This paper introduces a simple machining method for large-radius arc grooves, which can be processed efficiently by using a milling cutter on an ordinary milling machine or boring machine without investing in special tooling. And deduced the calculation formula of the inclination angle of the milling cutter, and the determination method of the theoretical error. The processing accuracy can meet the requirements, which is very suitable for single piece and small batch production.
1 Preamble
The backing plate structure for assembly of the large roller on the WD615 series rotary kiln is shown in Figure 1. The R510mm arc groove on the backing plate is usually processed on a planer after scribing, or processed on a vertical lathe with a clamping tool. The former has low processing efficiency and low precision; although the latter has high processing efficiency and precision, it needs to invest in special clamping tooling, and the clamping is troublesome and the processing cost is increased, so it is not suitable for single-piece production.
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Figure 1 Backing plate structure
After research, a simple processing method is adopted to realize the processing with the milling cutter disc on the ordinary milling machine or boring machine, which improves the production efficiency, and the precision fully meets the requirements of use.
2 Machining method of backing plate arc groove
The arc groove processing of backing plate is shown in Figure 2. The arc groove can be processed by tilting the milling cutter at an angle θ; the depth of the arc groove can be guaranteed by controlling the distance between the milling cutter and the workpiece. The processing process is shown in Figure 3.
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Figure 2 Schematic diagram of backing plate arc groove processing
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Figure 3 Processing process
Principle analysis: when the inclination angle θ is 0°, the radius of the processed arc groove is the radius of the milling cutter; when the inclination angle θ is 90°, the radius of the processed arc groove is infinite, which is a plane; when the inclination When the angle θ is between 0° and 90°, the processed arc groove is actually an elliptical arc groove whose long axis is the diameter of the milling cutter and whose short axis is the product of the diameter of the milling cutter and the cosine of the inclination angle. If allowed, it can be approximated as an arc groove [1].
3 Determination method of inclination angle
According to the simple processing method, the key is how to determine the specific inclination angle θ of the milling cutter disc. According to the four-center approximate drawing ellipse method shown in Figure 4 [2], let the major semi-axis of the ellipse be a, and the minor semi-axis be b. After simple mathematical calculation, the large arc radius R of the ellipse can be calculated [3]
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Figure 4 Four-center approximation ellipse drawing method
In Fig. 2, the long axis of the ellipse is the diameter d of the milling cutter, and the short axis is dcosθ. Substituting into formula (1), the relationship among d, θ, and R can be deduced as follows
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For a specific workpiece, the radius R of the arc groove is known, and the diameter d of the milling cutter used is also known, and the inclination angle can be calculated by substituting into formula (2). Of course, the calculation process is very cumbersome, and a calculation formula can be compiled on Excel to easily calculate the specific value of the inclination angle θ.
4 Error Analysis
Due to the simple processing method mentioned above, the circular arc surface is approximately replaced by the elliptical arc surface, so it is necessary to study its theoretical error.
The point farthest from the center line has the largest error. The theoretical error can be calculated by calculating the coordinate value of the point according to the circular arc and elliptical arc respectively. If it is within the allowable error range, it can be processed in this way; if it exceeds To meet the allowable error, the theoretical error can be reduced by increasing the diameter of the milling cutter disc and reducing the inclination angle until it meets the requirements.
The specific calculation process is more complicated, and the simple method is to draw and measure directly in CAD, which can quickly and conveniently determine the theoretical error value.
The circular arc groove of the backing plate in Fig. 1 adopts the φ250mm milling cutter disc, and the inclination angle calculated according to formula (2) is 76.9353°. Drawing measurement in CAD, the error of the furthest distance from the center line is only 0.1064mm, which meets the requirements.
5 Precautions
Since this simple processing method uses an elliptical arc groove to approximately replace the circular arc groove, in order to ensure the accuracy, the following points should be paid attention to when using this method.
1) The diameter of the selected milling cutter must be larger than the required arc groove width (ie, chord length) of the workpiece.
2) The width of the arc groove of the workpiece must be smaller than the chord length B of the large arc of the ellipse in Figure 4, and the calculation formula for the value of B is as follows
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3) The theoretical error value must be determined before use, and this method can only be used when the accuracy requirements of the workpiece are met.
6 Conclusion
This paper introduces a simple method for machining large-radius arc grooves on ordinary milling machines or boring machines. By controlling the inclination angle of the milling cutter disc, the approximate machining of arc grooves is realized by using elliptical arc surfaces, and the following conclusions are drawn.
1) Using a simple processing method to process large-radius arc grooves that meet the precision requirements can improve production efficiency and reduce production costs.
2) For the processing of large-radius arc grooves that do not require high precision, different inclination angles can be adjusted to process arc grooves with various radii under the condition that the diameter of the milling cutter remains unchanged, thereby reducing the reserve of tool specifications. volume, reducing production costs.
3) The simple processing method is especially suitable for single piece and small batch production.
Expert Reviews
The article introduces a simple method for machining large-radius arc grooves on ordinary milling machines or boring machines, and deduces the calculation formula of the inclination angle of the milling cutter disc, as well as the determination method of the theoretical error. Ideal for single piece, small batch production.
The content of the article has a certain degree of technical inheritance and technological innovation. The method is simple, economical and practical, and fully utilizes the advantages of ordinary machine tools and traditional processing. Reduce tool costs and improve production efficiency.
