According to different positioning characteristics, there are generally three clamping methods for precision parts processing: direct alignment method, planning alignment method and fixture clamping method.
Direct aligning method: Direct aligning method refers to the method of using dial indicator, drawing pin or visual inspection to directly find the design datum of the workpiece surface on the machine tool to obtain the correct position. In this clamping method, the surface to be aligned is the positioning reference for the workpiece. For example, for sleeve parts, in order to ensure a uniform machining allowance when punching, please pre-clamp the sleeve in a four-jaw single-action chuck, and then use a pointer or dial indicator to align the surface of the inner hole to make The axis is coaxial with the rotation center of the machine tool, and then the workpiece is clamped. Therefore, the positioning reference is the inside of the hole rather than the outer circle of the supporting surface. This method is suitable for single-piece small batch production.
Planning and alignment method: This clamping method is to mark the workpiece on the machining surface, and then align the straight line on the machine tool to obtain the correct position of the workpiece during the machining process. On the planer, you can align the clamping device according to the marking line. When aligning, a suitable paper or copper sheet can be placed on the bottom of the workpiece to get the correct position. You can also support the workpiece on multiple jacks and adjust the height of the jacks to obtain the workpiece. At this time, the bottom surface of the supporting workpiece has no positioning function, and the positioning reference line is a drawn line. This method is mainly used for small batch, low precision and large precision parts processing.
Fixture positioning: a positioning method that directly uses the positioning elements on the fixture to obtain the correct position of the workpiece during the processing of precision parts. The machine tool fixture refers to the additional device of the machine tool, which is used to clamp the workpiece during the machining process. There are two commonly used fixtures, general fixtures and special fixtures. The three-jaw self-centering chuck of the lathe and the flat vise of the milling machine are the most commonly used general fixtures and special fixtures.
