Understanding Draft Angle When Making Injection Mold

Injection molding is a manufacturing process used to produce parts in large quantities by injecting molten material into a mold. It is one of the most common and important manufacturing processes across countless industries.

Now, advanced rapid injection molding techniques are revolutionizing the capabilities of this vital production method.

Limitations of Traditional Injection Molding

Conventional injection molding relies on metal molds that are complex and expensive to fabricate. Lead times of weeks or months for mold design and CNC machining make the process unsuitable for prototyping and low volume production. Changing a product design requires creating a completely new mold tool.

The Promise of Rapid Injection Molding

Rapid injection molding aims to transform injection molding flexibility and economics using advanced technologies like:

• Additive manufacturing to 3D print mold tooling from metals or polymers in days rather than weeks
• Modular mold bases that allow rapid reconfiguration for design changes
• Smarter process monitoring and automation with IoT sensors and data analytics

Benefits for Manufacturers

Rapid injection molding provides manufacturers with:

• Faster design iteration and prototyping with molds in days rather than months
• Ability to quickly scale up to medium or high volumes
• Just-in-time production of custom or small batch parts
• Cost-effective on-demand manufacturing aligned with customer needs

The Future of On-Demand Manufacturing

Rapid injection molding enables agile, flexible, on-demand manufacturing not possible with conventional techniques. As the technologies continue advancing, rapid injection molding will become a critical tool for mass customization and competitiveness across many manufacturing sectors.

To ensure the success of Injection Molding, certain design considerations must be made, one of which is the draft angle.

A draft angle, also known as a taper angle, is a slight angle designed into the vertical surfaces of a mold. This angle allows for easy removal of the finished part from the mold. Without a draft angle, the part may become stuck in the mold, resulting in damage to both the part and the mold.

Why Draft Angle is Important

The draft angle is important because it helps to reduce the friction between the part and the mold. When the part is injected into the mold, it shrinks as it cools. If there is no draft angle, the part may become locked into the mold, making it difficult to remove. The draft angle also helps to prevent damage to the part during the ejection process.

When plastic solidifies in the mold, it shrinks onto the core and cavity surfaces. Without draft angle, the part would stick to the mold surfaces after cooling. Draft angles ease part ejection by providing the shrinking plastic a release path from the mold cores and cavities.

The draft angle is measured in degrees and is typically between 1 and 3 degrees, depending on the size and complexity of the part being produced. The angle should be consistent throughout the mold and should be designed to allow for easy ejection of the part from the mold.

Recommended Draft Angle Values

Typical draft angle values are:

• 1° to 2° draft for common engineering thermoplastics like ABS, nylon, and acetal
• 0.5° draft for more slippery plastics like polypropylene
• 3° or more for glass-filled plastics which shrink more

Draft Angle Design Tips

• Add draft angle to all significant vertical faces that require mold parting lines
• Balance draft angle with the need to maintain dimensional accuracy
• If a part has deep surfaces, a tapered core may be needed
• Provide fillets and radii at the base of walls to ease mold filling
• Allow room in the plastic part design to account for draft angle