Introduction of Die Casting (Hot Working Technology)

Casting is one of the oldest metal working techniques known to man. Our country made metal castings as early as 2000 B.C., and the process used then is not much different in principle from the one used today.

Foundry processes consist of making molds, preparing and melting the metal, pouring the metal into the molds, and cleaning the castings. The product of the foundry is casting, which may vary from a fraction of a kilogram to several hundred tons. It may also vary in composition as practically all metals and alloys can be cast.

The metals most frequently cast are iron, steel, aluminum and so on. Of these, iron, because of its low melting point, low price and ease of control, is outstanding for its suitability for casting and is used far more than all the others.

Casting is a widely used method of producing metal products, particularly those which are intricate. Since molten materials will readily take the shape of the container into which they are poured, it nearly as easy to cast fairly complex shapes as to produce simple forms.
The place where the metals are cast is called a foundry. The most important of cast metals is cast iron , which is made from pig iron by remelting it in a special melting furnace, called a cupola.

From the cupola, the cast iron flows into ladles of different size, and from these ladles it is poured into the molds.

The molds may be of two kinds: sand molds and metal molds. A metal mold consists of two hollow parts, which should be joined for pouring the metal into it. The inside of this mold is covered with carbon or graphite so that the metal could not stick to the wall of the form. When the metal has solidified, these hollow parts are disjoined and the casting is taken out. These are also special molds in which large blocks of steel can be cast. These molds are usually made of cast iron and are called ingot molds, which the blocks of steel produced by pouring the metal into these molds are called ingots and the process is called ingot casting.

    
A relatively wide range of nonferrous alloys can be die-cast. The principal base metals used, in order of commercial importance, are zinc, aluminium, copper, magnesium, lead, and tin. The alloys may be further classified as low-temprature alloys and high-temperature alloys; those having a casting temperature below 538°C , such as zinc, tin, and lead, are in the temperature class. The low temperature alloys have the advantages of lower cost of production and lower die-maintenance costs. As the casting temperature increases, alloy and other special steels in the best treated condition are required to resist the erosion and heat checking of die surfaces. The destructive effect of high temperatures on the dies has been the principal factor in retarding the development of high-temperature diecastings.

Another factor governing the choice of alloy is the erosive or solvent action of the molten metal on the respective machine parts and dies. This action increases with temperature, although it is more pronounced with some alloys than with others. Aluminium, in particular, has a destructive action on ferrous metals and, for this reason, is seldom melted in the machine, whereas the copper-base alloys are never melted in the machine. 

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Multi-Slide Die Casting

Multi-slide die casting is designed to use 4 perpendicular slides in the tool to enable very complex and accurate castings to be produced. In some cases, up to 6 slides can be used, which may be at angles other than 90 degrees. The die cast tooling process is used principally for small zinc components but Dynacast has also developed a multi-slide machine for die casting magnesium parts.

Dynacast’s proprietary Multi-slide die casting process:

The multi-slide tool is made up of the die block, sliders, crosshead and cover plate. Each die block has either a cavity and/or cores on its face, which together form the complete cavity and runner profile into which the molten metal is injected. These die blocks are mounted onto sliders, which fit precisely into a crosshead, ensuring repeatable opening and closing operations. A cover plate, bolted onto the top of the tool, holds all these components together.

Each slide is managed by our PC controller, and moves independently of the other, both during the closing and opening sequences. This provides tremendous flexibility, which ensures part integrity and prevents damage to the tool.

Ejection of the parts is achieved with an air-blast, which blows the shot clear of the cavity and into a padded collection mechanism.

The die casting machines themselves cycle at speeds of up to 75 cycles per minute (4,500 shots per hour). This is achieved by using pneumatics, rather than slower hydraulics, to operate the different parts of the machine. Mechanical toggle mechanisms and hydraulic thrusters supplement the weaker locking force available with pneumatics, ensuring that the die casting tool is held together securely during the injection process. Dynacast has also developed fully hydraulic multi-slide machines, allowing us to further match the process to the part.

http://www.dynacast.com/die-casting/die-casting-processes/multi-slide

Hot-Chamber Die Casting Process

The hot-chamber die casting process is only used for zinc and other low-melting-point alloys that do not readily attack and erode metal pots, cylinders and plungers. Development of this technology, through the use of advanced materials, allows this process to be used for some magnesium alloys. The basic components of a hot-chamber die casting machine and die are illustrated below.

During the hot-chamber process, the plunger and cylinder, which constitute the injection mechanism, are submerged in the molten metal in the crucible (or pot), which is integral to the machine. The operation sequence for the hot-chamber cycle is illustrated below.

Operating Sequence of the Hot-Chamber Die Casting Process

1. The die is closed and the piston rises, opening the port and allowing molten metal to fill the cylinder.

2. The plunger moves down and seals the port pushing the molten metal through the gooseneck and nozzle into the die cavity, where it is held under pressure until it solidifies.

3. The die opens and the cores, if any, retract. The casting remains in only one die half, the ejector side. The plunger returns, allowing residual molten metal to flow back through the nozzle and gooseneck.

4. Ejector pins push the casting out of the ejector die. As the plunger uncovers the filling hole, molten metal flows through the inlet to refill the gooseneck, as in step (1).

http://www.dynacast.com/die-casting/die-casting-processes/hot-chamber

Cold-Chamber Die Casting Process

During the cold-chamber die casting process, the molten charge (more material than is required to fill the casting) is ladled from the crucible into a shot sleeve, where a hydraulically operated plunger pushes the metal into the die. The extra material is used to force additional metal into the die cavity to supplement the shrinkage that takes place during solidification. The principle components of a cold-chamber die casting machine are shown below. Injection pressures over 10,000 psi or 70,000 KPa can be obtained from this type of machine.

Operating Sequence of the Cold-Chamber Die Casting Process

1. The die is closed and the molten metal is ladled into the cold-chamber shot sleeve.

2. The plunger pushes the molten metal into the die cavity where it is held under pressure until solidification.

3. The die opens and the plunger advances, to ensure that the casting remains in the ejector die. Cores, if any, retract.

4. Ejector pins push the casting out of the ejector die and the plunger returns to its original position.

http://www.dynacast.com/die-casting/die-casting-processes/cold-chamber/

ZINC DIE CASTING

Zinc Alloy Characteristics:Zn - From one hundredth of a gram to one kilogram, we have produced billions of zinc die castings. Its high strength and hardness make die cast zinc the ideal alternative to machined, pressed, stamped, and fabricated items. Zinc’s properties lend itself to so many solutions, we’ll probably have made another million castings in the time it takes you to pick up the phone and call us.

• High strength and hardness
• Excellent electrical conductivity
• High thermal conductivity
• Low cost raw material
• High dimensional accuracy and stability
• Excellent thin wall capability
• Ability to cold form, which eases joining
• High quality finishing characteristics
• Outstanding corrosion resistance
• Full recyclability

http://www.dynacast.com/die-casting/zinc-die-casting

MAGNESIUM DIE CASTING

Mg – Magnesium is strong, rigid, fully recyclable yet almost lighter than plastic and with superior shielding properties. It's the ideal alloy for saving weight without sacrificing durability.

Magnesium alloy characteristics:

• The lightest of all structural metals
• Excellent stiffness and strength-to-weight ratio
• Outstanding EMI & RFI shielding properties
• High conductivity, electrical and thermal
• Withstands high operating temperatures
• Cost-effective compared with many engineered thermoplastic materials
• High dimensional accuracy and stability
• Exceptional thin wall capability
• Good environmental corrosion resistance
• Good finishing characteristics
• Full recyclability

Magnesium is the ideal die casting material for applications where weight saving is a priority, having the lowest density of all structural metals. Almost as light in weight as plastic, magnesium has the advantage of greater strength and rigidity along with inherent EMI/RFI shielding, durability, heat-dissipation and full recyclability.

http://www.dynacast.com/die-casting/magnesium-die-casting

ALUMINUM DIE CASTING

Aluminum (Al) die castings are lightweight; yet withstand the highest operating temperatures of all the die cast alloys. Its strength, rigidity, and corrosive resistance offer significant heat dissipating advantages.

Aluminum is used in a broad range of networking and infrastructure equipment in the telecom and computing industries. Aluminum castings work for this application because RF filter boxes and housings require heat dissipation. It also provides EMI shielding, rigidity and durability with minimal weight for shields and housings for handheld devices. Because of aluminum’s excellent electrical performance and shielding properties, even in high-temperature environments, die casting aluminum is ideal for electronic connectors. Dynacast’s proprietary Thin Wall Aluminum Technology has made aluminum die casting an option for more applications.

Aluminum die castings improve automotive fuel efficiency by contributing to weight saving requirements. Our strength is in electronic applications, such as shields for telematic equipment and sensor housings, and safety-critical occupant restraint systems such as airbag housings and seat belt retractor spools.

Aluminum alloy characteristics:

• Highest operating temperatures
• Outstanding corrosion resistance
• Light-weight
• Very good strength and hardness
• Good stiffness and strength-to-weight ratio
• Excellent EMI & RFI shielding properties
• Excellent thermal conductivity
• High electrical conductivity
• Good finishing characteristics
• Full recyclability

http://www.dynacast.com/die-casting/aluminum-die-casting

Metal Injection Molding

Metal injection molding (MIM) is a metalworking process for creating fully dense, net-shape metal parts starting when metal powder suspended in a binder matrix (or feedstock) is injected into a tool, in a process very similar to injection molding, resulting in a green part. The green part is then debinded to remove most of the polymer carrier, resulting in a brown part. The brown part is heated in a furnace in a process called sintering to remove the remaining binder and form a fully dense (typically, 97 percent) metal part. MIM is a mature, established manufacturing process for molding relatively small metal parts.

Process

The MIM process starts with proper part design. Anyone familiar with designing parts for injection molding should find designing a MIM part to be very similar. However, in the case of a metal injection molded part, greater attention needs to be paid towards the need for smooth material flow through the part (thus, greater importance to thick and thin transitions, and proper filleting of joints). This process also requires that the parts be supported throughout debinding and sintering.

Mold production

When an order is placed, Proto Labs will design a metal injection molding tool. During this process, gates and vents are added to the part, and ejector pins to push the finished part out of the tool are selected and placed. The designer also adds side-actions for any undercuts. MIM tools are made of aluminum and use Protomold technology. Like a standard Protomold aluminum tool, a MIM tool is fabricated using a combination of CNC milling and CNC electrical-discharge machining (EDM). After milling, the tool is polished by hand to customer specifications.

Part production

The finished tool is loaded into a metal injection molding press for green part production. A MIM press is nearly identical to a standard plastic injection molding press, with a special screw and barrel designed to reduce separation of the binder and the metal powder during injection. Pellets of MIM feedstock are loaded into the hopper of the machine. Those pellets are then volumetrically metered into an injection barrel with a screw similar to an injection-molding press. Once the pellets are heated (through use of electric heaters and screw motion), the barrel is placed against the tool and the feedstock is injected. After solidification, the parts are ejected from the press and the cycle repeats. After ejection, green parts are de-gated and placed on ceramic substrates (or setters), which help retain the shape of the part throughout the debinding and sintering process.

Debinding

Pallets of green parts are loaded into a debind oven to remove most of the binder that carries the metal powder through the injection-molding process. The binder is about 20 percent of the feedstock volume. At Proto Labs, we use a feedstock that is debinded using a catalytic process. The length of time required for debinding is a function of the thickest section of your part, as the binder must migrate all the way out of the part. At the end of the debinding process, the resulting brown part is approximately the same size as the green part, but only 80 percent dense. Just enough binder remains to keep the powder particles together, so the brown part is quite fragile.

Sintering

Typically, pallets of parts are moved directly from the debind oven into a sintering furnace. The furnace precisely controls the temperature, cover gas and vacuum profile required to remove the remaining binder, and sinter the parts into the final product. During the furnace cycle, parts shrink about 20 percent into their final size. After sintering, any secondary operations are performed and the parts are complete.

Design Guidelines

Design guidelines for metal injection molding are very similar to guidelines for standard injection-molded parts, with one major difference — the parts must be designed to retain their geometry during the sintering process.

Size

Maximum part size limits at this time are approximately:

• 4 in. by 4 in. by 4 in. (10.1 cm. by 10.1 cm. by 10.1 cm.)*
• No deeper than 2 in. (5.1 cm.) from any parting line
• Maximum projected mold area of 10 sq. in. (64.5 sq. cm.)
• Maximum part volume less than 1.25 cu. in. (20.48 cc.)

Under some circumstances it may be possible to extend these limits, but there are tradeoffs to consider. If you need larger parts, please discuss your design and application with a Proto Labs engineer.
*Smaller if side-actions are required.

Recommended wall and rib thicknesses

Walls as thin as 0.040 in. (0.10 cm.) are possible, depending on the size of the wall and the location of adjacent thicker sections. Wall thicknesses generally should not exceed 0.5 in. (1.27 cm.). Rib thickness should be from 0.5 to 1.0 times the adjoining wall thickness. The radius of inside fillets should typically be approximately equal to the wall thickness. Radii that are much larger or smaller than this may cause porosity.

Uniform wall thickness

Typically, rapid changes in wall thickness can cause porosity and internal shrinkage. Porosity can develop in thick sections or where there is insufficient flow path from the gate to a thick section. If thick and thin sections are required, we recommend a gradual transition between the two. A good rule of thumb is to make the length of the transition three times the thickness of the thicker section.

Undercuts

Some simple undercuts on your part can be created using one of two methods: side-actions or pick-outs. Proto Labs can add simple side-actions to your tool. They must move perpendicular to the tool pull direction and must be on the parting line. During analysis of your part, we can determine if the location and depth of the undercut can be accommodated with a side-action. In some cases, Proto Labs can add manual features such as pick-outs to a MIM tool to create undercuts that are not otherwise possible. Pick-outs increase both the tool cost and the per-unit cost.

Part ejection

Ejector pins are required to eject your part after molding. Due to the constraints of the molding press, pins will always be placed on the B-side of the tool. The B-side will be the side of the tool where the part is retained when the mold is opened, and retention is generally governed by the geometry of the part (generally, the side with more cores). Proto Labs will propose ejector pin locations before manufacturing your tool.

Ejector pins range in size from 0.047 in. (0.118 cm.) to 0.375 in. (0.953 cm.), with sizes larger than 0.063 in. (0.158 cm.) preferred.

Draft

Generally, parts produced from metal injection molding need less draft than what is used in plastic injection molding, however, some draft may still be required in order for Proto Labs to machine the tool. A good rule of thumb is 0.5 degrees of draft per inch (2.54 cm.) of depth (depth is considered at the molded size, which is roughly 15 to 20 percent bigger than the finished size). While 0.5 degree of draft is common, zero draft can occasionally be tolerated on shallow parts with good surfaces for ejection.

Gating and venting

Metal injection molded parts require relatively large gates compared to plastic injection-molded parts due to the high metal content of the feedstock. Generally, a gate should feed into the thickest cross-section of the part, although feedstock flow considerations also need to be accounted for. Proto Labs can provide several types of gates, including hot-tip gates, edge gates (or tab gates), tunnel gates (or sub gates) and post gates. Gates will leave a vestige or blemish, so they should be placed on a surface that is not dimensionally or cosmetically critical, or a recess should be provided for gating.

In some cases, Proto Labs will need to add vents to allow air to escape while the part is filling. Often, vents can be added at the parting line, typically leaving a vestige too small to notice. In some cases, a venting pin must be added to allow otherwise trapped air to escape, leaving a blemish that looks like an ejector pin mark. Proto Labs will propose gate and vent locations (that require your approval) before manufacturing your tool.

Tool and part finishes

Finishes on MIM parts generally replicate the finish of the tool used to mold the green part. Proto Labs offers the following finishes on MIM tools:

• SPI-C1 600-grit stone
• SPI-B1 600-grit paper

Expected tolerances

Final dimensions are highly dependent on how well the part can be fixtured during sintering. The efficacy of sintering fixtures, in turn, is highly dependent on the geometry of the part. The skill of the original part designer in developing a part that can be sintered and fixtured properly is a major driver of meeting part tolerance requirements (see Fixturing guidelines). Typical achieved tolerances for a well-designed part are linear tolerances of ±0.005 in. (0.023 cm.), plus 0.001 in. (0.003 cm.) for each inch of dimension.

Material selection

Proto Labs currently offers the following metal injection molding materials: 316L and 17-4PH stainless steels. Consult the available 316L stainless steel data sheet and 17-4PH stainless steel data sheet for more information. These materials are standard offerings of BASF and can be sourced worldwide.

Fixturing

Two unavoidable facts greatly determine the success or failure of a metal injection molding project: first, a MIM part shrinks by about 20 percent during the debinding and sintering processes; and second, the MIM part becomes soft and responds to gravity during the sintering process. Proper MIM part design enables effective fixture design to overcome both of these phenomena. If necessary, Proto Labs will design a sintering fixture to support your part during sintering.

The basic challenge is that as a brown part is sintered, it shrinks to the final dimensions. At the same time, the part becomes soft as the metal powders partially melt and join together, and gravity pulls overhanging sections out of position. For the purposes of visualization, think of the part reaching the consistency and flexibility of children’s modeling clay.

As a part shrinks, some of it slides on the supporting surface to reach the final position. An ideal radially symmetric part would ideally shrink uniformly to the center, so the outside edges would move the most, the center would not move at all, and the center of mass would stay in the same spot during the process. The moving parts do experience some friction, which is often immaterial but can sometimes pose a problem.

The easiest parts to fixture have a common co-planar surface that can rest flat on a ceramic substrate or setter. Ideally, no portion of the part overhangs the planar surface, and there are no concave portions in the bounding polygon. Discs, or stacks of discs (e.g., visualize a wedding cake) are perfect. Unfortunately, the world only needs so many discs, and so we must develop ways to process real-world metal injection molded parts.

http://www.protolabs.com/

3D Printing Samples

Models in polyamide are constructed from a white, very fine, granular powder. The result is a strong, somewhat flexible material that can take small impacts and resist some pressure while being bent. The surface has a sandy, granular look, and is slightly porous.

Material samples

Pricing info

• All designs that fit within a bounding box of 125 cm3 and have a maximum dimension of 200 mm comes at 12,5€ a piece.
• If your design fits within a bounding box of 27 cm3 (for example 30 x 30 x 30 mm) and has a maximum dimension of 100 mm, you’ll only pay 5€ per copy of that same design (for example you’ll pay 32,5€ for 5 copies as 12,5+5+5+5+5 = 32,5)
• For copies of any other design that still fits within the 125 cm3 and have a maximum dimension of 200 mm, you will pay 10€ per copy (for example, you’ll pay 52,5€ for 5 copies as 12,5+10+10+10+10 = 52,5)

Typical use

Polyamide can be used for complex models, concept models, small series of models (several copies of a model), lamps, and functional models. This technique allows the greatest freedom of design of all 3D printing techniques.

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Technology

Selective laser sintering is used to build your design with this material. The models are printed layer by layer by a laser that draws thin lines in the powder, which melts and bonds it together in order to form a thin layer of the model. After a layer is printed, a new layer of fresh powder is spread over the surface by a roller. The printer has a print chamber that is heated to just below the melting point of the powder; the laser beam adds the extra energy to melt the powder, forming a solid model. After a print job is finished, the result is a big block of heated powder with the printed models contained inside.

The surface of your 3D printed model is defined by the material and technology. In addition, the number of post-finishing steps also determines the cost and quality of your polyamide model.

The natural surface of your polyamide model is perfect if you just want a physical model in your hands. You get to see and feel the basic material your model was built from because all we need to do is print your model, clean it up and ship it to you. The natural surface option is always the cheapest option.

Additional information

• Polyamide is a material that is perfect for beginning-designers who want a well-priced model, a maximum freedom of creation, and who don’t want to be bothered with the limitations of the printing process.
• Polyamide models are not suited for outdoor use as they absorb moisture. However, in some cases the material can be treated to make it watertight.
• Be careful for models with large, flat surfaces or plates (<25 cm). When such a model cools down, it can deform. The deformation process is known as warping.

Polished models

Polishing, also referred to as mechanical smoothing, is a special finishing process for polyamide. Your model is put into a tumbler with small "rocks" that smooth your model while the tumbler vibrates at a high frequency.

Things to keep in mind for polished models:

• We can only polish models that are between 10 x 10x 10 mm and 
  200 x 200 x 200 mm
• We can only smooth the A side (the outside of your models), it’s not possible to completely smooth the inside
• Polishing will take 0.1 mm of material off your model, so add extra wall thickness to avoid any problems.
• Small details could be worn away and may even disappear.
• Edges will be rounded and your model will become less’ crisp’ once polished.
• Applying the polishing adds 2 extra working days to the delivery time.
• Pricing: 0.2 € per cm³ (±$0.28 /cm3) per model on top of the natural white color price + a startup of 1€ (± $1.38 ) with a maximum of 3 € (± $4.5) extra in total.*

* Price in Dollars may vary due to exchange rate with Euro

Dyed Models

Although the outside surfaces are easily paintable, unfortunately, not all surfaces are easily reached with a spray gun. To color models with such surfaces, we use a dying process where your model is submerged into a bath containing color pigment. Dyeing is also referred to as pigmentation or impregnating. Like with most post-finishing processes, a lot of manual labor is required.

• Dimensions max 200 x 150 x 150 mm
• Pricing: 0.2 € per cm³ (±$0.28 /cm3) per model on top of the natural white color price + a startup of 1€ (± $1.38 ) with a maximum of 3 € (± $4.5) extra in total.*
• Dying adds 2 extra working days to the delivery time.

The dyeing process itself consists of several steps:

1. First, your model is washed by hand to make sure no contaminants influence the dyeing and to make sure the color pigment can properly penetrate the model.
2. Then, we mix the color pigment in the right ratio. In principle we can create any color but as each batch is a manual process it would be very expensive to do this only for one model. That’s the reason why we currently only offer black, dark gray, blue, and red, to keep prices as low as possible.
3. Afterwards, the pigments are put in warm water; at this point additional materials are added so the color pigment can better the impregnate the polyamide material.
4. Finally the mixture is heated and your model is added, your model remains in the mixture for at least 20 minutes so that the color can penetrate the surface(although it does not go through the entire model).
5. Your model is taken out and washed. Done!

* Price in Dollars may vary due to exchange rate with Euro

Polished and Dyed Models

It is possible to polish and dye your 3D printed model to create objects that are smooth and colored. Polishing and Dying is one finishing technique that includes 2 consecutive steps, namely polishing and dying, respectively. To polish models, we use a mechanical smoothing process. Your model is put into a tumbler with pebbles that smooth your model while the tumbler vibrates at a high frequency. To color models, we use a dying process where your model is submerged into a bath containing color pigment. Like with most post-finishing processes, a lot of manual labor is required. It’s important to keep the rules below in mind:

• We can only polish and color models that are between 10 x 10 x 10 mm and 200 x 150 x 150 mm.
• We can only smooth the A side (the outside of your model), it’s not possible to completely polish the inside.
• Sharp corners are hard to reach and will be polished less.
• Color variation may occur due to difference in level of smoothness (e.g. inside and inside of corners - see above) and production processes**.
• Polishing will take 0.1 mm of material off your model, so add extra wall thickness to avoid any problems.
• Small details could be worn away and may even disappear.
• Edges will be rounded and your model will become less “crisp” once polished.
• Colors will appear lighter than regular-dyed models.
• Polishing and dying adds 3 extra working days to the delivery time.
• Pricing: 0.4 € per cm³ (±$0.55 /cm3) per model on top of the natural white color price + a startup of 2€ (± $2.8 ) with a maximum of 3 € (± $8.3) extra in total.*

* Price in Dollars may vary due to exchange rate with Euro

** Because of the unique nature of this production process regarding parameters, building position, light deflection and mechanical polish can cause variation in the intensity of the colors.

Velvet models

Go beyond painting your model and discover a special finishing option that not only changes the way the model looks, but also how it feels.

The process of adding a velvet finish to your models is called flocking, a fairly straight forward process. First, a suitable adhesive is applied to the surface to be flocked. The flock is then applied, penetrating the surface of the adhesive to create the desired velvet finish.

Electrostatic flock applicators charge the flock particles which are then attracted to the grounded surface that is to be flocked. Electrostatic application ensures that the fibers all end up standing at right angles to the surface resulting in a velvet finish.

Things to keep in mind for velvet models:

• The minimum bounding box measurements are 3 x 3 x 10 mm
• The maximum bounding box measurements are 150 x 150 x 150 mm
• We can only add velvet fur to the A side of your models, the side that is facing outwards
• It’s not possible to add velvet fur to the inside of your models
• Velvet finish cannot be added to interlinked or moving parts
• The fiber applied is about 1 mm in length
• Velvet fur is pretty resistant against friction
• Applying velvet fur adds 2 days extra to the delivery time
• Applying velvet adds 10€ on top of the natural white color price for each model

Painting

When the natural color of polyamide doesn’t meet your needs, we can paint your model with a can of spray paint. You could also do this at home yourself if you prefer.

You can also have your model painted in a professional spraying booth. There are 4 types of paint (only available through an offline price request): dead matt, matt, satin, and high gloss. The difference lies in the gloss factor. In other words, how "shiny" your model looks when it’s painted. The higher the gloss factor, the more light will be reflected from the model. The bigger the surface is on which the paint is sprayed, the bigger the visual difference between the different paint options .

As an example we have painted 4 metal plates in the 4 types of paint and placed a small polyamide ball on top of it. The more the ball is reflected, the higher the gloss factor.

Dead matt paint degree of reflection 10%.

Matt paint degree of reflection 30%.

Satin paint degree of reflection 50%.

High gloss paint degree of reflection 90%.
http://www.i.materialise.com