Sand Casting Pattern

Process Overview

A mold made through pattern pressing on a sand mixture is used in our process of eco-friendly sand casting. A cavity is left by the pattern in which we pour the molten metal. For high-volume production, automated equipment can be very helpful.

Types of Patterns

There are three basic types of sand casting patterns:

• Loose Patterns – They are simply the replica of the cast piece. These patterns are not mounted on a plate and they are not linked to other patterns.
• Match Patterns – They are quite similar to drag and cope patterns except the fact that the drag and cope sides are combined into one piece.
• Cope & Drag patterns – Also known as split patterns, cope and drag patterns are much like loose patterns with a split and system attached with the parting line.

It is quite simple to produce cast metal parts and sand molds and they are best suited for automated methods which can reduce labor cost and cycle time. However, it is, sometimes, expensive, time consuming and difficult to fabricate the patterns.

Producing aluminum patterns through CNC machines is a certainly a common approach. The long lead time and high cost is the major issue in this approach. Design flaws and inaccurate shrink compensation are the major risks of problems. It means the initial pattern should be redone and it adds to the lead time and expenses.

Machining the intricate runner and gate systems is not commonly practical on CNC machines as it needs testing to finalize the design. Instead the runner system and gate is cut through a material called Ren board and it is hand-crafted and sanded to get the ideal shape. Building a gate system takes lead time and cost.

Due to the problems related to the production of traditional patterns, we have long been into 3D printing industry, which is also known as additive manufacturing. When the foundries of 3D printing system can fabricate the patterns using FDM technology, it can significantly save the labor, cost, and time and ultimately speed up the new production development.

Printing Steps

• 1. 3D Master Printing – We design a master in CAD which can improve the productivity of FDM and inkjet printer. After printing the master, it becomes a pattern with the best parameters for the desired surface strength and finish.
• 2. Accommodate Parting – Mount the pattern on parting line aspects that can be 3D printed fixtures by inkjet or FDM. The printing line is helpful to avoid issues through undercuts.
• 3. Apply surface release agent on master pattern.
• 4. Mount the parting line elements and casting pattern on wooden plate. These elements will be fixed to the plate.
• 5. Create a Mold – The sand is poured around the parting line element and pattern and the pattern is removed. A cavity is known to appear in the pattern shape and the upper half forms the cope and lower part forms the drag.
• 6. Using Mold – Molten metal is poured into the cavity. It can be finished and removed once it cools.

FDM Technology in Sand Casting

All of the thermoplastics that FDM technology uses have the high compressive strength required for green sand casting patterns. The surface finish of the FDM master can be optimized through build orientation and/or through a secondary process such as sanding. The Finishing Touch Smoothing Station uses a semi–automated process to smooth FDM parts to near–injection-molded quality. This also seals the mold surface, which keeps the release agent from penetrating and sand from sticking. The ability to build highly accurate, large, complex patterns fast and inexpensively makes FDM a clear advantage over traditional methods.