Overview of numerical control transformation of th

2022-08-07
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Overview of NC transformation of machine tools (Part 1)

1 preface

the use experience shows that in NC machine tools, the effective service life of a set of NC system is 6 ~ 8 years. Due to the rapid development of electronic technology, most famous CNC system manufacturing companies in the world replace their products within 3 ~ 5 years. Therefore, it is difficult to find spare parts even if they want to repair the CNC system after 6 ~ 7 years of use

with the development of electronic technology manufacturing level, the price of CNC system and supporting accessories (servo unit and motor, etc.) is getting lower and lower in the whole machine tool. For example, it reached 50% in the 1970s, and gradually dropped to less than 1/3 to 1/4 after the 1980s. Some large machine tools account for only about 1/10. Therefore, with a small amount of investment, many key equipment can be rejuvenated

in recent years, there are more than 100000 ordinary equipment and more than 4000 old CNC machine tools that need numerical control transformation in China. If the transformation funds can be implemented, it will be a broad market that can provide billions to tens of billions of yuan. Therefore, in the machinery manufacturing industry, especially in the machine tool manufacturing industry, we should make full use of our own technical expertise to quickly occupy the market and make our own industrial contributions to the rapid development of the national economy

based on the author's experience in many numerical control transformation projects undertaken by Beijing Machine Tool Research Institute, here are some experiences for your reference

2 feasibility evaluation of numerical control transformation project

whether a specific equipment needs numerical control transformation, transformation purpose, what application indicators are expected to be achieved, how much financial and human resources are required to be invested, how many risk factors are involved in the transformation project, and what performance price ratio can be obtained finally? These are important contents in feasibility assessment

after an old equipment has been used for a certain year, it will inevitably have frequent failures, difficult maintenance, reduced production efficiency, unstable processing accuracy, or even complete shutdown. Is such equipment to be completely scrapped or undergo medium overhaul and numerical control transformation? Before making such a decision, the residual use value of the existing equipment must be evaluated first. For example, a machining center mainly consists of mechanical and electrical components: ① CNC system and operation subsystem; ② Servo system (including motor); ③ Machine tool electrical; ④ Mechanical body (bed, column, guide rail, lead screw, etc.); ⑤ Tool magazine manipulator system; ⑥ Automatic workbench switching system (APC), etc. According to the actual situation, each subsystem can make an assessment of the residual use value of the reliable equipment that can withstand the environmental experiment under the continuous environment of extremely high temperature and extremely low temperature in an instant. For example, for the CNC system 20 years ago, it is impossible to rebuild it without finding spare parts. Its residual value is zero. According to the wear degree of the servo system, if it continues to be used, it should be considered that there is more than 50% of the residual value after renovation; However, considering the matching of the newly replaced CNC system and the pursuit of good servo characteristics, even if the old servo system is not completely damaged, or it is expected that its continuous service life will not be too long, it can also be considered to be completely replaced. In this way, the residual value of the servo system is also determined. The residual value of mechanical parts generally accounts for a high proportion. Many engineering practices have shown that the wear of large mechanical parts of a high-quality machine tool is limited. Two American horizontal machining centers have been transformed, both of which are products in the late 1970s. One set of X-direction travel is 1.5m and the other is 2.5m. The straightness and distortion of the guide rail can be adjusted to 0.008mm/1000mm. The guide rail itself has not been further polished. The two vertical machining centers produced by our institute 8 years ago have been continuously processed and used by the user in the factory for more than 6 years from two shifts to three shifts for 24h. Recently, they were brought back to our Institute for renovation and measured: the linear grinding concave of one meter guide rail is 0.003mm. The vulnerable parts of the manipulator tool magazine parts are concentrated on several parts (such as grippers, pins, etc.), and even the replacement cost is not much, so the mechanical parts have a high residual value

generally, for a piece of equipment, the mechanical part has more than 60% of the residual value, and the electrical part has more than 20% ~ 50% of the residual value. These factors can be considered when turning the gear rod to zero the pointer

the second step is to put forward hope for the transformation of equipment 3 Iso8644 (2) 006 motorcycle - light alloy wheels - experimental methods: the expected value of the target that can be achieved after the transformation, that is, what kind of machine tool accuracy and performance. Some people believe that the proposed transformation index should be linked with the inspection qualification index of similar new machine tools, and even the appearance quality requirements. There is a reasonable side here. However, it must be considered that its foundation is an old equipment, which is defective. If the requirements are raised too high, the cost of investment will inevitably increase greatly. It is reasonable to combine the numerical control transformation with the medium repair and overhaul plan of the equipment, which can achieve an ideal use effect. Therefore, the target value after transformation is not considered in terms of mechanical, electrical, hydraulic and appearance quality as a whole, but as long as an electrical system is simply changed, a lot of problems will be left after transformation

after determining the transformation target value, it is necessary to estimate the financial and human resources input, that is, the evaluation of the input funds. The amount of investment is closely related to the level of formulating transformation goals. The transformation cost mainly consists of the following items: ① CNC system and related servo system; ② Replacement of machine tool electrical and accessories; ③ Precision repair and maintenance of machine tool mechanical components; ④ Maintenance of machine tool auxiliary system (such as hydraulic system, cooling system, etc.); ⑤ Repair of machine tool appearance quality; ⑥ Commissioning and inspection after machine tool transformation; ⑦ Technical labor cost required for machine tool transformation. When limited by the transformation cost, we often modify the transformation target value and reduce some secondary requirements to reduce the input cost

after the above three stages of work, the transformation scheme of one equipment has been basically determined, but the risk assessment of this scheme must be carried out. Even if an old machine tool has a complete technical file, it does not exclude the existence of hidden dangers. There are some unforeseen factors, especially the equipment with high technical content. When making the transformation plan, it is impossible to dissect the current situation of the equipment and obtain the accurate test data of the current situation of the machine tool. Therefore, unexpected problems will be encountered in the future implementation of the transformation. For such problems, the contracting engineering department is required to make risk assessment and formulate corresponding countermeasures based on its own technical experience and on-site investigation. The other is that both the entrusting party and the contractor are aware of the objective existence of risks and set unforeseen costs in the project costs to jointly bear the risks. In a word, the experience of many reconstruction projects shows that: facing the risk factors of the project in advance, although there are many problems in the implementation of the project, it can avert the danger. Paying attention in advance and having Countermeasures in case of problems are one of the basic elements for the success of the project

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