ASTM D955: Thermoplastic Mold Shrinkage Testing Services
ASTM D955 is a standard test method of measuring shrinkage from mold dimensions of thermoplastics & thermosetting polymers and plastics. Mold shrinkage is the contraction of the polymer as it cools after the molding process.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
What Is ASTM D955 Thermoplastic Mold Shrinkage?
ASTM D955 is a standard test method for determining mold shrinkage, which is the contraction that a molded plastic part experiences relative to its mold cavity under a set of molding conditions.
This test is vital for understanding the behaviour that occurs as a thermoplastic cools and solidifies during a compression or injection molding process. The test results for mold shrinkage allow for the tailoring of mold designs and processing conditions to ensure that parts are manufactured with exact dimensions. The test is run on samples at both ends and at the middle of a processing range because mold shrinkage can vary with molding conditions.
Applications and Benefits of ASTM D955 Thermoplastic Mold Shrinkage Testing
Scope
ASTM D955 includes thermoplastic materials and test pieces made by injection molding and compression molding. ASTM D955 defines how much molded plastics shrink in size compared to the mold cavity, under controlled processing conditions, to see how the material responds to cooling and solidification. ISO standards for this test are ISO 294-4 for thermoplastics and ISO 2577 for thermosetting materials.
Applications
- Mold design optimization
- Injection molding process control
- Compression molding process validation
- Dimensional stability evaluation
- Material comparison and selection
- Quality control in plastic manufacturing
- Tooling adjustment and calibration
- Research and development of polymer processing
Benefits
- Ensures accurate final part dimensions
- Helps compensate for material shrinkage
- Supports mold cavity design corrections
- Improves dimensional consistency
- Enhances manufacturing repeatability
- Provides standardized shrinkage values
- Assists in material comparison
Our ASTM D955 Testing Procedure
Mold Measurement and Specimen Molding
Mold cavity dimensions are measured, and specimens are molded under specified conditions.
1Cooling
The molded specimens are allowed to cool for a defined period before further evaluation.
2Dimensional Measurement
After 48 hours, the stabilized dimensions of the specimens are measured.
3Shrinkage Calculation
Dimensional shrinkage is calculated by comparing the mold cavity dimensions with the final specimen dimensions.
4ASTM D955 Test Parameters and Requirements
| Parameter | Details |
|---|---|
| Applicable Materials | Thermoplastics |
| Specimen Geometries | Plaque: 5 × 5 × 0.125 in (128 × 128 × 3.2 mm) Disk: 4 × 0.125 in (114 × 3.2 mm) End-gated flame bar: 5 × 0.5 × 0.125 in (128 × 12.7 × 3.2 mm) |
| Measurement Timing | 48 hours after molding |
| Output Units | Inches per inch, percent (%), or mm per mm |
- Injection or compression molding machine
- Standardized mold cavities
- Precision calipers or micrometers
- 3-D measuring device
- Temperature and process control equipment
- Data analysis software
Equipment and Instrumentation Used for ASTM D955 Testing
What You Receive: Test Report, Data, and Certification
- Mold shrinkage values (in/in, %, or mm/mm)
- Dimensional comparison report
- Process parameter documentation
- Material shrinkage evaluation
ASTM D955 Thermoplastic Mold Shrinkage FAQs
ASTM D955 is standard test method for determining linear shrinkage of molded thermoplastic materials by comparing mold cavity dimensions to the final molded specimen dimensions.
Shrinkage affects dimensional accuracy, part fit, and tooling design. Understanding shrinkage helps manufacturers compensate in mold design to achieve desired final product dimensions.
The standard defines a number of specimen geometries, depending on the material and the desired use: Type A: 12.7 X 127 mm bar. Type B:100 mm diameter disk. Type D2: 60 x 60 mm square plaque.
Material type, filler content, processing temperature, cooling rate, mold temperature, and part geometry significantly influence shrinkage results.
The test measures mold shrinkage, expressed as a percentage of the original mold dimension, indicating dimensional change after cooling and solidification.
Why Choose Infinita Lab for Thermoplastic Mold Shrinkage Testing
At the core of this breadth is our network of 2,000+ accredited laboratories across the USA, offering access to over 10,000 testing methods and analytical services. From advanced materials characterization (SEM, TEM, RBS, XPS) to mechanical, chemical, environmental, biological, and standardized ASTM/ISO-compliant testing, we deliver unmatched flexibility, specialization, and scale. You are never limited by geography, facility, or methodology — Infinita Lab connects you to the right expertise and testing solution, every time.
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