Inspection of Turned Cones
CNC Machining a taper is a common process in machining. The fit accuracy of the taper surface directly affects the assembly performance and performance of the part, making precise inspection of the taper after turning crucial. Inspection criteria for a taper primarily include angle, diameter, length , and surface roughness. Common inspection methods include template inspection, gauge inspection, vernier caliper inspection, sine rule inspection, and coordinate measuring machine inspection. Different inspection methods are suitable for different precision requirements and production batches.
The template inspection method is a simple and intuitive method for inspecting cone angles, suitable for rapid inspection of cone angles in mass production. The template is a special measuring tool made according to the nominal angle of the cone, and the angle of its working surface is equal to the nominal angle of the cone. During inspection, the template is placed tightly against the end face of the cone, so that the working surface of the template is aligned with the generatrix of the cone, and the quality of the cone angle is judged by observing the gap between the template and the surface of the cone. If the gap is uniform and within the allowable range, the cone angle is qualified; if the gap is too large or uneven, it means that there is an error in the angle. The advantages of the template inspection method are simple operation, fast inspection speed, low cost, and it is suitable for cone inspection with low precision requirements. However, this method can only inspect the cone angle, and cannot measure the diameter and length of the cone. In addition, the inspection results are greatly affected by the operator’s experience. For cones with high precision requirements, it is difficult to meet the inspection needs.
The gauge inspection method is a comprehensive method for inspecting cone dimensions and angles. It is suitable for inspecting high-precision cones and is particularly widely used in mass production. Cone gauges come in two types: plug gauges and ring gauges. Plug gauges are used to inspect internal cones, while ring gauges are used to inspect external cones. Gauges typically have two lines, one indicating the maximum and one indicating the minimum limits of the cone’s dimensions. During inspection, the gauge is placed against the cone being measured. If the end face of the cone falls between the two lines, both dimensions and angles are acceptable. If the end face exceeds the maximum line, the cone is oversized; if it falls below the minimum line, the cone is undersized. The advantages of the gauge inspection method are that it can simultaneously inspect both dimensions and angles, offers high accuracy, and is easy to use. However, gauges require high manufacturing precision, resulting in high cost. Furthermore, they can only determine whether a cone is acceptable, but cannot provide specific error values. Therefore, when analyzing the cause of an error, other measuring tools are required.
The vernier caliper inspection method is suitable for measuring the diameter and length of a cone, and then calculating the cone angle. To do this, first use a vernier caliper to measure the cone’s large end diameter D and small end diameter d, then measure the cone’s length L. The cone’s half-angle α/2 is then calculated using the formula tan (α/2) = (Dd)/(2L). The calculated result is compared with the nominal angle to determine if the cone angle meets the requirements. The advantages of the vernier caliper inspection method are its simplicity, low cost, and ability to measure specific dimensions, making it suitable for single-piece, small-batch production and on-site inspection. However, this method’s measurement accuracy is significantly affected by the accuracy of the vernier caliper and the operator’s measurement skills. This is particularly true when measuring the cone’s length and diameter, where inaccurate measurement positioning can lead to increased errors. Furthermore, for cones with smaller tapers, since the difference between D and d is smaller, measurement errors have a greater impact on the angle calculation. Therefore, this method is suitable for inspecting cones with larger tapers.
The sine gauge method is a high-precision cone angle measurement method suitable for inspecting cones with high precision requirements. It is particularly widely used in metrology rooms or laboratories. The sine gauge consists of a precision rectangular parallelepiped and two cylinders of equal diameter, with the axes of the two cylinders separated by a distance L (usually 100mm or 200mm). During inspection, the sine gauge is placed on a flat plate, with the small or large end of the cone to be measured in contact with the plate. Based on the nominal half-angle α/2 of the cone, the required gauge block height h is calculated: h = L × sin (α/2). The gauge block is then placed under one of the cylinders of the sine gauge, so that the working surface of the sine gauge forms an angle α/2 with the plate. The cone to be measured is then placed on the working surface of the sine gauge. A dial indicator is used to measure the height difference of the cone surface, and the angle error is calculated based on this height difference. The advantage of the sine gauge method is its high measurement accuracy, with an angular error of a few seconds to a few minutes, accurately reflecting the actual value of the cone angle. However, this method is complicated to operate and has high requirements on the measurement environment. It needs to be carried out under constant temperature and humidity conditions. The accuracy of the gauge block and the sine rule will directly affect the measurement results. Therefore, it is suitable for the inspection of high-precision cones.
The three-dimensional coordinate measuring machine (CMM) inspection method is a modern measurement method suitable for comprehensive inspection of complex or high-precision conical surfaces. It can simultaneously measure parameters such as angle, diameter, length, and form and position tolerances. The CMM uses a probe to contact the cone surface, collecting coordinate data at multiple points. Computer software then processes and analyzes the data to calculate various parameters of the cone. This data is then compared with design requirements to determine the error value. The advantages of the CMM inspection method include high measurement accuracy, a high degree of automation, non-contact measurement, and reduced damage to the cone surface. It is suitable for inspecting cones with various precision requirements, especially those with unusual curves, such as elliptical cones. However, CMMs are expensive and complex to operate, requiring specialized technicians for operation and maintenance. Therefore, they are only suitable for inspecting high-precision, complex-shaped cones, as well as for applications with stringent requirements for inspection results.
