All About The Die Casting Draft Angle And Product Design

Through die casting, it is possible to create pieces that are exactly the same in very high volumes. Simply put, molten metal is injected under high pressure into a die. Because the dies can be used over and over again, the casts are always almost exactly the same. It is possible to choose different types of alloys in die casting, depending on how they are used. The hardest part of die casting is designing the product. Often, the requirements are not just mechanical but the way the finished product looks is also very important. Sometimes, they need very thin walls, bosses or ribs. There are different ways to achieve this, with each method requiring a specific kind of draft angle. The draft angle makes it possible for the piece to be ejected from the die after it has been cast. If the piece hasn't been designed properly, the entire process can go wrong. There are numerous things to consider in the design process, let's take a look at some of them.

Draft Angle

The draft angle, in essence, is the slope that is found on the walls of the die. When you look at the way the die and the sliding cores open, you can identify the angle. This way, a cast can easily come out of the die. The angle is hugely important, since it makes it possible for the cast to slide out rather than stick to the sides, thereby making the process more efficient and the product of higher quality.

Undercut

It is important to keep in mind that high velocity and high pressure is used to cast a die. Once it is then solidified, the two parts of the die open up, ejecting the part. This is why it is so important to make sure no undercut areas are present in the opening direction. So, the draft angel has to be determined before the die or tool is fabricated. Die casting is becoming ever more complex, which means new features are added. These features do have an undercut from time to time, which requires extra cores to be added. This way, the cast is still able to slide out of the die. This demonstrates the importance of calculating the die casting draft angle.

Uniform wall thickness

The wall thickness has to be completely consistent. If the thickness or the geometry changes suddenly, the flow of the molten metal coming into the die will be disrupted. As a result, air can come into the metal and the surface finish will be very poor. Again, ensuring the draft angle is properly calculated will avoid these problems.

Parting Line

Any part that has been made in a die cast will have a parting line. This is where you can see the two halves meet. The parting line or P/L is always indicated on the drawing of the part. Dimensions with critical tolerance should always relate to a specific side of the die. The two sides are the ejector and the cover. Critical tolerance is hard to control on the parting line itself. Also, the parting line should not be the site of a specific feature of the component, since it will not look aesthetically pleasing. Calculating the die casting draft angle will make the line more or less visible.

Fillets

It is very rare for a part that is made through die casting to be flat. Hence, a curved surface is added on the spot where two intersections meet. This stops sharp corners or edges from appearing. Very often, a rounded edge is added to the die casting draft angle so that the molten metal can easily flow into the die. Also, the thermal stress on the part is reduced this way, so the die lasts longer.

Bosses

A die cast part also regularly has a boss added, which is where other parts can be mounted. Generally, the bosses include center holes, so that other machining processes can function. It also makes sure that the thickness of the wall is more uniform. Bosses are very narrow and they are embedded on the die itself. They can make it very difficult for the molten metal to get into this area, which once again makes calculating the draft angle so important.

Openings

One of the most common applications for a die cast part is telecommunication and electronics. These types of products often have displays and keypads and they make it necessary for a die cast part to have an opening that the connectors and keys can hook into. They also need larger openings, for LED or LCD displays for instance. These are highly specific features and they make it more difficult for the molten metal to properly fill the die. So, cross feeders and bridges get added to the component of the die cast. Each of these areas needs to have the right temperature and overflows are also added. Because of this, it becomes easier to manufacture the component and it will make the part of greater quality. So long as the die casting draft angle has also been properly calculated, the features can be trimmed without difficulty. The draft angle will make it possible for the part not to grip too tightly to the die, so that it can be ejected with ease.

Lettering

Very often, lettering is also added to the part. This includes trademarks, identification numbers or logos for instance. Some also want a date added to the part so that it is clear when they were manufactured. It is possible to do this by having raised letters, which is cost effective and therefore generally the option of choice. In this option, the lettering is embedded into the cavity of the die itself. This produces higher quality lettering, since they will be protected from wear and tear. The second option is to use depressed lettering. Here, the feature will protrude on the die, and this makes it of less quality because it will wear and tear quicker. The draft angle must be properly calculated with both these options however, so that the lettering doesn't catch when it is ejected.