chengcg – Page 87 – CNC Machining & Turning, Milling, Metal parts

Factors affecting machining accuracy

Precision has a great relationship with the final results of the product. If the accuracy is not accurate, then not only the final effect of the product is not ideal, but also many problems will occur in the later use process. Later work will be very difficult, so in the process of production, we must pay attention to some factors that affect the accuracy of machining, so we will learn which factors will affect the accuracy of mechanical parts processing?

machining

When machining precision mechanical parts, the contour system controlled by digital program is widely used in milling machine, including simple, reliable and low-cost phase system with wide process capability. These systems are adopted by many factories, especially for controlling the machining of large-scale three-dimensional surface precision mechanical parts.

It is one of the main conditions to ensure the machining quality of precision mechanical parts by making control program correctly. For the digital program control phase system, the preparation of the control program is carried out by the automatic program preparation system, and its quality level largely depends on the price of the preparation control program.

The others are processing errors caused by manual control of equipment, which include accidental errors and systematic errors of process system. System error plays an important role in all machining errors, which will cause a series of NC process system errors for the whole machining of precision mechanical parts.

For example, the gap has the same consequence as the insensitive belt in the transmission chain of a machine tool, but does not include the clearance of the reverse drive chain; the amplification factor of the unstable transmission; the phase error on the control program tape; the periodic step instability of the sensor feedback, which is mainly in the form of phase instability

Inspection skills of mechanical parts

Inspection skills of heavy machinery parts in maintenance process

Main contents of parts view

In mechanical maintenance, parts should be checked one by one, and the main contents can be divided into the following aspects:

Check the precision of parts

Several precision includes scale accuracy and shape orientation accuracy, but sometimes maintenance work is not to pursue a few dimensions of a single part, but requires relative cooperation accuracy, which is often an important part of inspection work.

Roundness, cylindricity, concentricity, coaxiality, parallelism and straightness are common in the maintenance of shape and orientation accuracy.

Inspection of surface quality

The inspection of the surface quality of parts in maintenance is not only limited to the inspection of surface finish, but also the inspection of the defects such as scratch, burning and scuffing on the surface of used parts.

View of mechanical function

According to the characteristics of mechanical maintenance, in addition to checking the hardness of the mechanical function of the part data, other indicators are generally not checked, but some functions encountered in the process of parts manufacturing and maintenance, such as balance, spring stiffness, etc., can not be ignored.

CNC machining

Shadow defect check

In the process of manufacturing parts, there may be some original defects, such as slag inclusion and cavitation, and micro cracks may occur in the process of use. These shortcomings can not be found directly from the general investigation and measurement, but they may have severe consequences on machinery. Therefore, in the maintenance of machinery, it is necessary to have a comprehensive view of some parts.

How to check parts

There are many ways to view parts, and new viewing skills are developing rapidly. However, starting from the practice of mechanical maintenance, it can be summarized as follows:

Feeling check method

This is a way to identify the skill of parts by the intuitive feeling of the inspector without having to check the equipment. This method is simple, and in the mechanical maintenance, it is also relatively simple to distinguish the shortcomings of many parts to be disassembled and inspected. Therefore, this method is still useful. However, this method can not be used to view parts with high precision requirements, and requires the inspector to have rich experience.

Instrument and things check method

A lot of homework is done with instruments and things. Due to the different working principles and types of instruments and things, they can be divided into general measuring tools, special measuring tools, mechanical instruments and meters, optical instruments, electronic instruments, etc.

Physical view method

This is a method to detect the skills of parts by using the changes caused by electrical, magnetic, optical, acoustic, thermal and other physical quantities through the workpiece. The realization of this method is also combined with the instrument and the method of viewing things. This method is usually used to check the hidden defects inside the parts without damaging the parts themselves. It is widely known as non-destructive inspection. In recent years, nondestructive inspection technology is increasingly developed. Magnetic powder method, penetration method, ultrasonic wave and ray method are widely used in production.

Causes of abnormal noise of spindle in CNC machining center

In the process of work, mold failure is also a common thing. In general, when we encounter failure problems, we first need not to solve the problem, but to find out what causes the failure. In this way, we can better solve the fundamental problem. If the cause is not found, then even if it is solved, it is basically a temporary cure rather than a root cause. So let’s To understand the CNC machining center spindle abnormal noise causes what is it?

CNC machining

Overload.

Fault causes: excessive cutting amount, frequent positive and negative rotation, spindle motor failure, spindle drive device failure.

The spindle does not rotate

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

Spindle speed deviates from the command value

Fault causes: motor overload, problems with spindle speed command output from CNC system, fault of speed measuring device or disconnection of speed feedback signal.

Abnormal noise and vibration of spindle

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 drive spindle with variable speed gear, the main transmission spindle through belt drive, the spindle driven by dual motors and the spindle integrated by motor and spindle

Computer gong processing

What are the problems of computer gong processing?

In the process of processing products, when the size of height direction changes greatly, do not adjust the depth of wear tool compensation, first check whether there is aluminum slag in the handle and spindle, and then add wear cutter compensation after admitting that there is no slag.
When using the jaw to clamp the products, the thickness is different, the outer dimension is thinner and the inner dimension is thicker. This is when the product is jacked up by clamping the external jaw. It is necessary to pay attention to whether the movable parts of the jaw are too loose, and the problem of different product thickness can be handled after locking it.
When CNC machining deep hole has accuracy requirements, it simply presents taper, especially when the hole depth is longer, it is difficult to ensure that the upper and lower are reached. It can be rough first and leave a small amount of allowance before boring.
When processing products with high surface finish requirements, the rough blade pattern is difficult to meet the requirements of customers. At this time, the flying cutter can be used to install PCD cutter grain for large surface, and PCD flat cutter can be customized for small surface to improve the surface finish.

CNC machining

304 stainless steel material, it is very simple to wear the tool during processing, cold cutting fluid can be changed to oil cooling, oil cooling can improve the service life of the tool. The tapping diameter of aluminum material is small, the wire tapping is simple, and the oil cold cutting is also available.
Corner flick knife

When it is found that there is a product corner spring knife, the first analysis of the product corner size, the use of less than corner R angle of the tool. It can also be handled by reducing the spindle speed.

Burr on chamfering

When there are burrs after chamfering, the first thing to check is whether the tool is worn. If the tool is intact, then check the depth and range of chamfering. Generally, these two aspects can deal with the problem of chamfering burr.

Pinch injury

Pinch injury is a common problem in CNC machining. On the one hand, it may be that the operator is clamping the product or the tooling is not blown clean, which can be completed by strengthening training. On the other hand, it may be that the contact surface of clamping products is large, which can be treated by replacing the steel jaw. The tooling can also be placed in the direction of the oil pipe when adjusting the machine, so as to clean up the residual materials and reduce the formation of clamping injury.

CNC machining front mold processing items

Matters needing attention before CNC machining

① Cutter path sequence: large cutter curved surface grooving cutter path opening, small cutter contour contour cutter opening rough, large cutter (ball cutter) parallel milling cutter path smooth cutter, small cutter parallel milling cutter path smooth cutter. When the front die is manufactured, there is usually a matching copper male, mainly with a rough cutting path, supplemented by a local curved surface smooth knife.

② With parting surface and pillow surface, it is necessary to add time together. The parting surface pillow surface shall be machined in place without allowance, and the allowance of 0.2-0.5 shall be reserved at the cavity for spark. If only the young male is needed, a margin of 0.3 can be left. The allowance is 0.5. The allowance of 0.1 can be reserved at the position of collision and wear of front die, which is used for front and rear die matching.

③ When the diameter is too small, it is easy to break and snap the knife. It should also be selected as far as possible.

CNC machining

④ The tool path size in curved surface machining is calculated according to the moving track of the tool center axis, that is, the actual machining area is one more tool radius value than the one side of the selected tool path size constraint box, so the parameters of tool path size constraint frame should be set reasonably. To prevent the processing scale beyond the practical processing needs.

⑤ The data of the front die is hard. Check carefully before processing to reduce mistakes and not easy to weld!

Precautions after CNC machining

① Sequence of tool path of back die: large tool surface grooving, cutter path opening, small tool constraint scale, curved surface grooving and opening, angle cleaning, large cutter (ball cutter) parallel milling path smooth surface, small cutter (ball cutter) parallel milling path constraint scale, angle cleaning, smooth cutter, flat cutter and other high profile tool path angle cleaning.

② The data of the back die is the same as that of the front die, and the round nose knife (handle) should be used as far as possible.

Skills of NC machining

Some skills in NC machining

How to prepare NC programming

After determining the processing technology, the following should be understood before programming:

1、 Workpiece clamping method;

2、 Workpiece rough blank size – determine the processing range or whether multiple clamping is required;

3、 Workpiece material: select the tool for processing;

4、 What are the tools in stock? Avoid modifying the program due to the lack of this tool during processing. If you have to use this tool, you can prepare it in advance.

What are the programming principles for safe height setting?

Precision machining

Safety height setting principle: generally higher than the highest height on the island. Or set the programming zero point to the highest plane to avoid the risk of knife collision as much as possible.

Why do tool paths need post-processing?

Since different machine tools can identify different address codes and NC program formats, it is necessary to select the correct post-processing format for the machine tools to ensure that the program can run.

Reasonable selection of cutting parameters

For high efficiency metal cutting, the material to be processed, cutting tools and cutting conditions are the three major elements. They determine the processing time, tool life and machining quality. The economical and effective machining method must be the reasonable choice of cutting conditions.

The three elements of cutting conditions: cutting speed, feed rate and cutting depth directly lead to tool damage. With the increase of cutting speed, the tool tip temperature increases, resulting in mechanical wear, chemical wear and thermal wear. If the cutting speed is shortened by 2%, the tool life will be increased.

The relationship between feed condition and tool wear is very small. However, when the feed rate is large, the cutting temperature increases and the wear is large. It has less effect on cutting tool than on cutting speed. Although the influence of cutting depth on the tool is not as great as the cutting speed and feed speed, when the cutting depth is small, the hardened layer of the material to be cut will also affect the tool life. The user should select the cutting speed according to the processing material, hardness, cutting state, material type, feed rate, cutting depth, etc.

On this basis, the most suitable process conditions were selected. Regular and stable wear is the ideal condition for service life. Don’t want to work at the bottom, want to get rid of the status quo.

But in practice, the choice of tool life is related to tool wear, change of machining size, surface quality, cutting noise, processing heat and other factors. When determining the processing conditions, it is necessary to study according to the actual situation. For difficult to machine materials, such as stainless steel and heat resistant alloy, coolant or rigid blade can be used.

Method of processing thread

Universal threading method for CNC machining

There are generally four ways to process thread on CNC lathe. There are four cutting methods: direct cutting, oblique cutting, left and right cutting and rough cutting.

Direct development method; as shown in Fig. 1 (the depth of thread turning tool intermittently feeding to the teeth), when the trapezoidal thread is processed (all three parties are involved in cutting), the chip removal is difficult (increasing the cutting force and cutting heat), the tool tip of severe wear (too much feed), and the possible phenomenon of thorn. Obviously, machining large pitch trapezoidal thread and worm is not advisable.
Oblique method; as shown in Figure 2 (thread turning tool is the phenomenon that the Federal Reserve uses the depth of helical teeth and intermittent way along the direction of tooth angle) (when trapezoidal thread processing is in this way (thread turning tool always has only one edge to participate in cutting (so the chip discharge is relatively smooth) (the skill of force and thermal conditions is improved (not easy to cause tool turning).
Left and right cutting mode; as shown in Fig. 3 (the thread turning tool enters the tooth depth through the staggered gap in the direction of tooth profile angle).

CNC machining

Groove cutter rough groove cutting method: as shown in Fig. 4, (this method first uses slotting cutter to rough groove (then uses trapezoidal thread turning tool to process both sides of thread).

Characteristics and processing method of worm and trapezoidal thread with large pitch

The cutting resistance of turning worm and large guide wire (either oblique or left-right cutting mode) is very high (previously only high-speed steel turning tool is used for low-speed turning (production efficiency is very low). In order to be able to use carbide tools, I had to find a way to reduce the cutting depth of the blade.

The groove of thread or worm is divided into several layers (converted into several shallow trapezoidal grooves) for cutting.

Since the depth of the left cutting groove remains unchanged (the tool only needs to do left direction!) and feed along the guide rail direction (thus organically combining the left and right cutting methods with the oblique cutting method), the cutting edge can be cut once (and the cutting margin can be effectively controlled), which can guarantee the surface quality and tool life

Hardware processing technology

Hardware equipment, or the application of hardware processing machine tools, in today’s machinery industry, or silicone, or mold, steel, electronic products, other products, after the processing of mechanical equipment, the effect and efficiency are much faster, and reduce the processing pressure of employees. Now hardware manufacturers include a wide range, such as keys, or some metal plates, or etching, or other materials, iron.

What is the expansion effect of hardware processing industry

Spray painting: spray painting is widely used in some relatively large hardware parts. The existence of spray painting can not only make the products not easy to rust, but also produce some other effects, so that the performance of the products is better. It is a step that many hardware parts processing manufacturers will carry out when processing finished products.
Electroplating: electroplating is a relatively common hardware parts processing technology, because the use of this process for the product surface rust resistance performance is very good, can let the product in a long period of time can be normal and stable work, and is widely used in the current hardware products processing.

What is the expansion effect of hardware processing industry

Polishing: polishing is often used in some daily necessities of hardware parts processing technology. Polishing is not only to maintain the appearance of products, but also to make users feel better. Especially for some products which are easy to balloon and burr, polishing is a necessary step. Now China’s hardware industry is developing rapidly, and the continuous development of science and technology is also constantly promoting the improvement of hardware processing technology. I believe that there will be more processing technology to be created in the future, which will bring convenience to human production.

What is the expansion effect of processing industry

First of all, the most important error of secondary positioning and non coincidence is the error of non coincidence. When machining the workpiece on the machine tool, it is necessary to select some geometric elements on the workpiece as the positioning datum during processing. If the selected positioning datum does not coincide with the planning datum, the datum misalignment error will occur. Measurement error: when measuring parts during or after processing, the measurement method, measuring tool precision, workpiece and subjective and objective factors directly affect the measurement accuracy. There are fixture errors and tool errors: mechanical fixture errors: the role of the fixture is to make the workpiece equivalent to the tool and machine tool with the correct orientation, so the geometric errors of the fixture have a great impact on the machining errors. Spindle rotation error refers to the variation of the actual rotation axis of the spindle relative to its uniform rotation axis at each moment, which will directly affect the accurate density of the workpiece. Any tool in the cutting process can not prevent wear, and thus cause the size and shape of the workpiece to change.

Matters needing attention in NC lathe processing

The processing technology of CNC lathe is similar to that of ordinary lathe. However, as CNC is a kind of clamping, continuous automatic processing completes all turning process, so attention should be paid to the following aspects.

Reasonable selection of cutting parameters

For efficient metal cutting, machining materials, cutting tools and cutting conditions are the three main factors. These factors determine the processing time, tool life and machining quality. An economical and effective machining method must be a reasonable choice of cutting conditions.

Three factors of cutting conditions: cutting speed, feed and cutting depth directly lead to tool damage. With the increase of cutting speed, the tool tip temperature increases, resulting in mechanical, chemical and thermal wear. Increasing the cutting speed will reduce the tool life by half.

The relationship between feed condition and tool wear is very small. However, when feeding, the cutting temperature increases and the wear occurs. It has less effect on the tool than on the cutting speed. Although the influence of cutting depth on cutting speed and feed rate is not as great as that of cutting speed and feed rate, the hardened layer produced by cutting material will also affect the tool life when cutting at small cutting depth.

The user should select the cutting speed according to the material, hardness, cutting state, material type, feed rate and cutting depth. The following table:

According to these factors, select the most suitable processing conditions. The ideal state is to wear regularly and stably to reach the service life.

But in practice, the choice of tool life is related to tool wear, size change, surface quality, cutting noise, processing heat and so on. When determining the processing conditions, it is necessary to study according to the actual situation. For refractory materials such as stainless steel and heat resistant alloy, coolant or hard blade can be used.

Select a tool

1) The cutter with high strength and good durability shall be selected to meet the requirements of thick tooth turning, large back cutting and large feed.

2) Precision turning, select high precision, good durability tool, to ensure the machining accuracy requirements.

3) In order to reduce the tool change time and facilitate tool alignment, the machine clamping tool and the machine clamping tool should be used as far as possible.

CNC machining

Reasonable selection of fixture

1) Try to use general fixture to clamp workpiece and avoid using special fixture;

2) Parts positioning datum coincide to reduce positioning error.

Determine the processing route

Machining path is the exponential control of the tool path and direction relative to the part in the machining process.

1) Ensure machining accuracy and surface roughness;

2) The processing route should be shortened as much as possible to reduce the tool idle travel time.

Relationship between machining route and machining allowance

At present, it is not widely used in CNC lathe. Generally, the blank should be put on the surplus allowance, especially the allowance with forging and casting hard skin should be processed on the common lathe. If you must use CNC lathe processing, then you must pay attention to the flexible arrangement of the program.

Key points of fixture installation

At present, the connection between hydraulic chuck and hydraulic clamping cylinder is realized by pull rod. The critical point chuck of the hydraulic chuck is as follows: first, remove the lifting hand of the nut on the hydraulic cylinder, pull out the tube, and extract from the rear end of the shaft, and then put the chuck fixing screw on the raised hand, chuck can be removed.

The polished edge on the tool refers to a small part of the blade, which is worn along the side deviation direction behind the blade and parallel to the tool tip. The blade is mainly used for the second cutting after cutting edge cutting, which is equivalent to removing burrs and scars in the process of finishing. Its purpose is to improve the surface roughness of the workpiece, which is mainly used for the finishing of cutting tools.

CNC thread processing method

Thread machining is one of the important applications of CNC machining center. The quality and efficiency of thread processing directly affect the quality of parts and the production efficiency of machining center.

With the improvement of CNC machining center performance and tool performance, the thread processing method is also constantly improved, and the accuracy and efficiency of thread processing are also gradually improved. In order to make the technical personnel reasonably choose the thread processing mode in the processing process, improve the production efficiency and avoid quality accidents, several thread processing methods commonly used in the CNC machining center are summarized as follows:

Tap processing method
Classification and characteristics of tap processing

Tapping is the most commonly used method for machining threaded holes, which is mainly applicable to the threaded holes with smaller diameter (d < 30) and lower hole position accuracy.

In the 1980s, the flexible development method was adopted for all threaded holes. That is to say, the tap was equipped with a flexible tapping chuck. The clamping and tapping chuck could compensate for the errors caused by the uneven rotation speed of the spindle due to the axial propulsion of the machine tool, so as to ensure the correct pitch.

Flexible tapping chuck has complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC machining center has gradually improved, and the rigid tapping function has become the basic configuration of CNC machining center.

Therefore, rigid tapping becomes the main method of thread processing.

CNC machining

The rigid spring chuck is used to clamp the tap, so that the spindle enters the spindle, and the rotation speed is controlled by the machine tool to keep consistency.

Compared with the flexible tapping chuck, the spring chuck has the advantages of simple structure, low price and wide application. In addition to clamping taps, it can also clamp end mills, drills and other tools, which can reduce the cost of cutting tools. At the same time, the use of rigid tapping can carry out high-speed cutting, improve the efficiency of the machining center and reduce the manufacturing cost.

Determine the bottom hole of thread before tapping

The processing of thread bottom hole has a great influence on the service life of tap and thread processing quality. In general, the diameter of bottom hole drill is close to the upper limit of tolerance.

For example, if the diameter of the bottom hole of M8 threaded hole is Ф 6.7 + 0.27 mm, select some diameter of Ф 6.9 mm. In this way, the machining allowance of the tap can be reduced, the load of the tap can be reduced, and the service life of the tap can be improved.

Click Select

When selecting taps, the corresponding taps should be selected according to the different processing materials. Tool companies should produce different types of taps according to the different processing materials. Special attention should be paid to the selection.

Because the tap is very sensitive to the processed material relative to milling cutter and boring cutter. For example, using cast iron taps to process aluminum parts is easy to cause thread teeth, random thread and even broken tap, resulting in workpiece scrapping. Secondly, pay attention to the difference between through tap and blind tap. The guide rail at the front end of the through-hole tap is longer, and the chip removal is the front-end chip removal.

The front guide plate of the blind hole is short, and the chip removal is the rear guide plate. It is impossible to ensure the depth of thread processing by using through-hole tap to process blind hole. In addition, if a flexible tapping chuck is used, the diameter and width square of the tapping handle should be the same as that of the tapping chuck; the diameter of the rigid tapping tap handle should be the same as that of the spring sleeve. In short, only reasonable selection of taps can ensure the smooth processing.