What Is the Sand Cast Process?

Metal casting’s a major industry in the US today and a key part of our economy. Indeed, a whopping 90% of all durable goods utilize cast metal from the country’s foundries. 

If you’re like most people, though, you won’t know the first thing about how it all works! And that’s something we’d like to change. 

In particular, we intend to shed light on the magic of sand casting. This is the most common type of metal casting used today and a process that stretches back thousands of years! Understand this and you’ll realize what it takes to manufacture the everyday items most of us take for granted. 

Sound good? Check out our in-depth guide to the ins and outs of the sand casting process. 

What Is Sand Casting? 

Sand casting is the process of manufacturing metal items using (you guessed it) sand! Everything from valves and pump housing to cylinder heads and engine blocks is manufactured using this process. 

We’ll go into more detail in later sections of this guide. For now, though, the basic idea is to create a mold in a tray of sand, into which you pour molten metal. 

There’s no high pressure required! When the metal cools and sets into shape, you simply extract your trinket from the sand. You’d then create a new mold (with fresh sand) if you wanted to create more of them. 

Advantages and Disadvantages of Sand Mold Casting 

The popularity of sand casting in the manufacturing industry is well-founded. After all, the metal casting process is versatile, cost-effective, and easy to scale! That’s in large part down to the nature of sand itself, its ready availability, and impressive resistance to extreme temperatures. 

That latter attribute means you can use sand casting with almost every metal material (even those with high melting points). You can also cast parts of any size, shape, and weight, from the largest piece of manufacturing machinery to the smallest, most intricate widget. Last but not least, the low tooling cost of sand casting makes it a viable option whether you’re doing a single item or higher-volume runs. 

There are downsides too, though. 

For one thing, the surfaces of sand cast items tend to be rougher and need machining to create a smooth finish. Then there’s the issue of both creating and storing the patterns (AKA the replicas of the items being manufactured used to create the mold). Big and bulky, they take up space and require good care to keep them in usable condition. 

Steps Involved in Sand Casting 

It’s amazing to think that the basic process of sand casting has remained unchanged for millennia. You can trace it all the way back to the dynasties of Ancient China! Here’s what’s involved from start to finish:

Create YourMoldin the Sand 

You begin by taking one half of the pattern (the identical replica of your final product- usually made from wood, metal, or plastic) and laying it face down on a clean floor. From there, a wooden box (called the drag box) is laid over the top. You then fill this drag box with sand, covering the pattern in the process. 

When there’s no more room, you ram, compact, and level off the sand. When you’re done, you’ll have a solid, sand-filled box with the pattern on the underside! Finally, invert the drag box so the pattern sits exposed at the top. 

The next step is to repeat this process with the ‘cope box’. Lay the second half of the pattern on top of the first and place another empty box on top of the one now filled with sand. Fill this up with sand and ram it down in the same way you did before.

Remove the Patterns

The second stage of the sand casting process is nice and simple. All you have to do is separate your two sand-filled boxes so that each half of the pattern’s on top. Then, by inserting screws into the pattern, you can remove them (carefully!) from their position in either box and set them aside. 

In the process, you end up with the foundation of your mold. Without the patterns, the sand stays in place, revealing the contours of the outside of the product. At this point, you’d create a funnel in the cope (down which you’ll pour the molten metal) and channels in the drag to direct the molten metal into your mold. 

With all that done, the next step is to put the drag and cope boxes back together to create a complete mold. Clamp these tight and you’re ready to move on!

Melt and Pour the Metal

Whether you’re sand casting aluminum or anything else, the final stage is to melt your metal of choice in the furnace. From there, you pour it with extreme care into the funnel you made (also known as the sprue) in the cope. The molten metal will then move down the channels of the drag and into the mold, where you’ll leave it to cool. 

From there, it’s just a matter of removing the sand. This is done through a variety of non-destructive methods, including jets of water and shaking the cope and drag. With the sand removed, you can remove the excess metal and polish it to the desired finish. 

And that’s it! Once you’ve inspected the final product for any issues, you’ve officially finished the sand casting process. You’d then repeat it (using the same pattern) to create as many products as you need. 

Remember This Guide to Sand Casting 

Metal casting’s big business in America. Each of us benefits from both the economic impact it has on the country and the pivotal metal parts that couldn’t be made without it. Yet hardly anyone outside the manufacturing industry knows anything about the industry! 

With any luck, the insights in this article will have shed light on one of the primary processes taking place in foundries every day: sand casting. Would you like to continue your education on all-things manufacturing? Search ‘manufacturing’ on the website now.