March 2021 – Page 11 – CNC Machining & Turning, Milling, Metal parts

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.

Advantages of CNC computer gong processing

Master the processing principle and process. When using the common CNC machining technology, the processor should follow the principles of rough machining first, then finish machining, preventing the workpiece from thermal change, reducing vibration and so on. At the same time, also have the ability to deal with all kinds of unexpected problems, such as: how to adjust the tool speed.
Familiar with automatic or manual operation of CNC machining. The machinist should know clearly what process needs manual operation, what is the normal operation state of the machine tool when it is operated manually, what process is suitable for automatic operation, and what state the machine tool should be in. Professional CNC processing staff said, familiar with the above operation, help to carry out the processing work, and can deal with any situation freely.

The above is the basic skills of professional CNC processing personnel. Only by mastering these skills can we complete CNC processing operation independently. In order to become a qualified CNC machining worker, only by constantly asking questions and practicing in the work can we make our technology more solid.

Collision detection of NC machining simulation system

Due to the high cost of NC machining, in order to save the cost, a NC machining simulation system is developed. NC machining simulation system can reduce or even completely eliminate the process of trial cutting and manual verification. Before the actual processing of new NC machining program, the programmer can use NC machining simulation system to carry out virtual machining environment and machining process on the computer, and detect the possible problems in the program design.

In the process of NC machining, it is easy to over cut, under cut and other phenomena. At the same time, the damage of the tool, or the processing of waste products, the interference and collision between parts and tools, tools and fixtures, tools and worktable, will cause a certain waste of cost to the production. The NC machining simulation system can simulate the relevant programs well and reduce the loss to the greatest extent.

Before the actual processing, the programmer can confirm whether the finished cutting product is consistent with the original design drawing through the simulation system, and can make better detail analysis.

collision detection

In the actual processing, five axis NC machining has more advantages than three-axis NC machining, can achieve a wider range, has faster material and efficiency, can reduce processing time and improve surface accuracy. However, because of the high degree of freedom of the two additional rotating shafts, it is easy to collide and damage the machine tool.

Therefore, before the actual processing, we need to use the NC machining simulation system to detect the collision. The main detection algorithms are as follows

The machine tool includes many parts, but the collision detection algorithm between different parts is similar. The simulation system takes the tool, workpiece and fixture as the main research object to detect the possible global collision.

According to the tool location, the grid voxel model of the cutter head scanning body and the grid voxel model of the cutter handle scanning body are solved respectively. The tool holder scanning body is used to detect whether there is a global collision between the tool, workpiece and fixture, and the tool head scanning body is used to calculate the intersection between the tool and workpiece.
A feature attribute of voxel model is cuboid envelope box, which is used for rough judgment. If the envelope box does not intersect, the objects surrounded in the envelope box must not intersect. At this time, the position data information of the object envelope box is updated, and other information remains unchanged, so as to prepare for the generation of the next cutter scanning volume and collision detection. Rough judgment can speed up the detection Speed.
Once a collision occurs, the system stops reading the data and reports the error information and the exact location of the collision. If there is no collision, the system will continue the teaching operation between the cutter head and the workpiece.

How to install workpiece in CNC machining center

Selection of machining center positioning datum:

There are three basic requirements for selecting benchmarks

(1) The selected datum should be able to ensure the accuracy of workpiece positioning, convenient and reliable loading and unloading.

(2) The calculation of the selected datum and the size of each processing part is simple.

(3) Ensure the machining accuracy.

6 principles for selecting positioning datum:

(1) Try to choose the design datum as the positioning datum;

(2) When the positioning datum and design datum cannot be unified, the positioning error should be strictly controlled to ensure the machining accuracy;

(3) When the workpiece needs to be clamped for more than two times, the selected datum can complete the machining of all key precision parts in one clamping and positioning;

(4) The selected benchmark should ensure the completion of as many processing contents as possible;

(5) In batch machining, the positioning datum of parts should coincide with the tool setting datum of workpiece coordinate system as far as possible;

(6) When multiple clamping is needed, the datum should be consistent.

Determination of machining center fixture:

Basic requirements for fixtures:

(1) The clamping mechanism shall not affect the feed, and the processing part shall be open;

(2) The fixture can be installed directionally on the machine tool;

(3) The rigidity and stability of the fixture are better.

Common fixture types:

(1) General fixture: such as vice, dividing head, chuck, etc;

(2) Modular fixture: modular fixture is composed of a set of general components with standardized structure and standardized size;

(3) Special fixture: fixture designed and manufactured for one or several similar processing items;

(4) Adjustable fixture: the combination of modular fixture and special fixture can ensure the machining accuracy and more flexible clamping;

(5) Multi position fixture: it can clamp multiple workpieces at the same time;

(6) Group Fixture: it is specially used for clamping workpieces with similar shape, size, positioning, clamping and processing methods.

Selection principle of machining center fixture:

(1) On the premise of ensuring machining accuracy and production efficiency, general fixture is preferred;

(2) Simple special fixture can be used for batch processing;

(3) Multi position fixture and high efficient special fixture for air pressure and hydraulic pressure can be considered for mass processing;

(4) When group process is used, group fixture should be used;

The best clamping position of the workpiece on the worktable of the machine tool: the clamping position of the workpiece should ensure that the workpiece is within the processing stroke range of each axis of the machine tool, and make the length of the tool as short as possible to improve the processing rigidity of the tool

How to process part curved surface with computer gong

Using CNC machining center to process the surface of these heterogeneous parts, the key work is to work out a reasonable processing program and select the appropriate processing tools. The latter work is relatively simple and can be completed quickly according to the die drawing and process requirements. The preparation of processing program is the most important part of the whole processing preparation work, and also the most important and most important part of the whole die processing One of the main jobs.

1、 Establish mathematical model

Before establishing a model, we should first consider the order and method of establishing each feature of the model, what to do first, what to do next, what method to use, and which modeling function to use. We must deal with this relationship properly when establishing a mathematical model.

2、 Determine machining coordinate system

The establishment of solid model is based on the working coordinate system, while the generation of tool position source file of NC machining center is based on the working coordinate system. The origin position of machining coordinate system should be convenient for rapid and accurate tool setting and dimension calculation.

3、 Planning tool position source file

According to the structural characteristics of different product surfaces, we can select three machining modules, plane milling, cavity milling and fixed axis contour milling, which have their own characteristics and complement each other to plan the machining tool position source files of various types of surfaces.

In a word, we should flexibly grasp the application characteristics of each module according to the processing of mold surface and contour surface, so that we can process our satisfactory products with high quality and high efficiency through CNC machining center.

Basic knowledge of CNC machining center

1、 CNC machine tool and CNC system

CNC means computer numerical control.

CNC machine tools

(1) for metal cutting

Hole processing, tapping, boring, milling, turning, thread cutting, cutting plane, contour processing, surface grinding, cylindrical grinding, internal grinding, etc.

(2) wire electrode cutting machine.

(3) punch, step punch, stamping, metal forming, bending and other machine tools.

(4) industrial robots.

(5) injection molding machine.

(6) testing and measuring machine.

(7) woodworking machinery.

(8) special material processing machinery: such as processing stone, glass, radioactive mineral, etc.

(9) special processing machinery

Laser processing machine, gas cutting machine, welding machine, drawing machine, printing machine, etc.

With the development of electronic technology, computer technology and it technology, at present, these machine tools and processing equipment can be controlled by numerical computer with numerical data, which is called CNC control. Is a metal processing machine tool – vertical machining center of the general structure.

CNC system

CNC system means computer numerical control system. It is the basic configuration diagram of a CNC system. CNC control of machine tool is a kind of integrated control technology, which is a typical CNC control system.

A CNC system includes:

(1) CNC control unit (numerical controller part).

(2) servo drive unit and feed servo motor.

(3) spindle drive unit and spindle motor.

(4) PMC (PLC) controller.

(5) input / output (I / O) list of control signal of machine tool strong current cabinet (including tool magazine)

Yuan.

(6) position measurement and feedback unit of machine tool (usually included in servo drive unit).

(7) external shaft (Mechanical) control unit. Such as: tool magazine, exchange table, upper

Drive shaft of cutting manipulator, etc.

(8) information input / output equipment. Such as computer, disk drive, memory card, keyboard, special information equipment, etc.

(9) network. Such as Ethernet, hssb (high speed data transmission port), RS-232C port and local area network of processing site. I / olinki servo amplifier and motor are used to drive and control external machinery. The hardware of CNC unit (controller part) is actually a special microcomputer. It is the core of machine tool control designed and produced by CNC equipment manufacturer.

Basic skills of professional CNC processor

Master the processing principle and process. When using the common CNC machining technology, the processor should follow the principles of rough machining first, then finish machining, preventing the workpiece from thermal change, reducing vibration and so on. At the same time, also have the ability to deal with all kinds of unexpected problems, such as: how to adjust the tool speed.
Familiar with automatic or manual operation of CNC machining. The machinist should know clearly what process needs manual operation, what is the normal operation state of the machine tool when it is operated manually, what process is suitable for automatic operation, and what state the machine tool should be in. Professional CNC processing staff said, familiar with the above operation, help to carry out the processing work, and can deal with any situation freely.