Fixture Testing
Fixture testing is a tool used in the inspection process to detect various sizes and shapes of products, which is of great help to product quality. The gauge standards need to meet the requirements of the product to assist in improving its quality.
Basic Principles of Fixture Testing
As a tool for controlling product quality, fixture testing has the advantages of intuitive data, high efficiency and accuracy, and convenient operation, and is widely used in the manufacturing industry. Checking fixtures is widely used in the automotive industry, as well as in industries such as aerospace, electronics, and mechanical manufacturing.
Combination Design of Fixture Testing
Firstly, design basic universal functional modules with the same functionality and connection elements but different structures for each unit of the product, such as parts, components, or assembly systems; Based on the prediction of user needs, design some adaptive universal functional modules with different functions but the same connecting elements.
There are four main directions for the development of automotive fixture testing design, namely modularization, serialization, and parameterization. In the innovative market environment, this development trend has particularly important significance for the survival, competition, and development of enterprises. Combination is the use of interchangeable universal components and specially designed specialized components to combine into specialized mechanical products. Modularization is a universal functional module based on functional analysis that can be interchanged to form products of the same type and multiple variants.
The use of modular combination technology in vehicle checking fixtures extensively employs universal units and components, overcoming the drawbacks of strong specificity and short development cycles of previous vehicle checking fixtures, and possessing the following advantages.
① Easy to Operate. In the combination of automobile fixture testing, the installation of components is generally fixed by two pins and two screws. These components can ensure that the error of every 100mm in the assembly of the checking fixture must be within the range of 0.1mm, and the cumulative error should not exceed 0.2mm. When adjusting the positioning block or inspection block in a certain direction, only the components need to be adjusted to achieve the required dimensional accuracy.
② Shorten the Manufacturing Cycle. In the design of a set of checking fixtures, the number of different types of standard parts selected can account for about one-third of the total parts. Therefore, during manufacturing, single-piece processing can be transformed into batch processing, which can save processing time and greatly shorten the processing cycle. The standardized parts of fixture testing promoted by Shanghai General Motors provide a good material library for modular assembly of fixture testing, as shown in Figure 1-13.
③ High Manufacturing Accuracy. The manufacturing accuracy of automotive fixture testing is based on each component that makes up the gauge, so it is necessary to control the accuracy of each component when manufacturing checking fixture. Due to the use of universal units in the design, the mechanical processing technology of components is good: qualified units and components are processed according to technical requirements, and the overall accuracy is greatly improved by combining and installing fixture testing.
Design of Flip Structure for Fixture Testing
The design of the flipping structure plays an important role, serving as a transition and connection. The flipping structure is commonly used to detect the contour clearance, surface difference, and hole position of parts, which is beneficial for the storage of workpieces.
Large car fixture testing may have important detection elements in the middle area, requiring transitional mechanisms to serve as bridges; Smaller car fixture testing has more testing elements and is more concentrated, making the corresponding structural design more cumbersome and requiring transition mechanisms for conversion.
This structure is suitable for complex and low activity space checking fixture, with the advantages of saving space, reliable structure, and simple operation. The flipping structure design of automotive fixture testing has the following requirements.
① Multiple flipping mechanisms must not interfere with each other.
② When there is a detection and positioning function device on the flipping mechanism of the car fixture testing, a limited position or buffering device must be used to avoid the large impact force generated by the rapid descent of the flipping plate, which may cause vibration of the fixture testing.
③ When designing the flipping mechanism of two or more adjacent car fixture testing, it is required that the flipping plate bracket be in the same direction and horizontal state, and the flipping mechanism should be as high and low as possible to achieve good processing technology and convenient debugging.
④ The simulation block mounted on the flip arm should not be too long, as the imbalance in proportion can easily result in low accuracy and short lifespan. If necessary, additional support should be designed to increase stiffness and ensure repeatability.
⑤ The rotation center of the flipping mechanism and the connected simulation block should be lower than the lowest point of the simulation block to avoid interference with the parts.
⑥ The flipping mechanism of the car fixture testing should be able to quickly and conveniently close, and should not interfere with other components when in the open state.
⑦ The flipping mechanism has friction, and the parts need to be quenched or tempered. The surface of the parts should have corrosion resistance and friction resistance.
General Assembly of Fixture Testing
- Preparation Work for Fixture Testing
Research and familiarize oneself with the assembly drawings, process documents, and technical requirements of the assembled equipment: understand the structure of the equipment, the functions of the parts, and their interrelationships, and inspect the types and quantities of the assembled parts (such as standard parts, purchased parts, etc.), especially for repair parts, special attention should be paid to inspection.
- Design Assembly Method
After the preparation work is completed, it is necessary to choose an appropriate assembly method based on the size, quantity, and type of the fixture testing. The reasonable application of assembly methods can greatly shorten assembly time and improve assembly quality. In addition, the fitter tools should also be prepared and arranged in advance to reduce retrieval time and improve assembly efficiency.
- Final Assembly Steps for Automotive Fixture Testing
① Select assembly reference parts. Determine the reference parts based on the interrelationships of the working parts of the automotive fixture testing, ease of assembly, and ease of ensuring assembly accuracy requirements.
② Determine the assembly sequence. Determine the assembly sequence based on the relationship and distance between the parts and the assembly reference parts, ensuring that installing the parts first is beneficial for the positioning and fixation of the parts to be installed later.
③ Self-inspection. After the assembly of the car fixture testing is completed, product trial assembly is carried out under existing production conditions to detect some problems that may exist during the use of the fixture testing.
④ Testing. The overall assembly steps of automotive fixture testing are to arrange the reference parts for assembly and the assembly sequence before final assembly. The installation sequence of automotive fixture testing is four steps: selecting assembly reference parts, determining assembly sequence, self-inspection, and inspection.
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