A Complete Systems Approach to Micro Molding

The continually evolving demands of the medical industry constantly drive suppliers and manufacturers to expand their technical competencies into regions where they may have historically feared to tread. Doctors and surgeons are demanding instruments for less invasive procedures and quicker turnovers. Devices are becoming smaller and more complicated. Industry designers and procurement specialists are demanding smaller, higher precision components with exotic materials and tolerances that may not have been possible years ago. This trend in micro-molding processes and components advertised or written about in technical articles and industry publications has often led to confusion and to missed opportunities when it comes to supplier selections.
 
Defining Micro Molding
True micro molding can be defined in several different ways. One method would be part weight, with a typical range from 1 gram to smaller than 0.004 grams. Tolerances required are often much tighter than 0.001”. But more importantly, micro-molding can be defined as components with sizes or tolerances so small that they are not able to be manufactured correctly, robustly, or with a high degree of precision using traditional injection molding equipment and standard thought processes.
 
Think Small
To be successful with micro molding takes more than simply purchasing a small injection molding press and a microscope. All levels of the organization and those at each step of the manufacturing process must make the decision to commit to success. This must translate to a passion for problem solving, and thinking small, in the micro molding world. All phases of the process should be engineered to manage the specific subset of problems that come with making micro components. Careful thought toward resin selection, component design, equipment and molding processes, tooling construction, measuring equipment, and even component handling and packaging is critical. These may seem standard in today’s injection molding industry, but micro requires specialized solutions to ensure success and a happy customer.
 
Involve the Manufacturer Early
The specific type and grade of resin should be selected with input from the material supplier and the manufacturer’s engineering team. Semi-crystalline or amorphous resins, fillers, fibers, and even colorants can all have an impact on the product consistency required to meet critical dimensional requirements. Selecting the material appropriately is the foundation for the long-term manufacturability. Use consistent amorphous engineering grade resins for tight tolerances. Apply fillers for added dimensional stability where necessary.
 

Following general part design principals is recommended for any successful part design. In micro molding, not only meeting these guidelines but exceeding them is a challenging requirement. Slight areas of sink in ribs, slight warpage in sharp corners, or flowing thin to thick may cause slight problems in a large part. In a small part, they can be disastrous and result in deformation that can exceed the allowable tolerance. Suppliers need to be involved early in the design phase to ensure success and a robust design.
 
Tool construction is of the utmost importance as well. Traditional time-tested tool construction methods can cause problems when tolerances and geometries are microscopic and critical. In fact, this may be the most important phase of the development project. It is critical to manufacture the tooling using processes that are able to create fine, sharp corners; extremely flat surfaces; tricky geometries; and everything in the perfect detail required—the standard end mill and EDM need not apply.
 
Equipment selection is the next step in the development process. Many manufacturers now offer packages that are almost off the shelf for specialization in micro-molding manufacturing. Make sure to involve the manufacturer early in the process. Be prepared to disclose shot weights, material selections, part size, and critical features. Shot control may exceed what is possible for a check ring screw; a plunger or ram may best fit an application. Consistency is the key to long term success.
 
Full Control of Quality and Quantity
Once the molded component is finished, how does one verify that it is acceptable? Careful selection and possible investment in metrology and measurement systems will give provide the data necessary to be certain. The equipment must be able to measure small dimensions, with small tolerances, and demand Gage R&R results better than 10 percent. Calipers and micrometers will not lead to positive results. Each component offers different challenges for measurement. But technology has come a long way in this area in the past five years. Laser scanners, CT scanning, and non-contact optical vision systems are readily available and all offer packages that can be customized and programmed for specific needs.
 
An area that may be often overlooked, however, is packaging. It may almost be an afterthought for standard injection molding, but can cause many problems when trying to control delivery of micro molded components. Ensuring part counts are correct can be difficult when a month’s worth of production demand can fit into the palm of a hand. Traditional weigh scale verification is insufficient. Certain automated systems can help with this as they tie directly into the press interface and rely on camera controls to verify count and quality. Rely on optics and technology. Use small, sealable bags or vials where appropriate. Segregate into small quantities when possible.
 
Communication Is the Route to Success
Micro molding is a challenging venture, but it can be accomplished successfully. All interacting systems should be designed concurrently with careful thought as to how all components interact within the manufacturing process. Positive communication between engineers, project managers, equipment suppliers, designers, molders, and quality inspectors is required for success. Designers and engineers should contact their supplier of choice early in the project. This will lay the roadmap required, as there is little room for error in the micro molding world.