Hot metal gas forming (HMGF) is a method of
die forming in which a
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
tube
Tube or tubes may refer to:
* ''Tube'' (2003 film), a 2003 Korean film
* ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom
* "Tubes" (Peter Dale), performer on the Soccer AM television show
* Tube (band), a ...
is heated to a pliable state, near to but below its
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
, then pressurized internally by a
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
in order to form the tube outward into the shape defined by an enclosing die cavity. The high temperatures allow the metal to elongate, or stretch, to much greater degrees without rupture than are possible in previously utilized
cold
Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
and warm forming methods. In addition, the metal can be formed into finer details and requires less overall forming force than traditional methods.
History and comparison with previous techniques
HMGF is an evolution in the cost effectiveness and applicability of several existing commercial processes:
superplastic forming, hot
blow forming,
[Bill Dykstra (2001). “Hot Metal Gas Forming for Manufacturing Vehicle Structural Components”, MetalForming] and
hydroforming
Hydroforming is a cost-effective way of shaping ductile metals such as aluminium, brass, low alloy steel, and stainless steel into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotiv ...
.
Complex tubes can be made from multiple sheet components formed and welded together, but this adds unnecessary cost and creates quality concerns at the joints. Hydroforming uses liquid under extreme pressures to form metal tubes. It was developed for the plumbing industry and by 1990 achieved production efficiencies suited for high volume autos. Typically hydroforming is done at ambient temperatures, and limits the forming elongation of metals to 8–12% diameter increase for
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
, and 25–40% for
steel. This limits the part shape complexity that can be produced. In addition, the workcenters and tooling can be large and expensive because of the internal fluid pressures required to form ambient tubes. HMGF is able to form tubes with larger shape complexity in only one forming step and generally at a lower internal pressure than in conventional tube hydroforming.
Blow forming started with
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
long ago, and is now a widespread method for forming plastic into hollow structures. Again, the heated material properties provide for many processing advantages. Warm forming has been the subject of extensive research in the past decades. It is defined as forming above ambient but below the recrystallization temperature of an alloy, and using hydroform principles, can be done on tubes. Temperatures are typically limited due to safety concerns surrounding the heated forming fluids. At these temperatures, cycle times may still be relatively long, and elongations still do not approach that of hot forming.
Superplastic forming is often applied in the aerospace industry, but it requires the use of very fine grain metal alloys, deformed up to very large strain values, but at a very low strain rate. HMGF is therefore potentially faster than superplastic forming.
As a natural evolution, the need for HMGF created research starting in the 1990s. Fast cycle times, inexpensive
tooling and machinery resulting from pressures an order of magnitude lower than hydroforming, and extreme forming ratios due to high temperature forming create a compelling business case for high volume low cost manufacturing.
In 1999, development of the HMGF techniques began as an
Advanced Technology Program
The NIST Advanced Technology Program (ATP, or NIST ATP) is a United States government (U.S. Department of Commerce, National Institute of Standards and Technology) program designed to stimulate early-stage advanced technology development that woul ...
(ATP) project funded by the
US National Institute of Standards and Technology
The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...
(NIST). This project completed in 1993 and research showed up to 150% expansion ratios for aluminum and 50% with steel were possible, with further expansion capabilities by use of end feeding of material to minimize wall thinning.
In order to keep pace with the US research, a European project was funded by the
Research Fund for Coal and Steel (RFCS). Starting in July 2004, with a duration of 3 years, this project further investigated the HMGF process. By 2007, the consortium of European research and commercial entities proved concepts of simpler heating and die construction, and while focusing on the more demanding steel alloys, illustrated free deformation of 140% by use of end feeding to control wall thinning and delay
rupture
Rupture may refer to:
General
* Rupture (engineering), a failure of tough ductile materials loaded in tension
Anatomy and medicine
* Abdominal hernia, formerly referred to as "a rupture"
* Achilles tendon rupture
* Rupture of membranes, a "wate ...
.
The method used in these experiments is patented under .
Also in Europe, parallel research yielded an innovative approach to the concept. By 2006, the HEATform method of hot metal gas forming showed evidence of unique metal shapes that had "historically only been possible in the domain of
glass blowing
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a blowpipe (or blow tube). A person who blows glass is called a ''glassblower'', ''glassmith'', or ''gaffer''. A '' lampworke ...
and blow molded parts" with aluminum forming in excess of 270% expansion ratio at a production intended cycle time of 20 seconds. Citing that hardening and subsequent breakage will limit forming of the aluminum alloy below , the best flow behavior was observed at . This is significantly higher than the capabilities of warm liquid or warm gas pressure forming. The HEATform techniques of end feeding control achieved uniform wall thickness up to 300% strain values.
[Harry Singh (2006) “HEATforming: A new Freedom in Forming Tubular Structures” (conference report); 4th Annual North American – Hydroforming Conference & Exhibition – Sept. 2006]
While significant research into material compatibility and predictive analysis techniques is ongoing, hot metal gas forming has been commercialized by at least one company who is providing hot expansion coupled with material end feeding.
Applications
Typical applications are in the
automotive and
aerospace industries where the precursor technology of hydroforming is well known. Other applications include
sports equipment
Sports equipment, sporting equipment, also called sporting goods, are the tools, materials, apparel, and gear used to compete in a sport and varies depending on the sport. The equipment ranges from balls, nets, and protective gear like helmets. ...
and
furniture. The multi-material capability are used in decorative workpieces and
plumbing fixture
A plumbing fixture is an exchangeable device which can be connected to a plumbing system to deliver and drain water.
Common fixtures Supply
The most common plumbing fixtures are:
*Bathtubs
*Bidets
* Channel drains
* Drinking fountains
* Hose b ...
s.
Materials
The HMGF process is compatible with almost any metal. The most significant benefit of HMGF is that cold form resistant materials become viable for complex forming. Often, alloys are enhanced with expensive materials to enable cold forming and increase
machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...
, however with HMFG a less expensive alloy can be used, which reduces piece prices. One example is the use of
ferritic stainless steel
Ferritic stainless steel forms one of the five stainless steel families, the other four being austenitic, martensitic, duplex stainless steels, and '' precipitation hardened''. For example, many of AISI 400-series of stainless steels are ferritic ...
s, like the 1.4512 alloy for exhaust components. Typically, the more expensive austenitic
stainless is chosen, like the 1.4301 alloy, for parts requiring complex forming due to its 40% advantage in ambient formability (38.5% vs. 27.4% typical A%).
Hardenable metal alloys (e.g. boron steels) can be used in HMGF. In this case the die can be used not only as a shaping tool, but also as a tempering tool, so that the final hardness of the formed tube after forming and cooling is increased. The process is often called "press hardening" in this case.
Notes
External links
A process video
{{DEFAULTSORT:Hot Metal Gas Forming
Metal forming