CNC high-speed precision parts machining process

CNC high-speed precision parts machining mainly refers to the use of digital information recorded on the media to control the machine tool so that it can automatically perform the specified machining tasks. Numerical control cnc machining aluminum can ensure that the product achieves extremely high machining accuracy and stable machining quality; the operation process is easy to be automated; the productivity is high, and the production cycle is short; it can greatly reduce the process equipment to meet the needs of rapid product upgrading; it is usually closely connected with CAD Get up and realize the transformation of design ideas to final products. Students should focus on the connection between the processes and the meaning of each step in the study of the entire CNC high-speed precision parts machining process. Broadly speaking, the composition of the entire process includes product analysis-graphic design-process planning-path generation-path simulation-path output-machining-inspection. In this session, a specific case is completed by way of demonstration, focusing on understanding the connection of each link. The material processed in the case is two-color plate or plexiglass.

1. Product analysis Through product analysis, certain composition information and some specific machining requirements should be obtained.

2. Graphic design Graphic design should first be based on a detailed analysis of the product. For example, for stamp machining, we must analyze the cnc machining aluminum requirements to determine the font, text size, stamp type, etc.

3. Process planning. Through the analysis of the appearance and machining requirements of the workpiece product in the early stage, each machining step is reasonably established from the overall machining.

4. Path generation The process of path generation is actually that we implement process planning through software, and at the same time, we optimize the tool path to a certain extent through parameter settings.

5. After the path simulation path is generated, we generally have no intuitive feeling about its final performance on the machine tool. Here we can check the possible problems through path simulation, thus reducing the scrap rate of actual cnc machining aluminum. The general inspection focuses on the appearance of the workpiece, whether it is over-cut or under-cut, and then whether the process planning of the path is reasonable.

6. Path output Path output is a necessary step for software design and programming to be realized on the machine tool. Through path output, an intermediate reference can be used to establish a connection between the two. If the students have a professional background in CNC, it can also be understood as the post-machining of the tool path.

The main characteristics of the linear and hard rails of the CNC machining center are as follows:

  • 1. The advantages of hard rail:
    1. It can withstand larger loads and is suitable for roughing machine tools with large tool volume and large feed.
    2. Because of the large contact area of the guide rail, the machine tool runs more smoothly, which is suitable for machine tools with higher requirements for machine vibration, such as grinders.
  • 2. Disadvantages of hard rail:
    1. The material is not uniform. Because it is generally cast, it is easy to produce casting defects such as sand inclusion, air holes, and looseness in the material. If these defects exist on the guide rail surface, it will have a negative impact on the service life of the guide rail and the accuracy of the machine tool.
    2. The titanium machining is more difficult, because this type of guide rail is generally connected with the main parts of the machine tool, such as the base, column, worktable, and saddle, so in the process of machining, its shape and position tolerances, roughness requirements, and timeliness Machining, quenching and other processes are difficult to control, resulting in the titanium machining quality of parts cannot meet the requirements of assembly.
    3. It is difficult to assemble. The word “assembly” means to assemble as well as to assemble, and this arranging process is a process of combining technology and physical strength. It cannot be done by ordinary workers. It requires a relative quantity of skills. The overall accuracy of the machine tool can be completed by an assembly worker who is quite sure of it. At the same time, it needs to be equipped with a blade, flat ruler, square ruler, square ruler, dial indicator, dial indicator and other corresponding tools to complete it.

CNC lathe machining is a high-precision and high-efficiency machining method that uses digital information to control the displacement of parts and cutters by automatic machine tools. It is an effective way to solve the problems of aerospace products and parts with many varieties, small batches, complex shapes, and high precision, and to realize efficient automatic machining. Next, let’s take a look at the composition and working steps of CNC machine tools.

1. The composition of CNC machine tools. The CNC machine tool is composed of a program, an input and output device, a CNC unit, a servo system, a position feedback system and the machine tool body, which are briefly introduced below.

  •    1. Numerical control unit. The CNC unit is the core of the CNC machine tool and consists of three parts: information input, advance cnc machining and output.
  •    The numerical control unit receives the digitized information, and after decoding, interpolation and logical machining by the control software and logic circuit of the numerical control device, it outputs various instruction information to the servo system, and the servo system drives the executive parts for feed motion. Others include the speed change, reversing and start and stop signals of the main moving parts; the tool command signals for selecting and changing tools, the start and stop of cooling and lubrication, the loosening and clamping of workpieces and mechanical parts, the indexing of the indexing table and others Auxiliary command signal, etc.
  •    2. Servo system. It is composed of a driver and a drive motor, which together with the execution parts and mechanical transmission parts on the machine tool form the feed system of the CNC machine tool. Its function is to convert the pulse signal of the numerical control device into the movement of the machine tool moving parts. For a stepper motor, each pulse signal will make the motor rotate an angle, and then drive the moving parts of the machine tool to move a short distance. Each execution part of the feed motion has a corresponding servo drive system, and the performance of the entire machine tool mainly depends on the servo system.
  •    3. Position feedback system. Servo motor angular displacement feedback and CNC machine tool actuator (table) displacement feedback. Including gratings, rotary encoders, laser rangefinders, magnetic gratings, etc. The feedback device converts the detection result into an electrical signal and feeds it back to the numerical control device. Through the comparison, the deviation between the actual position and the command position is calculated, and the deviation command is sent to control the feed motion of the executing part.
  •    4. Machine tool mechanical part. For the CNC machine tools of the advance cnc machining center, there are also parts such as a tool magazine for storing tools and a manipulator for changing tools. The composition of the mechanical parts of a CNC machine tool is similar to that of an ordinary machine tool, but the transmission structure is simpler, and the accuracy, rigidity, and seismic requirements are higher. Its transmission and speed change system are more convenient for automatic expansion.

2. The working steps of CNC machine tools. The following steps should be passed through the CNC lathe machining:

  •    1. Preparation stage. According to the drawings of the processed parts, determine the relevant machining data (tool path coordinate points, machining cutting parameters, tool size information, etc.). And select other auxiliary information according to the process plan, selected fixture and tool type.
  •    2. Programming stage. According to the advance cnc machining technology information, compile the CNC machining program (machining technology description) in a language that can be recognized by the CNC system of the machine tool, and fill in the program sheet.
  •    3. Prepare information carrier. According to the compiled program list, the program is stored in an information carrier (punch tape, tape, disk, etc.). All machining information is transmitted to the CNC system through the information carrier. If the CNC machine tool is connected to the computer, the information can be directly loaded into the CNC system.
  •    4. Machining stage. When the CNC system of the machine tool executes the program, it decodes and calculates the machining program statements, converts them into action instructions, and drives the moving parts. Under the unified coordination of the system, the moving parts are driven to move in time, and the workpiece is automatically processed.

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.
Common name

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:
1. Durability
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.
2. Plasticity
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.
3. Security
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.