Surface roughness and flatness are not the same concept. There is no special connection between them.

Surface roughness refers to the unevenness of the processed surface with small spacing and tiny peaks and valleys. The distance (wave distance) between the two wave crests or two wave troughs is very small (less than 1mm), which is a microscopic geometric shape error. The smaller the surface roughness, the smoother the surface.

Flatness refers to the deviation of the macroscopic concave and convex height of the substrate relative to the ideal plane. The tolerance zone is the area between two parallel planes whose distance is the tolerance value t. Flatness belongs to the shape error among the shape and position errors, and it belongs to the macro geometric shape error.

Extended information:

1. Surface roughness measurement method

1. Comparison method

The comparison method is simple to measure and can be used in workshops On-site measurement, often used for measurements on medium or rough surfaces. The method is to determine the roughness value of the measured surface by comparing it with a roughness sample marked with a certain value. Methods that can be used for comparison: visual inspection when Ra > 1.6μm, magnifying glass when Ra1.6~Ra0.4μm, and comparison microscope when Ra < 0.4μm.

When comparing, the processing method, processing texture, processing direction, and material of the sample are required to be the same as the surface of the tested part.

2. Stylus method

Use a diamond stylus with a tip radius of curvature of about 2 microns to slowly slide along the measured surface. The up and down displacement of the diamond stylus is determined by an electrical length sensor. It is converted into an electrical signal, and after amplification, filtering and calculation, the surface roughness value is indicated by the display instrument. A recorder can also be used to record the profile curve of the measured section.

Generally, measuring tools that can only display surface roughness values ??are called surface roughness measuring instruments, while those that can record surface profile curves are called surface roughness profile meters.

Both measuring tools have electronic calculation circuits or computers, which can automatically calculate the arithmetic mean deviation of the profile Ra, the ten-point height of micro-irregularity Rz, the maximum height of the profile Ry and other various evaluation parameters. , high measurement efficiency, suitable for measuring surface roughness with Ra ranging from 0.025 to 6.3 microns.

2. Common methods for measuring flatness errors

1. Flat crystal interference method: Use the working surface of an optical flat crystal to represent an ideal plane, and directly determine the degree of curvature of the interference fringes. Measure the flatness error value of the surface. It is mainly used to measure the flatness error of small surfaces, such as the working surface of the gauge and the measuring surface of the micrometer probe.

The plane is composed of straight lines, so the ruler method, optical collimation method, optical self-collimation method, gravity method, etc. in straightness measurement are also suitable for measuring flatness error. When measuring flatness, first measure the straightness of several sections, and then define the values ??of each measuring point according to the flatness tolerance zone (see shape and position tolerance). Use graphical methods or calculation methods to perform data processing to obtain the flatness error. . There are also methods of measuring plane errors using light wave interference method and flat plate painting method.

2. Meter measurement method: The meter measurement method is to place the measured parts and the micrometer on a standard flat plate, use the standard flat plate as the measurement reference surface, and use the micrometer to measure point by point along the actual surface. Or measure along several straight lines.

The meter measurement method is divided into three-point method and diagonal method according to the evaluation datum plane: The three-point method uses the ideal plane determined by the three farthest points on the actual surface being measured as the evaluation datum. When measuring the surface, first adjust the three farthest points on the actual surface to be measured to the same height as the standard flat plate; when measuring by diagonal method, first adjust the four corner points on the actual surface according to diagonal lines to equal heights. high.

Then use a micrometer to measure. The maximum variation measured by the micrometer on the entire actual surface is the flatness error of the actual surface.

3. Liquid level method: The liquid level method uses the liquid level as the measurement reference plane. The liquid level is composed of the liquid level in the "connected tank", and is then measured with a sensor. This method is mainly used to measure the flatness error of large planes.

4. Beam plane method: The beam plane method uses a calibrated telescope and a sighting target mirror for measurement, and selects the beam plane formed by the three farthest points on the actual surface as the measurement benchmark for flatness error. noodle.

5. Laser flatness measuring instrument: The laser flatness measuring instrument is used to measure the flatness error of large planes.

6. Use a data collector to connect a dial indicator to measure the flatness error.

Measuring instruments: deflection meter, dial indicator, data acquisition instrument.

Measurement principle: The data collector can read data from the dial indicator in real time and calculate and analyze the flatness error. The flatness error calculation formula has been embedded in our data collector software, which is completely There is no need to manually calculate tedious data, which can greatly improve the accuracy of measurement.

Baidu Encyclopedia-Surface Roughness

Baidu Encyclopedia-Flatness