The Casting Process
Casting is a process whereby molten metal is poured into mould and cooled to create an object. The process of casting involves a number of key steps and is a daily process within our fully operational precious metal casting plant. Morris & Watson have been using this process or similar processes for the last 40 years.
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’ll note your spruing, processing and delivery requirements for one off casting and large runs for production manufacturing.
Before we begin, we work closely with our wax room to ensure all your special requirements are understood. Precious metal prices change often 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.
A new master pattern is photo imaged for personalised identification and tracking for ease when ordering in the future.
The new master pattern is rubber moulded either by standard rubber (rubber packed, pressure vulcanized, cut and quality checked) or cold liquid moulded (24hr cure) for waxes or delicate patterns that will not sustain any heat or pressure. The new rubber is then distributed to the waxer with all the details of the job – the client, code name, order number, alloy, number required, any notes and of course the image.
The waxing technician makes the waxes by an injection of a hot wax into the rubber mould by 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 alloy’s 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. The wax trees have stainless steel flasks (tubes) placed over them to allow a casting mould to be made.
Next, the flasked trees are invested, a process that covers the wax trees with a slurry of special material called an 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 request from the vault. Meanwhile, the moulds/flasks are placed in an oven which climbs slowly to 720 Celcius (1330 Fahrenheit) throughout the night. The flasks are then ready to cast the following morning.
Working out the Metal Requirement
The caster weighs out the different amounts of metal required and organizes the flasks into the correct casting sequence.
The 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. The hot flask is quenched into water approx. 10 minutes after casting. The water violently 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, pickle acid, very 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.
The castings are sorted into their styles and deposited onto the work cards, which dictate the client, alloy, number 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. The cast run is invoiced and couriered to the clients.