Tuesday, November 24, 2009

Conformal Cooling

Conformal Cooling
Conformal cooling is defined as the ability to create cooling/heating configurations within a tool that essentially follows the contour of the tool surface or deviates from that contour as thin/thick sections of the part may dictate for optimal thermal management. The objective typically is to cool or heat the part uniformly. Conformal cooling provides a tremendous advantage in mold tooling through significant reductions in cycle times. Other than the obvious piece-cost savings, other tangible benefits include tool, equipment and floor space savings.

Recent studies show conformal cooling may reduce cycle times between 30 to 60 percent over conventionally cooled tools. This savings is very much geometry-dependent. The more difficult thermal management is with traditional technology, the greater the opportunity for savings with conformal cooling. The Direct Metal Laser Sintering process naturally lends itself to the integration of conformal cooling into injection molds or other tooling.

It should be noted that in many cases, resurfacing the tool might not be necessary to enable the prototype tool to be used in production. Depending on the types of parts being produced, such as volume, surface requirements, abrasiveness of materials, and so on, the prototype tool may be sufficient for production as built.

Conformal Cooling PDF
Conformal Cooling Link

Cooling of injection molding tooling is crucial to the performance of the tooling, influencing both the rate of the process and the resulting quality of the parts produced. However, cooling line design and fabrication have been confined to relatively simple configurations, primarily due to the limits of the fabrication methods used to make tools, but also due to the lack of a design methodology appropriate for cooling lines.

For many years, mold designers have been struggling for the improvement of cooling system performance, despite the fact that cooling system complexity is physically limited by the fabrication capability of conventional tooling methods. Different methods such as helical channels, the baffled hole system, the spiral plug system and heat-pipes have been developed for uniform and efficient cooling of the part. Some mold manufacturers such as Innova Zug Engineering GmbH of Germany optimized the thermal conditions by building cooling channels following the part shape. Other manufacturers such as CITO Products, Inc., developed the pulse cooling technique for better control of the mold temperature, in order to reduce the energy consumption and enhance uniform cooling condition.

The emergence of new processes that can be used to create tools with conformal cooling channels placed with almost arbitrary complexity not only offers the designer new degrees of freedom in the design of injection molding tools, but also simplifies the methodology used to design cooling channels.

Conformal Cooling on the web


Solid Freeform Fabrication processes such as DMLS have demonstrated the potential to produce tools with complex internal geometry. This work explores the application of this capability to improve thermal management for injection molding tooling through: (i)cooling lines which are conformal to the mold surface which provide improved uniformity and stability of mold temperature and (ii)tools with low thermal inertia which, in combination with conformal fluid channels allow for rapid heating and cooling of tooling, thereby facilitating isothermal filling of the mold cavity. This work presents a systematic, modular, approach to the design of conformal cooling channels. Recognizing that the cooling is local to the surface of the tool, the tool is divided up into geometric regions and a channel system is designed for each region. Each channel system is itself modeled as composed of cooling elements, typically the region spanned by two channels. Six criteria are applied including; a transient heat transfer condition which dictates a maximum distance from mold surface to cooling channel, considerations of pressure and temperature drop along the flow channel and considerations of strength of the mold. These criteria are treated as constraints and successful designs are sought which define windows bounded by these constraints. The methodology is demonstrated in application to a complex core and cavity for injection molding. In the area of rapid thermal cycling, this work utilizes the design methods for conformal channels for the heating phases and adds analysis of the packing and cooling phases. A design is created which provides thermal isolation and accommodation of cyclic thermal stresses though an array of bendable support columns which support the molding portion of the tool where the heating/cooling channels are contained. Designed elasticity of the tool is used to aid in packing of the polymer during the cooling phase.

Conformal Cooling Research from NASA and MIT

3D Printing

Previous means of producing a prototype typically took person-hours, many tools, and skilled labor. For example, after a new street light luminaire was digitally designed, drawings were sent to skilled craftspeople where the design on paper was painstakingly followed and a three-dimensional prototype was produced in wood by utilizing an entire shop full of expensive wood working machinery and tools. This typically was not a speedy process and costs of the skilled labor were not cheap. Hence the need to develop a faster and cheaper process to produce prototypes. As an answer to this need, rapid prototyping was born.

One variation of 3D printing consists of an inkjet printing system. Layers of a fine powder (plaster, corn starch, or resins) are selectively bonded by "printing" an adhesive from the inkjet printhead in the shape of each cross-section as determined by a CAD file. This technology is the only one that allows for the printing of full colour prototypes. It is also recognized as the fastest method.

Alternately, these machines feed liquids, such as photopolymer, through an inkjet-type printhead to form each layer of the model. These Photopolymer Phase machines use an ultraviolet (UV) flood lamp mounted in the print head to cure each layer as it is deposited.

Fused deposition modeling (FDM), a technology also used in traditional rapid prototyping, uses a nozzle to deposit molten polymer onto a support structure, layer by layer.

Another approach is selective fusing of print media in a granular bed. In this variation, the unfused media serves to support overhangs and thin walls in the part being produced, reducing the need for auxiliary temporary supports for the workpiece. Typically a laser is used to sinter the media and form the solid. Examples of this are SLS (Selective Laser Sintering) and DMLS (Direct Metal Laser Sintering), using metals.

Monday, November 16, 2009

DMLS on Video

It will be just a matter of days before I put the DMLS video on youtube. I am going to run a short series along with some several key points in regards to additive manufacturing.

-GPI Into Video
-DMLS - Direct Metal Laser Sintering Process
-Conformal Cooling - The process that can save injection molders at least 30% cycle time.

I will put up the links so they can be followed and hope to see you all watching.