Studies On The CNC Retrofitting Of Hobbing Machine ZFWZ12

With the dramatic development of gear industry in China, its yearly production value has been up to 70 billion RMB, and ranked the forth in the world. Among the gear products, 60 percent was vehicle (automobile, engineering machinery and farming machinery) transmission gear. There are altogether 530 thousands gear cutting machines in China, however, 40 percent of them has been working for over 15 years, which leads to the quality inferiority, overdue delivery and less competitiveness in the world market .In order to meet the need of gear industry, manufacturing equipments must be improved. First of all, the replacement of equipment should be carried out. Numbers of foreign equipment have been introduced into China so far. It is predicted that 100 thousand pieces of equipment will be introduced with the yearly investment of 6 billion RMB from 2006 to 2010.Secondly, the renovation (retrofit, rebuild, remanufacture) of the old equipment needs to be initiated. After the renovation, the equipment will not only work as well as the new one, but it can also save the cost, 30 percent of the total initial purchase cost would be well enough. (Usually a sophisticated CNC Hobber costs at least 10 million RMB.) In addition, even the new-bought equipment, after having been used for several years would face the same problems as faults increasingly occur, functions outdate and difficult to maintain etc. Buying new one or renovating the old one will always be the problem.Retrofitting is becoming one of the new economic resources in the foreign countries. This method, has also been widely accepted in China because of its fitting for China, is going to have a promising future.Machine tools that need to be renovated are as many as the companies that are doing renovating, but most of them were universal machine tools like turning machine, milling machine and machining center, which has no special technics. And the study on the renovating with special technics is rarely carried out. CNC hobber was invented lately due to its technological difficulty. All-functions CNC hobber first appeared only in the 80' of last century in abroad. This article is going to study the CNC retrofitting of hobber from the planning, implementing all the way to the result analysis with the method of combining theory and practice, trying to do some research of the machine with special technics. This is the first CNC Hobber retrofitting case that has ever been done with Siemens Sinumerik 840D CNC system in China.First of all, it studied the theory of CNC and non-CNC hobber, pointed out that the CNC type is more advanced than the non-CNC type in the aspect of machining precision and efficiency.Secondly, at the basis of hobber structure, used Homogeneous Transformation method to establish the math model of 6-axis CNC hobber.Thirdly, the procedures of retrofitting were introduced in detail, and the key technologies were specially discussed: Electric Gear is used to control motor so as to dismantle the mechanical transmission linkage; Extended stop and Retrace are the necessary methods to protect tools, parts, and person from any danger at time of emergency.Fourthly, based on the hobbing technics, the technics route was designed, and so did the gearing NC program. To make the program clear, the gearing program was separated in several main and sub programs. Fixed cycle programs are also designed in the NC program. Due to the large number of part parameters, tool parameters and gearing parameters, the program must be designed in a proper way, so as to reduce the once overload and detailed works with these parameters when gearing different kinds of products. Customer interface has to be designed to represent these parameters and connects the parameters to the NC program. The interface design software is decided according to the customer's need.Fifthly, though the machining error of gear was caused by parts, tools and machine tool, but it is actually difficult to determine the exact causes of some errors. In order to clarify the problems, this article deals only with the causes by machine tool, due to the fact that only the machine tool itself has been ameliorated. The study is on 3 aspects: the errors caused by the unparallel degree of Z axis to the axial of C axis; the errors caused by the skewness of Z axis to the axial of C axis; the errors caused by the inclination of B axis.Finally, examine the retrofitted hobber with precision, efficiency and stability: the errors of gear are improved greatly compares to its previous values, turn out that the performance was obviously improved, meanwhile the hobber has been working normally since it was finished on April, 2006, which is to say the retrofitting is successful.