Workshops
2002

Workshop
Archive

 

 

 

 

 

 

 

Workshop #1, Investment Cast Ti-6Al-4V Alloy


Wednesday Oct. 19 & Thursday Oct. 21, 2004

Mr. Randall Diehm
Metallurgist
Howmet Castings, an Alcoa business
Ti-Cast
1600 South Warner Street
Whitehall, Michigan 49461

RDiehm@howmet.com

 

 

 

Introduction

   Titanium alloys are found in many applications because of their excellent corrosion resistance and strength to weight ratio. They have other attributes as well and are often found in the form of cast parts. Significant information on titanium alloys and Ti - 6Al - 4V alloys can be found in the text "Structure and Properties of Engineering Alloys" Second Edition, Chapter 10, by William F. Smith, McGraw Hill, 1993 and in Volume 3, Ninth edition of the Metals Handbook.

   The investment casting which will be examined in Workshop # 1 is a bearing support for a Honeywell engine. This casting will be kept in the casting design room for your inspection and use at your convenience. The casting is not a saleable part and can be tested in any way that you would like. Other information, specifications, heat treatments, chemical analysis of heats, etc. accompany the casting in room 216, the casting design room. Please leave this material in the casting design room.

 

 

 

Bearing Support Housing

Investment Cast Titanium - 6Al - 4V

 

Casting and Pattern

Microstructure

 

 

 

 

The casting is produced by the investment process, including the following:

  1. Wax pattern assembled onto a mold using a bottom feed or flush type gating.
  2. Risers are placed at select locations to help feed shrink.
  3. Wax pattern is then invested in a ceramic slurry.
  4. Invested mold is then dried and dewaxed in a steam autoclave.
  5. Mold is fired to sinter the shell.
  6. Mold preheated to 700oF.
  7. Alloy poured into investment in vacuum.
  8. After solidification the casting is air cooled to room temperature.
  9. Investment removed by high pressure water blast.
  10. Part is cut off the gating, remaining shell removed by abrasive blast and caustic shell removal techniques.
  11. Part is HIPped for shrinkage closure.
  12. Alpha case removed by acid cleaning.
  13. Welding to cap 2 passages and repair cosmetic flaws.
  14. Annealed at 1550oF.

 

 

 

 

Preparation for Workshop

   In preparation for the workshop in the week of September 30, each student (group assignments as per the attached table) should do the following:


Spend some time looking at the casting and accompanying material!

  1. Speculate where the gates and the riser(s) are located on the casting. Is this consistent with good gating and heat transfer principles?
  2. Can you detect evidence of machining?
  3. What does the casting weigh and what is the volume of metal?
  4. If possible, familiarize yourself with the microstructures. You might want to check the ASM handbook on metallographic structures. Is the dendritic nature of the structures obvious? Check out the pseudo-binary Al - 6Al - 4V phase diagram below. Can you observe any porosity? Any other obvious defects?

 

 

 

Reporting on Workshop

  1. Students construct a group report including details on the casting (size, shape, risering and gating requirements, microstructural and mechanical property requirements, etc.), and the function of the casting (i.e. What job must this casting do?) Students should also include in their report, discussion of :
    1. Why the investment casting process was chosen (why not another casting process, or some other means of fabrication (weldments, powder processing etc.?) What advantages does investment casting have over other casting processes?
    2. What HIPping is and what are its benefits?
    3. Why this specific material was chosen (why not another, perhaps less expensive, material?) What is the heat treatment and what is the purpose of the heat treament?
    4. What this casting costs to produce? (not what it is sold for)
    5. What significant environmental problems are involved, if any, in production?
    6. Casting yield, recyclability, etc.
  2. The report should be constructed in rough form before the end of the workshop session.

The students will be required to hand in a good copy (constructed on a suitable computer with accompanying graphics if necessary) within six days of the workshop, maximum three pages.

Groups (and Captains) assigned to this casting are given below. Captains are responsible for whipping the group into shape and are the contact persons. Each workshop will have new Captains/Co-captains so that each person will have the opportunity to do this job.

 

Tues AM

Tues PM

Thurs AM

Thurs PM

Group 1

Group 3

Group 5

Group 7

 

(Captain)

 

(Captain)

 

(Captain)

 

(Captain)

 

(Co-Captain)

 

(Co-Captain)

 

(Co-Captain)

 

(Co-Captain)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Group 2

Group 4

Group 6

-

 

(Captain)

 

(Captain)

 

(Captain)

 

-

 

(Co-Captain)

 

(Co-Captain)

 

(Co-Captain)

 

-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Return

Pseudo-binary Ti-6Al-4V Diagram

 

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