1. Classification of measuring instruments
A measuring instrument is an instrument that has a fixed form and is used to reproduce or provide one or more known quantities. Different measuring tools can be divided into the following categories according to their use:
1. Single value measuring tool
A gage that can only reflect a single value. It can calibrate and adjust other measuring instruments or directly compare them with the measured value as a standard quantity, such as gauge blocks, angle gauge blocks, etc. CNC MACHINING AUTO PART
2. Multi-value measuring tool
A gauge that can represent a group of homogeneous values. Other measuring instruments, such as a line ruler, can be calibrated, adjusted, or compared directly with the measurement as a standard quantity.
3. Special measuring tool
A gauge designed to test a specific parameter. Common ones are the smooth limit gauge for checking smooth cylindrical holes or shafts, the thread gauge for judging the qualification of internal or external threads, the test template for judging the qualification of surface contours of complex shapes, and the function of simulating assembly passability to test assembly accuracy gauges, etc.
4. Universal measuring tool
In our country, measuring instruments with relatively simple structures are called universal measuring tools. Such as vernier calipers, outer micrometers, dial indicators, etc.
2. Technical performance indicators of measuring instruments
1. The nominal value of the measuring tool
The quantity marked on the measuring tool indicates its characteristics or guides its use. For example, the size marked on the gauge block, the size marked on the ruler, the angle marked on the angle gauge block, etc.
2. Graduation value
On the ruler of a measuring instrument, the difference between the magnitudes is represented by two adjacent scale lines (minimum unit magnitude). If the difference between the values represented by two adjoining scale lines on the micrometer cylinder of an outer micrometer is 0.01mm, the graduation value of the measuring instrument is 0.01mm. The division value is the smallest unit value that a measuring instrument can directly read. It reflects the reading accuracy level and the measurement accuracy of the measuring instrument.
3. Measuring range
Within the allowable uncertainty, the range from the lower limit to the upper limit of the measured value that the measuring instrument can measure. For example, the measurement range of an outer micrometer is 0 to 25 mm, 25 to 50 mm, etc., and the measurement range of a mechanical comparator is 0 to 180 mm.
4. Measuring force
In the process of contact measurement, the contact pressure between the probe of the measuring instrument and the surface to be measured is measured. Too much measurement force will cause elastic deformation, and too little measurement force will affect the stability of the contact.
5. Indication error
The difference between the indicated value of a measuring instrument and the actual value being measured. Indication error is a comprehensive reflection of various errors of the measuring instrument itself. Therefore, the indication error is different for different working points within the indication range of the instrument. Generally, a gauge block or other measurement standard of appropriate precision can be used to verify the indication error of the measuring instrument.
3. Selection of measuring tools
Before each measurement, it is necessary to select the measurement tool according to the unique characteristics of the part to be measured. For example, calipers, height gauges, micrometers, and depth gauges can be used for length, width, height, depth, outer diameter, and level difference; micrometers can be used for shaft diameters. , calipers; plug gauges, block gauges, and feeler gauges can be used for holes and grooves; right angle rulers are used to measure the right angle of parts; R gauges are used to measure R-value; Use three-dimensional and two-dimensional; use hardness tester to measure the hardness of steel.
1. Application of calipers CNC ALUMINUM PART
Calipers can measure the inner diameter, outer diameter, length, width, thickness, level difference, height, and depth of objects; calipers are the most commonly used and most convenient measuring tools and are the most frequently used measuring tools on the processing site.
Digital caliper: resolution 0.01mm, used for dimensional measurement with small tolerance (high precision).
Table card: resolution 0.02mm, used for regular size measurement.
Vernier caliper: resolution 0.02mm, used for roughing measurement.
Before using the caliper, remove the dust and dirt with clean white paper (use the outer measuring surface of the caliper to jam the white paper and then pull it out naturally, repeat 2-3 times)
When using a caliper to measure, the measuring surface of the caliper should be as parallel or perpendicular to the measuring surface of the object to be calculated as possible;
When using depth measurement, if the measured object has an R angle, it is necessary to avoid the R angle but close to the R angle, and the depth gauge and the estimated height should be kept as vertical as possible;
When the caliper measures the cylinder, it needs to be rotated, and the maximum value is obtained for the segmental measurement;
Due to the high frequency of caliper users, maintenance work must be done to the best of its ability. After using it daily, it must be wiped clean and put into the box. Before use, a measuring block is required to check the accuracy of the caliper.
2. Application of Micrometer
Before using the micrometer, use clean white paper to remove dust and dirt (use the micrometer to measure the contact surface and the screw surface to jam the white paper and then pull it out naturally, repeat 2-3 times), then twist the knob to measure the contact When the surface and the screw surface are in quick contact, use fine-tuning instead. When the two surfaces are in complete contact, zero-adjust, and the measurement can be performed.
When the micrometer measures the hardware, mobilize the knob. When it is in close contact with the workpiece, use the fine-tuning knob to screw in, and stop when it hears three clicks, clicks, and clicks, and read the data from the display screen or scale.
When measuring plastic products, the measuring contact surface and the screw lightly touch the product. CUSTOMIZED METAL TURNING PART
When measuring the diameter of a shaft with a micrometer, measure at least two or more directions and measure the micrometer in the maximum measurement in sections. The two contact surfaces should always be kept clean to reduce measurement errors.
3. Application of height gauge
The height gauge is mainly used to measure height, depth, flatness, verticality, concentricity, coaxiality, surface vibration, tooth vibration, depth, and height gauge. First, check whether the probe and each connection part are loose when measuring.
4. Application of feeler gauge
The feeler gauge is suitable for themeasuringatness, curvature, and straightness.
Flatness measurement:
Place the part on the platform, and use a feeler gauge to measure the gap between the part and the platform (Note: The feeler gauge and the platform are kept pressed without gaps during measurement)
Straightness measurement:
Place the part on the platform, make one rotation, and use a feeler gauge to measure the gap between the part and the platform.
Curvature measurement:
Place the part on the platform and select the appropriate feeler gauge to measure the gap between the two sides or the middle of the part and the platform.
Squareness measurement:
Place one side of the right angle of the zero to be measured on the platform, make the other side close to the square, and use a feeler gauge to measure the most significant gap between the part and the square.
5. Application of plug gauge (pin):
It is suitable for measuring the inner diameter, groove width, and clearance of holes.
Suppose the hole diameter of the part is significant, and there is no suitable needle gauge. In that case, the two plug gauges can be overlapped, and the plug gauge can be fixed on the magnetic V-shaped block by measuring in a 360-degree direction, which can prevent loosening and is easy to measure.
Aperture measurement
Inner hole measurement: When the hole diameter is measured, the penetration is qualified, as shown in the figure below.
Note: When measuring the plug gauge, it must be inserted vertically, not obliquely.
6. Precision measuring instrument: two-dimensional
The second element is a high-performance, high-precision, non-contact measuring instrument. The sensing element of the measuring instrument is not in direct contact with the surface of the measured part, so there is no mechanical action of the measuring force; the second element transmits the captured image through the data line to the data acquisition card of the computer using projection, and then It is imaged on the computer monitor by the software; various geometric elements (points, lines, circles, arcs, ellipses, rectangles), distances, angles, intersections, geometric tolerances (roundness, straightness, parallelism, verticality) on the parts can be performed (degree, inclination, position, concentricity, symmetry) measurement. They can also produce CAD output for 2D drawings of outlines. Not only can the contour of the workpiece be observed, but the surface shape of the opaque workpiece can also be measured.
Conventional geometric element measurement: The inner circle in the part in the figure below is a sharp angle, which can only be measured by projection.
Observation of electrode processing surface: The lens of the second element magnifies the roughness inspection after electrode processing (magnifying 100 times the image).
Small size deep groove measurement
Gate detection: During mold processing, some gates are often hidden in the groove, and various testing instruments cannot measure them. At this time, rubber paste can be attached to the glue gate, and the shape of the glue gate will be printed on the glue. , and then use the second element to measure the size of the glue print to obtain the gate size.
Note: Since there is no mechanical force during the two-dimensional measurement, the two-dimensional measurement should be used as far as possible for thinner and softer products.
7. Precision measuring instrument: three-dimensional
The characteristics of the three-dimensional element are high precision (up to μm level), versatility (it can replace a variety of length measuring instruments), the ability to measure geometric aspects (in addition to the elements that the two-dimensional element can measure, it can also measure cylinders, cones), Geometric tolerance (in addition to the geometric tolerance that the two-dimensional element can measure, it also includes cylindricity, flatness, line profile, surface profile, coaxial), complex profiles, as long as the three-dimensional probe Where it can be touched, its geometric size, mutual position, and surface profile can be measured; and data processing can be completed with the help of a computer; with its high precision, high flexibility, and excellent digital capabilities, it has become an essential part of modern mold manufacturing and quality assurance: Means practical tools.
Some molds are being modified, and there is no 3D drawing file. The coordinate value of each element and the outline of the irregular surface can be measured and exported by drawing software and made into 3D drawings according to the measured elements, which can be processed and modified quickly and without error. (After the coordinates are set, you can take any point to measure the coordinates).
3D digital model import comparison measurement: To confirm the consistency with the design of the finished parts or find the fit abnormality during the fit mold assembly process, when some surface contours are neither arcs nor parabolas, but some irregular surfaces, when the geometric element measurement cannot be performed, the 3D model can be imported, and the parts can be compared and measured, to understand the processing error; because the measured value is a point-to-point deviation value, it can be easily corrected and improved quickly and effectively (the data shown in the figure below is the actual measured value) Deviation from the theoretical value).
8. Application of hardness tester
The commonly used hardness testers are Rockwell hardness tester (desktop) and Leeb hardness tester (portable). Rockwell HRC, Brinell HB, and Vickers HV are widely used hardness units.
Rockwell hardness tester HR (benchtop hardness tester)
The Rockwell hardness test method is to use a diamond cone with an apex angle of 120 degrees or a steel ball with a diameter of 1.59/3.18mm, press it into the surface of the tested material under a particular load, and obtain the hardness of the material from the depth of the indentation. The hardness of the material can be divided into three different scales, namely, HRA, HRB, and HRC.
HRA is the hardness obtained with a 60 kg load and a diamond cone indenter for rigid materials—for example, carbide.
HRB is the hardness obtained using a 100 kg load and a hardened steel ball with a diameter of 1.58mm and is used for materials with lower hardness—for example, annealed steel, cast iron, etc., and alloy copper.
HRC is the hardness obtained with a 150 kg load and a diamond cone indenter fortoughd materials. —forxample, hardened steel, tempered steel, quenched and tempered steel, and some stainless steel.
Vickers hardness HV (mainly for surface hardness measurement)
Suitable for microscopy analysis. With a load within 120kg and a diamond square cone indenter with an apex angle of 136°, press into the material's surface, nd measure the diagonal length of the indentation. It is suitable for hardness determination of larger workpieces and deeper surface layers.
Leeb Hardness HL (Portable Hardness Tester)
Leeb hardness is a dynamic hardness test method. During the impact process of the impact body of the hardness sensor with the measured workpiece, the ratio of the rebound speed to the impact speed when it is 1mm away from the workpiece surface is multiplied by 1000, defined as the Leeb hardness value.
Advantages: The Leeb hardness tester manufactured by Leeb Hardness Theory changes the traditional hardness testing method. Because the hardness sensor is as small as a pen, it can directly test the hardness of the workpiece in various directions on the production site by holding the sensor, making it difficult for other desktop hardness testers.
Post time: Jul-19-2022