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SAE J1345 Simplified: Specifying Automotive Plastic Parts with Performance Characteristics
SAE J1345 is a recommended practice that provides a specification system for automotive plastic parts based on performance characteristics, not raw material data. By using standard test-based statements, engineers can define the exact requirements needed for each part’s end-use application. The system includes property tables in both the main body and appendix, each with letter-number symbols representing quality levels.
Understanding the Specification System
The system is founded on the principle that plastic parts should be described in terms of specific performance characteristics desired in the molded part. An infinite number of descriptions can be formed using one or more standard statements, each designating a quality level of a property or characteristic.
The first letter in a call-out designates the property table and type of requirement. Additional letters and numbers fully define the characteristic. The material generic type must be identified per SAE J1344, for example:
Example Call-out: SAE J1345 ABS (C20, DF1060, M230, AAC83)
🛠️ Users can specify different combinations of requirements by selecting different performance characteristics.
Property Tables and Design Insights
The property tables are contained in two sections. Tables in the body have been found acceptable and useful for describing finished plastic parts. Tables in the appendix are also useful but have not yet been fully accepted; they require supplier-user agreement on interpretation. As development progresses, these will be moved to the main body. The Z suffix is used for partially defined properties to minimize ambiguity.
| Symbol | Property | Table Source |
|---|---|---|
| C20 | Impact Resistance | Body |
| DF1060 | Deflection Temperature Under Load | Body |
| M230 | Tensile Modulus | Body |
| AAC83 | Flammability | Appendix |
Remember: Not all property tables need to be used for every part. Select only those relevant to your application.
🔍 Design Insight: Focus on the molded part’s end-use performance characteristics, not just the material’s datasheet values. The system allows you to tailor specifications using only the property tables that matter. Always adapt to commercially available materials rather than inventing new property requirements. Parts must be uniform and free from defects like porosity, warp, and contamination.
Common Mistakes and Frequently Asked Questions
⚠️ Common Mistakes:
- Assuming every property table must be used for each part.
- Using the system to invent material properties rather than adapting to the part’s needs.
- Relying solely on resin specifications or manufacturer data sheet values for part requirements.
- Expecting test specimens cut from parts to yield the same results as standard molded specimens.
- Failing to establish appropriate specification limits through testing of actual part specimens.
- Misinterpreting appendix tables as fully accepted without supplier-user agreement.
How do I select which property tables to use?
Tables are to be selected according to the application and need of the part. Not all tables are intended for every part. Focus on the performance characteristics critical to the part’s function and durability.
What is the difference between body and appendix property tables?
Body tables have been fully accepted and are ready for use. Appendix tables are useful but still under development; they require mutual agreement between supplier and user, and will eventually be moved to the main body as more experience is gained.
When should I use the Z suffix in a specification?
The Z suffix is provided for properties that have been partially defined. It is used to avoid ambiguity while the table is being completed. Use it only when necessary and with proper documentation.
How are specification limits determined from parts rather than standard specimens?
Appropriate testing of specimens cut from parts must be conducted to establish specification limits. The user should indicate areas on the part drawing where specimens are to be taken. Values from cut specimens will differ from standard molded specimens and may require alternative functional tests.
For further details, refer to the full SAE J1345 document and the referenced test methods.
