SPI plastic injection mold classifications (originally called "Classifications of Injection Molds for Thermoplastic Materials") have been in place and copyrighted since 1978. They have been updated a few times throughout the years but remain largely the same as the original draft created for the Society of Plastics Industry.
"The original printing was in 1978 and several other revisions followed. The most meaningful change was in the 1990's and added larger molds as we originally addressed molds intended for 450 ton machines or less."
"The idea originated in the mid 1970's and around 1976 Chuck Brewer Jr. gathered some friends in the industry to discuss problems frequently encountered with losing jobs to shops quoting inferior tooling. Most toolmakers, at that time, acknowledged "Class A" molds to be the finest available but there were no written standards to describe exactly what that meant. As an example, I attended an SPI led forum one night and sat int he audience while a panelist proclaimed he could produce Class A aluminum molds."
"At that point, I knew something needed to be done since most buyers had no moldmaking expertise. I met with Chuck Brewer, Jack Kelly and Jim Atchison on numerous occasions as we hammered out what we envisioned a Class A mold to be. It was nearly unanimous that this mold, intended for high production, needed to be of hardened steel and built to exacting standards. We also recognized there was a need for prototype, low and intermediate volume molds so we discussed standards for those as well."
"After taking copious notes and discussing the need for standards over many months, I took the bull by the horns and wrote the initial draft. I sent it to Chuck for editing since he started this entire process. We recognized Class I through Class IV molds and inserts and gave descriptions for the buyers expectations and the moldmakers reference." (Today known as class 101 to 105).
"After completing our work, we assigned the entire effort to SPI for publishing. It was presented at a national moldmakers conference in 1978 and, to our pleasant surprise, immediately embraced by the membership. It was intended as a guideline so buyers could understand what they should expect when ordering a mold and to level the playing field by having the moldmakers quote similar tools. Later revisions changed the molds to Class 101, 102 etc. and larger molds were recognized as class 401 etc.Though copyrighted it is, as you noted, widely used for reference. And that is how the SPI guidelines came to be."
Here is a scan from SPI's origional book, "Classifications of Injection Molds for Thermoplastic Materials".
SPI Mold Standards
While these standards help level the playing field for those seeking to purchase molds and the moldmaking community at large they do not cover design issues such as gating, the balancing of runners, rational behind hot runner systems and many other concerns which could lead to problems. The standards are mostly used as guidelines for the materials to be used (steel types etc.) and the number of cycles a given mold will be under warrantee.
There are many factors that could lead to molds not acheiving the standards including lack of maintnence, mistreatment and improper mold set-up in a molding machine.
At Craftech Corporation we will help guide you through the process of designing parts that are manufactured, building molds that meet the standards you require and educating you on the rational behind them.
Special thanks to Mike Noggle and all of those involved in the creation and implementation of the SPI Mold Standards.
Click here to get your copy of the SPI Mold Standards.
Go to SPI's website to attain the most recent revision of the standard: Society of Plastics Industry
See the Wikipedia description of Injection Mold for some detailed information and historical background.
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