Research on Efficiency Improvement of Multi-Station Fixtures in Batch Impeller Production

As a key component of fluid machinery, the impeller features complex structure, high precision requirement, and inconvenient machining. In the context of mass production, faced with the comprehensive requirements of high tempo, high consistency, and low manual reliance, the traditional single-station fixture model has increasingly manifested shortcomings of long clamping time, large positioning errors, and low machining tempo, becoming a bottleneck force for capacity release.

Introduction

The introduction of multi-station fixtures provides a new way to solve the above problems. By arranging a number of stations within the same fixture, it realizes synchro machining and parallel operation of workpieces, which can greatly improve the utilization of CNC equipment and the level of automation. As a production technician on the front line, I have deeply felt that in the actual transformation of a number of FANUC machining centers, multi-station fixtures not only significantly enhance the rhythm of the process but also lay an essential foundation for subsequent development toward unmanned production lines and intelligent manufacturing systems. Therefore, systematic research on its design optimization and application benefit has important practical value and technical significance.

Analysis of Clamping Requirements for Impeller Parts

Impeller parts are typical high-precision rotary components, which feature complex structures, and the manufacturing accuracy has a significant impact on the overall machine performance. The clamping requirements for impeller machining need to be carefully addressed from the following points:

• Structural symmetry and high-speed operation characteristics: Require the fixture to have extremely high coaxiality control capability to avoid eccentricity and runout.
• Complex blade surfaces and thin walls prone to deformation: Need moderate and uniform clamping force to prevent local deformation.
• Most surfaces are free-form surfaces, making standardized positioning difficult: Require customized flexible support modules to balance stability and adaptability.
• High repeated positioning accuracy and fast replacement requirements: Especially in mass production, the fixture needs to achieve rapid positioning and one-key replacement to improve standardization.
• Tight coupling with subsequent processes (dynamic balance detection, spraying, electrolysis): The fixture should have external interface expansion capabilities to support process chain integration.

Briefly, the impeller machining clamping system is not only a geometric positioning tool but also an important node to achieve the flexibility of the manufacturing system effectively. The traditional fixture solutions can no longer accommodate the needs of impellers in precision and rhythm, and multi-station fixtures have to be introduced urgently as an improvement path.

Design Principles and Structural Classification of Multi-Station Fixtures

In the modern efficient production systems, especially five-axis simultaneous machining of batch impeller parts, multi-station fixtures, as important equipment to increase production capacity and decrease cycle time, their structural design quality directly affects the rhythm of the entire production line and product consistency. Since machining precision and automation levels continuously enhance, fixtures are not merely demanded to meet basic positioning and clamping functions but also have high adaptability in modularization, automation, heat management, and system integration. In this chapter, the engineering application of multi-station fixtures will be discussed systematically from the aspects of design principles and structural classification.

Design Principles of Multi-Station Fixtures

For multi-station fixture design, the process requirements must be intimately integrated with equipment characteristics in order to improve the workpiece switching and equipment usage efficiency, and ensure machining stability. Firstly, modular structure design is the key to improving flexible manufacturing capability. Through the use of standardized positioning modules and clamping modules, users can quickly change positioning parts for different workpieces, achieving the seamless switch of multiple product models, especially for mixed-flow production contexts.

Second, to achieve high-precision repeated clamping, the fixture should have high rigidity and repeated positioning capability. When choosing structural materials and part fitting design, high-strength alloy material, precision guide rail, positioning pin sleeve, etc., should be used to ensure the positioning error within ±0.01 mm after each replacement. In addition, the rational design of the cooling and chip removal system is also a prerequisite to ensure stable machining. The cutting area of each station should be provided with independent or shared coolant spraying passages and be coordinated with structures such as chip removal slots and chip suction holes to actively remove machining-generated debris and heat sources.

To prevent spatial interference between multiple stations, station layout and trajectory planning are also necessary. For the fixture arrangement, it must be able to ensure that the tool activity ranges of all stations do not interfere with each other in the machining state, according to the minimum gap safety control between the spindle motion track and the convex shape of the workpiece. Finally, compatibility design cannot be ignored. The fixture structure should be redesigned as per the demands of automatic loading and unloading devices (e.g., manipulators, truss mechanisms) and man-machine cooperation, providing interfaces in the operation interface, quick-change mechanism, and status recognition system to improve user-friendly automation levels.

Typical Structural Types of Multi-Station Fixtures

The structural type of multi-station fixtures can be freely selected according to machine tool types, workpiece shape, and tempo requirements. The most common multi-station fixture structural types applied in industry nowadays are as follows:

• Disc-type fixtures: This type is widely used in vertical machining centers or vertical five-axis machine tools. The fixture realizes station change through a rotary worktable, with advantages of compact structure, precise positioning, and clear rhythm, which is suitable for batch machining of medium-sized impeller products. In combination with a servo drive system and encoder feedback device, it can well support the automation of position change rhythm.
• Gantry frame fixtures: Designed for gantry machines or horizontal machining centers, the machining objects are usually large, heavy, or multi-curved impeller structural parts. The rigidity of the structure is good and the stability is high, convenient for multi-point supporting, wide-range locating, and easy to install multiple independent hydraulic or pneumatic clamping devices for improving safety and machining stability.
• Column tower fixtures: The fixture evenly distributes a number of stations on the four or six faces of the column, and can be used for multi-sided continuous machining together with a five-axis turntable. Its greatest benefit is high space utilization, especially for machining axisymmetric impeller workpieces with symmetrical structures, and is an ideal choice for compact machining units.
• Combined pallet fixtures: Based on the flexible manufacturing principle, this composition modularizes the pallets and realizes the quick installation and disassembly through a quick-change base. Suitable for small-batch and multi-variety workpiece machining situations. Together with visual recognition systems and RFID tag recognition technology, automatic station identification and quick matching of clamping schemes are possible.

In a number of impeller manufacturing projects that I have participated in, for the overall application of medium size and high-frequency machining requirement, I would prefer to use disc-type or column tower fixture structures, which not only can meet the requirements of quick station change and guarantee clamping precision but also are highly compatible with robot loading and unloading systems, significantly improving the automation degree and equipment usage rate of the entire line.

Analysis of Efficiency Improvement Mechanism of Multi-Station Fixtures

In the contemporary efficient manufacturing system, the primary objective of production line design is to improve machine tool utilization rate and machining tempo efficiency. As an intensive clamping solution, multi-station fixtures not only exhibit superior advantages in operation time saving and labor cost saving but also provide systematic support in process integration and product consistency control. Especially in the mass production of complex surface components such as impellers, multi-station fixtures have become an important pivot for realizing intelligent manufacturing and flexible production.

Reducing (replacement) Time and Realizing Parallel Processing and Loading/Unloading

Traditional single-station fixtures must close down and be changed after the processing of every workpiece, not only involving numerous operations and great human involvement but also resulting in excessive idle time for the machine tool spindle. In comparison, multi-station fixtures complete the setup of multiple workpieces with one clamping, adopting a parallel processing mode of “machining one piece, loading/unloading two pieces.”. For example, when using a six-station disc fixture, when one station is undergoing machining, the other stations can perform loading and unloading operations, greatly saving the clamping time. The average replacement time of each workpiece can be shortened from 36 seconds to less than 10 seconds, with the rhythm tightened by more than 70%, fundamentally improving the per-unit-time output efficiency of a single machine.

Improving Spindle Utilization Rate and Unleashing Equipment Potential

Multi-station fixtures significantly reduce spindle waiting time, keeping the machine tool in the status of high-speed work during the machining cycle, and greatly improving equipment utilization rate. According to production practice data, with the use of single-station fixtures, due to interference operations such as replacement and positioning, the useful working time of the spindle only accounts for approximately 55% of the total operation time; after the use of multi-station fixtures, the spindle utilization can be more than 85%. Spindle load increased use not only achieves the maximization of equipment energy efficiency ratio but also increases the unit time output value of the machine tool, creating greater return on investment for the company.

Parallel Integration of Processes and Breaking Through Manufacturing Bottlenecks

Multi-station fixtures not only have the ability to machine multiple workpieces simultaneously but can also realize parallel implementation of more than one operation such as rough machining, semi-finishing, finishing, and chamfering through distributing different processes into different stations. Such a mode of “process compounding + workpiece multiplexing” transcends the limitation of traditional linear process flows, and the comprehensive machining rhythm becomes compact. Especially on five-axis machining centers, the control of each channel’s tool paths separately by a zonal method greatly improves the general rhythm of production and reactivity, shortening the delivery cycle.

Reducing Manual Dependence and Improving Clamping Precision

Traditional clamping relies on manual centering and manual clamping, which is not only time and labor-consuming but also risks cumulative repeated positioning errors. Multi-station fixtures are typically constructed with precision guiding structures and pin sleeve systems for location, so repeat precision is excellent for every clamping, and the conventional errors are in the range of ±0.01 mm. In the meantime, their structure is more easily integrated with robot systems for achieving automatic workpiece position recognition, automatic clamping, and status feedback, greatly reducing dependence on manual experience and laying a technical foundation for the subsequent realization of unmanned machining units.

Improving Finished Product Consistency and Yield Rate

By utilizing multi-station fixtures, continuous machining of multiple workpieces is possible under a single datum positioning, which can successfully avoid cumulative errors caused by multiple clampings. When utilized for the machining of impeller components with high precision and consistency requirements, dimensional stability and consistency of form and position tolerances are significantly improved. At the same time, the high-rigidity structure of the fixture can also suppress thermal deformation and machining vibration, ensuring machining quality at the source. The data shows that the multi-station fixture solution can increase the product yield by 5% to 8% on some batch production lines and effectively reduce rework rates and inspection costs.

Analysis of Typical Application Cases

On a transformation project of an aviation manufacturing enterprise’s FANUC machining center, they needed to achieve an annual production capacity of 100,000 Φ60mm aluminum alloy impellers. The original process was single-station vertical machining, with a total processing time of 15 minutes per piece and a clamping time of up to 4 minutes. Following the use of a 6-station disc-type multi-station fixture, the effect was substantial:

This case completely demonstrates the huge benefits of multi-station fixtures for tempo improvement and quality control, and it reaches the targets of unit cost reduction by a large margin and production efficiency improvement by a great extent.

Conclusion

As the major process equipment for improving the production efficiency of batch impellers, multi-station fixtures have progressively replaced traditional fixture models and become an essential part of modern efficient manufacturing systems. Through the advantages of modular design, multi-process synergistic machining, and repetitive positioning precision, they have achieved significant improvement in many areas such as spindle utilization rate, production rhythm, product quality, and labor investment.