(1) Trial cutting method
That is, first cut out a small part of the processing surface, measure the size obtained by trial cutting, adjust the position of the tool cutting edge relative to the workpiece according to the processing requirements, and then try cutting and measuring again. After two or three trial cutting and measuring, when the processed size meets the requirements, cut the entire surface to be processed. The trial cutting method is repeated through "trial cutting-measurement-adjustment-trial cutting" until the required dimensional accuracy is achieved. For example, the trial boring processing of the box hole system. The accuracy achieved by the trial cutting method may be very high, and it does not require complex equipment, but this method is time-consuming (requires multiple adjustments, trial cutting, measurement, and calculation), inefficient, and depends on the technical level of the workers and the accuracy of the measuring instruments. The quality is unstable, so it is only used for single-piece small batch production. As a type of trial cutting method, matching, it is a method of processing another workpiece that matches the processed workpiece based on the processed workpiece, or combining two (or more) workpieces together for processing. The requirements for the final processed size in matching are based on the matching requirements with the processed workpiece. (2) Adjustment method: Use samples or standard parts to adjust the accurate relative positions of machine tools, fixtures, tools and workpieces in advance to ensure the dimensional accuracy of the workpieces. Because the dimensions are adjusted in place in advance, there is no need for trial cutting during processing. The dimensions are automatically obtained and remain unchanged during the processing of a batch of parts. This is the adjustment method. For example, when using a milling machine fixture, the position of the tool is determined by the tool setting block. The essence of the adjustment method is to use the fixed-range device or tool setting device on the machine tool or a pre-adjusted tool holder to make the tool reach a certain position accuracy relative to the machine tool or fixture, and then process a batch of workpieces. Feeding the tool according to the dial and then cutting on the machine tool is also a type of adjustment method. This method requires first determining the scale on the dial according to the trial cutting method. In mass production, fixed-range blocks, samples, templates and other tool setting devices are often used for adjustment. The adjustment method has better processing accuracy stability than the trial cutting method, has higher productivity, and is not as demanding on machine tool operators, but is more demanding on machine tool adjusters. It is often used in batch production and mass production. (3) Fixed-sizing method The method of using the corresponding size of the tool to ensure the size of the processed part of the workpiece is called the fixed-sizing method. It uses standard-sized tools for processing, and the size of the processed surface is determined by the tool size. That is, tools with certain dimensional accuracy (such as reamers, reamer drills, drill bits, etc.) are used to ensure the accuracy of the processed part of the workpiece (such as holes). The fixed-sizing method is easy to operate, has high productivity, and has relatively stable processing accuracy. It is almost independent of the worker's technical level and has high productivity. It is widely used in various types of production. For example, drilling and reaming. (4) Active measurement method During the processing, the processing size is measured while processing, and after comparing the measured results with the design requirements, the machine tool is either allowed to continue working or stopped. This is the active measurement method. At present, the values in active measurement can be displayed digitally. The active measurement method adds the measuring device to the process system (that is, the unity of machine tools, tools, fixtures and workpieces), becoming its fifth factor. The active measurement method has stable quality and high productivity, and is the development direction. (5) Automatic control method This method is composed of measuring devices, feeding devices and control systems. It combines the measuring, feeding and control systems into an automatic processing system, and the processing process is completed automatically by the system. A series of tasks such as dimension measurement, tool compensation adjustment, cutting processing and machine tool parking are completed automatically to automatically achieve the required dimensional accuracy. For example, when processing on a CNC machine tool, the parts are controlled by various instructions of the program to control the processing sequence and processing accuracy. There are two specific methods of automatic control: ① Automatic measurement, that is, the machine tool has a device that automatically measures the size of the workpiece. When the workpiece reaches the required size, the measuring device issues a command to automatically retract the tool and stop working. ② Digital control, that is, the machine tool has a servo motor, a ball screw nut pair and a complete set of digital control devices that control the precise movement of the tool holder or the worktable. The acquisition of the size (the movement of the tool holder or the worktable) is automatically controlled by a pre-compiled program through a computer digital control device. The early automatic control method was completed using active measurement and mechanical or hydraulic control systems. At present, program-controlled machine tools that are pre-programmed according to processing requirements and work by issuing instructions from the control system or digitally controlled machine tools that work by issuing digital information instructions from the control system have been widely used, as well as adaptive control machine tools that can adapt to changes in processing conditions during processing, automatically adjust processing quantities, and optimize the processing process according to specified conditions for automatic control processing. Automatic control processing has stable quality, high productivity, good processing flexibility, and can adapt to the production of multiple varieties. It is the current development direction of mechanical manufacturing and the basis of computer-aided manufacturing (CAM).
