CNC Technology – Page 39 – CNC Machining & Turning, Milling, Metal parts

CNC machining operation language

1) Computer numerical control (CNC) uses computer to control processing function to realize numerical control. 2) Axis (axis) the reference direction along which parts of a machine tool can move in a straight line or in a rotary motion. 3) The machine coordinate system is a Cartesian coordinate system fixed on the machine tool and based on the zero point of the machine tool. 4) The machine coordinate origin is the origin of the machine coordinate system. 5) The workpiece coordinate system is a Cartesian coordinate system fixed on the workpiece. 6) The origin of the workpiece coordinate system. 7) Machine zero is defined by the machine manufacturer. 8) A fixed point along the coordinate axis used for starting a machine tool. It can use the origin of the machine coordinate as the reference datum. 9) The straight line distance or angle between absolute dimension / absolute coordinates and the origin of a coordinate system. 10) Incremental dimension / incremental coordinates the distance or angle between each point and the previous point in the increment of a sequence of points. 11) Minimum input increment is the smallest increment unit that can be input in the processing program. 12) Minimum command increment is the minimum increment unit of the coordinate axis movement of the command issued by the numerical control device. 13) Interpolation is the operation process of determining the position coordinates of multiple intermediate points between two known points on the required path or contour line according to a certain mathematical function (such as line, arc or higher-order function). 14) This is an interpolation method. In this way, the interpolation between two points is approached along the point group of the line, and the motion of the tool is controlled along this line. 15) Circular interpolation (Circular: interpolation) this is an interpolation method. In this way, according to the interpolation digital information between the two ends, the point group approaching the actual arc is calculated, and the tool movement along these points is controlled to process the arc curve. 16) The tool reference point of clockwise arc is a path formed by rotating the tool reference point around the track center and rotating in the negative angle direction. 17) the tool reference point of counter clockwise arc rotates around the track center and rotates in the positive angle direction. 18) Manual part progranmiog (manual part progranmiog) is used to make the part processing program manually. 19) Computer part prograrrnrnlng (computer part prograrrnrnlng) uses a computer and appropriate general processing program and post-processing program to prepare the part program and obtain the processing program. 20) Absolute prograrming is programmed with control words representing absolute dimensions. 21) increment programming uses the control word representing the increment size to program. 22) a set of element symbols used to represent an organization or control of data. 23) the control character appears in the specific information text and represents the character of a certain control function. Address a character or group of characters at the beginning of a control word to identify data that follows. 25) block format the arrangement of words, characters and data in a block. 26) instruction code / machine code computer instruction code, machine language, used to represent the instructions in the instruction set. 27) program number is the number assigned at the front end of each program when the program is identified by a number. 28) program name is the name assigned to each program when the program is identified by its name. Command mode. 31) part program is a sequential instruction set written in a certain language or format in order to make automatic operation effective. Part program is written on the input medium processing program, can also be prepared for the computer input, after processing to get the processing program. In the automatic machining control system, a sequential instruction set written in automatic control language and format. These instructions are recorded on the appropriate input medium and can be operated directly. 33) end of program refers to the auxiliary function for the end of workpiece processing 34) the auxiliary function that makes the spindle function and other functions (such as cooling function) be deleted after all commands in the end of data program section are executed. After all the commands of progrm stop program section are executed, the spindle function and other functions are deleted, and the subsequent auxiliary functions of data processing are terminated. 36) preparatory function is a command that enables the machine tool or control system to establish a machining function mode. 37) miscellaneus A command that controls the switching function of a machine tool or system. 38) tool function

Debugging of CNC machine tool

How to adjust the CNC machine tool? Before debugging, the horizontal position of the machine bed should be adjusted first, the main geometric accuracy of the machine tool should be roughly adjusted, and then the relative position between the main moving parts and the host machine should be adjusted, such as the correction of the position of the manipulator, tool magazine and host machine tool change. After that, add lubricating oil, hydraulic oil and cutting fluid according to the requirements of the machine manual, and connect the external air source.

More than 80% of the machine tools must be debugged in the field before they can meet the technical specifications. The correctness of this step largely determines whether the CNC machine tool can play a normal economic efficiency and its own service life. Therefore, when the new machine tool is checked and accepted, the machine tool can be ensured to achieve its technical indicators and expected quality and efficiency at the beginning of installation. The new machine tool needs to be tested again after half a year’s use, and then it can be verified once a year. The machine tool error is detected regularly and the pitch and reverse clearance are corrected in time.

The NC machine tool should be started and debugged according to the following steps:

1、 Preparation before commissioning

Before debugging the machine tool, the horizontal position of the machine bed should be adjusted first, the main geometric accuracy of the machine tool should be roughly adjusted, and then the relative position between the main moving parts and the host machine should be adjusted, such as the correction of the position of the manipulator, tool magazine and the host machine tool change. After that, add lubricating oil, hydraulic oil and cutting fluid according to the requirements of the machine manual, and connect the external air source.

2、 Power on test run of machine tool

The power on test run of machine tool generally adopts the power on test of each component separately, and then makes a comprehensive power supply test. According to the machine tool manual, check whether the main parts of the machine tool function normally and completely, so that all parts of the machine tool can operate and move.

3、 Adjustment of machine tool accuracy and function

Using the precision level instrument and other testing tools, the level of the main bed of the machine tool is adjusted by adjusting the iron pad, so that the geometric accuracy of the machine tool can reach the allowable tolerance range;
For the automatic tool change device, adjust the position of the tool magazine, manipulator, travel parameters, etc., and then check the action with the command, which is required to be accurate;
For the machine tool with APC automatic exchange table, after adjusting the relative position, carry out automatic load exchange;
After the adjustment of the machine tool, carefully check whether the parameter setting values in the numerical control system and the programmable controller conform to the data specified in the random index, and then test the main operation functions, safety measures, execution of common instructions, etc.
Check the auxiliary functions and accessories of the machine tool.

CNC cutting machine

At present, in the normal work of the CNC cutting machine used in the factory, the operator can successfully complete the cutting work by using the breakpoint continuous cutting function of the cutting machine. The method is as follows: when the operator wants to stop the work and save the breakpoint of the cutting site in the process of cutting, press the s key to stop when running to the idle section, and then press the Enter key to exit the cutting operation. At this time, the breakpoint data is memorized by the system. At this time, the operator should remember the coordinate values in X and Y directions, and then turn to the idle path operation to make the cutter move in the opposite direction until the coordinate values in X and Y directions are the same as the coordinate values memorized above, and the positive and negative signs are different (this position is the starting point of the program and also the origin of the steel plate). Next time when starting the machine, enter the letter C at the corner of the steel plate to continue to complete the last interrupted cutting operation.

According to the above operation method, the operator must first control the cutter to return to the starting point of the program (or the origin of the steel plate) in order to continue cutting in the next work. Obviously, if the cutting machine breaks down suddenly in normal operation (such as power failure, servo system failure, control computer crash, etc.), the operator cannot make it return to the starting point of the program (or the origin of the steel plate) because it has no power-off memory function.

In this case, our general practice is: after the cutting machine is repaired and restored to normal, the remaining steel plate is aligned, and then a new program is compiled by the programmer for cutting. In this way, some parts at the breakpoint are not cut completely, which makes them unable to be used, resulting in the waste of raw materials, increasing the production cost, and also bringing repetitive labor to the programmer, which leads to the reduction of production efficiency.

In the production practice, we successfully solve the problem of returning to the program starting point (or steel plate origin) after the cutting machine failure occurs by setting the zero point artificially. The specific operation method is as follows: first, operate the cutting machine to make the longitudinal sliding seat contact the measuring rod slowly, and compress the spring to make it deform properly. At this time, set the dial indicator head to “0”; then use the same method to set the dial indicator head of another zero setting device to “0”. No matter how many X and Y coordinates are displayed by the cutting machine, press Z key to make them all return to zero. This position is the zero point set by human for the cutting machine. Then operate the cutting machine according to the position of the steel plate to set the starting point of the program (or the origin of the steel plate). After setting, remember the coordinates of X and Y directions at this time. This coordinate value is the relative position between the zero point of the cutting machine and the starting point of the program (or the origin of the steel plate). When the fault occurs, first remove the fault, after the cutting machine returns to normal, use the above method to make it zero, and then use the coordinate value remembered to find the starting point of the program (or the origin of the steel plate). In this way, the breakpoint continuous cutting can be realized smoothly until the whole steel plate is cut.

High precision characteristics of computer gongs

From the development of precision machining to ultra precision machining, is the development direction of the world’s industrial powers. Its precision ranges from micron level to submicron level and even nanometer level (< 10nm).

At present, under the requirement of high machining precision, the machining accuracy of ordinary computer gongs has been increased from ± 10 μ m to ± 5 μ m; the machining accuracy of precision machining center has been increased from ± 3 ~ 5 μ m to ± 1 ~ 1.5 μ m, or even higher; the ultra precision machining accuracy has entered the nano level (0.001 μ m), the spindle rotation accuracy is required to reach 0.01 ~ 0.05 μ m, the roundness is 0.1 μ m, and the surface is machined Roughness Ra = 0.003 μ m, etc. These machine tools generally adopt vector control variable frequency drive motorized spindle (motor and spindle integration), the spindle radial runout is less than 2 μ m, the axial movement is less than 1 μ m, and the shafting imbalance reaches g0.4 level.

There are mainly two types of feed drive of high-speed and high-precision machining machine tools: “rotary servo motor plus precision high-speed ball screw” and “direct drive of linear motor”. In addition, the new parallel machine tool is also easy to realize high-speed feed.

Due to its mature technology and wide application, ball screw not only has a high precision (ISO 3408 grade 1), but also has a relatively low cost to realize high-speed, so it is still used by many high-speed machine tools. The current high-speed machining machine driven by ball screw has a maximum moving speed of 90m / min and an acceleration of 1.5g.

Ball screw belongs to mechanical transmission. In the transmission process, there are inevitably elastic deformation, friction and reverse clearance, which will cause motion lag and other nonlinear errors. In order to eliminate the influence of these errors on machining accuracy, linear motor direct drive was applied to machine tools in 1993. Because of the “zero transmission” without intermediate link, it has small inertia and rigid system High speed and acceleration can be achieved with high speed and fast response, and the stroke length is not limited theoretically. The positioning accuracy can also reach a higher level under the action of high-precision position feedback system. It is an ideal driving mode for high-speed and high-precision machining machine tools, especially for medium and large-scale machine tools. At present, the maximum moving speed of high-speed and high-precision machining machine tools using linear motor has reached 208 M / min and the acceleration is 2G, and there is still room for development.

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”.