CNC Technology – Page 80 – CNC Machining & Turning, Milling, Metal parts

Maintenance rules of grinding machine for precision parts processing equipment

Grinding machine is one of the basic equipment used in precision parts processing, its shape will also have a positive impact on the processing quality, so if you want to improve the precision of precision parts processing, you must carry out regular inspection and care for the grinding machine, so that it will always maintain a good shape.

First of all, we need to know that as a precision parts processing equipment, the grinder should be specially assigned to be in charge of maintenance and application. When its homework is completed, it is necessary to clean all parts of the machine, especially the sliding parts, and then apply oil to maintain excellent smoothness. At the same time, it is also necessary to eliminate the grinding debris at all parts of the grinder, so as to avoid adverse effects on the processing process. Some parts are still subject to rust prevention treatment,

Before using the grinder, don’t forget to correct the grinding wheel average, and choose the grinding wheel carefully according to the material and hardness of the work materials, which is one of the key factors affecting the processing efficiency of precision parts. Don’t forget to pay attention to the rotation target of the grinder spindle, prevent the use of air to clean the work materials and machinery, and keep the dust collection pipeline clean, otherwise it will lead to burning.

Secondly, we pay attention to the suction cup of the grinding machine for precision parts processing equipment, whether it is the permanent magnetic casting suction cup or the electromagnetic suction cup, and the disk surface is the basis of whether the grinding precision of the working object can be dream, so we must properly and precisely care for and maintain it.

If the precision of the work object is poor or the disk surface is damaged, the disk surface must be grinded again. Only when the precision of the disk surface of the suction cup of the grinder meets the requirements, can the precision of the precision parts be ensured. In addition, there is a smooth system of conditioning, but it is nothing more than the replacement of smooth oil and wash filter.

CNC machining hardware parts suitable for processing

1. For the content of hardware parts suitable for NC machining, the following sequence research can be carried out during selection:

(1) The content that cannot be processed by general machine tool shall be the priority;

(2) General machine tools are difficult to process and their quality is difficult to guarantee;

(3) General machine tools have low machining efficiency and high manual operation intensity, which can be selected when there is abundant machining strength in CNC machine tools.

2. Hardware parts not suitable for NC machining

(1) It takes a long time to adjust. If the first fine datum is located and processed with the rough datum of the blank, the content of special tooling coordination is required;

(2) Processing location distribution, need to install and configure the origin repeatedly. At this time, it is very difficult to select CNC machining, and the effect is not obvious, so general machine tools can be placed for supplementary machining;

(3) The appearance of the profile machined according to certain manufacturing documents (such as sample plate, etc.). The key reason is that it is difficult to obtain data, easy to conflict with checking credentials, which increases the difficulty of programming.

Working range of AC rotating axis of CNC five axis machining center

Generally speaking, the axis around the x-axis of the five axis CNC machining center is defined as the a-axis. The working boundary of the a-axis is + 30 ° to – 120 °. The worktable of the five axis machining center is equipped with a rotating shaft. This rotating shaft ring rotates around the z-axis. We define it as the c-axis. The working boundary of the c-axis is 360 degree rotation. For the five axis machining center with a rotating shaft and C rotating shaft, the workpiece can be clamped once to finish machining other than the mounting surface. Generally, the small graduation value of a-axis and c-axis is 0.001 degrees. In this way, it is better to remove the other surfaces of the installation surface without angle, and to process the skew surface, skew hole and other complex processes. It can be realized that if the a-axis, c-axis and XYZ linear three-axis are processed in five-axis linkage, the complex curved surface workpiece can be processed. Of course, good CNC system, servo motor system and software support are needed.

Structural advantages of AC rotating shaft configuration in five axis machining center

The advantages of the above AC rotating shaft configuration are simple structure, good rigidity of the main shaft, low manufacturing cost and so on. Generally, the worktable can not be configured too large, and the load-bearing is also relatively small. The unique reason is that when the rotation axis of a turns to 90 degrees or more, when the workpiece is processed, it will bring a lot of load-bearing moment to the worktable.

Matters needing attention in the process of NC lathe machining

What should be paid attention to in the process of NC lathe machining. The machining process of CNC lathe is the same as that of ordinary lathe. However, since CNC is a clamping process, all the turning processes are finished continuously and automatically, the following aspects should be paid attention to.

1. Correct selection of cutting parameters

In terms of high efficiency metal cutting, the raw materials to be processed, cutting equipment and cutting conditions are three major factors. These decisions determine machining time, tool life and machining quality. The economic and useful machining method must be the correct choice of cutting conditions.

Three factors of cutting conditions: cutting speed, feed rate and cutting depth directly lead to tool damage. With the increase of cutting speed, the temperature of tool tip will rise, and mechanical, chemical and thermal wear will occur. If the cutting speed increases, the tool life will be reduced by 1 / 2.

The relationship between the feed condition and the wear of the back edge of the tool occurs within a very small boundary. But the feed rate is large, the cutting temperature rises, and the rear edge wear is large. It has less influence on the cutting tool than the cutting speed. Although the influence of cutting depth on the tool is not as high as the cutting speed and feed rate, when the cutting depth is small, the hard layer of the material to be cut will also affect the tool life.

Users should choose the cutting speed according to the raw material, hardness, cutting shape, raw material variety, feed rate, cutting depth, etc. The following table:

The selection of suitable processing conditions is based on these factors. Regular and stable wear and tear is the condition of dream.

However, in the essential work, the choice of tool life is related to tool wear, dimension change, surface quality, cutting noise, machining heat, etc. When confirming the processing conditions, the requirements are discussed according to the nature. As for stainless steel and heat-resistant alloy and other hard to process raw materials, it is advisable to choose a coolant or a rigid blade.

CNC lathe

2. Select tools correctly

1) During rough turning, the cutter with high strength and good durability shall be selected to meet the requirements of large back draft and large feed during rough turning.

2) When finishing, the cutting tools with high accuracy and good durability shall be selected to ensure the requirements of machining accuracy.

3) In order to reduce the time of tool change and make the tool setting easier, we should choose the clip knife and clip knife.

3. Select fixture correctly

1) Although the general fixture is used to clamp the workpiece, the special fixture shall not be used;

2） The positioning datum of parts are overlapped to reduce the positioning deviation.

4. Confirm the processing route

Machining route refers to the moving track and target of the tool relative to the part in the process of NC machining.

1) It shall be able to meet the requirements of machining accuracy and surface roughness;

2) It is necessary to reduce the processing route and the time of tool empty travel.

5. Correlation between machining route and machining allowance

At present, under the condition that the CNC lathe has not been widely used, it is usually necessary to place too much allowance on the blank, especially the allowance containing forging and casting hard skin layer on the ordinary lathe for processing. If the CNC lathe must be used for machining, it is necessary to pay attention to the sensitive placement of the program.

6. Key points of fixture installation

At present, the connection between hydraulic chuck and hydraulic clamping cylinder is completed by pull rod. The key points of hydraulic chuck clamping are as follows: first, remove the nut on the hydraulic cylinder with the handle, remove the pull tube, and pull it out from the rear end of the main shaft, and then remove the constant screw of the chuck with the handle to remove the chuck.

The polishing edge on the tool refers to a small section of the edge which is parallel to the tool tip milled by the target of the deviation angle of the back edge pair of the tool edge, which is mainly used for the second cutting after the cutting of the tool edge, which is equivalent to the direction burr in the finishing process. The goal is to increase the surface roughness of the workpiece, which is mostly used for the tool of finishing.

What are the characteristics of precision parts processing

What are the characteristics of precision parts processing? Five axis linkage processing center is a processing center with high technology content and high weekly density, which is specially used to process complex curved surface. This processing center system has full weight lifting influence on aviation, sail sea, military, scientific research, sophisticated equipment, high-precision medical equipment and other industries in a country.

1、 What is a five axis machining center

Five axis linkage machining has the characteristics of high efficiency and high precision, and the complex machining can be completed as soon as the workpiece is clamped once. It can be suitable for the processing of present moulds such as auto parts, aircraft structural parts, etc. There is a big difference between five axis machining center and pentahedral machining center. Many people don’t know this. They mistakenly regard the pentahedron machining center as a five axis linkage machining center. Five axis machining center has x, y, Z, a, C five axis, XYZ and AC axis to create five axis machining, specializing in space surface processing, special-shaped processing, hollow processing, drilling, oblique hole, oblique cutting, etc. The “pentahedron machining center” is the same as the three-axis machining center, but it may as well do five faces at the same time, but it can not do special-shaped processing, such as drilling, cutting bevel, etc.

For the rest, the practical boundary of the five axis CNC machining center is quite ordinary. It is understood that the current five axis CNC machining center system is the only way to process impellers, blades, marine propellers, heavy-duty generator rotors, automobile wheels, large diesel engine crankshafts, etc.

Precision parts processing

2、 Advantages of five axis machining center

1. Reduce processing time and improve processing accuracy.

The big characteristic of five axis machining center is that it is advisable to process all five surfaces by one-time clamping. That is the so-called processing angle avoidance. If it’s a linked bed, axis C can rotate endlessly, and axis a can rotate by 130 degrees. These characteristics of the equipment make it possible to process without interference.

The advantage of this method is that one-time clamping can not only finish the processing, but also prevent the repeated positioning deviation caused by repeated clamping. At the same time, it also saves a lot of time and improves the working efficiency. It can reduce the time from product to delivery and reduce the inventory.

2. Reduce equipment investment cost, workshop area and workshop number.

The five axis linkage machining center controls the compound machining machine, usually with turning performance, which can be included from lathe to milling machine to vertical mill. Everyone knows that the value of vertical mill equipment is quite high at present. After cost, processing beat and other accounting, we can find that the value of five axis is high. Before that, many people’s production and processing may be based on engineering segmentation. The problem with such a production method is that there is a lot of waiting time that cannot be eliminated. However, the engineering intensive production represented by the five axis compound processing equipment only needs the early waiting time for debugging, and with the popularity of all kinds of complete machine simulation software in China at present, even if only the introduction of rough data is required, the programming can be completed and the early planning can be greatly reduced. So at present, overseas auto parts and high-end manufacturing are basically based on five shafts.

3. No need for unique fixture, can complete automation.

Another prominent feature of the five axis is that the dependence on the fixture will be reduced. The rule workpiece can be clamped directly with three claws and four claws chuck, while the rule workpiece can be clamped with one side and two pins. At the same time, the five axis machining center can complete the automation of the workshop and reduce the number of people. For example, machining robot’s key point and base. In the past, horizontal plus and vertical plus combined processing were used. Now, only zero point tray and five axis linkage processing center are used to complete 24-hour operation processing.

The method of determining the tool clamping force in CNC machining

When designing the clamping device for NC machining tools, the clamping force must include three factors: the target, the action point and the size of the clamping force. So how to confirm the clamping force of NC machining tools?

1. The point of action of the tool clamping force in NC machining the point of action of the clamping force is a small area of contact between the clamping piece and the workpiece. The problem of selecting the action point is to confirm the position and quantity of the action point of the clamping force when the clamping target has been determined. The choice of the action point of the clamping force is the key factor to reach a good clamping shape. The correct choice of the action point of the clamping force must follow the following principles?

The roughness value of grinding surface is reduced from 2.0 to 1.1 CNC tool

2. The target of the clamping force of the tool in NC machining is related to the basic configuration of the positioning of the workpiece and the target of the external force on the workpiece. The following criteria must be followed when selecting NC tools:

① The target of the clamping force shall be helpful for the stable positioning, and the main clamping force shall face the key positioning base plane.

② The aim of the clamping force should be to reduce the clamping force to reduce the deformation of the workpiece and the working strength.

③ The target of clamping force should be the one with better rigidity of workpiece. Due to the different stiffness of the workpiece in different targets, the deformation of different stressed surfaces is also different due to the size of their contact area. More and more attention should be paid to make the target of clamping force point to the best target of workpiece rigidity when clamping thin-walled parts.

3. CNC machining tools simplify the process flow and reduce the cost of production in some use situations. The surface quality of high-speed milling can be comparable to grinding, and high-speed milling can be directly used as the final finishing process. Therefore, the process flow is simplified, the production cost is reduced, and the economic benefit is considerable.

4. The energy consumption of NC machining tools is low, and the volume of cutting layer material per unit power increases significantly when saving resources for high-speed cutting. For example, aluminum alloy high-speed cutting, spindle speed from 4000 1 /. When the cutting force rises to 20 000, the cutting force drops 30 ^, and the cutting rate of raw material increases 3 times. The material removal rate per unit power can reach 130? 160 (1) compared with 30? Avulsion in common milling). Due to the high removal rate, low energy consumption, the working time of the workpiece

How to improve the surface finish of precision parts

As engineers, we use our skills, knowledge and experience to make good appearance and accurate parts. We are very proud of the products we make. We hope the rest of us can see the conceit of the molded goods. But when we don’t get the result we want, what should we do? In terms of size, the parts meet the blueprint specifications, but the surface brightness and overall appearance are not very dream? When this happens, we need to return to the basics and make sure that we use the good processing methods we know.

We need to look at fixtures and other equipment to make sure that they are solid and that they do not contribute to harmonic problems or vibrations during processing. We need to make sure that we don’t use the long equipment we don’t need. These equipment can be easily turned to or added to the opportunity of waste. In high-speed process, we need to ensure the application of equipment with average quality, which has been rated according to the applied programming rpm. But if all the above are good, what should we do?

Study the following options:

1. Control chip: chip thinning is the main factor of excellent surface brightness. Controlling chips may be the first thing you should study. If the chip is in contact with the workpiece during machining, or if you are cutting the chip from scratch, it is likely to affect your surface brightness in a negative way. Study the possibility of changing the chip breaker style you are using to help break down the chip for better control.

Although the application of air and coolant is a good choice for chip removal, pay attention to the coolant. Prevent the application of coolant when cutting intermittently. Hot cracks in the cutting edge can occur… Due to intermittent heating and rapid cooling of the cutting edge… And can cause premature failure of the blade, which may at least initially affect your surface brightness, because of over stressed cutting edge and failure.

2. Speed up: This is more and more the case when using carbide tools. The increase in speed will ensure a shorter time for the material to come into contact with the tip… Thus reducing the edge accumulation on the tool, which may cause poor surface brightness. Increasing the rake angle of the cutting tool also helps to reduce and control edge accumulation.

3. apply accurate tip radius: larger tip radius will be suitable for faster speed. The inserts can be fed at about half of TNR per revolution and still have excellent results. If the TNR to IPR ratio is exceeded, the device will create more “linear” surface brightness, rather than the color and smooth surface you want. Therefore, the larger the TNR, the faster the feed rate it may contain, and the expected consequences still occur. However, the use of a considerable TNR can cause chatter – reduce cutting pressure – so pay attention to and study the speed required to cut raw materials – use TNR equipment that meets your needs.

It is also worth mentioning that the application of a larger tip radius means that you must leave more material for the finish. In order to ensure the normal operation of the equipment, you must have TNR equal to or greater than TNR, so as to complete the removal of the equipment.

If you run into waste around the corner, you may want to try a smaller TNR. Always apply a TNR smaller than the corner radius you are cutting – so you can “create” the radius you need – all the more on finishing equipment. This will help reduce cutting pressure and eliminate chatter.

When milling, try to use the fillet or spherical end milling cutter instead of the plane end milling cutter. Equipment with a fillet radius will give you higher brightness at sharp corners, and will certainly help to prolong tool life.

4. Try to insert the wiper: as far as possible. The wiper insert has a small flat area adjacent to the tip radius. When the device is fed along the workpiece, the plane essentially “wipes” the brightness and helps to eliminate the linear brightness that may be encountered by faster feed rates – this allows the use of smaller TNR to assist in flutter control.

5. Add the lead angle of the tool. A higher lead angle and a positive skew blade produce better surface brightness than a tool with a shallower cutting angle. For example, a face milling cutter with a 45 ° cutting angle will produce a better surface brightness than a face milling cutter with a 90 ° cutting angle.

6. Eliminate linger and pause: every time the equipment stops moving when contacting with the part surface, all traces will be left. Change the process if necessary, but try to make sure that the tool never stops or hesitates during the cutting process.

Die competitiveness determines product vitality in CNC lathe processing

Mould experts believe that the selection of advanced mould technology is the inevitable trend for fierce competition at the moment, and the most important thing is to increase the competitiveness of mould itself to meet the market demand. It is not only the requirement of mould industry development, but also the voice of automobile and other industries to improve the high precision of mould.

Strengthen the understanding of mould precision meaning

1. Die refers to the well formed equipment used for batch forming, stamping and other finished products. Mold accuracy includes the accuracy of parts obtained in machining and the quality consciousness of ensuring the accuracy of products during manufacturing. However, generally speaking, mold accuracy mainly refers to the accuracy of working parts of mold.

① Precision in die machining means that the essential geometric parameters of die parts after machining and assembly are in line with the design geometric parameters.

② Precision in mold making means that the enterprise employees gradually create a mode of thinking, a quality consciousness, which guides the employees to make actions. That is to say, in the actions of the enterprise employees, they always implement the quality consciousness of product precision.

2. The content of mould precision includes four aspects: dimension precision, form precision, position precision and surface precision. Due to the two parts of the upper die and the lower die during the working time of the die, the mutual position accuracy between the upper die and the lower die in the four kinds of accuracy is very important.

When the machining accuracy is very high, the mold often has more than enough force. Now the precision of a well-designed mold can reach within the range of 0.1-0.01 mm. Compared with the previous mold, the precision is still a big step higher. However, the accuracy of these components, such as engine, is required to be less than one thousandth of a millimeter, or even smaller. Therefore, it is impossible to replace the cutting process completely with the die at present.

Now, the brightness and roughness of the mould itself still have a great leap. However, the mold itself is also out of the machine tool manufacturing. If the accuracy of the machine tool manufacturing the mold itself can not pass the standard, the accuracy of the products manufactured out of the manufacturing will not be high.

The importance of CNC machining sequence

A CNC workpiece often has several surfaces to be machined. These surfaces not only have certain accuracy requirements, but also have certain position requirements between the surfaces. In order to achieve these accuracy requirements, the machining sequence of each surface of CNC machining parts can not be placed casually, but must be in accordance with the positive principle, that is, the selection and conversion of the positioning benchmark determines the processing sequence, and the principle that the previous process plans the positioning benchmark for the subsequent process.

1. Before the important surface machining, the precision datum should be trimmed once to ensure the machining accuracy of the important surface.

2. After finishing the fine datum machining, rough machining, semi finish machining and finish machining shall be carried out for the key surfaces with high precision requirements. The surface with unique high precision also needs finishing.

3. The surface used as the precision reference should be machined at the beginning of the CNC machining process, because it should be used to locate other surfaces in the subsequent process. That is, “benchmark before others”.

4. When machining the fine datum, it is necessary to use the coarse datum for positioning. In the process of single piece, small batch production and even batch production, for castings and forgings with complex form or large size, and workblanks with large size deviation, the marking process shall be arranged before the machining process, so as to provide the alignment benchmark for the precision machining.

5. As for the simple process of waste products, finishing and finishing can be properly placed in the front, and some secondary small surface processing can be placed later.

Spindle structure of CNC lathe

The accuracy of the horizontal spindle and vertical spindle on the base of CNC lathe plus Machine Tool Headstock decide the accuracy of the processed screw. At the same time, when the screw rotates at a high speed of several thousand revolutions in the shrinking machine, the screw with poor accuracy will cause the shrinking machine to have fever, vibration, low efficiency, fast wear and other phenomena. At present, there are two plans for the spindle structure of single screw machining machine in China.

1: The main shaft structure with non adjustable bearing radial clearance

The front bearing of the main shaft is composed of one double row cylindrical roller bearing and two thrust ball bearings. The main shaft uses the double row cylindrical roller bearing to receive the radial cutting force and two thrust ball bearings to receive the axial cutting force. The rear bearing of the main shaft usually adopts one double row cylindrical roller bearing or one centripetal ball bearing. The advantages of the spindle structure: the processing and equipping of the spindle are simple and the cost is low.

2: Spindle structure with adjustable bearing radial clearance

The front bearing of the main shaft is composed of a P4 level tapered double row cylindrical roller bearing and a P4 level double row radial thrust ball bearing. The spindle receives the radial cutting force by using the double row cylindrical roller bearing with tapered hole and the axial cutting force and partial radial cutting force by using the double row radial thrust ball bearing. The main shaft rear bearing is usually a P5 level tapered double row cylindrical roller bearing.

The inner ring and matching shaft diameter of tapered bore double row cylindrical roller bearing are both 1:12 tapered. If the bearing is locked with a round nut, a displacement will occur in the axial direction of the bearing and the inner ring of the bearing will expand, so as to reduce or eliminate the radial clearance of the bearing.

The advantage of this spindle structure: high spindle accuracy. Measure the end face runout of the spindle on the diameter of φ 230mm of the front end face of the spindle to be 0.010mm. Measure the radial run out value of the spindle on the outer circle of φ 230mm at the front end of the spindle to be 0.005mm. The accuracy of the second structure is 50% higher than that of the first one.