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What is Precision Injection Molding? 5 Things to Know

Author: Adelaide

Dec. 02, 2024

What is Precision Injection Molding? 5 Things to Know

What is precision injection molding? 

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  1. Creates precise plastic components

  2. Materials should have a low shrinkage capacity

  3. Rely on the precision injection mold

  4. A slow and steady process

  5. Uses polymer optics

Many molding processes are known to mass produce products that are used in daily life. However, various industries have parts and pieces that are too complex to be made with ordinary plastic injection moldings. A process called precision injection molding is used for such processes. 

But, what is precision injection molding? It is a highly technical process that makes use of precise molds. It is not used to develop whole products, instead, it develops more complex plastic parts. 

It differs from convection modeling in many ways, from the materials used to the mold created to the machine used in creating the product. This article tackles all you need to know about this technical process. By the end, you can assess if this is the molding process that you need for your next project. 

Creates precise plastic components

Compared to plastic injection molding, this method produces precise plastic parts. It does not mass produce whole parts. These products that are made in the process replace high-precision metal parts from different industrial appliances. 

The plastic components produced in precision injection molding require a tight tolerance. That means that the requirements for the product have precise and accurate procedures. When not followed, it can break inside the mold.

Products that are produced in precise injection molding are also comprised of complex geometric parts. These items have specific shapes that are needed for certain items in automotive, pharmaceutical, information technology, and medical fields. 

Materials should have a low shrinkage capacity

Precise injection molding can cause plastics to shrink during the manufacturing process. That&#;s why its materials are different from other injection molding materials. 

When materials have a high shrinkage capacity, they melt as they undergo the precise injection molding process. It ruins the product in the end. 

The materials used for this molding process need to have a low shrinkage capacity. The shrinkage required is around +/-0.01&#; or +/-0.02&#;. However, many materials can&#;t reach this range. 

An example of this would be ABS, a thermoplastic polymer. This kind of plastic can retain its elasticity while going through high temperatures. However, its shrinkage of +/-0.06 is still not appropriate for precision molding. Glass and other resin can be added to reach the desired shrinkage. These help the material absorb the excess heat while keeping the plastic stable. 

Rely on the precision injection mold

The precision made during this molding process is achieved through its mold. It needs to suit the design engineering requirements. 

To craft the mold, it needs to undergo accurate study, design, and testing. Many elements need to be taken into account for the mold. Here are some of the elements that need attention: 

  • The mold cavity size &#; its position and the number of cavities it has

  • The precision of the parting surface

    Link to Yihua Mould

  • The materials used for the mold (this can be made from steel alloys or cast irons)

  • The bottom plate&#;s thickness

  • The runner size

Precision injection models are made with tolerances between +/-0.02&#; and +/-0.01&#; or less. All elements mentioned are considered when considering the dimensions tolerance. 

A slow and steady process

A high-precision model is required when creating plastic parts that have tight tolerances. Each part made in a precise injection model needs to be identical. This process can only be applied to plastic parts that are placed and connected with other parts in a fixed form. 

Because of the precise products, the manufacturer should not rely on rapid tools for this method. Precise injection modeling is a slow and steady process that makes a high-precision tool. 

Uses polymer optics

Polymer optics are used in precise injection molding. This is when CNC machining is used to mold the plastics into precise and calculated shapes. The machines have high pressure that helps improve the quality and precision of the plastic parts. They also manage to repeatedly create an accurate product. 

The entire process is automated and conducted through computers through an automatic handling system. It allows the producer to customize the process for the product needed to be molded. 

This reduces the cost of labor while increasing production efficiency thanks to its automated process.

Key Takeaway 

Now that you&#;ve answered what precision injection molding is, you can check if you can apply it to some of your products. As stated above, it can also develop a wide variety of complex products. 

If you&#;re interested in this process or other molding processes, message Richfields today. We offer various tooling solutions including precision injection molding. Don&#;t hesitate to reach out to learn more about how our services can help your next project.

Precision Molding: Three Questions That Could Save You ...

If you need a plastic part molded with extreme precision&#;for example, to ensure there&#;s no air leak between two molded sections or to be certain there&#;s no visible seal gap line&#;you likely require precision molding. The difference between a typical injection molded part and a precision molded part is the tolerance, or acceptable range of variation in dimension: While the majority of injection molded parts have a tolerance of +/- .005&#;, precision molding holds tolerances between +/- .002&#; and +/- .001&#; (or less, in some cases).

Let&#;s say, for example, you&#;re planning to manufacture a military projectile. In order for the projectile to fit properly in the firearm, handle the acceleration when it&#;s launched, and explode on impact, it requires very high precision.

If your application requires precision molding, you can&#;t leave anything to chance&#;so you&#;ll want to ask yourself the following three questions before you begin the process:

1. Have you determined which areas of the mold require precision?

Because precision molding is more expensive than typical injection molding, be certain which aspects of your part require tight tolerances&#;and whether those tolerances can be achieved through injection molding&#;before moving forward. For example, a surgical handle may only require precision for the piece that will connect with a pin, not the entire handle. Identifying your precision requirements from the get-go ensures you&#;ll get what you need without wasting money. In the case of the surgical handle, your injection molding partner may advise you to add the tolerances you need through tooling after the injection molding process is complete.

2. Have you selected a plastic material with low shrinkage?

The plastic material you select for your part makes a big difference in whether you&#;ll be able to do precision molding. For example, polypropylene has a shrinkage range of +/- .014&#; to +/- .022&#;, with an average of +/- .018&#;. This is a wide range for shrinkage, which makes hitting a specific tolerance extremely difficult. If you&#;re molding a toothbrush (which commonly uses polypropylene), dealing with shrinkage isn&#;t a big concern, as the toothbrush will function appropriately regardless of whether it&#;s slightly bigger or smaller than its counterparts. Acrylonitrile butadiene styrene (ABS)&#;another common thermoplastic polymer&#;has a much narrower shrinkage average of +/- .006&#;. That gives you a much better chance of hitting a tighter tolerance, but it still won&#;t reach the +/- .001&#; or +/- .002&#; tolerance needed for a precision part.

One way to hit high tolerances with your plastic material is to add glass or another filler resin (like carbon fiber or mica) into the material. This can minimize shrinkage and warp by providing more structure in the material. For example, if you include long glass fibers in a polymer material, the part will shrink more perpendicular to those fibers.

3. Can the mold manufacturer you&#;ve selected tool with high precision?

The process of creating plastic parts with tight tolerances begins with a high-precision mold. If each plastic part you create is not identical, you won&#;t have a precise product&#;and a precise mold ensures there&#;s no variation for each part. Because of this, it&#;s extremely important to select a mold manufacturer who understands the slow, steady process of building a high-precision tool. Keep in mind that selecting a mold manufacturer that specializes in rapid tooling is likely not your best option, as the goal of rapid tooling is to finish the mold quickly&#;but not necessarily precisely.

Let&#;s get your precision molding project started.

We have years of experience in precision molding, and would love to answer any and all of your questions. You can either contact us with those questions, or, if you&#;re ready to get your project started now, simply request a free quote. Once you submit the short form, one of our representatives will be in touch with you shortly to get the ball rolling.

Contact us to discuss your requirements of precision mold parts. Our experienced sales team can help you identify the options that best suit your needs.

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