The design of fixtures and jigs is generally carried out according to the specific requirements of a certain process after the mechanical processing technology of the parts is formulated.

When formulating the process, full consideration should be given to the possibility of implementing fixtures, and when designing fixtures, if necessary, modification suggestions can also be proposed for the process.

The design quality of fixtures and jigs should be measured by their ability to stably ensure the machining quality of workpieces, high production efficiency, low cost, convenient chip removal, safe and labor-saving operation, and easy manufacturing and maintenance.

1、 Basic principles of fixture design

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

2. There is sufficient load-bearing or clamping force to ensure the machining process of the workpiece on the fixture

3. Satisfy the simple and fast operation during the clamping process

4. Fragile parts must be structures that can be quickly replaced, and it is best not to use other tools when conditions are sufficient

5. Ensure the reliability of repeated positioning of fixtures during adjustment or replacement processes

6. Try to avoid complex structures and high costs as much as possible

7. Choose standard components as much as possible as constituent parts

8. Systematize and standardize the internal products of the company

2、 Basic knowledge of fixture design

A good machine tool fixture must meet the following basic requirements:

1. The key to ensuring the machining accuracy of the workpiece lies in correctly selecting the positioning reference, positioning method, and positioning components. If necessary, positioning error analysis should also be conducted. Attention should also be paid to the influence of the structure of other components in the fixture on the machining accuracy to ensure that the fixture can meet the machining accuracy requirements of the workpiece.

2. The complexity of specialized fixtures for improving production efficiency should be adapted to the production capacity situation, and various fast and efficient clamping mechanisms should be used as much as possible to ensure easy operation, shorten auxiliary time, and improve production efficiency.

3. The structure of specialized fixtures with good process performance should strive for simplicity, rationality, and ease of manufacturing, assembly, adjustment, inspection, maintenance, etc.

4. Tools and fixtures with good performance should have sufficient strength and rigidity, and the operation should be simple, labor-saving, safe and reliable. Under the premise of objective conditions and economic feasibility, mechanical clamping devices such as pneumatic and hydraulic should be used as much as possible to reduce the labor intensity of operators. Fixtures should also be easy to remove chips. If necessary, a chip removal structure can be set up to prevent chips from damaging the positioning of the workpiece and damaging the tool, and to prevent the accumulation of chips from causing a large amount of heat and deformation of the process system.

5. Special fixtures with good economic efficiency should use standard components and structures as much as possible, striving for simple structure and easy manufacturing to reduce the manufacturing cost of fixtures. Therefore, necessary technical and economic analysis should be conducted on the fixture scheme based on orders and production capacity during design to improve the economic benefits of fixtures in production.

3、 Overview of Standardization in Fixture Design

1. Basic methods and steps for fixture design

The original materials for the preparation of fixture design before design include the following:

a) Design notification, finished part drawings, blank drawings, and process routes, and other technical information to understand the machining technical requirements, positioning and clamping schemes, machining content of previous processes, blank conditions, machine tools, cutting tools, inspection gauges used in machining, machining allowances, and cutting quantities for each process

b) Understand the production batch and the demand for fixtures

c) Understand the main technical parameters, performance, specifications, accuracy of the machine tool used, as well as the connection dimensions with the fixture connection structure;

d) Inventory status of standard materials for fixtures

2. Issues Considered in Fixture Design

Fixture design generally has a single structure, giving the impression that the structure is not very complex, especially with the popularity of hydraulic fixtures, which greatly simplifies their original mechanical structure. However, if the design process is not carefully considered, unnecessary troubles will inevitably arise:

a) The blank allowance of the processed part

Causing excessive blank size and interference. So before designing, it is necessary to prepare a rough drawing. Leave enough space

b) Smooth chip removal of fixtures

Due to the limited machining space of the machine tool during design, fixtures are often designed in a compact space, which often overlooks the accumulation of iron filings generated during the machining process in the dead corners of the fixture.

Including the poor flow of chip fluid, it brings a lot of trouble to future processing. So in practice, we should consider the problems that arise during the machining process, as fixtures are designed to improve efficiency and facilitate operation

c) The overall openness of the fixture

Neglecting openness makes it difficult for operators to install cards, time-consuming and laborious, and a major design taboo

d) Basic theoretical principles of fixture design

Each set of fixtures undergoes countless clamping and releasing actions, so it may meet the user's requirements at the beginning. However, the fixture should have its accuracy retention, so do not design anything that goes against the principle.

Even if luck allows for immediate success, it will not have long-term sustainability. A good design should withstand the test of time

e) The replaceability of positioning components

The positioning components are severely worn, so quick and convenient replacement should be considered. It's best not to design it as a larger component

The accumulation of experience in fixture design is very important. Sometimes design is one thing, but in practical applications it is another. Therefore, good design is a process of continuous accumulation and summarization.

The commonly used fixtures and jigs are mainly divided into the following types according to their functionality:

01 Clamp mold

02 Drilling and milling tooling

03 CNC and instrument chuck

04 Gas and water testing fixtures

05 Cutting and punching tooling

06 Welding Fixture

07 Polishing Fixture

08 Assembly tooling

09 transfer printing, laser engraving fixture

01 Clamp mold

Definition: Tool for positioning and clamping with product appearance

Design points:

1. This type of clamping mold is mainly used on vises, and its length can be cut as needed

2. Other auxiliary positioning devices can be designed on the clamping mold, usually connected by welding;

3. The above figure is a schematic diagram, and the size of the mold cavity structure is determined by the specific situation

4. Tightly fit the positioning pin with a diameter of 12 at the appropriate position on the moving mold, and slide the positioning hole at the corresponding position of the fixed mold to match the positioning pin

5. The assembly cavity needs to be offset and enlarged by 0.1mm on the outer surface of the blank drawing without shrinkage during design

02 Drilling and milling tooling

Design points:

1. If necessary, some auxiliary positioning devices can be designed on the fixed core and its fixing plate;

2. The above diagram 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 situation during processing, and commonly used is SDA50X50;

03 CNC, instrument chuck, A CNC chuck, internal beam chuck

Design points:

1. The dimensions not marked in the above figure are determined based on the actual internal hole size structure of the product

2. The outer circle in contact with the product's inner hole positioning needs to have a margin of 0.5mm on one side during production, and finally be installed on a CNC machine and precision machined to the size to prevent deformation and eccentricity caused by quenching process

3. It is recommended to use spring steel for the assembly part and 45 for the pull rod part#

4. The thread M20 of the pull rod is a commonly used thread, which can be adjusted according to the actual situation

Instrument internal bundle clamp

Design points:

1. The above figure is a reference diagram, and the assembly dimensions and structure depend on the actual product's external dimensions and structure

2. Material use 45 #, quenching treatment

03 Instrument external beam clamp

Design points:

1. The above figure is a reference diagram, and the actual size depends on the internal hole size structure of the product;

2. The outer circle in contact with the inner hole of the product should have a margin of 0.5mm on one side during production, and finally be installed on the instrument lathe for precision machining to prevent deformation and eccentricity caused by quenching process;

3. The material used is 45 # and has undergone quenching treatment.

04 Gas Testing Fixture

Design points:

1. The above figure is a reference diagram of the gas testing fixture. 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, so that the part that needs to be sealed is filled with gas to confirm its sealing performance

2. The size of the cylinder can be adjusted according to the actual size of the product, while also considering whether the stroke of the cylinder can meet the convenience of picking up and placing products

3. The sealing surface in contact with the product is generally made of materials with good compression capacity such as Yuli glue and NBR rubber rings. At the same time, attention should be paid to using plastic blocks of white glue as much as possible for positioning blocks that come into contact with the appearance of the product, and cotton cloth should be covered during use to prevent damage to the appearance of the product

4. When designing, the positioning direction of the product should be considered to prevent the occurrence of gas leakage trapped inside the product cavity and false detection

05 Punching Fixture

Design points: The above figure shows the commonly used structure of punching fixtures. The function of the bottom plate is to facilitate fixation on the worktable of the punch press; The positioning block is used to fix the product, and the specific structure is designed according to the actual situation of the product, with the center point surrounding it for easy and safe access and placement of the product;

The baffle is used to facilitate the detachment of the product from the punch; The pillar serves as a fixed baffle. The assembly positions and dimensions of the above-mentioned parts can be designed according to the actual situation of the product.

06 Welding Fixture

The welding fixture mainly fixes the position of each component in the welding assembly, controls the relative size of each component in the welding assembly, and 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 fixture, there should be no sealed space between the fixtures to prevent excessive pressure in the sealed space during the welding heating process, which may affect the size of the welded parts.

07 Polishing Fixture

08 Assembly tooling

Assembly fixtures are mainly used as auxiliary positioning devices in the assembly process of components. The design concept is to facilitate the retrieval and placement of products based on the structure of component assembly, without damaging the appearance surface of the product during assembly, and to cover the product with cotton cloth to protect it during use.

Try to use non-metallic materials such as white glue in the selection of materials.

09 transfer printing, laser engraving fixture

Design points:

Design the positioning structure of the fixture based on the engraving requirements of the actual product situation, paying attention to the convenience of product retrieval and placement, as well as the protection of product appearance. The positioning block and auxiliary positioning device in contact with the product should be made of non-metallic materials such as white glue as much as possible.