QUASAR FAQ What is the difference between Quasar and the Impulse system?

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1 1 QUASAR FAQ What is the difference between Quasar and the Impulse system? Impulse Testing is a method in which the part is struck with a hammer and a microphone is used to detect the vibration. A Fast Fourier Transform is then applied to compute the resonant spectrum. The advantage of the Impulse method is that it is fast and cheap. The disadvantage is that it is limited to detecting only the grossest defects. The primary reason for this limitation is that the normal process variations that are present in every manufacturing operation have a greater effect on the resonant frequencies than the effect of the defects. So the process variations mask the defects. While an Impulse system often seems to provide satisfactory results when only one production lot of parts is tested, when many lots that represent the entire range of process variation are tested, it is always unsatisfactory. Customers explain that the Impulse system just does not have the required selectivity to identify the difference between good and bad parts that are produced under normal production conditions. Quasar uses a completely different starting point for the testing and differentiates itself in four fundamental points: 1. Process compensation and the elimination of the variations that occur in every normal production process is produced by the use of several resonance's. Typically 5 to 8 resonance's are used for the evaluation. 2. Quasar uses Continuous Wave excitation (CW) of the resonance's. CW provides a measurement accuracy of about 0.01%. Impulse measurements are limited to about 1%. Since the effect of the defects is often less than 1%, many defects cannot be detected. 3. CW also allows Quasar to test at higher frequencies. Smaller defects are detected best at higher resonant frequencies (that is, shorter wavelengths). Impulse systems are typically limited to about 40 khz. The Quasar system can operate up to over 1000 khz. 4. Quasar uses temperature compensation. A part s resonant frequency decreases as it s temperature increases. For an iron part the decrease is 0.015% per degree Celsius. Since part temperatures often vary +/- 10 degrees or more, this temperature variation can mask defects. Quasar measures the temperature of each part and uses it to correct the measurement to a reference temperature. Quasar is not simply another type of impulse testing. It does not simply measure one or more resonance's for evaluation. First the mathematical composition of numerous resonance's give the powerful process compensation and the sorting capability that is unique. Is Magnaflux more than just a test system? Yes, Magnaflux Quasar is firstly Process Control System at first. The Process Control measures the current production in relation to the training set. The Process Control capability gives you added value by tracking your production, part by part.

2 2 With complex pieces is there the possibility that some zones (or parts of the piece) that are not resonated and therefore impacts the defect identification? The answer depends on the method. In theory, striking the part with an impulse excites all of its resonance's. In practice however, the impulse measurement can only resolve the lowest frequency resonance's, so it is likely that defects associated with a relatively small feature will not be detected. With CW excitation each resonance is excited individually (that is why it takes longer for a CW test.) So it is important that the part be evaluated over a broad frequency range to assure that all features are tested. If the CW method is implemented correctly, a sufficient number of resonance's will be measured and evaluated to assure that all of the part features of interest will be tested. Typically, Quasar gathers data on typically resonance's to select those that are needed to effectively sort the parts. Can the frequency spectrum be changed so that all areas of the piece are resonated? Yes, with CW testing the frequency range used is determined for each individual part. How can be certain that an entire complex part has been resonated and tested? This is a critical part of the set-up of any NDT system. Quasar refers to this as training the system There are two critical steps. 1. Data must be collected for a sample of parts that include all of the defect types and locations of interest. 2. Data must be collected over a sufficiently broad frequency range to assure that all feature resonance's are measured. If there is a defect in a feature that is not represented in the training set, then there is some question as to whether it will be rejected. If the defect is relatively large, it will be rejected, but if the defect is small it may be accepted. Does the Quasar method use impact sound (structure-borne sound) to test the pieces? No. The Quasar method measures the resonance of the part in direct contact. The measurement occurs via piezoelectric transducers. Three transducers are used whereby one is used to excite the piece (CW) and the other two are used to measure.

3 3 Is more than one resonance measured? Yes. The number used is determined by the complexity of the part, the amount of process variation and the severity of the defects. Quasar s pattern recognition program VIPR automatically determines how many resonance's are needed based on the statistics of the database. When training the system, the bad parts are classified into five categories from 1 (small) to 5 (fatal). VIPR takes this classification into account for its calculations. Unknown parts can also be trained into the system and later (for example after destructive testing) reclassified. Typically, VIPR uses 5-8 resonance. VIPR automatically calculates a frequency band in which the relevant frequencies occur and later only these bands are used during the production testing. Is the entire frequency band always measured? No, only the bands relevant to the individual part are measured. What ist he training process for newly developed parts? Quasar needs defective parts for developing the Sorting Module (the algorithm that controls the test). If none are available, we use one of two methods. The preferred method is to adjust the process to make defective parts. If this is not possible, good parts are made defective, for example by cutting them to simulate a crack. For what size production run does it make sense to use Quasar testing? It typically requires from a few days to two weeks to develop and check out the Quasar Sorting Module for a given part type. So the production run has to be large enough and continuous to justify this effort. The maximum run rate in operation is about 800 parts per hour, using a dual nest system with automatic loading. The amortisation of a Quasar System for a typical suspension part is generally completed in under one year. By the amortisation calculation, it must be considered that Quasar replaces other test systems and can thereby generally reduce testing costs by a factor of 3 to 5. How can be certain that no defective pieces make it through testing as good pieces? There is no way that you can be absolutely certain that a defective part will never be accepted. No NDT method is perfect. However, Quasar has been shown in many tests to be far superior to other NDT. For example, MPI (magnetic particle inspection) has been shown to have a false accept rate of 15% to 50% depending on the type of defect and the competence of the operators. In tests that our customers have performed, Quasar s false accept rate is from 0.2% to 1.5%. So Quasar is at least 10 times better than MPI. Similar results are obtained for comparisons to other NDT methods. Most importantly, Quasar is independent of human influence and is therefore reproducible.

4 4 How can be certain that no good pieces are rejected as defective? The answer is similar to the answer for the question above. There will always be some false rejects With Quasar, you have the opportunity to bias the test to avoid either false accepts or false rejects. Most of our customers are more interested in avoiding false accepts. Referring to MPI again, our customer tests have shown that the MPI false reject rate ranges from 30% to 95%. The typical Quasar false reject rate is about 1%. Can be trained to set up the Quasar system for a new part? Yes, the customer learns to handle all aspects of the system. How much time is required for a parts change? Quasar provides a Test Head that is customized to each part. Changing the part types requires changing the Test Heads and that takes about 15 minutes. What experiences do other customers have with Quasar? The general response from customers after introducing a Quasar System into their quality control process is that the number of defective pieces that are delivered to the customer were reduced (by a factor of 10) drastically. What defects can a Quasar System Identify? Quasar tests structural errors and identifies these common defects: Aluminium Cast Iron Cast PM Forge Oxides Oxides Oxides Bar Ends Cold Shuts Cold Shuts Chipped Teeth Double Strikes Porosity Porosity Porosity Laps (folds) Structural Carbide Sintering Non Fills Cracks Structural Missing Details Missing Details Blow Holes Cracks Coining Heat Treat Missing Details Non Fills De carb Inclusions Elongation Missing Details Inclusions Elongation Heat Treat Nodularity What defects are not identified with a Quasar System? Quasar Systems cannot be used for: Cosmetic indications (for example light scratches) Parts that do not resonate because they are not stiff enough.

5 5 How does Quasar work with tool changes? Different processes require special tooling to produce the part, for example, cavities for drop forge or dies for casting. These tools generally wear which leads to the condition that the part has an (acceptable) change in size. When the Quasar system is changed, the entire spectrum of process variations have to be included. That means parts from new tools as well as parts from tools at the end of their life cycle have to be included. The Quasar process is designed so that the normal process variations can truly identified and differentiated from defects. It learns that the changes in the tools are not defects but a normal process variation. Quasar therefore ignores the acceptable changes caused by older tools and will not identify these as defects. Hesselmann & Köhler Prozessautomation GmbH Zeppelinstr.3 D Limburg Germany phone +49 (0) fax +49 (0)