In the professional field of precision hardware processing,which is highly dependent on precision,the quality of processing precision is directly related to the quality and performance of products,and is the core factor to determine whether products can meet the stringent industrial standards and practical application needs.However,in the actual production process,the machining accuracy often deteriorates,and the factors behind it are complex,covering many dimensions such as equipment,tools,fixtures,material properties,processing environment and human operation.At the same time,in-depth understanding and accurate grasp of the process benchmark is of irreplaceable significance for maintaining the stability of processing accuracy and ensuring a high degree of conformity between the final product and the design requirements.Next,this paper will analyze the reasons for the deterioration of precision hardware processing accuracy in depth,and systematically and exhaustively elaborate the process benchmark.
First,the reasons for the deterioration of precision hardware processing accuracy
Equipment wear factor:The internal key components of the processing equipment,such as guide rail,screw,spindle,etc.,which are in the state of high strength and high load operation for a long time,are difficult to avoid wear under the continuous mechanical friction and stress.Taking the grinding machine as an example,if the guide rail is seriously worn,the grinding wheel will not be able to maintain a precise trajectory when moving along the guide rail,which will lead to a great reduction in the surface flatness and dimensional accuracy of the ground workpiece;while the wear of the lathe screw will directly affect the feed accuracy of the tool,resulting in a deviation between the actual processing size and the preset size of the workpiece.
Tool wear factor:In the cutting process,the cutting edge of the tool is always subjected to strong cutting force,high temperature and friction from the workpiece material.As the cutting operation continues,the cutting edge will gradually appear wear and passivation,and even collapse in extreme cases.Once the cutting edge of the milling cutter is worn,the contour size obtained by milling is very likely to deviate from the design value;after the drill is worn,the accuracy of the drilled hole diameter is also difficult to meet the expected standard.
Abnormal factors of fixture:As the key device for fixing and positioning the workpiece in the processing process,the performance stability of fixture is directly related to the processing accuracy.If the positioning element of the fixture is loose,the workpiece will be displaced in the processing process,resulting in the deviation of the processing size;when the clamping element of the fixture is deformed,it can not provide sufficient and uniform clamping force for the workpiece,and under the action of cutting force,the workpiece is prone to small displacement,which ultimately affects the processing accuracy.
Difference factors of material characteristics:the chemical composition,internal structure and mechanical properties of different batches of hardware raw materials may fluctuate to a certain extent due to the differences in production process and raw material sources.When the hardness distribution of the material is not uniform,the cutting force of the tool will be in an unstable state during the cutting process,which will not only lead to a significant increase in surface roughness,but also may lead to a decline in dimensional accuracy.
Processing environment interference factors:temperature,humidity,vibration and other environmental factors have a significant impact on the precision hardware processing accuracy.In the high temperature environment,the size of the equipment and the workpiece will change due to the thermal expansion effect,and then the original set accuracy parameters will be changed.The high humidity environment is easy to cause the corrosion of the workpiece and the equipment,which seriously affects the quality of the machined surface.The strong vibration will interfere with the relative motion between the tool and the workpiece,destroy the stability of the cutting process,and ultimately lead to the decline of the machining accuracy.
Human operation error factors:The professional skill level,work experience accumulation and work responsibility of the operator have a direct and key impact on the machining accuracy.Human factors such as programming errors,unreasonable parameter settings,and lack of in-depth understanding of the machining process may lead to poor machining accuracy.For example,in the process of NC machining,if the operator inputs the tool compensation value by mistake,the size of the machined workpiece will inevitably be inconsistent with the design requirements.
II.Process Benchmark for Precision Hardware Processing
Design datum:In the part design stage,the design datum is the fundamental basis for determining the position relationship of other points,lines and surfaces on the part.It is like the cornerstone of the building,laying the foundation for the dimensional accuracy and shape accuracy of each part of the parts.Taking the design of precision shaft parts as an example,the axis line is usually selected as the design basis,and the dimensions and positions of each excircle surface and step surface are determined by the axis line as the reference standard.
Positioning datum:In the actual machining process,the positioning datum is used to determine the specific position of the workpiece on the machine tool or fixture.Whether the selection of positioning datum is appropriate or not directly determines the positioning accuracy and subsequent processing accuracy of the workpiece.Generally,the rough positioning datum is preferred to select the surface on the blank that is relatively flat and smooth and can reflect the main shape characteristics of the workpiece,so as to ensure the uniform distribution of the machining allowance;while the precise positioning datum needs to select the machined surface with high precision and strong positioning stability,such as high-precision plane or hole,so as to ensure the position accuracy of the workpiece in the whole machining process.
Datum of measurement:Datum of measurement is the reference datum used when measuring the size,shape and position accuracy of the workpiece.By determining the relative position relationship between the measuring reference and the measured elements of the workpiece,it can be accurately judged whether the workpiece meets the pre-set design requirements.For example,when measuring the position of a hole,a machined plane of the part is usually selected as the measurement reference,and the distance and angle between the hole center and the plane are measured to determine whether the position accuracy of the hole is up to standard.
Assembly Datum:During product assembly,the assembly datum is used to determine the exact position of the part in the assembly or the complete product.Reasonable selection of assembly datum plays a decisive role in ensuring the assembly accuracy and overall performance of products.For example,when assembling a precision mechanical equipment,the bottom surface of the machine base is often used as the assembly reference,and other parts are installed on this basis,so as to ensure the precise relative position relationship and good assembly effect between the parts.
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