Basic requirements for fixture design

　　Due to the technical conditions of the product structure, the welding process and the specific conditions of the factory, there are different requirements for the selected and designed fixtures. At present, the common requirements for most fixtures used in the production of welded structures There are the following aspects:

　　1. The fixture should have sufficient strength and rigidity. The clamp must bear a variety of forces when it is put into use, such as the weight of the weldment, the clamping reaction force, the force caused by the welding deformation, and the eccentricity that may occur when the tool is turned over. Etc., so the fixture must have a certain strength and stiffness.

　　2, the reliability of clamping, can not damage the positioning position of the workpiece during clamping, and ensure that the shape and size of the product meet the requirements of the drawing, neither allow the workpiece to loosen and slip, nor make the workpiece constrained too large and produce a large The restraint stress, therefore, the force of the manual clamp operation should not be too large, and the action of the motorized compacting device should adopt the method of centralized control.

　　3, the flexibility of welding operation, the use of fixtures in production should ensure sufficient assembly welding space, so that operators have a good view and operating environment, so that the entire process of welding production is in a stable working state.

　　4. Facilitate the loading and unloading of the weldment. During operation, the component should be taken out of the fixture smoothly after assembly welding or welding. Also pay attention to the damage of the component when it is turned or lifted.

　　5, good processability, the designed fixture should be easy to manufacture, install and operate, easy to inspect, repair and replace wearing parts, design, but also consider the existing clamping force source, lifting capacity and installation site of the workshop Factors that reduce fixture manufacturing costs.

　　The basic method of fixture design:

　　In order to ensure that the designed fixture can produce the workpiece that meets the requirements, it is necessary to understand the characteristics and requirements of the workpiece in the production and its own construction. This is the basis for the design fixture, and is the original data that the designer should carefully study and master.

　　The original information of the fixture design includes the following:

　　The task description of the workpiece drawing number, the function of the fixture, the production batch, the requirements of the fixture and the position and role of the fixture in the manufacture of the workpiece, the task book is the basis for the fixture designer to accept the task.

　　The study pattern is to grasp the structure, dimensional tolerance and manufacturing accuracy level of the workpiece dimension chain. In addition, it is necessary to understand the parts that have a matching relationship with the workpiece, how they are related in manufacturing, and the technical conditions are to clarify that the pattern is not complete. Expressing problems and requirements, obtaining a complete concept of the technical requirements for workpiece production.

　　Technical conditions for fixture design:

　　This is the specific requirements of the assembly welding technician for the fixture according to the workpiece pattern and the process specification. Generally, the following should be included.

　　1. Use of the fixture: the connection between the process of using the fixture and the process before and after.

　　2. The position of the assembled workpiece in the fixture, the workpiece positioning reference, the positioning dimension, and the workpiece joint size are intermediate dimensions (specify machining allowance) or final dimensions.

　　3. When manufacturing and installing the fixture, the loading and unloading direction of the workpiece in the fixture should be considered, and the position of auxiliary equipment such as water and gas pipeline should be considered.

　　4. Put forward the principled opinions on the construction form of the fixture, whether to flip and move, and the positioning of the fixture and the mechanization procedure of the clamp.

　　5. Specify the amount of welding shrinkage of the workpiece to determine the position of the positioning member and the clamping member.

　　6. Standardization and standardization data for welding assembly fixtures, including national standards, enterprise standards, and standardized fixture structure drawings.

　　It should be pointed out that the large-scale mechanical equipment used in assembly welding production, such as displacement machinery and operation machinery, is mostly provided by specialized manufacturers. This section mainly introduces the design of the assembly fixtures that are commonly used in general.

　　Steps for fixture design:

　　The main toolings for determining the fixture structure, then sketching, and sketching are as follows.

　　Select the design basis for the fixture:

　　The fixture design basis should be consistent with the design basis of the assembled structure. The welding fixtures of adjacent structures with assembly relationship should select the same design reference as much as possible, such as the reference horizontal line and the vertical symmetry axis as the same design basis.

　　Draw the artifact diagram:

　　After the design basis is determined, the assembled workpiece drawing is drawn on the drawing by the two-dot chain line on the drawing, including the workpiece contour and the required joint position of the workpiece (note the shrinkage allowance).

　　Design of positioning and clamping parts:

　　Determine the positioning method of the part and the positioning point, the clamping force of the part and the requirements for the clamping force, and select the structural form, size and arrangement of the positioning part and the clamping part according to the positioning reference.

　　Tooling specific (skeleton) design:

　　The clip is specifically the basic component of the clamp on which the various components, mechanisms and devices required to form the clamp are mounted, and plays a role of supporting and connecting. The shape and size of the clamp depend on the outer dimensions of the workpiece, various components and The layout of the device and the nature of the processing, therefore, the design needs to meet the requirements of the welding process on the rigidity of the fixture, and determine the specific structural scheme and transmission scheme of the fixture according to the shape and size of the surface of the fixture component, such as determining the fixture structure. What are the components, the specific manufacturing method of the clip, and the use of several stages of transmission.

　　The basic requirements for the specific design of the tool holder mainly include 6 points:

　　1. It has sufficient strength and rigidity to ensure that the clamp works normally during assembly or welding, and does not cause unacceptable deformation and vibration under the action of clamping force, welding deformation restraint force, gravity and inertial force.

　　2, the structure is simple and light, under the premise of ensuring strength and rigidity, the structure is as simple and compact as possible, small in size, light in weight and easy to load and unload the workpiece, and can open windows, grooves, etc. in parts that do not affect strength and rigidity, to reduce the structure Quality, especially manual or mobile fixtures, generally do not exceed 10kg.

　　3, the installation is stable and reliable, the clip can be placed on the foundation of the workshop or installed on the workbench (frame) of the displacement machine. For stability, the center of gravity is as low as possible. If the center of gravity is high, the support area is correspondingly increased. The middle of the bottom surface is generally hollowed out to make the periphery protrude.

　　4, the structure of the process is good, should be easy to manufacture, assembly and inspection, the specific positioning of the base surface and the base surface of the installation of various components should be processed, if the casting should be cast 3mm-5mm boss to reduce processing Area, between the unmachined matte surface and the workpiece surface should ensure a certain gap, often take 8mm-15mm, so as not to interfere with the workpiece, if it is a smooth surface, take 4mm-10mm.

　　5, the size should be stable and have a certain precision, for the casting fixture to be aging treatment, the welding clip should be specifically annealed, each positioning surface, mounting surface should have appropriate size and shape accuracy.

　　6. Convenient cleaning. In the assembly and welding process, splashes, soot, slag shells, electrode heads, flux and other debris will inevitably fall into the fixture, which should be easy to clean.

　　Accuracy requirements for workpiece fixture manufacturing:

　　The accuracy of the welded structure is related to the accuracy of the preparation of each part and the dimensional accuracy in the middle of the machining process, and also depends to a large extent on the accuracy of the assembly-welding fixture itself, and the accuracy of the fixture mainly refers to the positioning dimension of the fixture positioning member. In terms of the tolerance of the position and size, this is determined by the accuracy of the workpiece to be welded. Therefore, it can be seen that the accuracy of the welded structure is closely related to the accuracy of the fixture.