C. Parting Line Treatment
Parting Line Protection
Different types of parts require different methods of parting line treatment. We can apply texture right up to your parting line or can leave a blank of .005" to .750" at the parting line if that suits your requirements. We can leave an undercut if required (and some PVC molds do require that), or leave a blank without an undercut if that is preferred. Either way, we fully understand the importance of the parting line to the quality of the finished part, and we stand ready to discuss it with you and to offer advice if you are uncertain as to how best to address this concern on your tool. In many cases, the pattern chosen will dictate the best way to protect the parting line.
More and more tooling is being built using "Flat Seal-offs". Flat Seal-offs are situations where the stock is on the core side of the tool, and there is no way to see where the part ends on the cavity side where the texture is going to be applied, since the steel on the cavity is flat. Since texture removes metal, this can pose a problem if the seal-offs cannot be accurately located on the cavity in order to protect them during the texturing process. It is imperative that you, the tool maker, locate these areas on the steel for the texture source. The most accurate way to do this is by scribing them in with a Cordax machine or some other digital gauge that scribes exactly where the part actually ends on the steel There is usually a temptation to simply use a part to layout the flat seal-off. We do not recommend that since the part is a different size from the steel due to shrinkage after molding. Use of a part means that the line is not accurate to begin with, and the likelihood of either texture overgrain or undergrain is almost assured. An overgrain can cause flash; while an undergrain leaves untextured areas that would require hand repairs to add the texture that is missing. In the case of some very fine patterns - up to .0015" in depth and metal removal - overgraining will not cause flash, but regardless, it is the toolmaker¡¯s responsibility to supply us with an accurate locating scribe that can be followed for the purposes of protecting the seal-off against etchant damage or blanks.
Do not trust witness lines from the core side bumping into the cavity, as these can be misleading if subtle changes have been made during spotting / matching of the tool before texturing. Also be sure that when you scribe the seal-off, that you apply only one.