There are three main problems with the quality of shaft forgings, namely, axial dimensional error, radial circular jump error, and thunder machining error (too loose or too tight, etc.). However, the dimensional and shape errors caused by measurement and machining trial cutting are also very small. Based on the feedback from the part inspection records (part nonconforming product notification), count the causes, quantities, processing equipment, and operators of each nonconformity, analyze the obtained data, and propose corrective measures.
1. Reasons for quality problems
To understand the quality control of the machining process of shaft forgings, it is first necessary to understand the causes of quality problems during machining.
1) Process system error. The main reason is the use of approximate methods for machining, such as using a shaped milling cutter to process gears.
2) Workpiece clamping error. Due to the unsatisfactory positioning method, the positioning benchmark does not coincide with the design benchmark, and other reasons.
3) Fixture manufacturing, installation errors, fixture wear, etc.
4) Machine error. There are also certain errors in various aspects of the machine tool system, which affect the machining error of shaft forgings.
5) Tool manufacturing errors and errors caused by tool wear after use.
6) Workpiece error. The positioning of shaft forgings itself breaks tolerances such as shape, position, and size.
7) During the processing of shaft forgings, due to the influence of force and heat, the workpiece deforms and produces errors.
8) Measurement error. Errors caused by the influence of measuring equipment and technology.
9) Adjust the error. Errors caused by measuring garbage, machine tools, and human factors when adjusting the correct relative position of the tool and shaft forgings.
2. Ways to improve machining accuracy
There are mainly two methods to improve machining accuracy, namely error prevention and error compensation (error reduction method, error compensation method, error grouping method, error transfer method, local machining method, and error averaging method).
(1) Error prevention technology
1) Directly reduce the original error. It is mainly an attempt to directly eliminate or reduce the main original error factors that affect the accuracy of machining shaft forgings.
For example, when machining slender shaft forgings, the main original error factor is the poor stiffness of the forgings. Therefore, the reverse feed cutting method is used to increase the tool holder and stretch the shaft forgings to reduce deformation.
2) Transfer the original error. That is, the original error that affects the machining accuracy is transferred to a direction that does not affect or does not affect the machining accuracy. For example, the error sensitive direction of a lathe is the diameter direction of an axial forging. Therefore, the turret lathe adopts the vertical knife installation method in production, placing the cutting base surface of the cutting blade on a vertical plane, and transferring the indexing error of the tool holder to the error insensitive tangent direction.
3) The average of the original error. Grouping adjustment is adopted and the error is evenly divided, that is, the workpiece is grouped according to the error size. If divided into n groups, the error of each group of parts is reduced by 1/n.
4) Local processing methods. For example, the axis of the top hole of the rear seat of the lathe is required to coincide with the axis of the main shaft, and on-site processing is used to assemble the tailstock onto the machine tool for final finishing. Another example is that the machining of the six large holes and end faces on the turret lathe for installing the tool holder is also on-site machining.
(2) Error compensation technology
1) Online testing. That is, during the processing process, the actual size of the workpiece is measured at any time, and the tool is compensated at any time.
2) Automatic grinding of accessories. This method controls the machining accuracy of another part based on a matching part.
Dongguan Lianshengwang Forging Factory focuses on aluminum alloy hot forging, cold forging, and 3D forging technology. Free quotation for aluminum alloy forgings, can be customized according to drawings and samples, welcome to inquire.