(1) Trial cutting method
First, try to cut a small portion of the machining surface, measure the dimensions obtained from the trial cut, adjust the position of the cutting edge relative to the workpiece according to the machining requirements, try cutting again, and then measure again. After two or three trial cuts and measurements, when the machined dimensions meet the requirements, cut the entire surface to be machined.
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 of the box hole system.
The precision achieved by the trial cutting method may be high, as it does not require complex equipment. However, this method is time-consuming (requiring multiple adjustments, trial cutting, measurements, and calculations), inefficient, and relies on the technical level of workers and the accuracy of measuring instruments. The quality is unstable, so it is only used for single piece and small batch production.
As a type of trial cutting method - matching, it is a method of processing another workpiece that matches the already processed workpiece, or combining two (or more) workpieces together for processing. The final requirement for the processed dimensions in the matching process is based on the matching requirements with the already processed parts.
(2) Adjustment method
Pre adjust the accurate relative positions of the machine tool, fixture, tool, and workpiece using samples or standard parts to ensure the dimensional accuracy of the workpiece. Because the size is adjusted in advance, there is no need to try cutting again during processing. The size is automatically obtained and remains unchanged during the processing of a batch of parts. This is the adjustment method. For example, when using a milling fixture, the position of the tool is determined by aligning it with the cutting block. The essence of adjustment method is to use the fixed distance device, tool alignment device or pre adjusted tool holder on the machine tool to achieve a certain positional accuracy of the tool relative to the machine tool or fixture, and then process a batch of workpieces.
Feeding and cutting according to the dial on a machine tool is also a method of adjustment. This method requires first determining the scale on the dial according to the trial cutting method. In mass production, adjustment of tool setting devices such as fixed distance blocks, samples, and templates is often used.
The adjustment method has better machining accuracy stability and higher productivity than the trial cutting method. It does not require high requirements for machine tool operators, but requires high requirements for machine tool adjustment workers. It is commonly used in batch production and mass production.
(3) Dimensioning method
The method of using the corresponding size of the cutting tool to ensure the size of the workpiece being processed is called the fixed size method. It is processed using standard sized cutting tools, and the size of the machined surface is determined by the tool size. Use cutting tools with certain dimensional accuracy (such as reamers, reamers, drills, etc.) to ensure the accuracy of the machined parts of the workpiece (such as holes).
The fixed size method is easy to operate, has high productivity, stable machining accuracy, and is almost independent of the technical level of workers. It has high productivity and is widely used in various types of production. For example, drilling, reaming, etc.
(4) Active measurement method
During the machining process, the active measurement method involves measuring the machining dimensions while machining, comparing the measured results with the dimensions required by the design, or allowing the machine tool to continue working or stop working.
At present, the values in active measurement can be displayed digitally. The active measurement method incorporates the measuring device into the process system (i.e., a unified entity composed of machine tools, cutting tools, fixtures, and workpieces), becoming its fifth factor.
The active measurement method has stable quality and high productivity, which is the development direction.
(5) Automatic control method
This method consists of measuring devices, feed devices, and control systems. It is an automatic machining system that combines measurement, feed device, and control system, and the machining process is completed automatically by the system.
A series of tasks such as size measurement, tool compensation adjustment, cutting machining, and machine tool parking are automatically completed to achieve the required dimensional accuracy. For example, when machining on CNC machine tools, the parts are controlled by various instructions in the program to control the machining sequence and accuracy.
There are two specific methods for automatic control:
① Automatic measurement refers to the device on the machine tool 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 refers to the servo motor, rolling screw and nut pair, and a complete set of digital control devices that control the precise movement of the tool holder or worktable in a machine tool. The acquisition of dimensions (movement of the tool holder or worktable) is automatically controlled by a pre programmed program through a computer digital control device.
The initial automatic control method was achieved through active measurement and mechanical or hydraulic control systems. At present, widely used programs that are pre arranged according to processing requirements, program controlled machine tools that receive instructions from the control system for work, or digital controlled machine tools that receive digital information instructions from the control system for work, as well as adaptive control machine tools that can adapt to changes in processing conditions, automatically adjust processing quantities, and achieve optimal processing according to specified conditions for automatic control processing.
