How to Accurately Obtain the Machining Dimensional Accuracy of Machine Parts?
During processing, due to the influence of various factors, it is actually impossible to process every geometric parameter of the machine part to be completely consistent with the ideal geometric parameter, and there will always be some deviations. This deviation is the machining error. If we want to reduce this error as much as possible, we must accurately obtain the machining dimensional accuracy of machine parts through the following methods.
(1) Trial cutting method
That is, first try to cut a small part of the machined surface, measure the size obtained by the test cut, adjust the position of the cutting edge of the tool relative to the workpiece according to the processing requirements, then try to cut and measure again, so after two or three trial cuts and measurements, when the machine is processed after the required size is reached, the entire surface to be machined is cut.
The trial cutting method is repeated until the required dimensional accuracy is achieved through "trial cutting-measurement-adjustment-retry-cutting". For example, the trial boring processing of the box hole system.
The precision achieved by the trial cutting method may be very high, it does not require complicated devices, but this method is time-consuming (requires multiple adjustments, trial cutting, measurement, calculation), low efficiency, and depends on the technical level of workers and the accuracy of 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 based on the processed workpiece, processing another matching workpiece, or a method of combining two (or more) workpieces for processing. The requirements for the final processed size in the matching process are based on the matching requirements with the processed parts.
(2) Adjustment method
The exact relative positions of machine tools, fixtures, tools, and workpieces are adjusted in advance with samples or standard parts to ensure the dimensional accuracy of the workpiece. Because the size is adjusted in place in advance, during processing, there is no need to try cutting, 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 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 the tool setting device on the machine tool or the pre-adjusted tool holder to make the tool reach a certain positional accuracy relative to the machine tool or fixture, and then process a batch of workpieces.
Feeding the tool on the machine tool according to the dial and then cutting is also a kind of adjustment method. This method needs to first determine the scale on the dial according to the trial cut method. In mass production, the tool setting devices such as fixed-range stops, samples, and templates are often used to adjust.
The adjustment method has better machining accuracy and stability than the trial cutting method and has higher productivity. It does not require high machine tool operators, but it has high requirements for machine tool adjustment workers. It is often used in batch production and mass production.
(3) Sizing method
The method of using the corresponding size of the tool to ensure the size of the workpiece to be machined is called the sizing method. It is processed with a standard size tool, and the size of the machined surface is determined by the tool size. That is, a tool with certain dimensional accuracy (such as a reamer, a reaming drill, a drill) is used to ensure the accuracy of the machined part (such as a hole) of the workpiece.
The sizing method is easy to operate, has high productivity, and has relatively stable machining accuracy. It has almost nothing to do with the technical level of workers and has high productivity. It is widely used in various types of production.
(4) Active measurement method
In the process of processing, measuring the processing size while processing, comparing the measured results with the size required by the design, or making the machine tool continue to work, or stop the machine tool, is the active measurement method.
Currently, values in active measurement can be displayed digitally. The active measurement method adds the measurement device to the processing system (i.e. the unity of the machine tool, the tool, the fixture, and the workpiece).
(5) Automatic control method
This method is composed of a measuring device, feeding device, and control system. It is an automatic processing system composed of measuring, feeding devices, and control systems, 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 is automatically completed to automatically achieve the required dimensional accuracy. For example, when machining on a CNC machine tool, the parts control the machining sequence and machining accuracy through various instructions of the program.
If we want to fully obtain the machining accuracy of machine parts, we need to consider not only the size but also the shape and position. If you want to know more about this, please stay tuned to our news.
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