Virtual Prototyping of Induction

Heat Treating

Robert Goldstein

www.fluxtrol.com

Overview

• Advantages of Induction Heat Treating

• What is Virtual Prototyping?

• Steps in Virtual Prototyping of Induction Heat Treatment

• Case Story – Wheel Hub Hardening

– Solve a Lifetime Issue on Production Machine

– Example of How Virtual Prototyping Could Have Been Used to Avoid Problem

• Conclusions

Advantages of Induction Heat Treating

• Favorable for industrial environment (in-line

heating, no pollution, “push button” performance,

no toxic waste disposal)

• Energy savings due to selectivity and high

efficiency

• Good control and repeatability

• Better metallurgical results due to fast and clean

heating

• More predictable energy costs

• Safer work environment

Advantages Ctd.

• Less and more predictable dimensional

movement

• Short heating cycles and high production rates

• Minimal surface oxidation and decarburization

• Some processes may not be accomplished other

than by induction

• Smaller machine footprint

• Typically, much cleaner environment

• More Favorable for Computer Modeling

What is Virtual Prototyping?

• Virtual

Prototyping is

the use of

computer

models to

develop and test

a process or

component

without having to

physically build

or run it

A

B

C

H

R

C

Position A Original Design

Optimized Design

Case depth at HRC 40

10 mm 10 mm

Total case depth

10.5 mm 10.7 mm

Scan speed 9.5

mm/sec 10.7

mm/sec

Position B Original Design

Optimized Design

Case depth at HRC 40

13.5 mm 11 mm

Total case depth

15 mm 11.75 mm

Dwell time 10 sec 8 sec

Position C Original Design

Optimized Design

Case depth at HRC 40

4.5 mm 6.5 mm

Total case depth

5.25 mm 7.5 mm

Dwell time 10 sec 8 sec

Both cases: 170 kW, 1 kHz

Advantages of Virtual Prototyping • Parts are not required to run tests

– Models can be exchanged between heat treating

process and parts developers

– Simulation does not take machine time

• Fewer coil modifications

• Fewer trials required with a given coil

• Narrower development time window

• Reduced time to adapt to part changes

• Ability to predict the process and product

reliability and variability

• Leaves an excellent record for “out of control”

condition in conjunction with PPAP

Steps in Virtual Prototyping • Preliminary analysis

of the specifications

and available

equipment.

• Preliminary process

design using

computer simulation

• Induction coil and

process design using

computer simulation

Steps ctd. • Coil and/or machine

engineering using

CAD

• Coil and machine

manufacturing

• Experimental tests

• Final modification if

required

• Industrial

implementation

Case Story – Wheel Hub Hardening

• Short coil life – (8,000

– 13,000 pieces)

resulting in:

– Machine downtime

– Unacceptable

personnel time due to

extended set-up

– Scrap parts

Problem

Typical process of induction heating of

wheel hubs

Note – Tooling Costs Not a Problem Due to

Manufacturer Warranty

Virtual Prototyping Selected

• Traditional means were not able to find a

solution

• Due to unplanned downtime, production

was always behind and tests were difficult

to schedule

• Besides hardening, other stations were

working adequately

• Production line was already existing, so

not all steps are required

Analysis of Problem and Equipment

• Copper Cracking Under

Laminations due to

Overheating

• Lamination Degradation

• Already Had Very High

Water Pressure and Flow

Rate

• Existing machine – 150 kW,

15 kHz Hardening

Induction Coil and Process Design • 2D EM + Thermal FEA to determine coil

required to produce required heat pattern

in specified time with current machine

• 2D EM + Thermal FEA to ensure all coil

components are kept cool enough to

survive for a sufficient period of time

(>50,000 pieces)

• Update of coil design as required to find

best combination of heat pattern and coil

copper temperatures

Model of Part

Temperature & Hardness

Predicted hardness pattern Temperature distribution in part with

new coil design

Flux 2D program

Model of Inductor Temperature

Color Shade ResultsQuantity : Temperature Deg. Celsius Time (s.) : 2.5 Phase (Deg): 0Scale / Color33.00854 / 36.8143436.81434 / 40.6201440.62014 / 44.4259444.42594 / 48.2317448.23174 / 52.0375352.03753 / 55.8433355.84333 / 59.6491359.64913 / 63.4549363.45493 / 67.2607367.26073 / 71.0665171.06651 / 74.8723174.87231 / 78.6781278.67812 / 82.4839282.48392 / 86.289786.2897 / 90.095590.0955 / 93.90131

Two cooling paths for

better heat extraction

from over-heated

copper regions

Heat transfer coefficient

applied, calculated from

water flow rate

Results: Max copper

temperature <100°C

CAD Design of Inductor

•Inductor needed to

reproduce predicted

heat treat results

•Contacts needed to

mount to machine

•Inductor had to fit

through primary quench

ring

•Inductor needed to be

compatible with material

handling system

Heating Tests of Inductor

•Hardness pattern

agreed well with

simulation results

•The hardness and

case depth were

verified to be within

specifications

•3rd Test Part

Shown

Longevity Testing of Inductor

Coil life and part

production

increased to

>170,000 hits

without coil

copper failure or

concentrator

degradation.

New induction coil after 170,000 heating cycles

Virtual Prototyping for Machine Design

• In this case, this problem could have been

avoided if Virtual Prototyping were used

before the machine was ever built

• Also, there was significant opportunity to

either increase productivity, or reduce the

number of stations on the machine to

reduce cost

Current Machine Layout • 300 parts per hour production (12 s / station)

– 2 Shifts of Production to Meet Demand

• 4 Stations

– Harden & Pre-Quench

– Quench Completion

– Temper

– Final Cool

• Heat Treat Machine In-Line with Final

Machining

Where’s the Bottleneck

Induction Heat Treat

• Can we reduce cycle time

with 4 stations?

– If yes, how much?

– If no

• What prevents us from it

• how many more do we

need

Machining Operation

• Can we reduce the

number of stations to

reduce machine cost?

Induction Heat Treating

Hardening

• Time to Load (1 s)

• Time to Lift & Rotate (1 s)

• Time to Heat (2.5 s)

• Time to Drop (0.5 s)

• Time to Quench (?)

Tempering

• Time to Load (1 s)

• Time to Lift & Rotate (1 s)

• Time to Heat (?)

• Time to Drop (0.5 s)

• Final Cool (?)

We Need to Fill in the Question Marks

Time to Quench after Hardening

After 4 s, Sufficient Heat Has Been Removed to

Complete Martensite Transformation

Time to Temper

After 2.5 s, Entire Hardened Area Has Been

Tempered to Within Specification

Two Potential Machines 600 parts/min – 4 station

• Station 1 - Harden

– Transfer (1 s)

– Lift & Rotate (4 s)

– Heat (2.5 s)

– Drop (0.5 s)

– Quench (4 s)

• Station 2 - Temper

– Transfer(1 s)

– Lift & Rotate (1 s)

– Heat (2.5 s)

– Drop (0.5 s)

– Final Cool (7 s)

300 parts/min – 2 station • Station 1 – Harden Heat

– Load (1 s)

– Lift & Rotate (2.5 s)

– Heat (2.5 s)

– Drop (0.5 s)

• Station 2 - Quench

– Transfer(1 s)

– Quench (5 s)

• Station 1 – Temper Heat

– Load (1 s)

– Lift & Rotate (1.5 s)

– Heat (3 s)

– Drop (0.5 s)

• Station 2 - Quench

– Transfer(1 s)

– Quench (5 s)

Eliminate 2 Stations or

1 Shift!

Conclusion • Virtual Prototyping Has Several

Advantages Compared to Other Development Methods

• Using Virtual Prototyping, Lifetime of a Production Inductor Was Increased More than 10 Times

• If Virtual Prototyping Were Used Up Front, the Production Rate Could Have Been Doubled or the Number of Heat Treating Stations Cut in Half