When choosing a stone to begin polishing a mold or die there are many factors that must be considered. A few of the most common are listed below.
a. Mold Material
• Steel (P20, Stainless Steel, H13, D2)
• Non Ferrous (Aluminum, Bronze)
b. Material Hardness
• Heat Treated
c. Finish quality left by the machining process.
d. Shape of mold surface.
• Rib or Slot
• Detail area
e. Desired final finish
In general, it is always better to start with a finer stone and if a coarser stone is needed you can always go coarser to achieve the best result. In most cases, you can start with a 220 grit stone for conventional machined surfaces. EDM surfaces may require a coarser grit stone to remove the hard re-cast layer. For ground surfaces, a finer stone can be used to start the polishing process. For radius surfaces, it is good to use a softer stone that will take the shape of the mold. For detail areas that require a mold feature to be maintained it is better to use a harder stone that will keep its shape. Always use a lubricant with harder stones to prevent stone loading.
Mold Polishing Basics
Always shape the mold polishing stone on a bench grinder or coarse abrasive paper to provide maximum contact with the work surface.
2. Whenever possible, use good quality stoning lubricants (and don't skimp). This will prevent the mold polishing stone from loading, particularly with harder stones.
3. Hold the polishing stone firmly for directional control, but press hard enough to make the stone cut.
4. All polishing stone marks from the previous grit size must be completely removed (crossed out). Change stoning direction by at least 45% with each successive grit.
5. After each grit change, clean the work area thoroughly to remove all larger abrasive grain particles.
6. To avoid contamination, keep each specific grit of stone in a separate stoning lubricant container. This is important and often overlooked.
7. Don't roll sharp edges and parting lines. Use masking tape to prevent stoning over parting lines.
8. Finish stone with a 320 grit only prior to sending mold cavities/cores to be heat treated.
9. When using polishing equipment for stoning (profiler, ultrasonic polisher, etc.), use moderate speed and pressure only. Excessive speed/pressure can cause minute stresses of the metal surface resulting in "ORANGE PEEL".
Diamond Polishing Basics to Get a SPI #1 or #2 finish
1. The first step with diamond polishing is to find an area in the shop that is clean and is away from other machining and polishing operations. Airborne dust and grit can greatly affect the final finish during the diamond polishing process. Make every effort to eliminate these conditions.
2. Make sure all stoning marks are brought to a 600 or 900 grit stone finish on the surface you would like to bring to a diamond finish.
3. Mold surface must be cleaned extremely well! All 600 or 900 grit stone residue must be cleaned from the mold surface.
4. Next use a rotary brush with DIAMAX Grade 25 or 14 (Red or Blue) compound to remove 600 or 900 grit stoning marks. Use a slow rotary speed and light pressure. If heavy pressure is used it can cause a surface condition called "Orange Peel". This can be caused by over-stressing the mold surface with excessive heat created by too much pressure and speed.
5. When all 600 or 900 grit stoning marks are removed, clean the mold surface. Cleaning is a very critical part of this polishing process. Extra care must be used to make sure all previous grade diamond compound is removed. It is recommended to use a very soft tissue to clean the surface. This will help eliminate unwanted scratches during the cleaning process.
6. Next use a medium to hard felt with DIAMAX Grade 14 or 8 (Blue or Green) to remove all brush marks from the previous polishing step.
7. Again, clean the mold surface and be sure all the previous grade diamond compound is removed.
8. Next use a medium/soft felt with DIAMAX Grade 8 or 6 (Green or Orange)
9. Again, clean the mold surface and be sure all the previous grade diamond compound is removed.
10. Next use a soft felt with DIAMAX Grade 3 diamond compound to get the #2 finish.
11. If you need a #1 finish, clean the mold surface and then use DIAMAX Grade 1 (White) diamond compound.
Rib & Slot Polishing Solutions
Mold makers and mold polishers have been faced for years with polishing thin ribs and slots. The pressure for weight reduction and material savings in plastic parts is increasing. In order to achieve this, mold designers are making ribs and slots smaller and more abundant. Removing the EDM scale from these mold features becomes even more challenging.
BORIDE Engineered Abrasives has been working with select polishers from around the world to develop a polishing system that can effectively reduce the time spent in these ribs and slots. Mold makers and polishers need these significant time reductions to remain competitive in today's market. Following are the recommended tools that will allow mold polishers to increase their efficiency and decrease time spent on ribs and slots.
TURBO-LAP LINEAR and TURBO-LAP SWING
- These short stroke profilers are the backbone of this polishing technique.
- Air operated profilers that produce 12,000 to 22,000 strokes per minute.
- Effective and efficient cutting action achieved by using light downward pressure and circular motion during operation.
- Clean, dry 80 psi air is needed to ensure trouble free operation of this tool.
CERAMIC SUPER STONES
- Extremely strong and thin for tight ribs and slots.
- Excellent for EDM removal on the bottom of ribs and slots.
- Ceramic Super Stones are best used for putting the final finish on a rib or slot.
- Ceramic Super Stones are also very effective when used with the Turbo-Lap profilers. Hand polishing with Ceramic Super Stones is also possible in areas not suitable for high speed polishing.
RIB LIGHT AND RIB LIGHT REACH
- High intensity pen lights that are excellent for illuminating those hard to see spots like ribs and slots.
- Allows the mold maker and polisher to see and ensure all EDM scale is removed from the ribs and slots.
- Rib Light Reach offers a long, flexible neck.
- Both pens are available as black pens with white or blue lights
- (3) AAAA batteries included - replacement batteries available.
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