March 2021 – Page 4 – CNC Machining & Turning, Milling, Metal parts

Method of reducing error in computer gong processing

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

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

Number of workpieces touched

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

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

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

What is the benchmark of computer gong processing

The broad meaning of benchmark is “basis”. The datum in mechanical manufacturing refers to the points, lines and surfaces used to determine the geometric relationship between the geometric elements on the production object. According to different functions and applications, datum can be divided into design datum and process datum, and process datum can be divided into process datum, positioning datum, measurement datum and assembly datum.

The technology of high-speed CNC machining is the premise to ensure the production of high-quality parts.

The movement of the workpiece and the movement of the tool on the drawing are used to change the shape and shape of the workpiece.

Ordinary machine tools are more and more difficult to meet the needs of processing precision parts,

The price of CNC machine tools is falling from time to time. CNC precision parts processing mainly includes ultra precision turning, mirror grinding and grinding.

The primary premise of CNC precision parts processing is the accuracy of process datum. Datum on mechanical drawings are represented by capital letters a, B, C, D, etc. with a specific reference symbol with circle. When the reference symbol is aligned with the surface and its extension line or the dimension limit of the surface, the surface is taken as the datum. When the datum mark is aligned with the dimension line, it means that the solid center line of the dimension is taken as the datum.

Assembly benchmark refers to the precision used to determine the position of parts in components or products during assembly.

Measurement datum refers to the specification for the size and position of the machined surface to be measured during the inspection of parts. Positioning datum refers to the datum used for positioning the workpiece in the machine tool or fixture during machining.

High speed and high precision

In order to improve the machining speed and precision of computer gong, we must pay attention to the influence of cutter tooth vibration on the surface roughness and tool life. In order to prevent the decline of machining accuracy and tool life, the selected machining center must be equipped with spindle with excellent dynamic balance performance, and the selected boring tool must also have high dynamic balance characteristics. Especially for the cutter teeth of boring tools, the geometry, tool material and clamping method suitable for high speed cutting should be selected. The R at the end of cutting edge should be larger in order to improve the processing efficiency; on the premise of ensuring the same surface roughness, the feed rate should be increased. But increasing the feed rate should be enough, otherwise it will increase the cutting resistance, which is not conducive to improving the processing efficiency. The cutting edge belt should be set with negative chamfering less than 0.1 mm, which can effectively maintain the stability of tool life. In addition to CNC cutting, boring and reaming can also be used for high precision machining. With the high speed of machining center spindle, boring tools can be used for high-speed precision machining of holes. It is reported that the cutting speed can be increased to more than 1500m / min when boring about 40mm on aluminum alloy. When CBN sintered body is used as cutting edge to process steel, cast iron and high hardness steel, such cutting speed can also be used.

As for the tool material, it depends on the nature of the material to be processed. For example, when machining steel below 40HRC, cermet tools can be selected. This kind of tool can obtain good surface roughness and long tool life under the condition of V = 300m / min or above. Coated cemented carbide tools are suitable for high speed cutting of steel below 60HRC. The tool life is very stable, but the cutting speed is slightly lower than cermet tools.

Sintered body tool is suitable for machining high hardness steel, cast iron and other materials, cutting speed can reach more than 1000m / min, and tool life is very stable. The edge belt of CBN cutter teeth should be chamfered properly, which is very beneficial to high speed cutting and tool life extension. In the ultra-high speed cutting of aluminum alloy and other non-ferrous and non-metallic materials, diamond sintered body tool can be selected. This kind of tool has the advantages of stable cutting and long tool life. It should be noted that when diamond tools are used, the cutting edge must be chamfered, which is an important condition to ensure the cutting stability.

Feed path of finishing

The feed route of finishing machining is basically carried out along the contour of the parts. Therefore, the key point of determining the feed route is to determine the feed route of rough machining and empty stroke. In the CNC lathe processing, the determination of the processing route should generally follow the following principles.

① It should be able to ensure the accuracy and surface roughness of the workpiece to be processed.

② The processing route is shortest, the idle travel time is reduced, and the processing efficiency is improved.

③ The workload of numerical calculation should be simplified as much as possible.

④ For some repeated programs, subroutines should be used.

Advantages and disadvantages of CNC CNC CNC machining has the following advantages:

① The number of tooling is greatly reduced, and complex tooling is not needed to process complex parts. If we want to change the shape and size of the parts, we only need to modify the processing program of the parts, which is suitable for the development and modification of new products.

② The machining quality is stable, the machining accuracy is high, and the repetition accuracy is high, which can meet the machining requirements of aircraft.

③ In the case of multi variety and small batch production, the production efficiency is high, which can reduce the time of production preparation, machine adjustment and process inspection, and reduce the cutting time due to the use of the best cutting quantity.

④ It can process complex surface which is difficult to be processed by conventional methods, and even process some parts which cannot be observed.

The disadvantage of NC machining is the high cost of machine tools and equipment, which requires high level of maintenance personnel.

CNC machining of stainless steel

In order to increase the cross-sectional area of the hole cutter as much as possible, it is generally enough to leave 1-2mm cutting allowance in the radial direction. The cutter bar should be circular, the main cutting edge of the cutter is in the longitudinal section through the cutter bar axis, and the shorter the cutter bar length is, the better,

When grinding the arc flank of the inner hole cutter, great attention is paid to it. It is a place with high technical content in inner hole machining, and it is also the main aspect to solve the chatter pattern,

In fact, the above is basically about the upper level, and the most important thing is the tool grinding. If the tool grinding is not good, it is difficult to process qualified parts,

a. First of all, the materials of cutting tools are different for different parts. For stainless steel, red copper and brittle materials, tungsten cobalt type cutting tools should be used. For plastic materials such as carbon steel, tungsten cobalt titanium type cutting tools should be used. For materials with high hardness, YW series cutting tools should be used, that is, tungsten cobalt titanium tantalum niobium type cutting tools,

b. The most important point is that the grindability of grinding wheel and grinding wheel is better, and the rigidity of grinding wheel machine is better. It is better to have two grinding wheels, one with brown corundum wheel (grinding cemented carbide) and the other with white corundum wheel (grinding high speed steel). If the above two kinds of grinding wheels are installed on one grinding machine at the same time, it is difficult to grind the standard cutting tools.

Generally, the machining of stainless steel parts is to first process the outer circle and then the inner hole, because the deformation of the outer circle is smaller than that of the inner hole,
Stainless steel parts processing is a very practical work, it needs a long time of actual operation to verify your idea

The density of aluminum profile is only 2.7g/cm3, which is about 1 / 3 of that of steel, copper or brass (7.83g/cm3 and 8.93g/cm3 respectively). Aluminum exhibits excellent corrosion resistance in most environmental conditions, including in air, water (or brine), petrochemical and many chemical systems.

conductivity

Aluminum profile is often used because of its excellent conductivity. On the basis of equal weight, the conductivity of aluminum is nearly twice that of copper.

Thermal conductivity

The thermal conductivity of aluminum alloy is about 50-60% of that of copper, which is beneficial to the manufacture of heat exchangers, evaporators, heating appliances, cooking utensils, as well as the cylinder head and radiator of automobiles.

Non ferromagnetism

Aluminum profile is non ferromagnetic, which is an important characteristic for electrical industry and electronic industry. Aluminum profiles are not self ignitable, which is important for applications involving handling or contacting flammable and explosive materials.

Machinability

The machinability of aluminum profile is excellent. In all kinds of wrought and cast aluminum alloys, as well as in all kinds of states of these alloys, the machining characteristics change greatly, which requires special machine tools or technology.

Formability

Specific tensile strength, yield strength, ductility and corresponding work hardening rate control the variation of allowable deformation.

Oil leakage in CNC machining

The oil change does not meet the requirements.

It often causes oil leakage in CNC machining center. There are three main problems in oil change. First, for the parts with high viscosity lubricating oil, it will affect the sealing performance of the corresponding box, shaft hole and other parts, and sometimes greatly reduce the sealing performance of these parts. Second, if the oil tank is not cleaned when changing oil, the dirt in the oil tank may enter into the lubrication system, block the oil circuit and wear the seals, causing oil leakage. Third, when changing the oil, the amount of oil is too much, especially in the parts with rotating parts, because of the stirring effect of rotating parts, it is more prone to oil spill.

Improper selection and adjustment of lubrication system parts cause oil leakage.

For example, when CNC machining and maintenance personnel select the oil pump with too high pressure or too large oil output, or when adjusting the system pressure, the pressure of relief valve, safety valve and pressure reducing valve is too high, and the flow of CNC machine tool lubrication system is too large, which does not match with the oil return system and sealing system, it will cause oil leakage.

In fact, it is not just the above points that cause the oil leakage of CNC machining center. If we encounter similar problems in operation, we must do a good job in checking and find out the reasons in time to avoid unnecessary losses. After the purchase of the machining center, do a comprehensive inspection to see if there are casting defects or parts damage, if any, contact the manufacturer in time. When operators use CNC machining center to process workpieces, they should also pay attention to the following points:

(1) For the first trial cutting process of CNC machining, the single-stage operation mode should be adopted.

(2) When the CNC milling machine starts to run automatically, the fast rate and feed rate s are in the lowest gear, and then the efficiency is improved after cutting into the workpiece.

(3) In the operation of NC milling machine, we need to pay attention to the coordinate display of CNC system.

(4) It is forbidden to touch tools and chips of CNC milling machine by hand. The chip must be cleaned with a brush.

The cutting problem of computer gong processing

1、 Exit angle (draft angle)

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

2、 Cutting problem

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

3、 Sharpen a knife

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

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

4、 Milling direction

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

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

Precision CNC machining

When the precision of precision machining is nanometer or even atomic unit (the atomic lattice distance is 0.1-0.2 nanometer), the cutting method can not adapt to it. It needs the help of special machining method, that is, the application of chemical energy, electrochemical energy, thermal energy or electric energy, to make these energies exceed the bonding energy between atoms, so as to remove the adhesion, bonding or bonding between some atoms on the workpiece surface In order to achieve the goal of ultra precision machining. This kind of processing includes mechanical chemical polishing, ion sputtering and ion implantation, electron beam exposure, laser beam processing, metal evaporation and molecular beam epitaxy. The characteristic of these methods is that the amount of material removed or added to the surface layer can be controlled very finely. However, to obtain ultra precision machining accuracy, it still depends on precision machining equipment and precise control system, and uses ultra precision mask as intermediary. For example, in VLSI plate making, electron beam is used to expose the photoresist (see lithography) on the mask to make the atoms of the photoresist polymerize (or decompose) directly under electron impact, and then the polymerized or unpolymerized parts are dissolved by the developer to make the mask. Electron beam exposure plate making requires ultra precision processing equipment with positioning accuracy of ± 0.01 micron.

What are the characteristics and functions of the system? It is an automatic machine tool controlled by program. The control system can logically process the program with control code or other symbol instructions, decode it by computer, so that the machine tool can execute the specified action, and the blank can be processed into semi-finished parts by cutting tools.

The traditional mechanical lathe processing is manual operation, ordinary machine operation, lathe processing with hand shaking mechanical tool cutting metal, rely on the eyes with calipers and other tools to measure the accuracy of the product. Modern industry has long used computer-controlled machine tools for operation, which can automatically process any product and parts according to the program compiled by technicians in advance.

The information is stored in the information carrier (such as disk, perforated tape, magnetic tape, etc.) and then read in by the CNC system on the machine tool (or directly input through the keyboard of the CNC system, or input through the communication mode). By decoding the information, the lathe can process the action and parts, and the modern CNC machine tool can be widely used It is a typical product of mechatronics and the technical foundation of new generation production technology and computer integrated manufacturing system.

The development trend of modern CNC lathe precision machining is high speed, high precision, high reliability, multi-function, compound, intelligent and open structure. The main development trend is to develop intelligent full-function universal numerical control device with open structure in both software and hardware. Numerical control technology is the basis of machining automation and the core technology of numerical control machine tools. Its level is related to the national strategic position and the level of reflecting the national comprehensive strength. It develops with the development of information technology, microelectronics technology, automation technology and detection technology. CNC machining is a kind of numerical control machine tool with tool magazine, which can automatically change the tool and process the workpiece in a certain range.

Independent performance of CNC machining

There is a certain difference between the two ways to make precision hardware processing parts. What’s more, they use different steel to make different workpieces. CNC lathe is composed of bed, headstock, turret feed system, cooling and lubrication system and CNC system. Different from ordinary lathe, CNC lathe feed system is qualitatively different from ordinary lathe

It does not have the traditional tool box, slide box and change gear frame, but directly uses servo motor or stepper motor to drive slide and tool through ball screw to realize feed movement. The CNC system consists of CNC unit, input and output module and operation panel.

Processing method of precision hardware parts:

Solid solution strengthening: because the solute atoms enter into the gap or node of the solvent lattice, the lattice will be distorted and the hardness and strength of the solid solution will be increased. This phenomenon is called solid solution strengthening.
Compound: a new crystal solid structure with metallic properties is formed by the combination of alloy components. Mechanical mixture: an alloy consisting of two crystal structures. Although it has two kinds of crystals, it is a component with independent mechanical properties.
Ferrite: interstitial solid solution of carbon in a-Fe (body centered cubic iron).
Austenite: interstitial solid solution of carbon in g-fe
Cementite: stable compound (Fe3C) formed by carbon and iron.
Pearlite: a mechanical mixture of ferrite and cementite (F + Fe3C contains 0.8% carbon)
Ledeburite: a mechanical mixture of cementite and austenite (containing 4.3% carbon) Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the performance of the workpiece by changing the microstructure inside the workpiece or the chemical composition on the surface of the workpiece.

Computer gong processing and clamping

Roughening: under the maximum load of the machine tool, in most cases of processing, select the largest possible tool, the largest possible feed amount and the fastest possible feed. In the case of the same tool, the feed is inversely proportional to the feed amount. In general, the load of the machine tool is not a problem. The principle of tool selection mainly depends on whether the two-dimensional angle and three-dimensional arc of the product are too small The principle is that the length of the tool is greater than the depth of processing. For large workpieces, it is necessary to consider whether the collet can be lowered. Otherwise, it is necessary to go as follows. 0 I4 Q6 x1 f5 l N& u

The purpose of light knife: to meet the workpiece processing requirements: finish, flying die allowance, copper male spark position, etc., at the same time, as large as possible, as fast as possible, because the precision knife takes a long time, with the most appropriate feed and feed, in the same feed, the larger the transverse feed, the faster. The surface feed is related to the finish after processing, and the feed size is related to the surface shape In the case of no damage to the surface, the minimum allowance should be left, the maximum knife should be used, the fastest Belt should be rotated, and the proper feeding should be carried out.

Clamping method:

All clamps are long horizontally and short vertically;
Vise clamping: the clamping height should not be less than 10 mm. When processing the workpiece, the clamping height and processing height must be specified. The processing height should be about 5 mm higher than the vise plane, so as to ensure the firmness and not damage the vise. This kind of clamping belongs to general clamping, and the clamping height is also related to the size of the workpiece. The larger the workpiece is, the higher the clamping height will be;
Splint clamping: the splint is fixed on the worktable with the code, and the workpiece is locked on the splint with the screw. This kind of clamping is suitable for the workpiece with insufficient clamping height and large processing force, generally medium and large workpieces, and the effect is very good. 1 ` Q( F9 k, n
When the workpiece is large, the clamping height is not enough, and it is not allowed to lock the thread at the bottom, it should be clamped with code iron. This kind of clamping needs secondary clamping. The procedure is as follows: A. code the four corners first, process other parts, then code the four sides, and process the four corners. The principle is that during the secondary clamping, be very careful not to let the workpiece loose, code first and then loosen. B. code both sides first, process the other two sides, 8 L # y% @# \: e’ N% P

Code iron has an advantage, large contact area, not easy to deformation, such as aluminum, magnesium within the soft metal must use code iron to prevent deformation;

Tool clamping: diameter more than 10 mm, not less than 30 mm; diameter less than 10 mm, not less than 20 mm,

Note: the impact of the tool on the workpiece can cause: a. the workpiece moves; B. the tool is broken; C. the tool is deformed and the workpiece is damaged; D. the tool is loose, the tool is dropped or the workpiece is not processed correctly

Therefore, the clamping of tool and workpiece should be firm. Strictly prevent Tool Collision and direct insertion of workpiece, & H #: X # {3 W

Classification of cutting tools and their application scope:% Q + e’c. B-Z

By material:

White steel knife: easy to wear, used for roughening of copper and small steel

Tungsten steel knife: used for angle cleaning (especially steel material) and light knife. . g4 k+ L1 U0 h/ s3 P+ T

Alloy knife: similar to tungsten steel knife

Purple knife; used for high speed cutting, not easy to wear

According to the cutter head:, ~. A “{2 s; t

Flat bottom knife: used for plane and straight body side cleaning (plane angle / m3 Z / M)_ , Z

Ball cutter: used for all kinds of surface medium light, light knife) F + I-m: B0 F8 G-V) H

Ox nose knife (one side, two sides and five sides): used for roughening steel (r0.8, r0.3, r0.5, r0.4) – X / F9 x, H: v

Rough leather knife: used to cut rough, pay attention to the remaining method (0.3)

According to the arbor: straight knife: straight knife is suitable for all kinds of occasions 9 a # x E + x0 a% E

Slant bar cutter: but not suitable for straight face and face with inclination less than the inclination of bar (S2 [7 d & D% O6 M0~

According to the blade: two blade, three blade, four blade, the more blades, the better the effect, but the more work, speed and feed corresponding adjustment, more blades, long life, ball knife and flying knife light knife difference: {: Q & i7 U3 | 0e

Ball knife: when concave ruler is smaller than ball ruler and plane ruler is smaller than ball R, the light can not reach (clear the bottom angle).