Challenges of medical part machining

As a life sciences, plastic machining contract manufacturer, Connecticut Plastics’ engineering and manufacturing departments never expect to make easy parts. Assignments range from merely difficult to premier feats of machining. To meet these expectations, the experienced staff relies on high-end CNC mills and multi-axis lathes, tied together with Mastercam from Tolland, Connecticut-based CNC Software Inc.

“About four or five times a year, a life sciences OEM will come to us with a challenging part that, in his mind, may not even be possible to machine,” says General Manager, Chris Connor. “If we think it’s possible, we will take it on and develop a manufacturing process, even though it may involve a considerable investment of time by our engineering and manufacturing people. The first time we deliver these parts, we will be lucky to break even. But our customer will be happy and, better still, we will have expanded our portfolio.”
 

Process specialists

Connecticut Plastics is part of Precision Engineered Products LLC (PEP), a group of 12 business units with specialties that emphasize manufacturing with a high degree of process engineering expertise. Engineering Manager Bob DiMaio explains that although the group has an array of multi-axis mills, lathes with live tooling, and metrology equipment, it’s the extensive process knowledge embodied in its engineers that is Connecticut Plastics’ key asset.

“Rather than equipment, what is most impressive to a customer is when we show them a clear machined acrylic laboratory equipment component with complex dimensions; very long high-quality finish drilled holes; and a blemish-free surface,” DiMaio says. “They know how difficult these are to make. Plastic workpieces are very sensitive to heat and chemicals, vary widely in their machining characteristics, and are very difficult to hold without excessive pressure that can cause functional or cosmetic defects. On a mill or a lathe, plastic walls and other features can be pushed around unless the machining strategy is carefully designed. We know how to deal with these and many other concerns for plastic parts.”

Connecticut Plastics engineers use Mastercam CAD/CAM software to create the manufacturing processes for complex parts. The company has five seats with floating licenses – including Mill level 3, Mill Multiaxis, Lathe, and Design. The software offers engineers and programmers complete control of tool motion and imports a wide range of solid models, which are the basis for quoting and manufacturing process development.

When CAD files arrive at the company, they are reviewed by engineering. DiMaio says that about 90% of the files they receive are parts ready for manufacturing that are immediately translated into Mastercam and made available for CNC programming. The other 10% have design-intent questions or manufacturability issues. At this stage, the focus is on giving the customer the benefits of their design while negotiating changes that will reduce manufacturing costs without sacrificing product functionality.
 

Rapid delivery

Once the manufacturing process has been determined, delivery becomes the customer’s biggest concern. This is where engineers rely on their computer aided manufacturing (CAD) capabilities – so they can reduce lead times and get customers the parts they need sooner. Some of the Mastercam-aided capabilities engineers have found particularly useful in knocking down lead times are:

Programming in solids: Programming directly from the model avoids the need to redraw the part so that programming can begin once the model has been reviewed and accepted. Work begins sooner, programming based on the solid model is more automated, and the potential for error is greatly reduced since data does not have to be re-entered.

Ubiquitous simulation: Extensive simulation options within the software allow programmers to visualize the manufacturing process and the condition of the part at every phase of manufacturing.

Parts that must be manufactured with intersecting holes can be a big challenge, for example, “It can be very difficult to get holes that must be drilled for long distances to meet accurately,” DiMaio says. However, using Multiaxis makes it easy to simulate and visualize operations to determine how to get the features to intersect properly.

“Simulation is particularly useful for small parts, some of which have to be inspected under a microscope. In the software’s high-resolution simulation views, it is possible to see toolpaths blown up to full screen, so that it is easy to catch blemishes and there is little chance of making a programming error. Simulation is a valuable tool for any type of CNC manufacturing and absolutely essential for 5-axis and mill-turn machining where there is so much happening all at once.”

Eliminating setups with 5-axis: In recent years, the company has invested heavily in multi-axis CNC equipment, 5-axis machining centers, and lathes with live tooling to improve machining accuracy and reduce setups. Parts that require four or five setups are now done in two, with the second step of simply trimming excess material used for part holding. When multiple setups can be eliminated, per-part productivity can more than double. In addition, when customers ask for one or two parts in advance of the delivery date, machinists can often accommodate them, because it is no longer necessary to tear down multiple setups.

For programming parts to be manufactured on 5-axis equipment, Mastercam’s Work Coordinate System (WCS) allows users to switch rapidly between various work planes. Most of these 3+2 programs are generated by creating a series of 3-axis programs in the required work planes. Simulation then assures that work created in one plane intersects appropriately with work created in others.

Mill-turn productivity: On the lathe side of the shop, multiple operations are eliminated by using the software to program mill/turn operations. Very sophisticated parts can be made with this equipment because the Lathe program has almost all of the toolpaths that can be found in the software’s Level 3 Mill software. Although some machinists still program their conventional CNC lathes manually, the CAM software has become an essential extension for advanced mill-turn process development, and the company now produces a wide variety of mill-turn designs that would not be possible without it.
 

Leveraging proprietary knowledge

“You can go to college for machining. You can learn about feeds and speeds and you know what you’ll run into most of the time. In the plastics world, you don’t have that. You have to figure it out. So we evolved over time to understand why certain plastics would stretch back and why others would absorb water, or have temperature variations, etc. That is the kind of knowledge you grow over time. The more knowledge we gain, the more difficult parts we can then do,” DiMaio concludes.

CNC Software Inc. (Mastercam)
www.mastercam.com

Connecticut Plastics
www.pepctplastics.com