Method for measuring thickness of film layer of injection molded part

Abstract

The invention discloses a method for measuring the thickness of a film layer of an injection molded part. The method comprises the following steps: S1, obtaining a sample: separating the sample from the surface of a coating of a to-be-measured product by using a cutting tool; s2, preparing a sample: placing the sample on a substrate, and cutting the sample by using a cutting tool to obtain a to-be-detected sheet; and S3, observation and measurement: placing the to-be-measured sheet on an objective table of an optical measurement device, adjusting the observation condition to a clear state, and measuring the thickness of the coating layer presented by the section of the to-be-measured sheet by using the measurement function of the optical measurement device. The detection efficiency can be improved, and the detection cost is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and in particular to a method for measuring the film thickness of injection molded parts. Background Technology

[0002] In the manufacturing sectors of automobiles, home appliances, and consumer electronics, accurate measurement of the thickness of coatings (such as primers, color coats, and clear coats) applied to the surface of injection-molded parts is a crucial aspect of quality control. The thickness and delamination structure of the coating directly affect the product's appearance, corrosion resistance, mechanical properties, and service life. Therefore, developing accurate, efficient, and low-cost methods for measuring coating thickness has significant industrial application value.

[0003] Film-based thickness measurement: This method requires the use of a special film thickness gauge for indirect measurement. Although fast, it is costly, cumbersome, and cannot measure the coating layer by layer of the product itself.

[0004] Non-destructive scanning thickness measurement: This method uses non-contact scanning and is highly efficient. However, it can usually only measure the total thickness of the coating and cannot distinguish and measure the thickness of each layer, making it difficult to meet the inspection requirements of layering processes.

[0005] Traditional metallographic sectioning involves preparing samples through mounting, grinding, and polishing, allowing direct observation and measurement of layer thickness under a microscope with accurate results. However, this method is complex, time-consuming (1-2 hours), and costly, and generates an irritating odor during sample preparation. Therefore, current technologies struggle to achieve rapid, low-cost, and easy-to-operate testing while maintaining measurement accuracy (especially layer separation capability), which has become a significant bottleneck in improving production quality control efficiency. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for measuring the film thickness of injection molded parts, which can improve detection efficiency and significantly reduce detection costs.

[0007] A method for measuring the film thickness of an injection-molded part according to a first aspect embodiment of the present invention includes: S1. Sample Acquisition: Use a cutting tool to separate the sample from the coating surface of the product to be tested; S2. Sample preparation: The sample is placed on a substrate and cut using a cutting tool to obtain a thin film to be tested; S3. Observation and Measurement: Place the sheet to be tested on the stage of the optical measuring device, adjust the observation conditions to a clear state, and use the measurement function of the optical measuring device to measure the coating layer thickness of the cross section of the sheet to be tested.

[0008] A method for measuring the film thickness of injection molded parts according to an embodiment of the present invention has at least the following advantages: It eliminates the complex and time-consuming pretreatment processes required by traditional metallographic sectioning methods, such as mounting, curing, lengthy grinding, and polishing. From sampling and sample preparation to observation and measurement, the entire process can be completed within minutes, achieving rapid coating detection. This method does not rely on expensive metallographic mounting materials, specialized mounting equipment, or a series of grinding consumables. It only requires conventional cutting tools and ordinary optical measuring devices (such as microscopes with measuring functions), significantly reducing equipment investment and material costs per test.

[0009] According to some embodiments of the present invention, in step S1, the cutting tool is an engraving knife, and the product tilt angle is 20°±5° when sampling.

[0010] According to some embodiments of the present invention, in step S1, the sampling length is 0.8 cm to 1.2 cm.

[0011] According to some embodiments of the present invention, in step S2, the cutting tool is a single-edged blade, and the blade is kept vertical during cutting.

[0012] According to some embodiments of the present invention, in step S2, the width of the sheet to be tested is 1 mm to 2 mm.

[0013] According to some embodiments of the present invention, in step S2, when cutting the sample, the sample is cut from both ends respectively, so that the sheet to be tested has two cross-sections that can be measured.

[0014] According to some embodiments of the present invention, in step S2, the substrate is white paper.

[0015] According to some embodiments of the present invention, in step S3, adjusting the observation conditions includes: adjusting the magnification of the optical measuring device to 200x to 300x.

[0016] According to some embodiments of the present invention, in step S3, the measurement function of the optical measuring device is a plane measurement parallel line function.

[0017] According to some embodiments of the present invention, after step S3, a cleaning step is further included: adding a protective cover to the cutting tool, resetting the stage and magnification of the optical measuring device, and finally turning off the power and cleaning the site.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of the method for testing a thin sheet according to an embodiment of the present invention.

[0020] Figure reference numerals: Thin film under test 100; Substrate 110. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0023] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0024] In the description of this invention, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of these terms in this invention in conjunction with the specific content of the technical solution. In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0025] Reference Figure 1 This invention discloses a method for measuring the film thickness of injection molded parts, comprising: S1. Sample Acquisition: Use a cutting tool to separate the sample from the coating surface of the product to be tested; S2. Sample preparation: Place the sample on the substrate 110 and cut the sample using a cutting tool to obtain the thin film 100 to be tested; S3. Observation and Measurement: Place the sheet to be measured 100 on the stage of the optical measuring device, adjust the observation conditions to a clear state, and use the measurement function of the optical measuring device to measure the coating layer thickness shown on the cross section of the sheet to be measured 100.

[0026] This method eliminates the complex and time-consuming pretreatment processes required by traditional metallographic sectioning, such as mounting, curing, and lengthy grinding and polishing. From sampling and sample preparation to observation and measurement, the entire process can be completed within minutes, enabling rapid detection of coatings. Furthermore, this method does not rely on expensive metallographic mounting materials, specialized mounting equipment, or a series of grinding consumables. It only requires conventional cutting tools and ordinary optical measuring devices (such as a microscope with measuring functions), significantly reducing equipment investment and material costs per test.

[0027] In step S1, the cutting tool is an engraving knife, and the product tilt angle during sampling is 20°±5°. The engraving knife's tip is typically sharp and thin-edged; its geometry allows it to easily wedge into the interface between the coating and the substrate or within the coating itself with minimal cutting force and precise control, thus initiating the peeling process. Compared to ordinary knives, it is more suitable for fine cutting and prying of coatings with smooth surfaces and relatively soft textures. The tip can more easily penetrate the coating edge at a sharp angle, reducing frontal resistance. As it advances forward, the tilt angle creates an upward component of the force, which helps to "pry" the coating from the substrate or separate it along the layering interface, rather than simply "scraping" the substrate, thus making it easier to obtain a complete sample block representing the true layered structure. The specific tilt angle optimizes the mechanical operation, allowing the engraving knife to more smoothly and completely peel out the sample block containing each coating, greatly reducing the risk of sample breakage, delamination tearing, or excessive deformation during sampling.

[0028] In step S1, the sample length is 0.8 cm to 1.2 cm. This provides ample operating space and a gripping area for subsequent handheld vertical cutting with a blade. The operator can firmly hold both ends of the sample with their fingers, ensuring a smooth and precise cutting motion, thereby efficiently preparing thin slices that meet the requirements.

[0029] In step S2, the cutting tool is a single-edged blade, which is kept perpendicular during cutting. The single-edged blade has an extremely thin and exceptionally sharp cutting edge, enabling clean cutting of coated samples (especially relatively soft or fragile coatings) with minimal force. This minimizes compression, tearing, or deformation of the cut surface during cutting, thereby protecting the original layered structure of the coating.

[0030] In step S2, the width of the section 100 to be tested is 1 mm to 2 mm. A section with a width of 1 mm to 2 mm is of moderate size and weight. When it is placed flat on the microscope stage, it has sufficient contact area and stability and is not easily tipped over, slipped or warped due to stage rotation, slight vibration or airflow.

[0031] In step S2, the sample is cut from both ends, giving the sheet 100 two measurable cross-sections. Having two cross-sections means that if one section is unsuitable for measurement due to imperfect cutting (e.g., slight tilt, debris attachment, or localized damage), the other section can be immediately observed without resampling or recutting. This avoids the scrapping of the entire sample and rework due to a single cutting failure, significantly improving the overall success rate and efficiency of each sample preparation attempt. Since the two cross-sections originate from different locations on the same sample (although close together), the two measurement results can be compared. If the results are consistent or close, it proves the reliability of the measurement data and the uniformity of the sample coating. If differences exist, it indicates potential localized unevenness in the coating, requiring further examination or additional measurements, thus making the final conclusion more scientific and representative.

[0032] In step S2, the substrate 110 is white paper. The high-contrast background solves the problem of quickly locating small samples on complex work surfaces, enabling the operator to instantly visually position the sample. During cutting, the relative position of the blade and the sample edge can be clearly seen, achieving more precise control of the cutting point, which is crucial for preparing thin slices only 1-2 mm wide.

[0033] In step S3, adjusting the observation conditions includes adjusting the magnification of the optical measuring device to 200x to 300x. The single-layer thickness of coatings (such as primer, color paint, and clear coat) on automotive injection molded parts is typically on the order of several micrometers to tens of micrometers. At a magnification of 200x to 300x, the microstructure at this scale can be sufficiently magnified to a size easily discernible and precisely manipulated by the human eye. At this magnification, the interfaces, textures, and potential defects (such as bubbles and impurities) of each coating layer can be effectively revealed.

[0034] In step S3, the optical measuring device performs a planar parallel line measurement. The operator manually or semi-automatically sets two parallel virtual reference lines on the sample cross-section image displayed on the monitor. The software automatically calculates the vertical distance between these two parallel lines and displays the distance value directly and in real-time in length units (e.g., micrometers) based on the system's currently calibrated pixel-to-size correspondence. Under a microscope, the coating cross-section appears as a banded region with clearly defined upper and lower boundaries (each coating layer corresponds to one band). The parallel line function perfectly suits this geometry. The operator only needs to align one line with the upper interface of a coating and the other with its lower interface; the software can then automatically and accurately calculate the normal thickness of the coating without requiring complex visual estimation or mechanical vernier measurements.

[0035] Following step S3, a cleaning step is also included: protective covers are fitted to the cutting tools, the stage and magnification of the optical measuring device are reset, and finally, the power is turned off and the work area is cleaned. Immediately fitting protective covers to used engraving knives, single-edged blades, and other sharp cutting tools physically isolates the exposed cutting edges, avoiding the risk of accidental cuts or damage to the blades themselves. Adjusting the magnification to its lowest setting (usually the objective lens at its lowest magnification position) ensures the optical components are in a stable state with minimal stress and a compact structure, preventing damage to high-magnification objectives from accidental impacts or vibrations when not in use. Providing a uniform and defined initial state for the next power-on helps maintain the stability of the measurement reference and reduces systematic errors that may be introduced due to inconsistent equipment conditions.

[0036] Preparation before testing: Engraving tool (blade width approximately 2mm) and plastic protective sleeve. Brand new single-edged blade (industrial grade) and plastic protective sleeve. A4 white printing paper (as substrate 110). Video microscope with CMOS camera (model: VMS-200), whose software has a planar measurement parallel line function, with a maximum magnification of 500x.

[0037] Testing Steps: S1. Sample Acquisition: Place the car door panel trim strip to be tested flat on the workbench and select a smooth, central area as the sampling point. The operator presses the product down with their left hand to hold it in place, while holding a carving knife in their right hand. Slightly lift one side of the sampling point to create an angle of approximately 20°. Gently wedge the tip of the carving knife into the edge of the coating and smoothly and slowly advance it forward to remove a strip of sample approximately 1 cm in length. The sample should contain all three layers: primer, color coat, and clear coat, and should be separated from the plastic substrate.

[0038] S2. Sample Preparation: Lay a fresh sheet of A4 white paper flat on the workbench. Place the strip sample obtained in S1 in the center of the paper. Its high contrast makes the black sample clearly visible. Gently hold both ends of the sample with your left index finger and thumb to fix it in place. Hold a single-edged blade in your right hand, keeping the blade perpendicular to the paper. First, quickly and vertically cut down on one end of the sample (about 2 mm from the end), cutting the sample. Then, quickly and vertically cut down again on the other end of the sample (about 1-2 mm from the new end). Finally, a thin slice 100 with a width of about 1.5 mm is obtained. Because the slice is cut from both ends, it has two fresh, parallel cross-sections (side A and side B).

[0039] S3. Observation and Measurement: Turn on the video microscope and initially adjust its magnification to 100x. Carefully pick up the thin slice with tweezers, placing it with one cross-section (side A) facing upwards and stably centering it on the microscope stage. Rotate the XY platform movement knob on the microscope to find a clear image of the coating cross-section on the display screen. Rotate the zoom ring to gradually increase the magnification to 250x (within the optimal range of 200-300x), while fine-tuning the focus to achieve the clearest interface between the primer, color coat, and clear coat. In the microscope's accompanying measurement software, select the "Plane Measurement" - "Parallel Line" function. On the clear cross-sectional image, move the mouse to first draw a parallel line close to the outer surface of the clear coat layer (at the top), then draw another parallel line close to the interface between the clear coat and color coat layers. The software automatically calculates and displays the vertical distance between the two parallel lines, which is the thickness of the clear coat layer (e.g., reading: 15.2 μm). Record this data in a table. Using the same method, measure the thickness of the paint layer (distance between the upper and lower interfaces of the paint layer) and the thickness of the primer layer (distance between the upper and lower interfaces of the primer layer). If a certain point on surface A is unclear, gently flip the slice with tweezers and use the cross-section on surface B to perform the above measurements to ensure that valid data is obtained.

[0040] S4. Cleaning and Resetting: After measurement, immediately cover the used engraving tools and single-edged blades with protective covers and place them in the designated toolbox. Use tweezers to remove the sample slices from the stage and dispose of them properly. Lower the microscope stage to its lowest position using the controller. Adjust the microscope magnification back to the lowest setting (e.g., 50x). Turn off the power to the video microscope. Clean the work surface, discard the used white paper, and wipe the work surface with a cloth to keep the area clean.

[0041] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for measuring the film thickness of an injection-molded part, characterized in that, include: S1. Sample Acquisition: Separate the sample from the coating surface of the product to be tested using a cutting tool; S2. Sample preparation: The sample is placed on a substrate and cut using a cutting tool to obtain a thin film to be tested; S3. Observation and Measurement: Place the sheet to be tested on the stage of the optical measuring device, adjust the observation conditions to a clear state, and use the measurement function of the optical measuring device to measure the coating layer thickness of the cross section of the sheet to be tested.

2. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, In step S1, the cutting tool is an engraving knife, and the product tilt angle is 20°±5° when sampling.

3. A method for measuring the film thickness of an injection-molded part according to claim 1 or 2, characterized in that, In step S1, the sampling length is 0.8cm to 1.2cm.

4. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, In step S2, the cutting tool is a single-edged blade, and the blade is kept vertical during cutting.

5. A method for measuring the film thickness of an injection-molded part according to claim 1 or 4, characterized in that, In step S2, the width of the sheet to be tested is 1 mm to 2 mm.

6. The method for measuring the film thickness of an injection molded part according to claim 5, characterized in that, In step S2, when cutting the sample, it is cut from both ends of the sample so that the sheet to be tested has two cross-sections that can be measured.

7. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, In step S2, the substrate is white paper.

8. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, In step S3, adjusting the observation conditions includes adjusting the magnification of the optical measuring device to 200 to 300 times.

9. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, In step S3, the measurement function of the optical measuring device is a plane measurement parallel line function.

10. The method for measuring the film thickness of an injection molded part according to claim 1, characterized in that, After step S3, a cleaning step is also included: adding a protective cover to the cutting tool, resetting the stage and magnification of the optical measuring device, and finally turning off the power and cleaning the site.

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