To us, being a leader in our industry means more than offering the most extensive selection of products and services. At MPC, it’s all about creating custom solutions for the unique needs of our valued customers. When we manufacture components from high performance semi-conductive urethanes, they need to be machined in order to achieve the exact specifications and traits required for the purpose they serve. As we outlined last week in our Custom is King blog, it’s a combination of machining techniques and expertise that allows us to confidently produce machined urethane products with the precision and accuracy that our clients deserve. In that blog, we discussed the cutting tools we use, and featured 3 of our advanced machining processes, including drilling, parting and milling. Today we will discuss the other machining services we offer, including contouring, grinding, sawing, facing and turning.
Contouring is a custom machining process which includes the machining of tapers, chamfers, grooves, radii, and other surface configurations into round, custom molded urethane components. This process takes place on the outer diameter or “OD” of the part in order to form it into a shape. The durometer or hardness of the part, combined with the desired result dictates the rpm and tools used. The necessary tools and configurations for grooving OD’s in harder durometer urethanes (90A to 75D) are basically the same. We find that a 10 to 20 degree front rake works the best without any top rake. In our experience, using a higher rpm (depending on the OD of the component), paired with light cuts and moderate feed rates produce beautifully clean and smooth surfaces.
One of the most efficient tool positions is .025″ to. 075″ inches below the center of the part being machined. We look for a continuous ribbon flow of cut-off material coming off the component as this shows we are shaping evenly and will achieve a desirable finish. During this process, care must be taken to prevent the ribbon from wrapping around the component and machine. Reducing the feed and speed rate on the working component can help prevent the ribbon from wrapping around. We contour softer polyurethanes (less than 90A) using a tool with 15 to 30 degrees of top rake and the ideal lathe speed depends on the OD of the component. When in doubt, a higher rpm is almost always preferable. Until we’re sure how a part will machine, we utilize slower speeds, increasing incrementally until the desired effect is achieved. At MPC, we’re committed to safety, so while machining polyurethane, we always protect ourselves with a full face mask for appropriate safety.
Grinding is the ideal machining process for parts made with urethanes in the middle of the durometric “road”, meaning that they aren’t extremely hard or soft, but somewhere in between. Urethanes in this range have a 50A to 85A durometer and can be ground successfully in a lathe using a grinder or in a cylindrical grinder. We use low to medium turning speeds with the lathe running in reverse and a feed rate of about .005 inches per revolution. This combination of speeds and techniques allows us to achieve an improved surface finish due to the ability to remove more material with a deeper grind. In this process, the grit of wheels of the lathe is extremely important. We generally use 40 to 60 grit, but up to 80 in certain circumstances, with a slight radius on the leading edge. Wheel rpm should be in a range of 1800 to 3600. Once the part has been ground, the surface finish can be further improved by polishing with finer abrasives.
During the grinding process, both machine and component can become very hot. Some urethanes above 75A usually require some type of coolant, but some can be ground dry. Coolant can be applied automatically, by brush, by spray bottle, nozzle, or fine mist, depending on how much the operator feels is needed for the part he is working on. The grinding machine should be equipped with a dust collector to prevent the operator from inhaling particles, but as mentioned before, we make every effort to be safe so our operators always wear an approved dust mask when grinding or polishing urethanes.
Sawing is a very common process used for machining urethane parts. We find that band saws are the best machines for sawing urethane for many different reasons. The ability to change blade length allows for a highly customized result, and at MPC, that’s exactly what we want. In our decades of experience, we’ve found that longer blades are optimal because they stay cooler to prevent heat build-up, melting, burning, etc. of the urethane. These blades should ideally run at 2600 feet per minute and have 4 teeth per inch with significant blade set alternating to the left and right of center. This will allow for the part to be sawed evenly and without the need to force the part. As we saw a part, we allow it to feed into the saw slowly, letting the blade cut at its own speed. Forcing a part can damage the part or the saw. When cutting thin low durometer sheet stock, our technicians must remember that it requires support under it and possibly fixturing so the urethane will not jump and move as it is being machined. Unlike some machining processes, coolant isn’t required, but for the best results we do use some type of lubrication on the blade such as water-soluble oil or a silicone spray applied as a mist to reduce friction heat and to improve the surface finish cut.
Facing and Turning
The last machining processes we will be talking about today are facing and turning. These common processes can either be completed on an engine lathe or a turret. Like many of our other processes, configuration of the tools used, including speed and placement depends on the durometer of urethane as well as the type of part. For example, harder durometer urethanes can be faced and turned to size using extremely sharp tools at high turning speed rates and slow feed rates with either carbide or high speed steel tools. We find that the top of the tool should be very smooth to assist chip (make more cut off product come off), prevent heat build-up, and reduce wrap-around (ensure that the cut off material doesn’t wrap around component or machine.) Like our other processes, facing may sometimes require a coolant but for turning a coolant is not necessary.
Well there it is, a breakdown of the machining processes that allow us to turn your ideas into custom urethane parts and components. In the next coming weeks we’ll be sharing more about the innovative processes, tools, and techniques that we use, as well as helpful information about our extensive product line. In the meantime, if you have any questions or you’re ready to start discussing the custom urethane parts you need, simply contact us and we’ll be ready to give you the information you need!