Secondary Operation
Burr is a small defect, but it directly affects the quality of the product. In the process of die-casting production, deburring and sharp corner removal are often the basic requirements of customers.
The deburring process is a process that combines mechanical and material science. There are usually the following methods of deburring.
Vibration grinding to remove burrs
Put the workpiece, abrasive, machining fluid, and abrasive into a rotating or vibrating tank. During the collision between the workpiece and the abrasive, the irregularities on the surface are removed to obtain a smooth processing surface, which is Barrel Finishing. At this time, the box that rotates with the workpiece is a barrel, and when the drum is usually lined with rubber to vibrate, it is particularly called vibratory finishing (Vibratory Finishing). The same method is Tumbling, which is to turn the cast or forged product into a Tumbler to remove burrs or useless protrusions. The precision of the workpiece and the roughness of the processed surface are far Not as good as barrel processing. The barrel processing is processed in the same way as the jog method, but it can be processed with high precision by using abrasives .
Thermal deburring:
The thermal deburring process is a process using thermochemical reactions. Place the parts to be deburred in a sealed working chamber, and then fill in a certain amount of methane gas (CH4) or gas and oxygen (O2) mixed gas. After the spark plug is ignited, the mixed gas reacts in an instant, releasing a large amount of Heat makes the burrs spontaneously combust under the action of high temperature (about 3000°C), high pressure (20 times the inflation pressure), and high speed (8 times the speed of sound) to achieve the purpose of deburring. Due to the extremely short reaction time (only 0.003 seconds), the original size, surface finish, metallographic structure and mechanical properties of the processed parts are basically unchanged. Generally used for medium and large die castings, because small parts are easily deformed by using heat to remove burrs
Cryogetic deburring method:
The thickness of the burr is much thinner than the thickness of the product, so the embrittlement speed of the burr is faster than the embrittlement speed of the product. During the period of time when the burr is brittle and the product is not embrittled, the frozen burr is hit by projecting projectiles. Products to remove burrs). Frozen deburring is a kind of rapid embrittlement of rubber, plastic products, zinc-magnesium-aluminum alloy flash by the ultra-low temperature of liquid nitrogen, and in this state, the frozen particles ejected at high speed hit the flash of the product to achieve both A special deburring process that can remove the burrs of products with high quality and high efficiency, while maintaining all the physical properties of the product itself. It can greatly improve the precision of deburring products and has a high degree of intensification.
Manual deburring:
If the workpiece cannot be processed by mechanical deburring (the workpiece is too complex), it will be removed manually. The factory personnel use equipment to manually scrape the burr, which is generally used to construct complex parts.
Use high-speed sand flow to clean the surface of the casting, so that the surface produces granular depressions or eroded surfaces, to remove rust, deburring, deoxidation, material stress treatment and the subsequent surface treatment can have better adhesion to the coating.
Examples of sandblasting uses are as follows：
Surface removal processing：
metal oxide layer or black skin after heat treatment, surface pores, metal or non-metal surface rust removal, ceramic surface black spots and color removal or color painting regeneration, rubber mold and gravity die-casting mold oxidation Removal of materials, residues or release agents.
Surface beauty/strengthening processing：
decorative processing of various metal products (such as gold, K gold jewelry, precious metal products), matting and soft matte treatment of electroplating products, and non-metal products (such as acrylic, wave (Li, glass, crystal glass) surface atomization/roughening treatment and can make the surface of the processed object become metallic luster. Let the surface have the feeling of "biting" and the irregular reflections caused by the rough surface and the light refraction are bright. At the same time, the surface hardness can be enhanced, so that it is not easy to scratch and wear.
Flash/head removal processing：
surface finishing for removing burrs (heads) of zinc-aluminum die-casting products, plastics, bakelite products, electronic parts, magnetic cores, etc.
Pre-treatment processing：
powder coating, electroplating, painting, Teflon (TEFLON), PU, rubber and plastic coating, metal spray bar, titanium plating, heat sink and other pre-treatment to increase surface adhesion.
Etching processing：
surface repair and etching processing of precious metal corrosion products, gems, jade, crystal, agate, semi-precious stones, elegant stones, antiques, seals, stones, marble tombstones, bamboo, glass, ceramics, wood, etc.
Workpiece stress relief processing：
parts cleaning and stress relief in the aerospace industry and precision industry, or stress relief processing in the refurbishment, matting, rust removal, and paint removal of defense weapons.
Electronic parts processing：
removal of surface impurities after the diffusion of silicon wafers, etching processing of silicon wafers by sandblasting and cutting into small round crystal grains, spraying of spilled burrs in the packaging industry of electronic parts, removal of printing on the surface of finished electronic parts, Cleaning of ceramic electric heating materials.
Types of sandblasting:
Dry sandblasting:
Dry sandblasting is a method in which the abrasive material is accelerated by using a vacuum tube and compressed air as the power, or is moved by a hoist on a high-speed turntable using centrifugal force to throw the sand material onto the workpiece, and then the surface treatment of the workpiece is performed. Most suitable for surface processing of work objects that are not suitable for water.
Features:
Because it is dry, there is no need to dry after sandblasting, and there is no fear of rust.
It can remove burrs (surface protrusions) and surface attachments without damaging the processed parts.
The pear ground surface (spotted pattern) processing with a uniform surface is particularly effective in processing the surface roughness required.
Because there is no need for waste liquid treatment, maintenance is easy.
Compared with spray washing machine, the processed surface is not rough
Wet blasting:
The so-called wet sandblasting is a method in which a mixture of abrasive materials and water is transported by a pump, and the surface is processed by using the power of high-pressure air to blast the workpiece.
Features:
Due to the use of water, there will be no environmental pollution problems such as scattering of fine powder.
It can remove burrs (surface protrusions) and surface attachments without damaging the processed material and clean.
The pear ground surface (spotted pattern) processing with a uniform surface is especially powerful in the processing required for surface roughness.
Only a small spray effect on the processing surface can improve and strengthen th
噴砂機
Polishing process:
Polishing refers to the use of mechanical, chemical or electrochemical effects to reduce the surface roughness of the workpiece to obtain a bright, smooth surface. It is the use of polishing tools and abrasive particles or other polishing media to modify the surface of the workpiece.
Polishing cannot improve the dimensional accuracy or geometric accuracy of the workpiece, but aims to obtain a smooth surface or mirror gloss, and is sometimes used to eliminate gloss (matting). Usually a polishing wheel is used as a polishing tool. The polishing wheel is generally made of multiple layers of canvas, felt or leather. The two sides are clamped by metal circular plates, and the rim is coated with a polishing agent that is uniformly mixed with micronized abrasives and grease.
During polishing, the high-speed rotating polishing wheel (circumferential speed above 20 m/s) is pressed against the workpiece, so that the abrasive can roll and micro-cut the surface of the workpiece, thereby obtaining a bright machined surface. The surface roughness can generally reach Ra0.63 ~0.01 micron; when non-greasy matting polishing agent is used, the bright surface can be matted to improve the appearance. When mass production of bearing steel balls, barrel polishing is often used.
During rough polishing, a large number of steel balls, lime and abrasives are placed in the inclined tank-shaped drum. When the drum rotates, the steel balls and abrasives are randomly rolled and collided in the drum to remove the surface bulge and reduce the surface roughness. Purpose, the margin of about 0.01 mm can be removed.
In the fine polishing, steel balls and fur fragments are placed in the wooden barrel, and continuous rotation for several hours can obtain a dazzling and bright surface. The polishing of the precision wire ruler is carried out by immersing the processed surface in a polishing liquid. The polishing liquid is a mixture of chromium oxide powder with a particle size of W5~W0.5 and an emulsion. The polishing wheel is made of wood or special fine felt with uniform material and degreased treatment. Its movement track is a uniform and dense mesh. The surface roughness after polishing is not greater than Ra0.01 micron. Observe under a microscope with a magnification of 40 times. There are no surface defects. In addition, there are methods such as electrolytic polishing.
Polishing classification：
Mechanical polishing：
Mechanical polishing is a polishing method that relies on cutting and plastic deformation of the material surface to remove the polished protrusions to obtain a smooth surface. Generally, oil stone sticks, wool wheels, sandpaper, etc. are used, and manual operations are mainly used. Special parts such as the surface of the rotating body. Auxiliary tools such as turntables can be used, and ultra-precision polishing methods can be used for high surface quality requirements. Ultra-precision polishing is the use of special abrasive tools, which are pressed against the processed surface of the workpiece in a polishing liquid containing abrasives for high-speed rotation. The surface roughness of Ra0.008μm can be achieved by using this technology, which is the highest among various polishing methods. Optical lens molds often use this method.
Wheel polishing：
The surface of the workpiece is rolled and micro-cut with a high-speed rotating flexible polishing wheel and extremely fine abrasives to achieve polishing. The polishing wheel is made of multiple layers of canvas, felt or leather, and is used for polishing larger parts.
Barrel polishing, vibration polishing：
Put the workpiece, abrasive and polishing liquid into the roller or vibrating box, roll the roller slowly or vibrate the vibrating box, so that the workpiece and the workpiece, the workpiece and the abrasive rub against each other, and the chemical action of the polishing liquid can remove the oil and dirt on the surface of the workpiece. The rust layer is polished off the convex peaks to obtain a smooth surface. Used for polishing small and large parts. The latter has higher productivity and better polishing effect than the former.
Chemical polishing：
Chemical polishing is to make the surface microscopic convex part of the material in the chemical medium dissolve preferentially than the concave part, thereby obtaining a smooth surface. The main advantage of this method is that it does not require complicated equipment, can polish workpieces with complex shapes, and can polish many workpieces at the same time, with high efficiency. The core problem of chemical polishing is the preparation of polishing liquid. The surface roughness obtained by chemical polishing is generally several 10 μm.
Electrolytic polishing：
The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, by selectively dissolving tiny protrusions on the surface of the material to make the surface smooth. Compared with chemical polishing, the effect of cathode reaction can be eliminated, and the effect is better. The electrochemical polishing process is divided into two steps: (1) Macroscopic leveling The dissolved product diffuses into the electrolyte, and the geometric roughness of the material surface decreases, Ra>1μm. (2) Low-light leveling: Anode polarization, improved surface brightness, Ra<1μm.
Ultrasonic polishing：
Put the workpiece into the abrasive suspension and put it together in the ultrasonic field, relying on the oscillation effect of the ultrasonic, so that the abrasive is ground and polished on the surface of the workpiece. Ultrasonic machining has a small macroscopic force and will not cause deformation of the workpiece, but it is difficult to manufacture and install tooling. Ultrasonic processing can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution, so that the dissolved products on the surface of the workpiece are separated, and the corrosion or electrolyte near the surface is uniform; the cavitation effect of ultrasonic in the liquid can also inhibit the corrosion process and facilitate surface brightening.
Fluid polishing：
Fluid polishing is based on the high-speed flow of liquid and the abrasive particles carried by it scouring the surface of the workpiece to achieve polishing. Common methods are: abrasive jet processing, liquid jet processing, hydrodynamic grinding and so on. Hydrodynamic grinding is driven by hydraulic pressure to make the liquid medium carrying abrasive particles flow back and forth across the surface of the workpiece at high speed. The medium is mainly made of special compounds with good flowability under lower pressure and mixed with abrasives. The abrasives can be made of silicon carbide powder.
Magnetic grinding and polishing：
Magnetic abrasive polishing is to use magnetic abrasives to form abrasive brushes under the action of a magnetic field to grind the workpiece. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. Using suitable abrasives, the surface roughness can reach Ra0.1μm.
plating process introduction：
The plating process uses the principle of electrolysis to coat a layer of metal on a conductor. Electroplating refers to a surface processing method that uses the base metal to be plated as a cathode in a salt solution containing pre-plated metal to deposit the cations of the pre-plated metal in the plating solution on the surface of the base metal through electrolysis to form a plating layer.
The coating performance is different from the base metal and has new characteristics. According to the function of the coating, it is divided into protective coating, decorative coating and other functional coatings.
During electroplating, the plated metal or other insoluble materials are used as the anode, the workpiece to be plated is used as the cathode, and the cations of the plated metal are reduced to form a coating on the surface of the workpiece to be plated. It can enhance the corrosion resistance of metals (corrosion-resistant metals are mostly used for coating metals), increase hardness, prevent abrasion, improve conductivity, smoothness, heat resistance and surface aesthetics.
Classified according to coating composition:
Chrome plating：
Chromium is a silver-white metal with a slight sky blue color. It has a strong passivation performance, passivation quickly in the atmosphere, showing the properties of precious metals, so the chromium plating layer of iron parts is a cathode plating layer. The chromium layer is stable in the atmosphere and can maintain its luster for a long time. It is very stable in corrosive media such as alkali, nitric acid, sulfide, carbonate and organic acid, but it is soluble in hydrochloric acid and other hydrohalic acid and hot concentrated sulfuric acid. The chromium layer has high hardness, good wear resistance, strong light reflection ability and good heat resistance. There is no obvious change in gloss and hardness below 500°C; it starts to oxidize and discolor when the temperature is higher than 500°C; it starts to soften when it exceeds 700°C. Due to the excellent performance of the chromium plating layer, it is widely used as the outer surface layer and functional coating layer of a decorative coating system.
Copper plating：
The copper-plated layer is pink, soft, has good ductility, electrical conductivity and thermal conductivity, and is easy to polish. After proper chemical treatment, decorative colors such as bronze, copper green, black and natural colors can be obtained. Copper plating tends to lose its luster in the air, and reacts with carbon dioxide or chloride. A layer of basic copper carbonate or copper chloride film is formed on the surface. Brown or black copper sulfide is formed under the action of sulfide. Therefore, it is used as decorative The copper plating layer needs to be coated with an organic coating on the surface.
Tin plating：
Tin has a silver-white appearance, with an atomic weight of 118.7, a density of 7.3g/cm^3, a melting point of 231.89°C, and atomic valences of divalent and tetravalent, so the electrochemical equivalents are 2.12g/A.h and 1.107g/A.h, respectively. Tin has the advantages of corrosion resistance, non-toxicity, easy iron welding, softness and good ductility.
The tin plating has the following characteristics and uses：
1、 High chemical stability;
2、Tin has good conductivity and is easy to solder;
3、After tinning, re-dissolve it in hot oil above 231.89℃ to obtain a shiny patterned tin layer, which can be used as a decorative coating for daily necessities.
Galvanized：
Zinc is soluble in acid and alkali, so it is called amphoteric metal. Zinc hardly changes in dry air. In humid air, a basic zinc carbonate film will be formed on the surface of zinc. In an atmosphere containing sulfur dioxide, hydrogen sulfide, and marine atmospheres, zinc has poor corrosion resistance, especially in an atmosphere containing organic acids at high temperature and humidity, the zinc coating is easily corroded. The standard electrode potential of zinc is -0.76V. For the steel substrate, the zinc coating is an anodic coating. It is mainly used to prevent corrosion of steel. The quality of its protective performance is closely related to the thickness of the coating.
Nickel plating：
The method of plating a layer of nickel on metals or certain non-metals by electrolysis or chemical methods is called nickel plating. Nickel plating is divided into electroplating nickel and electroless nickel plating. Nickel electroplating is in an electrolyte composed of nickel salt (called main salt), conductive salt, pH buffer, and wetting agent. Metallic nickel is used for the anode, and the cathode is the plated part. Direct current is applied to the cathode (plated part). Deposit a uniform and dense nickel coating. Bright nickel is obtained from the bath with brightener, and dark nickel is obtained from the electrolyte without brightener. Electroless nickel plating is also called electroless nickel plating, and it can also be called autocatalytic nickel plating. It refers to a process in which nickel ions in an aqueous solution are reduced by a reducing agent under certain conditions and deposited on the surface of a solid substrate.
Nickel plating has a wide range of applications and can be used as a protective decorative coating to protect the base material on the surface of steel, zinc die casting, aluminum alloy and copper alloy
The material is not corroded or has a bright decoration effect; it is also often used as an intermediate coating of other coatings, and a thin layer of chromium is plated on it, or a layer of imitation gold is plated,
Its corrosion resistance is better and its appearance is more beautiful. In terms of functional applications, nickel plating on parts in special industries is about 1~3mm thick, which can achieve repair goals
of. Especially in continuous casting molds, molds on the surface of electronic components, die-casting molds of alloys, and aerospace engines with complex shapes
The manufacturing of components and microelectronic components has become more and more widely used.
process：
Generally, it includes three stages: pretreatment before electroplating, electroplating and post-plating treatment.
The complete process：
1、 Acid pickling→full board copper electroplating→graphic transfer→acid degreasing→secondary countercurrent rinsing→micro-etching→secondary pickling→tinning→secondary countercurrent rinsing
2、Countercurrent rinsing→acid immersion→graph copper plating→secondary countercurrent rinsing→nickel plating→secondary water washing→citric acid immersion→gold plating→recycling→2-3 pure water washing→drying
The basic requirements of the process:
1. There should be good bonding force between the plating layer and the base metal, between the plating layer and the plating layer;
2. The coating should be finely crystallized, smooth and uniform in thickness;
3. The coating should have a specified thickness and as few pores as possible;
4. The coating should have the specified indicators, such as brightness, hardness, conductivity, etc.;
5. The plating time and the temperature of the plating process determine the thickness of the plating layer. The ambient temperature is -10℃～60℃;
6. The input voltage is 220V±22V or 380V±38V;
7. The maximum operating noise of water treatment equipment should not be greater than 80dB(A);
8. The relative humidity (RH) should not be greater than 95%;
9. The COD content of raw water is 100mg/L～150000mg/L.
Advantages and applications of electroplating:
Gold plating is mainly used for decoration and industrial purposes. The gold-plated layer has abrasion resistance, corrosion resistance, low porosity, and good contact characteristics. It is especially suitable for electronics, communication equipment parts, printed circuit contacts, and adapters. The advantage is that it is not easy to oxidize and discolor, but it is expensive and susceptible to market fluctuations in gold prices.