Dimensional Variations

Section 1 List

Description

Defect Type

Shape, Size

Appearance

Very difficult to detect without measurement tools

Size

Varies

Typical Location

Varies

Similar to

Method for defect determination

Visual using inspection measurement tools

Mechanism

Inconsistent and repeatable variables within process

Corrections

Area	Possible Cause	Potential Correction
Equipment	Out of calibration	See Best Practices Section
Equipment	Injection pressure variation	Maintain consistent injection pressure Note: Low pressure will reduce dimensions. High pressure will increase dimensions
Equipment	Injection time variation	Maintain consistent cycle time. Note: Short cycle will reduce dimensions. Long cycle will increase dimensions.
Equipment	Wax temperature variation	Maintain uniform wax temperature Note: Low temperature will increase dimensions. High temperature will reduce dimensions. Check wax temperature calibration.
Equipment	Die temperature variation	Provide proper cooling / heating to maintain consistent die temperature. Consult with equipment manufacturer if necessary.
Equipment	High nozzle temperature	Decrease nozzle temperature. Note: High nozzle temperature can lead to dimensional variation on small parts due to shot size. Consult with equipment manufacturer.
Equipment	Clamp pressure variation	Maintain sufficient clamp pressure to prevent opening of die.
Equipment	Uneven clamping of die	Use proper injection press or balancing blocks.
Pattern Die	Runner size too small or improperly designed	Ensure proper size and design of runner system to adequately feed pattern before solidifying.
Pattern Die	Die cleanliness	Clean die as needed and perform routine die maintenance.
Pattern Die	Die mismatch	Check guide pins for wear or proper alignment. Add additional guide pins
Pattern Die	Die manufacturing errors	Check die dimensions.
Wax	Incorrect shrink factor	Ensure that wax properties are within specifications. For filled waxes ensure proper melting and agitation to maintain uniform filler dispersion.
Wax	Contaminated wax	Check condition of the wax. Replace wax as necessary.
Wax	Filler separation	Use proper conditioning parameters including appropriate agitation in melting tank and in holding tank. Consult wax supplier for proper melting and conditioning procedures.
Other	Ambient temperature variation	Maintain consistent wax room temperature.
Other	Distortion of wax patterns	See “Distortion.”
Other	Missing chills	Ensure that required chills were used.