Technical difficulties and countermeasures for ultra-fine machining (Figure)

1 Introduction

Microfabrication technology refers to the manufacturing and processing technology of small-sized parts. With the development of aerospace, defense industry, modern medicine and bioengineering technology, more and more miniaturization, miniaturization equipment and small-sized parts have emerged, and various micro-machines such as micro-motors and miniatures manufactured by micro-machining technology have emerged. Sensors, micro pumps, etc. have an increasingly broad application prospect. Modern manufacturing technology has become more and more demanding for micro-machining, and has developed into ultra-fine processing; challenging the processing limits of existing manufacturing technologies, developing ultra-precision processing, ultra-fine processing and nano-processing technology, has become a modern manufacturing technology. A development direction.

Microfabrication technology not only includes various traditional precision machining methods, but also special processing methods such as electron beam processing, ion beam processing, and chemical processing. These special processing methods are currently well applied in the field of microfabrication, and there are some technical difficulties in the cutting process in the micro and ultrafine fields, which limits its wide application. Because even for conventional machining, the processing mechanism and method for small size and normal size are different. In this paper, by studying the mechanism of ultra-fine processing, the technical difficulties in ultra-fine processing and its influence on the processing process are analyzed, and the solutions are proposed. 2 Mechanism of ultra-fine cutting

Ordinary cutting and micro-cutting differ in the processing mechanism. In normal cutting, due to the large size of the workpiece, the allowable cutting depth and feed amount are large. In the case of fine cutting, due to the small size of the workpiece, it is not allowed to adopt a large depth of cut and strength in terms of strength and rigidity. In order to ensure the dimensional accuracy of the workpiece, the thickness of the surface finish layer of the final finishing must be less than the precision value, so the amount of cutting must be small.

A typical metal material is composed of crystal grains having a diameter of several micrometers to several hundreds of micrometers. Due to the very small depth of cut for micro-cutting, especially sub-micron and nano-scale ultra-fine cutting, usually the cutting depth is smaller than the grain diameter of the material, so that the cutting can only be carried out in the grain, and the cutting is equivalent to one by one. The discontinuous body cuts, so fine cutting is an intermittent cutting. Due to the microscopic defects of the material and the uneven distribution of the material, the cutting force of the tool changes greatly during cutting, and the cutting edge will be subjected to large impact and vibration.

2 Cutting force characteristics of micro cutting

Micro-machining is an ultra-micro-separation technique in which the cutting force near the cutting edge of a diamond tool is sub-Newtonian or even smaller. The cutting force clearly reflects the removal process of the chips, so studying the cutting force model helps to understand the cutting characteristics of the chips. The cutting force characteristics during micro-cutting are: the cutting force is small, the unit cutting force is large, and the depth of cut resistance is greater than the main cutting force; the cutting force increases with the decrease of the cutting depth, and the cutting force increases sharply when the depth of cut is small Big. This is the size effect of the cutting force.

The physical model of the cutting force during micro-machining is closely related to the sub-micron structure of the tool edge. Due to the existence of the arc radius of the cutting edge, the cutting edge has a large negative rake angle when cutting in the nanometer order, which increases the cutting deformation, so the unit cutting force during cutting is large. At the same time, due to the fine cutting The inside of the grain is carried out, and the cutting force must be larger than the molecular and atomic bonding force inside the crystal, so that the cutting force per unit cutting area is sharply increased.

The cutting force increases with the increase of the cutting depth during normal cutting, and the cutting depth and the feed amount during micro-cutting are small. Due to the existence of the radius of the tool nose and the radius of the cutting edge, the cutting deformation is significantly increased. When the depth of cut is small, the additional deformation caused by the radius of the tool nose is a large proportion of the total cutting deformation. Due to the size effect of the cutting force, the smaller the depth of cut, the greater the cutting force (the effect of the depth of cut on the cutting force during micro-cutting is shown in Figure 1).

Figure 1 Effect of depth of cut on cutting force

Minimum cutting thickness for fine cutting

Nano-scale continuous and stable cutting can be achieved with extremely sharp diamond tools when the machine conditions are optimal. The minimum effective cutting thickness for stable cutting is called the minimum cutting thickness. The minimum cutting thickness that can be achieved by micro-cutting is related to the radius of the arc of the diamond cutting edge and the physical and mechanical properties of the material being cut.

Figure 2 Effect of minimum cutting thickness on radius of the cutting edge

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