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Quick Reference Guide

Molding Processes

Molding Process Selection
The selection of the right process for a casting design should begin early in the design process. Some of the more important factors to consider are dimensional requirements, structural requirements, aesthetics, flow characteristics of alloy in mold, part complexity, machining requirements, surface finish, tooling cost, part cost and volume. Pentz Cast Solutions assists customers in determining the best process solution for their specific design requirements. To compare the different processes, refer to Aluminum Casting: Molding process Comparisons Chart (PDF).

Green Sand Molding Process - Precision
“Precision” means this process creates an improved surface finish, greater detail and higher degree of dimensional accuracy than conventional green sand molding processes.

Molten metal is gravity-fed into a mold made from a sand, clay and 3% moisture matrix (green sand). The moisture activates the clay to bond to the sand and impart the strength necessary to provide structure to the mold.

The mold is formed by packing the green sand mixture around a pattern. The pattern is removed and molten metal is poured into the mold cavity(s). The molten metal is allowed to cool and solidify as a casting in the mold. The sand mold is broken apart and the casting is removed for cleaning and secondary operations.

This process has many advantages. It is the most economical method of producing aluminum castings. The process is highly flexible and can be used to produce castings of any size, shape, or complexity. Castings can also be produced to near net shape, which reduces the amount of machining and finishing required. It is also environmentally friendly because the sand used to make the molds is reusable. We continuously circulate the sand every 2 hours to make new molds.

Automated Green Sand Molding Process
This process is similar to normal green sand molding except that a highly efficient automated molding system is used to build precision green sand molds in rapid succession. Our Sinto FOB II 16”X 20” can make a new mold every 30 seconds and handles molds up to 300 lbs. It also utilizes a quick tool change-over system that enables us to set up new tools in minutes.

Foundry Sands for Molding (bonded)
Sand is an aggregate material composed of tiny, loose grains of minerals and rocks which range in size from 10 mesh sieve to 250 mesh sieve or between 1/12th and 1/400th of an inch diameter. Pentz utilizes a high grade of sub-angular grained olivine sand. The sand is bonded by mixing it with bonding agent (bentonite clay) and activating the mixture with water. This sand produces superior molds that result in extremely high quality as cast finishes. Also see Foundry Sands for Core Making.

Green Sand Control
Green sand control is one of the most important elements of the green sand molding process. It enables the foundry to monitor and adjust the properties of the green sand mixture to the optimal levels for molding high quality precision castings. The moisture, grain size distribution, bond level and strength of the green sand mixture must be continuously monitored to maintain good sand control. Our sand control program includes lab testing based on continuous sampling plans and PLC-driven mulling control capable of controlling moisture to ±.1 % in real time. The end result of sand control is improved molding efficiency, less scrap, lower part cost and higher part quality.

Dry Sand Molding Process
Dry sand molding is similar to green sand molding in that it is a gravity-fed casting process that utilizes a sand mold. However, unlike green sand molds that are bonded by moisture and clay, dry sand molds use a dry sand and a binder devoid of moisture to form the mold. There are many types of dry sand molding including No Bake, Cold Box, Air Set, CO2, SO2 and chemically bonded. Dry sand methods are frequently used to make cores as well as molds.

Permanent Mold Process
The term “permanent mold” describes a mold that can be used repeatedly. This is in contrast to sand casting where the mold is destroyed each time a new casting
is poured. In the permanent mold process, molten metal is gravity poured into a cast iron two part mold coated with a ceramic mold wash. The mold is designed so it can be separated and the casting ejected after the casting solidifies in the mold.

Excellent for high strength (dense) and high volume castings. A single mold may produce up to 2 million castings before breaking down. Tooling cost can be significantly higher than for green sand processes.

Die Casting Molding Process
A casting process in which the molten metal is forced under high pressure (5000 psi or greater) into a metal mold cavity. It is widely used to produce large volumes of zinc, aluminum and magnesium castings in intricate shapes. Care must be taken with the design of the mold to avoid high pressure porosity in castings. It is most suitable for parts under 75 lbs. Equipment and die costs are high.

Investment Molding Process
A casting process in which a wax or thermoplastic pattern is used. The pattern is invested (surrounded) in a refractory slurry. After the mold is dry, the pattern is melted or burned out of the mold cavity and the molten metal poured into the resulting cavity. Accuracy and types of castings that can be made from this process vary greatly. Casting costs are typically higher and there are limitations on the size of the casting that can be produced. This process may be most beneficial for alloys that are difficult to machine, where casting costs can be offset by a reduction in machining costs.

Hog out
CNC machining a complete part from aluminum billet stock.

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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