How to control error in machining

At present, the demand for product precision is higher and higher, but the development time of China’s modern machinery manufacturing industry is shorter than that of developed countries, and the level of production technology still needs to be improved. How to control the error of machined products has become an important issue to be solved.

1. Current problems of machining in product error

1.1 The positioning of machinery and equipment is not accurate enough

The positioning of mechanical equipment is the premise of machining, and only after the accuracy of the equipment meets the requirements can we ensure that the product fits perfectly with the process benchmark. However, some of the current mechanical processing technology is not concerned about the initial positioning of machinery and equipment, which is very easy to cause the mechanical processing process in the implementation of the benchmark is far from the requirements. In addition, if there is an error in the positioning accuracy, the error will be further magnified in the production of the product, and in serious cases, even make the product parts in the production process because of mechanical processing equipment extrusion, scraping and deformation or even fracture, resulting in the processing work can not be carried out smoothly [1].

1.2 Errors in the mechanical manufacturing process

Mechanical processing equipment in the assembly line operating conditions is very easy to operate for a long time and lead to equipment aging, when the equipment drive chain, bearings and other components due to aging and deformation or other changes in performance, it is easy to make the overall operation of the equipment deviation. This will lead to the highest proportion of machining errors, including not only transmission chain errors, spindle rotation errors and other errors, but also affect the machining process of the assembly line, reducing the efficiency of the processing work, and in serious cases, even lead to various safety problems in the processing process [2].

1.3 The error of the machining equipment itself

The machining process requires the use of various types of machining equipment and machining tools, in the design of the part, the determination of the benchmark needs to be based on the equipment and tools (fixtures) to meet the standard requirements as a prerequisite. If there are errors in the machining equipment and tools themselves, no matter how to adjust the process design, it is impossible to eliminate the errors. However, at present, many workers rely too much on their own processing technology and processing experience, which greatly increases the error of processed products due to the error of machining equipment and tools.

2. Methods of machining error control

2.1 Preventive measures for errors

Before the machining, the staff can analyze the machining process, design drawings, equipment, tools and the actual situation of the processing operator, so as to determine or predict the types of errors that may occur in the machining process, and control the errors according to the types of errors, characteristics, and factors that cause them, so as to eliminate errors or reduce the effect of errors. In addition to the direct control of errors, we also control the errors according to the type of errors, their characteristics and the factors that cause them. In addition to the direct control of errors, the staff can also systematically carry out error control work. That is easy to reduce or eliminate the error is divided into a group, will be more difficult to reduce or eliminate the error in another group. For the easy to reduce or eliminate the error should be strictly controlled, and for the difficult to reduce or eliminate the error should be strongly avoided. Such a way can not only determine the direction of error control work, but also can reduce the cost of error control work at the same time, improve the efficiency of error control.

2.2 Establish a perfect error control system

In addition to the technical level, the management of machining error control is also essential. First is the need to build a perfect error control system. The system needs to clearly specify the responsible person for the supervision of each error-generating factor and the corresponding rewards and punishments, so that when a batch of parts has errors, the management can investigate the factors that may occur errors and complete the task of accountability according to the responsible person on record. Secondly, it is necessary to build a perfect error supervision system, which needs to clearly specify the supervision methods that should be taken for all kinds of factors that may cause errors, such as the inspection process, inspection standards, inspection period, responsible person and other important information for processing tools and gauges.

2.3 Technical methods of error control

In addition to the prevention of errors, the effective control of machining errors can also be achieved in the actual processing. For example, the training of processing workers before machining to improve their professional and technical execution ability. In addition to the technical aspects of training, technical personnel should also be instructed to de-experience in the work, to avoid excessive trust in work experience and ignore the importance of practical operation. In addition to the training of staff, before the production of machining equipment should also be calibrated to fundamentally control the generation of errors. In the process of machining, attention should also be paid to the control of errors.

2.4 For the error generated by deformation

In the process of machining, from time to time, there is a deformation of the parts after processing and exceed the poor situation, for such problems, I think the solution are: choose the right material; appropriate heat treatment; optimize the design; take appropriate clamping measures, as far as possible, the workpiece in rough and finish machining before the adjustment, clamping into a natural state, to minimize the deformation of the workpiece after processing due to the release of stress. Specific examples are shown in the figure below.

Note: The green model in the figure is the workpiece, the purple model is the process chuck, and the red screw is the adjusting screw. The workpiece is clamped into its natural state by the adjusting screw before semi-finishing and finishing.

2.5 Measures to compensate for errors that have occurred

First of all, we should apply the quality system to control the process and find out the problem in time through the way of operator’s self-inspection and first inspection of quality inspection to avoid the situation of batch over-error as much as possible. If there is an over-difference, we should communicate with the design department or the customer in time and take the following measures: adjust the tolerance of the parts with it (provided that the parts are not processed); scrap the workpiece and re-inject the material for processing; accept the concession by the design or the customer’s consent.

2.6 Control of high precision tolerances

For the high tolerance requirements of the product (to reach or even exceed the accuracy of the processing equipment itself), to fully achieve its accuracy, production is too difficult, the proportion of scrap, for these products, we can use the graded selection method, so that the parts with each other, graded selection of the corresponding tolerance, to achieve the required accuracy, so as to meet the requirements with, but also to reduce production costs. This is a practical and economic way to control such errors.

3. Conclusion

Machining in the current social production activities occupy an extremely important issue, and the field due to the strong technical, high requirements for accuracy, extremely easy to produce product errors. In this regard, we must treat the error control work of machining with the attitude of “governance as a supplement, prevention as the main focus, timely remedy”. Strengthen the technical ability of processing personnel, improve the technical accuracy of the equipment, so as to achieve high quality and efficiency of mechanical production.

Author: Liao zhiguo

Source: China machining solutions provider – Yaang Pipe Industry (www.machinedsgn.com)
Reference:

• [1] Zhaoyan Research on comprehensive error control technology of machining manufacturing under continuous operation [j] Mechanical design and manufacturing engineering, 2018, 47 (9): 100-104
• [2] Weixianglin Analysis of energy transmission model and optimization of energy consumption in machining process [j] Mechanical design and manufacturing engineering, 2018, 47 (10): 81-85