Machining Plastics: Case Study Nylon
In this Series of discussions, we will explore some past projects that involved some trouble shooting and some machining tips that were learned along the way. This might help you set your mind when certain problems arise in your next project.
Considered an affordable plastic, high strength, long lasting, resistant to chemicals and corrosion, great alternative to many metals that is very easy to machine. Nylon is extruded and cast in both filled or unfilled with glass and carbon fibers, common extruded grade is Nylon 66 and Nylon 6 is typically cast into large blocks and sheets. When machining Nylon carbide tooling is the recommended method and being a hygroscopic material. Care must be taken when using coolants, part swelling and subsequent drying cause dimensional issues. When Nylon is to be used in wet applications, it is a good idea to match the same wet environment during machining to hold tighter tolerances, hard to predict but possible to do. Nylons are available in lubricated or un-lubricated grades, general extruded stock dimensions are limited to 6" rod, 3" plate, and casted into rods to 38", discs to 80", and sheets to 4" thick.
Common Applications for Nylons:
Bearings, Bushings, Nozzles
Electrical and Pump Components
Food Contact Parts
Manifolds (Air, Liquid)
Pistons and Valves
Wear Pads and Strips
Coolants are generally not required for most machining operations (not including drilling and parting off). However, for optimum surface finishes and close tolerances, non-aromatic, water soluble coolants are suggested. Spray mists and pressurized air are very effective means of cooling the cutting interface. General purpose petroleum based cutting fluids, although suitable for many metals and plastics, may contribute to stress cracking of amorphous plastics.
Sawing Tip: Rip and combination blades with a 0° tooth rake and 3° to 10° tooth set are best for general sawing in order to reduce frictional heat. Use hollow ground circular saw blades without set will yield smooth cuts up to 3/4” thickness. Tungsten carbide blades wear well and provide optimum surface finishes.
Drilling Tip: Coolants are strongly suggested during drilling operations, especially with notch sensitive materials and glass or carbon reinforced products. The insulating characteristics of plastics require consideration during drilling operations, especially when hole depths are greater than twice the diameter.
Milling Tip: Sufficient fixturing allows fast table travel and high spindle speeds when end milling plastics. When face milling, use positive geometry cutter bodies. Climb milling is recommended over conventional milling. To ensure finished part flatness, always machine a plate flat to start. Do not force a plate flat with a vice or vacuum.
Threading and Tapping Tip: Threading should be done by single point using a carbide insert and taking four to five 0.001” passes at the end. Coolant usage is suggested. For tapping, use the specified drill with a two-flute coated tap. Remember to keep the tap clean of chip build-up. Use of a coolant during tapping is also suggested. Use of a coated tap will create radii at the root of the threads resulting in a stronger and tougher thread which is less prone to cracking from over-torquing.
Turning Tip: Turning operations require inserts with positive geometries and ground peripheries. Ground peripheries and polished top surfaces generally reduce material build-up on the insert, improving the attainable surface finish. Fine grained C-2 carbide is generally best for turning operations.
Post Machining Annealing: In our experience and parts we have produced this step was avoidable with a roughing in machine stage and leaving parts unclamped for 1 to 2 days. This worked great for critical tolerance work.
Case Study #Reduce Scrap/Lower Labor Cost: Nylon
This one is hard to explain and a proprietary machine so we can't provide pictures, a client with an existing product using both glass filled and unfilled Nylon parts. This part of the machine assembly had many moving parts all while sealing under a vacuum, in combination this assembly consisted of 10 separate parts. This was a laborious assembly on the production floor and was time consuming and costly to assemble, parts had to be oriented in a specific order. Client asked if there was a possible solution to reduce the chance of assembly error and save on labor costs by exploring a reduction in parts.
Challenge: Reduce the chance of assembly error and reduce labor costs by exploring alternative machining techniques to reduce an assortment of parts.
Solution: After examining the current parts and their respective role in the assembly, working with the manufacturer of the current design. We designed and built a working prototype of a single part that integrated the current components such as the slip rings (4) and (2) contact adapters while eliminating the need of (3) slip sleeves. This process did not stop current production and was phased in on the clients next run, this approach reduced the chance of errors on the assembly line, part performance remained intact, part aesthetic and finished remained the same. This single machined part reduced scrap and lower production cost by eliminating several injection molded parts, and proper orientation of the components during assemble was eliminated. This was a win for all 3 parties involved, current manufacture remained with the assembly of the new design, client saved money and we gained the right to solely manufacture and supply the new Nylon replacement component.
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