Checking Fixture
The design structures of inspection tools are diverse. This tool has unique performance, making the product more precise. Automotive inspection tools are mainly used for determining and adjusting the accuracy of molds during the production preparation stage, as well as for daily management of dimensions after mass production.
Checking Fixture: Inspection of Plastic and Metal Materials
A checking fixture is a special fixture used to check the hole position, peripheral shape, step difference, in-and-out volume, and other dimensions of parts with complex shapes. It is mainly divided into metal parts checking fixtures and plastic parts checking fixtures according to the material of the parts to be inspected.
The Structure of the Checking Fixture
According to the structure, checking fixtures are mainly divided into clamping mechanisms, positioning pins, inspection pins, inspection blocks, bases, sliding or flip inspection mechanisms, handheld inspection gauges, calibration mechanisms, and support columns. Its base is mainly a frame base and a plate base.
Traditional checking fixtures generally use 45 steel as the main material. Although it is strong and durable, it is also bulky and has poor mobility. With the popularization of lightweight concepts and the continuous advancement of lightweight technology, many new materials have been developed and invested in the manufacturing of checking fixtures, such as aluminum alloys, synthetic resins, bakelite, and carbon fiber. The density of new materials is much lower than that of structural steel, which can achieve lightweight checking fixtures.
From the structural classification of checking fixtures, inspection blocks, support columns, and bases account for most of their weight. The detection block is only used to detect the size of the product. After the product is clamped on the checking fixture, there is a gap between the product and the detection block (usually a 3mm gap), and the detection block does not need to bear the weight of other parts, so the strength requirement of the detection block is not high and does not need to be too large. However, the product may encounter the detection block during the assembly and disassembly process. Therefore, the strength and hardness requirements of the detection block are different for different types of products and factory environmental conditions. There are mainly two situations:
1.Metal Products
Generally, when the factory environment is poor, the product is easy to encounter the checking fixture during the assembly and disassembly process. It is recommended to choose structural steel for the detection block to ensure strength and wear resistance. If there is a requirement for lightweight and the factory environment is good, the detection block can choose aluminum alloy to reduce weight. If there is a requirement for wear resistance of the detection block, the aluminum alloy can be anodized. If there is a high requirement for lightweight, the factory is equipped with a special measurement room, and wood substitute materials can be selected. Commonly used wood substitute material grades are 460 and 5166. 460 wood substitute is relatively light and not very hard, which is suitable for temporary checking fixtures. For mass production of formal checking fixtures, it is recommended to choose wood substitute materials with higher density and higher hardness.
2.Plastic Products
Because it is relatively soft, the detection block can choose an aluminum alloy or wood substitute to achieve lightweight. Similarly, if the factory environment is poor, it is recommended to choose aluminum alloy for the detection block; if the lightweight requirement is high and the factory environment conditions are good, the detection block can choose a wood substitute to further reduce weight.
The support column mainly connects the positioning block, detection block, clamping, and other mechanisms and the bottom plate. The support column needs to bear the weight of the positioning block, detection block, and clamping mechanisms connected to it, so there are certain requirements for the strength of the support column, and it needs to ensure sufficient strength. If the mechanism on the support column is large and heavy, it is recommended that the support column choose structural steel material. In general, aluminum alloy can be selected for the support column to reduce weight.
Key Points of Checking Fixture
Checking fixture is used for inspecting and verifying both plastic and metal parts in industries like automotive and aerospace. Here are some key points on how checking fixtures are utilized for plastic and metal parts:
1.For Plastic Parts:
- Plastic checking fixture has locating elements like pins, clamps, and nests to accurately position and secure the plastic part for inspection.
- They integrate checking devices like go/no-go gauges, bore gauges, and height gauges to inspect critical dimensions of the plastic part against specifications.
- Checking surfaces/masters are used to check gaps, flushness, and surface profiles of the plastic part by using feeler gauges, templates, etc.
- Mirrors, borescopes, and other visual aids allow for inspecting internal features or hard-to-reach areas of complex plastic parts.
- Some plastic checking fixtures are designed for use with coordinate measuring machines (CMMs) and have integrated probes to take point measurements on the part surface.
2.For Metal Parts:
- Metal checking fixtures, especially for sheet metal stampings, have robust locating elements like datum pins/plates to establish part datums per drawings.
- They use checking surfaces, masters, and linear gauges to verify critical dimensions like hole locations, trim lines, flatness, etc. on stamped metal parts.
- Go/no-go gauges and slide calipers are employed to inspect hole sizes, radii, and other geometric dimensioning and tolerancing (GD&T) requirements.
- Checking fixtures for castings/machined metal parts integrate gauges to inspect complex geometries and surface finishes.
- Automated checking fixture uses sensors, and encoders for automated dimensional verification of high-volume metal parts.
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