What is Metal Casting?
Metal casting has been around for a long time! The first ever known casting appeared in 3200 BCE in Mesopotamia. It was a frog made from copper. Later, around 2000 BCE, people discovered iron, and that changed the way things have been done ever since.
It’s an interesting process. First, metal is melted down and poured into shapes. Then the metal is cooled, hardened, and formed, removing any rough edges.
But why should you use it for your next project? Well, friends, read on to find out why we love making magic with metal and why we think you should choose metal casting for your next project.
1. Cost Effective
If you’ve ever had to cut, weld, and shape some metal together to get the final result you’re looking for, you’re no doubt aware how much time is needed and ultimately wasted to get things looking right.
Since multiple castings can be poured at the same time, and since the molds used are pretty much what the final shape is going to look like, production time is cut almost in half.
Think of it this way. If you were making chocolate for Christmas and you wanted to make small Santa Claus’s, which would be a better and faster way to do it: grab a giant piece of chocolate and a knife and start carving and shaving just to get the shape, then intricately cut all the little details like the beard and face, or simply just melt the chocolate and pour it into a Santa mold?
And that’s not all! Imagine you had to make these chocolates a quarter of an inch thin? Would you be able to carve all those little details without snapping the chocolate in half?
This is how metal casting essentially works. We can cast walls as thin as 1/8 of an inch without any heavy-duty stress on the finished product.
There’s also the labor savings you get. Since casting doesn’t require a team of trained welders, metal cutters, or engineers, there’s not as many people in the production line to pay for.
Traditionally, a project could require upwards of a dozen people to complete. A team of metal casters can be significantly smaller. This saves time and, ultimately, money.
2. Structural Strength
Ever broke something very thin and very fragile and tried to glue it back together with Krazy Glue? Yeah, not very fun, and the result is something even more fragile than what it started as. That glue line is like a welded seam in metal. It’s messy and prone to cracking or breaking apart completely.
Let’s face it, there’s nothing stronger than something solid, no seams, no glued or welded connections – just one continuous hunk. Imagine if everything was built like this. Chairs would be stronger. Roofs would be less prone to leaking. What a wonderful world that would be.
By using metal casting, the whole shape is one solid chunk. No seams welded together.
Foundries have also developed alloys with different chemical properties and varying levels of strength. Need something with a little give to it? Or maybe you need something strong that will span thousands of years. Metal casting can do that.
3. Variety of materials
It’s true, iron and other metals have different grades of strength. But steel comes in much greater variety. There are different types of steel to serve different purposes, making it ideal for many different purposes.
Perhaps you need something with more temperature resistance. Or maybe you need something with a little more flexibility.
With steel casting you get a very wide range of properties including:
- Wear resistance
- Corrosion resistance
- High-temperature properties
- Low-temperature properties
The physical properties of cast steel change significantly depending on chemical composition, heat treatment, and other factors. We select these properties based on performance requirements of the intended application.
Cutting, bending, and welding the same structure over and over again in a production line takes times and is often prone to mistakes. Sometimes measurements are off and something gets welded in the wrong place, or maybe doesn’t even get welded at all.
If you’ve ever been on an assembly line or seen how they operate, you’ve probably seen the line shut down to recalibrate or fix something in one department. This shut down brings production to a halt and can significantly impact your bottom line.
With metal casting, molten metal is poured into a mold which can be carbon copied again and again. This speeds up production and can cut costs by upwards of 50%.
These molds are made out of a metal that has a higher melting point than the metal being poured into it. They have a smoother finish than other methods and avoid several types of defects. The trade off is that you can’t use these to pour as thin as other methods like die casting.
The main difference between permanent molds and semi-permanent molds is that the cores used in the casting process might be sand cores. Once the metal is poured, the sand core is destroyed and can’t be used again. The outside mold remain intact, but the core needs to be created again.
Die casting consists of a basin holding molten metal, a metallic mold, and an injection system that sucks up the metal and forces it under pressure into the die.
This is the same casting you learned about in shop class. It’s still the most popular method of casting metal, since sand is so cost effective and can take incredibly high temperatures.
The surface finish on sand casted metal is often rough and needs to be filed down to make a smooth surface. It’s great for producing large pieces from decorations to engine parts.
Like sandcasting, shell molds are an expendable and destroyed after pouring. They provide a closer dimensional tolerance, giving a more precise mold than sand. With shell molds, the sand mixture is mixed with a resin. This mixture melts and cools into a shell. The shells of the mold are brought together, usually supported by a flask filled with sand. With the resin providing extra support to the interior surfaces, these shells form a very nice, very precise mold.
Investment casting (lost-wax casting)
Lost-wax casting is an alternative to sand casting. It works with a wide array of metal, even ferrous metals that require a high-melting point, but it avoids a lot of the imperfections present in sand casting.
An investment casting designer makes a very accurate metal die into which wax or special plastic patterns are cast. These patterns are assembled then used to create a shell that will ultimately be used as the mold. The pattern is continuously sprayed with a slurry, allowed to set, then heated in an oven until the wax has ran out of it. The molds can then be supported with loose sand and poured in any of the manners mentioned in this article.
5. Shape complexity
Remember that Santa chocolate example? Imagine that chocolate at ten times that size and hollow. Again, you could grab a huge slab of chocolate, hollow it out and carve all the little details, but how long would that take you? Would you be able to get all those little details carved with out breaking it? Would you be able to pour some milk into it without having it leak everywhere?
Pouring big, complex, hollow shapes is something metal casting excels at. Things such as complicated internal cavities, cylinder blocks, and a host of other mechanical parts.
And because the finished product is one solid piece, there’s no seams and less chance of what you want pouring through it to leak out.
This is perfect for very complex shapes that would normally require a significant amount of welding and shaping. Imagine making an octopus and having to weld all the arms together. Or a sun with all the sun rays around the center.
Welding the arms of the octopus or the rays of the sun to the center shape would undoubtedly cause the structure to be less stable and more prone to breakage.
With metal casting, there are no seams and nothing needs to be welded together. What you pour is pretty much what the final product will be, minus some surface imperfections that will need some cleaning up, which we’ll talk about next.
6. Surface finishing
How rough and bumpy do you want it?
Seriously, casting can be as smooth or as bumpy as you want it.
Smooth surfaces like a wedding ring or the back of your smart phone are created with a machining process to take all the bumps out.
But not everything needs to be smooth as silk. A cast iron pan, for example, can actually benefit from the rougher metal finish, as well as anything you need to keep objects from sliding off the surface of.
Always remember, the smoother the finish, the more slippery the surface becomes. Good for things you’re going to handle a lot, bad for things that need grip like manhole covers.
All of this is, of course, application dependant. Knowing what and where the finished product is going to be used for is very important to metal casting.
Since there are several ways in which we can cast, each process produces a different surface when all is said and done. There are several things to consider before determining what kind of finish your project requires, such as:
- Where is the casted product going to be placed?
- If the surface is too bumpy, will this cause unwanted friction?
- How often will the finished product be handled and by what or whom?
- Is the finished product going to be for decorative purposes, or is it fulfilling something different?
Answering these questions as well as acknowledging things like wear and tear, longevity required for the finished piece, and the environment the finished piece is going to be placed in, will help you determine exactly what kind of finish you’ll require.
The very nature of metal casting makes it ideal for repetitive casts. If you manufacture a large quantity of the same thing (like a car), then having the same piece produced every time would be very important to you.
Unlike welding and cutting, which can be difficult to create exact replicas of shapes, casting utilizes a far more streamlined approach. Once a reusable mold is created, the process becomes much more repeatable and efficient, giving us the ability to produce multiple casts of the same object.
This also comes in quite handy if you design something once and then need the same design later. Rather than recreate the project, we simply can find the mold and recast it.
Let’s face it, paper blueprints, even computer applications, can be lost or erased. If this ever happens, your project either needs to be completely recreated from scratch or scrapped and started again.
With the repeatability of metal casting, we can store the mold for longer periods of times without worry of deterioration or losing it. Then, when the time comes and you need to create more of the same products, we can find the mold and start casting almost instantly.
8. Design flexibility
At MIRA, we have a wide range of choices for alloys, which give our customers the flexibility to configure a cast exactly how they want it.
This also includes the ability to make changes more quickly to the designs with a shorter time from design to finished product.
If you are bending, shaping, and welding metal, if a design change is made after productions starts, a new blueprint needs to be drafted, shapes need to be recut, and welds need to be remeasured.
With sandcasting, the mold can be destroyed and rebuilt quickly, allowing the cast to be reapplied with very minimal downtime.
When you create a design and then years later come back to the project but need to make adjustments, rather than drafting up a new blueprint, you can simply make changes on the fly to your design. Once we implement the changes, we can start casting again right away.
This makes it easier for longer projects that require frequent changes as time goes by. Traditionally each change would need to be documented and the whole scope of the project would need to be adjusted.
With casting, since changes can be done on the fly, there’s less scope creep and your project can continue as planned.
9. Size is no object
With casting, you can pour metal parts from something as small as a wedding ring, to a 100 ton crankcase.
The versatility of molten metal makes it ideal for those who need to pour very large projects. But it’s also great at pouring smaller things as well.
Imagine having a roof or wall made of two parts that were welded together. This would undoubtedly allow for leaks and even cracks as time went on.
Having a wall or roof (or any large item, really) cast as one shape limits deterioration and leaking, making the whole life of the project last longer.
Plus, the larger the project, the longer it will take several people to complete it. First you need a few people to cut the metal, then you need a few more to shape it, then a few more to weld it. This can take days, even weeks. With metal casting, the mold is made and then poured, often the same day. And there’s the added bonus that we can pour a bunch of the same mold at the same time.
Disadvantages of metal casting
So what do you think? Metal casting sounds pretty awesome, right! That’s why we love it. The flexibility of it, combined with the speed at which we can pour, makes us all love coming to work every day. But as with anything, there are of course some disadvantages to metal casting.
A number of these things come down to user error as well as the nature of working with metal. Many of them can easily be overcome without scrapping an entire projects, which makes a lot of the disadvantages of using metal casting very minor. But their worth pointing out, so we’re doing it here.
1. Casting is prone to fine pores and shrinkage
Porosity typically occurs when air is trapped in the metal by die casting machinery. It’s often caused when air is used to force molten metal into the mold and the air gets trapped. It can also occur when you fill a die or mold too slowly, allowing some solidification to occur.
Of course, porosity may be the look you are going for, so if this is the case, then this technique can be quite easily applied to metal casting.
2. Sandcasting usually has a more bumpy surface
We measure surface texture using a term called Root Mean Square, or RMS. This is calculated by measuring the peaks and valleys in metal. The lower the RMS, the smoother the surface. The lowest is around 20 RMS while the highest is about 800 RMS
The surface finish of sandcasting usually sits between 250 – 500 RMS. In order to get it smoother, machining will need to be added to the project which can be an extra cost and extra man hours.
As we mentioned earlier, the desired outcome of the finish might be slightly more bumpy. This is going to depend on several factors, including durability, traction, and usage. It’s imperative to know these things before starting a cast, since these, along with several other factors, will play an enormous role in the final finish of the product.
3. Permanent molds can only cast non-ferrous metals
Magnesium, copper, and aluminum are what we classify as non-ferrous metals. Basically metal that doesn’t contain any appreciable amount of iron is classified as non-ferrous. They tend to be more expensive, but they can be used in a variety of desired applications. However, if you need something poured using iron, you’ll need to look at a different mold than a permanent one.
It’s worth repeating but knowing what your final product is going to be used for and the environment you’re placing it in will play a very large part in determining the alloy used for your project.
Steel is a great example of a ferrous metal, and because of these properties, it can’t be used with a permanent mold. If working with steel is a requirement, the molds are going to need to be altered. This isn’t a huge challenge, but it is certainly one that needs to be addressed and understood.
Metal casting is used for so many of the things we enjoy on a daily basis. Chances are you use these things and don’t even realize it. From the keyboard used to type this, to the monitor you’re viewing it on, metal casting is everywhere.
It’s also ideal for decorative projects like fences and gates. And since everything can be poured as a solid chunk, there’s no threat of breaking or deterioration over time. Depending on the alloy used, your metal casted fence or gate can last for a very long time.
And why stop there? Gold and silver can also be casted using the same techniques mentioned in this article. From fancy jewellery to custom signs or decorations, gold and silver make incredibly attractive additions to any piece.
Indeed, metal casting has come a very long way. From its early use over 3,000 years ago, metal casting has become an integral part of modern society. It’s in our cars, our phones and computers, the buildings and structures we work and live in. So much of our lives depend on it. Shouldn’t your next project do the same?