The casting technique consists mainly in preparing a cavity called a “mould” which is a copy of the negative of the piece being made. The alloy is poured in its cast state. Once it has solidified, the alloy is extracted from the mould in its unrefined state.
It is very similar to the final piece but lacks some machining allowances (the parts to be taken away by the machine tools so that functional surfaces can be made). The sand casting (or green method) can only be carried out once and is destroyed after the unrefined form is extracted (see diagram).
Benefits:
- production versatility;
- economical;
- possibility of creating complex shapes;
- possibility of using different alloys (ferrous or non-ferrous);
Range of typical roughness for production process (expressed in RMS unit): 560 < RMS < 900
Ghisa grigia EN-GJL-200
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[/av_image] [/av_one_fourth][/av_section][av_section min_height=” min_height_px=’500px’ padding=’default’ shadow=’no-shadow’ bottom_border=’no-border-styling’ id=’#sabbia_resina’ color=’main_color’ custom_bg=” src=’https://staging.fv-cast.com/wp-content/uploads/2016/04/resin2-49-1412262467.jpg’ attachment=’72’ attachment_size=’full’ attach=’scroll’ position=’top left’ repeat=’no-repeat’ video=” video_ratio=’16:9′ overlay_enable=’aviaTBoverlay_enable’ overlay_opacity=’0.6′ overlay_color=’#162747′ overlay_pattern=” overlay_custom_pattern=”] [av_heading tag=’h2′ padding=’10’ heading=’RESIN SAND CASTING’ color=’custom-color-heading’ style=’blockquote modern-quote modern-centered’ custom_font=’#ffffff’ size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading] [av_textblock size=” font_color=’custom’ color=’#ffffff’] The resin sand casting process, conceptually similar to sand casting process, has peculiarities as the type of elements used in the making of the mold.
It takes, phenolic resins and urea-furan which, together with a chemical catalyst, are mixed before forming to the sand.
This mixture generates a significant hardening of the sand, considerably improving the quality of castings products both in terms of surface quality (with a reduction of the surface roughness), both with respect to the design dimensions, while also avoiding the possible breakage of the mold during the pouring phase.
Benefits:
- production versatility;
- economic;
- possibility of creating complex shapes;
- possibility of using different alloys (ferrous or non-ferrous);
- better surface ruoughness compared with standard sand casting.
Range of typicol roughness for production process (expressed in RMS unit): 200 < RMS < 560
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[av_heading tag=’h2′ padding=’10’ heading=’SHELL MOLD CASTING’ color=” style=’blockquote modern-quote modern-centered’ custom_font=’#ffffff’ size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]
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The shell mould casting process is a transient forming method similar to the green sand casting, in which the molten metal is poured into an expendable mold.
Here the mold is a shell characterized by thin-walled shell generated by the application of a sand-resin mixture on a pattern.
The pattern, made of metal as the piece to be produced, is reused for the entire production of the shells. This allows high production quantities, something not achievable with the use of disposable molds.
This technique can be used with both ferrous and non-ferrous alloys, but a limitation consists in the dimensions of the castings which are small – medium where, however, high accuracy is required.
Benefit:
- used on complex geometry items with complex details
- high surface quality
- reduction of dimensional tolerances
- possibility to use different alloys (ferrous and no-ferrous)
- high production quantities
- low cost of machinings
- small amounts of waste pieces
Range of typical roughness for production process (expressed in RMS unit): 120 < RMS < 200
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GIRANTE
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[av_heading heading=’PERMANENT MOLD CASTING’ tag=’h2′ style=’blockquote modern-quote modern-centered’ size=” subheading_active=” subheading_size=’15’ padding=’10’ color=’custom-color-heading’ custom_font=’#ffffff’][/av_heading]
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Permanent mould is a metal casting process where a metal mould is used and it can be reused for several thousand cycles. The mould is usually realized by steel or cast iron and it represent the negative shape of the final component. Inside the mould the metal is poured by gravity, contrarily to the die casting process where the metal is forcibly injected inside the mould.
This process is usually used for high-volume of small, with uniform wall thickness.
The permanent mould casting has three main characteristics: it is limited to low- melting-point metals (aluminum, copper…), cost and life durability of moulds higher than sand castings and resin sand castings, but lower than die casting moulds.
Benefit:
- possibility of using different alloys (typically non ferrous one)
- high mechanical properties
- high surface quality (low rugosity)
- low porosity
- low lobor cost
- scrab can be recycled
One of the chamber plate moves and pushes the mixture onto the other plate creating the mould. After squeezing, the second plate swings open and the opposite plate pushes the finished mould onto a conveyor until the pouring area. In the meantime the chamber is closed again and mew mixture is injected inside to create a new mould.
All process is totally automatic and this permit to produce castings with very high quality characteristics, with very high dimensional precision and high quantity. This last point is the only one disadvantage of the process: it needs very high quantity of items to be produced, as in the die casting process.
Benefits:
- high quality surface
- reduction of dimensional tolerances
- high production quantity
- reduction of wall thickness
Range of typical roughness for production process (expressed in RMS unit): 100 < RMS < 200
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[av_heading tag=’h2′ padding=’10’ heading=’LOST WAX CASTING’ color=’custom-color-heading’ style=’blockquote modern-quote modern-centered’ custom_font=’#ffffff’ size=” subheading_active=” subheading_size=’15’ custom_class=” admin_preview_bg=” av-desktop-hide=” av-medium-hide=” av-small-hide=” av-mini-hide=” av-medium-font-size-title=” av-small-font-size-title=” av-mini-font-size-title=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=”][/av_heading]
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The lost wax casting method (or micro-fusion) is another technique of disposable shaping whereby a wax model is prepared, usually by means of pressure casting, and is volatilized in an oven thus generating a cavity which is then filled with cast metal. The first step therefore involves producing the wax models with each mould making one piece.
After having placed the models in a cluster, complete with an alimentation channel which is also made of wax, it is covered with a ceramic paste followed by a watery refractory mixture which is then solidified (investment flask casting).
The thickness of the covering material must be sufficient to resist the heat and pressure when the cast metal is put in. If necessary, the covering of the cluster of models can be repeated until the density of the covering has the characteristics necessary to resist the heat.
At this point the structure is placed in the oven where the wax melts and it becomes, volatilised, leaving the shape ready to be filled with metal. The objects created by this method are very similar to the original and are accurate in detail.
Benefits:
- high quality surface;
- production flexibility;
- reduction of dimensional tolerance;
- possibility of using different alloys (ferrous and non – ferrous).
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[/av_image] [/av_one_fourth][av_one_fourth min_height=” vertical_alignment=” space=” custom_margin=” margin=’0px’ padding=’0px’ border=” border_color=” radius=’0px’ background_color=” src=” background_position=’top left’ background_repeat=’no-repeat’ animation=”] [av_image src=’https://staging.fv-cast.com/wp-content/uploads/2016/04/disco-1412349265.6657-1412868164.7347.jpg’ attachment=’105′ attachment_size=’full’ align=’center’ styling=” hover=” link=’lightbox’ target=” caption=” font_size=” appearance=” overlay_opacity=’0.4′ overlay_color=’#000000′ overlay_text_color=’#ffffff’ animation=’no-animation’ admin_preview_bg=”] GIRANTE
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[/av_image] [/av_one_fourth][/av_section][av_section min_height=” min_height_px=’500px’ padding=’default’ shadow=’no-shadow’ bottom_border=’no-border-styling’ id=’lost_foam’ color=’main_color’ custom_bg=” src=” attachment=” attachment_size=” attach=’scroll’ position=’top left’ repeat=’no-repeat’ video=” video_ratio=’16:9′ overlay_opacity=’0.6′ overlay_color=’#162747′ overlay_pattern=” overlay_custom_pattern=”] [av_heading heading=’LOST FOAM CASTING’ tag=’h2′ style=’blockquote modern-quote modern-centered’ size=” subheading_active=” subheading_size=’15’ padding=’10’ color=” custom_font=’#ffffff’][/av_heading] [av_textblock size=” font_color=” color=’#ffffff’] The Lost Foam casting is a type of the previously analysed ancient lost wax system. In this case the model is made of polystyrene foam (usually known as polystyrene) or polymethyl methacrylate (PMMA) and the liquid metal is directly poured into it. The latter undergoes a thermal degradation and is progressively replaced by the cast metal that produces the final casting by solidification.
The model, that is the positive side of the piece to be cast, is varnished in order to get the smoothest possible surface, it is then covered with a ceramic layer and then dipped in a refractory material. At this point, after having connected it to the power supply, it is put on a frame and it is completely immersed in un-bonded sand. During the casting process, the cast metal, that is put straight into the cavities occupied by the foam model, causes the volatilization of the polystyrene (pyrolysis) in this way filling up the cavity that stays intact thanks to the presence of the ceramic material.
Benefits:
- possibility to use it for castings of different materials (cast iron, steel, aluminium,…);
- use either for small castings with cluster manufacturing techniques) or for large castings;
- use with particularly complex and irregular moulds with any undercuts (also by coupling some polymer layers with a heat-melting glue);
- elimination of the lost cores used in the traditional casting processes.
Die casting is a manufacturing process for producing metal parts by forcibly injected molten metal into a die cavity.
These die or mold cavities are created with hardened tool steel that have been previously machined to the net shape or near net shape of the die cast parts. This process allows products to be made with high level of accuracy and repeatability.
The ability of producing high detailed and high accuracy parts make die casting a suitable choice for mass produced product.
The die casting process usually produce parts using primarily non-ferrous metals, such as aluminum, magnesium, zinc and copper.
Benefits:
- high production rate
- suitable to produce complex shapes
- high surface quality and accuracy
- suitable to produce large parts
- low labor cost
- high strength parts
Range of typical roughness for production process (expressed in RMS unit): 60 < RMS < 120
The heating process is an operation, or a series of operations, by which a metal or a metal alloy, obtains some mechanical properties.
The metals undergo one or more thermal cycles in a given environmental status, and there is a constant monitoring of: temperature, duration and speed of the temperature changes, below the casting point or the casting period. During the hardening process the component is heated over the austenization temperature of the AC1 metal (this phase must be extremely slow in order to minimize the changes of the temperature between the superficial zones and the core of the component) and after having exposed it to an appropriate period at this temperature, it is cooled down to the room temperature faster than the critical hardening speed, thus obtaining a martensitic structure.
Benefits:
- the martensitic structure gives the component a high mechanical resistance.
TEMPERING
The hardened metals have a more or less high internal tension state, which in most cases, is necessary to eliminate or, at least reduce, before their use because they are very strong and are less tough. In this case, we resort to the tempering heat treatment that more or less changes the martensitic structure of the hardening, cancelling out the tensions and the fragility.
The tempering must be carried out after the hardening in order to avoid the danger of the creation of cracks (caused by the state of high tension of the hardened pieces). The tempering temperature must be chosen in order to obtain the best compromise between the hardness and the toughness characteristics. In fact, as the temperature increases, we obtain a progressive increase of the toughness, of the elongation and of the contraction and, correspondingly, a decrease in the hardness, of the resistance to the traction and of the exhaustion.
The period of the tempering temperature is decided according to the dimensions of the pieces and to the type of oven. The whole of the two heating treatments in sequence is called austempering. It is the typical treatment of special steels, the so-called reclamation steels; once they have been reclaimed they still have a good workability with the tools by the removal of shavings.
Benefits:
- elimination of the tensions and fragilities caused by hardening;
- elimination of the cracks in the hardened components.
QUENCH ANNEALING
The quench annealing allows the softening of the steel in order to render it more suitable for mechanic workings, to eliminate residual tensions and the effects of a plastic deformation, a welding or a previous heat treatment.
The quench annealing is absolutely necessary for the raw materials of casting in which it is necessary to eliminate the strong structural heterogeneities: in this last case, the heating is obtained at a higher temperature and with long periods of permanence.
This treatment helps the workability of the steels by cold plastic deformation, while it doesn’t help the workability for the tools due to their excessive softening.
Benefits:
- elimination of the residual tensions in castings;
- high simplification during the cooling phase;
- economic process.
This treatment is aimed to sharpen and homogenize the structure, particularly in the weakly alloy steels, where the structure obtained is mostly made up of ferrites and flaky perlites.
The structure and the hardness obtained are strictly connected to the dimension of the casting and the material used.
Benefit:
- homogeneity of the components used in the process.
The powder varnishing process is based on the creation of a high tension electrostatic field. The component to be varnished is positively charged and an air flow directs the negatively charged powder particles on the surface of the component, where they settle down due to the attraction of the positive electrostatic field.
HOT DIP-GALVANIZING
The hot dip-galvanizing is the process by which it is possible to coat a metallic manufactured item, usually a steel one, with zinc, in order to prevent its galvanic corrosion. This process, also called galvanization, consists in coating the ferrous items with a zinc layer by dipping them into melted zinc. The manufactured items, before being galvanized, must undergo a de-greasing process, that can be either mechanic or by dipping, in order to eliminate the grease, enamels and residues of the welding which can remain on the item after the previous workings.
Then the manufactured items are stripped in chloridric acid or, in the case of cast iron, with very hot caustic soda and only after this has taken place is it possible to dip the item in the zinc.
SANDBLASTING
Sandblasting is a dry superficial treatment (that is carried out inside a machine called a blast cabinet) during which some very small abrasive elements, usually spherical or conical, are forcefully propelled towards a surface.
This process aims at improving the appearance of the item, such as the removal of cold formed oxides by corrosion (like rust), the removal of residuals from welding and brazing, the elimination of small drips and stripping. During this process no chemical agent is used for the treatment of the items.