Spin Testing for Manufacturing 101

In the quest to produce stronger, more durable, and cost effective rotating parts, manufacturers are turning to spin tests to help achieve these goals. Spin tests for manufacturers can be used to validate the stability and integrity of a part, or to enhance the desirable properties of the material. We will explore the differences between traditional spin testing and spin testing for manufacturing purposes. We will also discuss the benefits of spin-testing your rotating parts, the subtle but important factors necessary to run successful manufacturing spin operations, and the importance of finding the correct spin testing service provider for your specific needs.

Jet engines, power turbines, turbochargers, electric motors — all of these high-speed rotating parts are critical for a wide range of modern high-performance machines and key infrastructures. In order to ensure optimal reliability, durability, and quality, these components must undergo rigorous engineering and testing processes.

Spinning at high speed, a machine part, such as a jet engine disk, stores a significant amount of rotational kinetic energy. In the event of a part failure, this stored kinetic energy is released, and the end result can be catastrophic. To prevent this, a spin test is conducted to evaluate the structural integrity and robustness of high-speed rotating parts. The data collected from this test allows engineers to better understand rotors’ failure behavior and improve the design as needed. Introduced more than half a century ago, spin testing techniques have been integral to the evolution of high-speed rotating machines.

While there are a variety of spin tests available, most of them can be grouped into one of two major categories: Spin Testing for Research and Development and Design Validation, or Spin Testing for Manufacturing.

Spin Testing for R&D and Design Validation

• Custom-designed engineering tests used to validate the rotor design and/or certify the part
• Typically involve a prototype, first article, or purpose-designed test rotor assembly
• Design, build, and execution of the test should be carried out as a carefully managed engineering project
• Test rig designs aim to maximize measurability of engineering data, and create realistic conditions during the test to simulate the relevant operating environment of the machine
• Some examples of R&D and Design Validation spin testing include: Overspeed Certification Tests, Low Cycle Fatigue (LCF) Tests, High Temperature and Thermal Gradient Spin Tests, and Dynamic Spin/High Cycle Fatigue (HCF) Tests

Spin Testing for Manufacturing

• Involve processing batches or a large volume of parts to specified operation and inspection steps
• A quality-controlled manufacturing operation is streamlined to produce consistent, quality products
• Timeliness, quality, and efficiency are the key drivers of a successful manufacturing spin operation

Achieving Repeatable Success in Manufacturing Spin Tests

While manufacturing spin tests may appear simple and uninvolved in comparison to the more complex and sophisticated R&D spin tests, the success and usefulness of all tests depends on the expertise of the team you choose to partner with. Experienced technicians and engineers will have carefully planned quality processes in place to ensure smooth testing and reliable results.

In order to deliver products to customers’ specifications both cost-effectively and on time, manufacturing spin tests must make use of robust, high-quality manufacturing systems capable of achieving success over thousands (and sometimes millions) of iterations. In order to achieve this repeatability, a holistic approach that considers the details of each step in the operational workflow must be employed.

Manufacturing spin tests can be further broken down into two categories:

1. Overspeed Test

Overspeed tests are conducted to validate the stability of rotor balance and part integrity in a high-speed environment. Final machined parts, such as turbocharger impellers and turbines, are spun to a customer specified rotational speed to validate the parts’ integrity.

1. Forging Pre-Spin

The forging pre-spin method involves a material conditioning process for aero-engine and power turbine disks. Semi-finished or un-machined forgings are spun to a specified speed to yield the material. There are several benefits of pre-spinning forgings and disks, but typically this work is done to enhance the stability and durability of the material and final products. Forgings are carefully inspected and monitored at each step of the pre-spin process to ensure proper material conditioning.

Manufacturing Spin Operation at a Glance

1. Inspection: Examine the parts for any damage or anomalies; some customers also require part inspections for dimensional conformance
2. Assemble the part with spin tooling
3. Check rotor balancing, and perform corrections if necessary
4. Perform a spin test; monitor rotor balance and rotor dynamic stability over the test speed
5. Record and report the result
6. Disassemble the part from the spin tooling
7. Perform post-test inspections, and ship the part to the customer

Specific to forging pre-spin operations, customers also often require a “pilot run” during the earlier phase of process implementation; the pilot run is typically performed prior to launching a full-scale manufacturing spin operation. A series of pre-spin tests is performed to validate the tooling design performance and try out the handling equipment, operational processes, and documentation flow. These pre-spin tests also allow clients to confirm the material behavior (forging growth to a speed).

Several factors can disrupt successful pre-spin operations, however, including:

Poorly Designed Spin Tooling — Performing an efficient, repeatable operation requires well-designed tooling and handling equipment. Poorly engineered spin tooling can lead to unstable rotor behavior, rotor dynamics issues, and limited reusability in the tooling — ultimately resulting in incipient, recurring issues in pre-spin operation. Successful spin tooling design depends on:

• Tooling and handling equipment design performed by an experienced engineering team that understands the ins and outs of spin operation.
• Years of experience designing and routinely testing different types of spin tooling for different test disks.
• Comprehensive engineering work, from the selection of suitable materials to detailed stress and dynamics analyses of the rotor assembly. Careful engineering ensures reusability and high performance of the tooling in the manufacturing environment.

Balancing and Severe Vibration Issues — A critical step in rotating machine construction, proper rotor balancing helps ensure no time is wasted troubleshooting rotor dynamics and vibration issues. –

• Balancing is often overlooked and performed without a real understanding of its importance. Specific to pre-spin operations, the forgings coming off the production line typically have unfinished contours and are often severely unbalanced. Adding extra steps for machining and balancing forgings, however, results in added costs and downtime. In some cases, forgings may not be able to be easily balanced. (TDI’s high-performance damper system is specifically designed to manage vibration and rotor instability problems.)

Bad Quality Processes and Material Handling — For professionals working within the strict requirements of the aerospace standard, quality processes must be kept in mind throughout the entire operation. Here’s what to look for when sourcing for aerospace standard processes:

• Services based on the AS9100/ISO9001 quality standard, backed by experience with leading aeroengine OEMs.
• A culture of quality that ensures every step of the spin tooling process is performed to stringent standards. Through closely monitored parts tracking and receiving to meticulous inspection and pre-spin work, there should be a guarantee that all processed parts are of the highest possible quality and reliability.
• Highly trained staff, state-of-the-art spin rigs, CMM machines, and climate-controlled inspection rooms.

Inaccurate Speed Measurement and Control — Measuring and controlling rotational speed is critical for successful spin test operations, but this step is also often overlooked.

• Inaccurate speed data and spin test operational records can lead to catastrophic field accidents. Whether done intentionally or unintentionally, rotors spun to an incorrect speed severely compromise the integrity of the parts and the machines.
• In a nonconformance case with an exceeded speed target, the rotor may have sustained damage that is undetectable to inspectors.
• In a nonconformance case with an undershot speed target, there are two likely causes: 1) The rotor was not tested properly to the requirement, or 2) The rotor may not have achieved the required material conditioning at the specified target speed.
• Measuring, recording, and ensuring the accuracy of spin test speed is one of the most important steps in spin test operations, directly affecting the quality of the part. Plus, it’s very difficult and time consuming to examine the aftermath of an incorrectly executed spin test.

Rotor Bursts — Accidents can happen even in the most diligently planned and managed manufacturing environments. During spin testing, it’s important to take preventative measures to manage the risk of disk bursts, since rotors spinning at high speeds store a large amount of rotational kinetic energy that can be released in the event of a part failure, leading to catastrophic damage.

• The first priority in managing the risk of a disk burst is ensuring optimal safety. Spin pit containment alone is not enough; facilities must take necessary measures to protect spin pit operators and surrounding equipment from unexpected containment failures. Ideally, spin pits should be placed in a purpose designed test cell with a separate operator room so that workers are not at risk.
• Downtime in any manufacturing process can cause client dissatisfaction and added expenditures, so it’s critical to establish a practical contingency plan that will allow you to quickly respond to and recover from accidents, should they occur.
• Specific to forging pre-spin work, operators should carefully manage the risk of disk bursts. Forgings are heavy and typically spun to a relatively high speed, which means they can cause great destruction in the event of a burst.

Learn More

For over 40 years, Test Devices Inc. (TDI) has been a leading provider of spin testing services and equipment, developing and advancing the science of centrifugal, vibratory, and thermal stress testing. Whether you’re interested in setting up your own manufacturing spin operation or looking to outsource the work, you’ll need a dependable partner to ensure optimal performance, quality, and reliability.

Since first introducing pre-spin testing services to our range of capabilities ten years ago, TDI has become a trusted partner for various leading OEMs in the development, innovation, and implementation of their pre-spin operations. As a leading expert in spin testing and related applications, our team has a deep understanding of the many small details that can affect successful pre-spin operation design and implementation. Our equipment designs and engineering solutions embody 40 years of pragmatic innovation gained from hands-on experience performing spin tests and industrial spin operations in forging pre-spin work:

• TDI offers a high-performance drive control system built based on the latest PLC technology and TDI’s 1160 Precision Digital High-Speed Tachometer. The 1160 tachometer, built on a 16-bit digital technology platform, allows for fast and reliable speed measurement — thereby ensuring accurate control of rotors in high-rpm spin operations.
• TDI has performed numerous burst tests for different types and sizes of rotors. With years of experience and an accident-free record for many decades, we’re proud to offer the industry’s most robust risk mitigation services against high-energy disk bursts.

For help designing a facility, production processes, and spin tooling, contact us today. Our team can provide the necessary training and expert assistance needed to implement a highly successful operation.