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.
Using high speed sand flow to clean the surface of products and make surface has high surface consistency. It is means reducing rust , deburring , reducing oxide and stress treatment and make surface has better adhesion strength for surface treatment.
Examples of sandblasting uses are as follows：
Deburring：
Some products have a column foot structure (ex. die casting unit for PCB electrical plate). If the strength is note enough , it will break easily when using roller to deburring. If we use sandblasting to remove burrs, although the speed of deburring is slower than roller deburring. It greatly reduce the ratio of breakage.
Improve the product’s surface：
This is the main purpose of the sand blasting process.
The
die casting unit’s surface won’t be flat and smooth when it is produced from
mold. We usually use sandblasting process to make the surface flatness and
smooth. It also could to make plating layer adhered more easily in plating
process.
Change the physical and mechanical properties of the products：
Change the surface stress state of the products, make surface harden and increase the wear resistance and fatigue strength of the products.
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
Sandblasting machine
Polishing process:
Polishing process is a surface treatment that using mechanical , chemical or electrochemical method to reduce the surface roughness and make surface lightly , flat and smooth. It usually use polishing tools and abrasive particles or other polishing media to modify the surface of products.
Polishing process couldn’t increase dimensional accuracy , the purpose is receiving the smooth surface and specular gloss. Sometimes it also is used to remove the gloss.
Polishing usually uses a polishing wheel as a polishing tool. The polishing wheel is generally made of multiple layers of canvas, felt or leather, and the two sides are clamped by metal discs.
The High-speed polishing wheel will make abrasive grain to micro grinding the surface of products. Then it will make surface lightly and make the surface roughness reach Ra0.63~0.01 microns. If we use non-greasy matting polishing compound, it could make surface to be matted.
During the rough polishing , a large number of steel ball , lime and abrasive compound are placed in a inclined tank drum. When the drum rotates , the steel balls and abrasive compounds will rolled and collided in the drum and reduce the surface roughness ( a margin of about 0.01mm can be removed )
Polishing classification：
Mechanical polishing：
Mechanical polishing is the process that removes the uneven surface by cutting to obtain a smooth surface. We usually use whet stone , wool wheel and sandpaper and manual operation. Sometimes will use rotate table to polish some special products. If the requirement of surface is high , the ultra-fine grinding and polishing process could be used. this process is using special abrasive tool and polish liquid , then rotate with high speed. It could make surface reaching Ra0.08um.
Wheel polishing：
This process is using polishing wheel and extreme fine abrasive compounds to micro grinding products. The polishing wheels are made by canvas, felt or leather for polishing larger parts.
Barrel polishing, vibration polishing：
Putting products and abrasive compounds in the roller or vibrating box, and roller rolls slowly or box vibrates. It could make product and abrasive compound friction each other and reduce oil , rust layer and convex peaks. It usually is used to polish small size products(but the amount is large)
Chemical polishing：
The chemical polishing process is let the microscopically protruding parts of the material to dissolve preferentially over the concave parts in the chemical medium, thereby obtaining a smooth surface. The main advantage of this method is that it does not require complex equipment, it can polish workpieces with complex shapes, and can polish many workpieces at the same time, with high efficiency. 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, the principle is selectively dissolving tiny protrusions on the surface of the material and make the surface smooth. Compared with chemical polishing, the influence of cathode reaction can be eliminated. The electrochemical polishing process is divided into two steps: (1) Macroscopic leveling The dissolved products diffuse into the electrolyte, and the surface roughness of the material decreases, Ra>1μm. (2) Low light leveling Anodic polarization, improved surface brightness, Ra<1μm.
Ultrasonic polishing：
The workpiece is placed in the abrasive suspension and placed in the ultrasonic field together, and the abrasive is ground and polished on the surface of the workpiece by the oscillation of the ultrasonic wave. The macroscopic force of ultrasonic processing is small, and it will not cause deformation of the workpiece, but it is difficult to make and install the tooling. Ultrasonic machining 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 detached, and the corrosion or electrolyte near the surface is uniform; the cavitation of ultrasonic waves in the liquid can also inhibit the corrosion process, which is conducive to surface brightening.
Fluid polishing：
The fluid polishing process is to scour the surface of the workpiece according to the high-speed flowing liquid and the abrasive particles it carries to achieve the purpose of polishing. The commonly used methods are: abrasive jet machining, liquid jet machining, hydrodynamic grinding, etc. Hydrodynamic grinding is driven by hydraulic pressure, so that the liquid medium carrying abrasive particles flows reciprocating 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, and the abrasives can be silicon carbide powder.
Magnetic grinding and polishing：
Magnetic grinding and polishing process is to use magnetic abrasives to form abrasive brushes under the action of a magnetic field to grind workpieces. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. With suitable abrasives, the surface roughness can reach Ra0.1μm.
plating process introduction：
The plating process is using the principle of electrolysis to coat a layer of metal on a conductor. The 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 layer, decorative layer, and other functional layer.
During plating process, 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 of chromium is worked quickly in the atmosphere, showing the properties of precious metals. 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 layer of a decorative plating 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 layer 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 plating for daily necessities.
Zinc plating：
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 layer.
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 plating 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:
The electroplating process is mainly used for decorative and industrial purposes. The electroplating layer has wear resistance, corrosion resistance, low porosity and good contact characteristics, especially suitable for electronic, communication equipment parts, printed circuit contacts, and connectors.