How to realize lightweight checking fixtures
In the automobile development and production, the automobile checking fixture is a kind of special tool with high efficiency for quality control. The automobile is composed of thousands of parts, which are produced by the industrial chain composed of automobile factories and parts suppliers respectively. Quality problems will inevitably occur in the process of automobile development and production. When a quality problem occurs, the checking fixture is a good quality judgment standard to help analyze the problem. This may cause the parts supplier to transport the checking fixture to the automobile factory for verification. The measuring tool also needs to regularly recheck the accuracy of the CMM. In the early stage of product development, the product needs to be installed in the checking fixture and moved to the CMM for full size measurement. These will lead to the movement and disposal of the checking fixture in the automobile factory or the parts supplier. Therefore, the quality personnel pay great attention to the weight of the checking fixtures, which are light and easy to handle. This paper discusses and analyzes the light weight demand and development trend of checking fixtures from two aspects of inspection materials and structural technology.
- Light weight of checking fixture material
Traditional checking fixtures generally use 45 steel as the main material. Although it has high strength and durability, it has large volume and poor mobility. With the popularization of lightweight concept and the continuous progress of lightweight technology, many new materials, such as aluminum alloy, synthetic resin, bakelite, carbon fiber, have been developed and manufactured. From the structure classification of the checking fixtures, the inspection block, support column and base account for most of the weight of the checking fixtures, so the lightweight of the checking fixtures mainly starts from these three aspects. The detection block only detects the size of the product. When the product is clamped on the detector, there is a gap (usually 3) mm between the product and the detection block, and the detection block does not need to bear the weight of other parts, so the strength of the detection block is not required to be high, and it does not need to be done too much. However, the product may encounter detection blocks during loading and unloading. Therefore, for different types of products and factory environmental conditions, the strength and hardness requirements of detection blocks are different, mainly in the following two cases: first, for metal products, the factory environment is poor, and the product is easy to encounter detection blocks during loading and unloading. It is recommended to select structural steel for detection blocks to ensure strength and wear resistance. If there is a light weight requirement, and the factory environment is good, aluminum alloy can be selected to reduce the weight of the test block. If the abrasion resistance of the test block is required, the aluminum alloy can be anodized. If the requirement for lightweight is very high, the factory is equipped with a special measuring room, and you can choose to replace wood materials. The commonly used substitute wood brands are 460 and 5166460. The substitute wood is relatively light and has low hardness, which is suitable for temporary checking fixtures; For large-scale production, it is suggested to choose 516 with high density and high hardness to replace wood. Second, the plastic type block itself can achieve lightweight. Similarly, if the factory environment is poor, it is recommended to select aluminum alloy for testing the mold block; If the requirements for lightweight are high and the environmental conditions of the factory are good, you can choose to replace wood to further reduce weight.
The support column is mainly connected with the positioning block, detection block, clamping mechanism, etc. and the base plate. The support column needs to bear the weight of the above connected positioning block, detection block and clamping mechanism, 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 to select the structural steel material. Generally speaking, aluminum alloy can be selected for supporting column to reduce weight.
The base of the checking fixture is used to support all parts and products on the checking fixture, and ensure that the flatness of the measuring datum of the four corners of the base plate is 0.1mm. Therefore, there is a high requirement for the strength of the base, and it is necessary to ensure sufficient tensile strength and bending strength. The base is generally made of structural steel, aluminum alloy, bakelite, carbon fiber and other materials with high strength. In the first case, when the detection type block is made of structural steel and the support column is made of steel or aluminum alloy, the base needs to bear a large weight. At this time, the detection type base must be made of structural steel. In the second case, when the detection block and support column are made of aluminum alloy, the weight that the base needs to bear is not very large, so aluminum alloy can be used for weight reduction. In the third case, when the test block and support column are directly replaced with wood, the weight of the base is relatively light, and aluminum alloy materials can be selected. If the detection type is temporary detection type with high requirements for lightweight, bakelite materials can be used for the base. In the fourth case, there is a very high requirement for the detection type lightweight. High strength and low density carbon fiber materials can be selected as the frame base, and the detection type block can be selected as the substitute wood material. The detection type block and the detection type resin can be bonded to form a very high precision car front window through the paste resin. The lightweight of tools made of carbon fiber is first-class, but the cost is also rising. If there are certain requirements for lightweight and considering the cost, I suggest that the metal product detection block, support column and base should be made of aluminum alloy; The plastic product test block and support column shall be made of wood, and the base shall be made of aluminum alloy.
- Lightweight checking fixturestructure
In addition to using lightweight materials to reduce weight, the gauge can also reduce weight through structural optimization. Since the inspection block, support column and base occupy most of the weight of the checking fixture, the structural optimization will be analyzed from these three parts. First of all, the detection block is only used to measure the size of the product for reference, and it can mainly bear its own weight, so the design should be as small as possible. In some cases, the detection block is directly connected to the bottom plate, and no support column is required, so the detection block will be relatively large and can be hollowed out in the middle of the detection block. Second, the support column needs to support the weight of the positioning block, detection block and clamping mechanism, so it needs to ensure its own strength. When the supporting column supports more or larger parts, the volume of the supporting column will become larger, and if it is made into a solid, it will be very heavy. Two structural optimization methods are introduced here: (1) The support column is welded with flat plates, and the steel bars are welded at the overlap of flat plates to ensure the rigidity and strength of the support column. (2) For the integrated support column, when the volume is large, the weight can be reduced by drilling holes from the bottom of the support column. Third, the inspection base supports the inspection of all components and products on the equipment, and has high requirements on the strength of the base. If the components on the base are not dense and there is space, the base can be emptied to reduce weight on the premise of ensuring the strength and stiffness of the base.
This article introduces how to realize the lightweight of checking fixtures from the selection of checking fixture materials and the optimization of checking fixture structure, which can basically meet the requirements of most companies for the lightweight of checking fixtures. Although lightweight has many advantages, it is more expensive to choose materials with high strength and low density. Structural optimization and weight reduction will also increase processing costs. The lighter the checking fixture is, the higher the corresponding cost should be. Neither fish nor bear’s paw can have both. In fact, the competition in the automobile industry is very fierce, and the cost control is very strict, so we can’t blindly pursue the maximum lightweight, regardless of the cost, but we should comprehensively select materials according to the company’s own situation and needs, and find a balance between lightweight and cost.