very best out of every single part begins long before anything is cast.
It starts with knowing about the choices you can make to bring your
design to market—faster, better, at lower total cost—and finding out
how we’ve helped solve problems for others just like you.
INVESTMENT CASTING DESIGN GUIDE
In any manufacturing process, the price of a product will increase as the dimensional tolerance and inspection criteria become more stringent. Early involvement and input by Zealous’s technical staff allow customers to overcome traditional casting tolerance issues. This is accomplished by innovation and technology to provide 100% conformance to specifications as-cast, delivered on time, at the lowest total cost. The most important guideline to remember is to get Zealous involved early in the design stage.
Investment Casting Design Considerations
Size and Weight
Part size and weight are the most critical factors in determining part cost because mold capacity is limited by both size and weight. The more pieces that can run on a mold, the lower the part cost. Our design team will work with you to remove any unnecessary mass in an effort to reduce part weight.
Number of Gates
When possible, a part should be designed so that a single gate can feed the part. This will generally yield more pieces per mold and help to reduce the pour weight per mold. Single gate feeding also enhances the dimensional stability of a given part by providing a directional solidification pattern.
If a design contains features that will raise scrap or rework rates (and piece price), the Zealous Estimating Engineer will recommend design modifications to keep the piece price down.
Investment Cast Tooling
Zealous utilizes a system of tooling standards to ensure uniform high-quality design and fabrication of the wax injection die which is generally guaranteed for the life of the part. We offer several different types of tooling; manual, semi-automatic and fully automatic.
In addition, configurations that do not allow metal cores in tooling to be drawn due to undercuts or complicated internal shapes must be treated with one of our collapsible, soluble or ceramic core inserts.
Tolerances for Investment Casting
The investment casting process is capable of excellent repeatability. As-cast process capability of +/- three standard deviations when a single point location is repeatedly measured, is typically +/- .08 to +/- .1 per 25 mm. However, tolerance capability is largely influenced by part configuration. Symmetrical shapes with uniform wall sections will solidify with much less variation and distortion than non-symmetrical, non-uniform shapes.
Wall Thickness for Investment Castings
Minimum wall thickness and corner radii depend upon part configuration and size. Small investment castings may have walls cast to 1mm thickness. Medium to large castings require 1.5-2.5 mm walls depending on the part geometry.
Other design considerations include:
- Flatness and straightness
- Position and linear tolerance
- Surface texture
- Gate witness tolerances
- And holes
As-Cast Design Features
Did you know that Zealous is capable of casting other design features into components with little to no secondary operations? Our capabilities include:
Splines, Gears & Threads
Gear and thread profiles can be produced with accuracy of +/- .004” per .5” of pitch. Longer lengths or larger diameters can be held to normal or premium linear tolerances as necessary.
Normally, raised letters or numbers in protective depressed pads are easiest to manufacture. A .020” high character on a depressed pad yields sharp, castable features. Logos can be investment cast to almost any design.
Zealous performs a 100% visual inspection of
all parts. If dimensional verification is required, a sampling plan and
process control is less expensive than 100% gaging of each part. It is
important to remember that whenever custom gages are used, there should
be identical gages at Zealous and at the customer’s facility. Fixed
such as go-no-go are less expensive to use than gages with dial
Investment Casting Company
With world-leading engineering experts, rapid prototyping and delivery, and the most advanced investment casting facilities in the world, Zealous is redefining how today’s manufacturers create, refine, and deliver products. If you need high performance, design freedom, and flexibility, we should talk.
TOLERANCES FOR INVESTMENT CASTING
The investment casting process is capable of excellent, repeatable as-cast tolerances. With as cast capabilities of +/- three standard deviations when a single point is repeatedly measured—typically +/- 0.08 to +/- 0.1mm per 25mm. Since tolerance capability is largely influenced by part configuration, this can vary depending on your part design. However, symmetrical shapes with uniform wall sections solidify with significantly less variation than non-uniform and non-symmetrical wall sections.
Normal linear tolerances for normal dimensions reflect these three sources of variation:
- Prediction of part and shrinkage factors (20%)
- Diemaker and tooling, tolerance (10%)
- Process variation (70% of linear tolerance)
The variation in tolerance is a combination of part configuration effects that result in non-uniform shrinkage and all other process variation in producing a wax pattern, ceramic mold, and the casting.
Premium Linear Tolerances
All three sources of variation can be reduced by:
- Part redesign, including addition of tie bars, ribs, and gussets
- Tuning of wax injection tooling after the first sample to meet nominal dimensions
- Additional inspection/gaging
Premium tolerance capability can be achieved but must be considered on a part-by-part, dimension-by-dimension basis. Zealous is capable of holding +/- 0.05mm in some features, although +/-0 .1mm per 25mm is a more typical premium cast tolerance. It is important to designate tight tolerances that are necessary to part function and leave the rest open to normal linear tolerances.
General Linear Tolerances
Customers often ask us “What about dimensions that are on a drawing or CAD file simply to describe the shape?” These dimensions can be most economically produced by applying a broader general linear tolerance.
Another strategy that works well is to incorporate these types of features into a 3D CAD file for the part, but not dimension them for inspection purposes. The feature is then tooled per the design, but valuable inspection and evaluation time is used only for features important to the customer.
The Zealous Difference
Investment casting can produce parts of virtually any size, to almost any level of complexity, and can hold tolerances simply impossible using other methods. With our state-of-the-art equipment and automation, we can deliver the best performance and the lowest total cost for every component you develop. Contact our team today to experience the Zealous difference.