The Installation Of Machined Workpieces

Standard

 

Parts are composed of a number of surfaces, each surface has a certain size and mutual position requirements. The relative position requirements between the surface of the part include two aspects: the distance between the surface dimensional accuracy and relative position accuracy (such as coaxiality, parallelism, verticality and circular runout, etc.) requirements. The study of the relative position relationship between the surface of the part is inseparable from the benchmark, without a clear benchmark can not determine the position of the surface of the part. In its general sense, the benchmark is the point, line, and surface on the part used to determine the position of other points, lines, and surfaces. According to its different role, the benchmark can be divided into two categories: design benchmark and process benchmark.

1. Design basis

The reference used to determine other points, lines and surfaces on the part drawing is called the design reference, and in the case of the piston, the design reference refers to the center line of the piston and the center line of the pin hole.

2. Process standard

The reference used in the processing and assembly of parts is called the process reference. According to different uses, the process reference is divided into positioning reference, measurement reference and assembly reference.

Positioning reference: The reference used to make the workpiece occupy the correct position in the machine tool or fixture during processing, called the positioning reference. According to the different positioning elements, the most commonly used are the following two categories: automatic centering positioning: such as three-jaw chuck positioning. Positioning sleeve positioning: the positioning element is made into a positioning sleeve, such as the positioning of the stop disk and other positioning in the V-shaped frame, positioning in the semicircle hole.

② Measurement benchmark: When parts are inspected, the benchmark used to measure the size and position of the machined surface is called the measurement benchmark.

Assembly benchmark: The benchmark used to determine the position of the part in the component or product during assembly, called the assembly benchmark.

 

How the workpiece is installed

 

In order to produce a surface that meets the specified technical requirements on a certain part of the workpiece, it is necessary to make the workpiece occupy a correct position on the machine tool relative to the tool before machining. This process is often referred to as the "positioning" of the artifact. After the workpiece is positioned, due to the role of cutting force, gravity, etc., in the processing, a certain mechanism should also be used to "clamp" the workpiece so that its determined position remains unchanged. The process of holding the workpiece in the correct position on the machine tool and clamping the workpiece is called "installation". The quality of the workpiece installation is an important problem in machining, which not only directly affects the machining accuracy, the speed and stability of the workpiece installation, but also affects the level of productivity. In order to ensure the accuracy of the relative position between the machined surface and its design reference, the workpiece should be installed so that the design reference of the machined surface occupies a correct position relative to the machine tool. For example, in order to ensure the circular runout of the bottom diameter of the ring groove and the skirt axis, the workpiece must be installed so that its design reference and the spindle line of the machine tool must coincide. When machining parts on a variety of different machine tools, there are various installation methods. The installation method can be summarized into three kinds: direct rectification method, line rectification method and fixture installation method.

1. Go straight to the Dharma

With this method, the correct position of the workpiece on the machine tool is obtained through a series of attempts. The specific way is to install the workpiece directly on the machine tool, use the dial indicator or the needle on the dial dial to correct the correct position of the workpiece by visual inspection, and find the correct position while checking until it meets the requirements.

The positioning accuracy and the speed of the direct alignment method depend on the alignment accuracy, the alignment method, the alignment tool and the technical level of the worker. Its disadvantage is that it takes much time, low productivity, and it has to be operated by experience, and it has high technical requirements for workers, so it is only used in single piece and small batch production. For example, seeking righteousness by hard imitation of form belongs to seeking righteousness directly.

2. Line to find the correct method

This method is a method of finding the correct position of the workpiece according to the line drawn on the blank or semi-finished product with the stroke needle on the machine tool. Obviously, this method requires an additional marking process. The line itself has a certain width, and there are scribing errors when scribing, and observation errors when correcting the position of the workpiece, so the method is used for small production batches, low blank accuracy, and large workpieces should not be used in the roughing of the fixture. For example, the location of the two-stroke product pin hole is determined by using the marking method of the dividing head.

3. Fixture installation method is adopted

This method is used to clamp the workpiece, so that it occupies the correct position of the process equipment called machine tool fixture. The fixture is an additional device of the machine tool, which has been adjusted in advance before the workpiece is not installed on the machine tool, so in the processing of a batch of workpieces do not have to find positive positioning one by one, it can ensure the technical requirements of the processing, both labor and labor saving, is an efficient positioning method, widely used in batch and mass production. Our current piston processing is the use of fixture installation method.

After the workpiece is positioned, the operation that keeps the positioning position unchanged during the processing is called clamping. The device that keeps the positioning position unchanged during the processing of the workpiece in the fixture is called the clamping device.

The clamping device should meet the following requirements: When clamping, the positioning of the workpiece should not be damaged; After clamping, it should be ensured that the position of the workpiece does not change during the processing, and the clamping is accurate, safe and reliable; Clamping action is fast, easy to operate, labor saving; Simple structure, easy to manufacture.

(3) Precautions when clamping: the clamping force should be appropriate, too large to cause deformation of the workpiece, too small will cause the workpiece in the process of displacement, destroy the positioning of the workpiece.