No matter whether you make parts through rapid precision prototyping machining for structural or appearance verification, surface treatment is a must. Through surface treatment, we can remove the burrs and machining marks as well as get a product as real ones. Below is a detailed list of the surface treatments that are applied in rapid precision prototype machining.

1. Grinding

Grinding is one of the most common surface treatment techniques for rapid prototype machining. With the help of rough objects (such as sandpaper containing higher hardness particles, etc.), it changes the physical properties of the material surface through friction, thus removing the burrs, machining traces, bonding marks, and other defects on the surface of the workpiece. By grinding, we improve the flatness of the workpiece, reduce the roughness and make the surface smooth.

2. Polishing 

With flexible polishing tools and abrasive particles or other polishing media, polishing achieves a smooth surface or mirror luster and sometimes eliminates the luster (matting). It cannot improve the accuracy or geometric shape accuracy of the components.


3. Sandblasting 

By winding sand to the surface of the workpiece through a sandblasting machine, it forms a layer of dense craters. Due to the abrasive’s impact on the surface and cutting effect, it gets a certain degree of cleanliness and different roughness. It improves the mechanical properties and fatigue resistance. Sandblasting also increases the adhesion between the component and paint coating and prolongs the durability of the paint. It is conducive to the leveling and decoration of the paint.

4. Painting

Painting is one of the most widely used surface treatments. The results can be matte, semi-matte, glossy (high-gloss), various colors, various textures, etchings, brushed effects (only metallic paint can be brushed), leather effects, elastic hand effects (rubber-like paint), etc.

Painting has the following advantages:

(1) It can cover the surface defects of the parts after rapid prototype machining

(2) The surface can get a variety of colors, different gloss, different visual effects of appearance, and various hand feeling

(3) It enhances the hardness and scratch-resistance of the surface

5. Powder coating

Electrostatic powder coating has the powder adsorbed on the surface of the parts based on the corona discharge phenomenon. The coating is of good quality with high adhesion, mechanical strength, and corrosion resistance. The curing time is short. There is no need to use the primer and low requirements for workers. Also, the powder recycling rate is high.

However, the coating is very thick with ripples on the surface. There are two effects semi-matte and glossy.

6. Printing

(1) Silk screening

The main principle of silk screening is that of camera film imaging. It is mainly used on a flat surface. If there are deep pits, it is necessary to use pad printing.

The advantages of silk screening: 

A. low cost, fast results

B. available to the irregular substrate surface

C. strong adhesion, good inking

D. thick ink layer, strong three-dimensional sense

E. strong spin resistance, good color

F. wide range of materials available, large printing area


(2) Pad printing

It refers to printing text or patterns to the surface of plastic components via precision prototyping machining with the curved or slightly concave and convex surface using a piece of flexible rubber. Firstly, you put the ink into the gravure plate engraved with text or pattern, then copy them onto the rubber. After that, you use the rubber to transfer the text or pattern to the surface and dry the ink by heat treatment or ultraviolet light irradiation.

7. Brushing

Brushing is a surface treatment to form a line pattern on the surface of the parts by grinding for decoration purposes. The metal surface obtains a non-mirror-like metallic luster after brushing. The surface effects can be divided into straight wires (hairline) and messy wires (snowflake).

Arc (the intersection between the arc and the straight surface is ugly and uneven) and lacquer parts are not suitable for brushing (metal-colored surfaces can have tiny line patterns). It only fits aluminum.

8. Electroplating

Through electroplating, a chemical reaction, a layer of metal is attached to the surface of the prototypes to increase its corrosion resistance or change the size. It also has an aesthetic function. Electroplating is a common surface treatment. It includes zinc electroplating, nickel electroplating, etc. Electroplating is generally divided into two types: wet plating and dry plating. Wet plating is commonly known as water plating. Dry plating is commonly known as vacuum plating.

The adhesion of water plating is good, and no other treatments are needed afterward. The adhesion of vacuum plating is poor and usually needs to do PU or UV on the surface. 

PC prototypes can not be plated, and vacuum casting parts can not be water plated only vacuum plating. The colors of water plating color are monotonous. They can just be chromium, nickel, gold, etc. While vacuum plating can achieve seven colors. the cost of water plating is generally very high and that of vacuum plating is relatively low.



9. Oxidation 

Oxidation is normally for aluminum parts to oxidize the metal on the surface to form a dense protective film and increase the corrosion resistance. There are two ways of conductive oxidation and anodic oxidation. It also is a common surface treatment.

After oxidation treatment, especially anodic oxidation, the oxide film formed on its surface of aluminum and aluminum alloy has good protective and decorative properties. Therefore, it is widely used in aviation, electrical, electronic, machinery manufacturing and light industries, etc.


10. Laser engraving

Laser engraving, also called laser etching, is a kind of surface treatment with optical principles. 

Limitations of laser engraving

(1) The depth is 0.1mm for aluminum, 0.2-0.3mm for paint-coated plastic parts, and up to 0.08mm for other metals such as iron.

(2) The limit surface area of laser engraving is 100X100mm. If it is larger than 100X100mm, the laser engraving needs to be done separately. But the articulated position is not good-looking, and the articulated trace is more obvious.

(3) Parts in the white color and the color close to white can not be carved out. The characters can be easily deformed.

11. Passivation

Passivation can improve the passivation performance of metal materials, make the metal materials passivated while using, and improve the mechanical strength of the metal. It is one of the most effective ways to control corrosion and enhance the adhesion of the metal and coating film.

12. Water transfer printing 

It is a way to use water pressure to print the colorful pattern on the transfer paper on the surface of three-dimensional products via precision rapid prototyping. As people's requirements for product packaging and surface decoration are improving, the use of water transfer printing is becoming more and more popular.

13. Blackening

Blackening treatment, also known as bluing. There are two methods traditional alkaline heating blackening and blackening under normal temperature.

The protective film is black, improving the corrosion resistance and mechanical strength of the metal surface. It can also be a good base layer of paint. Stainless steel can not be blackened. The blackening effect for iron is the best.

14. Phosphating

Phosphating is to treat the metal surface in manganese, zinc, iron, and other metals orthophosphate solution, so that it generates a layer of insoluble phosphate protective film. The protective film can improve the insulation and corrosion resistance of metals, as well as the protection and decorative properties. It can also act as a good base layer of paint. Phosphating treatment for metal parts is divided into cold phosphating (room temperature phosphating), hot phosphating, electrochemical phosphating, and others. 

In the automotive industry, it is the main pre-painting method of painting parts such as car covers, cabs, trunk panels, etc. It requires that phosphate film is fine, smooth, uniform, moderate thickness, and has heat resistance.

Common surface treatment methods for plastic parts

Grinding, polishing, painting, printing, electroplating, vacuum plating, sandblasting, and water plating (ABS parts can not be water plating when they are not made in one piece).

Common surface treatment methods for metal materials

Grinding, polishing, electroplating, vacuum plating, blackening, passivation, sandblasting, etching, brushing, baking paint, oxidation, laser engraving, water plating (aluminum, copper), passivation, and blackening apply to steel.

Knowing the available surface treatments for precision prototyping machining helps you improve your design verification plans. If you have further questions, X Rapid Technologies is always here to respond.