Zero Draft Angle in Die Casting: Why Is It Important?

Achieving zero draft angle is one of the most critical steps in the manufacturing of a product. It plays a vital role in developing parts for plastic injection moulding.

To improve the product’s moldability, applying a draft to the part’s faces is critical in plastic injection moulding. Without this done, the parts will have a low cosmetic finish and wrap, break or bend due to the moulding stress caused by plastic cooling.

Worst of all, an absence of draft may prevent the parts from ejecting the mould damaging the part and the mould alike.

To avoid this costly and time-consuming detour, it is crucial to include a zero draft angle in injection moulding.

The zero draft angle concept is usually considered to achieve tighter tolerances for creating parts with the right specifications. 

What is a draft angle, and what is its importance? 

As discussed above, engineers and designers should consider how a part should be ejected from the die to get damaged.

Draft angles mean the degree of taper incorporated into the die-cast tool’s cores and the side walls to help remove a part. It is measured in degrees or mm/mm.

In the last few decades, die casting has become an integral part of the manufacturing industry. And the removal of unwanted parts during the production process is vital during the process. Draft angles minimize the friction between parts so that the angles do not get stuck, stripped, or dented during the process. 

Manufacturers continually try to achieve a zero draft angle when creating products with fine features and precision. 

The prime purpose of the draft angle is to minimise the friction between the part and the tool as it is ejected. Without a draft angle, the part will get stuck, stripped, or dented in the mould.

One of the best examples can be seen in the manufacture of soda cans. Since the broadest part of the can is crescent-shaped(where the die separates), cans are quickly ejected when the die opens.

As the die casting process can also involve designing metal materials without creating a draft on platforms, zero draft angles help achieve tight and closer tolerance. With this, items can be assembled as per the desired specification.

Draft angles are important for multiple reasons. Here are some important ones:

  1. Mold health- the use of draft angles during die casting reduces wear and tear or any other damage to the mold providing better uniformity to the finished products. 
  2. Ejection of parts- The removal or ejection of parts is the main reason to incorporate draft angles. Without these in place, the abrasive force can create dents or damage to the parts during the release process. Therefore, it is important to have draft angles to maintain the specifications and aesthetics of the parts. 
  3. Reduces production cost- Defective parts take time and cost for repair. Having zero or minimal draft angle in place means reducing the chance of damage to the part’s final finish during the ejection process. This, in turn, is a big cost-saver for the manufacturing units. 
  4. Increases cosmetic finish- Accurate draft angles help make the ejection process easier. This also means that the surface/finish of the parts is cleaner and visually more appalling. 
  5. Reduce the overall time for cooling by eliminating the need for unconventional ejection setups.

The concept of zero draft angle thus evolved to get close tolerance results. The concept might lead to a visible change in the features of the final product. It, therefore, allows the manufacturer to have control of the accuracy of the design. 

How to achieve zero draft angles in die casting?

Under the proper engineering conditions, a good zero draft angle is achievable. Make sure that the part is the case using the metal zinc.

This is because zinc has excellent shrinkage and physical properties. For Zinc castings, the standard draft angle is 0.5 degrees, mainly because the metal is thin and fluidic. This will also help the material to eject from the mould very quickly.

As Aluminium is relatively heavier and abrasive than zinc, engineers will incorporate a draft angle of ± 1-2°.

Best practices to consider while incorporating zero draft angles.

Following are some quick tips to adhere to when incorporating draft angles in your die casting process:

  • The draft angle should move in the direction of the mold as it separates. 
  • For parts that require textures on the surface finish, an additional draft of 1½ degrees per thousandth-inch of surface depth should be added. 
  • All areas of contact with the mold need to incorporate a draft angle.
  • An additional draft may be provided for metal on metal moldings.
  • Half a degree draft may be incorporated for vertical surfaces. 

Functionalities of Draft angles

One of the crucial aspects of die casting is to remove unwanted material during the process of production.

Zero draft angle will immensely help to preserve the equipment and casting container used in production. Having a perfect draft angle will help to reduce the friction that occurs between different moving parts.

That said, different materials can achieve different cast angles. For example, Zinc and its alloys can be cast with lower or close to zero draft angles than other materials like aluminum, magnesium, and their alloys. The zero drafts with Zinc permits better manufacturing results a well as lower production costs. 

Final words

Draft angles are not just an additional feature for design to manufacturing (DFM). They are, thus, not merely a requirement but a necessity for a well-designed part. While some engineers may be reluctant to use it, the lack of it may lead to many damaged and rejected parts. In money terms, it means a significant rise in the cost of production. 

The closer you get to a zero draft angle, the better is the chance of your part having a uniform finish and functionality. 

This article is a part of our comprehensive guide on “Die casting: Process, Equipment, Uses, and More

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