Mold CNC Machining: Characteristics, Equipment and Accuracy Requirements

2022.5.28

What types of machine tools are used in mold CNC machining or processing? Based on the characteristics of mold machining, the CNC machines or machining centers need to meet some requirements.

Characteristics of Mold Machining & Making

1. Most molds need to process complex spatial curved surfaces on solid core metal modules. With the continuous development of molds to large-scale, the weight of modules will become larger and larger, and now some have reached tens of tons.

2. Most molds are cuboid or cube in shape, few are narrow and long, and the main processing quantity is concentrated on concave and convex molds.

3. As the requirements for mold products become more and more precise and complex, the requirements for mold processing accuracy are also higher and higher. Now the processing accuracy of many molds has reached ± 1~2 μ m. It will soon develop to less than ± 1 μ M.

4. As the user’s requirements for the mold production cycle become shorter and shorter, the mold processing must meet the requirements of high efficiency, fast, certain flexibility, and long-term full load non-stop operation.

Requirements of CNC Machining Centers in Mold Processing

According to the above characteristics, the following basic requirements are put forward for CNC machining centers for mold processing:

1. The machine tool shall have good rigidity and large bearing capacity corresponding to the weight of the module;

2. The dimension of the worktable should be consistent with the overall dimension of the mold, suitable for rectangles, squares, and circles, not narrow and long, while the height direction and stroke require a large space;

3. High accuracy and accuracy retention;

4. The allowance shall be removed quickly and efficiently with high reliability to maintain continuous and long-term full load operation;

5. In order to adapt to complex spatial surface machining and have a large number of machining quantities, the machine tool is required to be capable of multi-axis linkage and equipped with a CNC system with a large information capacity.

Accuracy Requirements in Mold Machining

– The manufacturing accuracy of mold size should be within the range of 0.005 ~ 0.02mm; The perpendicularity should be within the range of 0.01 ~ 0.02mm; Coaxiality shall be within 0.01 ~ 0.03mm; The parallelism of the upper and lower planes of the movable and fixed mold parting surfaces shall be within the range of 0.01 ~ 0.03mm.

– After the mold is closed, the gap between the parting surfaces is less than the overflow value of the formed plastic. The parallelism of other formwork mating surfaces shall be within the range of 0.01 ~ 0.02mm; The fitting accuracy of the fixed part is generally within the range of 0.01 ~ 0.02mm; If the small core has no requirements for butt joint or has little impact on the size, a clearance fit of 0.01 ~ 0.02mm on both sides can be taken; Generally, H7/e6, H7/f7, and H7/g6 are selected for the fitting accuracy of sliding parts.

– If there is an insert attached to a step on the mirror surface, the fit should not be too tight, otherwise when the insert is knocked back from the front, the tool used to knock easily damages the mirror surface. If the product size is not affected, a clearance fit of 0.01 ~ 0.02mm on both sides can be taken.

 

In addition, for the workpiece to be processed by heat treatment, a 0.25mm grinder allowance should be added to one side of the overall material preparation size before heat treatment, 0.2mm allowance shall be reserved at one side for the part of the die core and insert to be roughly processed by CNC, 0.3-0.5mm allowance should be reserved at one side for the rough milling of the fitter milling machine, and 0.05mm allowance should be reserved at one side of the forming part and 0.1mm grinding allowance should be reserved at the rough side of the shape after wire cutting. After CNC finishing and electric pulse, the mirror polishing should be done, and a 0.03mm polishing allowance shall be left on one side.