March 2021 – Page 3 – CNC Machining & Turning, Milling, Metal parts

Methods of improving CNC machining

(1) The size and structure of all kinds of parts are very different, and the universality of machine tools and other process equipment is not high.

(2) Many companies are usually faced with the production task of multi variety, small batch and short production cycle, so the process system is required to have a higher response speed.

(3) The structure of product parts is complex and the processing is difficult.

(4) Thin wall, easy to produce processing deformation. There are a lot of thin-walled and deep cavity structures, which are typical weak rigid structures.

(5) It is difficult to select cutting tools and cutting parameters. Because the development of tool industry can’t catch up with the development and application of new materials, and lack of the support of machining database.

So how to improve the efficiency of CNC machining? Generally speaking, the methods to improve the machining efficiency of CNC machine tools are as follows:

1、 Change the understanding of numerical control technology.

Numerical control technology is a comprehensive technology, in addition to the numerical control machine tool, there must be corresponding supporting technology and personnel support, especially in the numerical control processing process, people play a decisive role, the technical ability of management personnel, engineering and technical personnel, engineering maintenance personnel and operators will affect the production efficiency of numerical control machine tool.

2、 Develop effective tool management measures.

For example, the tool is pre adjusted to reduce the installation and adjustment time of the tool on the machine tool, and the tool is managed through the management system to reduce the errors caused by manual management.

3、 Fixture management.

Because the selection of fixture is directly related to the installation time and measurement time of workpiece, the management of fixture should be realized.

CNC machining center milling cutter

CNC machining center used on the milling cutter, should choose all cemented carbide, general milling machine used on the selection of white steel material. The hardness of white steel milling cutter is softer than that of cemented carbide milling cutter. Cemented carbide milling cutter has good thermal hardness, wear resistance, but poor impact resistance. The carbide is made by powder metallurgy. Its hardness can reach about 90hra and its thermal property can reach about 900-1000 degrees.

Number of milling cutter teeth

When selecting a milling cutter, the number of teeth should be considered. For example, the coarse tooth milling cutter with a diameter of 100 mm only needs 6 teeth, while the dense tooth milling cutter with a diameter of 100 mm can have 8 teeth. The size of pitch will determine the number of cutter teeth to be cut together in milling, which affects the smoothness of cutting and the requirement of cutting rate.

Chip holding tank

Coarse tooth milling cutter is mostly used for rough machining, because it has a large chip holding groove. Assuming that the chip holding groove is not large enough, it will make it difficult to roll the chip or the conflict between the chip and the tool body or workpiece aggravate. At the same feed rate, the cutting load of coarse tooth milling cutter is larger than that of dense tooth milling cutter.

Cutting depth

In finish milling, the cutting depth is shallow, generally 0.25-0.64mm. The cutting load of each tooth is small (about 0.05-0.15mm), and the power required is small. It is able to select dense tooth milling cutter, and it is able to select larger feed rate.

Application of rough milling

In heavy load rough milling, excessive cutting force can make the machine tool with poor rigidity vibrate. This kind of chatter will lead to the edge collapse of cemented carbide blade, and then shorten the tool life. Selecting coarse tooth milling cutter can reduce the requirement of machine power.

CNC machining center workpiece processing process is no longer like the traditional processing equipment, the need for uninterrupted control of the machine tool to end, control the function parts of the machine tool for messy and precise action, and then high-precision, efficient end of the processing process. The programming of workpiece processing is the key of workpiece processing in machining center. However, if the programming is not reasonable or the parameters are not set properly, the machining accuracy and power of the workpiece will be seriously affected, such as overcutting. Overcutting is a serious problem in workpiece processing, which can lead to the invalidation of workpiece. For some reason, the front-line processing personnel have worked out the processing program which is sure to be overcut. If the system can announce the alarm signal in advance in the working process, the overcut can be avoided.

Computer gong processing workpiece collision number

After the workpiece is placed on the pad iron, it is necessary to pull the table for the workpiece datum according to the drawing requirements. For the workpiece that has been ground on six sides, it is necessary to check whether its verticality is qualified.

The nut must be tightened after the work-piece is pulled to prevent the work-piece from shifting during the processing due to the loose clamping; pull the work-piece again to ensure that the error does not exceed the tolerance after the clamping.

Number of workpieces touched

For the clamped workpiece, the contact head can be used to set the processing reference zero position. The contact head can be used in photoelectric type and mechanical type. There are two kinds of methods: middle collision number and unilateral collision number

Photoelectric static, mechanical speed 450 ~ 600rpm. Manually move the x-axis of the worktable according to the collision number to make the collision number head touch one side of the workpiece. When the collision number head just touches the workpiece and the red light is on, set the relative coordinate value of this point to zero. Then manually move the x-axis of the worktable to make the collision number head touch the other side of the workpiece. When the collision number head just touches the workpiece, record the relative coordinate at this time.

According to the relative value minus the diameter of the collision head (i.e. the length of the workpiece), check whether the length of the workpiece meets the requirements of the drawing.

Batch conditions of computer gong processing

The type of blank should be determined according to the material, shape and size of the parts, and the batch and production conditions of the parts should also be considered in the computer gong processing. Transmission shaft, small diameter, the diameter of each section of the outer circle is not big, optional round steel blanking. In order to save materials and processing time, if the gear shaft has large quantity and forging conditions, the forging blank should be selected; otherwise, round steel cutting should be selected. The material of bearing cover is cast iron, and the blank should be cast. Processing gear, its material is 40 steel, and the outer circle diameter is small, small outer circle is short, optional round steel blanking. Due to the large diameter of the outer circle and hole of the gear, the gas cutting of the steel plate with the corresponding thickness can be selected for a single piece, and the forging can be selected for a large batch to forge the ring-shaped blank. In this way, the material can be saved, the processing time can be reduced, and the mechanical properties of the forging blank are better.

Determine the processing sequence of parts

The processing sequence should be determined according to the type, structure, size, processing accuracy, surface roughness, heat treatment and other technical requirements of the blank.

Determine the processing procedure

Determine the machine tool, workpiece clamping method, processing method, processing size and detection method used in each process, including the allowance for the next process. Generally, for small and medium-sized parts, the outer cylinder and the inner cylinder and the plane in CNC machining all refer to the unilateral allowance. In the small batch production of a single piece, the larger the blank size is, the smaller the blank size is. Total allowance: 3-6 mm for hand molded castings, 3-7 mm for free forging or gas cutting parts and 1.5-2.5 mm for round steel. Process: semi finish turning is 0.8-1.5mm; high speed finish turning is 0.4-0.5mm.

Determine the cutting amount and man hour quota

The cutting parameters of single piece and small batch production are generally selected by the producers themselves, and the man hour quota is set by the management personnel.

CNC machining center spindle fault

The spindle is the power auxiliary device of CNC machining center. The spindle drives the workpiece to rotate to process the workpiece of the rotating body. Spindle is an important guarantee for high-speed and high-precision machining of CNC machining center, so the maintenance methods and skills of spindle fault are the basic knowledge that operators and maintenance personnel of CNC machining center must master. In the operation of CNC machining center, the spindle will inevitably have some faults. What is the specific reason?

Different types of CNC machining centers adopt different types of spindles. According to the different transmission systems, the spindle system can be divided into the main transmission spindle with variable speed gear, the main transmission spindle with belt transmission, the dual motor drive spindle and the motor spindle integrated spindle. No matter what type of spindle application, the common faults in use are as follows:

Overload.

Fault causes: excessive cutting amount, frequent forward and reverse rotation, spindle motor fault, spindle drive device fault.

The spindle does not rotate

Fault causes: spindle drive failure, CNC device can not output speed signal, spindle motor failure, spindle drive failure, drive belt fracture.

The spindle speed deviates from the command value

Fault causes: motor overload, CNC system output spindle speed command output problem, speed measuring device failure or speed feedback signal disconnection.

Mold maintenance mode

Management of mold field use

Dispatchers should go through relevant procedures according to the corresponding management system when collecting and returning the molds, and be responsible for the whole process of the molds from receiving to returning.
The die should be processed according to the stamping process and the corresponding tonnage of punch press. The mold should be adjusted and installed by the mold adjuster, and ensure that the leakage is smooth, the spring top is normal, the feeding is convenient, the stroke is reasonable, and the production can be started after the qualified sample is tested.
The punch operator shall strictly follow the operation procedures. If any abnormal phenomenon is found in the production process, it should be reported in time, and the production can be carried out after troubleshooting. In case of mold damage caused by barbaric operation, the responsible person shall fill in the mold accident liability sheet and give certain punishment.
In case of die waste fracture, guide plate guide deformation, die and punch damage caused by pressing and bending die stuffy, it is necessary to trace the responsibility of the adjuster.
The usage of the mould shall be clear during the shift handover of day shift and night shift. The successor shall be responsible for the accident after the handover.
After the completion of the production task, the dispatcher shall be informed in time to handle the warehouse return procedures. The production site should not keep the mold without production instructions or complete the batch task. If the mould is lost, the responsibility of the final receiver will be traced.

Purpose of mold maintenance system

Master the history of the mold 2. Maintain the mold in time after mold production 3. Improve the service life of the mold 4. Ensure the quality of the mold and smooth production

Mold maintenance mode mold maintenance is divided into four modes

Preventive inspection: take every 15 days as a cycle to check the mold status directly on the production machine, and record the results in the “mold preventive inspection record form”. This part of the inspection is in the charge of the mold group, assisted by the injection molding department.
General maintenance (A-level maintenance): it refers to the general maintenance items of the mold during the daily mold test and trial production, which are responsible and recorded by the production department.
Regular quantitative maintenance (B-level maintenance): when the mold has not been used for more than one year or has accumulated more than 50000 beer each time, detailed inspection shall be carried out, and the inspection results shall be recorded in the “mold maintenance inspection record form”. The production department is responsible for and records.
Mold maintenance (C-level maintenance): when the injection molding material has serious appearance problems or the mold is damaged, the parts need to be replaced or repaired.

The motor does not run;

Switching power supply (± 15V) transformer TL and power switch tube v69 are abnormally hot.

This is a typical case of syndrome, and there may be some causal relationship between the faults, so we need to deal with the faults in sequence, otherwise we may get twice the result with half the effort, or even cause the fault area to expand. Through the analysis, we make the following maintenance order: switching power supply one > under voltage light > motor running. Firstly, check the power supply board. After measuring the 150V DC voltage of the main circuit and disconnecting the ± 15V load, we know that the fault is inside the switching power supply board. In the check of the power supply board, we find that the voltage of the 10V regulator V32 is only 9.5v. From this, we can find the cause of the fault: the current limiting resistance rl85 of V32 becomes larger. After replacing rl85, the ± 15V power board and “under voltage” lamp returned to normal, but the motor still did not run. It can be seen that the above flashing lights and hot components are caused by rl85 variation, and there is another reason for the motor not running. According to the usual inspection method, it can be detected step by step, but due to experience, we only did a simple transformation and steering test, and found that the reverse operation was normal, so we quickly found out the cause of the fault: the integrated block N5 (tl084) of the commutation circuit failed, and everything was normal after replacing N5

PC interface method

Because the signal transmission and control between each unit (except driver) of NC machine tool and NC system are realized through PC interface (1 / O), many faults will be reflected through PC interface signal. We can diagnose various complex machine tool faults or judge whether the fault is in NC system or in machine tool electrical by consulting 1 / O signal of PC machine tool side. The method is very simple, that is, it is required to be familiar with the current state and normal state of all PC (machine side) interface signals (or make a table). During diagnosis, check and compare the current state and normal state of all PC (machine side) interface signals one by one to find out the faulty interface signals, and then find out the fault causes according to the external logic relationship of the signals. When you are familiar with the PC interface signal, the application of this PC interface comparison method is very simple and fast, and avoids the complicated ladder program.

Recovery of abnormal data in Siemens 3GG system

The grinder s45-6 of Switzerland is equipped with Siemens 3GG system, which is a dual n C dual PLC structure. The system has a strong self diagnosis function. When a fault occurs, it can quickly diagnose and repair the fault with the help of the screen prompt. However, if the system cannot be started, and the PLC is in the stop state, the screen is not bright, then the self diagnosis function of the system will not play a role, leading to the difficulty of diagnosis. If the battery voltage is lower than 2.7V, the battery must be replaced; if the NC or PLC hardware is damaged, the circuit board needs to be replaced; if the 24 V power supply of the machine tool is lower than 21 V, the power supply circuit and load need to be checked.

But we encounter more faults, the reason is not the hardware fault, but the machine data abnormal such as soft fault. The reasons are complex, such as power grid interference, electromagnetic wave interference, battery failure, operation error and so on, which may cause the loss or confusion of machine data, so that the system can not start.

Abnormal noise of spindle in CNC machining

Cause of failure: it usually occurs in the process of deceleration, and there is something wrong with the spindle drive device, such as the regeneration circuit fault in AC drive.

CNC machining center spindle abnormal noise is most operators will encounter things, understand the cause of the failure, we should take what measures to solve it?

When the machining center is in use, some customers often find that the spindle is transported by belt. After a long time of use, there will be abnormal noise. When the forward transmission and reverse transmission are switched, there will be noise. According to years of assembly experience, it is determined that most of the problems are caused by the belt, The belt tension at the joint of servo motor and spindle is too tight, which leads to the phenomenon of belt slipping, so the spindle will make abnormal noise.

Another situation is that the tension of the belt connecting the servo motor is not enough, so it will appear that the belt of the motor is too loose, which can be seen intuitively. When the machining center is used for heavy chip, it will slip and make abnormal noise. After the machining center is used for a long time, the belt will be worn, which is part of the cause of abnormal noise.

After the abnormal noise of CNC machining center spindle occurs, some economical customers will choose to replace the drive wallet. After the replacement, the belt drive gear and the tooth profile of the motor and the spindle do not match, and they can make do with it. However, there will be a lot of abnormal noise during use, which seriously causes the wear and damage of the gear of the servo motor and the spindle. It is suggested to observe whether the belt model purchased is the same as that replaced. Spindle is an important guarantee for high-speed and high-precision machining of CNC machining center, so the maintenance methods and skills of spindle fault are the basic knowledge that operators and maintenance personnel of CNC machining center must master. In the operation of CNC machining center, the spindle will inevitably have some faults. What is the specific reason?

Overload.

Fault causes: excessive cutting amount, frequent forward and reverse rotation, spindle motor fault, spindle drive device fault.

The spindle does not rotate

Fault causes: spindle drive failure, CNC device can not output speed signal, spindle motor failure, spindle drive failure, drive belt fracture.

The spindle speed deviates from the command value

Fault causes: motor overload, CNC system output spindle speed command output problem, speed measuring device failure or speed feedback signal disconnection.

Abnormal noise and vibration of spindle

Computer gong processing tool

The main matching dimensions of parts are guaranteed by computer processing, so it is very important to choose a reasonable tolerance, especially some product design drawings do not consider the matching problem. Bottom, surface, shell fit, shape is no doubt 0 to 0 fit, positioning is guaranteed by the mouth, concave mouth and convex mouth tolerance is generally 0.1 mm, unilateral. The fit on the big body is like a transparent mirror. The shape of the general accessories is 0.1 ~ 0.2 smaller than the size on the big body. The shape of the movable accessories on the big body, such as buttons, is 0.1 ~ 0.5 smaller than the shape on the big body. The surface shape of the accessories on the big body is generally consistent with the surface shape on the big body, which can be removed from the big body.

1、 Exit angle (draft angle)

All plastic molds should have a mold angle, otherwise they will be scratched. If it is not indicated in the drawing, you can discuss with the mold maker. The mold angle is generally 0.5 ~ 3 degrees. If the mold is etched, the mold angle should be larger, 2 ~ 5 degrees, depending on the thickness of the etched pattern.

2、 Cutting problem

Most of the time, when the cutter is just milled, the amount of cutting is relatively large, which is easy to cause the cutter to break and bounce. At this time, you can first roughen the lower cutter position, or lift the cutter away, or lower the cutter outside the material in the daytime. In a word, this problem should be fully considered. Grab the knife, spring the knife, drop the knife, when the processing capacity is relatively large, the knife clip is too long, the knife is too small, this often happens. When the processing capacity is relatively large, especially when the concentration feed is large, it is easy to occur. For example, when the depth of the smooth side is 50 mm and the diameter is 3 / 4, we can process it in 25 mm twice, so it is not easy to occur. Tool clamping is too long, the length of the tool is very important for processing, should try to clamp short, beginners are easy to ignore this problem, the program paper must indicate the length of the tool clamping. It’s easy to grab the knife when turning the corner. The solution is to use a smaller knife to clear the corner layer by layer, and then change the larger knife to smooth the side.

3、 Sharpen a knife

The shapes of computer gongs are different, so we often need to grind all kinds of knives. When all kinds of molding knives are worn out, we also need to grind them. Only when we reach the following points can we grind a usable knife.

The four corners of the tool should be the same height.
A is higher than D.
The forward (tool face) of the tool is higher than the back, that is, it has a certain back angle.

4、 Milling direction

The reason is that the rigidity of the computer gong is relatively good, it is not easy to let the cutter, the back clearance is small, and the milling shape or inner groove is left compensation. When machining left and right symmetrical shapes, the profile tool path cannot be mirrored, otherwise the processing effect of the mirrored side is not good. In order to communicate with the operator of the machine tool, the program paper should include:

Program name
Tool size and length
Method of machining tool path
Machining allowance
Rough or light knife

Key points of complex parts processing

The continuous fine blanking die for complex parts is the frontier basic technology of fine blanking technology. Taking this as the leader, the research is expected to promote the whole fine blanking technology in our country. Taking the synchronizer ring, clutch plate, longitudinal compound continuous fine blanking process and die for complex parts as the breakthrough point, the key technology of fine blanking die design and manufacturing is studied, and the development of fine blanking die technology in our country is realized The gap between China and advanced countries should be shortened 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 material, small process and supporting product level. 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 material, 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.

Computer gong processing vertical processing

The height of the vertical machining center is limited, which reduces the processing range of the workpiece, which is the disadvantage of the vertical machining center. However, the workpiece clamping and positioning is convenient for vertical machining center; the cutting path is easy to observe and debug, the program inspection and measurement is convenient, the problems can be found in time, and the treatment or modification can be stopped; the cooling conditions are easy to establish, and the cutting fluid can directly reach the cutting tool and machining on the surface; the three-axis and Cartesian coordinate system, intuitive feeling, conforms to the design point of view, and the chip is easy to eliminate, Surface treatment to avoid scratches.

Vertical machining center

Mainly used for:

Using grease and oil circulation in machining center will produce abnormal heating.
Spindle, need high-definition washing, high-speed bearing sealing place

working principle:

The use of compressed air flow pipe, transmission oil along the pipe caused by continuous flow, stirring and transportation of oil and gas processing center spindle part and other parts of the screw need lubrication. The constant pressure dry compressed air (bar) 5 – 8 continuous supply, according to the spindle and lubricating oil lubrication, screw oil and other parts of the fuel consumption different quantitative supply. Therefore, each lubrication circuit must use a separate micro pump power supply of oil. After the oil pump, it must enter the oil and natural gas mixing valve. In the oil and natural gas mixing valve, the compressed air flow blows into small oil drops and adheres to the wall to form an oil film. The flow direction of the air flow between the oil film and the pipe wall, and the thickness of the medium oil film gradually becomes thinner, but not together.

CNC machine tool processing principle, all kinds of processing tools, all kinds of workpiece processing tool path method, all kinds of workpiece feed and speed, cutting amount.

Maximum depth allowed for each cutting, actual m auxiliary function, s speed, t tool change, R radius, u, W are relative G: preparation command M: auxiliary command T: tool s: spindle speed, R: arc radius, and then p q R, where R means different.