Research on thermal deformation error compensation method of NC machining accuracy of wooden door hi1

Abstract: The precision of NC machining for wooden door hinge assembly holes is crucial for ensuring the overall quality of the hinges. One of the main factors affecting machining accuracy is the thermal deformation error in the machine tool. This paper proposes a genetic algorithm-based thermal deformation error compensation model for the NC machining of wooden door hinge assembly holes, aiming to achieve higher precision CNC machining.

Traditionally, holes and grooves on wooden doors for assembling hinges are processed using general-purpose equipment such as routers and woodworking drilling and milling machines. However, the efficiency of these machines is low, equipment adjustment is difficult, production interchangeability is poor, and the processing accuracy is often inadequate. To overcome these challenges, a modern advanced processing technology, the numerical control processing method, is adopted. This method utilizes a special machine tool equipped with a multi-head drilling and milling device to process the hinge assembly holes and grooves based on CNC machining graphic parameters.

The main factor affecting the machining accuracy of this method is the quality of the machine tool itself, which refers to its processing capability. The thermal deformation error of the machine tool, accounting for approximately 28% of the total error, stands out as a key factor affecting machining accuracy. Therefore, developing a thermal error compensation method is essential for improving the precision of CNC machining for wooden door hinge assembly holes.

The CNC machine tool used for machining wooden door hinge assembly holes and grooves is shown in Figure 1. It is developed and manufactured by Northeast Forestry University. Driven in the Y direction, the machine tool is powered by a high-precision servo motor with a rapid response rate. The controller integrates various shapes of wooden door hinge assembly hole grooves, enabling modification of their size parameters through graphical dialogue. This machine tool can process not only hinge assembly hole grooves but also lock grooves, lock holes, and handle hole grooves. Figure 2 demonstrates the simulation model of the shape of a wooden door hinge assembly hole groove.

When machining a workpiece on a CNC machine tool, the relative displacement error between the tool and the workpiece determines the machining accuracy. Geometric error, thermal deformation error, load error, and tool error of the machine tool are the primary factors influencing the machining accuracy. To improve machining accuracy, two main methods are commonly employed: error prevention method (hardware method) and error compensation method (software method). The error prevention method focuses on improving the processing and assembly accuracy of machine tool components, reducing errors caused by load changes, and maintaining a constant temperature working environment. On the other hand, the error compensation method utilizes the programmability and intelligence of CNC machine tools to achieve "low-precision machine tools process high-precision workpieces" effect. With the increasing specialization and standardization of CNC machine tools, error compensation has become an integral part of enhancing their machining accuracy.

The thermal error compensation modeling method proposed in this paper is based on genetic algorithm. Genetic algorithm is a self-organizing and adaptive artificial intelligence technology that imitates the biological evolution process to solve extreme value problems. By simulating the genetic mechanism of nature and biological evolution theory, genetic algorithm establishes an efficient process search optimal solution algorithm. With a solid biological foundation, genetic algorithm proves valuable in solving non-linear and multidimensional space optimization problems.

To establish the thermal error compensation model for NC machining of wooden door hinge assembly holes and grooves, the genetic algorithm is first utilized. It starts by defining the objective function and optimizing the key points of thermal error compensation to obtain the optimal solution for the unknown coefficients of the objective function. Real number coding is used to represent the coefficients in decimal form, expanding the search space and improving accuracy. The thermal error model of the genetic algorithm can be written in the following form (Equation 2):

In the actual compensation process, thermal error compensation points are distributed on the tool mechanism of the spindle assembly 1 of the wooden door hinge assembly hole groove CNC machining machine tool. Key points for thermal error compensation are selected for optimization, and the corresponding compensation model analytical formulas for axial and radial thermal error compensation are obtained.

In conclusion, using the wooden door hinge assembly hole groove numerical control machining machine tool with thermal error compensation technology can effectively correct thermal deformation errors, ensuring high precision machining. This technology plays a crucial role in achieving high precision and efficiency in the CNC machining of wooden door hinge assembly holes and grooves.