Classes of Steel Molds for Custom Plastic Molding

Custom plastic molding requires custom designed and built steel molds to produce the part to design specifications, functionality and volume. It’s important to choose the right type of steel for your mold to manufacture quality parts. As any good molder knows, the key to quality custom injection molded parts begins with a quality tool.

Most custom injection molders run production with Class 101 tools, unless working with a prototype tool for prototype parts only, in which case, a Class 104 tool may be used. The SPI (Society of Plastics Industry) Mold Classifications were developed by the Society of Plastic Engineers (SPE) to standardize mold type definitions based on mold material, features and volume. Injection molds are typically constructed of hardened steel, unless referring to a prototype mold constructed of aluminum, volume is always defined as cycles in plastic injection molding.

Custom Plastic Molding Tool Classifications Range from Class 101 to 105

The SPI Mold Classifications dictate differences in tool design, materials, construction and components and are intended to be used as a guideline. Tool classes from 101 to 105 simplify the type of injection mold required for thermoplastic molding based on production needs. SPI Mold Classifications refer to injection molds up to 400 tons.

Class 101: Extremely High Volume

Class 101 tools are used for extremely high volume plastic molding, with the following considerations:

  • Cycles exceeding one million
  • Requires a detailed mold design
  • Tool structure components should have a minimum hardness of 28 Rc
  • Cavity and cores must be hardened to a minimum of 48 Rc, with other components such as slides, gibs, wedge blocks, heel blocks, sub-inserts, lifters etc. in hardened steel
  • Ejection should be guided
  • Slides must have wear plates
  • Parting line locks should be on all tools
  • Temperature control provisions must be in all cavities, cores and slide cores when possible
  • Plates and inserts containing cooling channels should be of a corrosive resistant material

Class 102: High Volume

Class 102 tools are required for high volume production, less than one million cycles:

  • Medium to high volume not to exceed one million cycles
  • Requires a detailed tool design
  • Mold structure and components should have a minimum hardness of 28 Rc
  • Cores and cavities should have a minimum hardness of 48 Rc with all other functional components heat treated
  • Recommended parting line locks
  • Temperature core provisions with corrosive resistant control channels

Class 103: Medium Volume

Class 103 tools are constructed for medium volume production:

  • Not to exceed 500,000 cycles
  • Recommended detailed tool design
  • Cores and cavities should be minimum 28 Rc hardened steel

Class 104: Low Volume

Class 104 tools are constructed for low volume jobs only, usually as a prototype tool. 

  • Class 104 tools are not to exceed 100,000 cycles
  • Can be constructed of mild steel or aluminum
  • Cavities may be in aluminum, metal or other mild steel agreed upon

Class 105: Prototype Only

Class 105 tools are used only for prototyping and should never be constructed to support any amount of production. Class 105 tools are designed to not exceed 500 cycles, with options for all components.

Class 101, 102 and 103 tools should be designed for fully automatic production with automated ejection. All classes of tools with the exception of Class 105 should be designed with adequate cooling for temperature control. All tools should also contain transport eyebolt holes on the topside. As in any custom plastic molding project, the customer must approve all tool design prior to tool build and manufacturing.

QT Manufacturing Provides Mold Making for Custom Plastic Molding

QT Manufacturing is an experienced custom plastic molding company providing skilled mold making from journeymen mold makers. We build quality tools to support quality injection molded production that meet all your specifications and critical tolerances. QT Manufacturing takes the jobs other molders shy away from, producing tight tolerance products to meet challenging geometric specifications. 

When it comes to tooling, price should never be a deciding factor as cheap steel will undoubtedly cost more in the long run. We utilize only the highest grade of steel in our Class 101 high volume production molds and offer suggestions when possible for any cost saving activities. We help customers with prototype mold builds in Class 104 molds when possible. You can rely on QT Manufacturing to design and construct quality molds to meet your most demanding production requirements, with quality product delivered on time.

QT Manufacturing is a valued supplier to many industries including aerospace, telecom and fiber optics, defense, medical and many other industries. We follow a strict quality policy as part of our ISO9001:2015 and AS9100 rev D registrations, committed to continual improvement. Contact us with any questions and for quality tools to support your custom plastic molding requirements.