1 Introduction

Experience shows that in CNC machine tools, the effective service life of a CNC system is 6-8 years. Due to the rapid development of electronic technology, the world's leading CNC system manufacturing companies basically replace the first generation products within 3 to 5 years, so after 6 to 7 years of use of the CNC system, it is difficult to find spare parts even if they want to repair. With the development of electronic technology manufacturing, the price of CNC systems and accessory accessories (servo units and motors, etc.) is getting lower and lower in the entire machine tool, for example, 50% in the 1970s and 1/3 in the 1980s. Below 1/4, some large machine tools only account for about 1/10, so as long as a small amount of investment, many key equipment can be restored to "youth."
In recent years, there are more than 100,000 ordinary equipments that need to be digitally transformed in China, and more than 4,000 old CNC machine tools. If the transformation funds can be implemented, this will be a vast market that can provide billions to billions of yuan. Therefore, in the machinery manufacturing industry, especially in the machine tool manufacturing industry, we should make full use of our technical expertise to quickly occupy the market and make our own industry contribution for the rapid development of the national economy.
The following is based on the experience of the author's participation in several CNC transformation projects undertaken by the Beijing Machine Tool Research Institute.

2 Feasibility evaluation of numerical control transformation project

Whether it is necessary to carry out numerical control transformation and transformation purposes for a specific equipment, what kind of application indicators can be achieved, how much financial and human resources need to be invested, how many risk factors are involved in the transformation project, and what performance price ratio can be obtained in the end? These are all important aspects of the feasibility assessment.
After an old equipment has been used for a certain number of years, it will inevitably lead to frequent failures, difficult maintenance, reduced production efficiency, unstable machining accuracy, and even complete shutdown. Is this equipment completely scrapped, or is it modified by CNC? Before making such a decision, first assess the remaining value of the existing equipment. For example, a machining center, the main components of the electromechanical components are: 1CNC system and operating subsystem; 2 servo system (including motor); 3 machine tool electrical; 4 mechanical body (bed, column, guide rail and screw), etc.; Library manipulator system; 6 automatic workbench exchange system (APC). Each subsystem can make a corresponding residual use value assessment based on actual conditions. For example, for a numerical control system 20 years ago, it is now impossible to renovate it without the need to find spare parts, and its residual value is zero. According to the wear level of the servo system, if you continue to use it, you should consider more than 50% residual value after the renovation; but considering the matching of the new replacement CNC system and the pursuit of good servo characteristics, even if the old servo system is not completely damaged, or expected Continued service life will not be too long, you can also consider a complete replacement. In this way, the residual value of the servo system is determined. The residual value of mechanical components generally accounts for a high proportion. Many engineering practices have shown that the mechanical wear of a high-quality machine tool is limited. We have transformed two American horizontal machining centers, all of which were products in the late 1970s. The X-direction stroke is 1.5m and the one is 2.5m. The straightness and distortion of the guide rail can be adjusted to 0.008mm/1000mm. There is no further grinding itself. The two vertical machining centers produced by our company 8 years ago have been used in the customer factory for more than 6 years and two shifts to three shifts for 24 hours. Recently, we have pulled back to our factory for the actual measurement: one meter guide linear wear concave 0.003mm. The consumable parts of the robot tool magazine are concentrated on several parts (such as the claws, bolts, etc.), and even if it is not replaced, the mechanical parts occupy a high residual value.
Usually, for a piece of equipment, the mechanical part has more than 60% residual value, and the electrical part has 20% to 50% of residual value. These are all factors that can be considered for retrofitting.
The second step is to put forward the expected value of the equipment that can be achieved after the transformation, that is, what kind of machine precision and performance. Some people believe that the proposed transformation indicators should be linked to similar new machine tool inspection qualification indicators, and even the appearance quality requirements, etc., there is a reasonable side here. However, it must be considered that the basis of it is an old equipment, which is flawed. The cost of requiring too much investment will inevitably increase. The combination of numerical control transformation and equipment repair and overhaul planning is more reasonable and can achieve better results. Therefore, the target value after the transformation is not considered from the machine, electricity, liquid and appearance quality as a whole, and it is regarded as a simple replacement of an electrical system, which will inevitably leave a pile of problems after the transformation.
After determining the target value for the transformation, an estimate of the input of financial and human resources, that is, the evaluation of the input funds, is required. How much money is invested is closely related to the development of the target of the transformation. The cost of the transformation is mainly composed of the following items: 1 CNC system and related servo system; 2 machine tool and accessory replacement; 3 machine tool component repair and maintenance; 4 machine tool auxiliary system (such as hydraulic system, cooling system, etc.) Maintenance; 5 repair of the appearance quality of the machine tool; 6 commissioning test after the transformation of the machine tool; 7 technical labor costs required for the transformation of the machine tool. When the cost of the transformation is limited, the target value of the transformation is often revised, and some minor requirements are reduced to reduce the input cost.
After the above three stages of work, the transformation plan for one piece of equipment has been basically determined, but the risk assessment of this plan must be carried out. An old machine tool does not exclude hidden dangers even if it has a complete technical file. There are some unforeseen factors, especially those with high technical content. When making a transformation plan, it is impossible to carry out a large-scale dissection of the equipment, and it is impossible to obtain accurate test data of the current situation of the machine tool, so that unexpected problems will be encountered in the future implementation of the transformation work. 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 the basis of on-site investigation. Another approach is that both the principal and the contractor are aware that the risk exists objectively, and that unforeseen expenses are set in the project project fee to share the risk. In short, the experience of a number of renovation projects shows that the risk factors of the project are faced in advance, although there are many problems in the implementation of the project, it can be saved. Paying attention in advance, once there are problems and countermeasures, it is one of the basic elements of project success.
The fifth content is the performance price ratio assessment. This is actually a comprehensive assessment of the second and third items above. In order to have a basis for quantitative analysis in the economy, it is often preferred to compare the price of a commodity with similar performance on the market as a standard. For example, there is a horizontal machining center produced 15 years ago. The electronic control part has been seriously damaged and cannot be repaired. The mechanical precision has been lost by about 20%. The estimated residual value is about 300,000 yuan. 10,000 yuan, the mechanical part of the renovation needs to invest 100,000 yuan, the whole machine will also invest 100,000 yuan in technical labor costs, a total investment of 750,000 yuan. It takes 1.8 million yuan to buy a similar machine tool now. After the transformation, the performance and efficiency of the machine tool can reach 70%-80% of the new equipment, and the service life is more than 6-8 years (above a major overhaul period), that is, the performance price ratio of this retrofit scheme is desirable.
In the assessment, it should be noted that equipment with too low residual value is not worthy of great efforts; it is not advisable to make a retrofit with low residual value and high input value. Therefore, in the numerical transformation of old equipment, the primary object is the old CNC machine with higher residual value. The mechanical structure and function of these devices are easily matched with the new electronic control system, and the comprehensive effect is better. Secondly, heavy and large-scale equipment in ordinary machine tools, these equipments have high original values, and they are still often key equipments in the department. It is worth making great efforts to transform them. For some equipments with low original value, I feel that it is a pity to scrap immediately! I also want to use the first-stage equipment after the transformation, and I should be cautious when determining the application index. That is to say, from the practical point of view, it is proposed to put the application index not too large. The electronic control part should use a cheap and simple system as much as possible, and the transformation workload should be compressed within a certain range, and the investment should be reduced to strive for practical economic effects.

3 Basic steps of CNC transformation

There are generally three modes of operation for the numerical control transformation of equipment: that is, the equipment manufacturers own the own, which requires these manufacturers to have strong technical transformation strength; the second method is that the equipment manufacturers can hire technology according to their own technical weaknesses. The brothers of the letter participated and cooperated to undertake the project; the third way was to completely entrust a unit to contract the project. The selection contractor must pay attention to its technical capabilities and business reputation. The numerical control transformation work is a work with large technical content and wide technical field. The selected objects must have solid technical capabilities and comprehensive capabilities of organic electricity. Both parties should have the sincerity of cooperation and be a trusted partner; otherwise, relying on simple contracts It is difficult for the relationship to restrain each other and make the project slow or unable to end.
The transformation steps are basically as follows: (1) basic evaluation of old equipment; (2) determination of transformation plan; (3) implementation of transformation investment funds; (4) search for entrusted units, signing relevant transformation contract agreements; (5) collating existing information on digesting machine tools (6) On-site surveying and mapping of electrical and mechanical components of old equipment; (7) Designing, ordering and manufacturing CNC, PLC, machine tool electrical and mechanical transformation contents; (8) For the remaining electromechanical systems, hydraulic systems and accessories of machine tools On-site disassembly, maintenance, replacement; (9) on-site construction, installation and connection of machine tool transformation; (10) machine tool joint adjustment test; (11) repair and restoration of machine tool geometric accuracy, positioning accuracy; (12) machine tools and All parts of the control system function linkage test, work reliability operation; (13) machine tool inspection and acceptance; (14) machine tool trial production cutting operation.
Of course, there may be an increase or decrease in the content of a specific project, but the basic content is roughly included.

4 Difficulties often encountered in the transformation work

1. Assessment difficulty

It is difficult to make an accurate assessment of an old device that has been used for many years. In particular, many devices often lack the necessary technical documentation of the system. Some used equipment has been lost, some equipment has been damaged and can not be re-tested, so it is very difficult to accurately understand the degree of wear of each component and quantitatively evaluate the residual value of each component. Too high or too low evaluation has a lot of impact on the determination of the transformation plan and the performance and price ratio after the transformation. Therefore, when doing this work, it is necessary to hire experienced experts, do the necessary mapping, test and test, and conduct necessary market research, especially quantitative analysis.

2. Choice of the best solution

When doing each machine tool transformation plan, there are often multiple plans. In general, the transformation of investment funds should be directly proportional to the results achieved. It is unnecessary to blindly pursue high indicators and high investment. Objectively speaking, the price of spending more is not a new device. Therefore, proper investment and practical use of indicators are the basic principles for selecting the best solution. When making a plan, several alternatives should be made according to the actual level of the machine tool. The client and the contractor negotiate to take the minimum investment under the premise of meeting the actual service life of the user. The transformation plan can be considered as a better solution.

3. Modification of systems and replacement parts

It is inevitable to replace many parts and electronic control systems when rebuilding a machine tool. As a machine tool user, I always hope that the components that can be used are retained as much as possible, such as retaining the servo motor, hydraulic system, auxiliary components, etc. of the original equipment. In this modified equipment, it is necessary to mix new and old components, and the effect will be What? We have modified a five-axis five-link horizontal machining center. The numerical control system uses a better Japanese FANUC 16M. The CNC system works well when the total commissioning vehicle is used, but the hydraulic oil pipe is continuously ruptured due to severe aging. Oil, in the multi-month commissioning phase, the light oil pipe takes up several working days. Therefore, when determining the selection of components, it is necessary to consider the matching of equivalent and equal use time. That is to say, the full-function machine tool is equipped with a full-function CNC system. When the new component has been used for more than four years, the service life of the retained old component is also required to match it, or there are corresponding measures. For example, the machine tool is designed to take into account the precision repair of large mechanical parts, the accuracy of ball screw repair and re-adjustment preload, the replacement of hydraulic tubing and seals, the digital control of the new CNC system and the servo motor of the analog control on the old machine. It is necessary to consider replacing the servo motor or using an older analog control CNC system. For some old foreign machine tools of various kinds, we must also consider the standardization of metric and imperial systems. Inch standard parts, threads, pipe joints and bearings will bring some new problems to the replacement, and even prepare the British universal tools.

4. Determination of acceptance technical conditions

The acceptance conditions must be considered in each transformation project. This is often the place where the principal and the undertaker are most likely to have differences when implementing the transformation project. This is reflected in the fact that the entrusting party has a high hope value for the equipment, the underlying party has insufficient loopholes in estimating the original equipment, and there is no uniform standard for the acceptance conditions, so it is most likely to appear in the later stages of the project. situation. Therefore, when formulating the acceptance conditions, we can refer to the industry standard of the same new machine tool and the original record of the factory-qualified list of the machine tool, analyze the current precision of the machine tool, and if necessary, do the actual accuracy test of the machine tool. Reasonable acceptance of technical conditions. For example, if a machine tool transformation only replaces the CNC system, then the function and work reliability should be specified in the acceptance conditions, but the requirements for the machine geometry accuracy are lacking. In short, the old equipment transformation work is a comprehensive high-tech work, and there are many unforeseen factors. Therefore, there will always be some iterations during the acceptance. At this time, the two sides can negotiate friendlyly in the spirit of the partners. Most of the problems are Properly solved.

5. Mastering the project construction plan

The project transformation period is about 1 to 6 months depending on the complexity of the equipment. The shorter the cycle, the better the quality is. The construction period for a more complicated medium and large equipment is as follows.
1. It takes 20 to 40 days for the old equipment technical data digestion, electrical mapping, mechanical mapping, and machine tool raw performance test;
2. Mechanical, electrical, CNC design ordering and manufacturing takes 90 to 150 days (mainly used for import component parts ordering cycle and large complex parts manufacturing cycle);
3. The installation and connection of the machine tool transformation part takes 30 to 60 days;
4. Machine tool joint adjustment and acceptance takes 30 to 40 days.

The above cycle is for reference only. The technical ability of the contractor is strong, the preparation work is completed, and the construction period can be greatly shortened. The worst thing is that in the on-site commissioning, it was found that the missing parts or damaged parts, and then re-ordered or designed and manufactured, so that the construction period is far away, and both sides will suffer great economic losses.

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