The quality control of brass casting is mainly guaranteed through two aspects, one is to strictly control the chemical composition of casting brass. Brass is a Cu Zn binary alloy with zinc as the main alloy element, which is generally called brass or ordinary brass. Ordinary brass has certain strength, hardness and good casting performance, […]
Invar alloy-basic information
Invar (Invar, also known as Invar, changed its name to a brand name), is a nickel-iron alloy with a composition of 36% nickel, 63.8% iron, and 0.2% carbon. Its coefficient of thermal expansion is extremely low and can Maintain a fixed length over a wide temperature range.
Invar alloy, also known as “invariant steel”, is commonly known as Invar machining in Chinese. It is an iron-nickel alloy and a special steel with 36% nickel. Because of its very small expansion coefficient, it is suitable for measuring components.
Invar alloy-processing technology
The alloy material contains nickel content as high as (31.5%,-37%). Although nickel can increase the strength, plasticity, and toughness of the material, the thermal conductivity is reduced. Although the hardness of the alloy is not high, the toughness is high, and it is soft and sticky during cutting, which significantly reduces the cutting performance. Therefore, the processing performance is poor, and it is a difficult-to-cut metal material. It has the following characteristics:
- (1) The cutting force is large. Because the metallographic structure of the alloy in the as-cast state is austenite, the tensile strength and hardness of the material are not very high, but the toughness is good. The plastic deformation is large during cutting, the lattice distortion is high, the section shrinkage is also high, the work hardening is serious, the strength is obviously improved, and the cutting resistance increases.
- (2) The cutting temperature is high. The material has high thermal strength and large friction coefficient, consumes large cutting deformation work and friction work during cutting, and generates a large amount of heat energy. The thermal conductivity of the material is low, and a large amount of cutting heat accumulates in the cutting zone, resulting in a high cutting temperature.
- (3) The tool wears out quickly. Due to the characteristics of the alloy material, the large amount of heat generated during cutting is not easily taken away by the chips, and is concentrated on the tool, causing severe wear of the tool, and sometimes even plastic deformation, chipping, chipping, and peeling of the tool edge. At the same time, the material is soft, viscous and plastic, which increases the friction between the chips and the front edge of the tool during cutting, which intensifies the wear of the tool, which not only reduces the durability of the tool, but also reduces the invar machining accuracy.
By selecting appropriate tool materials and tool geometric parameters, using the correct machining technology and cooling lubricant, the cutting performance is improved and the machining accuracy of the mold is guaranteed. Tungsten carbide cemented carbide with good heat resistance, high wear resistance, low oxidation resistance and low adhesion is selected as the cutting tool material. When the mold is turned, the tool adopts a large rake angle, the cutting edge is sharp, and the cutting is brisk. The front of the tool is provided with a chip breaker and the front and rear corners have a certain roughness to make the chips and the tool difficult to stick. Cutting process parameters include cutting speed, depth of cut and feed. The cutting speed should not be too high to reduce the cutting temperature. Generally, the cutting depth should not be too small to avoid leaving the work hardened layer. The feed amount should not be too large to avoid too heavy cutting load, but it should not be too small. This will cause the tool to work in the chilled layer formed after the last invar machining, accelerate the wear of the tool, and generally control the feed. When finishing the mold surface, in order to ensure the surface finish, the cutting speed is selected as 1.8/S, and the feed rate is 0.05mm/r. In order to reduce the large amount of cutting heat generated during cutting, sufficient cooling and lubrication must be carried out. The cooling lubricant is mixed with kerosene and mechanical oil.
Common defects of cast iron parts include: pores, sand sticking, sand inclusion, sand hole, expansion sand, cold barrier, insufficient pouring, shrinkage porosity, shrinkage cavity, lack of meat, sarcoma, etc. Why are there always defects in the lost wax casting process?
The gas does not escape in time before the molten metal is crusted, and thus the hole-like defects generated in the casting.
However, casting defects have always been a major problem that plagued foundry enterprises. Poor solutions to casting defects will affect the quality of castings. Various casting defects such as wear, scratches, blisters, pinholes, cracks, defects and deformations, reduced hardness, and damage occur in the process of producing machine tool parts, which increase the production cost of the enterprise.
Commonly used welding machines: currently on the market, welding repairs are used to repair defects, and generally there are the following types:
First, argon arc welding: aluminum alloy die castings are mostly welded with argon arc welding machines. Some mold manufacturing and repair manufacturers also use this welder to repair mold defects. Advantages: high welding repair efficiency and higher accuracy than electric welding machines. Disadvantages: Used for defect repair. When repairing small defects (pores, sand holes), there are traces on the edge of the molten pool (undercut phenomenon) due to excessive impact. Welded steel parts have hard spots. Due to thermal influence, thermal deformation is likely to occur when welding non-ferrous castings or thin-walled parts. Operational technical requirements are high.
Second, electric welding machine: the traditional method of welding and repairing cast iron and steel lost wax casting. Advantages: Repair major defects. Disadvantages: After welding, the hardness of the solder joints is too high, there are internal stresses, and cracks are easy to occur. Generally, annealing heat treatment is required to meet the processing requirements. In addition, due to the limitation of welding conditions, secondary defects such as pores and slag inclusion are prone to occur inside.
Cold welding machine: Imported foreign technology is introduced, and the special welding wire is cladding to the damaged part of the workpiece through the high heat energy generated by the micro-electric instantaneous discharge, and it is firmly welded to the original base material. After welding, it only needs to go through the post-treatment with little polishing.
Advantages: 1. No need to preheat, so there is no deformation, no blackening, undercut and residual stress, and no local annealing.
2. High efficiency and energy saving: Although only 1200W power, the welding repair speed and effect are several times that of the same 4000W.
3. Power supply: inverter power supply, energy saving and environmental protection, high efficiency, stable performance, light and smart machine
4. High repair accuracy: The thickness of the surfacing welding is from a few microns to a few millimeters, and only needs to be polished and polished. After the repair, the color difference is small or no color difference.
5. Environmental protection: There is no pollution in the working process.
6. Usability: It is easy for anyone to use, no operating license is required, and surfacing can also be carried out in places that are difficult to weld.
7. Economical: Repair immediately on site, improve production efficiency and save costs.
China’s population has always been a big problem, because the country with a large population has a great demand for all aspects. In many cases, the use of materials is relatively large. At this time, materials are particularly important. Just like S136 die steel, although there are a lot of this kind of steel, the […]
The feed motion of a CNC machining machine tool is the direct object of digital control. Regardless of point control or contour control, the final dimensional accuracy (accuracy) and contour accuracy of the workpiece are affected by the transmission accuracy and sensitivity of the feed motion. (Sensitivity) and stability (explanation: stability and stability; no change). For this reason, the feed system of CNC machining invar machine tools should pay full attention to reducing friction resistance, improving transmission accuracy and rigidity, eliminating transmission gaps and reducing inertia of moving parts.
- 1. Reduce friction resistance
In order to improve the rapid response performance and motion accuracy (precision) of the CNC machine tool (attribute: automated machine tool) feed system, the friction resistance and the difference between dynamic and static friction of the moving parts must be reduced. In order to meet the above requirements, in the feed system of CNC machine tools, ball screw nut pairs, hydrostatic screw nut pairs, rolling slides (TTW guide), hydrostatic guides and plastics (structure: synthetic resin, plasticizer) are commonly used , Stabilizer, pigment) guide rail. While reducing frictional resistance, it is also necessary to consider that the transmission components should have appropriate damping to ensure the stability of the system (explanation: stable and stable; no change) (The stability of).
- 2. Improve transmission accuracy (precision) and rigidity
The transmission accuracy (precision) and rigidity of the feed transmission system are mainly determined by the transmission clearance and the accuracy and rigidity of the screw nut pair, worm gear pair (circumferential feeding) and the supporting structure from the mechanical structure consideration (consider) . CNC machining CNC is also called computer gong, CNCCH or numerical control machine tool. It is actually a kind of name in Hong Kong, which greatly reduces the number of tooling. CNC machining machining parts with complex shapes does not require complex tooling. CNC machining is a new type of machining invar technology. It is to compile the machining program, that is, to convert the original manual work to computer programming. If you want to change the shape and size of the part, you only need to modify the part machining program, which is suitable for new product development and modification. In the numerical control machining, the control system issues instructions to make the tool perform various motions that meet the requirements. The shape and size of the workpiece are expressed in numbers and letters in the form of technical requirements and machining requirements. It generally refers to the process of machining parts on CNC machine tools. In order to improve production automation, shorten programming time and reduce CNC machining costs, a series of advanced CNC machining technologies have been developed and used in the aerospace industry. Transmission clearance mainly comes from the transmission gear pair, worm gear pair, screw nut pair and its supporting parts. Pre-tightening force should be applied or measures to eliminate the gap should be taken (refer to the solution to the problem). Shortening the transmission chain and setting a reduction gear in the transmission chain can also improve the transmission accuracy. Enlarging the diameter of the screw, and applying pre-tightening force to the screw nut pair, supporting parts, and the screw itself are effective measures to improve the transmission rigidity. Insufficient stiffness can also cause crawling and vibration of the workbench (or carriage).
- 3. Reduce the inertia of moving parts
The inertia of the moving parts has an impact on the startup and braking characteristics of the servo mechanism (organization), and the inertia of the parts in high-speed operation has a greater impact. CNC machining General CNC machining usually refers to computer digital control precision machining, CNC machining lathe, CNC machining milling machine, CNC machining boring and milling machine, etc. The feed route of finishing is basically carried out along the part contour sequence. Therefore, the focus of determining the feed route is to determine the feed route of rough machining invar and idle stroke. Therefore, on the premise of satisfying the strength and rigidity of the component, the mass of the moving component and the diameter and mass of the rotating component may be reduced as much as possible to reduce the inertia of the moving component.
The weight and size range of cast aluminum parts are very wide. The lightest weight is only a few grams, the heaviest can reach 400 tons, the thinnest wall thickness is only 0.5 mm, the thickest can exceed 1 meter, and the length can be several millimeters to ten. A few meters can meet the requirements of different industrial sectors. Generally, for the appearance quality of aluminum castings, comparison samples can be used to judge the surface roughness of lost wax aluminum casting, and the fine cracks on the surface can be inspected by the coloring method and the magnetic powder method. The internal quality of aluminum castings can be inspected and judged by audio, ultrasonic, eddy current, X-ray and γ-ray methods.
The quality of aluminum castings has a great influence on the performance of mechanical products. For example, the size, accuracy and surface roughness of the impellers, casings and hydraulic parts of various pumps directly affect the working efficiency of pumps and hydraulic systems, energy consumption and the development of cavitation, etc. Internal combustion engine cylinders, The strength and shock resistance of aluminum castings such as cylinder heads, cylinder liners, piston rings, exhaust pipes, etc. directly affect the working life of the engine.
The principle of casting aluminum casting method selection: aluminum casting is preferred to sand casting. The main reason is that sand casting has lower cost than other casting methods, simple production process, and short production cycle. When the wet type cannot meet the requirements, consider using clay sand surface dry sand type, dry sand type or other sand types. The casting method of aluminum castings should be compatible with the production batch. Low pressure casting, die casting, centrifugal casting and other casting methods are only suitable for mass production because of the expensive equipment and molds. Aluminum castings can be cast in single pieces or mass production.
Shrinkage porosity of cast aluminum generally occurs in thick parts at the root of the fly riser near the inner runner, the wall thickness transition part and the thin wall part with a large plane. The fracture is gray in the as-cast state, and the light yellow is grayish white, light yellow or gray black after heat treatment.
Cleaning method of aluminum casting:
1. Casting shell cleaning: Generally speaking, aluminum castings can be further cleaned up after they are completely cooled. After the aluminum castings are cast in the shell, the cooling time of the castings in the mold is related to the material and lost wax aluminum casting. The shape and size of the parts are directly related to the production conditions. Generally, if the cleaning of aluminum alloy castings is done early, it will easily cause deformation and cracks of the aluminum castings. The cooling time of castings with larger size and more complicated process should be longer, and the cooling time of castings with smaller size and thin wall and simple process can be shorter.
2. Cutting pouring riser: The main methods of cutting pouring riser are: gas cutting, grinding wheel cutting, sawing machine, hydraulic cutting, anode cutting, etc.
3. Surface cleaning of aluminum castings: After the shelling of aluminum castings, there will always be iron oxide scale remaining on the surface of the castings, especially the castings with complex cavities, deep grooves, and blind holes, which cannot be cleaned completely, and surface cleaning must be performed .
4. Shot blasting treatment: If castings with special requirements can be shot blasting, shot blasting is to use the centrifugal force generated by the high-speed rotating shot blasting impeller to throw iron shots on the surface of the castings to make the surface of the cast aluminum Sand, sticky sand or iron oxide scale is removed. Generally speaking, the surface of the casting after shot blasting is related to the size of the iron shot.
5. Repair welding: usually refers to castings that do not meet the acceptance technical conditions or the requirements of the order agreement, and have casting defects but can be repaired. First of all, we must clean up the repair welding parts, so that the surface of the aluminum casting is completely clean and exposed to the metallic luster. The size of the defects should be welded from small to large. For example, the area of repair welding is large and the defects should be annealed after welding in important parts of the casting.
Aluminum castings have low cost, good manufacturability, remelting and regeneration to save resources and energy, so the application and development of this material are enduring. Such as research and development of cupola-electric furnace double smelting technology and equipment; extensive use of advanced molten iron desulfurization and filtration technology; thin-wall high-strength iron casting manufacturing technology; cast iron composite material manufacturing technology; iron casting surface or local strengthening technology; isothermal Yanghuo nodular cast iron complete set of technology; using metal mold casting, metal mold sand-coated casting, continuous casting and other special processes and equipment. Because of its low density, high specific strength, and corrosion resistance, cast lost wax aluminum casting light alloys will be more widely used in aviation, aerospace, automobile, machinery and other industries. Especially in the automobile industry, in order to reduce fuel consumption and improve energy utilization, it is a long-term development trend to replace steel and iron castings with aluminum and nickel alloy castings.
Among them, it focuses on solving pollution-free, high-efficiency, easy-to-operate refining technology, metamorphism technology, grain refinement technology and rapid detection technology before the furnace.
In order to further improve the material performance and maximize the potential of the material, high-quality aluminum alloy materials, especially aluminum-based composite materials, can be developed to meet the performance requirements of different working conditions; strengthen the research on the cluster alloy melting process, and continue the alloy die casting and squeeze casting Process and related technology development research; perfect ferroalloy smelting equipment and related technology and process development research.
Characteristics of cast aluminum parts:
Aluminum has strong stability and oxidation resistance, aluminum alloy castings will not rust and corrosion;
The surface adopts electrostatic powder spraying and fluorocarbon paint, and the various large-scale indoor and outdoor decorative products manufactured can keep the color for a long time.
Aluminum has good ductility and is convenient for various shapes and designs.
It has toughness, can be used repeatedly, and has a wider range of applications.
After various rigorous tests, the aluminum products’ resistance to earthquakes, wind pressure and weathering are guaranteed.
The unique aluminum alloy casting method makes the work weight lighter, reduces the burden in the handling and construction operations, and reduces the risk.
Repetitive production parts processed by CNC lathes: The preparation time of procedures using CNC grinders occupies a relatively high proportion. For example, process analysis preparation, programming, adjustment and trial cutting of the first part of the part, the total of these comprehensive man-hours is often dozens to hundreds of times the man-hours of a single part titanium machining, but the work content of these CNC lathes can be saved and used repeatedly, so When a part is successfully trial-produced on a CNC grinder and then repeatedly put into production, the production cycle is greatly reduced, the cost is less, and better economic benefits can be obtained.
It is required to focus on ensuring the quality of the key parts in small and medium batches that can be produced efficiently: CNC grinding machines can achieve high-precision, high-quality, and high-efficiency grinding machining under computer control. Compared with special grinding machines, it can save a lot of special process equipment, has strong flexible manufacturing capacity and obtain better economic benefits. Compared with ordinary grinders, it can eliminate many man-made interference factors in the long process flow of complex machining, and the accuracy of machining parts is good, the interchangeability is good, and the machining efficiency is high.
The parts processed by the CNC lathe should meet the technological characteristics of the multi-process centralized titanium machining of the CNC grinder. When the CNC grinder processes the parts, the grinding wheel cuts the workpiece and the corresponding non-nc grinder is exactly the same, but it can perform some machining accuracy requirements For example, in terms of grinding range, ordinary grinders are mainly used to grind cylindrical surfaces, circular CNC lathe cones or the end faces of stepped shoulders. In addition, CNC cylindrical grinders can also grind circles. Torus, as well as the above complex combined surfaces in various forms.
The machining batch of parts should be larger than that of ordinary lathes and batches. When machining small and medium batches of parts on non-CNC grinding machines, the pure cutting time only accounts for 10%-30% of the actual working hours due to various reasons. When machining on a multi-process centralized CNC grinding machine such as a grinding machining center, this ratio may rise to 70% to 80%, but the man-hours for preparing adjustments are often much longer, so the parts batch will become too small. uneconomic.
Considerations for the titanium machining of some special parts processed by CNC lathes. Although some parts are processed in small batches, ordinary lathes have complex shapes, high quality and good interchangeability. This cannot meet the above requirements on non-CNC grinders and can only be arranged. Machining on CNC grinders, such as parabola, cycloid cams and special-shaped mirrors.
In the machining process of the CNC machining center, whether the selection of the positioning reference is reasonable determines the quality of the parts, and has a great influence on whether the dimensional accuracy and mutual position accuracy of the parts can be guaranteed and the machining sequence arrangement between the parts. When the workpiece is installed with a fixture, the choice of positioning datum will also affect the complexity of the fixture structure. This requires the fixture not only to withstand greater cutting force, but also to meet the requirements of positioning accuracy. Therefore, the choice of positioning reference is a very important technical issue. So how to choose a positioning datum when machining parts with a CNC machining center? Here is a brief introduction:
1. The selected datum should ensure the accurate positioning of the workpiece, facilitate the loading and unloading of the workpiece, quickly complete the positioning and clamping of the workpiece, the clamping is reliable, and the fixture structure is simple.
2. The CNC machining center has simple operations between the selected datum and each size of each processed part, which can minimize the calculation of the dimensional chain and avoid or reduce the calculation links and calculation errors.
3. Ensure machining accuracy. When determining the part positioning datum, the following principles should be followed:
1) The origin of the workpiece coordinate system, that is, the “program zero point”, does not have to coincide with the part positioning datum, but there must be a certain geometric relationship between them. The choice of the origin of the workpiece coordinate system is mainly for the convenience of programming and measurement. For parts with high dimensional accuracy requirements, when determining the positioning datum, it should be considered whether the positioning datum can accurately measure the coordinate origin of the CNC machining center.
2) When machining benchmarks and finishing at each station of the CNC machining center, the selection of positioning benchmarks should consider as much machining content as possible for finishing. For this reason, it is necessary to consider a convenient positioning method for each surface to be processed. For example, for the box, it is best to use the positioning method of two pins on one side, so that the tool can process other surfaces.
3) Try to choose the design datum on the part as the positioning datum. This requires that when roughing, consider what kind of roughing datum to use to machine each surface of the finishing datum, that is, each positioning datum used by the CNC machining center must be processed on the previous ordinary machine tool or other machine tool. In this way, it is easy to ensure the accuracy relationship between the machining surfaces of each station.
4) When the positioning datum of the CNC machining center parts is difficult to coincide with the design datum, the assembly drawing should be carefully analyzed to determine the design function of the part design datum, and through the calculation of the dimensional chain, strictly specify the shape and position between the positioning datum and the design datum Tolerance range to ensure machining accuracy.
5) When the station machining including the design datum cannot be completed at the same time in the CNC machining center, try to make the positioning datum coincide with the design datum. At the same time, it should be considered that after positioning with this datum, all key precision parts can be processed by one clamping.
There are two types of cutting fluids used in CNC machining in Dongguan: one is oil-based cutting fluid and the other is water-based cutting fluid;
The cutting fluid used in cnc machining is divided into four types: cutting oil, emulsion, semi-synthetic fluid, and synthetic fluid; for the above four cnc machining cutting fluids,
You may commonly use cutting oil, emulsion (called soapy water in some places), synthetic fluid (many people call it environmentally friendly fluid), and you may know less about semi-synthetic nights;
How do you choose cutting fluid during machining? Let’s take a look at the advantages and disadvantages of each cutting fluid:
1. Cutting oil for CNC machining in Dongguan:
- a. Very high physical lubrication
- b. Suitable for low speed, less cutting allowance
- c. Provide very good surface finish
- a. Poor heat transfer
- b. Fire hazards
- c. High usage cost
- d. Smoke/fog
2. Emulsion used in Dongguan CNC machining:
- a. Safe for multiple metals
- b. It has better cooling compared with cutting oil
- c. Better scouring ability of iron filings
- d. Lower cost than cutting oil
- e. Better anti-rust
- f. Easy to treat sewage
- a. Increase in dosage
- b. Emulsify dirty oil
- c. Poor odor control
- d. Dirty equipment
- e. Poor stability against hard water
- f. Poor filtering
- g. Poor mixing
3. Semi-synthetic fluid used in Dongguan CNC machining:
- a. Better cooling than emulsion
- b. Better anti-rust
- c. Use cleaner than emulsion
- d. Better filterability
- e. More suitable for hard water and dirty oil
- f. More suitable for hard water and dirty oil
- g. It has better antibacterial properties than emulsion
- a. There is a tendency to foam in soft water
- b. Oil repellency is worse than synthetic fluid
- c. When used in high concentrations, there may be skin allergies
- 4. Synthetic fluid used in Dongguan CNC machining:
- a. Very good cleanliness
- b. Will not smell
- c. High operator acceptance
- d. Low consumption turnover rate (12-20 weeks)
- e. Very good cooling
- f. Repellent oil completely
- g. Low foam
- h. Long service life
- i. Very good filtration/fast settling performance
- a. Low physical lubrication
- b. Difficulty in sewage treatment
- c. Sticky residue, especially in hard water
- d. Not compatible with emulsion
- e. React with some polycarbonate
- f. Paint that may damage the machine tool
The machining center is a highly mechatronics product. It has a variety of technologies and comprehensive machining capabilities. It performs multiple cutting functions based on the use of a cutting machine. It also belongs to a compound machine tool and a CNC machine tool with more functions.
Of course, the system of a titanium machining center is not only a numerical control system, but also many other very important systems to assist machining, such as servo systems, lubrication systems, and cooling systems. The function of each system is different, except for the mechanical mechanism of the whole machine, it can only rely on these systems to form a complete cycle.
Commissioning of machining center:
1. Add oil to each lubrication point according to the requirements of the manual, fill the hydraulic oil tank with the required hydraulic oil, and connect the air source.
2. Power on, each component is powered on separately or each component is powered on after a power-on test. Investigate whether each component has an alarm, manually investigate whether each component is normal, whether each safety device is working, so that all links of the machine tool can be operated and Get in motion.
3. Grouting. After initial operation, roughly adjust the precision of the machine tool, and adjust the titanium machining relative orientation of the main moving parts and the host after disassembly. Align the manipulator, tool magazine, communication workbench, position, etc. After these tasks are completed, the anchor bolts of the main engine and various accessories can be filled with quick-drying cement, and the reserved holes for the anchor bolts in various places can be filled flat.
4. Debugging. Prepare various inspection tools, such as fine level, standard square ruler, parallel square tube, etc.
5. Fine-tune the level of the machine tool to make the accuracy within the range of the error allowed. Using multi-point pad support, adjust the bed to a level in a comfortable state to ensure the stability of the bed after adjustment.
6. Use manual operation to adjust the position of the manipulator relative to the spindle, and use an adjustment mandrel. When installing a large-weight tool holder, it is necessary to carry out active communication between the tool magazine and the spindle position repeatedly to ensure accuracy and no impact.
7. Move the worktable to the communication position, adjust the relative position of the pallet station and the exchange workbench, to achieve the active communication action of the workbench is stable, and the workbench is installed with a large load for titanium machining repeated communication.
8. Check whether the setting parameters of the CNC system and the programmable manipulator PLC device match the specified data in the random data, and then test the main operating functions, safety measures, and the execution of common instructions.