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Syntactic Foam for Plug Assist

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1 Syntactic Foam for Plug Assist
Hello. I’m Conor Carlin with CMT Materials. This is the 3rd module in our learning series, “Syntactic Foam for Plug Assist.” Each session is slides and approximately 8-10 minutes in length. Please visit our website for product data sheets, machining guidelines and other technical information, including some great notes from our blog. Syntactic Foam for Plug Assist Module 3

2 Agenda Processing HYTAC Syntactic Foam A Best Practice Guide to
CNC Milling HYTAC Syntactic Foam In the first two modules, we looked at the basics of HYTAC plug materials as well as some design principles for plug assists. In this module, we’re going to focus more on the actual processing of HYTAC. Specifically, we’re going to look at CNC milling. All the design work in the world just goes to waste if the plug is not correctly machined. An improper surface finish results in more than just scratches on the part; it also affects repeatability and consistency from part to part, cycle to cycle. Over the past few years, we have found that a more hands-on approach to this topic is required. In almost all cases, processors and operators have come away with a new appreciation for the solid fundamentals that underpin best practices for machining syntactic foam.

3 Machining Syntactic Foam is Different
Most machining experience relates to wood or metal Syntactic foam is a combination of hollow glass microspheres bound together by epoxy, copolymer blends or thermoplastic materials It is not like wood or metal It requires a different approach Ask anyone about machining and they’ll typically picture some type of metal or wood – materials that have been machined for years and about which volumes have been written. But what is syntactic foam? It is a combination of hollow glass microspheres bound together by epoxy, copolymer blends or thermoplastic materials. You cannot assume that a machine operator who cuts metal will automatically know how to cut syntactic foam. Because it is abrasive by nature, it requires a different approach. More importantly, it requires sharp tools actually designed to cut abrasive plastics.

4 General Machining Guidelines
Syntactic foam behaves like plastic during machining Big chips are better than small chips Controlling the heat of the cutting tool is critical Start a conversation with your tool vendor These general guidelines are a starting point for those who need to cut and machine syntactic foam. CMT developed these guidelines after many months of evaluations with tool vendors. We also rented out a machine shop for specific research. The end result combines the material science of syntactic foam with the cutting mechanics of specific machine tools. Use these guidelines as a starting point. Most of our customers have been surprised at how good the results can be. They find that, like thermoforming itself, there are many options that can improve or worsen results.

5 Goal: Consistent Surface Finish
Feed rate = chip load x spindle RPM x # flutes Remove the largest chip possible as quickly as possible Avoid heat build-up in the tool In order to mill syntactic foam most effectively and to get the best possible surface finish, it is critical to understand the feed rate. This is determined by the following equation = Chip Load x Spindle RPM x # of Flutes. Let’s look at each variable in turn: the chip load, typically provided by your tool vendor for a tool’s use with a specific type of material; the spindle RPM is generated by your machining center; and the number of flutes is based on the actual cutting tool used. In our experience and during our testing, we found that single flute tools did not perform well. Two flute tools worked consistently well. Some three flute tools with similar geometries were suitable for material removal, but overall consistency was higher with a two-flute configuration. The feed rate is critical to removing the largest chip possible as quickly as possible.

6 Where to Start: Milling Tools
2 flute Straight “Z” Solid Carbide or PCD Good for rapid removal of large amounts of material Reasonable “floor” finish Climb milling generally required Generally must be “ramped” 2 flute upcut spiral Solid Carbide Good for rapid removal of large amounts of material Excellent “floor” finish Conventional milling recommended May be “ramped” or “plunged” 2 flute Ball Solid Carbide Excellent finish for contoured surfaces Conventional milling recommended Syntactic foam machines like plastic, but it is highly abrasive. Sharp, solid carbide tooling is required for successful processing. When we looked for cutting tools for syntactic foam, we found that tools specifcally designed to cut abrasive plastic offered the best performance. As mentioned in the previous slide, the cutting profile for material removal, slotting, profiling and floor finish that proved to be the most consistent was the 2-flute upcut spiral. For countouring (or shaping), an aggressive upcut-and-polished 2-flute ball mill surpassed all others. This tool design met the criteria of taking as large a chip as possible as quickly as possible, eliminating heat buildup and surface damage while controlling any chance of chip-out. Taking large chips instead of small ones means that the tool and the plug remain at an acceptable temperature which will result in a better finish.

7 Conventional vs. Climb Milling
Similar tools from different manufacturers will perform differently depending on the direction of travel. As mentioned before, a conversation with your tool manufacturer will help perfect your cutting process. The specific tools recommended by CMT in our machining guidelines performed best when cutting in the conventional direction.

8 Optimizing & Refining the Process
Increase feed rate until part finish begins to deteriorate Reduce rate by 10% to get starting point Decrease RPM by set increment until surface finish begins to deteriorate Increase speed back to last “good” RPM where results were satisfactory When measuring the success of your HYTAC milling process, one major goal is to get the maximum possible chip size. This helps to keep both the cutting tool and the plug material at optimum temperatures. We encourage processors to experiment with settings until the desired finish is achieved. Following our optimization approach, the operator should increase the feed rate until the part finish begins to deteriorate. Reduce the rate by 10% and use this as “your” starting feed rate. Next, you can decrease RPM by a set increment until the surface finish begins to deteriorate. Then, increase the speed back to the last “good” RPM rate, where the results were satisfactory. By following these two steps in combination, you will maximize tool life and surface quality for the plug. For additional tool life, you can rotate the finish tool to roughing tool when the part finish deteriorates.

9 Optimizing & Refining the Process
Coolant not required Pay attention to proper settings Keep tool at room temperature Thermoset Epoxy Syntactics Very Dusty (HYTAC-W, WF, WFT) Copolymer Syntactics Small shavings/curls (HYTAC-FLX, FLXT, C1R) Thermoplastic Syntactics Large shavings/curls (HYTAC-XTL or B1X) Coolant is not required when machining syntactic foam, assuming use of correct tools, feeds and speeds. Based on our observations, we generally recommended the use of air blast to clear cut chips. Machining dust from W, WF, WFT can quickly clog coolant recycling pumps. The use of liquid will not harm the machining of W, WF, WFT, FLX, FLXT or C1R, but it will create irreparable damage when machining B1X or XTL. Fortunately, B1X and XTL machine well with large chip shavings and no dust. Proper settings will result in a tool that runs at or near room temperature. It is important to keep chips clear to prevent re-cutting and premature tool wear. There are two reasons why a tool is hot: either it is dull or the feed rate is too slow.

10 Machining: Best Practices
Use sharp tools for abrasive plastics Keep heat out of the tool Understand the variables Refine the process So, we covered a lot of specific information in this module. Let’s summarize the most important points: Use sharp tools that are specifically designed for abrasive plastics. These are purpose-driven tools, not substitutes from another job. Keep the heat out of the tool: dull tools will create imperfect plugs. If the tool is too hot, it’s either dull or the feed rate is too slow. Understand the variables: the feed rate formula will keep you on track. Knowing the chip load, the RPM and your tool geometry will allow you to determine the optimal feed rate. Remember – it’s good to refine the process until you get it just right.

11 Online Resources
We have published extensive machining guidelines in both metric and English units. These are available on our website for download. In addition to the machining guidelines, we also provide details on turning, adhesives and best practices. The next module will focus on these areas.

12 End of Module 3 +1 508 226 3901
Thank you for your attention. Be sure to sign up for our technical blog where we discuss many of these topics in more detail. The next module will focus on additional processing techniques for syntactic foam, including polishing – a simple process that is often overlooked.

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