May 2020 – Page 2 – CNC Machining & Turning, Milling, Metal parts

How is CNC precision machining programmed

（1） It can be expressed by diameter value programming or radius value programming and radius value programming.

The default programming mode of the CNC system is diameter value programming, which is because the radial dimensions of the processed parts are expressed by diameter value when they are measured on the drawing, so it is most convenient to use diameter value programming, that is, in the diameter direction, when absolute value programming is used, X is indicated by diameter value; When programming with increment value, it is expressed as twice of the actual radial displacement and attached with direction sign (positive direction can be omitted).

（2） Absolute value programming, incremental value programming or mixed programming are used to mark the dimensions according to the drawings of the processed parts. From the point of view of programming convenience, in a program section, absolute value programming, incremental value programming or mixed programming are used. When programming in absolute coordinates, the coordinate words X and Z are used; when programming in incremental coordinates, the coordinate words u and W are used.

（3） Most CNC lathes have the function of tool automatic compensation, which can realize the compensation of tool tip radius, tool wear and the position error when installing the tool. Before CNC precision machining, the operator only needs to input the relevant compensation value into the specified memory, and the CNC system can automatically compensate the cutter. There is no need to change the machining program no matter the radius of the tool tip arc, the tool wear or the change of the tool position, so the programmer can program according to the actual contour size of the workpiece.

Definition and function of automatic plate processing

As the name implies, automatic sheet metal processing is the process of deformation or fracture of iron, aluminum, copper and other metal plates used for metal punch and die, and has a certain shape and size. At present, precision punch is usually used in the hardware processing of metal plate in the manufacturing industry. This processing method not only has high efficiency and low processing cost, but also has stable and uniform quality precision stamping products. However, the use of precision stamping processing method also has certain limitations, general. It is used for metal sheet cutting, the whole forming punch and the processing of precision parts. The process is complex. You need to cooperate with other processing or stamping automation equipment to complete.

At present, the stamping industry is a very extensive industry, which goes deep into all aspects of the manufacturing industry. In foreign countries, stamping is called sheet forming. In our country, there are also such names. But there is a slight difference. The so-called plate forming refers to the use of plates, thin-walled tubes, thin profiles, etc. as raw materials. The forming method of plastic processing is generally called sheet forming. At this time, the deformation in the direction of thick plate is generally not considered. The great development of stamping is attributed to the development of automobiles, airplanes and household appliances. The stamping automation production has been stably formed in many production enterprises, which will completely replace the traditional processing technology. Precision punch is generally suitable for blanking, punching, bending and forming of medium-sized, continuous die or single engineering sheet steel parts of multi-material products. It can be used for single punching, continuous die, manipulator connection or adding transmission system. It can be widely used in a variety of mass production of metal sheet metal processing, punching, forming and drawing. Such as traffic vehicles, clocks, home appliances, stationery, hand tools, hardware, computers and other products processing. At the same time, it can also be equipped with an automatic feeder, which is engaged in automatic transfer of the whole production line processing.

Introduction to slow wire processing

1. Anti electrolysis (BS) pulse power supply for slow wire processing

Water quality working fluid is used in low speed WEDM. Water has a certain conductivity, even after deionization treatment, reducing the conductivity, but there is a certain amount of ions. When the workpiece is connected to the positive electrode, under the action of the electric field, OH ions will continuously gather on the workpiece, resulting in the oxidation and corrosion of iron, aluminum, copper, zinc, titanium and tungsten, and the ionic state of the binder cobalt in the cemented carbide material dissolves in the water, forming a “softening layer” on the workpiece surface. The measures of increasing resistivity (from tens of thousands of Ohm? Cm to hundreds of thousands of Ohm? Cm) have been adopted to reduce the ion concentration as much as possible. Although they have played a certain role in improving the surface quality, they still cannot solve the problem of “softened layer” effectively. Anti electrolysis power supply is an effective technical means to solve the “softening layer” of workpiece. The anti electrolysis power supply adopts alternating pulse and the average voltage is zero, which makes the OH – ion electrode wire in the working liquid in the state of oscillation between the workpiece and does not tend to the workpiece and electrode wire, so as to prevent the oxidation of the workpiece material. The surface modification layer can be controlled below 1 μ m by WEDM with anti electrolysis power supply, which can avoid the precipitation and dissolution of cobalt in cemented carbide material and ensure the service life of cemented carbide die.

2. Nanosecond high peak current pulse power supply for slow wire processing

There are two kinds of metal erosion in EDM, melting and gasification. The wide pulse duration is long, which is easy to cause melting processing, poor surface morphology of the workpiece, thickened metamorphic layer, increased internal stress, and easy to produce cracks. When the pulse width is small to a certain value, the action time is very short, forming gasification processing, which can reduce the thickness of the modified layer, improve the surface quality, reduce the internal stress and avoid cracks. The pulse power supply used in the advanced low speed WEDM machine is only tens of NS in pulse width, and the peak current is more than 1000A, forming gasification erosion, which not only has high machining efficiency, but also greatly improves the surface quality.

Treatment of chip removal in deep hole machining of mould

The treatment method of chip removal in deep hole machining is as follows:

In order to remove the chips smoothly, the iron chips need to come out as thin strips and bring out small pieces. At the same time, the coolant is easy to enter. The grinding method of the drill can adopt the grinding method created by Ni Zhifu, who has three points and seven edges (group drilling for the sake of not highlighting individuals in the Cultural Revolution). The simple grinding method of the deep hole of the mold is

1. Increase the included angle of the drilling edge to 130-140 degrees to increase the chip thickness and change the direction of chip discharge (the direction of chip discharge is perpendicular to the edge)

2. Grind the transverse edge to reduce the axial cutting tool and generate an angle at the cutting edge against the core to facilitate chip separation.

3. If the drilling diameter is large, the chip separating groove can be grinded on one side of the cutting edge, which should be one wider, so as to balance the cutting force of two cutting edges. If the diameter is large, the chip separating groove can be grinded on two cutting edges.

4. Make an angle of 1 mm 45 degrees at the outer corner of the cutting edge to reduce wear and improve the finish.

5. The drilling speed is slightly lower, and the feed amount should be larger, so that the chip thickens and is discharged in strips.

6. The nozzle of the coolant should face the hole inward so that the coolant can enter the cutting area,

Die deep hole manufacturers found that when the hole diameter ratio is more than 8 times larger, it’s best to drill on a special deep hole drilling machine, with very high efficiency. I once tried to produce lathe spindle diameter 32, length about 850mm, material 45 steel in only 13 minutes.

Deep hole drilling is divided into two types: external chip removal and internal chip removal;

For the smaller diameter, the external chip removal method is adopted, because the drill pipe is too small. For the larger diameter hole, the internal hole of drill pipe has enough space for chip removal. High pressure oil is pressed between the hole wall and the drill pipe to discharge the chip and heat from the rod. The drill bit is made of special general hard alloy, with two parts of the direction and chip edge, The height and width of the chip breaking groove depend on the material of the workpiece and the feed rate to ensure that the chip shape is tight and small C shape or tile shape is better.

Treatment of chip removal in deep hole machining of mould

The treatment method of chip removal in deep hole machining is as follows:

2. Grind the transverse edge to reduce the axial cutting tool and generate an angle at the cutting edge against the core to facilitate chip separation.

4. Make an angle of 1 mm 45 degrees at the outer corner of the cutting edge to reduce wear and improve the finish.

5. The drilling speed is slightly lower, and the feed amount should be larger, so that the chip thickens and is discharged in strips.

6. The nozzle of the coolant should face the hole inward so that the coolant can enter the cutting area,

Deep hole drilling is divided into two types: external chip removal and internal chip removal;

Deep hole processing method of mould

The common processing methods of deep hole drilling are as follows

① The cooling water hole and heating hole of small and medium-sized mold are usually processed on vertical drilling machine and radial drilling machine by common drill or lengthened drill. During processing, it is necessary to timely discharge and cool the chips, with small feed rate to prevent hole deflection.

② The holes of medium and large moulds are generally processed on radial drilling machine, boring machine and deep l drilling machine. The more advanced method is that they can be processed together with other holes on the machining center machine tool.

③ Long low precision holes can also be drilled from both ends after marking.

④ The holes with high requirements for verticality shall be guided by certain technological measures, such as the use of drilling jigs.

When drilling deep holes, attention shall also be paid to:

a. When the drilling depth is 3 times of the diameter, it is necessary to lift the drill bit for chip removal, and then every time a certain depth is entered, the drill bit shall exit for chip removal, so as to prevent the drill bit from breaking due to chip blocking.

b. When the depth of some deep holes exceeds the total length of the bit or is deeper, lengthening rod bit or connecting rod bit can be used for drilling. These two kinds of bits can be purchased or self-made.

c. For some special deep holes, such as the processing of some through holes, special equipment is generally used or carried out on the machine tool. At this time, special lengthening rod drill bit is required. This kind of bit needs to be developed on its own according to the specific conditions of the workpiece. In general, deep hole machining process, it is impossible to process all the hole depths with a single cutting. It is necessary to feed several times to solve the problems of chip removal, cooling, etc. and the machining accuracy is low. Gun drill can solve these problems, so deep holes with diameter less than 20 mm, such as cooling water holes, can be processed by gun drill. WeChat official account: hcsteel gun drill. The working part of gun drill is made of high-speed steel or hard alloy and seamless steel pipe by butt welding. During operation, the workpiece rotates the drill bit to feed, and at the same time, the high-pressure cutting fluid is injected from the tail of the drill pipe. After the cutting area is cooled, the cuttings are washed out along the drill pipe groove.

The characteristics of gun drilling hole are as follows:

① The ratio of length to diameter of the hole can reach 100:1 or greater;

② High production efficiency, only one process can obtain high quality holes;

③ In a long period of continuous machining, the change of hole size is very small (within 0.02-0.05mm);

④ When the hardness of workpiece material is up to 45hrc, it can still be processed;

⑤ The quality of the hole is very good, usually no further processing is needed;

⑥ Do not need skilled operation technology;

⑦ The tool durability is 10-15 times higher than that of twist drill, and it can process hundreds to several dry workpieces every time;

⑧ The position accuracy of the hole is the same as that of the adjustment.

What role does metal cutting fluid play in deep hole machining

Lubrication

The lubrication function of metal cutting fluid (cutting fluid) in the cutting process can reduce the friction between the front cutter face and the chip, and between the back cutter face and the machined surface, forming part of the lubricating film, so as to reduce the cutting force, friction and power consumption, reduce the surface temperature and tool wear of the friction part between the cutter and the workpiece blank, and improve the cutting performance of the workpiece material for deep hole machining 。 In the process of grinding, after adding grinding fluid, the grinding fluid infiltrates into the abrasive grains of the grinding wheel, the workpiece and the abrasive grains to form a lubricating film, which reduces the friction between the interfaces, prevents the abrasive cutting edge from wearing and adhering to the chips, thus reducing the grinding force and friction heat, and improves the durability of the grinding wheel and the surface quality of the workpiece.

Cooling action

The cooling function of cutting fluid is to take the cutting heat away from the cutter and workpiece through the convection and vaporization between it and the cutter (or grinding wheel), chip and workpiece, so as to effectively reduce the cutting temperature, reduce the thermal deformation of workpiece and cutter, maintain the hardness of cutter, and improve the machining accuracy and tool durability. The cooling performance of cutting fluid is related to its thermal conductivity, specific heat, heat of vaporization and viscosity (or fluidity). The thermal conductivity and specific heat of water are higher than that of oil, so the cooling performance of water is better than that of oil.

Cleaning function

Deep hole machining in the metal cutting process, the cutting fluid is required to have a good role in cleaning. Remove the generated chips, grinding chips, iron powder, oil and sand particles, prevent the contamination of the machine tool, workpiece and cutter, keep the cutting edge of the cutter or grinding wheel sharp and do not affect the cutting effect. For oil-based cutting oil, the lower the viscosity, the stronger the cleaning ability, especially for cutting oil containing kerosene, diesel oil and other light components, the better the permeability and cleaning performance. The water-based cutting fluid containing surfactant has a good cleaning effect because it can form an adsorption film on the surface, prevent particles and sludge from adhering to the workpiece, cutter and grinding wheel, at the same time, it can penetrate into the interface of particles and sludge, separate it from the interface, take it away with the cutting fluid, and keep the cutting fluid clean.

Antirust effect

In the process of metal cutting, the workpiece should be corroded by contacting with corrosive media such as environmental media and oil mud produced by decomposition or oxidation of cutting fluid components, and the surface of machine tool parts contacting with cutting fluid will also be corroded. In addition, when the workpiece is temporarily stored after processing or in the process of flow between processes, the cutting fluid is also required to have a certain anti rust ability to prevent corrosive substances such as environmental medium and oil mud in the residual cutting fluid from eroding the metal. Especially in the wet and rainy seasons in the south of China, more attention should be paid to the rust prevention measures between processes.

Five excellent performances in practical application of deep hole drilling machine

Deep hole drilling machine is different from the traditional way of hole processing. It mainly relies on specific drilling technology (such as gun drill, BTA drill, spray drill, etc.), and the special machine for drilling deep hole system and precision shallow hole with length diameter ratio greater than 10 is called deep hole drilling machine.

Deep hole drilling machine has the following five characteristics in practical application:

1. The whole casting adopts high-quality mihanna cast iron, and after aging treatment, the structure of the casting is uniform and stable, with high rigidity and good stability.

2. Three coordinate deep hole drilling machine adopts imported high rigidity and high precision screw rod, which provides more powerful torque and durability during processing.

3. High quality servo motor and driver are used in the three-axis feed drive, which are directly connected with the ball screw. The transmission is stable and has no backlash. At the same time, its good rigidity and optimized shock absorption performance greatly improve the dynamic rigidity of the transmission system, which can realize rapid movement.

4. The spindle adopts powerful motor, which can meet the processing requirements of high and low speed, and is equipped with automatic oil cooling system to ensure constant temperature during processing.

5. The operating system adopts Taiwan system, which can be compatible with CAD / CAM software to use more metadata.

How to maintain the deep hole drilling machine

Compared with the traditional drilling machine, the deep hole drilling machine has made great progress in efficiency and quality. Especially combined with special processing technology, the application of deep hole drilling machine makes more and more industries taste the sweetness. Deep hole drilling machine is a kind of special machine tool with high precision, high efficiency and high automation for deep hole processing. Relying on advanced hole processing skills (gun drilling, BTA drilling, spray suction drilling, etc.), it can reach the processing accuracy and surface roughness which are usually achieved by drilling, expanding and reaming processes after one successive drilling. The application of deep hole drilling machine reduces the cost of labor to a great extent, and makes the original tedious work more simple and convenient. Moreover, the fully mechanized control workflow also makes the deep hole drilling machine much better than the manual participation in the accuracy. After all, it is a kind of work that needs to be repeated constantly. When there is always a human error, the deep hole drilling machine also reduces the possibility of this kind of error to the minimum.

How to maintain the deep hole drilling machine? Pay attention to the following points:

1. Take good care of the deep hole drilling machine, adhere to the regular appearance of the deep hole drilling machine and accessories, and clean them.

2. Tools, tools and fixtures shall be placed in order. Deep hole drilling machine

3. The door switch, anti-collision switch and other safety maintenance devices in the operation room of the deep hole drilling machine shall be put into use normally and shall not be dismantled at will.

4. Before connecting the power switch of the electric cabinet, check whether the output voltage of the voltage regulator is 380V and whether the three phases are balanced. If there is any abnormality, do not connect the power of the machine tool

5. It is required to run warm-up program before drilling every day. If necessary, it is required to move each axis of the machine tool 3-5 times to smooth the guide rail

6. Check the smooth oil level every day, make up in time, and use iso68 guide rail smooth oil

7. Go to work every day and observe whether there is any oil leakage on the ground

8. Check whether the pressure of the hydraulic station is normal once a week. The pressure is 2MPa

9. Check the oil level of the cooling oil tank once a week and check whether the filter paper is sufficient. Pay attention to make up for 10. Clean the dust on the back cover of the motor, the air conditioner of the electric cabinet and the protective net of the refrigerator every two months. 11. Regularly clean the impurities deposited in the cooling oil return tank. Pay attention to observe the oil pressure at the outlet of the return pump. 12. Regularly change the oil to the protective cover of the machine tool to avoid embroidery and excessive collision

13. At least once in half a year, the maintenance of large deep hole drilling machine shall be carried out, including checking whether the guide rail is worn, whether the motor sound is abnormal, whether the function of limit maintenance and anti-collision switch of deep hole drilling machine is normal, whether some moving cables are worn, whether there are dust and other abnormalities in the main electric cabinet, whether the external control circuit is completely normal (such as oil level, oil circuit control Function), whether the oil circuit joint is loose, whether the balance chain is loose, etc. Do not use lint (head) cotton when scrubbing guide rail

How to adjust the accuracy of deep hole drilling machine?

The adjustment contents and methods of geometric accuracy in the application of deep hole drilling machine are as follows:

1. The adjustment of sizing block and anchor bolt is mainly to adjust the geometric accuracy of the machine tool through sizing block and anchor bolt. If necessary, the accuracy requirements can be achieved by slightly changing the inlay and pre tightening roller on the guide rail.

2. Adjust the relative position between the manipulator, the spindle and the tool magazine, so that the machine tool can automatically run to the tool change position, and complete the tool exchange action step by step in a manual way, and check whether the actions such as grabbing, loading, pulling and rotating exchange are accurate and stable.

3. Adjust the relative position of the pallet and the exchange worktable. This kind of machine tool is double worktable or multi worktable. Adjust the relative position of the pallet and the exchange worktable to ensure the stable and reliable automatic exchange of the worktable.

The application scope of deep hole drilling machine mainly includes the following three aspects:

1. Parts that are not easy to be machined on general machine tools, or need to be equipped with complex special clamps on general machine tools and need a long adjustment time to be machined;

2. For the parts that need to be produced in small batch and multiple batches (generally less than 100 pieces), the mold parts with complex contour and shape, high machining accuracy requirements or complex curves and surfaces that must be solved by digital methods, and the parts that need to be remodeled for many times;

3. It is a high-value precision part that needs to be processed by many processes such as boring, milling, drilling, expanding, reaming, spot facer and tapping thread, and can be clamped once