Many engineers are guilty, at one point or another, of designing a component without stopping to ask themselves how they are going to make it. Fortunately, the first step in deciding the best production method for you is actually thinking about the last step, the finished product.
Start at the end and work your way backwards. Understand your end goals and think about the simplest way to meet them. Depending on the dimensions, tolerances and scheduling of a new product, permanent mold may be the best solution, then again, you may be better served by machining the parts or another molding method like sand or die casting.
The best method for your operation largely will be dictated by the size, geometry and quantity of your production goals. But factors like wall thickness, inserts and other surface finish requirements can play critical roles.
When designing your product, think about the qualities and tolerances that you absolutely need for the part to serve its purpose. Everything else is likely going to be a detriment to your operation.
There are four main forms of casting, and each includes its own advantages and disadvantages, depending on the needs and abilities of an operation.
Some parts can also be produced by shaping metal through machining, which offers a wider array of alloy options but also produces much more waste.
Sand is the single-use version of metalcasting. Each mold is only used to cast a single part, like a coffee pod is used to brew one cup.
Sand casting molds and tooling can be relatively inexpensive, making it ideal for operations producing simply shaped, low-volume parts. Sand handles heavier metals than permanent mold or die casting, which use steel molds that can’t stand up to the heat of molten metals like iron. But sand casting operations have to produce as many molds as they produce parts, so many times it isn’t efficient for larger-scale productions unless the process is automated.
It’s also difficult to create fine details or high surface finishes with sand casts, so they probably aren’t the best option for highly visible products.
If you’re annually running tens or hundreds of thousands of parts, like an automotive company, you’re going to want to go with die casting.
Where a sand mold can only be used to cast a single part, one steel die mold can cast thousands. But preparation is key because tooling is expensive and requires longer lead times.
The die casting process forces molten metal into the mold under pressure, filling the cavity. Die casted products can have thinner walls and less drafting than other casting methods. They also exhibit a decent as-cast surface and can hold tighter as-cast tolerances.
Permanent mold casting
Permanent mold casts are produced by pouring molten metal into steel molds, much like with die casting, but permanent mold casting is gravity induced, rather than pressure forced. The permanent mold casting process is slower than die casting, but it also causes less turbulence in the molten metal, resulting in denser casting.
The process is best for moderate- to high-volume operations producing parts with demanding tolerance requirements. Castings come out of permanent molds at near net shape with high-quality finishes, so minimal secondary machining and finishing is needed.
Investment casting is based on lost-wax casting. A shell made of ceramic, plaster or plastic is formed around a wax pattern. The wax is melted and removed in a furnace, then metal is poured into the shell to create the casting. A variety of metals can be cast into intricate shapes with this versatile process, but it’s also the most expensive casting method when comparing apples to apples.
Machining parts involves taking a mass of metal and cutting it down to size, rather than shaping it with a mold. Machining therefore requires much more time and waste to produce a final part.
This method is usually good for small batches with high part tolerances as machining is a slow process but can be performed with a high degree of accuracy. This is also a great way to prototype or prove out a design.
Machined parts can be made from a wider variety of metals than casting can offer. However, much more of that metal will be wasted on the cutting room floor. We’ve seen machining operations that lose 70% of their material to waste.
Now let’s take a look at what makes permanent mold casting stand out in the industry.