Questions About Investment Castings

1. What is a “lost wax” “investment casting”? What advantages do I have switching to this method?

Wax is injected into an aluminum tool to produce a pattern. This wax is a positive replica of the actual part increased by a calculated shrinkage of the wax and steel (approx 3%). For every casting one wax pattern must be made. The patterns are then assembled on a common “sprue” The assembly is commonly referred to as a “tree” of parts. The tree is repeatedly dipped into a ceramic slurry followed immediately with a refractory material (sand or stucco with excellent thermal properties). After a proper shell thickness is built, usually taking a week, the wax is removed (usually by autoclaving). The hollow shells are then preheated up to 2000 deg. F and molten metal is immediately poured into the hot shells. After cooling, the spent shell material now cracked and fractured is removed. Cleaning operations (cut off, grind, heat treat, straightening, blasting) takes place.

The goal is to supply near net shape parts often requiring little or no further machining or minimal operations. This process offers cost savings, design improvement, broad alloy selection including material interchangeability, close tolerances, and weight reduction. Once the initial tool is made you can start producing consistent parts order after order.

2. What alloys do we pour?

Our company specializes in Stainless and Alloy steels including carbon, low alloy, stainless-(austentic, ferritic, martensitic, duplexes, age hardening), some nonferrous materials – nickel and cobalt base. Also including ultra high strength steels, heat resistant, corrosion resistant, wear resistant, and some tool steels. For a more comprehensive list go to “Alloys Poured”.

Value add services include machining, precision grinding, assembling, spray coating, plating, painting etc. Occasionally we are asked to support custom alloy requirements for our customers.

3. What size range of parts can be produced by our process?

We can produce parts from ounces up to approx 150 lbs. Dimensionally we are able to handle parts that when assembled on a sprue fit into a cube of approximately 20” x 18” x 18”. If unsure or you have any questions about our capacity contact us at inquiry@precisecastings.ca

4. What “as cast” dimensional tolerances I can expect?

The Investment casting institute publishes a standard generally accepted and adopted by Investment casting operations across the globe. This varies depending on the size and complexity of the part. In addition straightening or specialty foundry operations may be used to improve tolerances on critical dimensions. We recommend that every part and its application be discussed and designed with input from our technical people.
Premium tolerances should be applied only to those “as cast” features which are considered critical relating to function and reliability or where a feature cannot be machined.

Examples of our tolerances include:
A. Linear Tolerances.
Up to 1/2″ +-.007″
up to 1″ +-.010″
every inch after add another +- .005″

B. Minimum Wall Thickness.
Alloy Small Area Normal
300 Series SS .050″ .80″
Cobalt Alloys .50″ .80″
400 Series SS .060″ .90″
Carbon Steels .60″ .90″

C. Angles.
As cast tolerances of angles depends on their location in casing. They range from +- ½ deg. Design tolerance may be as large as 2 degrees (or more) where a large distortion could be expected.

For a more comprehensive list of tolerances see design data.

5. What type of surface finish can I expect from an investment casting?

Because of the type of process – fine ceramic shell is built around smooth pattern made by injecting of the wax into a polished aluminum die. Casting surface is excellent. See the table below.

Casting Surface Finish.
RMS Range 60-170 (depending on material)
Standard RMS 125

6. How to get the best value from Investment castings

When you consider any process consider the total finished cost of the item. Be it forging, fabrication, machined or casting, it is your total cost that is often the key driver in your decision. Value added features such as consistent near net shape castings, superior as cast surface finish and appearance, cast part numbers, logos and other important branding considerations and are enhancements not easily included with other processes. Many parts that require miscellaneous machining operations or fabrication can be investment cast to full customer satisfaction. Often our parts become an integral part of a fabrication or machined assembly. Again, it is important for our customers to meet us and discuss your requirements to realize the potential value and savings.

7. How many pieces do I need to order to make precision investment castings the right solution?

Tooling amortization is often a key factor when deciding whether or not an investment casting is feasible. Our ability to provide rapid prototype patterns will actually allow us to make castings without hard tooling costs. The answer is to simply contact us at inquiry@precisecastings.ca or give us a call and together we can explore your best options. Investment casting is one of the most versatile casting processes known.

8. What is the most efficient way to quote an investment casting?

The best way to quote a new investment cast part is to establish direct communication with one of our team members. Discuss your needs and supply as much information as possible including a drawing (and sample if possible). If you can, provide an actual weight, material specs, condition required (kind of heat treatment, NDT, any special requirements such as surface quality, etc.). Also indentify critical dimensions or surfaces and service of the part. Our technical team may offer suggested design changes or considerations when mutual benefit may be realized.

9. What type of tooling is necessary to make a wax pattern?

With today’s technology on low volume, one offs, rapid prototype wax patterns can be produced avoiding hard tooling costs. For any type of future or repeat production needs we strongly encourage the development of hard tooling right from the start. Usually, a split cavity aluminum die is manufactured which is a negative of the final part increased by a shrink factor of the wax and steel. Depending on the complexity of the casting, various combinations of the aluminum, ceramic or soluble cores may be employed to produce a desired configuration. Most tooling price range is within $1,500 – $10,000. Very complicated tooling or high production automated tools can exceed this price range. This tooling is a customer’s property.

10. What about casting integrity?

Investment castings are in a league by themselves and are being used for many commercial and critical applications with a great success. In many material applications and in the appropriate size range investment casting is the “go to” process of choice. We go to extra lengths to ensure your confidence often doing pre-production x-ray and other examinations to bring confidence in your experience of purchasing from Precise Castings Inc.

11. What lead times can I expect when ordering an investment casting?

With rapid prototype capabilities lead times can be very short such as three weeks from receipt of your drawing but a regular quote standard might be 6-12 weeks for tooling and sample castings and another 6-8 weeks for production. The best time to start is now. It does take a few days to generate the initial quote as we work with local toolmakers to design the most reliable, competitive tooling for your needs. If you even remotely think you may have an application or need for lost wax investment castings contact us today.

12. When Should I Contact Precise Castings?

Make the Investment Caster an important part of your product design team. No one will know your product better than you but we can certainly identify areas of concern if your intention is cost, material and time savings in the casting process. Our knowledge of the metal processing industry will enable you to choose the right steps to produce your parts in the fastest, most cost effective manner.

Often, simple, non-functional design changes can be incorporated which will drastically reduce tooling costs.

One of the most attractive aspects of the investment casting process is the versatility of design. The casting buyer should take full advantage of the expertise offered by the foundry’s engineers. This will not only ensure the lowest possible product cost, but will help to prevent costly delays due to re-engineering.

Quick contact at any time is inquiry@precisecastings.ca