Die casting vs. screw machining

Choosing the right process for your metal component

If you're considering screw machining or die casting for your next part, your project probably requires tight tolerances, short lead times and high production volumes. These characteristics make a part a viable candidate for either process.

Although precision metal components can be produced through both processes, the choice often comes down to efficiency and cost—which production process will add more value to your project? In this blog, we'll cover the respective benefits of screw machining and die casting, and what you stand to gain by converting your precision component from screw machining to die casting.

Benefits of screw machining

Screw machining offers two main benefits.

The first is that screw machining enables you to manufacture steel alloys that cannot be die cast. Die casting tooling is made from hardened steel to withstand the high pressure and heat of the die casting process. Since aluminium and zinc have significantly lower melting temperatures than steel, these metals do not fuse with the steel tool. Attempting to die cast a steel component, on the other hand, would produce one large mass of fused steel.

The second benefit is that screw machining can achieve tight tolerances with a lower initial tooling cost. CNC machining of any type is sometimes considered capable of achieving the tightest tolerances of any manufacturing process.

While it is true that machining produces tight tolerances and precise parts, Dynacast engineers maintain that die casting can produce parts with almost equal precision and greater complexity at a lower unit price, more quickly. When efficiency and cost are factors in your decision, the benefits of die casting will consistently outweigh those of screw machining.

Benefits of die casting

The benefits of die casting are largely associated with production speed and unit cost savings.

Dynacast's Multi-Slide machines can be designed with multiple cavities, enabling our engineers to cast highly complex parts quickly. Our Multi-Slide die casting machines operate at speeds of up to 75 cycles per minute, delivering 4,500 shots per hour. In a two-cavity tool, this means 9,000 parts per hour.

A faster cycle time contributes to a lower overall cost per piece. In addition, die casting tooling enables unmatched complexity in internal and external geometries, resulting in fewer secondary operations associated with die casting. With Multi-Slide die casting, you can cast complex geometries that would otherwise need to be manufactured from two or more pieces and assembled using other processes.

While screw machining offers a lower up-front tooling cost, die casting more than compensates through overall unit cost savings. For an ideal part (one that is small, high volume and can be cast in zinc), the tooling cost is fully recovered somewhere between 10-14 months of production. Every part made after that contributes to your bottom line.

Would you like to know whether your currently selected alloy can be converted to a zinc alloy with similar properties? Consult our interactive metal selector tool, or ask one of our engineers.

What do you gain by converting from screw machining to die casting?

Perhaps you currently manufacture your precision metal component by screw machining. While this can effectively produce a complex part, our die casting engineers recognise the limitations of screw machining compared with die casting. In addition to offering greater efficiency at a lower overall unit price, die casting also provides greater design freedom, tight tolerances and reduced material waste.

Available capacity for parts that cannot be screw machined

One of the greatest advantages of converting from screw machining to die casting is that die casting enables you to produce shapes that cannot be achieved through screw machining. When using screw machining as a manufacturing process, you are limited to parts that can be machined from bar or tubular stock on a rotating axis. Parts requiring complex internal geometries or dissimilar features are virtually impossible to produce by screw machining.

Tight tolerances, faster

When converting to die casting, design engineers are often concerned that die casting will not be able to achieve tolerances as tight as those of screw-machined parts. Generally speaking, if screw machining is performed slowly enough, the achievable tolerances are unmatched. However, taking the time to do so slows the entire production process, and often the tolerance required by a project can be achieved through Multi-Slide die casting.

Any compromises for tight tolerances are minor. Multi-Slide die casting produces precision components with tolerances of +/-0.02mm. With Dynacast, design engineers can work with customers to refine the part design for optimal manufacturability, delivering faster cycle times and improved part performance.

Reduce scrap and raw material waste

Finally, converting from screw machining to die casting drastically reduces wasted material.

Screw machining works by cutting material away from a solid piece of metal or tubular stock. This means that, as the customer, you pay for all the raw material that goes into the tubular stock, not just the material in the finished part. You are paying for the wasted metal that ends up on the floor.

In contrast, in a four-cavity die casting tool, the gating system produces only waste roughly the size of the tab on a pen cap. By using die casting, you reduce waste and additional costs while improving your overall yield.

Die casting is ideally suited to high-volume projects requiring tight tolerances and rapid delivery.