Monthly Archive September 2020

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CNC Machining for the heat sink parts

Radiator machining parts

Our factory is a professional CNC plus factory. The processed parts adapt to various industries. The accessories of the heat sink have been processed for more than ten years in our factory. The heat sink material is aluminum or copper. which is processed by CNC, drilled, tapped, deburred, cleaned, sandblasted, and then surface oxidized.

The principle of the heat sink is to increase the surface area and speed up the heat dissipation. As the material of heat sink is the metal with smaller specific heat, it absorbs heat very quickly, at the same time, the speed of heat loss is also relatively fast, so the effect of rapid heat dissipation is achieved through heat transfer.

For example, CPU of the computer use a heat sink,It can reduce the temperature of CPU and ensure the work of CPU.

For the material of heat sink, the thermal conductivity of each material is different, which is arranged from high to low: silver, copper, aluminum and steel.

However, if silver is used for heat sink, it will be cost too expensive, so the best solution is to use copper. Although aluminum is much cheaper, its thermal conductivity is not as good as copper.

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Processing automobile parts with computer gong

With the development of society, gold casting technology has been greatly improved. In the production process, it also reduces the environmental pollution, improves the working environment, improves the production technology and level, which is of great help to the development of the casting industry, so as to promote the development of the automobile industry. 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

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 / final 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, it takes two wedges to complete from ∮ 55 to ∮ 23, 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.

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Tools for cutting stainless steel

Cutting tool is the most important for cutting stainless steel.

How to select tool geometry parameters when cutting stainless steel?

Front angle G0: the hardness and strength of stainless steel are not high, but its plasticity and toughness are good, and the thermal strength is high, and the chip is not easy to be cut off during cutting. In order to reduce the plastic deformation of the metal to be cut, cutting force and cutting temperature can be reduced, and the depth of hardened layer can be reduced. The front angle of turning various stainless steels is about 12 ° to 30 °. For martensitic stainless steel (such as 2Cr13), the front angle can be larger; for austenitic and austenitic + ferritic stainless steel, the front angle should be smaller; for the stainless steel without quenching and tempering treatment or with low hardness after quenching and tempering, the larger front angle can be adopted; for the small diameter or thin-walled workpiece, the larger front angle should be adopted. For high-speed steel milling cutter, GN = 10 ° – 20 °, for carbide milling cutter, GN = 5 ° – 10 °, for reamer, G0 = 8 ° – 12 ° and for tap, G0 = 15 ° – 20 ° for machine use or G0 = 20 ° for manual use.

Back angle A0: increasing the rake angle can reduce the friction between the flank and the machined surface, but reduce the strength and heat dissipation capacity of the cutting edge. The reasonable value of the back angle depends on the cutting thickness. When the cutting thickness is small, the larger back angle should be selected. Stainless steel turning tool or boring cutter is usually taken as A0 = 10 ° to 20 ° for finish machining or A0 = 6 ° to 10 ° for rough machining); A0 = 10 ° to 20 ° for high-speed steel end milling cutter and A0 = 15 ° to 20 ° for end milling cutter; A0 = 5 ° to 10 ° for hardness alloy end milling cutter and A0 = 12 ° to 16 ° for end milling cutter; A0 = 8 ° to 12 ° for reamer and tap.

Selection of cemented carbide: YG cemented carbide has better toughness, larger front angle can be used, and the blade can be grinded sharper, so that cutting is light and fast, and the chip and cutter are not easy to bond, so it is more suitable for stainless steel processing. Especially in rough turning and intermittent cutting, the advantage of YG alloy is more important. In addition, the thermal conductivity of YG alloy is better than that of high-speed steel by nearly two times and that of YT type alloy. Therefore, YG alloy is widely used in stainless steel cutting, especially in the manufacture of rough turning tool, cutting tool, reamer and reamer.

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CNC machining instructions

CNC machining refers to the processing with CNC machining tools. CNC index controlled machine tool is programmed by NC machining language, usually G code. NC machining G code language tells CNC machine tool which Cartesian position coordinates, and controls the tool feed speed and spindle speed, as well as tool converter, coolant and other functions. Compared with manual machining, CNC machining has great advantages, such as the parts produced by CNC machining are very accurate and repeatable; CNC machining can produce parts with complex shapes that cannot be completed by manual processing. CNC machining technology has been widely promoted, most of the machining workshops have the ability of NC machining. The most common NC machining methods in typical machining workshops are CNC milling, CNC lathe and CNC EDM wire cutting (WEDM). The tool for NC milling is called CNC milling machine or CNC machining center. CNC turning lathe is called CNC lathe center. NC machining G code can be manually programmed, but usually the machining workshop uses CAM software to automatically read CAD file and generate G code program to control NC machine tool. Leading CNC machine tool brands include Hass, DMG (Deckel MAHO GILDEMEISTER), Mazak, Mori Seiki, fadal and wasino.

Several groups of common instructions for CNC machining

1、 Pause instruction g04x (U)_ /P_ It refers to the tool pause time (feed stop, spindle does not stop), the value after address P or X is the pause time. The value after X should have a decimal point. Otherwise, it should be calculated by one thousandth of this value in seconds (s). The value after P cannot have a decimal point (i.e., an integer), and the unit is Ms. For example, G04 x2.0; or G04 X2000; pause for 2 seconds G04 P2000; but in some hole series processing instructions (such as g82, G88 and g89), in order to ensure the roughness of the hole bottom, when the tool is machined to the hole bottom, there must be a pause time, which can only be expressed by the address P. if the address x is used, the control system thinks that x is the x-axis coordinate value for execution. For example, g82x100.0y100.0z-20.0r5.0f200p2000; drilling (100.0100.0) to the bottom of the hole for 2 seconds; g82x100.0y100.0z-20.0r5.0f200x2.0; drilling (2.0100.0) to the bottom of the hole will not be suspended.

2、 The difference and connection of M00, M01, M02 and M30 are program unconditional pause instructions. When the program is executed, the feed stops and the spindle stops. To restart the program, you must first return to the og state, press CW (spindle forward rotation) to start the spindle, and then return to the auto state and press the start key to start the program. M01 is the program selective pause instruction. The op stop key on the control panel must be opened before the program is executed. The effect after execution is the same as that of M00. Restart the program as above. M00 and M01 are often used in the inspection or chip removal of workpiece size in the process of machining. M02 is the end instruction of main program. Execute this command, feed stop, spindle stop, coolant off. But the program cursor stops at the end of the program. M30 is the main program end instruction. The function is the same as that of M02, except that the cursor returns to the program head position, regardless of whether there are other program segments after M30.

3、 The meaning of the address D and H is the same. The tool compensation parameters D and H have the same function and can be interchanged arbitrarily. They all represent the address name of the compensation register in the CNC system, but the specific compensation value is determined by the compensation number address behind them. However, in order to prevent errors in the machining center, generally, h is the tool length compensation address, the compensation number is from No. 1 to No. 20, D is the tool radius compensation address, and the compensation number starts from No. 21 (tool magazine of 20 tools). For example, g00g43h1z100.0; g01g41d21x20.0y35.0f200;

4、 Mirror instruction mirror processing instruction M21, M22, M23. When only the x-axis or y-axis is mirrored, the cutting sequence (forward milling and reverse milling), cutter compensation direction and circular interpolation steering will be opposite to the actual program. When the x-axis and y-axis are mirrored at the same time, the tool feed sequence, tool compensation direction and circular interpolation direction remain unchanged. Note: after using the mirror instruction, M23 must be used to cancel, so as not to affect the following program. In G90 mode, if mirror or cancel command is used, it can be used only after returning to the origin of workpiece coordinate system. Otherwise, the NC system can not calculate the motion track behind, which will lead to the phenomenon of random tool walking. At this time, it is necessary to implement manual origin reset operation to solve the problem. The spindle rotation does not change with the mirror command.

5、 Circular interpolation instruction G02 is clockwise interpolation, G03 is counter clockwise interpolation, in XY plane, the format is as follows: G02 / g03x_ Y_ I_ K_ F_ Or G02 / g 03 x_ Y_ R_ F_ Where x and y are the coordinates of the end point of the arc, I and j are the increment values from the starting point of the arc to the center of the circle on the X and Y axes, R is the radius of the arc, and F is the feed rate. In circular arc cutting, it should be noted that Q ≤ 180 ° R is positive; Q > 180 ° R is negative; I and K can also be specified by R. when both are specified, R command has priority, I and K are invalid; R cannot be used for whole circle cutting, and can only be programmed with I, J and K, because there are countless circles with the same radius passing through the same point. When I and K are zero, they can be omitted; regardless of G90 or G91 mode, I, J, K are programmed according to relative coordinates; when circular interpolation, tool compensation instruction G41 / G42 cannot be used.

6、 The advantages and disadvantages between G92 and G54-G59 are the coordinate system set before machining, while G92 is the coordinate system set in the program. If G54-G59 is used, there is no need to use G92, otherwise G54-G59 will be damaged

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Collision detection of NC machining simulation system

In the process of NC machining, it is easy to appear over cutting, undercutting and other phenomena. At the same time, the damage of cutting tools, or the processing of waste products, the interference and collision between parts and tools, tools and fixtures, tools and worktables, will cause a certain cost waste. The NC machining simulation system can simulate the related program well and reduce the loss to the greatest extent.

Before the actual machining, the programmer can confirm whether the finished cutting product is consistent with the original design drawing through the simulation system, and can make better detailed analysis.

collision detection

In the actual processing, five axis CNC machining has more advantages than three axis CNC machining, can achieve a wider range, has faster material and efficiency, can reduce processing time and improve surface accuracy. However, due to the high degree of freedom of the two additional rotating axes, it is easy to cause collision and damage to the machine tool.

Therefore, before the actual processing, it is necessary to detect the collision with the help of NC machining simulation system. The main detection algorithms are as follows:

The machine tool includes many parts, but the collision detection algorithm between different parts is similar. The computer gong machining simulation system takes the cutter, workpiece and fixture as the main research object to detect the possible global collision.

  1. According to the tool location, the grid voxel model of the tool head scanning body and the grid voxel model of the tool holder scanning body are solved respectively. The tool holder scanning body is used to detect whether there is a global collision between the tool, workpiece and fixture, and the tool head scanning body is used to calculate the intersection between the tool and the workpiece.
  2. A feature attribute of voxel model is cuboid envelope box. The envelope box is used to make rough judgment. If the envelope box does not intersect, the objects enclosed in the envelope box will not intersect. At this time, the position data of the object envelope box will be updated, and other information will not change. It will prepare for the generation of the next tool point scanner and collision detection. Rough judgment can speed up the detection Speed.
  3. Once a collision occurs, the system stops reading data and reports the error message and the precise location of the collision. If there is no collision, the system continues to carry out the teaching operation between the tool head and the workpiece.
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Circular interpolation instruction of computer gong machining

When I and K are zero, they can be omitted; regardless of G90 or G91 mode, I, J, K are programmed according to relative coordinates; when circular interpolation, tool compensation instruction G41 / G42 cannot be used.

  1. Advantages and disadvantages between G92 and G54-G59

G54-G59 is the coordinate system set before machining, while G92 is the coordinate system set in the program. If G54-G59 is used, there is no need to use G92 again, otherwise G54-G59 will be replaced and should be avoided, as shown in Table 1.

Table 1 difference between G92 and working coordinate system`

Note: (1) once G92 is used to set the coordinate system, G54-G59 will not work unless the system is restarted after power failure or G92 is used to set the required new workpiece coordinate system. (2) After using G92 program, if the machine tool does not return to the original point set by G92, the program will be started again, and the current position of the machine tool will become the new workpiece coordinate origin, which is prone to accidents. Therefore, we hope that readers will use it carefully.

  1. Compile tool changing program.

In the machining center, tool change is inevitable. However, there is a fixed tool change point when the machine tool leaves the factory. If it is not in the position of tool change, it is impossible to change the tool. Moreover, before changing the tool, the tool compensation and circulation must be cancelled, the spindle is stopped and the coolant is turned off. There are many conditions. It is not only easy to make mistakes but also inefficient to ensure these conditions before each manual tool change. Therefore, we can compile a tool change program to save the memory and MDI status

Under the call of M98, the tool change action can be completed at one time.

Taking pmc-10v20 machining center as an example, the program is as follows:

O2002; (program name)

G80g40g49; (cancel fixed cycle, cutter compensation)

M05; (spindle stop)

M09; (coolant off)

G91g30z0; (Z axis returns to the second origin, i.e. tool change point)

M06; (tool change)

M99; (end of subroutine)

When the tool needs to be changed, just type “t5m98p2002” in MDI state to replace the required tool T5, thus avoiding many unnecessary mistakes. According to the characteristics of their own machine tools, the majority of readers can work out the corresponding tool change program.

  1. Others

The sequence number of the program segment is represented by address n. Generally, the memory space of NC device itself is limited (64K). In order to save storage space, the sequence number of program segment is omitted. N only means the segment label, which is convenient to find and edit the program, and has no effect on the processing process. The sequence number can be increased or decreased, and the continuity of the value is not required. However, some loop instructions, jump instructions, calling subroutines and mirror instructions can not be omitted.

  1. In the same program segment, the later occurrence of the same instruction (the same address symbol) or the same set of instructions takes effect.

For example, tool change procedure, t2m06t3; instead of T2, T3 is replaced;

G01g00x50.0y30.0f200; G00 is executed (although there is f value, G01 is not executed).

If the instruction codes are not in the same group, the effect is the same if they are exchanged in the same program segment.

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Tool changing program of computer gong processing

A circle passing through the same point

When I and K are zero, they can be omitted; regardless of G90 or G91 mode, I, J, K are programmed according to relative coordinates; when circular interpolation, tool compensation instruction G41 / G42 cannot be used.

  1. Advantages and disadvantages between G92 and G54-G59

G54-G59 is the coordinate system set before machining, while G92 is the coordinate system set in the program. If G54-G59 is used, there is no need to use G92 again, otherwise G54-G59 will be replaced and should be avoided, as shown in Table 1.

Table 1 difference between G92 and working coordinate system`

Note: (1) once G92 is used to set the coordinate system, G54-G59 will not work unless the system is restarted after power failure or G92 is used to set the required new workpiece coordinate system. (2) After using G92 program, if the machine tool does not return to the original point set by G92, the program will be started again, and the current position of the machine tool will become the new workpiece coordinate origin, which is prone to accidents. Therefore, we hope that readers will use it carefully.

  1. Compile tool changing program.

In the machining center, tool change is inevitable. However, there is a fixed tool change point when the machine tool leaves the factory. If it is not in the position of tool change, it is impossible to change the tool. Moreover, before changing the tool, the tool compensation and circulation must be cancelled, the spindle is stopped and the coolant is turned off. There are many conditions. It is not only easy to make mistakes but also inefficient to ensure these conditions before each manual tool change. Therefore, we can compile a tool change program to save the memory and MDI status

Under the call of M98, the tool change action can be completed at one time.

Taking pmc-10v20 machining center as an example, the program is as follows:

O2002; (program name)

G80g40g49; (cancel fixed cycle, cutter compensation)

M05; (spindle stop)

M09; (coolant off)

G91g30z0; (Z axis returns to the second origin, i.e. tool change point)

M06; (tool change)

M99; (end of subroutine)

When the tool needs to be changed, just type “t5m98p2002” in MDI state to replace the required tool T5, thus avoiding many unnecessary mistakes. According to the characteristics of their own machine tools, the majority of readers can work out the corresponding tool change program.

  1. Others

The sequence number of the program segment is represented by address n. Generally, the memory space of NC device itself is limited (64K). In order to save storage space, the sequence number of program segment is omitted. N only means the segment label, which is convenient to find and edit the program, and has no effect on the processing process. The sequence number can be increased or decreased, and the continuity of the value is not required. However, some loop instructions, jump instructions, calling subroutines and mirror instructions can not be omitted.

  1. In the same program segment, the later occurrence of the same instruction (the same address symbol) or the same set of instructions takes effect.

For example, tool change procedure, t2m06t3; instead of T2, T3 is replaced;

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Computer gong processing route

CNC Lathe Feed processing route refers to the path that the turning tool starts to move from the tool setting point (or the fixed origin of the machine tool) to CNC machining until it returns to the point and ends the processing program, including the path of cutting and the path of non cutting idle stroke such as cutting in and cutting out.

The feed path of finish machining is basically carried out along the contour sequence of the parts. Therefore, the key to determine the feed path is to determine the feed path of rough machining and idle stroke.

In CNC lathe processing, the determination of processing route generally follows the following principles.

① The accuracy and surface roughness of the workpiece to be processed shall be guaranteed.

② It can shorten the processing route, reduce the idle travel time and improve the processing efficiency.

③ Simplify the workload of numerical calculation and simplify the processing program.

④ Some subroutines should be reused.

Advantages and disadvantages CNC machining has the following advantages:

① A large number of tooling is reduced, and complex tooling is not needed to process parts with complex shapes. In order to change the shape and size of parts in CNC machining, we only need to modify the part processing program, which is suitable for the development and modification of new products.

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

③ In the case of multi variety and small batch production, the production efficiency is higher, the time of production preparation, machine tool adjustment and process inspection can be reduced, and the cutting time is reduced due to the use of the best cutting amount.

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

The disadvantage of CNC machining is the high cost of machine tools.

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Advantages of CNC machine tools over ordinary machine tools

The advantages of CNC machine tools are as follows:

  1. Processing efficiency, saving processing time.
  2. Work intensity. After the workers have finished programming, they can go to drink tea after the first piece is qualified.
  3. Reduce the number of waste products. As long as the first piece is qualified, the processed parts will generally be qualified.
  4. High safety, the farther the workers are from the processing equipment, the lower the probability of accidents.

For effective metal cutting, machining materials, cutting tools and cutting conditions are the three main factors. These determine the processing time, tool life and machining quality. Cutting conditions must be selected reasonably for economical and efficient processing methods.

The three elements of cutting conditions: cutting speed, feed and cutting depth directly cause damage. With the increase of cutting speed, the point temperature will rise, resulting in mechanical, chemical and thermal wear. If the cutting speed is increased by 20%, the tool life will be reduced by 1 / 2.

Back feed conditions and tool wear are kept to a minimum. But feeding behind, cutting temperature rise, wear. It is less than the effect of cutting speed. Cutting depth has no effect on cutting speed and feed, small cutting depth, but cutting material in hardened layer will also affect tool life.

According to the user’s processing material, hardness, cutting conditions, material selection, feed and cutting depth, the cutting speed is used.

Based on the selection of the most suitable process conditions, these factors are selected. Regular life and stable wear are the most ideal conditions.

However, in practice, the selection of tool life and tool wear, through machining size, surface quality, noise reduction, heat and so on. Under certain processing conditions, it is necessary to study CNC machining according to the actual situation. Difficult to machine materials such as stainless steel, heat-resistant alloy, can use coolant or choose a good rigid blade.

Reasonable selection of cutting tools

1。 Rough rotation, should choose high strength, good durability knife, in order to meet the large car turning, feedback.

2。 The essence of automobile is to select high precision, durable and good cutting tools to ensure the machining accuracy.

3。 Reduce the conversion time and knife convenience, should try to use machine knife and machine clip blade.

Select fixture

1。 General fixture should be selected to clamp workpiece as much as possible, and special fixture should be avoided;

2。 The coincidence of parts positioning datum reduces the positioning error.

Determine the processing route

Machining path is the part of tool path and direction relative to each other in the process of exponential control.

1。 It should be able to meet the requirements of machining accuracy and surface roughness;

2。 Shorten the processing route as far as possible and reduce the idle travel time of the tool.

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High gloss and high precision machining method

Machining surface roughness is one of the important marks to measure the quality of machined surface. It has a great influence on the wear resistance, corrosion resistance, fatigue strength and matching properties of parts. However, there are many factors affecting the surface roughness in machining. In order to achieve good surface roughness, we will learn what these factors are.

1、 The reason of rough machining surface

  1. Residual area: residual area refers to the area that remains on the machined surface after cutting by the main and auxiliary cutting edges of the tool.
  2. In the process of high speed machining, it is often called as stainless steel with low speed. The appearance of scale will increase the surface roughness of the machined surface significantly.
  3. Scab: in the process of cutting, when a chip is formed, the protruding part can replace the cutting edge to cut into the workpiece by computer gong machining | Dongguan computer gong machining | Shenzhen computer gong machining | mechanical parts processing | Guangzhou computer gong processing. The grooves of different depths are drawn on the machined surface; when the chip accretion falls off, part of the accumulated debris adheres to the machined surface and forms Small burr will increase the surface roughness.
  4. Vibration: in cutting process, due to the periodic vibration of the process system, the machined surface appears streaks or ripple marks, and the surface roughness value increases significantly.

Machining: all factors that affect the residual area, scale, scale and vibration affect the surface roughness.

  1. Cutting parameters: feed rate has the greatest influence on the residual area. When the feed rate decreases, the residual area decreases.

When cutting plastic metal, when cutting speed is very low or high, the surface roughness value is small. The reason is that it is not easy to produce chip lump at low speed, and the plastic deformation decreases when cutting speed is high, which can eliminate the formation of scale. When cutting brittle materials, the influence of cutting speed is small, because the deformation of material is small, the surface roughness value also decreases.

  1. Geometric parameters of tool: the radius of tool tip arc, main deflection angle and secondary deflection angle have great influence on residual area and vibration. Generally, when the radius of the tool tip arc increases and the main and secondary deflection angles decrease, the surface roughness value is small. However, if the machine tool stiffness is low, the tool tip arc radius is too large or the main deflection angle is too small, the vibration will occur due to the increase of cutting force, which will increase the surface roughness value.
  2. Tool material: the size of the edge arc radius and the time to keep sharp are different with different tool materials. High speed steel cutting tools can be grinded very sharp, but the holding time is short, so the surface roughness value is small when cutting at low speed. After grinding, the radius of the edge arc is larger, and the surface roughness is smaller at high speed.
  3. Workpiece material: when processing plastic materials, the lower the plasticity and the higher the hardness of the workpiece material, there will be scaling, scaling and hardening, and the surface roughness will be smaller. Therefore, the surface roughness of high carbon steel, medium carbon steel and quenched and tempered steel is smaller than that of low carbon steel. When processing cast iron, the surface roughness value of cutting cast iron is larger than that of steel because the chip is of crumbling type.