Vibration fixture design is a necessary component of vibration testing that is often a challenge for many engineers. When it comes to the design of fixtures, the choice of materials used is very important. For example, common materials include: magnesium, aluminum, and steel.
The experts at JTL America are ISO/IEC 17025:2017 certified and have years of experience in custom vibration fixture design using a variety of different materials. In this article, we describe each of these materials and how they’re useful in the design of vibration fixtures; furthermore, we’ll address technical details and common questions about this process.
Before the fixture can be designed several factors should be considered.
- Define the frequency range and amplitude.
- Define the axis. (i.e. global or locale coordinated, sample in-vehicle position)
- How many samples are to be tested?
- Can multiple samples be tested at once?
- What is the required control strategy? (i.e. single accelerometer, control, or multiple)
Vibration Fixture Design Materials
Magnesium – There are many benefits to using magnesium in vibration fixture designs. For instance, magnesium remains the best choice regarding weight to stiffness ratio. Moreover, magnesium has higher damping than other materials. One of the best types of magnesium for these designs is AZ31B Magnesium Alloy.
Aluminum – Aluminum alloy is a good material choice for small to medium fixtures because it’s cheaper than other materials such as magnesium. Two reliable types of alloy for the design of medium vibration fixtures include: 6061 aluminium alloy, and 7075 aluminium alloy.
Steel – Steel is the heaviest of the aforementioned metals; however it has a very high strength to cost ratio and as a result, is less cost-efficient. Steel is not a good choice for higher frequency testing due to the dynamic response. For example, steel will “ring” when resonance is detected; this “ringing noise” is a result of low damping. Many software applications actually use a decay filter to force this ringing event (dynamic response) back to zero.
Frequently Asked Questions
What is the frequency range and amplitude?
Frequency ranges for ED shakers run from 5-3000HZ. We will define this range as our usable frequency range. Amplitude can also vary. It can be a fixed amplitude or have multiple amplitudes. FEA simulation can help with this design criteria.
Define the axis. (i.e. global or locale coordinated, sample in-vehicle position)
Defining in-vehicle position will position the sample on the test fixture. Once this positioning is defined, we can design the overall footprint. Pay close attention to the center of gravity. The higher the center of gravity the larger the base plate needs to be. If the sample can be in local coordinates, then we can position the sample on the fixture with the lowest center of gravity. Let’s look at a radiator. In-vehicle position will stand the radiator upright. This will have a high center of gravity. If the radiator can be laid horizontal, we have a very low center of gravity. X and Z-axis globally will now be Z and X-axis locally. This isn’t always an option; It’s best to discuss this option with the OEM and supplier.
How many samples can be tested?
Samples determine how many can be tested at once. Each ED shaker has a certain footprint and weight capability.
Can multiple samples be tested at once?
Small samples can have multiple samples at once. Larger samples will either be tested individually or only a few samples at a time.
What is the required control strategy? Single accelerometer control, or multiple?
Control strategies and repeatability are critical for vibration testing. Many times, multiple control accelerometers are needed. Multiple control accelerometers are averaged together to insure the samples are not over/under tested. Horizontal testing may only require 1-2 control accelerometers. Vertical testing may require up to 4 control accelerometers. Does the OEM or supplier have a defined control strategy? Please contact JTL America today. Our experts will help you.