Views: 0 Author: Site Editor Publish Time: 2022-05-04 Origin: Site
Fixture in the final analysis is: positioning and clamping
The purpose is only one: not deformation
This is a summary of the industry people fixture design, but things are far from so simple, we have found in the process of contact with various solutions there will always be some initial design positioning, clamping is not very good solution, so, then innovative solutions will lose practical significance, understand positioning and clamping basic knowledge, In order to fundamentally ensure the integrity of fixture design and processing scheme.
When positioning from the side of the workpiece, the same as the support, the 3 point principle is the most basic principle. This is the same principle as the support principle, called the three-point principle, which is derived from the principle that three points not on the same line determine a plane. Three of the four points can determine one surface, so a total of four surfaces can be determined, but no matter how it is positioned, it is quite difficult to keep the fourth point in the same plane.
Bring 3 points
For example, when four fixed height positioners are used, only three points at a certain point can contact the workpiece, and the possibility that the remaining fourth point does not contact the workpiece is very large.
Therefore, when configuring the locator, it is generally based on three points, and the distance between these three points should be increased as much as possible.
In addition, when the locator is configured, the direction of the processing load needs to be confirmed in advance. The direction of processing load is also the direction of the handle/tool, in the direction of the end of the positioning, can directly affect the overall accuracy of the workpiece.
Generally in the workpiece blank surface positioning, the use of bolt type adjustable positioner, in the workpiece machining surface positioning, the use of fixed type (workpiece contact surface after grinding) positioner.
When positioning with holes machined in the workpiece prior to the process, the use of tolerance pins for positioning. By matching the precision of the workpiece hole with the precision of the pin shape, the positioning precision can be combined according to the fitting tolerance.
In addition, in the use of pin positioning, the general use of a straight pin and a diamond pin, so the assembly and disassembly of the workpiece will become more convenient, there will be few workpiece and pin stuck.
Of course, it is also possible to adjust the fitting tolerance so that both pins use straight pins. For more accurate positioning, a straight pin and a diamond pin are usually the most effective.
When using a straight pin and a diamond pin, usually the configuration direction of the diamond pin (contact with the workpiece) and the straight pin and the diamond pin vertical line into 90°, such configuration is to angular positioning (workpiece rotation direction).
Knowledge of clamping device
1. clamping device classification
1） clamping device pressed from above
The clamping device from the top of the workpiece clamping deformation is the least, and the workpiece processing is the most stable, so in general, the first consideration is from the top of the workpiece clamping. The most common clamps pressed from above the workpiece are manual mechanical clamps. For example, the pine-leaf clamp is shown below. The clamping device composed of pressure plate, stud, jack and nut is called the "loose leaf" clamping device.
2）A clamping device that clamps from the side
Originally, the clamping method from the top of the workpiece is the most stable accuracy, workpiece processing load is the smallest. But the workpiece above the need for processing, or clamping from the workpiece above is not very appropriate, resulting in not clamping from the workpiece above, you can choose to clamp from the side of the workpiece. But the workpiece is relatively clamped from the side will produce a floating force, how to eliminate this force, is must be in the design of fixture attention.
3）A clamping device that tightens the workpiece from down
When the thin plate workpiece is processed on the surface, it cannot be clamped from the top, and it is not reasonable to clamp it from the side. It can only be clamped from the bottom. When pulling the workpiece from below, if the workpiece is made of iron, it is usually possible to use a magnet clamp. Non-iron metal workpiece, generally can use the way of vacuum suction cup to tighten.
4）Clamp with hole clamp
When using 5-axis machining machine for multi-surface simultaneous processing or mold processing, in order to prevent fixture and tools from affecting the processing, it is generally appropriate to choose the way of using hole clamping. Compared with the way of tightening and clamping from the top of the workpiece, the way of using the hole clamping has less load on the workpiece, which can effectively deform the workpiece.