2021 – Page 30 – CNC Machining & Turning, Milling, Metal parts

CNC computer gong processing high precision parts attention

Don’t think that high-precision parts processing is a common processing without attention. If we ignore some details, it may have a great impact on the processing of parts. Then, what are the precautions for high-precision parts processing?

For high-precision parts, the processing is very strict. The processing procedures include feed and output. There are specific requirements for the size and accuracy, such as 1 mm plus or minus micrometers. If the size is too wrong, it will become a scrap. At this time, it is equivalent to reprocessing, which is time-consuming and laborious. Sometimes, the whole processing material will be scrapped, resulting in an increase in cost. At the same time, the parts are definitely unusable.
For the processing of high-precision parts, the main requirements are the size, such as the diameter of the cylinder, there are strict requirements, positive and negative errors within the specified range are qualified parts, otherwise they are unqualified parts; There are also specific and strict requirements for length, width and height, as well as positive and negative errors. For example, if the diameter of an embedded cylinder (take the simplest basic parts as an example) is too large and exceeds the allowable error range, it will cause the situation that it cannot be inserted. If the actual diameter is too small and exceeds the lower limit of the allowable negative error, it will cause the problem that it is too loose and not firm. These are all unqualified products, or the length of the cylinder is too long or too short, which is beyond the allowable range of error. They are all unqualified products, and they have to be scrapped or reprocessed, which will inevitably lead to the increase of cost.
The requirement of high-precision parts processing is actually the most important dimension problem. It must be processed in strict accordance with the additional drawings. The actual size of the processed parts will not be exactly the same as the theoretical size of the drawings, but as long as the processing size is within the allowable error range, they are all qualified parts. Therefore, the requirement of precision parts processing is to process in strict accordance with the theoretical size Line processing.
The second is the advanced precision parts processing equipment and testing equipment. The advanced processing equipment makes the processing of precision parts simpler, higher precision and better effect. The detection device can detect the parts that do not meet the requirements, so that all the products sent to customers can really meet the requirements.

CNC computer gong processing complex parts technology

The continuous fine blanking die for complex parts is the frontier basic technology of fine blanking technology, and it is expected to promote the whole fine blanking technology in China. Taking the synchronizer gear ring, clutch plate, longitudinal compound continuous fine blanking process and continuous fine blanking die for complex parts as the breakthrough point, the key technology of fine blanking die design and manufacturing is studied, so as to realize the rapid improvement of fine blanking die technology in China and shorten the gap with advanced countries as soon as possible.

Study on the life promotion of fine blanking die and its related key technologies

Die life is a comprehensive reflection of die materials and the level of supporting products. Taking the life of fine blanking die as the leader to carry out technical research can not only solve the problem that the life of fine blanking die is too low, but also drive the technical development of die materials, fine blanking process, supporting tooling and other auxiliary products.

Research and development of fine blanking precision forging composite technology

Precision blanking and precision forging are two advanced manufacturing technologies developed in parallel. If the precision blanking parts are too thick and need precision forging, the precision forging must be too thin. They are closely related. The basic idea of developing precision forging and fine blanking compound process is to find the combination point of the two processes (such as gear parts with wheel hub and cam parts with short shaft). The precision forging in China has a long history and has a high level, so it is a good way to improve the overall level of precision blanking technology in China.

Types of CNC metal processing technology

Time effect elimination method

Aging elimination is a traditional method to reduce quenching residual stress. As aluminum alloy materials, especially aviation aluminum alloy materials, are very sensitive to temperature, the increase of aging temperature will obviously reduce the strength index, resulting in excessive precipitation of mgzn2 and other strengthening phases, resulting in over aging phenomenon. Therefore, aging treatment after quenching is usually carried out at a lower temperature (less than 200-250 ℃), which affects the stress relief effect (only 10-35%)

Mechanical stretching the principle of mechanical stretching is to apply a certain amount of permanent tensile plastic deformation to the quenched aluminum alloy plate along the rolling direction, so that the plastic deformation will occur after the superposition of tensile stress and the original quenching residual stress, so that the residual stress can be relaxed and released. The results show that more than 90% of the residual stress can be eliminated by mechanical stretching. However, this method is only suitable for the parts with simple shape, and it has high requirements on the microstructure uniformity of aluminum alloy sheet before drawing, so it is mostly used in aluminum processing plants.
Die cold pressing method

Die cold pressing method is to eliminate the residual stress of aluminum alloy die forgings with complex shape through strictly controlled limited cold shaping in a special finishing die. In fact, the term “die pressing” is not accurate enough, because its main mechanism is to make the local material of aluminum alloy die forgings subject to “tension” or “compression”. When the finishing die is pressed down, the finishing punch is embedded into the draft angle of the end face and edge (rib) of the aluminum alloy die forging, which actually causes the “tensile” effect on the web part of the die forging. Therefore, this method is to adjust rather than eliminate the overall stress level of the parts. It can release the residual stress in some parts of the aluminum alloy die forging and increase the residual stress in other parts.

Properties of various materials processed by CNC

The positioning accuracy and repeated positioning accuracy of CNC lathe are very high, so it is easy to ensure the consistency of the size of a batch of parts. As long as the process design and program are correct and reasonable, combined with careful operation, the parts can obtain higher processing accuracy, and it is also convenient for the quality control of large-scale computer gong processing. CNC lathe is a technology intensive Mechatronics typical large-scale computer gong processing products, maintenance personnel need to understand both mechanical and microelectronic maintenance knowledge, but also equipped with better maintenance equipment.

Using metal mold, filling mold under high pressure and high speed, rapid solidification under pressure is a metal forming method with high efficiency and high precision, but the manufacturing cost of die-casting machine and die-casting mold is high; mass production, small and medium-sized thin-walled castings mainly composed of zinc alloy, aluminum alloy, magnesium alloy and copper alloy, are also used for iron and steel castings.
Use wax mould to make a whole refractory shell mold outside the wax mould. After the wax pattern is melted off by heating, it is poured by gravity. The casting has high precision and good surface quality, but the cost of die making is high and there are many processes. Manual operation, poor working conditions; various production batches, mainly carbon steel, alloy steel alloy and difficult to process high melting point alloy complex parts are suitable, casting quality is generally less than 10kg.
Casting with metal mold under gravity can refine the structure of non-ferrous alloy castings. Gray iron castings are easy to produce white, with high productivity, no dust, high equipment cost, and poor labor conditions in manual operation. Mass production is mainly made of non-ferrous alloy, and can also be used for thick wall, simple or medium complex small and medium-sized castings of cast steel and cast iron.
Using metal mold, graphite mold and sand mold to fill mold and solidify under gas pressure, the casting is compact, the metal yield is high, and the equipment is simple; single piece, small batch or mass production, medium large thin-walled casting mainly made of non-ferrous alloy.
High precision pattern, self hardening refractory slurry, gravity casting, high precision casting, fine surface roughness, but expensive ceramic slurry; single piece, small batch production of medium, small, thick wall medium complex castings, especially suitable for metal mold, template, hot box and various kinds of hot forging die.
Casting with metal sand or sand mold under the action of centrifugal force, and processing with computer gong, the structure of casting is compact, the equipment is simple, the cost is low, and the productivity is high, but the machining capacity is large; large quantities of iron pipe, copper sleeve, roller, metal bearing bush, cylinder sleeve and other rotary body castings are produced in single piece and batch.
use foam polystyrene plastic moulds to replace wood or metal mold parts locally or completely, and burn them when pouring. It can save wood and simplify the working procedure, but the dust and harmful gas are relatively large; for medium and large castings produced in single piece or small batch, 1-2 pieces are suitable, or for the parts of castings with difficult mold removal. Machining is now accessible to many industries, it also has a lot of processing methods, such as, gantry grinding and so on, the machining center can choose the best process line and cutting parameters, effectively reduce the auxiliary time in processing, so as to improve production efficiency. The production efficiency of machining center is high. And because of its automatic tool changing function, it can usually save complex tooling, reduce the installation, adjustment and multiple tool setting of processing parts and other relatively complex and tedious work.

CNC computer gong vmc-650 model

Vmc-650 mechanical characteristics and control system characteristics: mechanical characteristics:

1、 High rigidity, heavy cutting

All of them are made of high-quality resin sand wear-resistant casting, strong and tough rib, super large column, wide and low seat, honeycomb structure. After annealing treatment, the stress is removed and the deformation does not occur for a long time.
The three-axis adopts the rectangular guide rail with strong rigidity, which can bear heavy cutting, precision grinding of worktable and quenching treatment, greatly enhancing the surface hardness.

2、 High precision

The three-axis drive adopts Taiwan C3 precision ball screw and P3 bearing, which ensures the positioning accuracy and repeated positioning accuracy.
The three-axis adopts Mitsubishi servo motor and spindle motor, direct drive, which provides strong power and ensures the feeding accuracy under the strong bearing capacity.
P3 grade spindle of international famous brand is adopted to ensure the advantages of high reliability, long service life, low noise, small vibration and high precision of the spindle.

Control system characteristics:

1、 Good stability, fast speed and high precision

It adopts the world’s advanced Mitsubishi CNC system, and the M60s series adopts servo drive, which ensures the high stability, high speed and smooth surface of the control system.

2、 It has the advantages of high precision, has the function of manufacturing mold, and is the best choice for mold production.

All M60s series controllers are equipped with RISC 64 bit CPU.
It can correspond to Ethernet and IC card interface.
Coordinate display value conversion can be freely switched (program value display or manual insertion display switching)
Standard internal waveform display function, working position coordinate and center point measurement function.
Buffer correction function expansion: can correspond to IC card / computer link B / DNC / record MDI mode.
The editing mode in the editing screen can be automatically switched to full page editing or full name editing.
Graphic display function improvement: can contain props path data to fully display the working coordinates and the actual position of props compensation.
Simple dialogue program software (developed by APLC, magicpro)_ Navimill dialog program).
It can develop PLC software corresponding to Windows95 / 98 / 2000nt40 / me / XP.

CNC computer gong processing instructions

When only x-axis or y-axis is mirrored, the cutting sequence (forward milling and reverse milling), cutting direction and arc interpolation direction will be opposite to the actual program. When the x-axis and y-axis are mirrored at the same time, the sequence of tool feeding, the direction of tool compensation and the direction of arc interpolation remain unchanged.

Note: after using the mirror command, you must cancel it with M23 to avoid affecting the following program. In G90 mode, the mirror or cancel command can only be used after returning to the origin of workpiece coordinate system. Otherwise, the CNC system can not calculate the movement track behind, and the phenomenon of random tool walking will appear. At this time, we must implement manual origin reset operation to solve the problem. The spindle steering does not change with the mirror command.

[pause instruction]

G04X(U)_ /P_ It refers to the tool pause time (feed stop, spindle not stop). The value after address P or X is the pause time. The value after X should have a decimal point, otherwise it is calculated as one thousandth of the value in seconds (s), and the value after P cannot have a decimal point (that is, an integer), but in milliseconds (MS). However, in some hole system processing instructions (such as g82, G88 and g89), in order to ensure the roughness of the hole bottom, when the tool is processed to the hole bottom, there is a pause time. At this time, it can only be expressed by the address P. if it is expressed by the address x, the control system thinks that x is the x-axis coordinate value for execution.

[differences and relations among M00, M01, M02 and M03]

M00 is the program unconditional pause instruction. When the program is executed, the feed stops and the spindle stops. To restart the program, you must first return to jog state, press CW (spindle forward) to start the spindle, and then return to auto state, press start key to start the program.

M01 is program selective pause instruction. Before the program is executed, the opstop key on the control panel must be opened. The effect after execution is the same as that of M00. To restart the program, it is the same as above. M00 and M01 are often used for inspection of workpiece size or chip removal during machining. M02 is the main program end instruction. Execute this command, feed stop, spindle stop, coolant off. But the program cursor stops at the end of the program. M30 is the main program end instruction. The function is the same as M02, the difference is that the cursor returns to the program head position, regardless of whether there are other program segments after M30.

[address D and H have the same meaning]

Tool compensation parameters D and H have the same function and can be interchanged at will. They all represent the address name of compensation register in CNC system, but the specific compensation value is determined by the address of compensation number after them. However, in the machining center, in order to prevent errors, it is generally stipulated that h is the tool length compensation address, the compensation number is from 1 to 20, D is the tool radius compensation address, and the compensation number starts from 21 (the magazine of 20 tools).

CNC computer gong processing parts features

Due to the centralized process and automatic tool change, the machining center reduces the time of workpiece clamping, measurement and machine adjustment, so that the cutting time of the machine tool reaches about 80% of the starting time of the machine tool (only 15-20% for ordinary machine tools); at the same time, it also reduces the time of workpiece turnover, handling and storage between processes, shortens the production cycle, and has obvious economic effect. Machining center is suitable for small and medium batch production with complex shape, high precision and frequent product replacement. Now, manufacturing large-scale aircraft in China is one of the important development directions of China’s aviation industry in the future. The development of large-scale aircraft needs high support, elegant and sharp related technology. The very large wall part refers to the whole wall part which is widely used in large aircraft with large scale (20m) length direction. This part has the characteristics of large size, complex structure and high precision, which makes it difficult to manufacture large aircraft structure.

Very large parts of the wall have different loopholes to strengthen the overall structure, such as the rod due to high dimensional accuracy requirements, most of the production CNC processing means to complete. The development of China’s domestic large aircraft is used for the structural parts of large wall. The accuracy requirements are as follows: the thickness tolerance of network and rod is + / – 0.15mm, the height tolerance of rod is + / – 0.2mm, the outer wall surface is flat, and the distortion is not more than 5mm, which cannot be encouraged. It is necessary to have scientific and reasonable processing deformation control technology to meet the processing requirements.

Research on deformation control technology of super large wall parts processing, the whole deformation control technology, the whole verification in the actual processing deformation control technology, can effectively control the deformation of super large wall parts, the general processing accuracy is 0.2mm, has achieved good results, has important engineering application value.

Deformation control process of integral machining

The whole process of the super large wall part is analyzed, and the whole size blank large tensile aluminum alloy plate is formed. Finally, the asymmetric integral wall part with “one side smooth, one side” structure is formed. Generally, the material removal rate reaches 95%. In the process of creating pre stretched aluminum alloy plate, the machining deformation is mainly caused by the release of residual stress, especially for large-size parts. In the process of machining removal rate, if the residual stress release of this problem can not be well solved, it is easy to lead to the machining and treatment process of large deformation parts, resulting in the size out of tolerance scrap or the product does not meet the requirements.

Combined with the machining process of the very large wall part, the following deformation is set to control the whole process. The process includes: large edge cavity, positioning, surface finishing, roughing, seasoning, vacuum clamp, online measurement and completion, etc. The main purpose of the process of releasing residual stress in a large margin groove cavity is not to form the characteristic size. It is the key to control the deformation process by quickly deleting a large number of residual stress releasing blanks in surplus materials; positioning surface finishing, rough machining and natural aging rough machining release residual stress, and further release residual stress, Processing process has formed a unified allowance part blank, and the role of natural aging, easier to control processing deformation. During the preparation of vacuum clamp and on-line measurement allowance process, vacuum clamp is a way to ensure the stability of clamping part. Through the change of on-line measurement, through rough machining and natural aging allowance, the processing technology can be adjusted to ensure the accuracy of feature size. After finishing the finishing process, the wall plate can be treated,

In the above processes, each process considers releasing pressure and unified pressure to control the part of machining deformation. No matter in the process of form feature size rough machining or dimension precision machining, the analysis and consideration of parts machining is an important part of deformation control, so as to realize the overall control of machining deformation, Controlling the influence of machining deformation is to ensure the machining accuracy of parts.

In the process of precision parts processing, because of its complex structure and special materials, there will be a variety of stress and deformation problems that can not be predicted by engineers in the process of processing

Vertical machining center and horizontal machining center

Machining center is usually divided into vertical machining center and horizontal machining center according to the state of spindle in space.

The vertical machining center whose spindle is vertical in space is called vertical machining center, and the horizontal machining center whose spindle is horizontal in space is called horizontal machining center. Spindle can be vertical and horizontal conversion, known as vertical and horizontal machining center or five machining center, also known as composite machining center. According to the number of machining center columns, there are single column type and double column type (gantry type).

According to the coordinate number of machining center movement and the coordinate number of simultaneous control, there are three axis two linkage, three axis three linkage, four axis three linkage and five axis four linkage.

Six axis five linkage, etc. Three axis and four axis refers to the number of motion coordinates of the machining center. Linkage refers to the number of coordinates that the control system can control at the same time, so as to realize the position and speed control of the tool relative to the workpiece. Machining center can be divided into vertical, horizontal and composite machining center from the appearance. The spindle of the vertical machining center is perpendicular to the worktable, which is mainly used for processing plate and shell workpieces, and can also be used for mold processing.

The spindle axis of the horizontal machining center is parallel to the worktable, and its worktable is mostly a CNC rotary table controlled by servo motor. In the one-time clamping of workpieces, multiple machining surfaces can be processed through the rotation of the worktable, which is suitable for the processing of box workpieces. The compound machining center mainly refers to that there are two vertical and horizontal spindles on one machining center, or the spindle can change the angle by 90 degrees, so it can realize the machining of five surfaces in one clamping of workpiece.

CNC machining parts process

CNC 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 processing tasks. Numerical control machining can ensure the products to achieve high machining accuracy and stable machining quality; the operation process is easy to achieve automation; high productivity, short production cycle; can reduce a large number of process equipment to meet the needs of rapid product upgrading; it is usually closely linked with CAD to achieve the transformation of design ideas to the final product.

In the whole CNC process, we should focus on the relationship between the processes and the significance of each step. Broadly speaking, the whole process consists of product analysis graphic design process planning path generation path simulation path output processing inspection.

Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
Graphic design graphic design should be based on the detailed analysis of the product, determine the type of graphics by analyzing the processing requirements, and draw through the graphics software.
Path generation the process of path generation is that we realize the process planning by software, and optimize the tool path by setting parameters.
Through the analysis of the appearance and processing requirements of the workpiece product in the early stage of process planning, each processing step is reasonably established from the overall situation of processing.
After the path simulation path is generated, we generally have no intuitive sense of its final performance on the machine tool. Here we can check the possible problems through path simulation, so as to reduce the scrap rate of actual processing. The general inspection focuses on the effect of the workpiece appearance, whether it is overcut or undercut, and whether the process planning of the path is reasonable.
Path output path output is a necessary step for software design and programming to realize on the machine tool. Through path output, the intermediate reference can establish a connection between the two. If you have NC professional background, it can also be understood as the post-processing of tool path.

Computer gong processing – how to make surface finish of parts

First of all, you need to ensure the stability of the lathe, that is, the fixation of the lathe, that is, whether the spindle will vibrate at high speed, and that the coolant is very important, Secondly, your cutting tool should be well ground, and the chip removal groove should be well opened to prevent the workpiece from being scratched due to poor chip removal, and the turning tool should be made into an arc angle when chamfering. In addition, the tool should not be resistant when loading.

Generally speaking, the more precise ones must go through the following steps: blanking, roughing, fine grinding, finishing and surface treatment.

Cutting. Generally, the work of cutting is handed over to the apprentice or the special staff, so the requirements of cutting are not high. Generally, 3-5mm allowance will be left for roughing. When laying down materials, too much allowance shall not be left to reduce the roughing time, and too little allowance shall not be left to prevent material waste due to insufficient allowance.
Rough. If it’s rough, you can also give it to an apprentice or a master who has not enough experience to operate it. The so-called roughing is to roughen the material and make the material smooth. Generally, a 0.2-0.5mm allowance is left for fine grinding. Too much allowance is not enough.
Fine grinding. This work should be operated by experienced masters. Fine grinding is to carry out precision machining on roughened materials, so as to ensure the perpendicularity and parallelism of the workpiece and prepare for the finish machining. Fine grinding is convenient, so we should pay attention to the precautions of grinding machine processing. For details, please refer to the internal grinder processing safety specification.
Finish machining. Master, must be master, must determine the order of machining, first understand the drawing requirements, determine the datum, select the fastest and most convenient processing steps.
Surface treatment. Generally, there is no surface treatment equipment. We need to choose our own high-quality surface treatment plant, and then match the spindle speed and feed speed. If your lathe doesn’t work very well, it’s recommended to buy some sandpaper to make it. When making sandpaper, it’s suggested to make it according to the working direction of the lathe tool, so as to make the texture better.

In order to ensure that the die steel has good original precision – the quality of the original die steel, in the manufacturing process, it is necessary to reasonably select high-precision processing methods, such as EDM, WEDM, CNC machining, etc., and pay attention to the accuracy inspection of the die steel, It includes the machining accuracy, assembly accuracy of die steel parts and the accuracy of die steel through the test and acceptance work. It is necessary to select high-precision measuring instruments as far as possible during the inspection. For those die steel parts with complex surface structure, if the ordinary ruler and vernier card are used, the accurate measurement data can not be achieved. At this time, the coordinate measuring instrument should be selected To ensure the accuracy of measurement data.

Advantages of machining center

After the workpiece is clamped on the machining center once, the digital control system can control the machine tool to automatically select and replace the cutting tool according to different processes, automatically change the spindle speed, feed rate, the movement path of the cutting tool relative to the workpiece and other auxiliary functions, and complete the multi process processing on several surfaces of the workpiece in turn. And there are a variety of tool change or tool selection functions, so that the production efficiency is greatly improved.

① The selection of die steel materials should not only meet the customer’s requirements for product quality, but also take into account the cost of materials and their strength in the set period. Of course, the selection should be based on the type of die steel, working mode, processing speed, main failure forms and other factors. For example: the main failure mode of blanking die is edge wear, so it is necessary to select the material with high surface hardness and good wear resistance; the stamping die mainly bears periodic load, which is easy to cause surface fatigue crack and lead to surface spalling, so it is necessary to select the material with good surface toughness; the drawing die should select the material with low friction coefficient; the die casting die should be selected due to the effect of cyclic thermal stress For injection mold, when the plastic parts are ABS, PP, PC and other materials, the mold steel material can be pre hardened and tempered steel; when the plastic parts are high finish and transparent materials, the corrosion-resistant stainless steel can be selected; when the products are in large quantities, the quenching and tempering steel can be selected. In addition, it is also necessary to consider the use of mold steel materials with less affinity with the parts, so as to prevent the mold sticking from aggravating the wear of mold steel parts, thus affecting the quality of mold steel.

② In the design of die steel structure, the structure should be compact and easy to operate, and the die steel parts should have enough strength and rigidity; when the die steel structure allows, the corners of each surface of die steel parts should be designed as fillet transition as far as possible to avoid stress concentration; for the die, cavity, part of punch and core, the combined or inlaid structure can be used to eliminate stress Appropriate protection measures shall be taken for the structure of the long and thin punch or core with concentrated force; for the cold stamping die, devices shall be provided to prevent the blockage of the parts or waste materials (such as spring pin, compressed air, etc.). At the same time, we should also consider how to reduce the impact of sliding parts and frequent impact parts wear on the quality of die steel.

③ In the design, it is necessary to reduce the scope of disassembly and assembly when maintaining a certain part, especially when replacing the vulnerable parts.

The manufacturing process of die steel is also an important part to ensure the quality of die steel, The processing method and precision in the manufacturing process of die steel will also affect the service life of die steel. The precision of each part directly affects the overall assembly of die steel. In addition to the influence of the precision of equipment itself, it is necessary to improve the processing method of parts and the technical level of fitter in the grinding process of die steel to improve the processing precision of die steel parts If the overall assembly effect of the die steel can not meet the requirements, the probability of the die steel in abnormal state will be increased, which will have a great impact on the overall quality of the die steel.