When, why and how to move from die casting to CNC machining

Deciding which manufacturing process to choose can be difficult; There are many different factors to consider. You can start with the die casting process, as it can provide the quantity you need and meet your required tolerances. However, you may need to switch to a different manufacturing process next. This can happen if the demand for parts changes, or if your delivery cycle or quality needs to change.

When to choose CNC machining over casting

If you started with die casting, why did you choose to redesign your parts and switch to CNC machining? Although casting is more cost effective for high volume parts, CNC machining is the best option for low to medium volume parts.

CNC machining is better able to meet tight delivery cycles because there is no advance tooling, time or cost involved in the process. In addition, in any case, die casting usually requires machining as an auxiliary operation. Post-finishing is used to achieve certain surface finishes, drilling and tapping holes, and to meet strict tolerances for cast parts that fit with other parts in the unit. And the post-processing needs to customize the fixture, which itself is very complicated.

CNC machining can also produce higher quality parts. You can be more confident that each part will be manufactured consistently within your tolerance requirements. CNC machining is naturally a more accurate manufacturing process and does not have the risk of defects that occur during casting, such as pores, dents and improper filling.

In addition, casting complex geometry requires more complex molds, as well as additional components such as cores, sliders, or inserts. It all adds up to a huge investment in cost and time before production has even begun. Not only complex parts are more meaningful for NC machining. CNC machines, for example, can easily make flat plates by machining stock materials to the desired size and thickness. But casting the same sheet of metal can easily lead to filling, warping, or sinking problems.

How to transform casting design into CNC machining design

If you decide to redesign the part to make it more suitable for CNC machining, there are several key adjustments that need to be made. You must consider drawing angles, grooves and cavities, wall thickness, key dimensions and tolerances, and material selection.

Remove the drawing Angle

If you originally designed the part with casting in mind, it should include the draw Angle. As with injection molding, the drawing Angle is important so that the part can be removed from the mold once cooled. During machining, the drawing Angle is unnecessary and should be removed. Designs that include drawing angles require a ball-end milling cutter to process and increase your overall machining time. Extra machine time, extra tools and extra tool change operations mean extra cost - so save some money and forgo drawing Angle design!

Avoid large, deep grooves and hollow cavities

Shrinkage and hollow cavities are usually avoided in casting because thicker areas tend to be poorly filled and can lead to defects such as depressions. These same functions take a long time to process, and doing so creates a lot of wasted material. And, since all the force is on one side, once the part is released from the jig, the stress of machining the deep cavity causes warping. If grooves are not a key design feature, consider filling them in if you can afford the extra weight, or adding ribs or corner brace plates to prevent warping or deformation.