CNC加工鋁件變形怎麼辦?

造成鋁構件變形的原因有很多, 與材料有關的, 處理工具, 零件的形狀, 以及加工設備. 主要有以下幾個方面: 毛坯內應力引起的變形, 由切削力和切削熱引起的變形, 以及夾緊力引起的變形.

一, 減少加工變形的製程措施
1. Reduce internal stress of aluminum blank
自然或人工時效及振動處理可部分消除毛坯內應力. 前處理也是一種有效的處理方法. 對於大毛坯, due to the large margin, the deformation after processing is also large. If the excess part of the blank is processed in advance and the margin of each part is reduced, the processing deformation in the subsequent process can be reduced. 而且, after pre-processing and placing it for a period of time, part of the internal stress can also be released.

Reasons for milling deformation of aluminum parts

2. Improve the cutting ability of the tool
The material and geometric parameters of the tool have an important influence on the cutting force and cutting heat. 正確選擇刀具對於減少零件變形至關重要.
(1) Reasonably choose the tool geometry parameters.
① The rake angle of the tool: 在保持刀刃強度的情況下, 前角應適當大一些. 一方面, 它可以磨削鋒利的切割刃, 另一方面, 可以減少切削變形, 使排屑順利, 然後降低切削力和切削溫度. 切勿使用負前角刀具.

② The clearance angle of the tool: 後角的大小直接影響後刀面的磨損和加工表面的質量. 切削厚度是選擇後角的重要條件. 粗銑時, 由於進給量大, 切削負荷大、發熱大, 要求工具有良好的散熱條件. 所以, the angle of the relief angle should be smaller. 精銑時, the cutting edge is required to be sharp, reduce the friction between the flank face and the machined surface, and reduce the elastic deformation. 所以, the angle of the relief angle should be selected larger.

③ The helix angle of the tool: 為了使銑削順利並減少銑削力, 螺旋角應選擇盡可能大的.

④The entering angle of the tool:
Properly reducing the entering angle of the tool can improve the heat dissipation conditions and reduce the average temperature of the processing area.

Cutting ability of milling tool

(2) Improve the tool structure.
①Reduce the number of teeth of the milling cutter and increase the chip space. 由於鋁材的可塑性大, 加工時切削變形大, 並且需要更大的晶片容量空間, 因此容屑槽的底部半徑應較大，銑刀齒數應較少.

② Finely sharpen the teeth. The roughness value of the cutting edge of the cutter tooth should be less than Ra=0.4um. 使用新刀之前, you should use a fine oil stone to gently grind the front and back of the knife’s teeth to eliminate the residual burrs and slight serrations when the knife is sharpened. 這樣, 不僅可以降低切削熱, 而且切削變形也比較小.

③ Strictly control tool wear standards. 工具磨損後, 工件表面粗糙度值增加, 切削溫度升高, 且工件變形增大. 所以, 除了選擇耐磨性好的刀具材料外, 刀具磨損標準應不大於0.2mm, otherwise it is easy to produce accumulated chip edges. 切割時, 工件溫度一般不超過100℃，以防變形.

銑刀幾何參數

3. 改進工件裝夾方法
適用於剛性差的薄壁鋁工件, 可採用以下裝夾方法來減少變形:
① For thin-walled bushing parts, if a three-jaw self-centering chuck or spring chuck is used to clamp from the radial direction, 一旦處理後釋放, 工件不可避免地會變形. 此時, the method of pressing the axial end face with better rigidity should be used. 定位零件的內孔, 自製一個穿過心軸的螺紋, 將其套入零件的內孔中, 用蓋板壓住端面，然後用螺帽旋緊. 外圓加工時可避免裝夾變形, 從而獲得滿意的加工精度.
② When processing thin-walled and thin-plate cavity workpieces, 最好使用真空吸盤以獲得均勻分佈的夾緊力, and then process with a smaller cutting amount, 可以很好的防止工件變形.

另外, a packing method can also be used. 為了增加薄壁工件的加工剛性, 可在工件內部填充介質，減少工件裝夾、切削時的變形. 例如, 倒入含有尿素熔體 3% 到 6% 硝酸鉀進入工件, and after processing, immerse the workpiece in water or alcohol to dissolve the filler and pour it out.

Three-jaw self-centering chuck

4. Reasonable arrangement of processing procedures
高速切削時, due to the large machining allowance and intermittent cutting, 銑削過程經常產生振動, 影響加工精度和表面粗糙度. 所以, the CNC high-speed cutting process can generally be divided into: Rough machining-semi-finish machining-clear corner processing-finishing and other processes. 對於精度要求高的零件, it is sometimes necessary to perform secondary semi-finishing and then finishing. 粗加工後, 零件可自然冷卻，消除粗加工產生的內應力，減少變形. 粗加工後留下的餘量應大於變形量, 一般來說 1 到 2 毫米. 整理過程中, 零件的精加工表面應保持均勻的加工餘裕, 一般0.2-0.5mm為宜, 使刀具在加工過程中處於穩定狀態. 可大幅減少切削變形, 獲得良好的表面加工質量, 並確保產品精度.

High-speed cutting of aluminum parts