A Quick Guide to Investment Casting - Thomasnet

A 5,000-year-old process, investment casting has evolved to become one of the most essential casting methods used by manufacturers today.

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During the investment casting process, hot wax is first injected into a metal mold in order to create a detailed model of the part. This wax model is then repeatedly coated with a refractory ceramic material, forming multiple hardened layers. The wax is removed via high-temperature melting, leaving only a hollow, molded shell representation of the original part. Next, hot metal is poured and solidified into the mold.

In order to remove the metal casting from the original shell, various techniques can be employed, from hammering to water jetting. The final part may be customized and finished with heat treating or other machining processes.

The Advantages of Investment Casting

Also known as “lost-wax casting,” investment casting allows for unique benefits across a range of different industries. First off, the process allows for the production of extremely complex parts with thin, intricate features and excellent overall dimensional accuracy, achieving tolerances as tight as +0.003 in. (0.076 mm).

Finished investment casting parts also offer smoother surface finishes without any visible parting lines that may require removal. With investment casting, whole parts can be manufactured without the use of machining, welding, or assembly. Complex, multipart assemblies can also be cast in a single run.

And for investment casting manufacturers, the technique can be utilized for a variety of components across countless industries, allowing for expanded production capacity. Thanks to the wide range of metals available for use with investment casting, manufacturers are afforded greater design flexibility.

The Disadvantages of Investment Casting

In rare cases, parts such as turbine blades, aircraft door frames, and other heavy components may be made using investment casting techniques. However, the process is usually ideal for smaller castings or complex parts weighing less than 250 lb. It’s important to remember that there are hole-size limitations for the mold; no less than 1/16” diameter is achievable before problems begin to occur.

While this casting technique is both flexible and reliable, it’s not ideal for high-volume runs due to the labor, setup, and cycle times required for initial wax patterns and shell molds. Investment casting manufacturers must also think carefully about the economics of part production, as overall quality may be affected. And finally, investment casting does entail fairly expensive startup costs.

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Industries Served by Investment Casting

From dental fixtures to heavy gears, investment casting is the go-to technique for multiple applications. Jewelers use investment casting for rings, pendants, and other small or intricate pieces. In the aerospace sector, numerous alloys are cast for interior components, landing and braking parts, bearing cages, and more.

For firearms manufacturers, investment cast parts offer greater precision and smoother surfaces than traditional machining offers, as well as near-net shape results that eliminate waste. In commercial and private hydraulic applications, common investment casting products include gate, rotary, and plug valve configurations made from stainless steel, iron, and brass. Other industries making use of investment casting include military, home hardware, automotive, medical, food and beverage, oil and gas, and railroad.

Materials and Products Produced Using Investment Casting

Virtually any metal can be investment cast — from durable brass plumbing components to lightweight magnesium-alloy aircraft canopies to stainless steel flywheels in automobiles. Whether users require a simple hammer from the hardware store or a customized, complex vacuum relief valve for railroad cars, investment casting provides the versatility needed to create a range of small- to medium-sized metal products.

Commonly used materials include steel, bronze, aluminum, cobalt, stainless steel, Monel, and both ferrous and non-ferrous metals. New automation technology has also improved some areas of the investment casting process, allowing for the creation of products that were previously unobtainable with this technique.

Investment Casting Through the Ages

Investment casting is based on an ancient manufacturing process that was used by Egyptian and Chinese civilizations. The materials, methods, and processes involved have evolved over the course of thousands of years, and manufacturers can now achieve low- or medium-volume production for complex metal components without the need for extensive post-processing.

And with new advancements in metal alloy compositions introduced to the market every year, the product and material options for investment casting continues to broaden, helping today’s manufacturers to compete on a global scale.

Resources:

• Investment Casting
• What’s the Difference Between Investment Casting and Sand Casting?
• Investment Casting
• Investment Casting Institute
• Investment Castings

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If you are looking for more details, kindly visit stainless steel precision casting.

Thinking about working on a project with my dad reproducing some muscle car parts, have one part in particular we want to work on - trunk lock bezel. They are a chrome plated diecast part that is hard to come by for some cars. I want to make them from stainless to avoid the chrome plating step and make a more durable longer lasting part. I'm sure with the right machines it could be machined from solid, but I don't have those machines. I'd like to do a casting, then machine the features that need machined,and polish it.

Any idea on a ballpark per piece cost get something like this done? Qty is 25 - 100. Is investment casting the right method? I don't have a 3d model yet - I'd like to get an idea before I waste time making a model to find out it's too expensive.

Get an accurate estimate of the volume and weight of the stainless steel part. Then find a local dental lab and talk to them to see if they can do a piece that size. Dental labs routinely make small stainless steel investment castings and are certainly used to small quantity jobs, because every bridge or partial is unique. You will have to provide the wax models for each part you want cast. The lab or a manufacturing jeweler or an actual investment foundry can help with information on rubber or machined aluminum molds for making numerous wax models of a single item. Jewelers do not do stainless steel, but do know how to make duplicate wax patterns. Maybe there is a way to use a 3D printer to make wax models, but the printers I have seen work very slowly. Foundries are able to cast multiple items at once by connecting many small models with wax rods/wire into a sort of tree array. That keeps costs down.

Investment casting does involve some skilled hand work to prepare the wax model and attach sprues and runners, so it is not going to be a cheap process. Then the castings have to have all those sprues and runners carefully cut off, again a hand process.

Larry Some dentists (not dental labs) now have handheld 3D scanner wands and minature 5D milling machines, together with special suites of the necessary software, to make inlays and crowns from unfused ceramic blanks. After milling, the ceramic is fired in a minature oven, right in the dentist's office. Once they grind out the necessary recess in your tooth, the whole scanning, milling, firing, installation and trimming process can take less than an hour. I have had the crown for an implant and an inlay done with this process, the inlay just this morning!

So, the day of stainless dental castings is (just now) beginning to fade away. Larry is correct, though, if you have wax masters, a dental lab can probably do the work. It will depend on the size (max dimensions and total mass) of the castings you need, as dental labs are naturally specialized to do work the size of a tooth.

You definitely want to talk to your foundry/lab about multiples, because there will be hundreds of dollars of per-run cost. The only way to get per-part costs down is to do lots of parts in a single run. Hi All:
I read this thread with interest and perked up my ears when dental labs were first mentioned as a source for investment castings. (I used to be a dentist so I know the subject).
There are a couple of misconceptions worth addressing.

First, partial denture frameworks are not cast from stainless steel, they are cast from cobalt chrome which is harder than a woodpecker's lips and therefore expensive to work with.(think high 40's RC and fairly brittle)
It's also expensive to buy and expensive to cast because it needs a special refractory investment and has a higher melt temperature and lower density than gold which is what dental labs cast routinely.
(The fluidity, high density and comparatively low melt temperature is what makes gold easy to cast accurately, and the biocompatibility and ductility is what makes it attractive for dental restorations)

The whole process of making a partial denture framework is completely different from the process used to make a commercial investment cast part...a refractory model of the patient's teeth and gums is poured, a technician custom waxes the framework up by hand using plastic patterns of the individual bits that go into the framework, then the whole thing is sprued and gated and buried in more refractory investment.
It's then burned out and cast.
Only one part is cast at a time, and the whole works is devested, trimmed, polished, then the teeth are put onto it.

Back in my day, this was expensive...a completed partial denture was fifteen hundred bucks give or take.
The prices haven't improved since then.

So knock the idea out of your head that you can get a dental lab to make these for you.

A commercial investment casting house can work with stainless steels of all kinds, and can make these for you.
The problem is making the waxes.
Traditionally a metal mold was made and the waxes were shot just like injection molded plastic parts are produced, then they were assembled on a sprue, invested and cast.
The mold cost about like a prototype plastic injection mold costs...twenty grand at a guess for what I can see of the OP's parts.

Nowadays all that cost can be circumvented by 3D printing the waxes, but as has been pointed out, the cost per wax is higher because the 3D printing is so slow.

Another alternative is to get the parts 3D metal printed.
There are several competitors in the market, the most common is direct metal laser melting...EOS is the most widely known and used system, but there are others.
A new system has just come on the market and show exceptional promise...it is the Rapidia system which uses sintering to consolidate a green printed part made from a water soluble metal paste that's 3D printed just like a filament printer does, and it has similar resolution.

For low volumes these are an acceptable and lower cost way to get a metal part that is about equivalent to an investment cast part...not as good for consistency and detail in stainless as die cast part, but workable for many things and much cheaper for small volumes of parts.

That's where I would look first.

Cheers

Marcus
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