There is only one purpose for positioning and clamping: no deformation

In the process of contacting various solutions, we have found that there are always some positioning and clamping problems in the preliminary design. As a result, no matter how innovative the solution is, it will lose its practical significance. Understanding the basic knowledge of positioning and clamping can Fundamentally guarantee the integrity of fixture design and processing plan.

Locator knowledge

1. The basic principle of positioning from the side of the workpiece

When positioning from the side of the workpiece, as with the support, the three-point principle is the most basic principle. This is the same as the principle of the supporter. It is called the three-point principle, which is derived from the principle that "3 points on a straight line determine a surface." Among the 4 points, 3 points can determine a surface, so a total of 4 surfaces can be determined, but no matter how the positioning is done, it is quite difficult to make the 4th point in the same plane.

▲Three-point principle

For example, when using 4 fixed-height positioners, only 3 points in a certain place can touch the workpiece, and the possibility that the remaining 4th point does not touch the workpiece is still very high.

Therefore, when configuring the positioner, generally use 3 points as the reference, and increase the distance between these 3 points as much as possible.

In addition, when positioning the positioner, it is necessary to confirm the direction in which the machining load is applied in advance. The direction of the machining load is the direction of travel of the tool holder/tool. The positioning device at the end of the feed direction can directly affect the overall accuracy of the workpiece.

Generally, when positioning the blank surface of the workpiece, use a bolt-type adjustable positioner, and when positioning the workpiece surface, use a fixed type (workpiece contact surface is ground).

Second, the basic principle of positioning from the workpiece hole

When using the holes machined in the previous process of the workpiece for positioning, it is necessary to use a pin with tolerance for positioning. By matching the accuracy of the workpiece hole with the accuracy of the pin shape, and combining according to the fit tolerance, the positioning accuracy can reach the actual demand.

In addition, when using pins for positioning, generally one uses a straight pin and the other uses a diamond-shaped pin, so it will become more convenient to assemble and disassemble the workpiece, and it is rare that the workpiece and the pin are stuck.

▲Use pin positioning

Of course, it is also possible to use straight pins for both pins by adjusting the fit tolerance. For more precise positioning, it is usually most effective to use a straight pin and a diamond pin.

When using a straight pin and a diamond-shaped pin, usually the line of the arrangement direction of the diamond-shaped pin (contact with the workpiece) is perpendicular to the line of the straight pin and the diamond-shaped pin at 90°. This configuration is for the angle To positioning (the direction of rotation of the workpiece).

Knowledge of clamps

1. Classification of clamps

According to the clamping direction, it is generally divided into the following categories:

Next, let us look at the characteristics of various clamps.

1. Clamp pressed from above

The clamp that is pressed from the top of the workpiece has the least amount of deformation during clamping, and the workpiece is the most stable in processing, so in general, the first consideration is to clamp from the top of the workpiece. The most common type of fixture that is pressed from above the workpiece is a manual and mechanical fixture. For example, the following picture is called a "Matsuba type" clamp. The clamp composed of the pressure plate, stud bolt, jack, and nut is called the "loose leaf" clamp.

In addition, according to the shape of the workpiece, different shapes of pressing plates can be selected to correspond to various different shapes of workpieces.