The Casting Process

Casting is a process whereby molten metal is poured into mould that has created a negative impression of a pattern (such as a ring) to create an cast metal object. The process of casting involves a number of key steps and is a daily process within our extensive precious metal casting department. Morris & Watson have been using this process or similar processes for the last 40 years.

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Initial Contact

We will discuss all your requirements whether it be a re-run or a brand new master pattern or if you required a CAD design and 3D print. We will note your spruing, processing and delivery requirements for one off casting and large runs for production manufacturing.

Order Placement

Before we begin, we work closely with our wax room to ensure all your special requirements are understood. Precious metal prices change often (daily) so we use the order placement date and time stamp to denote the metal price used for the order. This is the base of the invoice. Electronic instruction is given to the wax room.

Image Creation

A new master pattern is photo imaged for personalised identification and tracking for ease when ordering in the future.

Jewellery Casting Process Yellow Gold Tree

Rubber Moulding

The new master pattern is rubber moulded either by standard rubber (rubber packed, pressure vulcanized, cut and quality checked) or cold liquid (silicone) moulded (24hr cure) for waxes or delicate patterns that will not sustain any heat or pressure. The newly created mould is then given to the waxing technician with all the details of the job, such as; client name, mould code, order number, alloy, number of casts required, special order notes and an image of piece.

Jewellery Casting Process Furnace Melting

Waxing

The waxing technician creates the waxes by injecting hot wax into the mould, using a pressurized vacuum assisted wax pot. These wax impressions as well as any waxes that come from the 3D printing process, are grouped into their respective alloys and treed (connected onto a main stem) by a solder iron. There are approximately 120 waxes per tree.

The wax trees are weighed to determine the amount of precious metal required to cast the tree in each particular alloy, using the specific gravity conversion factor for that specific alloy.

The wax trees have stainless steel flasks (tubes) placed over them to allow a casting mould to be made.

Investing

Next, the flasked trees are invested. Investing is a process that covers the wax trees with a slurry of special material called investment. This is done under vacuum by a special investing machine, forming the cast mould. The moulds/flasks are allowed to dry until they are hard. They are then marked with a number that denotes the amount of metal required to cast the trees plus the alloy type. The total amount of the metal required for the cast run is requested from the vault.

Next, the moulds/flasks are placed in an oven to vapourise the original wax mass in a process called "burn out". To ensure the best impression is made, the burn out cycle utilises a specific heating programme structure and eventually climbs to 720 Celcius (1330 Fahrenheit) over many hours (typically throughout the night). The burn out process is smokeless and produces steam as the gas product. This over process is called "Lost Wax Casting"

The investment mass is now hollow with the negative impression of the wax patterns and the flasks are now ready to accept molten metal.

Determining the Metal Requirement

The casting techician weighs out the different amounts of metal required and organizes the flasks into the correct casting sequence.

Casting

The casting metal is melted in a special casting machine that is programmed to insert the metal under vacuum into the flask at the right time, temperature and rate. After the cast has taken place, the hot flask is quenched into water approx. 10 minutes after casting. The water reacts and dissolves the majority of the investment material around the flask exposing the cast tree. The cast tree is an exact replica of the wax tree.

Cleaning & Sprue Removal

The tree is cleaned with water-blasting, pickling in acid, fine glass bead blasting and ultrasonic cleaning. The dried tree is weighed and compared with the start weight. The melt loss is recorded. The tree has the castings removed from the main stem by a pneumatic cutter. The trees and casting are weighed again to double check the original weight is correct and no casting pieces have been misplaced in the cutting off process.

Quality Control

The castings are sorted into their styles and deposited onto the work cards, which dictate the client name and number, alloy, number castings required and order number. The castings are quality checked, with rejects ordered to be recast in the following days cast. The castings have all their sprues and feeders hand clipped off.

Invoicing & Dispatch

The castings are laid out in client and numeral sequence ready for dispatch. The castings are weighed, computer recorded and bagged for dispatch. After all the castings have been processed the cast is balanced, invoiced castings + scrap + rejects must equal the cast weight. All the scrap and left over metal is returned to the vault to be recycled or refined. The cast run is invoiced and the resulting castings are supplied to clients.

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