Yearly Archive September 29, 2020

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.

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.

In large-scale computer gong processing, the workpiece can enter the automatic processing stage after the alignment and program debugging are completed. In the process of automatic machining, the operator should monitor the process of cutting to prevent the quality problems and other accidents caused by abnormal cutting. Monitoring the quality of cutting tools largely determines the machining quality of the workpiece. In the process of automatic machining and cutting, the normal wear condition and abnormal damage condition of cutting tools should be judged by means of sound monitoring, cutting time control, pause inspection during cutting and workpiece surface analysis. According to the processing requirements, the cutting tools should be treated in time to prevent the processing quality problems caused by the cutting tools not handled in time. Monitoring the cutting process mainly considers the following aspects:

Monitoring of cutting sound in the process of automatic cutting, the sound of cutting tool cutting workpiece is stable, continuous and light, and the movement of the machine tool is stable. With the cutting process going on, when there are hard points on the workpiece, tool wear or tool clamping, the cutting process will become unstable. The instability performance is that the cutting sound changes, the tool and workpiece will collide with each other, and the machine tool will vibrate. At this time, the cutting parameters and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine tool should be suspended to check the condition of cutting tools and workpieces.

The main consideration of rough machining in process monitoring is the rapid removal of excess allowance on the workpiece surface. In the process of automatic machining, according to the set cutting parameters, the tool automatically cuts according to the predetermined cutting path. At this time, the operator should pay attention to observe the change of cutting load in the process of automatic machining through the cutting load table, and adjust the cutting parameters according to the bearing force of the cutter, so as to give full play to the maximum efficiency of the machine tool.

Finish machining process monitoring finishing, mainly to ensure the machining size and surface quality of the workpiece, high cutting speed and large feed rate. At this time, we should pay more attention to the effect of chip accretion on the machined surface. For cavity machining, we should also pay attention to the over cutting and tool passing at the corner. To solve the above problems, the first is to adjust the spray position of cutting fluid to keep the machined surface in the best cooling condition at all times; the second is to observe the quality of the machined surface of the workpiece, so as to avoid the quality change as much as possible by adjusting the cutting parameters. If the adjustment still has no obvious effect, we should stop to check whether the original procedure is reasonable. Special attention should be paid to the position of the tool when the inspection is suspended or stopped. If the tool stops in the cutting process and the spindle stops suddenly, tool marks will be generated on the surface of the workpiece. In general, when the tool leaves the cutting state, the shutdown should be considered.

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.

When machining the surface of aircraft and automobile parts, impeller, computer gong, propeller and various curved surface forming molds, the CNC machining center can ensure the accuracy requirements of special-shaped parts and curved surfaces, and greatly improve the processing efficiency. Next, let’s take a look at how the CNC machining center processes the special-shaped parts and curved surfaces?

In the latter, it is the most important to prepare the whole machining process, and the most important thing for the latter is to finish the machining process according to the machining process The most important and important job.

Through the application of UG software in recent years, Shandong Weiwei Heavy Industry Machine Tool Co., Ltd., a manufacturer of CNC machining center, has summed up a set of NC programming methods suitable for all kinds of complex surfaces according to the common technical difficulties in the manufacturing process. The process of computer gong machining includes: establishing mathematical model, determining machining coordinate system, planning cutter location source file, etc.

1、 Establish mathematical model

Before establishing the model, we should first consider the order and method of establishing the features of the model. What should be done first, what should be done later, what method should be used, and what kind of modeling function should be used. This relationship must be properly dealt with when building a mathematical model.

2、 Determine the machining coordinate system

The establishment of solid model is based on working coordinate system, while the generation of machining tool location source file of CNC machining center is based on machining coordinate system. The position of the coordinate origin of the machining coordinate system should be convenient for the processor to quickly and accurately set the tool and to facilitate the size calculation needed in the processing process.

3、 Planning tool location source file

According to the structural characteristics of different product profiles, we can select three processing modules with their own characteristics, such as plane milling, computer gong machining cavity milling and fixed axis contour milling, to plan the machining tool location source files of various types of surfaces.

In a word, we should grasp the application characteristics of each module flexibly according to the different mold surface and contour surface, so that we can process the satisfied products with high quality and efficiency through the CNC machining center.