An important phase of additive manufacturing production is that dedicated to post-processing activities. For metal productions, our internal finishing department carries out various activities useful to guarantee the expected result: from depowdering to EDM, from painting to welding.
Following the extraction of the piece from the machine, the residual powder is removed. This is a crucial operation, especially when there are internal cavities or cracks, or when the component has complex geometries; in the subsequent phases, such as cutting or heat treatments, the residual powder could partially sinter, and it is therefore necessary to proceed with an accurate removal. Depowdering can take place mechanically, or through special blowing and 5-axis vibro-rotation systems.
Detachment of the plate
After depowdering, the piece is detached from the construction plate. This phase is made easier if, during the definition of the production job, the supports are correctly designed. A correct design allows not only to obtain a simple and minimally invasive detachment, but also to guarantee adequate heat dissipation during production so as to avoid the formation of residual stresses and deformations.
Electrical discharge machining (EDM)
To cut the piece we use an EDM system with a water jet that does not include submerging in a tank, but which only works on the affected area. The process is thus faster than normal erosion and avoids the loss of conductivity. The extreme precision given by this type of cut allows to reduce the quantity of support material, to reduce the printing time and, consequently, to reduce costs for the end customer.
The main operation that characterises this phase is the removal of construction supports through manual or sometimes even CNC operations. The component is then roughed using abrasives with different grits and cutters up to the polishing with felt. According to the project specifications, tumbling can also be used at this stage.
The result is a finish equal to that of the micro-melting process, characterised by uniform roughness (Ra of 4/5µm); all pieces are finished unless specifically requested by the customer.
The pieces will then be checked within the quality control department in order to certify the finishing phase.
Sandblasting blasting allows to make the surface of the piece uniform and uses different types of abrasives such as:
- corundum, particularly abrasive, makes the surface satin and removes all impurities;
- zirconia, which allows to obtain a very shiny surface and is a good decontaminant; it is often used after shot peening with steel to eliminate oxide residues;
The abrasive is chosen according to the finish to be obtained or, in some cases, according to the metal with which the piece was made.
Unless specifically requested by the customer and with the exception of medical prostheses, all parts are sandblasted.
Polishing, satin finishing and brushing
Components made in additive manufacturing are generally complex in shape and more rough than other production methods. Polishing therefore requires specific preparation and only expert and specially trained employees can take care of this activity.
Polishing can also take place in the internal cavities by means of special micro-brushes that allow to eliminate the partially sintered dust on the component or through chemical milling systems.
The satin finish and brushing give aesthetic homogeneity, the first giving the surface a matt appearance, the second creating a brushed finish.
Polishing, satin finishing and brushing are manual activities. Additive manufacturing is largely used for prototypes, pre-series, and small productions and it is therefore not very convenient to adopt industrial solutions that can replace manual processing.
The Zare Additive Team includes specialised personnel equipped with the techniques and manual skills that allow to obtain an excellent result on the piece produced via additive manufacturing.
The painting allows the customer to define the colour from RAL or Pantone and can be made with powders, by spray or by cataphoresis.
Screen printing and pad printing
Screen printing and pad printing allow the application of a layer of paint selectively using a screen printing frame. Screen printing is used on flat surfaces, whereas pad printing is for curved surfaces.
Laser marking is imprinted on the components and is particularly useful for tracing the pieces, it can also be carried out on curved surfaces.
Additive integration allows you to take full advantage of both the benefits of additive design and the precision of CNC machines, integrating additive and subtractive manufacturing. Additive integration also means industrialising the product in view of a combined production.
A common example is the provision, with relative insertion in the drawing of the piece that will be produced through additive manufacturing, of specific clamps for the CNC machine in order to reduce the placements in the machine tool and allow a precise and quick production.
Additive integration also means short supply chain, it means setting each phase in the best possible way so that it facilitates the next.
When a component is produced through additive manufacturing, a direction that reduces supports is usually preferred in order to speed up production and reduce manual post-processing. If, on the other hand, a subsequent CNC machining is required, a direction will be preferred that eliminates the risk of deformations on the component and facilitates the process by machine tool, improving the precision of the final piece.
Mechanical machining is essential when tolerances are tight, when special finishes are required or when very low roughness is expected.
Threading and boring
Also in additive components it is possible to place inserts, bushings, pins according to the characteristics of the project or to make threads or bores of nominal size directly on the component.
Impregnation is a protective treatment that allows to close the micropores of the material ensuring a greater seal of the component.
Welding and gluing
Welding allows the union of two joints by melting them, or by means of filler metal; TIG welding is mainly used.
The gluing allows the joining between several parts not through the fusion of the edges, but through structural adhesives and requires an ad hoc design. Different types of glue are used, specific for each application (eg for the marine environment, for applications where resistance to chemical agents is required, etc.).