Fundamentals of High-Performance Fixture Configuration
The design of fixtures is typically based on the specific requirements of a particular manufacturing process after determining the machining steps for the parts. When developing this process, it is important to fully consider the feasibility of the fixture. Additionally, during the design of the fixture, suggestions for modifying the process can be made if necessary.
The quality of fixture design should be evaluated based on its ability to consistently ensure the workpiece’s processing quality, achieve high production efficiency, minimize costs, facilitate easy chip removal, promote safe operation, save labor, and allow for straightforward manufacturing and maintenance.
1. Basic principles of fixture design
- Meet the stability and reliability of workpiece positioning during use;
- Have sufficient load-bearing or clamping force to ensure the processing process of the workpiece on the fixture;
- Meet the simple and fast operation during clamping;
- The vulnerable parts must be a structure that can be quickly replaced, and it is best not to use other tools when conditions are sufficient;
- Meet the reliability of repeated positioning of the fixture during adjustment or replacement;
- Avoid complex structures and high costs as much as possible;
- Use standard parts as components as much as possible;
- Form the systematization and standardization of internal products of the company.
2. Basic knowledge of fixture design
A good machine tool fixture must meet the following basic requirements:
- The key to achieving accurate machining of a workpiece is to properly select the positioning reference, method, and element. If needed, perform an analysis of positioning errors. It’s also important to consider how the structure of other components in the fixture may impact machining accuracy. This ensures that the fixture meets the required precision standards for the workpiece.
- Enhance production efficiency by adapting fixture complexity to capacity. Utilize various fast and efficient clamping mechanisms to ensure convenient operation, reduce auxiliary time, and improve overall production efficiency.
- The structure of special fixtures with good process performance should be simple and reasonable, easy to manufacture, assemble, adjust, inspect and repair.
- Fixtures that perform well should possess adequate strength and rigidity, while also ensuring that their operation is straightforward, labor-saving, safe, and reliable. When conditions allow and it’s economically feasible, pneumatic, hydraulic, and other mechanized clamping devices should be utilized as much as possible to reduce the operator’s labor intensity. Additionally, the fixture should facilitate easy chip removal. If necessary, a chip removal system can be integrated to prevent chips from disrupting the positioning of the workpiece, damaging the tool, or accumulating and generating excessive heat, which could lead to deformation of the process system.
- To achieve a cost-effective economy, special fixtures should utilize standard components and structures whenever possible. The design should aim for a simple structure that is easy to manufacture, which in turn will help reduce production costs. Therefore, it is essential to conduct a technical and economic analysis of the fixture design based on order requirements and production capacity. This approach will improve the economic benefits of the fixture during production.
3. Overview of the standardization of fixture design
1. Basic methods and steps of fixture design
Preparation before design The original data of fixture design include the following:
a) Technical data must include the design notice, finished part drawings, blank drawings, and process routes. It’s essential to understand the processing technical requirements for each step, including the positioning and clamping schemes, the processing content from the previous stage, the status of the blank, the machine tools, cutting tools, inspection tools, as well as the processing allowances and cutting amounts utilized during machining.
b) Understand the production batch and the need for fixtures;
c) Understand the main technical parameters, performance, specifications, accuracy of the machine tools used and the connection dimensions of the structure of the fixture connection;
d) The inventory of standard materials for fixtures.
2. Issues to be considered in fixture design
The design of fixtures typically features a straightforward structure, giving the impression of simplicity. This is particularly true with the rise of hydraulic fixtures, which significantly streamline the traditional mechanical design. However, if details are not carefully considered during the design process, it can lead to unnecessary complications.
a) The size of the blank allowance for the processed part is too large, causing interference. Therefore, it is necessary to prepare a rough drawing before designing and to leave enough space.
b) The removal of chips from the fixture is a significant consideration. Due to the limited processing space of the machine tool during its design, fixtures are often created with compact dimensions. However, this can lead to the accumulation of iron chips in hard-to-reach areas of the fixture, as well as poor drainage of cutting fluid. These issues can cause considerable difficulties in subsequent processing. Therefore, it’s important to address potential problems during the initial design phase. Ultimately, the goal of the fixture is to enhance efficiency and facilitate operations.
c) The overall design of the fixture’s openness is crucial. Neglecting this aspect makes it challenging for the operator to install the card, leading to time-consuming labor, which is a significant design flaw.
d) The fundamental theoretical principles of fixture design dictate that each set of fixtures must endure numerous clamping and loosening actions. While a fixture may initially meet the user’s requirements, it is essential for the fixture to retain its accuracy over time. Therefore, designs should not contradict these principles. Even if a fixture works by chance initially, it is unlikely to maintain its effectiveness in the long run. A well-designed fixture should be able to withstand the test of time.
e) The replaceability of positioning components is important. The positioning element is significantly worn, so a quick and convenient replacement should be considered. It is advisable not to integrate it into a larger part.
The accumulation of experience in fixture design is crucial. Sometimes, design theory differs from practical application; thus, effective design involves ongoing accumulation and reflection.
Commonly used tooling and fixtures are mainly divided into the following categories according to their functionality:
- Clamp
- Drilling and milling tooling
- CNC and instrument chuck
- Gas test and water test tooling
- Trimming and punching tooling
- Welding tooling
- Polishing jig
- Assembly tooling
- Pad printing and laser engraving tooling
01 Clamp
Definition: A tool for positioning and clamping using the product shape.
Design points:
- This type of clamp is mainly used on the vise, and its length can be cut as needed;
- Other auxiliary positioning devices can be designed on the clamp, and the clamp is generally connected by welding;
- The above figure is a simple diagram, and the cavity structure size is determined by the specific situation;
- The locating pin with a diameter of 12 is tightly fitted at the appropriate position on the movable mold, and the locating hole at the corresponding position of the fixed mold slides with the locating pin;
- When designing the assembly cavity, it is necessary to offset and enlarge the outer surface of the blank drawing without shrinkage by 0.1mm.
02 Drilling and milling tooling
Design points:
- If necessary, some auxiliary positioning devices can be designed on the fixed core and its fixed plate;
- The above figure is a simplified structural diagram. The actual situation needs to be designed according to the product structure;
- The cylinder is determined according to the product size and the stress during processing. SDA50X50 is commonly used;
03 CNC and instrument chuck
CNC chuck, inner beam chuck
Design points:
- The dimensions not marked in the figure above are determined according to the inner hole size structure of the actual product;
- When creating the outer circle that fits against the inner hole of the product, a 0.5 mm margin should be left on one side. Afterward, the piece should be installed on the CNC machine tool and finely turned to the correct dimensions. This process helps prevent deformation and eccentricity that may occur due to the quenching process.
- The material of the assembly part is recommended to use spring steel, and the pull rod part is 45#;
- The thread M20 of the pull rod part is a common thread, which can be adjusted according to actual conditions.
Instrument internal clamp
Design points:
1. The above figure is for reference only. The assembly dimensions and structure are determined according to the actual product dimensions and structure;
2. The material used is 45#, quenched.
Instrument external clamp
Design points:
1. The above figure is for reference only. The actual size depends on the inner hole size structure of the product;
2. When creating the outer circle that will contact the inner hole of the product, a margin of 0.5 mm should be left on one side. Once this is done, the piece should be installed on the instrument lathe and finely turned to the correct size. This process helps prevent deformation and eccentricity that can occur as a result of the quenching process.
3. The material used is 45#, and it is quenched.
04 Gas test tooling
Design points:
1. The image above shows a reference for the gas test tooling. The design must be tailored to match the actual structure of the product. The goal is to seal the product in the simplest manner possible and fill the area to be tested with gas to verify its seal.
2. The cylinder’s size can be adjusted based on the product’s actual dimensions, and it is important to consider whether the cylinder’s stroke allows for easy retrieval and placement of the product.
3. The sealing surface that comes into contact with the product typically utilizes materials that offer good compression, such as polyurethane (PU) and nitrile butadiene rubber (NBR) rings. Additionally, if there is a positioning block that touches the product’s surface, it is advisable to use a white plastic block and cover it with a cotton cloth during use to prevent scratches on the product’s appearance.
4. The product’s positioning direction must be considered during design to prevent gas from being trapped inside the product cavity, which could lead to misdetection.
05 Punching tooling
Design points:
The figure above illustrates the typical structure of punching fixtures. The bottom plate is designed to secure the fixture to the workbench of the punching machine, while the positioning block holds the product in place. The specific design of these components can be tailored to fit the actual requirements of the product.
The center point can be conveniently and safely positioned around the product, and the baffle assists in the easy detachment of the product from the punch. Additionally, the pillar serves to secure the baffle in place. The assembly positions and dimensions of these CNC machined components can also be customized according to the specific needs of the product.
06 Welding fixture
The welding fixture is essential for securing the position of each component during the welding assembly and for controlling their relative sizes. Its main structural element is the positioning block, which must be designed according to the specific structure of the product. It is important to ensure that when the product is placed on the welding fixture, no sealed spaces are created between the fixtures. This is to prevent excessive pressure from building up in any sealed areas during the welding heating process, as this could affect the dimensions of the components after welding.
07 Polishing fixture
08 Assembly tooling
Assembly tooling primarily serves as a device to assist with the precise positioning of milling components during the assembly process. The design concept focuses on facilitating the placement of products in accordance with the assembly structure. It is important to ensure that the assembly process does not damage the product’s appearance. To protect the product during use, it is advisable to cover it with cotton cloth. When selecting materials, it is recommended to use non-metallic options, such as white glue.
09 Pad printing and laser engraving tooling
Design points:
Design the positioning structure of the tooling based on the specific engraving requirements of the product. Ensure that the product is easy to place, while also protecting its appearance. Use non-metallic materials, such as white glue, for the positioning block and any auxiliary positioning devices that come into contact with the product whenever possible.
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