High precision injection for critical parts
High precision injection of high performance plastics or of engineering plastics is required for critical parts. Such parts, with low tolerances or ultra low thickness, can produced by different means. But Injection molding is the only affordable solutions when it comes to high volume or complex shapes. This is where high precision injection molding occurs.
What is high precision injection molding?
High precision injection molding focuses on the production of complex parts in thermoplastics. It involves high performance plastics as well as engineering plastics.
Generally, to know if your part requires high precision injection, you must check if you meet at least 3 of the 4 following items
- Strong dimensional precision: with low tolerance. Typically for thermoplastics the interval of tolerance in association to CPK requirements will be below 100 µm (for small parts);
- Low wall thickness, usually below 500 µm for small parts. This is a general guideline, as some thermoplastics are more prone to low wall thickness than others;
- Complex part, usually with undercuts, that need specific tools and extra care while they are extracted from the mold;
- High volume. This is important as it will impact the process capability (CPK). For small volumes, other solutions like machining may be more adapted.
In comparison to metal parts, thermoplastic high precision molding increases global performance
When reviewing the different criteria, it appears that metallic parts may present less restrictions on dimensions, and so may be more affordable.
It is true. It is true also that lots of parts produced by thermoplastics high precision injection were first based on metallic parts. This means that while it is technically harder to substitute high performance plastics to metal parts, there are in fact important assets. Typically, substituting critical parts made of metal by thermoplastics materials allow gains of weight, of efficiency (for moving parts) or of noise and vibration (NVH: noise vibration and Harshness). With composites and high performance plastics, you may even gain in mechanical properties or in tribology.
One typical example for such gain are gears. Standard gears in thermoplastics are common. But when it comes to high precision gears, metal gears were the most common solution. With the development of high precision injection however, high precision thermoplastics gears achieve better efficiency, low torque and a clear reduction of noise, with no lifetime reduction.
Moreover, if you fear for lifetime, mechanical resistance or thermal dilatation, high precision injection is totally compliant with metallic insert overmolding. This solutions solutions combines the assets of metallic and thermoplastic parts on different functional surfaces, for a global gain on the final product.
So substituting metal with thermoplastics for critical parts can greatly increase the added value of the final product, and thus, overcomes the challenges of high precision injection.
Metal substitution with thermoplastic high precision injection requires strong co-development
Metallic solutions for critical parts can’t change directly into thermoplastics solutions. Technical constraints are not the same between the two processes. A full redesign won’t be needed, but some functional surfaces may need modifications. This is why a good understanding of the critical parts and their functional parts are needed.
As such combining the understanding of the critical parts with the constraints of high performance thermoplastics and the high precision injection challenges is the key for a successful development, and a successful product.
This is why, for such developments, 3P co-develops the solution with its customer, by working closely with the full design and production stakeholders.
Strong relationships with the mold makers and with the technical studies office allow to integrate the full know-how for high performance polymers and their thermal behavior. 3P works on the original drawing to optimize mechanical strength and shrinkage but also cost, as high performance polymers are generally more expensive than common ones.
