(1) to ensure the quality of plate and frame filter machining needs. When in rough machining parts due to a large amount of metal is removed, so will produce larger cutting force and cutting heat, at the same time also need large clamping force, under the action of the force and heat, parts will produce a large deformation. After rough machining and parts of internal stress redistribution, will result in deformation of parts. If not classified processing stage and continuous processing, will not be able to avoid and correct the above reasons caused by the machining error. After processing stage, divided into rough machining error caused by the through semi-finishing and finish machining can be fixed, and gradually improve the machining accuracy and surface quality of the parts, to ensure the parts processing requirements.

(2) the needs of the rational use of machine tool equipment. Rough machining generally require the use of power is great, good rigidity, high productivity and precision of machine tool equipment. And finishing with the high precision machine tool equipment, after processing stage can be divided into rough and finish machining equipment into full play their respective performance characteristics, avoid using, accomplish the rational use of the equipment. Such not only improves the efficiency of rough machining, and it also helps maintain the accuracy of finish machining equipment and service life.

(3) plate and frame filter blank defects in time. The various defects of blank (such as porosity, sand holes, slag or insufficient machining allowance, etc.) can be found after rough machining, facilitate timely repair or to decide whether to scrap, so as not to continue processing after a waste of time and processing costs.

(4) easy to arrange heat treatment. Machining process of heat treatment process was divided into several stages, such as precision spindle after rough machining for artificial aging treatment to remove the stress, semi-finishing after quenching treatment, low temperature tempering and cold processing, after finishing the final finishing process. This heat treatment is the whole process is divided into rough machining, semi-finishing, finish machining, finishing processing stages.