The fixture design is generally carried out in accordance with the specific requirements of a certain process after the machining process of the parts is formulated. In formulating the technological process, the possibility of fixture realization should be fully considered, and when designing the fixture, it is possible to propose amendments to the technological process if necessary. The design quality of tooling fixtures should be measured by whether it can stably guarantee the processing quality of the workpiece, high production efficiency, low cost, convenient chip removal, safe operation, labor-saving, easy manufacturing, and easy maintenance.
1. The basic principles of fixture design
1. Satisfy the stability and reliability of workpiece positioning during use;
2. There is sufficient load or clamping force to ensure the processing of the workpiece on the fixture;
3. Satisfy simple and fast operation in the clamping process;
4. The fragile parts must be of a structure that can be replaced quickly, and it is best not to use other tools when the conditions are sufficient;
5. Satisfy the reliability of repeated positioning of the fixture during adjustment or replacement;
6. Avoid complex structure and high cost as much as possible;
7. Choose standard parts as component parts as much as possible;
8. Form the systemization and standardization of the company's internal products.
2. Basic knowledge of fixture design
A good machine tool fixture must meet the following basic requirements:
1. To ensure the machining accuracy of the workpiece, the key to ensuring the machining accuracy is to correctly select the positioning datum, positioning method and positioning components. If necessary, positioning error analysis is also required. Pay attention to the structure of other parts in the fixture to the machining accuracy. The influence of this to ensure that the fixture can meet the machining accuracy requirements of the workpiece.
2. The complexity of the 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 should be simple and reasonable, which is convenient for manufacturing, assembly, adjustment, inspection, maintenance, etc.
4. Good use performance. The fixture should have sufficient strength and rigidity, and the operation should be simple, labor-saving, safe and reliable. Under the premise that objective conditions permit and are economical and applicable, pneumatic, hydraulic and other mechanized clamping devices should be used as much as possible to reduce the labor intensity of the operator. Tooling fixtures should also be convenient for chip removal. When necessary, a chip removal structure can be set to prevent chips from damaging the positioning of the workpiece and damaging the tool, and preventing the accumulation of chips from bringing a lot of heat and causing deformation of the process system.
5. The special fixture with good economy should adopt standard components and standard 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, the necessary technical and economic analysis of the fixture plan should be carried out according to the order and production capacity during the design to improve the economic benefits of the fixture in the production.
3. Overview of the standardization of tooling and fixture design
1. Basic methods and steps of fixture design
Preparation before design. The original data of tooling and fixture design includes the following:
a) Design notices, finished parts drawings, blank drawings and process routes and other technical data, understand the processing technical requirements of each process, positioning and clamping schemes, the processing content of the previous processes, the rough conditions, the machine tools and tools used in the processing , Inspection of measuring tools, machining allowance and cutting amount, etc.;
b) Understand the production batch and the demand for fixtures;
c) Understand the main technical parameters, performance, specifications, accuracy of the machine tool used, and the connection size of the structure of the connection part with the fixture, etc.;
d) Standard material inventory of fixtures.
2. Issues considered in the design of fixtures
The fixture design generally has a single structure, which gives people the feeling that the structure is not very complicated. Especially now that hydraulic fixtures are popular, the original mechanical structure is greatly simplified. However, if the design process is not considered in detail, unnecessary troubles will inevitably occur:
a) The blank margin of the workpiece. The size of th
e blank is too large and interference occurs. Therefore, the rough drawing must be prepared before designing. Leave enough space.
b) Unblocked chip removal of the fixture. Due to the limitation of the machining space of the machine tool during design, the fixture is often designed to be compact. At this time, it is often ignored that the iron filings generated during the machining process are stored in the dead corners of the fixture, including the poor outflow of the chip liquid, which will cause problems in the future. Processing brings a lot of trouble. Therefore, at the beginning of the actual situation, we should consider the problems in the processing process. After all, the fixture is based on improving efficiency and convenient operation.
c) The overall openness of the fixture. Ignoring the openness makes it difficult for the operator to install the card, time-consuming and laborious, and design taboos.
d) The basic theoretical principles of fixture design. Each fixture has to undergo countless clamping and loosening actions, so it may be able to meet the user's requirements at the beginning, but the fixture should have its accuracy retention, so don't design something that is contrary to the principle. Even if you are lucky now, there will be no long-term sustainability. A good design should stand the temper of time.
e) Replaceability of positioning components. The positioning components are severely worn, so quick and convenient replacement should be considered. It is best not to design into larger parts.
Accumulation of fixture design experience is very important. Sometimes design is one thing, but it is another thing in practical application, so good design is a process of continuous accumulation and summarization.
Commonly used fixtures are mainly divided into the following types according to their functionality:
01 clamp
02Drilling and milling tooling
03CNC, instrument chuck
04 Gas and water test tooling
05 Trimming and punching tooling
06 welding tooling
07 Polishing fixture
08 Assembly tooling
09 Pad printing, laser engraving tooling
01 clamp
Definition: a tool for positioning and clamping with the product shape
Design Points:
1. This type of clamp is mainly used for vise, and its length can be cut according to needs;
2. Other auxiliary positioning devices can be designed on the clamping mold, and the clamping mold is generally connected by welding;
3. The above picture is a simplified diagram, and the cavity structure size is determined by specific conditions;
4. Tightly fit a positioning pin with a diameter of 12 at an appropriate position on the movable mold, and the positioning hole at the corresponding position of the fixed mold slides to fit the positioning pin;
5. The assembly cavity needs to be offset and enlarged by 0.1mm on the basis of the outline surface of the non-shrinking blank drawing file during the design.
02Drilling and milling tooling
Design Points:
1. If necessary, some auxiliary positioning devices can be designed on the fixed core and its fixed plate;
2. The above picture is a structural diagram, and the actual situation needs to be designed according to the product structure;
3. The cylinder is determined according to the size of the product and the force during processing. SDA50X50 is commonly used;
03CNC, instrument chuck
A CNC chuck
Inner beam chuck
Design Points:
1. The unmarked size in the above figure depends on the inner hole size structure of the actual product;
2. The outer circle that is in contact with the inner hole of the product should be made with a margin of 0.5mm on one side, and finally installed on the CNC machine tool and then finished to the size to prevent deformation and eccentricity caused by the quenching process;
3. It is recommended to use spring steel as the material of the assembly part, and the tie rod part 45#;
4. The thread M20 of the tie rod part is a common thread, which can be adjusted according to the actual situation
Instrument chuck
Design Points:
1. The above picture is a reference diagram, and the assembly size and structure are determined according to the actual product's external size and structure;
2. The material uses 45#, quenched.
Instrument external beam chuck
Design Points:
1. The above picture is a reference diagram, the actual size depends on the inner hole size structure of the product;
2. The outer circle that is in contact with the inner hole of the product should be made with a margin of 0.5mm on one side, and finally installed on the instrument lathe and then refined to the size to prevent deformation and eccentricity caused by the quenching process;
3. The material uses 45#, quenched.
04Testing tooling
Design Points:
1. The above picture is a reference picture of the gas test tooling. The specific structure needs to be designed according to the actual structure of the product. The idea is to seal the product in the simplest way possible, and fill the part to be tested and sealed with gas to confirm its tightness;
2. The size of the cylinder can be adjusted according to the actual size of the product, and it is also necessary to consider whether the stroke of the cylinder can meet the convenience of taking and placing the product;
3. The sealing surface that is in contact with the product is generally made of materials with good compression, such as NBR rubber and NBR rubber ring. At the same time, please pay attention to the use of white plastic plastic blocks as much as possible if there is a positioning block in contact with the appearance of the product. Cover the middle cover with cotton cloth to prevent damage to the appearance of the product;
4. The positioning direction of the product should be considered when designing to prevent the internal leakage of gas from being trapped in the product cavity and false detection.
05Punching tooling
Design points: The picture above shows the common structure of punching tooling. The bottom plate is used to facilitate fixing on the workbench of the punching machine; the positioning block is used to fix the product, the specific structure is designed according to the actual situation of the product, and the center point is around to facilitate and safe picking and placing of the product; the baffle is to facilitate the product to be separated from the punching knife ; The pillar serves as a fixed baffle. The assembly position and size of the above several parts can be designed according to the actual situation of the product.
06 welding tooling
The welding tool is mainly used to fix the position of each part in the welding assembly, and control the relative size of each part in the welding assembly. Its structure is mainly a positioning block, which needs to be designed according to the actual structure of the product. It is worth noting that when the product is placed on the welding tooling, it is not allowed to create a sealed space between the tooling to prevent excessive pressure in the sealed space during the welding and heating process, which affects the size of the parts after welding.
07 Polishing fixture
08 Assembly tooling
Assembly tooling is mainly used as a device to assist positioning in the assembly process of components. The design idea is that the product can be easily picked and placed according to the assembly structure of the component, the appearance of the product cannot be damaged during the assembly process, and the cotton cloth can be covered to protect the product during use. In the selection of materials, try to use non-metallic materials such as white glue.
09 Pad printing, laser engraving tooling
Design points: Design the positioning structure of the tooling according to the actual lettering requirements of the product. Pay attention to the convenience of product access and the protection of the product appearance. The positioning block and the auxiliary positioning device in contact with the product should be made of non-metallic materials such as white glue as much as possible. .
