Fundamentally, sand casting is a process where a mold is produced by shaping a refractory material to form a cavity of a desired shape such that molten metal can be poured into the cavity. The mold cavity needs to retain its shape until the metal has solidified and the casting is removed. This sounds easy to accomplish, but depending on the choice of metal, certain characteristics are demanded of the mold. As a sand casting manufacturer, Monmet has the knowledge and experience required to produce efficient molds.
Green Sand Molding
The most common method used in sand casting manufacturing is green sand molding. In this process, granular refractory sand is coated with a mixture of bentonite clay, water and, in some cases, other additives. The additives help to harden and hold the mold shape to withstand the pressures of the molten metal.
The green sand mixture is compacted through mechanical force or by hand around a pattern to create a mold. The mechanical force needed for the sand casting process can be induced by slinging, jolting, squeezing or by impact/impulse. 
For many metal applications, green sand casting processes are the most cost-effective of all metal forming operations; these processes readily lend themselves to automated systems for high-volume work as well as short runs and prototype work. In the case of slinging, manual jolt or squeeze molding to form the mold, wood or plastic pattern materials can be used. High-pressure, high-density sand casting and molding methods almost always require metal pattern equipment. High-pressure, high-density molding normally produces a well-compacted mold, which yields better surface finishes, casting dimensions and tolerances. The properties of green sand casting are adjustable within a wide range, making it possible to use this process with all types of green sand molding equipment and for a majority of alloys poured. As a sand casting manufacturer, Monmet offers green sand casting services which produce better molds.
Chemically Bonded Molding Systems
This category of sand casting processes is used widely throughout the metalcasting industry because of the economics and improved productivity each offers. Each process uses a unique chemical binder and catalyst to cure and harden the mold and/or core. Some processes require sand casting manufacturers to add heat during the process to facilitate the curing mechanism, though others do not. 
Gas Catalyzed or Coldbox Systems—Cold box sand casting systems utilize a family of binders where the catalyst is not added to the sand mixture. Catalysts in the form of a gas or vapor are added to the sand and resin component so the mixture will not cure until it is brought into contact with a catalyst agent. The sand-resin mixture is blown into a corebox to compact the sand, and a catalytic gas or vapor is permeated through the sand mixture, where the catalyst reacts with the resin component to harden the sand mixture almost instantly. Any sand casting mixture that has not come into contact with the catalyst is still capable of being cured, so many small cores can be produced from a large batch of mixed sand.
Several coldbox processes exist, including phenolic urethane/amine vapor, furan/SO2, acrylic/SO2 and sodium silicate/CO2. In general, coldbox processes offer good dimensional accuracy because the cores are cured without the use of heat, excellent casting surface finish, short production cycles that are optimal for high production runs, and excellent core and mold shelf life.
Nobake or Airset Systems—In order to improve productivity and eliminate the need for heat or gassing to cure mold and core binders, a series of resin systems referred to as nobake or airset binders were developed by sand casting manufacturers. 
In these sand casting systems, sand is mixed with one or two liquid resin components and a liquid catalyst component. As soon as the resin(s) and catalyst combine, a chemical reaction begins to take place that hardens (cures) the binder. The curing time can be lengthened or shortened based on the amount of catalyst used and the temperature of the refractory sand.
The mixed sand is placed against the pattern or into the corebox. Although the sand mixtures have good flowability, some form of compaction (usually vibration) is used to provide densification of the sand in the mold/core. After a period of time, the core/mold has cured sufficiently to allow stripping from the corebox or pattern without distortion. The cores/molds are then allowed to sit and thoroughly cure. After curing, they can accept a refractory wash or coating that provides a better surface finish on the casting and protects the sand in the mold from the heat and erosive action of the molten metal as it enters the mold cavity.
In nobake process, wood and in some cases plastic patterns and coreboxes can be used. Due to the rigidity of the mold, good sand casting dimensional tolerances are readily achievable, casting finishes are good, most of the systems allow easy shakeout (the separation of the casting from the mold after solidification is complete), and cores and molds can be stored indefinitely.
Rapid Prototyping (RP) is a general name that encompasses numerous methods used to fabricate objects from CAD data. There are a number of different RP processes, and new developments are constantly being made. RP most commonly is used with sand casting to produce an actual cast part to test for form, fit and function, as well as to determine the approximate final properties of the cast parts. In sand casting, RP-generated parts can be used as patterns for fabricating a sand mold. RP processes that use a material similar to wood are common. The sand casting molds are created in a fraction of the time and then affixed to the pattern board by the sand casting manufacturer before sand is packed around to create half of a mold cavity.
To save even more time, RP processes can be used to directly fabricate molds and cores. These sand casting processes build the cores and molds layer by layer by fusing either polymer-bonded sand together or using a wide-area inkjet to bond the sand. The molds and cores also may be created by forming a block of sand and machining out the cavity. For more information about our sand casting processes, please contact us.