Mold Surface Preparation

Of all the tasks faced in the mold-making trade, texture and its related problems are probably among the most challenging.   Cutter marks, welds, EDM and Heat Affected Zones (HAZ) must be handled properly on tool surfaces that are to be textured.  Failure to properly prepare the mold surface can cause uneven or inconsistent texturing on the mold surface.

• EDM SURFACES:  
  

The problem with EDM surfaces is the hardness of the scale plus the Heat Affected Zone (HAZ).  If not properly removed from the surface, the texture will be inconsistent.

It is important to remove all of the EDM and the HAZ, which can be anywhere from .001" to .0015" deeper than the EDM.

You can tell if all of the EDM and the HAZ is properly removed by using a copper etching solution (copper sulfate) and diluting it with water.  This testing fluid can be easily spread over the area to be textured with a brush, spray bottle, q-tip or even tissue paper.  This will turn the surface copper colored or black in the applied area after a few moments.  This will show silver, gray or gold spots where any remaining EDM is on the surface.  HAZ will show itself as the shape of the electrode and will be silver in color.  If the steel being tested will not turn color, there is a surface hardness problem, which may cause the texture to be inconsistent.  Using this simple test can save a lot of time and grief.  Once the surface turns uniform in color, the tool is ready for texturing.

• MILLED SURFACES: 

Milled surfaces are simply stoned flat with the correct draw on the sidewalls and to the required finish grit.  Cutter marks and other surface irregularities need to be completely removed to produce an even textured surface.  Most textures will not hide cutter marks or surface imperfections. 

• WELDS: