With the rapid advancement of the machinery and electronics industries, CNC machine tools—particularly vertical machining centers—have become increasingly prevalent in manufacturing. The structural design of these machines plays a critical role in determining their rigidity, manufacturability, service life, and overall cost. Vertical machining centers typically use two types of weight systems: mechanical weights and hydraulic weights. While hydraulic systems offer a more compact design, they tend to be more expensive. As a result, most applications still rely on mechanical weighting systems.
The support frame used in such systems comes in two primary configurations. This paper employs finite element analysis (FEA) software like ANSYS to evaluate both structures, comparing their performance in terms of strength, stability, and efficiency. This study provides valuable insights for optimizing the structural design of vertical machining centers.
**1. Program Development**
The support frame is usually mounted on the top surface of the vertical column of the machining center. Holes are drilled at the front and rear of the frame to accommodate the shaft. A deep groove ball bearing, a shaft retaining ring, and a sprocket are installed on the shaft. One end of the chain connects to the headstock, while the other end is attached to the counterweight. The chain moves back and forth between the front and rear sprockets. The schematic diagram and dimension drawing for Scheme 1 are shown in Figures 1 and 3, respectively, while those for Scheme 2 are illustrated in Figures 2 and 4.
**2. Part Analysis**
Structurally, the first scheme has a support frame weighing 41 kg, with a bottom contact area of 500 mm × 80 mm = 40,000 mm². It uses a single-side support method for the shaft end. In contrast, the second scheme weighs 19 kg, with a bottom contact area of 205 mm × 50 mm = 10,250 mm², and employs a dual-side support system for the shaft.
From a technical perspective, the first scheme offers better precision, as it requires tight tolerances for both the large f40 mm holes and the smaller f25 mm holes. However, from a mechanical standpoint, the second scheme is superior. Under the same load (approximately 5,000 N each for the weight and the headstock in an 850-type vertical machining center), the second configuration supports the shaft from both ends. This reduces the bending moment significantly compared to the first scheme, making it more efficient and structurally sound.
For more detailed information, please refer to the attached file or consult the journal *Metalworking (Cold Processing)*, Issue 19, 2013.
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