Monthly Archive September 29, 2020

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.

The touch of the first generation iPad back shell with CNC technology has a certain particle sense. In terms of internal design, the internal performance of the first generation iPad back shell is relatively rough, the fixation method of internal screws and the design of “baffle” are relatively abrupt, and the overall design sense of the back shell is poor. However, the existence of the stripe design can better provide space for components and ensure the performance of the product. The thickening design at the back shell key position can ensure the fixed mode of the function key to a certain extent.

In addition, the internal screw fixing method and “baffle” design of the iPad using CNC technology are more prominent. It can be seen that the preliminary CNC process applied to flat products is still relatively rough. There are still many areas to be improved in the internal design. However, the strict product precision and outstanding texture make the process superior to the injection molding and stamping molding process. Of course, this is only the initial CNC process, so what progress has been made in this process? Let’s go on to look.

CNC processing technology tends to be mature. Nokia N1 and iPad air2 adopt this technology. With the development of CNC technology, more and more tablet products are applied. The most representative ones are Apple’s latest series of tablet ipadir2 and Nokia N1 tablet computer. Both of these two products adopt CNC technology on the back shell. What are the improvements in technology and design?

Nokia N1 uses the latest CNC technology back shell, which improves the process and makes the appearance more beautiful. In terms of CNC processing, the products made by this process are more “slim”, the overall visual and sensory impact of the back shell is enhanced, and the product appearance becomes more exquisite (of course, this is also related to the upgrading and improvement of the screen), and the surrounding border becomes more rounded, not a rigid “frame” shape Design, more comfortable to hold, the change can be said to be a technological improvement.

Nokia N1 peripheral border becomes more rounded, not a rigid “frame” design. In addition, there are some improvements in the details of the key position, so that the key position does not stay on the side border, but is close to the back plate to a certain extent. In this way, the thickness of the body is reduced and the user’s operation is not affected. It can be said that killing two birds with one stone. To a certain extent, the realization of the design also depends on the improvement of the process.

The details of the key position are also improved to facilitate operation, but also more beautiful. The concave design of the interface has also been improved in the previous technology. There is a certain gap between the two key positions. The design makes the volume key position and the shutdown key set adjacent, which makes the side of the machine more beautiful.

The precision of CNC process perfectly supports the design with the close distance between two key positions. It can be seen that the appearance of today’s CNC technology has been greatly improved compared with that before. The round frame, more refined appearance and more mature grinding technology are available. The high-precision grinding fuselage will have a kind of industrial design aesthetic feeling. But these are only the improvement of appearance process, so whether the inner process of the back shell is also improved? Please go on to see.

The classification of machining is as follows:

Design datum: the datum used to determine the position of other points, lines and planes on the part drawing, which is called design datum.

Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, the process datum of die and mould can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

(3) Positioning datum: the datum used for workpiece positioning during machining, which is called positioning datum. For the surface (or line, point) as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning datum in the following processes, and the positioning surface is called the precise datum. Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, process datum can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

(3) Positioning datum: the datum used for workpiece positioning during machining, which is called positioning datum. For the surface (or line, point) processed by CNC as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning reference in the following processes, and the positioning surface is called the precise reference.

In the process of turning a blank into a finished product, the total thickness of the metal layer cut off on a machining surface is called the total machining allowance of the surface. The thickness of the metal layer cut by each process is called the machining allowance between processes. For the rotating surface such as outer circle and hole, the machining allowance is considered from the diameter, so it is called symmetrical allowance (i.e. bilateral allowance), that is, the actual thickness of the metal layer cut off is half of the machining allowance on the diameter. The machining allowance of the plane is the unilateral allowance, which is equal to the actual thickness of the metal layer removed. The purpose of leaving machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as the surface cold and hard layer, air hole and sand inclusion layer on the casting surface, oxide scale, decarburization layer and surface crack on the forging surface, internal stress layer and surface roughness after cutting. The precision and surface roughness of the workpiece are improved. The size of machining allowance has great influence on machining quality and production efficiency. If the machining allowance is too large, it not only increases the labor of machining, reduces the productivity, but also increases the consumption of materials, tools and power, and increases the processing cost. If the machining allowance is too small, it can not eliminate all kinds of defects and errors in the previous process, and can not compensate for the clamping error in this process, resulting in waste products. The selection principle is to make the allowance as small as possible on the premise of ensuring the quality.