Why Micro Molding Is Ideal for Small Medical Products
Micro molding is a unique form of plastic injection molding used for making parts on a small scale. These finished components weigh as less as 1 gram and they measure smaller than 1 mm in cross-section. There are a number of benefits of micro molding for small plastic parts. We will first look at how different the process is from conventional plastic injection molding and then understand the applications it’s best suited for, especially in medicine and related diagnostics.
Size Matters
Generally plastic injection moulding machines are rated by the clamping force used to hold two halves of the mould. Small conventional machines generally have a clamping force of 50 tons. Tonnage rating of a machine is based on the maximum amount of injection pressure a machine can withstand and safe forces that the machine can handle. So operators keep the pressure below threshold. If the pressure is too low, there won’t be enough force to fill the mould before the resin solidifies.
Can Big Machines Make Small Parts?
Small parts require smaller moulds and these smaller moulds have smaller cavities, gates and runners. The resulting parts are highly sensitive to fine adjustments in pressure or temperature. Larger machines are more difficult to control precisely. Using a large machine to make small parts is not advisable because they have larger barrels with a big volume of molten resin. During one cycle, only a small amount of resin is used in each shot. The remaining resin is in the barrel, staying hot for too long. This may lead to degradation and can ruin the part. Smaller machines have faster cycle times and shorter barrels. Generally bigger machines also consume more electrical power regardless of the size of the finished part. These operating costs when passed to the customer increase the price and decrease process efficiency.
What Are The Advantages of a Micro Moulding Machine?
Generally for product developer, micro-moulding machines represent five distinct advantages when making small parts.
1. Mold tools are much smaller and thus less expensive, costing approximately 40% of the price of a full-sized tool.
2. Micro molding consumes much less raw material. This includes not only material used to make the part but also leftover resin in the gate and runner system as well as the barrel.
3. Fast changeovers are aided by using an online digital database that can hold one thousand unique job set-up parameters. And it’s also easier and faster to flush old resin out of the system to prepare the machine for a different material.
4. Hot runner systems are used to precisely control the temperature of the mold during production.
5. Micro molding machines have short, compact barrels and the gates and runners are also of short length. Thus even multi-cavity molds can be run in cycles much more quickly than their larger counterparts.
Are There Challenges For Micro Molding?
There are a few areas where micro-sized parts pose a greater challenge for the molder.
1. Small cavities with tiny features and thin walls are harder to machine into tool steel. That is why NAK80 or H13 polished stainless steel is used to make small mould tools. These steels generally have a fine grain with a dense molecular structure so that we can use multi-axis CNC machines to make fine features with high accuracy and tight tolerances.
2. Resins behave differently when compared to their full-sized counterparts. This is because resins generally experience high sheer force as they are forced to fill small cavities quickly. Since sheer is closely related to resin temperature and injection pressure, it’s important to use dedicated micro machines that can be adjusted with fine gradations to achieve optimal results.
Measuring Small Parts
It is not possible to make small parts accurately until & unless they can be measured reliably. That is why we have advanced 3D scanners and coordinate measuring machines that we can use at every critical step to monitor physical dimensions.
What are Micro Parts Used For?
It is very important that hospitals, insurance companies and patients are all interested in limiting any invasive procedures inside the body and they want to control the costs. There is a constant pressure to develop new products on the small scale that offer diagnostic and therapeutic remedies. Advanced applications that combine passive enclosures with sophisticated electronics, sensors and mechanical actuators shall create an entirely new class of healthcare devices.
Some devices are injected into the bloodstream of the human body or they are placed under the skin where they monitor many functions of the human body. There are other sophisticated mini-machines that might use micro fluidic pumps to deliver small doses of medicine at required rate. They are generally made from bio absorbable materials that naturally dissolve inside the bloodstream or automatically send alerts to doctors about health conditions that fall outside a predetermined range of values.
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