Neal Demazure serves in a sales capacity at DATRON Dynamics. His superior technical aptitude has been critical to his success in helping customers solve complex manufacturing challenges through the placement of custom, application-specific solutions. Neal has extensive knowledge in both industrial manufacturing and dental milling technology.
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When it comes to CNC milling strategies for bulk material removal you may be asking the wrong question.
As the account manager for industrial CNC sales in the Northeast USA, I routinely get asked, “What is the biggest tool you can put in a DATRON machine?” And while I always take time to answer this question, it gives me a bit of a chuckle because DATRON high speed CNC milling machines are all about efficiency with small tools! Now, of course I understand that in spite of the fact that this equipment has huge headroom in the RPM department, it must at the same time be capable and efficient when it comes to milling out larger features and bigger parts – most of our equipment does after all have a work envelope of 30” by 40” – but in the world of high RPM and high speed cutting strategies large features or bulk material removal does not necessarily warrant a large diameter tool.
An easy example is the simple process of pocketing: taking a workpiece and milling out an area to create an open space. In this example we’ll assume the pocket is to be 0.75” deep by 2.75” wide by 7” long. Traditional machining methods would involve the use of something on the order of a 1” diameter end mill making a traverse path along the length of this part with standard step down and step over values at typical RPMs of less than 15,000.
In the world of high speed cutting and new school cnc milling strategies, a more efficient toolpath can be realized by use of a comparatively small tool, such as a 6mm end mill, and beginning with a helical toolpath that circles all the way down to the final depth. From there, a large percentage of the cutting flute can remain engaged in the material as the tool circles around removing material continuously as it widens it’s circular X/Y path until the full pocket has been created. This type of strategy, when combined with the right RPM and cutting tool geometry, can outperform a physically larger tool that is using lower RPM and traditional strategies.
To summarize, in the world of high speed machining it’s all about making a lot of small chips very quickly. The necessity of a dimensionally large tool to create a dimensionally large feature have been eclipsed by the advent and proliferation of high speed milling machines with the CAM strategies and cutting tool geometry to go along with them.
For more information on the CNC Milling Strategy used on the aluminum housing shown above:
Download CNC Milling Strategy Application Notes with Bulk Material Removal (Aluminum Housing):
Technology that allows small to moderate sized labs to mill their own PFMs understructures, custom abutments and implant bars has matured significantly in the past few years. Not long ago, an average lab had to choose to either paying top dollar to have a large company mill these types of units, or go through the labor intensive process of casting. Today, a wide variety of milling equipment has become available which has unlocked the ability for CAD/CAM savvy labs to be more self-sufficient and profitable; however, there is still some uncertainty when it comes to when this is an appropriate and prudent step to take. In this post, we’ll focus on three key-indicators that your lab is ready to take its milling game to the next level.
1. You’re Already Scanning, Designing and Milling Soft Materials
If your lab already has built up the workflow and knowledge base to successfully operate CAD/CAM equipment for the purposes of milling zirconia, wax or PMMA – then you’re already half way there! In general, I advise against going right from having zero milling in your lab to bringing in metal milling – it’s a little akin to biting off more than you can chew. However, the process and workflow of a successful zirconia milling laboratory is very similar to that of a titanium or chrome-cobalt milling laboratory.
It is important to note that you might not necessarily be integrating metal milling equipment with your existing CAD/CAM infrastructure. Depending on the focus of your lab and your client base, new or upgraded scanning systems and/or CAM software may be necessary to achieve desired results (for example: implant bar manufacture places different demands on the CAD/CAM system compared to crown and bridge work). The thing to keep in mind is that if your team already has a good foundation of knowledge in CAD/CAM, the learning curve for new technology will be much more manageable.
2. Your Clients are Asking for Added Value from your Lab
Ever turn work away? Or worse yet, take a case on just to realize that it’s costing you money because you have to depend heavily on outsourced work to complete it? If your clients have been asking your lab to provide additional services and they’ve been doing it for a while – you have a market in your area that is hungry for a more capable and comprehensive laboratory to meet their needs. There are many ways to quantify this potential, which is a very necessary step on the path to making a business decision. Many labs will survey their client base, either via email, snail mail survey, or with a phone outreach program. If your clients aren’t getting their milled PFM crowns and bridges or titanium bars and abutments from your lab – where are they getting them? And most importantly, would they consider using your lab for a source of these units if you were to offer this service? This approach gives you a good idea of what the initial revenue impact will be if and when you begin to market additional capabilities.
3. Your Monthly Cost for Outsourced Milled Units is Regularly Greater Than $6,000
A few chrome-cobalt copings here, couple of abutments there, that bar case last week, plus the full arch that you weren’t quite sure your light duty table top mill could do a good job with…. It adds up quickly doesn’t it? Sure does. If you already have CAD/CAM technology in your lab and you’re confident that your client base would send more business your way if you had the capability in house, then it’s time to brush the dust off the last 18 months of your lab’s financial records. Why? Because the first two criteria alone are not sufficient to justify an equipment purchase. In order to move forward in full confidence that you’re making the right decision for your business you need to analyze your lab’s outsourced consumption for at least the past year and a half, preferably longer. This will give you both reliable information on both how much your lab outsources in an average month, but also data on growth trends which will allow you to forecast your labs needs in the future. The more data you have, the more clarity and confidence you will have in your decision.
Why are we looking at outsourced cost per month? Viewing the situation in this manner allows us to break the big question; “Will this equipment investment yield a good return?” into an easier question to answer; “Will this equipment make my business money on a monthly basis and if so, how much?”.
With the significant investment that is required to bring qualified metal milling equipment into your lab (generally from $100,000 to $300,000 or more) it is quite common for business (dental labs or otherwise) to lease the equipment instead of going with an outright purchase. In addition to making a “monthly ROI” easy to calculate, many financial advisors will tell you that leasing is the preferred method for purchasing capital equipment as it allows your business to maintain financial liquidity. Typical lease packages for manufacturing equipment will have a $1 buyout at the end of the lease period – so your manufacturing can continue uninterrupted at the end of the lease. At common rates, the monthly payment for a five year lease on a quality piece of milling equipment that is robust enough to handle regular milling in titanium or chrome-cobalt will range anywhere from $2,000 to $4,000 per month. With this in mind, a lab that consistently outsources $6,000 per month will see a return on investment in just over 2 years.
Many labs put off the decision on whether or not to adopt titanium or chrome-cobalt milling capabilities out of a fear that it’s too complicated or too costly, and for some labs it is. But when emotions are removed from the equation and the situation is reviewed logically, lab owners are often surprised at how easy and beneficial of a decision it can be.
Download Brochure detailing a Business-in-a-Box solution that delivers an all-inclusive CAD/CAM production center for screw-retained & fixed restorations.
The term “High Speed Cutting” (also known as high-speed machining) is one that has grown in the manufacturing industry significantly in the past 5 to 10 years. In spite of its newfound ‘buzzword’ status, the definition of this process remains somewhat elusive, or at best is defined loosely as simply milling at a sufficiently high RPM. The reality of high speed cutting is a bit more nuanced, but nonetheless demands attention due to the significant efficiencies it affords. In this post we will take a look into the inception and development of the high-speed cutting as a process. Research and development of high speed cutting methodology was advanced most significantly in the late 70’s and early 80’s by way of the Advanced Manufacturing Research Program, funded by DARPA. The goal of this program was to identify a means of faster material removal by use of significantly higher RPM and feed rates than were traditionally employed. This program tested cutting speeds (Vc) that ranged from as little as 0.05 in/min to as high as 960,000 in/min and beyond. Similar research was being done in Europe during the mid 1980’s at the Technical University of Darmstadt. The results of these research efforts was the realization that the ‘sweet spot’ of a high speed cutting process varies depending on that material being milled as well as geometry of the cutting tool. In general, these sweet spots are defined as follows:
Once the threshold into the HSM range has been reached, the benefits of this cutting method start to show themselves. The advantages of high speed cutting are realized in four major areas:
1.) Increased machining accuracy
As the cutting speed increases, the cutting force decreases due to a phenomenon called thixotropy – or the property of a material to be “work softened” due to the shear strain imparted on it by the tool’s cutting edge, and then to revert back to the original hardness properties once the cutting process is complete. This property is particularly true for aluminum alloys, which makes aluminum an ideal candidate for high speed cutting processes.
2.) Improvements in surface finish
General machining knowledge tells us that friction heat in a milling processes is generated equally on each side of the tools cutting edge (accounting for nearly 80% of all induced friction heat) with another 20% being generated by the deformation or bending of the resulting chip. In a high speed cutting process the chipload is evacuated at such a high rate that the majority (approximately 60%) this friction based heat does not have sufficient time to conduct into the surrounding workpiece or to the tool itself. As a result the machined surface finish exhibits superior quality with an appreciable reduction in temperature induced workpiece degradation.
3.) Reduced bur formation
Based on studies focused on high speed machining best practices, a notable decrease in bur formation is observed once a sufficiently high cutting speed has been achieved. This reduction in bur formation is a function of both the cutting speed itself but also proper geometric design of the cutting edge. In short, a cutting tool that has been properly design to suit the work material which is rotated at sufficient speed affects a cut that is rapid enough to shear the material completely and cleanly – thereby reducing or eliminating the formation of a bur.
4.) Improved Chip Evacuation
Similar to the reduction in bur formation, the improvement in chip evacuation enjoyed by those employing high speed cutting practices is primarily a result of the cutting tool geometry combined with the high energy state produced by the RPM being applied. With a cutting speed in excess of 500 m/min, and a cutting tool optimized to evacuate a large volume of chips in a short period of time, the resulting chipload can be ejected from the processing area with a high velocity, greatly reducing the possibility of re-machining of chips or damage to the work piece due to an abundance of residual chips. With spindle speeds in the range of 8,000 to 12,000 RPM becoming very common in the machine tool market, the ability to leverage the advantages of high speed cutting in steel, cast iron and nickel-based alloys is already available to manufacturers who are willing to adapt their strategies to those that fit with HSC best practices. High speed cutting of non-ferrous materials such as brass, aluminum and engineered plastics demands a significantly higher RPM capability, and as such those wishing to take advantage of the benefits of high speed cutting for these materials must focus on milling equipment capable of operating at high speed spindle speeds of 25,000 to 50,000 RPM or more. With the need for machined parts which display ever increasing levels of precision and quality, high speed cutting offers a means of working “smarter, not harder” – by taking advantage of a CNC milling system where a synergy between material, cutting tool and cutting speed allows performance levels unseen in traditional machining practices.
Learn More: Download the High Speed Cutting White Paper:
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