1. Introduction

2. Overview of Precision Machining

(1) Definition and Scope of Precision Machining

(2) Characteristics of Precision Machining

1. High Precision Requirements: The dimensional tolerances of precision machining are usually in the micrometer or even nanometer range. For example, in semiconductor chip manufacturing, the line width on the chip may be only a few tens of nanometers, which requires the machining equipment to have extremely high positioning accuracy and motion control accuracy; any slight deviation may lead to a serious decline in chip performance or even scrap.
2. Excellent Surface Quality: It is necessary not only to ensure dimensional accuracy but also to achieve extremely low surface roughness and no surface defects. In the field of medical devices, such as the surface processing of artificial joints, it is required to achieve extremely high smoothness to reduce friction and wear, thereby improving the service life and biocompatibility of the implants.
3. Complex Machining Processes: It often requires the combination of multiple machining processes and precise control and optimization of process parameters. For example, in the manufacturing of aircraft engine turbine blades, it may first form a rough shape through precision casting, and then use CNC milling, grinding, and electrical discharge machining processes to accurately shape the complex curves and fine structures of the blades, while adjusting cutting speed, feed rate, cutting depth, and other parameters according to different materials and machining requirements.

3. Requirements of Precision Machining for Constant Temperature and Humidity Clean Environment

(1) Temperature Stability Requirements

1. The Impact of Thermal Deformation on Machining Precision: During the precision machining process, various components of the machine tool, cutting tools, and workpieces will undergo thermal expansion and contraction due to temperature changes. Even slight temperature fluctuations can lead to elongation or contraction of the machine tool spindle, deformation of the worktable, etc., thereby changing the relative position accuracy between the tool and the workpiece. For example, in precision milling, if the temperature of the machine tool spindle changes by 0.5°C, its axial elongation may reach several micrometers, which is unacceptable for micrometer-level precision machining.
2. The Importance of Temperature Uniformity: In addition to the overall temperature stability, the uniformity of temperature within the machining area is also critical. Local temperature differences can cause uneven thermal deformation of the workpiece, leading to shape errors after machining. For example, in the grinding of large precision plates, if there is a temperature gradient between the grinding area and the surrounding area, the plate may warp and deform, failing to meet flatness requirements. Generally, the temperature uniformity in a precision machining environment should be controlled within ±0.5°C, and the temperature fluctuation range should be between ±0.1°C and ±0.3°C.

(2) Humidity Stability Requirements

1. Moisture Absorption and Expansion of Materials and Machining Precision: Many machining materials, such as metals, ceramics, and composites, have a certain degree of moisture absorption. When the environmental humidity changes, the materials will absorb or release moisture, leading to dimensional changes. In optical glass processing, fluctuations in humidity may cause the glass to undergo slight expansion or contraction, affecting the curvature accuracy of the lens. For some high-precision measuring instruments and standard parts, material deformation caused by humidity changes can severely impact their calibration accuracy.
2. Humidity and Equipment Corrosion and Oxidation: High humidity environments can easily lead to the corrosion and oxidation of metal materials, reducing the service life and precision of cutting tools and machine tool components. In humid environments, the surfaces of machine tool guide rails and screws may rust, increasing motion resistance and wear, thereby affecting machining precision. At the same time, corrosion products may adhere to the workpiece surface, damaging surface quality. Therefore, the humidity in precision machining environments is usually required to be controlled between 30% - 60% RH, with humidity fluctuation ranges within ±3% RH - ±5% RH.

(3) Cleanliness Requirements

1. The Damage of Dust Particles to Machining Surfaces: Even small dust particles can embed into the surface of the workpiece or between the tool and the workpiece during precision machining, causing scratches, pits, and other surface defects, severely affecting surface quality. In ultra-precision cutting of optical lenses, a dust particle with a diameter of a few micrometers can lead to the scrapping of the lens.
2. Cleanliness and Equipment Reliability: Dust particles can also enter the moving parts and electrical systems of machine tools, increasing friction and wear, leading to equipment failures. For example, in semiconductor manufacturing equipment, tiny dust particles can contaminate the chip manufacturing process, affecting the electrical performance and yield of the chips. The cleanliness of precision machining environments is usually required to reach Class 100 or even higher, meaning that the number of dust particles larger than 0.5 micrometers in one cubic meter of air should not exceed 3500.

4. Construction and Maintenance of Constant Temperature and Humidity Clean Environment

(1) Environmental Control System Design

1. Selection of High-Precision Constant Temperature and Humidity Air Conditioning UnitsA specially designed air conditioning system for precision machining environments, equipped with cooling, heating, humidifying, and dehumidifying functions, can achieve high-precision regulation of temperature and humidity through advanced sensors and intelligent control systems. For example, some high-end constant temperature and humidity air conditioning units can achieve a temperature adjustment accuracy of ±0.1°C and a humidity adjustment accuracy of ±2% RH. The air conditioning system should be reasonably selected and laid out based on the area, spatial layout, and thermal and humidity load of the processing workshop to ensure uniform distribution of temperature and humidity.
2. Clean air treatment systemThis includes the reasonable configuration of air filters. Pre-filters are used to filter large particles of dust, medium-efficiency filters further remove medium-sized particles, and high-efficiency filters capture fine dust particles to meet cleanliness requirements. At the same time, airflow distribution devices, such as static pressure boxes and diffusers, are used to evenly deliver treated clean air into the processing area, creating a stable airflow field and avoiding dead zones and turbulence.

(2) Thermal insulation and sealing measures

1. Thermal insulation of enclosing structuresThermal insulation materials are used to treat the walls, roofs, and floors of the processing workshop to reduce heat transfer between the external environment and the interior. For example, walls can use thermal insulation materials such as polystyrene foam boards and polyurethane foam boards, roofs can have thermal insulation waterproof layers, and floors can be laid with thermal insulation mats or use flooring materials with good thermal insulation properties. These measures reduce the impact of external temperature changes on indoor temperature and humidity, lighten the load on the air conditioning system, and improve environmental stability.
2. Sealing treatment of doors and windows and gapsDoors and windows are the main channels for heat, moisture, and dust exchange between indoors and outdoors, so materials with good sealing performance should be used, such as broken bridge aluminum doors and windows, plastic steel doors and windows, and high-quality sealing strips should be installed to ensure there are no gaps when the doors and windows are closed. For precision machining areas with extremely high environmental requirements, airlock rooms or buffer zones can be set up to reduce the intrusion of external air during personnel and material entry and exit. At the same time, sealing treatments should be applied to various gaps such as pipe and cable penetrations in the workshop to prevent air leakage and dust entry.

(3) Environmental monitoring and calibration

1. Layout of temperature, humidity, and dust particle sensorsTemperature and humidity sensors and dust particle counters should be reasonably arranged in the processing workshop to monitor changes in environmental temperature, humidity, and cleanliness in real-time. Sensors should be distributed in different processing areas, around equipment, and in corners to comprehensively grasp the distribution of environmental parameters. For example, multiple sensors should be installed near high-precision machine tools to monitor temperature and humidity changes and dust particle concentrations in the machine tool working area, providing data support for precise control. The accuracy of temperature and humidity sensors should meet the requirements of precision machining environments, generally using high-precision sensors with an accuracy of ±0.1°C and ±2% RH, and dust particle counters should accurately measure the number of fine particles and meet cleanliness level standards.
2. Regular calibration and maintenanceTemperature and humidity sensors, dust particle counters, and environmental control equipment such as air conditioning systems need to be regularly calibrated and maintained to ensure their measurement accuracy and operational reliability. The calibration cycle can be determined based on the frequency of use and stability of the equipment, generally ranging from 1 to 3 months. During the calibration process, standard temperature and humidity measuring instruments and dust particle standard samples are used to compare and adjust the sensors, ensuring that their measurement errors are within acceptable limits. At the same time, regular checks and cleaning of components such as filters, humidifiers, and dehumidifiers in the air conditioning system should be conducted, and damaged or aging parts should be replaced in a timely manner to ensure the normal operation of the air conditioning system.

V. Conclusion