Business: Industrial
Getting Ideas for Energy Management Opportunities
2.1.3 Design influences
Ideally, the design process should lead to optimized mould design, allowing
production of good quality casting, fit for use, in the shortest time possible,
with a high yield ratio and at the lowest cost. Some of the features of good
design, which can improve yield, are described below. Design includes more
than the casting. It must consider also the technology employed in making the
casting. In such cases, experiences and good practices described in other chapters
may be applied.
The traditional reliance on foundry experience and a trial-and-error
approach makes development of new casting designs expensive and slow. Trying
to solve
unexpected casting faults is a hit-and-miss affair and takes time and effort.
The majority of casting defects are caused by the use of inadequately or incorrectly
placed feeders and runners. Rapid prototyping technology uses
computer simulation and X-ray videography to optimize their placement.
reduces lead times in supplying sample castings, reduces mould-making
and modification costs, reduces scrap due to shrinkage porosity and,
by reducing customer rejects, improves customer confidence.
Computer
simulation
The use of computer simulation (e.g., by such powerful software programs as
Magmasoft®, Finite Element Solidification Analysis EKK®,
CastView®,
Pro/Engineer®, Flow-3D®, Unigraphics®,
SolidEdge®) substantially
speeds up casting design development and has a number of other benefits:
- Produces
a three-dimensional, solid geometry model of the casting, which includes
the proposed arrangements of feeders and runners; - Predicts the cooling sequence
of various sections and of the entire casting. It can make the solidification
visual, and images can be combined in sequence
to produce a casting/cooling video; - Any number of alterations to the design
is possible, and a permanent record is made of each stage and the resultant
predictions; - Helps to cut down on the use of metal (increasing the casting yield)
by careful positioning of feeders and the use of exothermic insulators
and chills; - Predicts
where shrinkage is likely to occur; - Allows optimization of adjustments to feeders
and runners, before making
a casting; and - Helps with troubleshooting, by modeling, to identify the cause
of unexpected casting faults.
All of the above result directly in energy efficiency
improvements. The start-up cost for a computer simulation set-up, including
the software and training,
may run well over $100,000, with substantial yearly maintenance charges. However,
in a documented case of two offshore foundries, the yield improvement rate
was over 20%, and paybacks ranged from three to eight months.
X-ray videography
This technology helps to validate the computer simulation and takes a scientific
approach to mould design. It allows viewing of molten metal flow through mould
cavities and helps to achieve optimized mould design.
Filters
When designing moulds (or dies) for non-ferrous castings, consider incorporating
ceramic filters for the molten metal in order to realize numerous benefits
(see Section 2.3.6, “Pouring,” page 66).
Lighten risers
Consider emulating the steel foundries practice of insulating risers as a way
to reduce their weight. Reduction of weight to one sixth or less of the original
may be possible.
Lighten castings
Investigate whether removing metal from the casting designed by the customer
would be possible without impairing the required functional properties (such
as strength and durability). Apart from the practical cost/profit considerations
(more pieces produced per tonne of metal), the process would save energy normally
required.
Robotic casting
A designing process using robots for casting (where warranted by the type and
size of foundry operations, as well as for other tasks) improves throughput,
quality – i.e., uniformity and consistency – of the product, as
well as energy efficiency, since the number of rejects is reduced.
Lost foam casting
For applicable foundries, this emerging technology has many advantages. It
reduces costs and enhances design capabilities. It allows casting even very
complex parts in a single pour, and more features can be designed into the
casting. The parts produced with lost foam casting are highly accurate and
the process does not leave appreciable blemishes or surplus metal that must
be machined away. To introduce lost foam casting is a major technology change,
but it has impressive economics stemming from a higher line throughput (by
a factor of three or four), a much longer lifetime of lost-foam casting tools
compared to conventional ones, and up to 30% energy savings.
Annealing in
the mould
For some metals and casting designs, you may wish to investigate whether self-annealing
in the mould is practicable. Then, subsequent heat treatment would be eliminated.
This, too, could be part of a smart design.