The surface quality of metal spun products requires to do a lot of details, many factors effect the surface quality. Such as the roller surface, mold surface, spindle speed, material thickness, roller gap, hydraulic pressure, nylon bottom and clamp. This article help you to analysis the problem of the surface quality of CNC spinning.

1. Mold surface 
Mold exterior surface effect the interior quality of metal spun products .

At first, Mold exterior hardness requires harder than the metal spinning material, such as you spin aluminum, you need 45# steel to make mold that hardness is harder than aluminum, you spin stainless steel, you can choose the Cr12 steel and heating treatment to make mold that hardness is harder than stainless steel, if you use 45# steel to spin stainless steel, the mold surface is deformed as the mold hardness is not enough.

When you choose the right mold materials, when you do the finishing tool in the CNC metal spinning machine, it needs to polishing meet 4K to remove turning tool grain to achieve the smooth surface of mold.

2. Roller surface 
Roller exterior surface effect the exterior quality of metal spun products.

At first, roller exterior surface requires harder hardness than CR12mov with hearing treatment, because roller is point touch in the spinning process, the wear rate is more obvious. If you use roller to spin stainless steel 304 or harder metal, there are abvious scratches on the surface of the roller after making 5 pieces of spun products, when the roller have scratches, it will scrath the workpiece and make it break or the surface of metal spinning products is worse after finishing spinning.

In order to have a better hardness, many factory choose SKD-11 (high speed steel) to make roller, SKD -11 is harder than Cr12mov after heating treatment, but SKD-11 is very brittle after heat treatment, it is easily to break when it bear high temperature or minor collision. 
The better way is to use Cr12mov to make roller, then heating treatment to improve hardness. At last, we can use plating to cover a hard coating on the exterior surface of roller.

3. Clamp and mold bottom  
Clamp force is not enough can cause the sheet slide relative to the spindle and the bottom of the metal spinning product will be scrathes, you can increase a little hydraulic pressure of tailstock cylinder still there is no slide. 

If the hydraulic pressure is enough, the bottom of metal spinng product still have scratches. you can design a soft material (the white and hard nylon) inside the bottom of mold like the first image. Third, the clamp material is used the nylon.

4. Roller gap
When roller and mold quality is good, you need to adjust the right gap to achieve the smooth exterior and interior surface. If the roller gap is little, the workpiece flow too fast and cause  the material accumulation, it produce the machine vibration the exterior will have uneven grain, if the roller gap is big, the workpiece can not touch the mold, the interior have fatigue line. 

Someone ask, what is right roller gap? Roller gap is related to the output spinning force of metal spinning machine, materials types, material thickness, such as thicker and same material need bigger gap than thin material, heavy duty CNC metal spinning need little gap than light duty CNC metal spinning machine, harder material of same thickness need little gap than softer material. 

How to judge the roller gap is right＞＞

5. Material thickness 
When you spin the thick metal, even you reduce the roller gap, you find that interior of workpiece can not touch the mold still. Except the spinning force of CNC metal spinning machine is not enough, the interior material flow more slowly than exterior materials in thick material spinning, you can use the heating to increase the interior material flow speed.  

6. Spindle speed 
The finishing spinning path can increase the spindle speed and slow the feed speed, it can improve the interior and exterior surface quality of meta spun products.

7. Turning edge 
If you turning the edge produce the machine vibration and edge is not smooth, you need to adjust path and gap to make the workpiece clamp the mold more tightly.