CNC Machining of hardware parts is completed in a process system consisting of machine tools, fixtures and workpieces. Various errors in the processing system will be reflected as machining errors of parts in different degrees and ways.

1. Reasons for machining errors of hardware parts

(1) Processing principle error

CNC Machining principle error refers to the error caused by the use of an approximate blade profile or an approximate transmission relationship for processing.

(2) Geometric error of the processing system

The errors caused by the deviation of the actual geometric parameters and positions of each component in the processing system relative to the ideal geometric parameters and positions are collectively referred to as process system geometric errors. The geometric error of the processing system is only related to the geometric elements of each link of the processing system.

(3) Errors caused by force and deformation of the processing system

The processing system will be deformed under the action of cutting force, clamping force, gravity and inertia force, etc., thus destroying the mutual positional relationship of the components of the adjusted process system, resulting in the generation of machining errors and affecting the stability of the machining process.

(4) Errors caused by thermal deformation of the processing system

During the CNC processing of hardware parts, the temperature of the processing system will have complex changes due to the influence of cutting heat, friction heat and heat sources around the workplace. Under the action of various heat sources, the processing system will be deformed, resulting in changing the correct relative position of each component in the system, resulting in processing errors.

(5) Machining error caused by internal stress of the workpiece

Internal stress is the error factor of the workpiece itself. After the workpiece is hot and cold processed, certain internal stress will be generated. Under normal circumstances, the internal stress is in a balanced state, but when a workpiece with internal stress is processed, the original internal stress balance state of the workpiece is destroyed, thereby causing the workpiece to deform.

(6) Measurement error

When measuring the workpiece during the process of adjustment and processing, the error caused by the influence of the measurement method, the accuracy of the measuring tool and other factors on the accuracy of the measurement result is collectively referred to as the measurement error.

2. Solutions for errors in hardware parts processing

(1) Preparatory heat treatment process

Normalizing, annealing and quenching and tempering of metal before quenching will have a certain impact on the final deformation of the metal, and directly affect the change in the metal structure. The use of isothermal quenching during normalizing can effectively make the metal structure tend to be uniform, thereby reducing the amount of deformation.

(2) Use a reasonable cooling method

The faster the cooling rate of metal heat treatment, the more uneven the cooling, and the greater the stress generated. Pre-cooling can be used as much as possible under the condition of ensuring the hardness of the mold. The use of graded cooling and quenching can significantly reduce the thermal stress and tissue stress generated during metal quenching. An effective method to reduce the deformation of some workpieces with complex shapes.

(3) Reasonable design of parts structure

The workpiece should try to maintain the symmetry of the structure, material composition and organization to reduce distortion caused by uneven cooling. The workpiece should try to avoid sharp edges and corners, grooves, etc., there should be rounded transitions at the junction of thickness and steps of the workpiece, and minimize the asymmetry of holes and grooves on the workpiece, and parts with uneven thickness should be reserved…

(4) Use reasonable clamping methods and fixtures

The purpose of a reasonable clamping method is to make the workpiece heat and cool evenly, so as to reduce the uneven thermal stress and the uneven stress of the structure to reduce the deformation. The clamping method can be changed, the disc parts are perpendicular to the soil surface, and the shaft parts are installed vertically. Use compensating washers, support washers, superimposed washers, etc., spline hole parts can be carburized mandrels, etc.