Eight Things to Think About When Design for Die Casting
Rarely do we meet anyone who spends all their time designing die castings. For that reason many product designers need a few tips. Adherence to the following suggestions will save time, money, and headaches during the tooling and production processes:
- Draft -
- Wall Thickness -
- Ejector Pins -
- Beware of Undercuts -
- Models -
- Thin Steel
- Machine Stock –
All features on the casting that are created by the cavity or core side should contain draft. We generally recommended draft of 1°. This draft helps the part separate from the die. Failure to put necessary draft into the design of the casting will result in parts sticking. Excessive sticking, created from a lack of draft, will cause premature die wear and damage. It can also make running a die less efficient and more costly. (For a more in depth explanation on draft for castings please visit:
Quality die castings are very reliant on the flow of material. Smooth edges will promote better flow than sharp edges. For that reason, whenever possible, generous radiuses should be used to help material in the casting flow. Radiuses also add significant strength to corners, thus preventing cracks and breakage from occurring.
Wall thickness for die castings should be no less than 0.060” thick and should actually be more in the range of 0.100”. Walls smaller than that will be very weak and will have a very difficult time filling out.
Ejector pins (along with draft) help the casting separate from the die. It is important to keep in mind ejector pins will appear somewhere in the die and on the shot. If you have areas where ejector pins are not allowed, it is best for the people quoting the product and/or designing the tool, to know this ahead of time. If known, the designer should note where on the casting ejector pin marks are not allowed. If ejector pin marks are allowed but must be raised, flush or below the surface this too should be noted.
Undercuts are features in the casting, that if produced, would actually lock the die shut or tear the casting apart once it was cast. In the tool design process this will be looked at to make sure that the casting does not create an undercut. In fact many of the CAD programs have features that will point out undercuts in the model. In the case that an undercut feature is necessary, it is best to make the casting without the feature and then machine it in afterwards.
Ensure your part design is presented in the form of a 3D model. At some point you will need a 3D model so it makes the quoting and development process easier. We typically recommend models are provided in an .stp format, however we have the ability to use other file formats if necessary.
Designers should keep in mind that when two features are too close together the die will have to have a point where the steel is very thin. When this occurs it presents an area where the tool can easily crack or break. If the features are relatively short this is not an issue but when the features are tall (or deep) care should be taken to make sure there is ample steel in the tool to prevent breakage.
When parts are cast, they create a thin “skin” of material that is much less porous than the rest of the casting. So when machine stock is added it is best to try and keep it in the same thickness of the skin if the designer wants to avoid porosity on machined surfaces. We recommend machine stock to be between 0.010” and 0.020”.