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You are in the section: Production techniques
 
Le tecniche di progettazione e produzione
 

The foundry process is an ancient technology for casting metal objects.
Simply put, a cavity is created in a heat-resistant medium such as sand, earth or plaster.
The negative shape of the cavity mirrors the desired form of the finished piece. Molten metal is poured into this cavity and when cooled forms a duplicate of the original model.

The two principal casting techniques used by De Venieri are earthen casting (terra) and lost wax casting (cera persa). The particular shape and surface contours of the object under design will determine which of these two methods is employed.
In either process, it is essential that the original master model be created with the utmost precision.



EARTHEN MOLDS

Several rules govern the preparation of a model and its mold when earthen casting is to be used:

- The model must not have sharp, inside corners as these tend to propagate cracking during the cooling process.
- The model should be very slightly oversized to allow for the shrinkage that occurs when molten metal cools.
- Certain portions of the model may require additional thickness or diameter in anticipation of an eventual machining phase where a final dimension must be achieved with high precision.
- The form and surface of the model must be made in such a way as to avoid “undercuts” that would make it impossible to remove the model from the earthen mold after making an impression of its surface.

This last consideration is the one that determines whether earthen casting or lost wax process is required. Casting in earth requires a molding box. This is basically a pair of bottomless containers with registration keys allowing them to fit together perfectly time after time.
They are usually made of steel for strength and stability.

The basic steps in this casting technique are the following:

- Divide the master model into two halves that are mirror images of each other with small, precise registration points at the parting surfaces that allow the precise eventual coupling of the two halves;
- Place each of the two halves on a flat surface;
- Place a molding box over one half-model and fill with foundry sand through ports on the top surface and compact it;
- Invert the molding box and place the other half of the split model onto the half that is immersed in the casting earth;
- Place the second molding box over the first and fill with foundry earth and compact it;
- Separate the two molding boxes and remove the two halves of the model, leaving a perfect half-impression of the full model on the surface of the casting earth in both boxes;
- Carefully sculpt identical pouring channels leading from the perimeter to points on the model so that when the two boxes are joined together, there is a pathway for the molten metal to enter the formed cavity;
- Put the two molding boxes together once again, creating between them a cavity that is the precise negative shape of the object being cast;
- Place the joined boxes so that the openings to the pouring channels are uppermost and pour molten metal until the entire cavity is filled and the material begins to overflow the pouring channels;
- After the metal has cooled, the two halves of the molding box can be parted and the casting removed.

Once the casting process is completed, the final machining and polishing can be performed.



LOST WAX PROCESS

This technique is adopted in cases where the specific shape or contours of the model cannot be captured in the earthen casting method.
There are two traditional approaches to lost wax casting.
One uses an original found object as the casting model while the other approach requires the artisan to create an original casting model by careful mechanical up-scaling of the original and meticulous hand sculpting.
In each case, because of the shrinkage factor, the cast part will be somewhat smaller than the object used as the casting model.

When the goal is to realize an object that exists only as a drawing of an idea in the mind of the designer, the inevitable shrinkage can be compensated for in the crafting of the model.
Frequently, however, the goal of the craftsmen is to create exact duplicates of a found object.
This will always require the artisan to fashion a unique casting model that is, in fact, slightly larger than the object to be duplicated.

This technology of fusion is developed using the following procedure:

- A perfect model must be created;
- A mold of flexible rubber or silicone is made in two halves from this model in order to create multiple wax duplicates of the model;
- Liquid wax is injected under pressure into the mold;
- when cooled down, the wax model is extracted from the flexible mold;
- The wax model is completed by connecting funnel-shaped wax parts to create pouring channels for the wax to exit and for the molten metal to enter the cavity;
- The model is then coated with a mixture of refractory silica sand to create a firm, heat-conducting support;
- Then, the mold is placed upside down in a heated kiln until the wax melts out through the pouring channels, leaving behind a perfectly-formed empty cavity;
- Molten metal is then poured into this empty cavity;
- After cooling, the refractory sand is chipped away, freeing the cast piece, now ready for the finishing process.




De Venieri is able to duplicate precious objects or realize original pieces in quantity using these time-tested techniques.

The photo gallery that follows illustrates the various stages of workmanship necessary to create a model suitable for casting.

 
Interno laser
Risultato scansione
Disegno oggetto 3D
Interno laser
Risultato scansione
Disegno oggetto 3D
 
Disegno matrice 3D
Disegno matrice 3D
Percorso utensile per matrice
Disegno matrice 3D
Disegno matrice 3D
Percorso utensile per matrice
 
Percorso utensile per matrice
Lavorazione fresa CN
Lavorazione fresa CN
Percorso utensile per matrice
Lavorazione fresa CN
Lavorazione fresa CN
 
Matrice
Creazione modello per fusione in resina
Matrice
Creazione modello per fusione in resina
 
 

 

 
 
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