High-precision machining with fine grinding, honing and polishing

Grinding, honing and polishing can not only achieve reasonable efficiency but also achieve high-Precision Machining. As the reduced dimensional tolerances of Turned Parts reach the nanoscale range, special special equipment is required. For high-precision machining tasks, piece-processing operations can be taken to achieve high-precision results and economic benefits.

Figure 1 Double grinding wheel equipment for fine grinding. High-precision machining requires the machine's running accuracy to be ±2μm

At present, the miniaturization of processing components and the diversification of functions are increasingly becoming the focus of attention in the cutting shop, as shown by Commonrail-Technik: When an oil injection system of an injection engine is used in an automobile manufacturing industry, one branch has multiple branches. The fuel in the common oil inlet pipe that supplies oil to each cylinder will always be under pressure, so the pump set needs to be used. The pump set contains turned parts, which require extremely high dimensional accuracy (such as tolerances, flatness and plane parallelism). In the automotive industry, these requirements are expressed as the Cpk value of process statistical control (SPC): This property value is used to judge the efficiency of the processing process and has become more stringent in recent years. Several years ago, a Cpk value of 1.33 μm was sufficient, and the dimensional accuracy was within ±10 μm. Today this value needs to reach 1.67 μm so that the tolerance range can be reduced to ±5 μm.

This trend will affect the equipment. The device's ability to work is reflected in the static process control Cmk value. It is proportional to the Cpk value, ie, the Cmk value is also limited. If the maximum dimensional tolerance is ±5 μm, the accuracy of the equipment operation should be maintained at ±2 μm. The limit of the cutting process is very close to the boundary of micron and nanometer. Therefore, in the machining process of precision automotive parts, not only special equipment such as fine grinding, honing and polishing, but also a very special processing flow are used.

Figure 2 Single wheel machine for honing and polishing. This machine is designed for high-precision machining in clean room conditions

Growing demand

Due to these conditions, piece-processing units such as FLP Microfinishing (formerly FLP Staehle) in Halle-Zoerbig have achieved economical processing operations. FLP Microfinishing can provide grinding, honing, polishing and deburring services. Since 2001, it has started micro-cutting operations. It has also invested in a second processing workshop. Since then, the company has shifted its focus to high-precision machining. The key technologies are based on the development and manufacture of single and double grinding wheels, honing and polishing equipment, and trading of tools and materials.

Since the Cpk value is greatly limited, the requirements for the equipment have also been greatly improved. Although the ±10 μm dimensional tolerance was reduced by half, the equipment requirements were not increased exponentially. Instead, new precision specifications were required for equipment manufacturing. The practice of still using traditional means has been unable to leap forward. In order to be able to reach the limit of repeatable tolerances of ±5 μm, new technical solutions need to be adopted. This is not just a matter of equipment manufacturing.

Fig. 3 High-precision turning with a maximum tolerance of ±5 μm due to the use of piece processing

High-precision machining requires specialization

Due to the processing conditions, fine grinding, honing and polishing can also be divided into two precision grades. The FLP Microfinishing company is divided into gray and white areas. High-precision machining – that is, the white area – is carried out in an air-conditioned clean room, which is the result of a progressive increase in processing requirements. This calls for better energy economics management today, and considers energy recyclability or energy-saving measures such as heat recovery. In addition, the processing and recycling of liquid auxiliary materials required for processing is also one of the tasks. Only in this way can customers maintain a good cost structure in the face of increasing costs.

The three processes of high-precision machining can achieve a good rationalization effect. FLP Microfinishing Corporation uses the results of process specialization to gather fine grinding, honing, and polishing on micromachining into the overall machining process of mechanical components and systems. Therefore, FLP Microfinishing is not only a device manufacturing and piece processing unit, but also a system integrator with a wide range of applications. It not only serves the automotive industry, but also extends to aerospace, aerospace and machine manufacturing, and medical devices. For example, high-precision turning of hydraulic and turbine components.