Data Bases • Custom Term Papers • Free Term Papers • Free Research Papers • Free Essays • Free Book Reports • Plagiarism? Links • Top 100 Term Paper Sites • Top 25 Essay Sites • Top 50 Essay Sites • Search 97,000 Papers @ DirectEssays.com • Search 101,000 Papers @ ExampleEssays.com • Search 90,000 Papers @ MegaEssays.com Free Essays • Term Paper Sites • Chuck III's Free Essays • Free College Essays • TermPaperSites.com • My Term Papers • Get Free Essays • Essay World • Planet Papers	Search Lots of Essays Back to Subjects - Engineering An Introduction to Plastic Gears An Introduction to Plastic Gears As an employee of a world-class plastic gear manufacturer for many years, I see how this is an undeniably growing part of the gear industry. I hope to briefly describe how something seemingly simple as a plastic gear requires the culmination of many very state-of-the-art processes. Within one word I’ll say that at every level precision is required. Initially, a gear engineer must design a gear that meets the design intent while remaining cognizant of all variables that result from using materials such as plastic. This engineer must design a gear electrode that will actually determine the form of the gear. This electrode is then burned into the mold cavity using a method commonly referred to as EDM or electrical discharge machining. It is essential that the gear electrode be cut identical to the finished gear tooth form. Some compensation is normally made for the shrinkage of plastic as well as the overburn that occurs during the EDM process. The gear engineer normally will alter the gear tooth geometry to relieve stress and strengthen the gear tooth form. This alteration is normally done at the base or root of the gear tooth and at the tip or peak of the tooth. Next, a mold maker then will evaluate what the expected life of the gear program will be so that he can build a mold that is robust and capable producing the many millions of parts with the highest of accuracy. He will ensure that the plastic that will be entering the mold will travel along balanced pathway or runner system that will allow for consistent fill into each mold cavity. His tool for evaluating this flow is done through a computer model commonly referred to as mold flow analysis. He must be capable of understanding what makes a good mold as well as a good gear. Once the mold is completed it is then set into an injection-molding machine. It is important in the precision gear molding industry that the molding unit has a highly controlled system in place to monitor the molding process. It is equally important during this process that there is a means by which all peripheral variables can be controlled. This is done utilizing a central processor, which will maintain balance on all settings for every parameter. Transducers relay all of their information into a central processor that will monitor and maintain this consistent process. In the case that any of these parameters are not met the computer will not allow for the process to continue forward or the machine must be intelligent enough to compensate for variables by offsetting those changes. This is known as artificial intelligence. Once all these criteria have been met, and gears are now being molded we must now check them for their accuracy. I will discuss two methods by which we will determine whether these gears are acceptable to print. Initially, analysis of the gear tooth geometry itself must take place. Secondly, analysis of the entire gear and its relationship to its axis must take place. Analysis of the gear tooth geometry is done typically by a touch probe method. This probe will scan across the entire tooth in order to determine how much deviation there is to the theoretically perfect tooth form that was intended. The touch probe is controlled by sophisticated computer numerical controlled inspection machine program that will undertake the arduous task of scanning into the minutest areas of the tooth. Some touch probes required to perform this task can be as small as.3 mm. Once we have determined that this tooth geometry is correct we will proceed to the second phase of the gear inspection. This next phase is known as the roll test. This will determine the relationship between the pitch line of the gear to its axis. This test can be done using the same touch probe technique described earlier but it can be slow and in efficient for extensive inspection. Therefore, a functional gear tester or rolled tester will provide a faster more economical and repeatable method to determine the gears’ relationship to its axis. Roll testing our molded gear at tight mesh with another gear that has the theoretically perfect gear geometry does this. During this process we can record any runout (T.I.R.) or concentricity error to determine the overall quality of the gear. This method can be automated and is very good at determining the overall quality of the gear. The quality of a gear is determined by how little runout (T.I.R.) it has and how little error there is in the tooth form. I have not mentioned how the plastic material itself plays into this equation. An engineer must always be mindful that like any plastic he may encounter non-uniform shrinkage. This may or may not meet the engineers design intent. Therefore engineers must be mindful of the capabilities of each unique material and educate themselves on the benefits and drawbacks of this material. Plastic material manufacturers are constantly developing more sophisticated engineering grade materials that have overtime been an economical alternative to metal. I hope that this brief introduction basically gives you at least somewhat of an idea of everything that is involved with producing something as seemingly simple as a plastic gear. Bibliography: Word Count: 899
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