November 2020 – Page 5 – CNC Machining & Turning, Milling, Metal parts

CNC machine tool coordinate system

When determining the coordinate axis of CNC machine tool, the Z axis is generally determined first, and then the X axis and Y axis are determined.

(1) Z axis. The axis parallel to CNC machine tool spindle (transmitting cutting power) is regarded as z-axis, and the direction of tool away from workpiece is the positive direction of z-axis. For CNC machine tools with spindle, such as horizontal lathe and vertical lifting table milling machine, the spindle axis of CNC machine tool is taken as Z axis; for CNC machine tools without spindle, such as shaper, the coordinate axis perpendicular to the clamping surface is specified as Z axis. For CNC machine tools with several spindles, such as gantry milling machine, one of the main spindles perpendicular to the worktable surface is selected as the main spindle, and the z-axis direction is determined by it.

(2) X axis. The x-axis is located in the horizontal plane, perpendicular to the Z-axis and parallel to the workpiece clamping surface. For CNC machine tools with workpiece rotation, such as lathe, the X axis is in the radial direction of the workpiece and parallel to the horizontal carriage, and the direction of the cutter leaving the workpiece rotation center is the positive direction of the X axis. For CNC machine tools with tool rotation: if z-axis is horizontal, such as horizontal milling machine, boring machine, etc., the positive direction of x-axis points to the right when viewed from the back end of the tool (spindle) to the workpiece. If the z-axis is vertical, such as vertical milling machine, drilling machine, etc., the positive direction of x-axis points to the right when looking at the column when facing the cutter (spindle). For CNC machine tools without spindle: such as planer, the main cutting direction is x axis.

(3) Y axis. The y-axis direction is determined according to the selected Z and X axes according to the Cartesian coordinate system of right-hand right angle.

(4) Steering of a, B and C. After selecting the X, y and Z axes, the positive rotation directions of a, B and C are determined according to the right hand helix rule.

(5) Additional coordinates. If the CNC machine tool is outside the basic rectangular coordinate system X, y, Z, and other axes are parallel to their coordinate system, the additional rectangular coordinate system is designated as u, V, W and P, Q, R.

Computer gong processing machine tool guide

The guide rail of machine tool is mostly made of steel or cast iron. If this kind of guide rail is scratched, it should be repaired, otherwise it will enlarge the scratch and even affect the use of machine tool. In the long-term use of machine tool guide rail and other friction pairs, due to the different degree of friction between the two contact surfaces, the friction pair surface has different degrees of wear, which seriously affects the machining accuracy and production efficiency of the machine tool. The repair of machine tools and other worn parts usually adopts the methods of inlaying or replacing metal plates and polymer materials, which not only requires a large number of accurate processing and manufacturing, but also often requires manual scraping and grinding of the machined surface. There are many repair procedures and a long construction period.

Solution: using the international advanced polymer 2211f metal repair material to repair the scratch of the guide rail of the gantry milling machine, the scratch part of the guide rail can be repaired in a few hours and put into use. Practice shows that this method is simple, time-saving, good repair quality and low cost. With its unique adhesion, excellent compressive strength, oil resistance and wear resistance, it can provide a long-term protective layer for components, effectively solve the problems that cannot be solved by traditional maintenance methods for large-scale equipment that can not be disassembled. The performance of the equipment is improved, the fit clearance of parts is improved, and the normal operation of production is guaranteed to the maximum extent It saves a lot of time and money, and provides a long-term good guarantee for the normal operation of enterprise equipment.

Repair Principle: polymer composite material is a kind of composite material, which is made of polymer, metal or ceramic superfine powder, fiber, etc. under the action of curing agent and curing accelerator. All kinds of materials draw on each other’s strong points and complement each other in performance, resulting in synergistic effect, so that the comprehensive performance of the composite is better than that of the raw materials. Because of its strong adhesion, mechanical properties and chemical corrosion resistance, it is widely used in the repair of mechanical wear, scratch, pit, crack, leakage and casting sand hole of metal equipment, as well as the chemical anti-corrosion protection and repair of various chemical storage tanks, reaction tanks and pipelines.

Repair process:

Burn the scratched part with oxygen acetylene flame (control the temperature, avoid surface annealing), and bake the oil on the surface of permeating metal all the year round until there is no spark.
The scratched part shall be treated with angle grinder, the grinding depth shall be more than 1 mm, and the groove shall be polished along the guide rail, preferably dovetail groove (as shown in the figure). The scratch on both ends of the hole is deepened to change the stress condition.
Clean the surface with absorbent cotton dipped in acetone or absolute ethanol.
Apply the mixed and uniform 2211f to the scratched surface; the first layer should be thin and evenly covered with the scratch surface to ensure the best bonding between the material and the metal surface. Then, apply the material to the whole repair part and press repeatedly to ensure that the material is filled and reaches the required thickness, which is slightly higher than the rail surface.
It takes 24 hours for the material to reach all properties at 24oc. In order to save time, the temperature can be increased by halogen lamp. The curing time will be shortened by half when the temperature is increased by 11oc. The best curing temperature is 70oC.
After the material is solidified, the material higher than the surface of guide rail shall be repaired and leveled with fine grindstone or scraper, and the construction is completed.

Computer gong processing – plane grinder

As an important processing method of precision factory, the plane grinder must formulate strict process specification. Strict and standard operation can ensure the stable precision and quality of the processed parts.

first, you must be familiar with the operation of the plane grinder and understand the performance of the plane grinder.
before starting the machine, wear protective glasses and work clothes, fasten clothes and sleeves, and put long hair plate into the working cap. Do not wear scarves or gloves to operate the grinder.
before operation, tools, measuring tools and workpieces shall be placed in order to remove any sundries that hinder the operation and operation of the equipment. Before operation, check whether the safety shield of transmission part is complete and fixed, and handle the abnormal of plane grinder in time.
before starting, check whether the transmission part and operating handle of the plane grinder are normal and sensitive, and see whether the lubricating oil system of each part is smooth and whether the electronic ruler displays data.
before starting the machine, adjust the limit block of the left and right impact blocks according to the grinding length of the workpiece and lock it tightly.
the grinding wheel must be installed in static balance, and it should be balanced again after correction. The diamond of the grinding wheel dresser must be sharp, and the height of the point should be consistent with the horizontal plane of the center line of the grinding wheel. It is forbidden to use the blunt diamond to trim the grinding wheel. When finishing, the dust collector must be started.
start the spindle of grinding machine to idle for 1 to 2 minutes, observe the operation, pay attention to the height of the grinding wheel about 5 cm from the table surface; confirm that the lubrication and cooling system is smooth and all parts are running normally before grinding.
check the workpiece, load and unload the grinding wheel and handle the machine tool fault, and then stop the grinding wheel after it is withdrawn from the workpiece.
it is not allowed to place non processed goods on the working face, workpiece and electromagnetic disc, and it is forbidden to knock or calibrate the workpiece on the working face and permanent magnet suction disk.
when moving the disk switch to mount the workpiece after adsorption, it must be checked firmly and then ground. When absorbing the higher or smaller workpiece, the proper height of the back plate shall be added to fix it to prevent the workpiece from loosening and causing potential accidents.
when the grinding wheel approaches the workpiece, it is necessary to touch the workpiece in a forbidden state to move away. If the grinding wheel does not leave the workpiece, it is not allowed to stop running. The grinding feed shall be small and large, and it shall not increase suddenly. The cutting shall be conducted evenly to prevent the grinding wheel from hitting the workpiece to break.
during operation, attention must be paid to the work, and nothing related to processing shall be done. After the grinding machine or the workpiece is finished, the table surface shall not be blown by air pressure to prevent dust from entering the track of the plane grinder to affect the hand feeling and accuracy. It is not allowed to allow others to operate the grinder without authorization or allow idle personnel to walk around the machine tool. Especially on the side of the grinder

Computer gongs – electrode requirements

Modern mold enterprises, almost no lack of EDM, because EDM can effectively process all kinds of special-shaped, all kinds of cavities or high hardness parts, so it has become an indispensable processing means in mold manufacturing and metal processing industry.

According to the feedback information from the enterprise, the accuracy has reached ± 0.002 mm, and the roughness Ra = 0.4 μ M. In order to pursue the machining accuracy, the condition of the WEDM machine tool should be checked at the beginning. The deionization degree of ionic water, the temperature of ionic water, the perpendicularity of wire cutting, the tension force, the cutting wire and the material of the workpiece to be cut should be checked to ensure the good processing speed and accuracy. For WEDM, it is a kind of cutting or cutting material from a whole blank. Therefore, the original stress balance is destroyed in the process of processing, resulting in stress concentration at the corner. When the radius r of the inner corner is less than 0.2, the design department should be advised to improve the die structure. The method of dealing with stress concentration can apply the principle of vector translation. The allowance of 0.8-0.9mm should be reserved before finishing, and the approximate shape of the cavity should be pre processed, and then heat treatment should be carried out to release the machining stress as much as possible before finishing, so as to ensure the thermal stability.

When processing punch, the cutting position and path of cutting wire should be carefully considered. The position of clamping blank should be selected after the first feeding, the workpiece does not form a hanging wall, which always makes the workpiece in good stress state and does not affect the subsequent processing; for the punch with high requirements, the blank can be drilled and threaded, and the processing effect is better than that of cutting in the shape. Now high-precision workpieces, in order to ensure the quality of the parts, four times of cutting is generally used. When there is a part of taper machining in the thickness direction of female die, in order to pursue efficient machining, the straight edge is usually roughened for the first time, tapered for the second time, and then finished for the third time. This process feature is that there is no need to finish the existing taper edge vertically, only the straight edge of the edge section is finished, and the edge of the straight edge is refined after the fourth pass.

Rough and fine electrodes should be made respectively in EDM. The shape of the finishing electrode is required to meet the requirements of the cavity, and the good precision electrode has been processed by CNC machine tool. In terms of electrode material selection, copper electrode is mainly used for general steel parts processing; Cu-W alloy electrode has good comprehensive performance, especially the electrode loss during processing is obviously smaller than that of red copper electrode. Under good chip removal conditions, it is suitable for finishing difficult to machine materials and parts with complex cross-section shape; Ag-W alloy electrode has better performance than Cu-W alloy electrode because of less resources and high price In addition, graphite electrode has been widely used. At present, there are domestic graphite and imported graphite. Imported graphite has the advantages of low loss, high hardness, fast electro etching speed and low surface roughness, and has been applied in many complex parts finishing. When designing the electrode, the clearance and the number of electrodes are calculated. When machining large area or heavy electrode, the workpiece and electrode clamping should be stable and have certain strength to prevent loosening during processing. However, the surface after EDM is more difficult to grind than the surface after conventional machining or heat treatment. Therefore, before the end of EDM, the surface should be trimmed with precision gauge to remove the hardened thin layer formed on the surface.

Surface treatment of mould parts

The content of forming surface treatment includes no porosity on steel surface, uniform hardness, small difference in anisotropy characteristics, low inclusions and stress concentration places such as tool marks and grinding marks left on the surface of parts during processing. Therefore, after the end of processing, it is necessary to strengthen the surface of the parts, through mechanical polishing, fitter grinding, polishing, processing hidden dangers. Blunt the useless edge, acute angle and orifice of the workpiece. Generally, there will be 6-10 μ m metamorphic hardened layer on the surface of EDM, which is gray white in color. This layer is brittle and has residual stress. Before use, the hardened layer should be eliminated completely by polishing the surface and polishing off the hardened layer. In order to obtain high-quality polishing effect, the material, shape, hardness and surface quality of cutting must be fully considered. It is necessary to have high-quality polishing tools, high-quality polishing materials, correct polishing process, rigorous and consistent personnel quality, and good cleaning environment.

Assembly of mould parts

In the process of grinding and electrical machining, the workpiece will be magnetized to a certain extent, with weak magnetic force, which is easy to absorb some small impurities. Therefore, before assembly, the workpiece should be fully demagnetized and the surface should be cleaned with ethyl acetate. During the assembly process: (1) first understand the assembly drawing and complete all kinds of parts; (2) list the assembly sequence of each part; (3) check the dimensional accuracy of each part and make clear the matching requirements; (4) complete the required tools, and then start to assemble the mold; (5) assemble the guide pillar and guide sleeve of the mold base and the assembly of the cavity forming block; (6) assemble the mold (7) open and close the mold, check whether the mold action is reliable.

Computer gong processing – automobile mold

The domestic and international markets have more and more stringent requirements on the quality and cost price of automobile forgings, such as draft angle, weight tolerance, size, machining allowance, etc., and the price is not ideal, but the batch is large. In order to meet the needs of the market, this paper analyzes the process and repeated practice, and finds an ideal process, which is of great significance to the production of similar products.

Introduction of products and determination of process plan

Product introduction

The arm body is a part used on the brake pump of a heavy vehicle, and the structure is shown in Fig. 1. There are several difficulties in forging: (1) the draft angle is small, only 3 ° outside and 5 ° inside, while the ejection device only has one place in the ∮ 62 hole; (2) the machining allowance is small, only boring and broaching are used for ∮ 62 and square groove of 23.2mm; (3) 10 – ∮ 6.2 * 5 these 10 nails are difficult to fill, and the location requirements are high, and the root fillet of the nails is r0.2, which makes the die wear faster and easy to bump and cause deformation in the production process.

Determination of process plan

In order to adapt to mass production and improve efficiency, we have determined the following processes: (intermediate frequency furnace) heating / (cross wedge rolling) / (25000kN hot die forging press) bending / pre forging / forging / (3150kN double-point Press) punching / trimming / normalizing / shot peening / precision pressing. In the technological process, two pieces at a time are used for heating billet, the handle of the part is long and thin, and the blank making efficiency of single piece by free forging is low. The cross wedge rolling billet (as shown in Fig. 2) is adopted and cut into two pieces on the rolling mill at the same time. Because the cross-section of the parts changes greatly, from ∮ 55 to ∮ 23, it takes two wedging to complete, so it is difficult to process and repair the rolling die.

In addition to ensuring the size of the head and shank, it is more important to correct the position of the 10 nails, the fillet of the root and the bending of the handle. Therefore, two standard platens with 5 holes are used to ensure the position of nails and the root fillet, and improve the service life of forging die.

Key points of mould design and manufacture

Generally, the bending die design only considers that the shape of the extruded blank is consistent with that of the forging. Due to the large difference in the thickness between the big end and the handle of the arm body, the handle of the bending billet will be suspended when it is put into the pre forging die. During the pre forging, the transition between the handle and the big head will be folded. Due to the suspension of the handle of the bending billet, the metal flow in this part is too large.

Shape and position tolerance of computer gong machining

1、 Interchangeability of parts

Precision parts manufacturers introduced that after long-term production and operation of the machine, some parts are bound to wear, deformation and scrap, replaced with new parts. These parts are called accessories or spare parts. Accessories or spare parts without repair or selection, installed on the machine can run, known as interchangeability.

In order to achieve interchangeability, the size and geometry of parts should be consistent when manufacturing parts. The so-called consistency does not mean that the score is exactly the same (this is neither economical nor possible). As long as the size and geometric shape of the parts are controlled within an allowable range, it is necessary to make the parts and other parts have the same binding performance. The allowable error range is the geometric tolerance.

2、 The machining quality of precision parts is expressed by machining precision

Geometric accuracy

Geometric accuracy refers to the accuracy of geometric shape of each surface or axis, such as whether the line is straight, whether the surface is flat, whether the normal section on the cylinder is circular, etc. The allowable variation range is represented by “geometric tolerance”. The smaller the geometric tolerance number is, the higher the shape accuracy is.

Dimensional accuracy

According to the analysis of precision parts processing manufacturers, the dimensional accuracy refers to the accuracy of the size of the parts after processing, which is represented by “dimensional tolerance”. When the dimensions of parts are the same, the higher the accuracy, the smaller the tolerance number.

Position accuracy

According to the introduction of precision parts processing manufacturer, position accuracy refers to the accuracy of mutual position between the surfaces of parts, such as whether the two planes are parallel, whether they are vertical, whether the two axes are coaxial, and so on, which is represented by “position tolerance”.

The tolerance of the above shape and position is referred to as “form and position tolerance”.

Troubleshooting of four axis machining

Analysis and processing of four axis machining: the alarm may be caused by the poor SQL3 of the table loosening position sensor or the CNC did not receive the clamping signal of the turntable, because similar faults occurred before were caused by poor plug contact. To confirm, open the side cover of the turntable, and close a small saw blade to the end of SQ13: the SQL3 lamp is on, which proves that SQL3 is normal. Meanwhile, the data of PLC and ladder iaxbul can be highlighted, indicating that the system can receive signals. Therefore, it is suspected that there are problems in the hydraulic part, such as insufficient hydraulic pressure, oil leakage of hydraulic cylinder rising the turntable, mechanical stagnation when the turntable rises, which makes the turntable rise not in place. The hydraulic pressure of four axis machining is checked. When the machine stops moving, the pressure is 5.5mpa. When the turntable or machine is manually operated, it is found that the pointer of the system pressure gauge is shaking obviously and the hydraulic pump has obvious noise. Therefore, it is suspected that the hydraulic pump inhales air: check the oil level of the oil tank and find that the oil tank is empty. After filling the tank, turn the turntable again, normal. The variable pump is used to supply oil in the hydraulic system. When the hydraulic pressure is not operated, the system keeps pressure, the hydraulic pump absorbs less oil, and the oil level of the oil tank basically meets the requirements. When the hydraulic pump is operated, the hydraulic pump shall supply oil. Because the oil tank is not enough, the system pressure is insufficient, which leads to the failure of the turntable to rise in place. Half an hour later, the machine alarm again, and then look at the oil level, and the oil is gone, indicating that the hydraulic system leaks oil: finally, it can find the oil pipe of the turntable rising is broken and leaking; after replacement, the fault is completely eliminated.

CNC machining of revolving parts

CNC lathe machining center is a common name of CNC lathe. The key difference between turning and milling is that it is mainly used for the machining of rotary parts such as shafts, ring parts, disk parts and threads.

CNC lathe can be divided into horizontal CNC lathe and vertical CNC Lathe according to spindle configuration. There are many kinds of horizontal CNC lathe. The function of early CNC lathe is relatively simple, only x, Z axis linkage function to achieve digital control turning processing. Based on the need of expanding the processing range on the CNC lathe, the power tool is added to the tool holder of the NC lathe, and the milling function is increased. On this basis, the turning and milling machining center is developed. However, the processing range of the traditional turning and milling machining center is limited due to the fact that the cutting tool of the CNC lathe always faces the rotation center of the spindle Drilling, reaming, reaming, etc. toward the spindle rotation center. With the continuous development of numerical control technology, as well as the requirements of new product development and rapid response, the main structure of CNC equipment forms serialization and modularization, increases Y-axis and its rotation axis, and develops into a real turning and milling machining center.

As one of the important parts of CNC lathe, the turret determines the overall layout and working performance of CNC lathe. There are turret turret and linear array turret. Turret turret is the most common horizontal CNC lathe.

Numerical control lathe is very popular in the factory, and it plays an important role in the field of processing as the machining center. Industrial statistics show that CNC lathes are generally considered to be relatively simple compared with machining centers, although CNC lathes can produce high-quality parts. CNC lathe is mainly used to process high-precision, good surface quality requirements of rotary parts, so it needs few programs and start-up operation, but this does not mean that CNC lathe can not be used for processing short cycle and ordinary parts, just because the ratio of parts to be machined by turning is much higher than that by milling.

Characteristics of CNC lathe

(1) CNC lathe can automatically complete the following operations: spindle speed change, forward and reverse rotation, start or stop, feed and rapid movement in two coordinate directions, release, rotation and clamping of tool rest, switch of cutting fluid, etc.

(2) The feed of NC turning tool must be connected with the rotation of the spindle, because the turning of NC lathe is calculated by the number of pulse equivalent that the turning tool moves along the feed direction when the spindle rotates a circle.

(3) Since the dimension marking and measurement of part design drawings are diameter values, in order to improve the accuracy of radial dimension and facilitate programming and measurement, X-direction pulse equivalent is taken as half of Z-direction, so when the diameter direction is programmed with absolute value, x-coordinate value is expressed as diameter value. When using incremental programming, the program is programmed by twice the actual radial displacement, and the direction symbol is attached.

(4) When machining parts with horizontal CNC lathe, based on the needs of surface quality and machining accuracy of the parts, the spindle must have a large speed range, which can adopt either constant surface speed or constant speed.

(5) It has the function of tool compensation and skip instruction.

(6) CNC lathe is usually a two coordinate machine tool, which can realize two coordinate (x, z) linkage processing of revolving body contour parts.

(7) Due to the large machining allowance of blank and die forging, CNC lathe often has different forms of fixed cycle function, which can carry out a variety of turning cycles

Factors of deformation and crack of parts

In the production practice, the author found that the deformation and crack in WEDM are related to the following factors.

1.1 it is related to the structure of parts

1) The size of deformation is related to the complexity of shape, the ratio of length to width, and the ratio of cavity to frame width. The more complex the shape, the larger the ratio of length to width and the ratio of cavity to frame width, the greater the deformation of the die. The law of deformation is that the middle part of the cavity is shrunk in, and the punch is usually warped;

2) It is easy to crack or even explode in the sharp corner of quenching cavity with complex shape and clear angle. The frequency of its occurrence is related to the material composition and heat treatment process;

3) Cylindrical parts with thin wall thickness are easy to deform if they are cut on the inner wall, which generally changes from round to ellipse. If it is cut through the notch, it is easy to crack when it is about to be cut through;

4) The deep notch cut in from the outside of the part is easy to deform. The deformation law is that the mouth is retracted. The deformation amount is related to the depth of the notch and the material properties.

1.2 related to hot working process

1) The parts whose initial forging temperature is too high or too low and the final forging temperature is low when forging die blank;

2) When the final forging temperature is too high, the grain grows up, and the cooling rate is too slow after final forging, and there are net carbide precipitated in the die blank;

3) The forging billet annealing is not carried out according to the spheroidizing annealing process, and the parts with spheroidized pearlite more than 5 grades are annealed;

4) When the quenching temperature is too high, the austenite grain is coarse, which reduces the strength and toughness of the material and increases the brittleness;

5) The quenched parts are not tempered in time and the parts with insufficient tempering.

1.3 related to machining process

1) If the die with large area is cut off in the middle without hollowing out in advance, the size of the frame will be deformed due to cutting off the larger volume in the frame;

2) No matter what the shape of punch tempering and shape is, it is easy to deform, especially for the quenched part, which has to be cut in from the outside of the blank;

3) For the grinding parts after heat treatment, there are no process requirements such as grinding wheel granularity, feed rate, cooling mode, etc., and the parts with defects such as burn and microcrack on the surface after grinding.

1.4 material related

1) There is serious carbide segregation in raw materials;

2) Materials with poor hardenability and easy deformation, such as T10A, T8A, etc.

1.5 related to wire cutting process

1) It is easy to deform due to improper selection of WEDM path; Dongguan computer gong Processing Factory Dongguan Mechanical Parts Processing Factory Dongguan plastic mold factory Shenzhen computer gong Processing Co., Ltd

2) It is easy to deform due to unreliable clamping method and improper selection of clamping points;

3) Improper selection of electric gauge may lead to cracks.

Machining and polishing of mechanical parts

The basic principle of electropolishing is the same as that of chemical polishing, that is, the surface is smooth by selectively dissolving the small protruding part of the material surface. Compared with chemical polishing, the effect of cathode reaction can be eliminated and the effect is better. The electrochemical polishing process is divided into two steps: (1) macro leveling solution diffuses into the electrolyte, and the geometric roughness of the material surface decreases with RA > 1 μ M. (2) The results show that the surface brightness is improved and RA is less than 1 μ M.

1.4 in ultrasonic polishing, the workpiece is put into the abrasive suspension and placed in the ultrasonic field together, and the abrasive is ground and polished on the surface of the workpiece by the oscillating action of the ultrasonic wave. The macro force of ultrasonic machining is small, which will not cause deformation of workpiece, but it is difficult to make and install tooling. Ultrasonic machining can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution to separate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is uniform; the cavitation effect of ultrasonic in the liquid can also inhibit the corrosion process and facilitate the surface lighting.

1.5 fluid polishing fluid polishing is to achieve the purpose of polishing by washing the workpiece surface with high-speed flowing liquid and abrasive particles. The common methods are abrasive jet machining, liquid jet machining, hydrodynamic grinding and so on. Hydrodynamic grinding is driven by hydraulic pressure to make the liquid medium carrying abrasive particles flow through the workpiece surface at high speed. The medium is mainly made of special compound (polymer material) with good flowability under low pressure and mixed with abrasive. The abrasive can be silicon carbide powder.

1.6 magnetic abrasive polishing magnetic abrasive polishing is the use of magnetic abrasive under the action of magnetic field to form abrasive brush to grind the workpiece. This method has the advantages of high efficiency, good quality, easy control of processing conditions and good working conditions. The surface roughness can reach ra0.1 μ m with proper abrasive.

The basic method of mechanical polishing in plastic mold processing is different from the surface polishing required in other industries. Strictly speaking, mold polishing should be called mirror processing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy. Surface polishing generally requires only a bright surface. The standard of mirror machining is divided into four levels: Ao = ra0.008 μ m, A1 = ra0.016 μ m, A3 = ra0.032 μ m, A4 = ra0.063 μ M. due to the fact that it is difficult to accurately control the geometric accuracy of parts by electrolytic polishing, fluid polishing and other methods, and the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods can not meet the requirements, so the mirror processing of precision mold is mainly mechanical polishing.