Experience: The Key Points Of Fixture Design

Introduction

Fixture design is the process of determining the specific requirements of a part’s machining process, performed according to the specific requirements of one or all processes. Fixture design should consider the feasibility, safety, cost-effectiveness, ease of operation, and sustainable maintainability of the part’s machining process. The quality of the fixture design directly affects the quality and efficiency of part machining.

Application classification of fixtures:

1, Universal fixture:

The structure of universal fixture has been standardized, and there are fixtures with a wide range of applications, such as three-jaw chucks and four-jaw chucks, flat-nose pliers and indexing heads.

2, Special fixtures:

Special machine tool or robot fixtures are specially designed and manufactured for a specific process of a workpiece. They are suitable for applications where the product is relatively stable and the output is high.

3, Modular fixture:

A modular fixture is assembled from standard components and assembly parts. This type of fixture is flexible and versatile, with a short design and assembly cycle and long-term reusability of parts. It is suitable for small-batch production of multiple products or trial production of new products.

4, Travel fixture:

This is a mobile fixture used on automated production lines. Before a workpiece enters the automated production line, it is first placed in the fixture. The fixture and the workpiece are then moved from one station to the next along the automated production line. The workpiece is not removed from the fixture until it exits the automated production line. A travel fixture is a fixture that always moves along the automated production line with the workpiece.

Basic principles of fixture design

1. Satisfy the stability, reliability and convenience of workpiece clamping and positioning;
2. Satisfy the clamping strength, bearing strength and cutting strength of the workpiece;
3. It can realize the rapid replacement of wearing parts without affecting the maintenance of other states. If conditions are sufficient, it is best not to use other tools;
4. Ensure the reliability of repeated positioning of the fixture during adjustment or replacement;
5. Considering economy, standard parts should be used as components as much as possible to avoid complex and expensive designs;
6. Form a systematic and standardized specification for fixture design within the company;

Basic knowledge of fixture design

A well-designed fixture must meet the following basic requirements:

1. Ensure the machining accuracy of the workpiece . The key lies in correctly selecting the positioning reference, positioning method and positioning elements. If necessary, positioning error analysis should be performed. At the same time , attention should be paid to the impact of the structure of other components in the fixture on machining accuracy to ensure that the fixture as a whole can meet the machining accuracy requirements of the workpiece.
2. Improve 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 easy operation, shorten auxiliary time, and improve production efficiency .
3. Good process performance. The structure of the special fixture should be simple and reasonable, and easy to manufacture, assemble, adjust, inspect, and maintain .
4. Good performance. Fixtures and fixtures should possess sufficient strength and rigidity, and be easy to operate, labor-saving, safe, and reliable. Wherever possible, pneumatic, hydraulic, or other mechanized clamping devices should be used to reduce operator workload. All fixtures and fixtures should also facilitate chip removal. Chip removal mechanisms should be incorporated when necessary to prevent chips from disrupting workpiece positioning and damaging cutting tools, and to prevent chip accumulation from generating excessive heat and causing deformation in the process system.
5. Economical. Specialized fixtures should utilize standard components and structures whenever possible, striving for simplicity and ease of manufacture to reduce manufacturing costs. Therefore, during design, the necessary technical and economic analysis of the fixture solution should be conducted based on order volume and production capacity to maximize the economic benefits of the fixture in production.

Overview of standardization of fixture design

1, Basic methods and steps of fixture design

The following original materials are required for the preparation before design:

a) Design notice, finished part drawing, rough drawing and process route and other technical information, understand the processing technology requirements of each process, positioning and clamping scheme, the processing content of the previous process, the rough condition, the machine tools, cutting tools, inspection tools used in processing, processing allowance and cutting amount, 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, and the dimensions of the connection part with the fixture;

d) Inventory status of standard materials for fixtures.

2, Issues to consider in fixture design

The fixture design must be systematically considered, otherwise unexpected troubles may occur if you are not careful:

a) The rough allowance of the workpiece. This can cause the rough size to be too large, resulting in interference. Therefore, a rough drawing must be prepared before designing. Leave enough space.

b) Ensure smooth chip removal in the fixture. Due to the limited processing space of machine tools, fixtures are often designed to be compact. This often leads to the accumulation of chips in the fixture’s dead corners, which can lead to poor chip removal and subsequent processing complications. Therefore, consideration should be given to potential issues arising from the machining process from the outset. After all, fixtures are designed to improve efficiency and facilitate operation.

c) The overall openness of the fixture. Ignoring the openness will make it difficult for the operator to install the fixture, which will be time-consuming and labor-intensive, and is a major design taboo.

d) Basic theoretical principles of fixture design. Every fixture undergoes countless clamping and loosening cycles, so while it may initially meet user requirements, the fixture must maintain its accuracy. Avoid designs that violate these principles. Even if it works temporarily, it won’t be sustainable in the long run. A good design should stand the test of time.

e) Replaceability of positioning components. Positioning components are subject to severe wear, so quick and easy replacement should be considered. It is best not to design them as large parts.