NADCA Die Materials Committee

Rough Machining of Die Casting Dies:

Allowing for Distortion and Avoiding Cracking During Heat Treatment

Stephen P. MidsonThe Midson Group, Inc.

NADCA Die Materials Committee

Rough Machining Booklet

• New booklet from NADCA

• Provide guidelines to die builder, heat treaters & die casters

• Avoiding problems during heat treatment of dies

NADCA Die Materials Committee

Scope of Booklet

• Leaving appropriate amounts of machining stock on die

• Reducing stress that can lead to gross cracking

• Notifying heat treater of any welding performed on die

NADCA Die Materials Committee

Acknowledgements

• Need for booklet was identified by:» Mark Baleja» Joe Price» Gene Hainault

• Content is based on a presentation developed by: » Bohler Uddeholm Corp» Paulo Products Company

NADCA Die Materials Committee

Outline of Booklet

• Two main sections

1. Briefly review heat treatment processes for die casting dies

2. Describe sources of stresses & warping

» Identifying factors that must be considered during rough machining

NADCA Die Materials Committee

First Section

• Describes importance of maximizing quench rate during heat treatment

• Summarizes data from recent paper from Schwam, Wallace & Birceanu

NADCA Die Materials Committee

First Section

• Also describes problems that can occur if quenching rate is too fast

• Stresses originating from:

» Expansion & contraction of steel

» Expansion during phase transformation from austenite to martensite

NADCA Die Materials Committee

First Section

• Emphasizes the important of controlling the quenching rate

• NADCA recommends 50oF/min for Premium Grade H-13

NADCA Die Materials Committee

Second Section

• Outlines factors that die builders and heat treaters must consider during rough machining

» To ensure stresses developed during quenching do not damage die

» To ensure appropriate machining stock is left on die

NADCA Die Materials Committee

Machining Stock

• Discuss

» Ballooning

» Die corners pulling up

» Bowing of die edges

NADCA Die Materials Committee

Minimizing Stresses During Quenching

• Use generous radii

• Use generous shoulders between transitions in cross sections

• Avoid thin walls & thin webs

• Remove white layer after EDM

NADCA Die Materials Committee

Recommendations

• Specific recommendations NOT made in report

» Minimum machining stock

» Minimum radii

• HIGHLY RECOMMENDED that machine shops communicate closely with heat treaters

» Before the die is machined