Key points of tooling and fixture design

Tooling fixture design is generally carried out after the machining process of a part is formulated, according to the specific requirements of a certain process. When formulating the process, the feasibility of fixture implementation should be fully considered. When designing tooling fixtures, modifications to the process can be proposed if necessary. The quality of tooling fixture design should be measured by its ability to consistently guarantee workpiece machining quality, high production efficiency, low cost, convenient chip removal, safe and labor-saving operation, and ease of manufacturing and maintenance.

A. Basic Principles of Tooling Fixture Design

1. Ensure the stability and reliability of workpiece positioning during use;

2. Provide sufficient load-bearing or clamping force to ensure the machining process of the workpiece on the tooling fixture;

3. Ensure simple and quick operation during clamping;

4. Wear parts must be easily replaceable, ideally without the need for additional tools;

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

6. Avoid complex structures and high costs as much as possible;

7. Use standard parts as component parts whenever possible;

8. Achieve systematization and standardization of products within the company.

B. Basic Knowledge of Tooling and Fixture Design

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

1. Guaranteeing workpiece machining accuracy: The key to ensuring machining accuracy lies first in correctly selecting the positioning datum, positioning method, and positioning elements. Positioning error analysis is also necessary when required. Attention should also be paid to the influence of the structure of other components in the fixture on machining accuracy to ensure that the fixture can meet the workpiece's machining accuracy requirements.

2. Improving production efficiency: The complexity of the special fixture should be adapted to the production capacity. Various fast and efficient clamping mechanisms should be used as much as possible to ensure convenient operation, shorten auxiliary time, and improve production efficiency.

3. Good process performance: The structure of the special fixture should be as simple and reasonable as possible, facilitating manufacturing, assembly, adjustment, inspection, and maintenance.

4. Good usability: Tooling and fixtures should have sufficient strength and rigidity, and operation should be simple, labor-saving, safe, and reliable. Where objective conditions permit and it is economically feasible, pneumatic, hydraulic, and other mechanized clamping devices should be used as much as possible to reduce the operator's labor intensity. Tooling and fixtures should also facilitate chip removal. If necessary, a chip removal structure can be installed to prevent chips from damaging the workpiece positioning and the cutting tool, and to prevent the accumulation of chips from generating excessive heat and causing deformation of the process system.

5. Good Economic Efficiency: Specialized fixtures should use standard components and structures as much as possible, striving for simplicity and ease of manufacturing to reduce manufacturing costs. Therefore, during the design phase, necessary technical and economic analyses should be conducted on the fixture design based on order volume and production capacity to improve the economic efficiency of the fixture in production.

C. Overview of Standardized Tooling and Fixture Design

1. Basic Methods and Steps of Tooling and Fixture Design

The original data for tooling and fixture design includes the following:

a) Design notification, finished part drawing, blank drawing, and process route, etc., to understand the processing technical requirements of each process, positioning and clamping schemes, processing content of the previous process, blank condition, machine tools, cutting tools, inspection gauges used in processing, machining allowances, and cutting parameters;

b) Understanding the production batch and the need for fixtures;

c) Understanding the main technical parameters, performance, specifications, accuracy, and connection dimensions of the machine tools used and their connection with the fixture;

d) Inventory status of standard fixture materials.

2. Issues to Consider in Tooling and Fixture Design

Fixture designs are generally simple in structure, giving the impression of being not very complex, especially with the widespread use of hydraulic fixtures, which greatly simplifies their original mechanical structures. However, if detailed considerations are not taken into account during the design process, unnecessary problems will inevitably arise:

a) Blank allowance of the workpiece. This can result in an excessively large blank size, causing interference. Therefore, a blank drawing must be prepared before designing. Sufficient space should be provided.

b) Chip removal efficiency of the fixture. Due to the limited machining space of machine tools, fixtures are often designed to be compact. This often overlooks the accumulation of metal chips in dead corners of the fixture, as well as poor flow of cutting fluid, causing many problems for subsequent machining. Therefore, problems that may arise during machining should be considered from the outset, as fixtures are designed to improve efficiency and facilitate operation.

c) Overall openness of the fixture. Ignoring openness makes clamping difficult for operators, wasting time and effort, a major design flaw.

d) Basic theoretical principles of fixture design. Each fixture undergoes countless clamping and releasing actions. While it may initially meet user requirements, fixtures should maintain their precision. Therefore, designs that contradict these principles should be avoided. Even if they work initially, they will not be sustainable. A good design should withstand the test of time.

e) Replaceability of positioning elements. Positioning elements wear out quickly, so quick and convenient replacement should be considered. It's best to avoid designing them as large parts.

Accumulating experience in fixture design is crucial. Sometimes design is one thing, and practical application is another; therefore, good design is a continuous process of accumulation and summarization.

Commonly used tooling fixtures are mainly classified into the following categories according to their functionality:

01 Clamping Mold

02 Drilling and Milling Fixtures

03 CNC and Instrument Chucks

04 Air Testing and Water Testing Fixtures

05 Edge Trimming and Punching Fixtures

06 Welding Fixtures

07 Polishing Fixtures

08 Assembly Fixtures

09 Pad Printing and Laser Engraving Fixtures

01 Clamping Mold

Definition: A tool for positioning and clamping the product using its shape.

Design Points:

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

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

3. The above diagram is a simplified diagram; the mold cavity structure dimensions are determined by specific circumstances;

4. A 12mm diameter locating pin is tightly fitted at an appropriate position on the moving mold, and the locating hole at the corresponding position on the fixed mold slides to fit the locating pin;

5. When designing the assembly cavity, it needs to be offset and enlarged by 0.1mm based on the outer surface of the blank drawing without shrinkage.

02 Drilling and Milling Fixture

Design Points: If necessary, auxiliary positioning devices can be designed on the fixing core and its fixing plate.

03 CNC and Instrument Chucks

Inner Clamp Design

1. Leave a 0.5mm allowance on the outer circle contacting the inner hole.

2. Final precision machining.

3. Spring steel is recommended.

4. M20 thread is commonly used for the tie rod.

Instrument Chuck

1. Material: 45# steel.

2. Requires quenching treatment.

04 Gas Testing Fixture

Design Points:

1. Use urethane or NBR for the sealing surface.

2. Prevent false detection.

3. Pay attention to the gas discharge path.

4. Avoid gas retention in the internal cavity.

05 Punching Fixture

Structural Components

1. Base plate.

2. Positioning block.

3. Baffle.

4. Support column.

06 Welding Fixture

The welding fixture mainly serves to fix the position of each component in the welding assembly and control the relative dimensions of each component 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 important to note that when placing the product on the welding fixture, a sealed space must not be created between the fixtures to prevent excessive pressure in the sealed space during welding heating, which could affect the dimensions of the welded parts.

07 Polishing Fixture:

Used to fix the product and ensure uniform polishing.

08 Assembly Fixture:

Assembly fixtures are mainly used as auxiliary positioning devices during component assembly. The design concept is to facilitate easy product handling based on the component assembly structure, to avoid damaging the product's surface during assembly, and to protect the product by covering it with a cotton cloth during use. Non-metallic materials such as white glue should be used as much as possible.

09 Pad Printing and Laser Engraving Fixture:

Design points: The positioning structure of the fixture should be designed according to the actual engraving requirements of the product. Attention should be paid to the ease of product handling and the protection of the product's appearance. Positioning blocks and auxiliary positioning devices that contact the product should preferably use non-metallic materials such as white glue.