TEAM Lab Equipment and Techniques: Casting and Injection Molding Machine
Overview of Casting:
With our various casting techniques, hollow molds can be used to create both solid and hollow objects. Custom molds for casting can also be manufactured by TEAM using our other fabrication services.
A plastic mold is acquired or manufactured and then filled with a synthetic resin until hardened.
Roto-casting is also referred to as centrifugal casting and rotomolding. Roto-casting is when a small amount of liquified thermoplastic is put into a heated mold. The mold is rotated rapidly until the resin has evenly coated the inside, and then left to harden. This is a technique used primarily for creating thin plastic shells in the shape of the mold. Example products in your everyday life made using this technique include: water bottles, bins, plastic toys, road cones, and many more.
Silicone is a very flexible and durable material that can withstand a wide range of temperatures (-65º to 400º C), making it a smart choice for very complex structures. The flexibility of silicone allows for easier removal of the part from the silicone mold with a lesser likelihood of damage compared to harder plastic molds. The durability makes it resistant to a wide variety of chemicals, however will degrade overtime the more you use it.
Overview of Injection Molding and Compression Forming/Molding:
The TEAM lab possess a bench-top, industrial-grade injection machine meant for small-batch rapid prototyping (i.e. not designed for large-batch manufacturing like most machines). The machine works by way injecting molten plastic pellets (resin) into a user-created mold-cavity to create plastic parts.
The advantage this technique has 3D printing, is the wide range of available engineering grade plastics, and their associated (superior) mechanical properties. However, a very significant drawback to the process is the added time to design and manufacture a mold-cavity (typically machined from aluminum or steel) for the process. For small parts, it may be possible to 3D print a mold cavity (SLA high-temp is our preferred material, but there are others as well), but this still presents an added expense, and more development.
Figure 1: Bench-Top Injection Molding Machine in the TEAM lab
All materials available for this process are thermoplastics – a family of plastics that can be heated to a molten state, formed, and left to cool (with no damage to the polymer). Common materials include (but are not necessarily limited to):
In all instances, polymer (resin) would need to be supplied, as the TEAM lab doesn’t typically store resin for use in the injection molding machine.
Figure 2: Resin Used in Injection Molding (via advanceplastics.ca)
Development of the Cavity:
Once a target shape is defined (by way of CAD – Solidworks, Inventor, etc), many software packages have tools included to aid in the development of a mold cavity. While not perfect, this is a good starting point. Please consult with the TEAM lab manager for complete development details. The most important considerations when developing a mold cavity are: Part wall thickness, Draft Angles (to allow extraction of the part from the cavity), and Sprue/Runner/Gate placement. This is not a trivial process, and will require a significant amount of invested thought, and perhaps some trial-and-error.
Figure 3: Injection Mold Simulation (via Dassault Systems)
Manufacturing the Cavity:
The TEAM lab uses two primary methods for mold cavity manufacturing:
CNC machining: Machining the cavity (typically from aluminum, sometimes steel) will give the best overall results (finish, number of parts that can be manufactured, reliability of cavity), but the trade-off will be in manufacturing time as machining is a time-consuming process.
3D printing: Some of the TEAM lab’s 3D printers are uniquely qualified to manufacture mold-cavities that can survive a “handful” of cycles. This is an excellent technique in cases where: 1. The desired part is small (less than ~1.5 inches cubed), 2. Only one or two units is required. Not that in many cases, a machined frame may be required to support compression on the printed part (see example below, via Formlabs)
Figure 4: A 3D Printed Injection Mold Cavity, Made of "Digitial ABS" 3D Printer Polyjet Resin (via Stratasys)
Figure 5: A 3D Printed Injection Mold Cavity, Made in "High Temperature" SLA 3D Printer Resin (via Formlabs)
Shot Size: 4 Oz (maximum), = 6 cubic inches in volume.
Maximum Plan Area: 8”x11”
Maximum Injection Pressure: 9000 PSI
Maximum Clamping Force: 20 Tons
This machine is only to be used by a qualified operator (Typically, the TEAM lab manager). Further, as molds loaded into the machine will undergo very height compression loads, the manager must approve all entries into the machine. Please confirm your design with the TEAM lab manager prior to manufacturing to avoid delays.
Figure 6: Example of Injection Molded Part (Via linal.com)
Figure 7: Example Part Demonstrating Different Features, and Pitfalls in Injection Molding (via Protolabs)
Sources and Resources:
Designing for Moldability: https://www.protolabs.com/resources/guides-and-trend-reports/
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