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

 

1. Ensure stability and reliability of workpiece positioning during use.
2. Provide sufficient load-bearing or clamping force to ensure machining process of workpiece on tooling and fixture.
3. Ensure simple and quick operation during clamping.
4. Wearable parts must be easily replaceable; ideally, no additional tools should be needed.
5. Ensure reliable repositioning during adjustment or replacement.
6. Minimize complex structures and high costs.
7. Use standard parts as components whenever possible.
8. Achieve systematization and standardization of products within company.

A good machine tool fixture must meet following basic requirements:
1. Ensure workpiece machining accuracy. The key to ensuring machining accuracy lies first in correctly selecting positioning datum, positioning method, and positioning elements. Positioning error analysis is also necessary when required. Attention should also be paid to influence of structure of other components in fixture on machining accuracy to ensure that fixture meets workpiece's machining accuracy requirements.
2. Improve Production Efficiency: Complexity of specialized fixtures should be commensurate with production capacity. Various fast and efficient clamping mechanisms should be employed as much as possible to ensure convenient operation, shorten auxiliary time, and improve production efficiency.
3. Good Process Performance: Structure of specialized fixtures should be as simple, reasonable as possible, facilitating manufacturing, assembly, adjustment, inspection, maintenance.
4. Good Usability: Tooling fixtures should possess 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, or other mechanized clamping devices should be used as much as possible to reduce operator's labor intensity. Tooling fixtures should also facilitate chip removal. If necessary, chip removal structures can be installed to prevent chips from damaging workpiece positioning and cutting tools, to prevent accumulation of chips from generating excessive heat and causing deformation of process system.
5. Good Economy: Specialized fixtures should use standard components and standard structures as much as possible, striving for simple structure and easy manufacturing to reduce manufacturing costs. Therefore, during design phase, necessary techno-economic analyses should be conducted on fixture solutions based on order volume and production capacity to improve economic efficiency of fixtures in production.

Preparation before design: Original data for tooling and fixture design includes following:
a) Design notification, finished part drawing, blank drawing, and process route, etc., to understand processing technical requirements of each process, positioning and clamping schemes, processing content of previous process, blank condition, machine tools, cutting tools, inspection gauges used in processing, machining allowances, and cutting parameters, etc.
b) Understanding production batch and need for fixtures.
c) Understanding main technical parameters, performance, specifications, accuracy, connection dimensions of machine tools used and their connection with fixture structure, etc.
d) Standard material inventory of fixture.

Fixture designs are generally simple in structure, giving impression of being not very complex, especially with widespread use of hydraulic fixtures, which greatly simplifies their original mechanical structures. However, if detailed considerations are not taken into account during design process, unnecessary problems will inevitably arise:
a) Blank allowance of workpiece
This can result in an excessively large blank size, causing interference. Therefore, a rough sketch must be prepared before designing. Sufficient space must be allowed.
b) Chip removal efficiency of fixture
Due to limited machining space of machine tool, fixtures are often designed to be compact. This often overlooks accumulation of metal chips in dead corners of fixture during machining. This includes poor flow of cutting fluid, causing many problems in subsequent machining. Therefore, problems that may arise during machining should be considered from outset, as fixtures are designed to improve efficiency and facilitate operation.
c) Overall openness of fixture
Ignoring openness makes clamping difficult for operators, wasting time and effort—a major design mistake.
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, avoid designing anything that contradicts these principles. Even if it works temporarily, it won't be sustainable in long run. A good design should withstand test of time.
e) Replaceability of positioning elements
Positioning elements wear out quickly, so quick and easy 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 process of continuous accumulation and summarization.
Common tooling fixtures are mainly classified into following types according to their functionality:
01 Clamping molds; 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 molds
Definition: A tool for positioning and clamping products using their 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 clamping mold, generally connected by welding.
3. Above diagram is a simplified one; dimensions of mold cavity structure are determined by specific circumstances.
4. A 12mm diameter locating pin is tightly fitted at an appropriate position on moving mold, and corresponding locating hole on fixed mold slides to fit locating pin.
5. When designing assembly cavity, it needs to be offset and enlarged by 0.1mm based on the outer surface of blank drawing without shrinkage.
02 Drilling and milling fixtures

 

Design points:
1. If necessary, auxiliary positioning devices can be designed on fixed core and its fixed plate;
2. Above diagram is a simplified structural diagram. Actual design should be based on product structure;
3. Cylinder size depends on product size. Size depends on stress conditions during machining; SDA50X50 is commonly used.
03 CNC, Instrument Chuck, A-type CNC Chuck, Internal Clamp Chuck.

 

Design Points:
1. Dimensions not marked in above image are determined based on actual product's internal hole dimensions and structure.
2. A 0.5mm allowance should be left on each side of outer circle that contacts product's internal hole during manufacturing. This allowance is then precision-machined to required dimensions on CNC machine tool to prevent deformation and eccentricity during quenching process.
3. Spring steel is recommended for assembly parts, and 45# steel for tie rod.
4. M20 is a commonly used thread for tie rod; this thread can be adjusted according to actual conditions.
04 Instrument Internal Clamp
Design Points:
1. Assembly dimensions and structure will be determined based on actual product's external dimensions and structure.
2. 45# steel is used, and it undergoes quenching treatment.
05 Instrument External Clamp

 

Design Points:
1. Above image is for reference only. Actual dimensions will be determined based on product's internal hole dimensions and structure.
2. A 0.5mm allowance should be left on each side of outer circle that contacts product's internal hole during manufacturing. It should then be precision machined to required dimensions on an instrument lathe to prevent deformation and eccentricity during quenching.
3. 45# steel is used, and it undergoes quenching treatment.
06 Gas Testing Fixture

 

Design Considerations:
1. Image above is a reference drawing of gas testing fixture. Specific structure needs to be designed according to actual structure of product. Idea is to seal product in the simplest possible way, filling part to be tested with gas to confirm its sealing performance.
2. Size of cylinder can be adjusted according to actual size of product. Cylinder stroke should also be considered to ensure convenient product handling.
3. Sealing surfaces in contact with product generally use materials with good compressibility, such as urethane rubber or NBR rubber rings. For positioning blocks that contact product's exterior, use white plastic blocks and cover them with a cotton cloth during use to prevent damage to product's appearance.
4. Product's positioning direction needs to be considered during design to prevent leaked gas from being trapped inside product cavity and causing false detections.
07 Punching Fixture

 

Design Considerations: Image above shows a commonly used structure for punching fixtures. Base plate facilitates fixation to punch press worktable; positioning block secures product, its specific structure designed according to product's actual condition, with center point surrounding it for easy and safe product placement and removal;
Baffle facilitates product detachment from punch; support column secures baffle. Assembly positions and dimensions of these parts can be designed according to product's actual condition.
08 Welding Fixture
Welding fixture mainly fixes position of each component in welding assembly and controls relative dimensions of each component. Its structure is mainly a positioning block, which needs to be designed according to actual structure of product.
It is important to note that when placing product on welding fixture, a sealed space should not be created between fixtures to prevent excessive pressure in sealed space during welding heating, which could affect dimensions of welded components.
09 Polishing Fixture

 

 

Notes: 1. Tire dimensions are based on product design;
2. The first three types of tire rods are recommended. Dimensions not specified are in mm;
3. Material is 45#.

 

10 Assembly Fixture
Assembly fixture is mainly used as an auxiliary positioning device during assembly process of components. Its design concept is to facilitate easy product placement and removal based on assembly structure, to prevent damage to product's surface during assembly, and to protect product by covering it with a cotton cloth during use. In terms of material selection, non-metallic materials such as white glue should be used as much as possible.
11 Pad Printing, Laser Engraving Fixture

 

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