Cincinnati Milacron of Cincinnati,
Ohio is an acknowledged world leader in advanced manufacturing
technologies for the metalworking and plastics processing industries,
with expertise in a variety of fields, including machinery, computer
controls, software, cells and systems, metrology, inspection and
robotics. The company recently redesigned its entire line of injection
molding machines utilizing Ductile Iron. The resulting machines were not
only simpler in design, with fewer parts, but also highest quality,
lower in cost and capable of superior performance.
|
Mechanical
Properties |
|
AISI
1020
|
Grade
60-45-15
|
| Tensile
Strength |
55,000
psi |
60,000
psi |
| Yield
Strength |
30,000
psi |
45,000
psi |
| Elongation |
25% |
15% |
| Reduction
of Area |
50% |
17% |
| Modules of
Area |
30
x 10 psi |
23
x 10 |
|
Table 1 |
The company's previous line of injection
molding machines had platens made from AISI 1020 plate steel. These
steel plates ranged in size from 5 inches thick by approximately 40
inches wide and 40 inches long for smaller machines to over 20 inches
thick by 100 inches wide and 100 inches long for large 3,000-ton
machines. Because the plates required a large amount of machining time
for cleanup and lost a large amount of material due to machining chips,
it was decided that Ductile Iron castings should be used for the
platens, and several other parts, in the new design. This decision was
made for several reasons; first, the properties of Ductile Iron are
similar to the properties of the AISI 1020 steel that had previously
been used; second the use of castings would allow the company to
consolidate several parts into one; and third, the use of Ductile Iron
would substantially reduce machining costs.
 |
|
Above and
Below: Cincinnati Milacron's VISTA VL1000 injection
molding
machine is used for making large, plastic parts. |
 |
Most of the parts for which the design
team at Cincinnati Milacron was considering Ductile Iron castings were
subject to high cycle fatigue. Therefore, the mechanical properties of
the Ductile Iron to be used had to be comparable to the properties of
the plate steel. It was decided that grade 60-45-15 ferritic Ductile
Iron was a suitable match for these critical parts. Table 1 below lists
the typical mechanical properties of the AISI 1020 steel plate and the
properties of the gide 60-45-15 Ductile Iron that the company specified
as a replacement for the majority of the cast parts in the new design,
In addition to the typical mechanical properties listed, Ductile Iron
has fatigue and fracture toughness properties that allow it to be used
in fatigue applications. back
to top
The design team for the castings included
people from several different groups, including design engineers,
manufacturing engineers, purchasing personnel and representatives from
Cast-Fab Technologies, a foundry. Working together from the start of the
project, the team designed the parts with a collective eye not only
toward surpassing strength and fatigue requirements, but also toward
improving both castability and machinablity.
One of the goals for the redesign of
these complicated machines was a simplification of the existing design
through a consolidation of parts. Toward this end, several parts on the
moving platen of the VLl1000 (a hydraulic machine with 1,000 tons of
clamping force) were eliminated by casting the stuffing box as an
integral part and by casting on several support brackets that otherwise
would have been machined and bolted to the platen. Other instances of
parts consolidation include the die height and moving platens on the
company's Vista toggle line of machines. In this instance the steeples
were cast as integral parts of the platens, which not only greatly
reduced the number of parts but also reduced the amount of machining
required to finish them. (See Photographs below.)
 |
| These platens,
made of ANSI 1020 steel plate, were used in Cincinnati
Milacron's previous line of injection molding machines. |
 |
| Cincinnati
Milacron's newly designed line of injection molding macines uses
Ductile Iron castings for several parts, including platens. |
Finite Element Analysis (FEA) was used in
the design of the critically stressed parts to determine the stress
levels in all areas of the casting. FEA was completed before any
patterns were made. Once stress levels were determined, the designs were
altered to add material in highly stressed areas to reduce stress levels
and remove material in areas of low stress.
 |
| Critically
stressed parts were designed using finite elements analysis to
determine stress levels in all areas of the casting. |
This design technique gave the design
engineers the ability to design highly reliable parts with stress levels
well within the fatigue limit values and to remove any material that
does not contribute to the strength of the casting, thereby reducing
weight. An example of an FEA is shown at right. Each of the colored
areas represents a stress level. FEA can also be used to determine part
deflection in various areas of the casting when rigidity is an important
factor. back to top
Foundry that input in the early stages of
the redesign project proved to be very important because it averted
several potential casting problems. By showing the foundry high stressed
areas of the casting, they were able to design the pattern and gating
and risering systems to assure sound metal in these areas. They were
also able to suggest design changes that improved castability and
prevented designed-in casting problems. Machining stock was adjusted to
the proper thickness to avoid having casting defects, dross, slag or
sand on machined surfaces, highly stressed areas or areas that have
hydraulic sealing surfaces. Casting dimensional tolerances were
determined to avoid interference between castings at assembly and assure
that core tolerances and machining stock could be adjusted so that core
holes would clean up without excessive machining.
Manufacturing engineering was also
involved at this early stage, designing castings both for ease of
machining and fixturing and for reduced tooling costs. The use of
Ductile Iron reduced machine costs since it machines more like gray iron
than steel. It also permitted an increase in rough machining feeds and
speeds, thus reducing machine time as compared to steel. In addition,
tool life increased due to the fact that the graphite in Ductile Iron
reduces wear. And deburring was also reduced because the size of the
burr was reduced or eliminated.
The design advantages described above
were only realized thanks to the superior capabilities of Ductile Iron.
With mechanical properties similar to steel and castability and
machinability similar to gray iron, Ductile Iron enabled Cincinnati
Milacron to optimize the design of its new line of injection molding
machines, making them more reliable at lower cost.
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