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Quick Reference Guide

Casting Design

Near Net Shape
Casting a part very close to the required end shape so that it requires almost no machining. Pentz produces castings to the closest to near net shape in the industry.

Reverse Engineering
In the casting industry, reverse engineering (RE) is the process of using an existing part as a model to create a CAD file to produce either a prototype or production parts. At Pentz, the CAD file is created from highly accurate digital images produced by laser scanning or by CMM measurement of an existing part. The CAD files may be used to produce prototype models from SLA or FDM prototyping methods or CNC machined tooling for production parts. Find out more about our Reverse Engineering Process.

Datum Points & Planes for Castings
A datum is the origin of dimensions. It is a feature on a part from which other dimensions or points are referenced to specified limits. The use of datum plane designations and locating points are critical factors in casting design. Careful consideration should be give to where datums are placed. They directly impact the ability of tooling, machining and inspection to meet requirements. We strongly recommend contacting us early in the design process to assist you in establishing datum locations. Contact our casting engineers for additional information about datum points and planes for castings.

Draft for Patterns & Castings
The term draft can apply to either a pattern or casting. Pattern Draft is the taper allowed on the vertical surface of a pattern to permit withdrawal of the casting from the mold. Casting draft is the actual draft angle on the casting. It is determined during the design process. Normally draft begins at the parting line. Draft angles vary up to 5° with 3° typical on most patterns.

Parting Line and Parting Line Tolerances
The mark or line on a casting formed at the junction of cope and drag section where the mold parts. Its location and draft are determined during the design process. It is normally removed by grinding and or sanding. The tolerances across parting lines are added to basic linear tolerances. See Dimensional Tolerance Tables.

Cast In Features
Features of a casting formed by the pattern, mold and cores rather than machined as a post-casting operation. Typical cast in features include walls, fillets, ribs and bosses. There are some general design guidelines for these features. The designer should, whenever possible, create tapers in features that widen as they get closer to metal feed points in the tool. In addition, when joining thicker and thinner features it is generally preferable to use a gradual taper to make them of uniform thickness where they intersect. Fillets should be used at intersecting surfaces for improved flow characteristics in tooling and to provide for more uniform distribution of stress in service.

Cored Out Features
Features formed by cores inserted into a mold. Typically they are hollowed-out interior or cavity features in a casting which could not be formed using a pattern or by machining. Tolerances for cored out features should be somewhat looser than tolerances for features formed by the pattern.

Metal Inserts, Cast in Part
Metal inserts may be cast into parts by placing the inserts into the mold before pouring the alloy. Cast in insets are typically used when they are to function under very heavy stress loads. Most inserts are made of steel or iron that is machined or cast. Sufficient metal thickness should be allowed around the insert to encapsulate it sufficiently to prevent it from cracking the casting.

Finish Allowance
Additional cast on material (machine stock) that is to be machined away from the surface of the casting. Finish allowances should be specified on the part drawing using commonly recognized symbols for finish allowance Pentz can assist with this. See Dimensional Tolerance Tables for Typical Machine Tolerances.

Surface Finish “As Cast”
"As cast” finish is typically 200-500 RMS depending on alloy, size of part, molding process and tooling quality.

Pressure Tight / Vacuum Tight
The ability of a casting to be impenetrable to gas or liquid under pressure. With our processes there is no need to impregnate the metal with special coatings to achieve
pressure tight/vacuum tight performance. Our processes are engineered to produce pressure tight/vacuum tight castings using rotary degassing, flux injection and special certified alloys. Click here to see pressure tight/vacuum tight applications.

Corrosion Resistance
Corrosion resistance is the resistance of alloys to loss of volume, strength, or surface appearance after exposure to various environments. Contact a Pentz engineer for help in selecting the aluminum alloy best suited to meeting your corrosion resistance requirements.

Basic Linear Tolerances
Basic linear tolerances refer to dimensional tolerances that are attainable within the same mold half. Additional tolerances for machine allowances, coring and parting lines should also be considered in dimensioning the overall casting. See Dimensional Tolerance Tables below.

Dimension Tolerance Tables
View Dimension Tolerance Tables (PDF) for tables of basic linear tolerances, additional tolerances for dimensions across parting lines and typical machine finish allowances for green sand and permanent mold processes.

Pattern Shrink Factor

The allowances made in the pattern to compensate for changes in volume of metal during casting. Rates of shrinkage vary with the type of alloy cast, tool design and casting process used. Pentz calculates the shrink factor required in the pattern for you.

Lettering and Graphics
Letters or graphics can be cast in as raised or recessed images. The image may be created by several methods. The most common method is to use customer-supplied art work to create a photo-etched plate that is assembled into a pattern. Another increasingly popular method is to use data from 3D CAD files to CNC machine a 3D image directly into the pattern.

Letter or graphic images should be oriented at or near parallel to the parting plane, whenever possible. Cores can be used to incorporate lettering or graphics that are oriented perpendicular or vertical to the parting plane.

RMS (Root Mean Square)
Standard method to specify the texture/roughness of a surface of a casting finish.

Note: Each section contains information about specific subjects or terms as they apply to Pentz Cast Solutions. The Guide is as accurate as possible; however, all material is provided without warranty of any kind.

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