GPI specializes in producing injection molding tooling with integrated conformal cooling channels using direct metal laser sintering technology. DMLS produces solid metal parts by melting metal powder with a focused laser beam layer by layer. Building layer by layer allows for the manufacture of highly complex geometries directly from 3D CAD data. This is especially true for part geometries where slides, inserts or other tool components with complex characteristics are required.
Tooling is a primary application for DMLS, allowing the manufacture of tooling inserts and components in a timely manner. On top of the value of short turn-around times, additional value is created by the unique geometric freedom of design. This helps to improve both the quality and economics of injection molded parts by reducing cycle time and scrap, increasing productivity by 30%-60%. DMLS tools are used to produce millions of parts for injection molding operations. The challenge for integrating a system of this kind is to find the optimal design for the channels. Complexity of the channel design does not impact the manufacturing process, as the DMLS system builds channels directly into the tool. The advantages of these systems maintain a wide range of benefits for injection molding production.
In terms of Tool Geometry:
• Routing options for cooling channels are almost infinite. This makes it possible to create an ideal cooling channel with a well defined distance to the cavity. A conventional drilled cooling mechanism cannot achieve this.
• Cooling channel cross sections can take almost any shape (e. g. oval vs. round). Turbulence of the coolant within the system can thus be controlled by actively choosing different cross sections and by switching between different cross sections. As a result, turbulence inside of the coolant is generated, close to cavity along the entire channel path.
• Changing cross sections or forking the cooling channel can be done easily without splitting up the form. This allows for additional heat/cooling advantages in areas that cannot be reached by conventional methods.
In terms of Quality in the Process of Injection Molding:
• A more effective mold temperature control system saves time and production costs.
• The quality of injection molded parts is improved by better control of the injection molding process. Warping and sink marks are minimized by evenly cooling injected plastics, thus minimizing internal stress.
• Scrap rates are reduced or eliminated. Avoiding internal stresses helps to produce better parts with the same amount of required material. Certain geometries can only achieve required quality standards with conformal cooling.
• Combined systems with separate cooling and heating channels are also possible. The split between main systems for the control of the global temperature, and specific systems for the handling of close to cavity critical temperatures, can be performed with DMLS.
In terms of Process Costs:
• Heating/cooling at critical parts inside the tool, which cannot – or only hardly - be reached by conventional methods, becomes feasible (e.g. long and lean cores, areas around hot-runners or small sliders). Using special copper heat conductors or other complex measures becomes obsolete.
• If necessary, it is possible to under-cool mold cavities, thus reaching optimal cycle times by minimizing cool down times in tooling cavities.
• An evened out temperature level can help to improve tool life time. This is especially relevant in die casting tools that are exposed to extreme temperature variations.
Conventional cooling has the following drawbacks:
• The distance from cavity to cooling channel differs as only straight line drilling channels are possible and as a consequence the heat dissipation cannot take place uniformly in the material.
• Uneven temperature levels on the cavity surface.
• Uneven cooling-down processes resulting in internal stresses that negatively impact part quality (warpage).
• Actively influencing cooling-down processes inside the melt often can not be achieved.
Design for conformal cooling:
The distance from cavity to cooling channel differs as only straight line drilling channels are possible in top figure and as a consequence the heat dissipation cannot take place uniformly in the material resulting in:
-Uneven temperature levels on the cavity surface
-Uneven cooling-down processes resulting in internal stresses and thus negative impact on quality (warp)
-Actively influencing cooling-down process inside the melt can often not be achieved.
-On top clogging of dead drilling ends creates areas with zero flow velocity thus facilitating dirt agglomeration. The drilling procedure itself is not without certain risks: in case of deep drilling there is always a danger to hit ejector holes (wandering drill) or the drill can even break. As a consequence, the whole insert could be unusable.
Design recommendations for the layout of heating/cooling channels with DMLS are the same as the ones given for convention designed channels: they are both based on the plastic recrystallization and heat conductivity theories. In order to achieve a constant temperature level, the channel diameter should be chosen depending on the distance between the heating/cooling channel and cavity.
According to experience the optimal diameter should be chosen between 4-12 mm (depending on the design of the product). Some inserts make it tough to adhere to this rule ie: closely placed ejector pins or thin walls etc. DMLS can build channels down to 1 mm, but take into consideration that you must use specially treated fluids to avoid clogging. Simulation software can help!
With DMLS it is possible to vary the channel cross section shape of the manufactured tool inserts: Additionally to circular ones, the designer can choose complex other shapes. The feasibility criterion supposes a cross section, which is self supporting. This means the angle of overhanging areas should be above 40° to horizontal.
On the last picture the cooling performance can be increased due to the ribbed shape and the higher expected turbulence in the channel.
- Mike Shellabear
- Joseph Weilhammer
- Tooling Applications With EOSINT
- Olaf Zollner
- Optimized mold temperature control
DMLS opens new frontiers for the implementation of very efficient heat/cooling systems and also offers the designer possibilities for the manufacturing of high performance tools without having to consider the many limitations which characterize conventional processes. The real challenge is designing the correct channels during the first steps of the project. The manufacturing process of the mold inserts is not influenced by the complexity of the chosen cooling solution because the DMLS machine simply builds the channels at the same time, without having any major impact regarding the job time.
If you have a product which requires injection molding tooling, steel/aluminum molds, or production manufacturing, give us a chance to quote your project.