LAWRENCE TECHNOLOGICAL UNIVERSITY



LAWRENCE TECHNOLOGICAL UNIVERSITY

Submitted in partial fulfillment of requirements for Co-op Practicum

Course ECO3001

Professor Richard Maslowski

Summer 2003

CO-OP ASSIGNMENT 1

By

Michael A. Pyrkosz

Student #000002723 ME

MetalDyne Corporation

TABLE OF CONTENTS

|INTRODUCTION |…...……………………………………………………… |1 |

|DISCUSSION |……………………………………………………………… |3 |

|Rubber in Vibration |………………………………………………………… | |

|The Basic Crankshaft Damper |………………………………………… | |

|Crankshaft Damper Analysis |...……………………………………………… | |

|Bonding Rubber to Titanium |……………………………………… | |

|CONCLUSION |...……………………………………………………… | |

INTRODUCTION

This work term was spent at MetalDyne Corporation Group Operations Tech Center in Plymouth, Michigan. MetalDyne Corporation is an automotive parts supplier that designs and manufactures a wide range of metal-based components, assemblies and modules for chassis, engine, driveline and transmission applications. Specifically, this Coop work term was spent in the Noise, Vibration, and Harshness or NVH group at MetalDyne Corporation. NVH products include crankshaft dampers, balance shafts, isolators, driveline dampers, viscous dampers, brake drums, brake calipers, wheel hubs, knuckles and spindles, and wheel end assemblies. Crankshaft dampers are of particular interest; they are used extensively and are unique within MetalDyne (being chemically bonded with rubber in addition to being machined), and are therefore, the main subject of this report.

During this work term the co-op student had opportunity to work on a variety of assignments, including: damper analysis of field returns, special testing to validate new product design, design and analysis activities, and assisting with research and development activities. Because of the large variety of projects worked on the discussion will be narrowed down to those that the author feels best describe the work term. These will be addressed under three main topics. First, a discussion of the basic principles of rubber in vibration and damping utilizing rubber will be provided for the reader who may not be familiar with these topics. Second, there will be a discussion on the basic crankshaft damper, how it works, and damper analysis testing. This will give the reader a good understanding of the physical dynamics of the part as well as a further understanding of what characteristics make a good damper. Third, there will be a

discussion about a specific project that the co-op student worked on: determining a good procedure for bonding rubber to titanium alloy. This project is particularly worthy of discussion because it is both interesting and delves more deeply into one of the most important characteristics of a good damper, which is bond strength.

DISCUSSION

Rubber In Vibration

This section will discuss the basic principles behind rubber in vibration. This section is intended for the reader who is not familiar with this topic, and only briefly discusses basic principles about damping vibrations with rubber. The reader who is familiar with this topic may choose to skip ahead.

The analysis of rubber in vibration is analogous to the simple harmonic motion of a mass suspended from a spring. Like any other spring, rubber springs have a spring rate, KL, in pounds per inch such that [pic], where W is the weight of the mass in pounds and d is the static deflection in inches. It can be shown that the natural frequency, in cycles per minute, of undamped free vibration may be calculated from [pic]. In the case of the crankshaft damper, where vibrations are torsional, KT is used, where KT is in lb(in/rad. It can be shown then that the natural frequency is found by the following equation: [pic], where I is the moment of inertia of the mass: [pic].

When the disturbing force is periodic and continuous the resulting motion is called forced vibration. Exciting frequency is designated by ff. When the exciting frequency become equal to the natural frequency of the system, the system will go into resonance. Without damping, this resonance can cause the amplitude to increase quickly and the forces to become destructive. Rubber has inherent damping properties due to internal friction between the polymer chains. This internal friction is inversely proportional to the frequency, and the effective damping is similar to viscous damping. Figure 1 below compares the two basic types of damping: viscous and coulomb.

|a) | |

|[pic] |[pic] |

| |[pic] |

|b) | |

|[pic] |[pic] |

| |[pic] |

Figure 1: a) Example of free vibration with viscous damping. b) Example of free vibration with coulomb damping or dry friction. an = amplitude at cycle n.

There is a constant of proportionality between viscous resistance and velocity indicated by C [pic], this is called actual damping. Critical damping, CC, is defined as the amount of damping where the friction becomes just large enough to absorb the vibrational energy to stop the system from passing through its equilibrium position. The ratio of actual damping to critical damping, [pic] the damping ratio is a useful method of measuring damping. It can be shown that [pic], where fd is the frequency in cycles per minute under damped free vibratory conditions.

The Basic Crankshaft Damper

The crankshaft of any engine is exposed to constantly changing torsional forces. Some of these are from the piston cylinders firing, while others are resistance forces during the compression stroke. The result is torsional vibration, which can be translated to other systems of the car, creating additional noise, and wear. The crankshaft damper is therefore used to dampen these vibrations, and limit any resonance.

The basic crankshaft damper is comprised of three components: the hub, the inertia ring, and the rubber strip. See Figure 2 below for visual. The rubber strip is adhesively bonded to the inside surface of the inertia ring and to outer surface of the hub. The hub is bolted directly to the nose of the crankshaft, and translates any vibration to the rubber. The inertia ring, like any other mass body, creates a reaction force that resists any change in rotational momentum. This causes the rubber to shear, and much of the vibrational energy is absorbed.

[pic]

Figure 2: Basic damper example

Damper Analysis

The difficulty in making crankshaft dampers is that ostensibly erratic problems can occur including variations in adhesive application, poor adhesion strength, high variability of bond strength, high radial and axial runout of the ring with respect to the central axis of the hub, and improper location of the ring with respect to the hub. It therefore becomes necessary to run quality checks on test sample parts. These checks are lumped together in what is called a damper analysis. This includes non-destructive and destructive testing. Non-destructive testing includes checking that axial and radial runouts, ring assembly location, and the natural torsional frequency of the part are all within print specification. Destructive testing is usually either a slip torque test or a section-pull test. For obvious reasons only one of the destructive tests can be performed on any given part.

Radial and axial runout are measured with a ballpoint indicator placed appropriately as the part spins about its central axis. Significant radial and axial runouts have several possible effects including high belt wear, a thrown belt, belt system noise, and a poor-looking product.

Assembly location is measured as the lateral deviation from the back face of the hub to the nominal of the ring. Incorrect assembly location of the ring has one critical effect, belt stress. When placed in excessive lateral stress the belt is likely to fail prematurely or possibly jump from the damper.

It should be clear the importance of the damper being tuned to the correct damping frequency. Every engine application will have a different dynamic system, and therefore a different range where resonance is likely to occur. Dampers are tuned to effectively dampen the resonance in this range, depending on application. Torsional frequency of a damper is checked using accelerometers on the ring and hub while the hub is mounted on a vibrating post. These accelerometers are connected to a computer, which tracks the movement of each and determines the damping frequency. Using the equations mentioned in the rubber in vibration section, the computer can also calculate the damping ratio as well as the percent damping. Temperature of the rubber is also tracked with a thermocouple; since rubber stiffness changes with temperature, the frequency range is usually specified at a specific temperature.

The fundamental determinant of damper life is bond strength. Should either surface of the rubber slip at the hub or the ring vibrational energy can no longer be absorbed. One of two methods is used for determining bond strength. The first method is a slip torque test. Here the ring is clamped to a rigid body and torque is applied to the hub until the bond breaks. The maximum torque value is recorded. The other method is a section-pull test, where eight even sections are cut through the ring and rubber using a band saw. The sectioned part is loaded into a tensile machine and each section is then pulled off of the hub, and the maximum tensile strength is recorded. This provides a little more information on the bond strength than the slip torque test since strength is rarely even throughout the part. However, the slip torque test is more realistic to the types of stresses that the part will see during service.

Bonding Rubber to Titanium

One of the more interesting projects that the co-op was involved in was developing a good technique for bonding vamac rubber to titanium alloy. This technique needed to be developed to provide a customer with a lightweight part that would still perform well in high stress conditions. The inertia ring would still be made from steel, but the hub, which can see high amounts of stress, would be made out of titanium alloy. This is a topic is particularly noteworthy, for it delves a little further into bond strength, the primary determinant of damper life.

In order to determine a good procedure for bonding vamac rubber to titanium five test samples were made from titanium slugs (as hubs), steel rings, and vamac rubber. The slugs and rings were first put in an alkaline wash and the samples were assembled using Chemlock 250 cement and Flexrin P4 assembly oil. Samples 1, 2, and 3 were baked at 265°F and maintained at that temperature for a curing time of 30 minutes. Samples 4 and 5 were baked at 300°F and maintained at that temperature for the same curing time of 30 minutes. The parts were then cut with a band saw through the steel ring and vamac rubber in six places, and each section was torn off. Data was not collected at this time, the test was simply to observe how well the rubber bonded to the titanium as compared to how well it bonded with the steel.

| | |

|[pic] |[pic] |

| | |

|[pic] |[pic] |

| | |

|[pic] | |

Figure 3: a) Results for test sample 1, b) Results for test sample 2, c) Results for test sample 3, d) Results for test sample 4, e) Results for test sample 5

Test results were better than predicted.; Overall more rubber was bonded to the titanium than to the steel. These results can be seen in Figure 3 above. As seen in Figure 3-a, the rubber remained bonded to the titanium and tore away from the steel for most of the sections of part 1; the only exception was a small portion of section 3 (indicated by the arrow), where the rubber remained bonded to the steel and tore away from the titanium. Similar results were observed in the other test samples: that is, most of the rubber remained bonded to the titanium and tore away from the steel. The small regions on each sample that were the opposite of this were determined to be the result of improper curing time. It should also be noted that samples 4 and 5 had slightly less favorable results than the samples cured at the lower temperature.

Based on the results of this test, it was determined that vamac rubber can be bonded to titanium with relatively good strength using an alkaline wash, Chemlock 250 cement, and Flexrin P4 assembly oil. The recommended curing method determined from this test is as follows: first set oven to 275°F, once parts have reached 265°F turn oven down to 265°F and leave parts in oven for a curing time of 45 to 60 minutes. This increased curing time should allow a full bond to occur uniformly throughout the part.

CONCLUSION

This work term was both enlightening and enjoyable. The full impact of the experiences that the Co-op gained and variety of projects worked on during this work term cannot be summarized in a short report such as this one. This report is a brief synopsis by comparison. Overall, it is the opinion of the co-op that this work term was an extremely beneficial learning experience, and would recommend the Lawrence Technological University co-op program to any student who has an interest in gaining work experience in their field.

Although the overall experience was favorable, the author would also like to provide some constructive criticism for the co-op program. First there does seem to be some communication difficulties between the school, student and employer. As the program is presently set up, most communication responsibilities seem to fall on the student alone, but the greatest lack of communication appears to be between the school and the employer.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download