2020 – Page 83 – CNC Machining & Turning, Milling, Metal parts

Factors affecting the dimensional accuracy of CNC machining

、 Preventable factors affecting dimensional accuracy of CNC machining

1. Processing technology

Most of the essential machining deviations are formed by different machining process theories. In order to ensure the basic machining process (such as “first rough and then fine, first surface and then hole, first large surface and then small surface” in milling numerical control machining, or “reduce the number of clamping, although select combined clamp” and other basic machining process details in fixture application), the machining deviation of iron chips to aluminum parts is reduced For the aluminum is very soft, the iron scraps removed are very simple to form processing deviation. For example, in FANUC or Huazhong machining center, although the g83 instruction is used to drill deep holes, the scrap iron may be removed instead of the G73 instruction.

2. Numerical calculation in manual programming and automatic programming

3. Three factors of cutting: cutting speed VC, feed F, cutting depth AP and tool compensation

In this respect, in simple words, under the condition of ensuring the machining quality and tool wear, adjust the parameters to fully develop the tool cutting function, so that the cutting efficiency is the highest and the machining cost is the lowest.

In the CNC lathe, there are some factors such as compensation for tool wear. Because I haven’t touched the lathe for a long time, I dare not talk about it in detail. Please search by myself.

4. Inaccurate tool setting is also a factor to form dimensional deviation. Therefore, although a good edge finder is selected, if the machine tool has an automatic tool setting device, it will be better

2、 Irresistible factors:

1. Cooling deformation of workpiece after processing

This is basically impossible to prevent, although in the processing of attention to the use of coolant, and in place measurement, attention to the workpiece deformation after cooling.

2. Stability of machine tool itself

If it is not a new machine tool or the machine tool has been processed a lot without debugging, the size deviation formed by the machine tool itself will appear. There are several factors to form the deviation of machine tool itself:

Mechanical

a. Loose between servo motor and lead screw

b. Ball screw bearing or nut worn

c. Insufficient smoothness between lead screw and nut

Electrical:

a. Servomotor obstacle

b. There is dirt inside the grating ruler

c. Servo amplifier obstruction

PMC recovery can be carried out for system parameters, so it is omitted

You need to know what non-standard parts are before processing

The non-standard parts processing professionals elaborate that if the country does not set strict standards and specifications, there is no related parameter regulations, other parts are under the control of the enterprise. There are many kinds of non standard parts, and there is no standard classification at present. The general classification is as follows:

Metal non standard parts:

The drawings are provided by the customer, and the manufacturer swindles the equipment according to the drawings to produce the corresponding products. Usually, there are more molds, yamen runner’s requirements, and the brightness are all in the customer’s regulations, and there is no positive paradigm. Products from forging to finishing need corresponding quality control. The process is complex and variable, and the cost is usually higher than the standard parts.

Non metallic non standard parts:

It is the processing of some non-metallic materials. For example, plastic, wood, stone, etc., in recent years, the development of injection molding industry and plastic mold has been increasingly refined. The quotation of curved surface design and programming numerical control has greatly improved the cost of non-standard processing and the grade of yamen runner.

Some tips of CNC machining programming

1. Using computer simulation system

With the development of computer technology and the constant enlargement of NC machining education, there are more and more NC machining simulation systems and their performance is improving day by day. Therefore, it can be used to start the inspection program and watch the tool movement to determine if there is a possibility of collision.

2. Using the simulation performance of CNC machining center

Generally, the more advanced CNC machining centers have graphic performance. After inputting the program, it is advisable to call graphic simulation to show the performance and watch the moving path of the tool in detail, so as to check whether the tool may collide with the workpiece or fixture.

3. Idling performance of CNC machining center

Using the idling performance of CNC machining center, we can check the accuracy of tool path. When the program is input into CNC machining center, it is advisable to install the tool or workpiece, and then press the idle operation button. At this time, the spindle does not rotate, and the worktable automatically operates according to the program track. At this time, it is advisable to find out whether the tool may collide with the workpiece or fixture. However, in this case, it must be ensured that when the workpiece is installed, the cutter cannot be installed; when the cutter is installed, the workpiece cannot be installed, otherwise there will be collision.

4. Locking performance of CNC machining center

Generally, CNC machining centers have locking performance (full lock or single shaft lock). When the program is entered, the z-axis is locked and the collision can be inferred from the z-axis coordinate value. The use of this performance should avoid tool change and other operations, otherwise the program cannot pass.

5. The configuration of coordinate system and cutter compensation must be accurate

When starting the CNC machining center, it is sure to configure the CNC machining center reference point. CNC machining center working coordinate system should be maintained as the same as programming, which is more and more z-axis target. If there is a mistake, it is quite possible for the milling cutter to collide with the workpiece. For the rest, the configuration of tool length compensation must be accurate. Otherwise, it is either empty machining or collision.

6. Raise programming skills

Programming is an important part of NC machining. To improve programming technology, we can prevent some unnecessary collisions at a great level.

For example, when milling the inner cavity of workpiece, the milling cutter is required to return to 100mm above the workpiece quickly. If programming with N50 G00 x0 Y0 Z100, the CNC machining center will linkage the three axes, and the milling cutter may collide with the workpiece, resulting in the breakage of the cutter and the workpiece, which will affect the accuracy of the CNC machining center, the following programs N40 G00 Z100; N50 x0 Y0 can be selected; That is to say, the tool first moves back to 100 mm above the workpiece, and then returns to the programming zero point, so as to avoid collision.

In a word, to be in charge of the programming technology of CNC machining center can improve the machining efficiency and quality, and prevent unnecessary errors in machining. This requires us to constantly sum up experience in practice and constantly increase, so as to further strengthen the strength of programming and processing

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