The 3-2-1 method is a commonly used tooling fixture assembly method that helps designers and manufacturers determine the positioning and clamping method of a tooling fixture. This method is widely used in fields such as machining, manufacturing and assembly lines.
Specifically, the 3-2-1 method refers to using three reference points (Point 3), two reference faces (Side 2), and one reference edge (Side 1) to position and clamp the workpiece. The selection of these reference points, faces and edges is based on the workpiece geometry and manufacturing requirements.
Here are the detailed steps for the 3-2-1 method:
1. Reference point (point 3): Select three reference points of the workpiece. These points are three non-collinear positions on the workpiece. These points are usually located on the bottom of or inside the workpiece and provide stable positioning and clamping.
2. Reference surface (surface 2): Select two flat surfaces of the workpiece as reference surfaces. These surfaces should provide stable clamping and positioning. Typically, one plane serves as the datum and the other plane is used for vertical positioning.
3. Reference edge (edge 1): Select an edge of the workpiece as the reference edge. This edge is usually used to align the position of the workpiece to ensure the rotation or tilt direction of the workpiece.
With this 3-2-1 combination, the fixture can provide fixed positioning and clamping, ensuring accuracy and consistency of workpieces during machining or assembly. This method can simplify the fixture design and manufacturing process and improve production efficiency and product quality.
It is necessary to select reference points, faces and edges according to the specific workpiece shape, processing requirements and process flow, and design corresponding positioning and clamping devices to achieve accurate fixation.
It should be noted that although the 3-2-1 method can provide many advantages, it is not necessarily suitable for all workpieces and machining tasks. There are several aspects to consider when selecting reference points, faces, and edges:
1. Workpiece shape: The shape and structure of the workpiece will affect the selection of the corresponding reference surfaces and edges. Different workpiece shapes require different reference surfaces and edges to achieve stable clamping and positioning.
2. Processing requirements: The processing process has different requirements for the precision and accuracy of the workpiece. Appropriate reference points, faces and edges must be selected to achieve the necessary processing accuracy.
3. Production cost: The cost of manufacturing fixtures is an important factor restricting the design and manufacturing of fixtures. An economical and practical clamping solution must be selected to reduce production costs.
4. Production efficiency: The operation and adjustment time of the fixture have a direct impact on production efficiency. Designers need to choose a clamping solution that is as simple and easy to use as possible to improve production efficiency.
In summary, when designing tooling fixtures, appropriate reference points, surfaces, and edges should be selected based on factors such as specific workpiece shape, processing requirements, production cost, and production efficiency, and corresponding positioning and clamping devices should be designed. The 3-2-1 method provides a commonly used tooling fixture assembly method, but it also needs to be combined with the actual situation to evaluate the effect of use. 
