In the machining process, errors are inevitable. However, there are ways to minimize that situation to ensure the accuracy of the CNC machine and CNC machine automotive parts. This article Import CNC Machine will inform you about the accuracy of CNC machines and in-depth research methods. To help you reduce errors and operate the machine better.

Causes affecting CNC machining accuracy

Precision of CNC machine

The accuracy of the machine in the idle state is called geometrical accuracy. Depending on the accuracy of the CNC machine, they are divided into 4 types:

• The machine has normal accuracy.
• Similarly, The machine has a relatively high accuracy.
• The machine has high precision.
• Moreover, the machine has very high accuracy.

What are the factors affecting accuracy of the CNC machine automotive parts?

When checking the accuracy of the CNC machine automotive parts, it is necessary to determine the following factors:

• Geometric accuracy and relative position of surfaces for positioning workpieces and cutting tools.
• Motion accuracy of machine actuators on guide mechanisms.
• Similarly, machining precision and surface roughness.
• Accuracy of the linear position of the actuators when changing the direction of motion.
• Furthermore, accuracy returns to the original position of the actuators.
• Possibility of stable displacement of actuators to a specified point.
• In addition, curve interpolation accuracy and tool position stability after automatic feed execution.

CORRECTIVES OF INTERINTERNAL SETTINGS AND INTERNAL MODES

The error of the interpolator has a significant effect on the CNC machine automotive parts error. For the interpolator, the geometric error (error of the executed trajectory relative to the set trajectory) depends on the angle of inclination of the trajectory relative to the coordinate axes and does not exceed the pulse value per detail paragraph.

For new generation CNC machines the value of ∆ is in the range of 0.001÷0.002 mm. Therefore it does not affect the machining error much; however it does affect the surface roughness.

DIFFERENCE OF CURRENT METHOD

When applying straight line interpolation to contour details, the approximate method must be used to determine the coordinates of the points. This will cause machining errors. To reduce machining errors, the approximation step must be reduced. That is, decrease ∆Ꝕ.

Knife ADJUSTMENT DIFFERENCE

Modern measuring CNC machine automotive parts have very high accuracy (gradations up to 0.001mm). And the projection magnification is up to 30 times. However, even though the accuracy of the devices is very high, there are still errors, due to measuring instrument errors and tool clamping errors on the machine when adjusting to size.

MACHINE ADJUSTMENT DIFFERENCE

Machine adjustment error is determined synthetically when adjusting the tool, adjusting the machine’s mechanisms and jigs, taking into account the factors that occur during machining to achieve the required tolerance dimensions. The relative position of the technological system (machine – tool – fixture – part) is called “adjustable size”.

Knife

Tool wear has a great influence on machining errors, especially when making parts from refractory materials and high-strength materials.

TECHNOLOGY SYSTEM STRUCTURE

The technology system includes: machine, knife, CNC machine automotive parts, jig – work piece. During machining, the system is elastically deformed under the action of shear force. In addition, the cutting force also causes contact deformation between the components in the technology system. These two types of deformation have a great influence on machining errors in CNC machines. This error decreases gradually over the operations.

Methods of studying machining accuracy on CNC machines

In machine building technology, the most widely used distribution rules to study machining accuracy are:

STANDARD RULE OR GAUSS LAW

In fact, the diameter dimensions or the length dimensions in CNC machine automotive parts are distributed according to this rule.

STANDARD RULES OR SIMSON’S RULES

When the rigidity of the technology system is not high, the machining size is usually distribute according to this rule.

LAW of Eccentricity

Shape errors (oval, taper, multi-sided. And the relative position errors (eccentricity, face-to-face, parallelism, perpendicularity) are all distributed according to this rule.

Distribution rules of machined dimensions

• Standard Law
• Raw of triangles
• Law of Eccentricity
• Law of Equal Probability
• A combination of the normal and the uniform probability

Graph method of points

The study of machining accuracy using the distribution curve method (distribution law) does not reflect the change in accuracy over time.  Meanwhile, the method of plotting points avoids the above disadvantages of the distribution rule method. According to the method of plotting points, on the horizontal axis is the ordinal number of the work pieces over time, and on the vertical axis represents the machining size.

Graph of points

1. Outer processing
2. Inner processing

One of the factors that cause CNC machine automotive parts defects over time is tool wear. Therefore, when programming machining on a CNC machine, it is possible to enter a value of tool wear correction in the program. But still have to rely on the results of checking the machining dimensions.

Accuracy graph method

Machining accuracy research methods such as distribution curve method and point plot method are only effective when the parts are large enough. Meanwhile, the accuracy graph method allows studying the variation of machining accuracy (error) over time even with a small number of parts.

If we choose a small number of details to study in a short period of time of a shift, we can evaluate the accuracy and stability of the operation throughout the entire shift. Applying the precise graphing method to study operations on CNC machine automotive parts allows reducing waste and improving machine use efficiency.

Method to ensure machining accuracy on CNC machines

To achieve the accuracy of the part when machining on CNC machines, an automatic method of dimensioning must use. The essence of this method is to calculate the displacement of the actuator (of the machine). And solve the dimension string to determine the displacement precision. The dimension series call the sum of the related dimensions to form a closed contour.

Adjusting the tool size on the outside of the machine

To adjust the direction outside the CNC machine automotive parts, we must have a specialized jig. Furthermore, this method allows for high accuracy, but has the following disadvantages:

• The dimension sequence has shorter positioning but is more complex.
• Failure to compensate for positioning errors, rotational errors of the rotor head and not promoting the superiority of the multi-blade alloy piece (because the superiority of the alloy piece is the ability to quickly rotate on the machine).