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Design of tooling fixture

Fixture design is generally carried out according to the specific requirements of a process after the formulation of the machining process of parts. When formulating the process, the possibility of fixture realization shall be fully considered, and when designing tooling fixtures, if necessary, modification suggestions can also be put forward for the process. The design quality of tooling and fixture should be measured by whether it can stably ensure the processing quality of workpiece, high production efficiency, low cost, convenient chip removal, safe operation, labor saving and easy manufacturing and maintenance.

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Basic principles of fixture design

  • 1. Meet the stability and reliability of workpiece positioning during use;
  • 2. Have enough bearing or clamping force to ensure the machining process of the workpiece on the tooling fixture;
  • 3. Meet the simple and fast operation in the clamping process;
  • 4. The vulnerable parts must be of a structure that can be replaced quickly. When the conditions are sufficient, it is best not to use other tools;
  • 5. Meet the reliability of repeated positioning of fixture in the process of adjustment or replacement;
  • 6. Avoid complex structure and high cost as much as possible;
  • 7. Select standard parts as component parts as far as possible;
  • 8. Form the systematization and standardization of the company’s internal products.

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 elements. If necessary, it is also necessary to analyze the positioning error, and pay attention to the influence of the structure of other parts in the fixture on the machining accuracy, so as to ensure that the fixture can meet the machining accuracy requirements of the workpiece.
  • 2. To improve the production efficiency, the complexity of the special fixture shall adapt to the production capacity, and various fast and efficient clamping mechanisms shall be adopted as far as possible to ensure convenient operation, shorten the auxiliary time and improve the production efficiency.
  • 3. The structure of the special fixture with good process performance shall be simple and reasonable to facilitate manufacturing, assembly, adjustment, inspection and maintenance.
  • 4. With good performance, the fixture shall have sufficient strength and stiffness, and the operation shall be simple, labor-saving, safe and reliable. On the premise of objective conditions and economic applicability, pneumatic, hydraulic and other mechanized clamping devices shall be used as far as possible to reduce the labor intensity of the operator. The tooling fixture shall also be convenient for chip removal. If necessary, a chip removal structure can be set to prevent chips from damaging the positioning of the workpiece and damaging the tool, and prevent the accumulation of chips from bringing a lot of heat and causing the deformation of the process system.
  • 5. The special fixture with good economy shall adopt standard components and standard structure as far as possible, and strive to have simple structure and easy manufacturing, so as to reduce the manufacturing cost of the fixture. Therefore, the necessary technical and economic analysis of the fixture scheme should be carried out according to the order and production capacity, so as to improve the economic benefits of the fixture in production.

Overview of standardization of fixture design

1. Basic methods and steps of fixture design
Preparation before design the original data of fixture design include the following contents:

  • a) Design notice, part finished product 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 condition, machine tools, cutting tools, Inspection measuring tools, machining allowance and cutting amount used in processing, 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, as well as the contact size of the structure connected with the fixture;
  • d) Standard material inventory of fixture.

2. Problems considered in fixture design
The fixture design generally has a single structure, which makes people feel that the structure is not very complex. In particular, the popularity of hydraulic fixture has greatly simplified its original mechanical structure. However, if it is not considered in detail in the design process, unnecessary trouble will inevitably occur:

  • a) Blank allowance of workpiece. The blank size is too large, resulting in interference. Therefore, the blank drawing must be prepared before design. Leave enough space.
  • b) Smooth chip removal of fixture. During the design, due to the limited processing space of the machine tool, the fixture is often designed with a compact space. At this time, it is often ignored that the iron filings generated in the processing process accumulate at the dead corner of the fixture, including the poor outflow of chip liquid, which brings a lot of trouble to the future processing. Therefore, the problems in the processing process should be considered at the beginning of practice. 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 load the card, which is time-consuming and laborious, and the design is taboo.
  • d) The basic theory and principle of fixture design. Each fixture has to undergo countless clamping and loosening actions, so it may meet the user’s requirements at the beginning, but the additive should have its accuracy retention, so don’t design something contrary to the principle. Even if we can get away with it now, it will not last long. A good design should withstand the tempering of time.
  • e) Replaceability of positioning elements. The positioning elements are seriously worn, so quick and convenient replacement should be considered. It is best not to design into larger parts.

The accumulation of fixture design experience is very important. Sometimes design is one thing, and it is another thing in practical application. Therefore, good design is a process of continuous accumulation and summary.
Common tooling fixtures are mainly divided into the following types according to their functions:

  • 01 clamping die
  • 02 drilling and milling tooling
  • 03 numerical control and instrument collet
  • 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

Clamping die

Definition: a tool for positioning and clamping with product shape.

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Key points of design:

  • 1. This kind of clamping die is mainly used for vise, and its length can be cut as needed;
  • 2. Other auxiliary positioning devices can be designed on the clamping die, and the clamping die is generally connected by welding;
  • 3. The figure above is a schematic diagram, and the structural dimensions of the mold cavity are determined by the specific conditions;
  • 4. The locating pin with diameter of 12 is tightly matched at the appropriate position on the moving die, and the locating hole at the corresponding position of the fixed die slides with the locating pin;
  • 5. When designing the assembly cavity, it is necessary to offset and enlarge 0.1mm on the basis of the outline surface of the non shrinking blank drawing.

Drilling and milling tooling

20210812084458 41439 - Design of tooling fixture

Key points of design:

  • 1. If necessary, some auxiliary positioning devices can be designed on the fixed core and its fixed plate;
  • 2. The above figure is the 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 stress during processing. SDA50x50 is commonly used.

CNC, instrument collet, a CNC collet, internal beam collet

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Key points of design:

  • 1. The dimensions not marked in the figure above are determined according to the inner hole size structure of the actual product;
  • 2. The outer circle in contact with the positioning of the inner hole of the product shall be made with a margin of 0.5mm on one side, and finally installed on the NC machine tool to finish turning to the size to prevent deformation and eccentricity caused by the quenching process;
  • 3. It is recommended to use spring steel and pull rod 45#;
  • 4. The thread M20 of the pull rod part is a common thread, which can be adjusted according to the actual situation.

Instrument cluster collet

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Key points of design:

  • 1. The above figure is a reference diagram, and the assembly dimension and structure are determined according to the overall dimension and structure of the actual product;
  • 2. Material use 45#, quenching treatment.

Instrument external beam collet

20210812085805 46755 - Design of tooling fixture

Key points of design:

  • 1. The above figure is a reference diagram, and the actual size is determined according to the inner hole size structure of the product;
  • 2. The outer circle in contact with the positioning of the inner hole of the product shall be made with a margin of 0.5mm on one side, and finally installed on the instrument lathe to finish turning to size to prevent deformation and eccentricity caused by quenching process;
  • 3. Material use 45#, quenching treatment.

Gas test tooling

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Key points of design:

  • 1. The above figure is the reference diagram of the gas test tooling. The specific structure shall be designed according to the actual structure of the product. The idea is to seal the product in as simple a way as possible, so that the part to be tested and sealed is filled 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 in contact with the product generally adopts materials with good compression such as Youli rubber and NBR rubber ring. At the same time, it should be noted that if there is a positioning block in contact with the appearance surface of the product, white rubber plastic block should be used as far as possible, and cotton cloth should be covered during use to prevent damaging the appearance of the product;
  • 4. The positioning direction of the product shall be considered in the design to prevent false inspection due to the internal leakage of gas trapped in the product cavity.

Punching tooling

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Key points of design:
The figure above shows the common structure of punching tooling. The function of the bottom plate is to be conveniently fixed on the workbench of the punch press; 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, which can easily and safely take and place the product; The baffle plate is used to facilitate the separation of the product from the punching knife; The strut acts as a fixed baffle. The assembly position and size of the above parts can be designed according to the actual situation of the product.

Welding tooling

The welding tooling 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 should be noted that when the product is placed on the welding tooling, no sealing space shall be generated between the tooling to prevent excessive pressure in the sealing space during welding heating from affecting the size of parts after welding.

Polishing fixture

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Assembly tooling

Assembly tooling is mainly used to assist positioning in the assembly process of components. The design idea is that the product can be easily taken and placed according to the structure of component assembly, the appearance surface of the product can not be damaged during assembly, and the product can be covered with cotton cloth to protect the product during use. In the selection of materials, try to use non-metallic materials such as white glue.

Pad printing, laser engraving tooling

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Key points of design:
The positioning structure of the tooling shall be designed according to the lettering requirements of the actual situation of the product. Attention shall be paid to the convenience of taking and placing the product and the protection of the product appearance. The positioning block and auxiliary positioning device in contact with the product shall use non-metallic materials such as white glue as far as possible.

Source: Network Arrangement – China Pipe Sleeves Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com

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