S&R prevention and simulation: Saves cost and spares nerves

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1 S&R prevention and simulation: Saves cost and spares nerves By Christian Berndt, Guido Rybczynski, Markus Scheider und Dr. Hans-Jürgen Daams (ZINS) Klaus Steinberg (7senses) 1 Introduction When squeak, rattle, clatter, etc. are detected by the customer in the car, not only the image of the car make suffers due to the negative perception of S&R but the cost of warranty and goodwill rocket by several orders of magnitude in comparison with remedial measures in the factory and once more by several more orders of magnitude in comparison with the cost of eliminating possible risks at the CAD phase. Most car repair centers do not have the necessary know-how, personnel or equipment for the systematic excitation of S&R to locate the sources and apply a sustainably solution there. When defects cannot be localized, complete assemblies are replaced and the cost of warranty and goodwill tend to get out of control. Hardware is already available when the final inspection is made in the factory. Technically trained personnel and necessary required equipment are available in most cases so that the contact points can be located. The remedial measures are limited to solutions outside the CAD phase and require the use of aids such as felt, buffer or anti-friction coating. Each of these measures, extrapolated for the life of the car, add up to an amount the price of a house, which is very expensive indeed. The lowest cost and the best opportunity to avoid squeak and rattle is during the CAD phase; and it is really possible to produce a virtually S&R free design. But it is not easy to identify the risks associated with the relevant contact points and develop appropriate solutions. ZINS has that know-how and applies it in the CAD together with the design engineers.

2 2 Number of potential risks and processing times S&R prevention was developed by BMW and practiced for the first time 20 years ago. At that time, the software Systematic elimination of S&R was developed which contained every possible contact point (about 600 such points in a car s interior). A contact point was and is a distance of less than 3 mm between any two parts. Now, after 20 years of experience, the number of contact points can be reduced substantially. The table below shows the number of issues that on average can occur in the different assemblies. As a rule, three passes through the CAD data are required to keep pace with the change management: 1. First pass shortly before completion of the CAD data for the first prototypes (loop 1), 2. Second pass shortly before completion of the CAD data for the auxiliary tools (loop 2), and 3. Third pass shortly before completion of the CAD data for the final tools (loop 3) The required time input for an experienced S&R engineer is also given in the table below: Zahl der kritischen Zeit 1. Loop Zeit 2. Loop Zeit 3. Loop Stunden/Ko Modul Kontaktstellen in Tagen in Tagen in Tagen ntaktstelle Instrumententafel ,80 Mittelkonsole vorne ,40 Türverkleidung ,80 Vordersitz ,27 Sitzbank hinten ,40 Säulenverkleidungen, Himmel, G ,13 Schiebedach (einfach) ,13 Anbauteile außen ,80 Karosserie ,52 Mechanismen und Dichtungen ,40 Gesamt ,61 The average number of hours per contact point depends to some extent on the complexity of the component. For example, a seat contains a large number of mechanically moving parts so that more time is needed. The car body is

On average, a vehicle has about 190 critical contact points which require an input of 2.61 hours per contact.

3 comprised of large panels and welding points, which makes the examination time consuming. On the other hand, seals/gaskets require less input. But you have to bear in mind that there are no research-based technical solutions in the market. On average, a vehicle has about 190 critical contact points which require an input of 2.61 hours per contact. This adds up to about 500 man-hours provided an experienced S&R engineer is doing the job. 3 Systematic elimination of S&R 3.1 Locating contact points Rattle is produced by 2 hard parts banging against each other. Squeaking or creaking is the result of 2 parts rubbing against each other tangentially when the materials are incompatible with each other and stickslip results.

So the first and foremost task is to find in the CAD data all contact points where these possibilities can occur. This is shown by the example of a door lining in the illustration on the right. 3.

4 So the first and foremost task is to find in the CAD data all contact points where these possibilities can occur. This is shown by the example of a door lining in the illustration on the right. 3.2 Risk assessment Several algorithms from different OEMs are available for risk assessment. A mention may be made of BMW PR 315.1, the TPJLR or the Ford L In addition to these, ZINS provides an SAR evaluation tool and, from 7senses, a risk assessment tool with proposed solutions SAL-Software Tool, which is available commercially. Rattle and creak are examined separately because their causes are of fundamentally different nature. Rattle is mostly a result of poor fastening of the parts, lack of stiffness or hardness of the involved materials. Creaking is always a consequence of incompatible materials and therefore of stick-slip. In addition, so called lip effects, burrs and tuning fork effects are involved, which are not considered here in detail. The rattle and creak risk is indicated as a risk priority index (RPZ) on a 1 to 10 scale, with ten signifying the highest risk. Alternatively, traffic lights have come to be used in the last few years. In the course of time, totally 18 classes of problems have been defined where mistakes are made time and again. These are: 1. Gap not wide enough

5 2. Material combination incompatible 3. Creaking due to edge effect 4. Creaking due to sharp/pointed parts 5. Long loops 6. Narrow design gap 7. Lack of stiffness 8. Fastening elements 9. Fastening strategy 10. Lack of tolerance compensation with moving parts 11. Design for contact (zero gap) 12. Springs 13. Cables 14. Plus 15. Positions detector (locator) 16. Chromium 17. Overspray 18. Connection of 3 parts 3.3 Solutions There are one to three potential solutions to each of the above problem classes. Their description would go far beyond the scope of this article. The appropriate document comprises almost 100 pages. Despite that, a few of these solutions will be discussed briefly below Gap not wide enough The 3 millimeter gap rule is violated time and again. This value comprises the nominal gap plus tolerance chains plus dynamic movement during road drives. If the distance between the parts is less than 3 mm, the parts may touch each other. This is often not possible on the A side because designers specify narrow gaps distinctly smaller than 3 mm. However, the spacing is easy to maintain in the hidden areas, e.g. inside an instrument panel or a door lining. Despite that, each car has up to 10 contact points at which the gap is smaller. Considering that these hidden contact points are very difficult or even impossible to spot without having to remove parts in a finished car, you have ten good reasons why a customer should be annoyed.

3.3.2 Material incompatibilities There are combinations of materials that are absolutely incompatible.

, PP or nylon are fairly comfortable in contact with other materials. PEM is a materials database which contains about 18,000 test results.

S&R tests are made on stickslip machines. Both materials are clamped in the machine and moved in relation to each other. Special measuring heads record friction and stick-slip.

6 3.3.2 Material incompatibilities There are combinations of materials that are absolutely incompatible. These include classes such as leather, artificial leather and fabrics, which are almost always incompatible with ABS or ABS+PC. Other materials, e.g., PP or nylon are fairly comfortable in contact with other materials. PEM is a materials database which contains about 18,000 test results. So it is possible to forecast at an early stage whether there will be S&R problems. The database also contains solutions such as alternative material combinations, grains, coatings, etc. S&R tests are made on stickslip machines. Both materials are clamped in the machine and moved in relation to each other. Special measuring heads record friction and stick-slip. The risk is shown as risk priority index (RPZ) and provides information about the S&R risk of the selected pair of materials. 4 Summary and outlook If the warranty and goodwill cost of several OMSs amount to about 50 million for each model and that of rework to some 5 million, 50K-100K for the complete prevention of S&R with material pair tests are a nere trifle. If these

7 measures help to eliminate only a single risky contact point which is not repaired with felt later, the price of prevention has already been recovered. ZINS offers a Don t Worry Package in this connection, which adapts to the customer s needs. Complete prevention is an option, as is training-on-the-job or seminars and training sessions. Moreover, ZINS also takes over the testing of all material pairs for the customer. Empirically based prevention will be enhanced by numerical simulation in the near future. This will substantially improve the level of information specifically for the fixing and stiffness of parts and increase the accuracy further.

Squeak and Rattle Solutions: Prevention in CAD

Squeak and Rattle Solutions: Prevention in CAD By Christian Berndt, Guido Rybczynski, Patrick Schimmelbauer (ZIEGLER-Instruments GmbH) Klaus Steinberg (7senses) Dr. Hans-Jürgen Daams (Hajuveda) Full vehicle