offer good aesthetic appeal and functional features.

Besides, if you want to make the filling process more balanced and reduce material waste, then optimize the runner systems.

Plaatsing van de poort

Locatie poort: Place gates at the thickest section of the part to minimize sink marks and ensure proper filling.

Gate size: Size gates to ensure a smooth flow of material, typically 0.5-2.0 mm in diameter.

Rib Design

Rib thickness: Keep ribs thin (0.5-1.5 mm) to minimize material usage and prevent sink marks.

Rib height: Limit rib height to 3-4 times the rib thickness to prevent warping.

Boss Design

Boss diameter: Ensure the boss diameter is at least 2-3 times the screw or insert diameter.

Boss depth: Limit the boss depth to 1-2 times the boss diameter to prevent warping.

DIY Injection Molding: 3D-printed Molds

Introduction to DIY Injection Molding

DIY injection molding is an option for manufacturers just to make cost-effective in-house production for rapid prototyping. Whether you plan to design your own part or outsource the development, this process can reduce lead times for limited production runs.

However, manufacturers need to have a basic understanding of injection molding. So that they can produce complex parts without relying on external suppliers.

3D-Printed Injection Molds

It’s really common in DIY injection molding to use stereolithography (SLA) 3D printers to create molds with intricate details and a tight tolerance. 3D-printed injection molds are quicker and less expensive. This may sound great, but there is one big obstacle. They are often not beneficial for large-run production because of material fatigue under repetitive stress.

Low-volume Production and Prototyping

3D-printed molds offer a solution that can eventually be efficient for small-quantity applications such as concept validation and functional testing.

Desktop Injection Molders

Desktop injection molders are a kind of mechanical process. You can use it to mold multiple materials into functional parts. A couple of benefits examples that these molders offer are:

• They provide compact, affordable solutions for small-scale manufacturing.
• It can produce complex-shaped parts.
• You will find them relatively low-cost as they offer unmatched flexibility for rapid injection molding.

However, the limitation of desktop injection molders over output capacity is that’s something to keep in mind. They are less competitive than industrial-grade machines.

Low Volume Plastic Injection Molding

Understanding Low-Volume Production

Low-volume plastic injection molding is mostly needed when you have to meet lower product demand or short-run production needs than traditional high-volume production. You can employ this technique, typically producing parts ranging from 100 to 10000.

Benefits of Low-Volume Injection Molding:

There are several benefits of low-volume injection molding, especially for those developers, OEMs, and Tier suppliers.

Continuous Product Development Cycle: As there is no commitment to large-scale production so low-volume molding offers iterative improvements.

Rapid Tooling and Prototyping Services: Another thing you can benefit from it is quicker turnaround times for testing and validation.

Demanding Specifications and Timelines: Because the production scale is small so you can get precision and speed for projects with strict requirements.

Budget-Friendly Solutions: It supports smaller production runs, cutting down on upfront investments.

Key Considerations for Low-Volume Production

Kosteneffectiviteit:

If you compare the lower tooling costs against higher per-part costs, it may cost you more. This is because fewer units amortize tooling expenses.

Finding Suitable Suppliers:

It’s a really common mistake to hire suppliers who have no experience with low-volume injection molding. However, some reputable suppliers, like Plastic Mold, are highly skilled and can offer exceptional outputs.

Maintaining Repeatability:

Careful parameter control and high-quality tooling are important steps. That must be strictly followed when achieving shot-to-shot consistency.

Conclusie:

We highlight the fundamental characteristics of small-part injection molding. These are the elements that make it important for high-to-low-volume plastic injection molding. However, emerging advanced technologies and using DIY injection can be advantageous for small setups due to their low tooling cost and maintenance requirement.