CNC Technology – Page 81 – CNC Machining & Turning, Milling, Metal parts

What are the material requirements for precision parts processing

Precision machining, not all raw materials can be carefully processed. Some raw materials are too hard, beyond the hardness of the processing machine parts, the machine parts may collapse, so these raw materials are not suitable for precision machining, unless they are made of unique raw materials, or laser cutting.

The raw materials for precision machining are divided into two categories: metal raw materials and non-metal raw materials.

As for the metal raw materials, the hardness is greater for stainless steel, followed by cast iron, followed by copper, followed by aluminum.

The processing of ceramics and plastics belongs to the processing of non-metallic materials.

1. First of all, the hardness of raw materials is required. For some scenes, the higher the hardness of raw materials is, the better it is. It is only limited to the hardness requirements of machining parts. The processed raw materials cannot be too hard. If they are harder than the parts, they cannot be machined.

2. Secondly, the material is of moderate hardness, at least one level lower than the hardness of the parts. At the same time, it depends on the function of the processed parts and the correct selection of materials for the parts.

In a word, precision machining still has some requirements for materials, not all materials are suitable for processing, such as too soft or too hard raw materials, the former is not necessary for processing, the latter is unable to process.

Therefore, before processing, we must pay attention to the density of the material. If the density is too large, it is equal to the hardness. If the hardness exceeds the hardness of the machine (lathe tool), it is impossible to process. It will not only damage the parts, but also cause danger, such as the tool flying out and hurting people. Therefore, generally speaking, for machining, the material of raw materials should be lower than the hardness of the machine tool, so that it can be processed.

报错

The cause and solution of the abnormal machining accuracy of CNC machine tools

1、 Causes of abnormal machining accuracy

The causes of abnormal machining accuracy are hidden and difficult to diagnose. Based on years of practical experience, the author sums up five main reasons: the feed unit of the machine tool is changed or changed; the zero point offset of each axis of the machine tool is abnormal; the reverse clearance of the axis is abnormal; the running state of the motor is abnormal, that is, the electrical and control parts are abnormal; the mechanical fault, such as the lead screw, bearing, coupling and other parts. In addition, the programming of machining programs, the selection of cutting tools and human factors may also lead to abnormal machining accuracy. Wechat for metal processing, good content, worthy of attention.

2、 Fault diagnosis principle of CNC machine tools

1. The first external and then internal CNC machine tool is a machine tool integrating mechanical, hydraulic and electrical, so the occurrence of its fault will also be comprehensively reflected by the three. The maintenance personnel shall check one by one from the outside to the inside first, and try to avoid opening and disassembling at will, otherwise the fault will be enlarged, the machine tool will lose precision and performance.

2. Generally speaking, mechanical fault is easy to detect, while the fault diagnosis of CNC system is more difficult. Before troubleshooting, first of all, pay attention to eliminate mechanical faults, which can often achieve twice the result with half the effort.

3. The machine tool can be powered on only when it is confirmed as a non-destructive fault through understanding, observation, test, analysis under the static state of power failure of the machine tool; under the operation condition, it can be dynamically observed, inspected and tested to find the fault.

For destructive faults, the danger must be eliminated before power on.

4. Simple first, then complex. When there are many kinds of faults interwoven and covered up, and there is no way to start for a while, the easy problems shall be solved first, and then the difficult problems shall be solved. Often after simple problems are solved, difficult problems may become easy.

CNC machining

3、 Fault diagnosis method of CNC machine tools

1. Intuitionistic method (looking, hearing, asking and cutting) – machine tool fault phenomenon, processing status, etc.; look at CRT alarm information, alarm indicator light, capacitor and other components deformation, smoke burning, protector tripping, etc.; listen to abnormal sound; listen to electrical components burnt smell and other peculiar smell; touch heat, vibration, poor contact, etc. Wechat for metal processing, good content, worthy of attention.

2. Parameters of parameter inspection method are usually stored in RAM, sometimes the battery voltage is insufficient, the system is not powered for a long time or external interference will cause parameter loss or confusion, so relevant parameters shall be checked and calibrated according to fault characteristics.

3. Some faults of isolation method are difficult to distinguish whether they are caused by numerical control part, servo system or mechanical part. Isolation method is often used.

4. In the same kind of method, the spare board with the same function is used to replace the suspected faulty template, or the templates or units with the same function are exchanged with each other.

5. The function program test method compiles some small programs for all the instructions of G, m, s, t and functions, and runs these programs when diagnosing faults to judge the lack of functions.

How to select blank for precision parts machining

1、 Casting

The forging method should be used to manufacture the parts with complex forms. At present, most castings are forged by sand mold, which can be divided into wood mold manual type and metal mold mechanical type. It has low precision, large machining surface allowance and low production efficiency. It can be used for single small batch production or forging of large parts. Metal mold machinery has high production rate and casting precision, but the cost of equipment is high and the component of casting is limited, so it can be used in a large number of small and medium-sized castings. Secondly, special forging can be selected for small castings with high quality requirements, such as pressure forging, centrifugal manufacturing and investment forging.

2、 Forging

For steel parts with high mechanical strength requirements, forging blanks are usually used. There are two kinds of Forgings: free forging and die forging. The free forging forging can be obtained by hand forging (small blank), mechanical hammer forging (medium blank) or press forging (large blank). This kind of forging has the advantages of low precision, low production rate, large machining allowance, and simple structure. It is applicable to single piece and small batch production, and large forgings.

The small braid in the well-organized parts processing field tells you that the accuracy and surface quality of die forgings are better than that of free forgings, and the form of forgings can be more complex, so the machining allowance can be reduced. The production efficiency of die forging is much higher than that of free forging, but it needs unique equipment and forging die, so it is used for large batch of medium and small forgings.

3、 Profile

Profiles can be divided into round steel, square steel, hexagonal steel, flat steel, angle steel, channel steel, I-beam and other profiles with unique sections. There are hot rolled and cold drawn sections. The hot-rolled profile has low precision but low value, which is used for the blank of common parts; the cold drawn profile has small size and high precision, which is easy to complete the automatic feeding, but it has high value, which is mostly used for the production of large batch, and it is practical for the processing of self-propelled bed.

The speed control method of machining spindle with CNC lathe

In order to meet the requirements of machining main drive of CNC lathe, the stepless speed regulation system of electric motor is often selected for CNC lathe. In order to expand the speed regulation boundary and meet the requirements of low speed and large torque, the stepless speed regulation of gear and motor is also commonly used to complete the spindle speed regulation.

1. Mechanical gear shifting

In the main drive system of CNC lathe machining, the traditional spindle box structure is greatly simplified due to the use of stepless speed regulation of electric thoughts. However, due to the limitation of the spindle motor and driving power, the constant torque transmission is often used in its low speed section. In order to make the main shaft provide the high transmission power of the main electric idea within the full speed limit as far as possible, and meet the demand of low-speed powerful cutting of CNC machine tools, it is often selected to use the combination of 1-4 gear speed change and stepless speed change, that is, the so-called stepless speed change in sections. The selection of mechanical gear slows down, which not only enlarges the transmission power, but also enlarges the speed regulating boundary.

When the CNC lathe is cutting, the spindle operates automatically according to the rotation speed specified by the s command in the part processing program. Therefore, there must be two kinds of spindle speed command information in the numerical control system, that is, to control the drive and speed regulating circuit of spindle motor by using analog or digital information (s code), and to control the implementation and organization of automatic gear shifting by using switch information (M code). Automatic shift organization is a kind of electric mechanical conversion device, commonly used are hydraulic fork and electromagnetic clutch.

2. Electric drive

There are two main types of speed regulating electric thoughts used in NC lathe machining spindle drive: DC and AC.

(1) DC motor speed regulation? The speed regulation boundary of ordinary CNC machine tools is relatively large. For DC motor speed regulation, two methods of voltage regulation and magnetic regulation are used simultaneously. The typical characteristic curve of DC spindle electric? Machine is shown in Figure 6-1. From its characteristic curve, it can be known that the electric idea is a constant torque speed regulation under the speed N0, that is to say, the armature voltage is selected to be changed to complete; the speed above N0 is a constant power speed regulation, which is completed by changing the excitation current.

The more commonly used “FANUC DC separately excited spindle electric machine” is a three-phase fully controlled thyristor non circulation reversible speed regulation system, which can complete the speed regulation of voltage regulation and magnetic regulation, and the speed regulation boundary is 35? ～ 3500r / min.

(2) AC motor speed regulation

At present, the cage type induction motor is used in the AC spindle drive of CNC machine tools, and the vector control variable frequency speed control method is commonly used.

With the improvement of the new DC and AC spindle speed control electric ideas, electric ideas speed control will be used in the ordinary, but in order to reduce the cost of economic CNC machine tools, mechanical gear shifting is often used to change the spindle speed.

The division of CNC machining stage

When the machining quality of parts is high, it is often impossible to use one process to meet the requirements, but to use several processes to gradually reach the required machining quality. In order to ensure the quality of CNC machining parts and the correct use of equipment and manpower, the machining process of parts can be divided into four stages: rough machining, semi finishing, finishing and finishing.

The differentiation of CNC machining stage should be based on the quality requirements, structural characteristics and manufacturing program of parts, and should not be absolute. It is unnecessary to distinguish processing stages for equipment with low processing quality requirements, good equipment rigidity, high blank precision, small machining allowance and small production program. For heavy workpieces with good rigidity, due to clamping, transportation and time-consuming, all rough and finish machining are often completed under one clamping.

As for the workpiece without distinguishing the processing stage, in order to reduce the impact of various deformations on the processing quality during the rough processing, it is necessary to loosen and accelerate the organization after the rough processing, park the workpiece for a period of time, make the workpiece fully deformed, and then use a small accelerating force to accelerate from the beginning for finishing.

Instructions for use of steel wire joint clamp accessories

Instructions for use of wire joint clamp accessories. Clamp accessories, transportation belt clamp accessories, lifting belt clamp accessories, joint clips, transportation belt connector clips, lifting belt connector clips, belt clamp plates, transportation belt connector clamp plates, lifting belt connector clamp plates, transportation belt connector installation methods, how to install the transportation belt connector.

Our company has been making steel wire rope lifting belt for more than 10 years, specializing in manufacturing steel wire rope lifting belt and its accessories: alloy clamp accessories, steel plate clamp accessories, high-strength galvanized hopper bolts, heat-resistant rubber pad, etc

Introduction to fixture accessories

1. Product classification: special alloy clamp fittings, steel plate clamp fittings

2. Product composition

Special alloy band clamp composition:

Main belt clamp: 1 inner clamp and 2 outer clamps

Accessories: special clamp bolt, steel wire buckle, filler, filling rubber, filling box

Composition of steel plate with clamp:

Main belt clamp: 1 internal clamp, 2 external clamps accessories: special clamp bolt, steel wire buckle

3. Product specification:

Width: 200mm ~ 1700mm

Fixture accessories

4. Installation method of fixture accessories:

1) . use the main belt clamp to clamp the two ends of the lifting belt with bolts.

2) . after clamping, peel off the cover glue at both ends of the lifting belt, and peel off the wire rope core.

3) . fasten the wire rope cores at both ends of the belt with the U-shaped buckle of the wire rope in sequence.

4) . cover the filling box with filling material and filling glue, wait for 15 minutes until it solidifies.

Clamp accessories, transportation belt clamp accessories, lifting belt clamp accessories, joint clips, transportation belt connector clips, lifting belt connector clips, belt clamp plates, transportation belt connector clamp plates, lifting belt connector clamp plates, transportation belt connector installation methods, how to install the transportation belt connector.

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How to determine the machining coordinate system of CNC lathe

CNC lathe processing is a cause with high requirements. If there is a small error in coordinate configuration during the processing and manufacturing of workpieces, the products will be scrapped, and even may bring safety incidents. So how to confirm the coordinate system of CNC lathe?

(1) Reference point of CNC machine tool: the reference point is also an invariable point on the machine tool. It is the limit position of the tool holder movement limited by mechanical stop or electrical device. Its key function is to locate the coordinate system of machine tool.

(2) Machine coordinate system: the right-hand Cartesian Cartesian coordinate system is selected as the coordinate system on the CNC machine tool.

(3) Workpiece coordinate system: workpiece coordinate system is the coordinate system set by the programming staff during programming, also known as programming coordinate system.

Origin of workpiece coordinate system:? In NC programming, first of all, set a point on the part drawing as the origin of programmed coordinate according to the form characteristics and dimensions of the parts to be processed, which is called the origin of programmed coordinate. From the point of view, it’s OK to choose the origin of the workpiece coordinate system at any point on the workpiece, but this may represent tedious calculation problems and add programming troubles. In order to make the calculation simple and simplify the programming, the origin of the workpiece coordinate system is usually selected on the turning center of the workpiece, and the detailed position can be studied and configured on the left end face (or right end face) of the workpiece, even if the programming datum coincides with the design datum and positioning datum.

Tool setting: the coordinate system of machine tool is the only benchmark of machine tool, so it is necessary to know the position of program origin in the coordinate system of machine tool and finish the tool setting. The essence of tool setting is to confirm the only position of the origin of workpiece coordinate system in the machine coordinate system. Tool setting is an important skill in NC machining. At the same time, the efficiency of the tool also directly affects the efficiency of NC machining.

Tool change: when it is necessary to change the tool in the process of NC machining, it is necessary to study and select the appropriate tool change point when programming. The so-called tool change point refers to the position of tool holder rotation and tool change. When the CNC lathe confirms the workpiece coordinate system, the tool change point may be a fixed point or an arbitrary point relative to the workpiece origin. The tool change point shall be set on the outside of the workpiece or fixture, so as to ensure that the tool holder does not touch the workpiece and other parts during tool change.

What causes the abnormal machining accuracy of CNC machine tools

1、 Causes of abnormal machining accuracy of CNC lathe

The reasons for the abnormal machining accuracy of CNC lathe are highly hidden and difficult to diagnose. Five main reasons are summed up: the feed unit of machine tool is changed or changed; the zero point offset of each axis of machine tool is abnormal; the reverse clearance of axis is abnormal; the running state of motor is abnormal, that is, the electrical and control parts are abnormal; the mechanical faults, such as lead screw, bearing, coupling and other parts. In addition, the programming of NC lathe, the selection of cutting tools and human factors may also lead to the abnormal machining accuracy of NC lathe.

2、 Fault diagnosis principle of CNC machine tools

For destructive faults, the danger must be eliminated before power on.

3、 Fault diagnosis method of CNC machine tools

1. Intuitionistic method: (looking, hearing, questioning and cutting) ask – the fault phenomenon of machine tool, CNC lathe processing status, etc.; see – CRT alarm information, alarm indicator light, capacitor and other components deformation, smoke burning, protector tripping, etc.; listen – abnormal sound; smell – the smell of electrical components burning and other peculiar smell; touch – heating, vibration, poor contact, etc. Wechat for metal CNC lathe processing, good content, worthy of attention.

2. Parameter inspection method: the parameters are usually stored in RAM. Sometimes, the battery voltage is insufficient, the system will lose or be confused due to long-term power failure or external interference. The relevant parameters shall be checked and calibrated according to the fault characteristics.

3. Isolation method: for some faults, it is difficult to distinguish whether they are caused by CNC part or servo system or mechanical part, isolation method is often used.

4. In the same kind of method, the spare board with the same function is used to replace the suspected faulty template, or the templates or units with the same function are exchanged with each other.

5. The function program test method compiles some small programs for all the instructions of G, m, s, t and functions, and runs these programs when diagnosing faults to judge the lack of functions.

Classification and repair of lathe common faults

Because the CNC lathe adopts the computer control skills, the mechanical structure is greatly simplified compared with the common machine tools, and the opportunity for the mechanical system to expose the defects is greatly reduced. The common mechanical defects are mainly as follows: the defects of lathe spindle components. Because of the application of adjustable speed motor, the structure of spindle box of CNC lathe is simple, the disadvantages of which are the tool handle active tension equipment, active speed control equipment, etc.

Disadvantages of ATC. More than 50% of the disadvantages of machining center machine tools with active tool change equipment are related to active tool change equipment, which are mainly revealed in: the disadvantages of tool magazine activity, large missing of positioning difference, unstable clamping handle of manipulator, large error of manipulator activity, etc. When the disadvantages are serious, the tool change is stuck and the lathe is forced to stop working.

It is used to detect the disadvantages of the travel switch voltage in the moving direction of each axis. On CNC machine tools, in order to ensure the reliability of active homework, a lot of travel switches are selected to detect the active position. During the long-term operation of the machine tool, the moving characteristics of the moving parts change. The reliability of the travel switch pressing equipment and the change of the quality characteristics of the travel switch itself have a great impact on the generation and elimination of the defects of the lathe.

Disadvantages of lathe feed drive chain. Because the rolling collision pairs are widely used in the guide rail of CNC machine tools, the main disadvantages of the feed transmission chain are caused by the falling of the active quality, such as the mechanical parts are not moving to the regular position, the operation is stopped, the positioning accuracy is falling, the reverse leisure is increased, the mechanical crawling, the noise of the bearing is increased (usually exposed after the collision), etc., which can be adjusted and maintained from beginning to end Force, adjust the loose link, improve the accuracy of activities and adjust the compensation link.

The method of eliminating the shape error of the spherical surface in CNC machining

When CNC machining spherical surface is more and more quadrant ball and surface, due to improper adjustment, it is very easy to produce shoulder, shovel back and other conditions. The reasons are as follows:

1. System gap formation

In the driving pair of CNC machining equipment, there is a certain gap between the lead screw and the nut. With the increase of the time when the equipment is put into operation, the gap increases gradually due to wear. Therefore, the key factor for the shoulder on the machining surface is to compensate for the corresponding gap during the reverse movement. The clearance measurement usually adopts dial indicator measurement method, and the deviation control is within 0.01-0.02MM. It should be pointed out here that the base and rod should not be extended too long, because the cantilever is long, the base is easy to be moved by force, resulting in inaccurate counting, and the compensation value is not true.

2. Uneven formation of workpiece machining allowance

Before finishing the design surface of CNC machining parts, whether the machining allowance of the surface to be machined is average is also an important reason for forming whether the forming surface can reach the design requirements, because the machining allowance is not uniform, which is easy to form a “reflection” deviation. Therefore, for the parts with high requirements on surface form, before forming, the machining allowance should be as average as possible to reach the design requirements by machining one more profile.

3. Improper tool selection

In the cutting process, CNC cutting tools remove the raw materials through the main cutting edge. However, after the arc passes the quadrant and the arc is tangent to the cutting edge (the intersection of the back edge and the base surface), the cutting may be added to the back edge. Therefore, when choosing or grinding tools, we must study the wedge angle of the tools.