How to detect the surface quality problems in the process of automobile stamping die processing?

To detect the surface quality problems in the process of automobile stamping die processing, visual inspection, roughness measurement, hardness inspection and flaw detection are usually used. The following are specific introductions:

visual detection

Direct observation: inspectors directly observe the surface of the mold with naked eyes to see if there are obvious defects such as knife marks, scratches, pits, air holes and sand holes. This method is suitable for detecting large and obvious surface defects, but it may be difficult to detect small defects.

Tools: You can use magnifying glass, endoscope and other auxiliary tools to observe, which can more clearly see the nuances of the mold surface and help to find tiny cracks, pinholes and other defects that are difficult to identify with the naked eye. For example, using a magnifying glass of 5-10 times can observe smaller defects on the surface of the mold.

Roughness measurement

Roughness measuring instrument: this is a common testing tool, which measures the surface roughness by moving the stylus on the die surface. It can accurately measure the micro-roughness of the die surface, such as Ra (arithmetic mean deviation of contour), Rz (ten-point height of micro-roughness) and other parameters, so as to judge whether the surface roughness meets the requirements. Different automobile stamping dies have different requirements for surface roughness. Generally speaking, the surface roughness of the die is higher, and the Ra value usually needs to reach 0.8-1.6μm or even lower.

Hardness detection

Hardness tester: the hardness of the mold surface is tested by hardness tester, such as Rockwell Hardness Tester and Vickers Hardness Tester. Different durometers are suitable for different materials and hardness ranges. For example, for die steel with high hardness, HRA or HRC scale of Rockwell hardness tester can be used for measurement; Vickers hardness tester is more suitable for soft materials or when micro-area hardness needs to be measured. The hardness of the die surface should meet the design requirements, and uneven hardness may lead to local wear or deformation of the die during use.

Flaw detection

Penetrant inspection: coating the penetrant containing color dye or fluorescent agent on the surface of the mold to make it penetrate into the defects such as cracks on the surface, then removing the excess penetrant and coating the developer, and judging whether there are cracks and other defects on the surface by observing the traces displayed on the developer. This method can detect the surface crack of the opening, but it may not be able to detect the internal crack or shallow surface crack.

Magnetic particle flaw detection: It is suitable for molds made of ferromagnetic materials. By applying magnetic particles to the mold surface, when there are cracks and other defects on the surface, a leakage magnetic field will be formed at the cracks, and the magnetic particles will be absorbed to form magnetic marks, thus showing the position and shape of the defects. Magnetic particle inspection can only detect ferromagnetic materials, but it is not applicable to non-ferromagnetic materials.

Ultrasonic flaw detection: based on the principle that ultrasonic waves will reflect, refract and scatter when they encounter defects in the mold, it is judged whether there are defects inside and on the surface of the mold by analyzing ultrasonic signals. It can detect internal and surface cracks, pores and other defects, but the qualitative and quantitative analysis of defects is relatively complicated, which requires professional technicians to operate and judge.

X-ray flaw detection: Through X-ray or γ-ray penetrating the mold, different images are formed on the negative film to judge the type, size and position of the defect according to the different absorption and scattering degrees of the ray at the defect and the normal part. X-ray flaw detection can detect tiny defects inside and on the surface of the mold, but the equipment cost is high and radiation protection should be paid attention to.

optical measurement

Optical microscope: The surface of the mold can be magnified by dozens or even hundreds of times, and its microstructure and surface morphology can be observed, and defects such as scratches, wear and micro cracks on the surface can be detected. For example, through the optical microscope, we can observe the tiny scratches on the die surface caused by tool wear during machining, and the changes of surface structure caused by improper heat treatment.

Three-dimensional optical measuring instrument: based on the optical principle, the three-dimensional scanning measurement of the mold surface can obtain the accurate shape and size information of the mold surface, which can not only detect the macro defects of the surface, but also analyze the micro-morphology of the surface, such as surface fluctuation and waviness. It can be compared with the design model, showing the deviation of the die surface intuitively, and providing accurate data support for subsequent processing adjustment and quality improvement.