How to Improve Machining Accuracy

Fixture design is generally carried out in accordance with the specific requirements of a certain process after the formulation of the machining process of parts. The possibility of fixture realization should be fully considered in the formulation of process. When designing fixture, if necessary, modification suggestions can be put forward for the process.

The design quality of fixture should be measured by whether the machining quality of workpiece can be stably guaranteed, the production efficiency is high, the cost is low, the chip removal is convenient, the operation is safe, labor-saving, and the manufacturing and maintenance are easy.

Basic principles of fixture design

1. Meet the stability and reliability of workpiece positioning during use

2. There is enough load or clamping force to ensure that the workpiece is processed on the fixture

3. Meet the requirements of simple and fast operation in clamping process

4. Vulnerable parts must be of a structure that can be replaced quickly. It is better not to use other tools when conditions are sufficient

5. Meet the reliability of repeated positioning of fixture during adjustment or replacement

6. Try to avoid complicated structure and high cost

7. Standard parts shall be selected as component parts as far as possible

8. Form the systematization and standardization of the company’s internal products

A good jig must meet the following basic requirements:

1. The key to ensure the machining accuracy of workpiece lies in the correct selection of positioning datum, positioning method and positioning elements, and the analysis of positioning error if necessary. In addition, attention should be paid to the influence of the structure of other parts in the fixture on the machining accuracy to ensure that the fixture can meet the machining accuracy requirements of workpiece.

2. The complexity of special fixture for improving production efficiency should be adapted to the production capacity, and various fast and efficient clamping mechanisms should be adopted as far as possible to ensure convenient operation, shorten auxiliary time and improve production efficiency.

3. The structure of the special fixture with good process performance shall be simple and reasonable, convenient for manufacturing, assembly, adjustment, inspection, maintenance, etc.

4. The fixture with good performance shall have enough strength and rigidity, and the operation shall be simple, labor-saving, safe and reliable. On the premise that the objective conditions permit and are economical and applicable, pneumatic, hydraulic and other mechanical clamping devices should be used as far as possible to reduce the labor intensity of the operator. The fixture shall also be convenient for chip removal. If necessary, the chip removal structure can be set to prevent the chip from damaging the positioning of the workpiece and damaging the tool, so as to prevent the chip from accumulating and bringing a lot of heat to cause the deformation of the process system.

5. The special fixture with good economy should adopt standard components and structure as much as possible, and strive to be simple in structure and easy to manufacture, so as to reduce the manufacturing cost of the fixture. Therefore, in order to improve the economic benefit of fixture in production, the necessary technical and economic analysis should be carried out according to the order and production capacity.

The original data for the preparation of fixture design before design includes the following contents:

a) Design notice, finished part drawing, blank drawing, process route and other technical data, understand the processing technical requirements of each process, positioning and clamping scheme, processing content of previous process, blank situation, machine tools, cutting tools, Inspection measuring tools used in processing, machining allowance and cutting amount, etc

b) Understand the production batch and the need for fixture

c) Understand the main technical parameters, performance, specification, accuracy of the machine tool used and the connection dimension of the structure of the connecting part of the fixture;

d) Standard stock of fixture

Generally, the structure of fixture design is single, which gives people a feeling that the structure is not very complex. Especially now, the popularity of hydraulic fixture greatly simplifies the original mechanical structure. However, if the design process is not considered in detail, there will inevitably be unnecessary troubles:

a) Blank allowance of machined parts

The size of the blank is too large, resulting in interference. So we must prepare the rough drawing before design. Leave enough space

b) Chip removal smoothness of fixture

Due to the limited machining space of the machine tool, the fixture is often designed in a compact space. At this time, the iron chips generated in the machining process are often ignored to accumulate in the dead corner of the fixture.

Including chip liquid outflow is not smooth, which brings a lot of trouble to the later processing. So at the beginning of practice, we should consider the problems in the process of machining. After all, the fixture is based on improving efficiency and convenient operation

c) Overall opening of fixture

Neglecting the openness makes it difficult for the operator to install the card, which is time-consuming and laborious

d) Basic theoretical principles of fixture design

Each set of fixture has to go through countless clamping and loosening actions, so it may meet the user’s requirements at the beginning, but the fixture should have its accuracy retention, so don’t design something contrary to the principle.

Even if you can get away with it now, it won’t last long. A good design should be tempered by time

e) Replaceability of positioning elements

The positioning element is seriously worn, so it should be considered to replace it quickly and conveniently. It is better not to design large parts

The accumulation of fixture design experience is very important, sometimes design is one thing, in practical application is another thing, so good design is a process of continuous accumulation and summary.

The commonly used tooling and fixture are mainly divided into the following categories according to their functionality:

01 clamping die

02 drilling and milling tooling

03 numerical control and instrument collet

04 gas and water testing tooling

05 trimming and punching tooling

06 welding tooling

07 polishing fixture

08 assembly tooling

09 pad printing, laser lettering tooling

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