I am starting to get this LinkedIn thing. Articles get hundreds of views and posts get thousands, even tens of thousands. So, I am going to condense and repost some things from earlier articles.
Most toolholders other than side-locks use friction to hold the endmill shanks. So you need help to get repeatable tool changes. We found these wrench-free aluminum shaft collars from @Ruland. The aluminum won't damage the cutting edges and holds up to the heat of shrinking.
Starting with a balanced and preset tool assembly. Slip the collar over the endmill until it it against the end of the toolholder. Use the slot in the collar to orient the tip of one tooth, like a gunsight. Look through the slot and rotate the collar until the tip lines up with the slot. If you are using variable pitch endmills, identify tooth #1 and set to that each time. Close the collar lever. Put a witness mark on the end of the toolholder (an automatic center punch works well) and use that as your target when orienting the new tool with the collar's slot. You can use a caliper depth rod or depth micrometer to record the collar location from the tool point. Remove the collar and place on the next sharp endmill at that measured depth and sight in a tooth. Balance and offset are retained with each tool change!
We don't want our airline pilots to fly by the seat of their pants and by just looking out their windows. We don't want our doctors to diagnose us by just putting their hand on our forehead. Even in machine shops, we don't ship parts that just look good, we measure and approve them, but for some reason, deciding what speed to run a cutting tool is still treated as some sort of magical black art knowable by only a precious few. Applying science and technology has been met with resistance. We have had wrenches thrown at us on shop floors and our cars keyed in plant parking lots. We have had more than one operator intentionally override the speed we gave them to make sure the tool snapped off during our demo. We do this at our own peril. Having "magic ears" is not a teachable skill, nor does it really produce optimum results. Who is going to setup tomorrow's jobs? We are freely sharing what we have learned and discovered now, in this venue, in hopes that we can reach a larger more receptive audience and help the industry move forward.
By the way, Dr. Grace Hooper (1906-1992) was a pioneer in computer languages and invented COBOL which is still in use today.
One more time. Figure 1 are the stability lobe diagrams for the same endmill in the same machining center, sticking out exactly the same amount from five different toolholders. Which one is the shrinkfit? The hydraulic? The power shrink? The milling chuck? The side lock? I am not telling (and not stupid enough to do so). In Figure 2 we changed to the same type endmill, but longer, and you can see the results are vastly different. Winners and losers are different. Take-aways: you cannot predict the best toolholder without measuring the system's dynamics and shorter is not always better.
Here is a cool tip. NASCAR pit crews glue lug nuts to wheels to speed tire changes during pit stops. We applied this to carbide inserts. Use small rare earth magnets to hold the insert and a replacement screw. The inserts have enough magnetic material in their substrate to hold them in place, but the steel insert screw will hold both securely. You probably should replace inserts screws more often than you do (have you ever stripped the head and everything came to a halt?), but here you can at least alternate them and inspect them while the machine runs. It is easy to grab the insert/screw and pull it away from the magnet and you are ready to reload.
Milling tools can be removed from the ATC to change inserts if you have redundant assemblies, but turning toolholders and boring bars usually stay in the turret so changing inserts is serious downtime. We actually devised this for a customer who's machinists were often not using the second edge of the insert, doubling their tooling cost. They used a Dremel grinder to break off any built up edge and a Sharpie to mark the used edge. Then they could stage the next index with the magnets.
Once during a gain share exercise with an aerospace company we calculated that their centralized tool crib to issue and change cutting tools added 20% to the true tool cost for this facility (one location, not a definitive study). We have also had to wait extra days because vending machines ran out of the tools we were onsite to test. The reasons for this are in a prior article: https://goo.gl/h6rDKX
Now, what if you had a mini-vending unit that dispensed only the consumable cutting tools for that machine or cell? Maybe it would be a portable electronic tool box that the machinist picked up at the crib before each shift (I saw a concept of something like this in the UK, don't know if it ever made it to market). What if it could capture not just the units, a time and date stamp, but also the current part count when the tool or inserts were changed? Below is the kind of actionable data that you could calculate if you added just this one more piece of information.
My colleagues Dr. Andy Henderson and Dr. Dean Bartles have written great pieces about the future of machining (links below). I would like to humbly add my two-cents. I am guided by a graphic that appeared in an issue of Morris Group’s Throughput Magazine. I recreated it below. Essentially, we must bring functions, capabilities and supplies closer to the point of use, closer to the machine and the machinist.
You can already see part of this with the latest design of Haas machining centers. They include a workbench, tool clamp and storage rack for toolholders. What if builders also had options for a mini heat shrinker, PG or Tribos clamping unit attached to, and powered by their machine tools? Vending machines are big, expensive and centralized. What if there was a mini-version on the machine that dispensed consumables used by that machine? It doesn’t have to be expensive or complicated. Lamina designed a clever package for dispensing their carbide inserts that can be attached to the machine’s enclosure. What if you added something like an Amazon Dash Button or a smartphone app to capture tool consumption at the point of use? There are some real advantages to this that I will mention in my next post.
There are three types of vibration in the physical world and this is how they apply to my favorite subject, Milling.
FREE vibration occurs naturally in an object and can dissipate over time. On a machine tool, a cold spindle may start off running a little rough, but as temperatures rise and lubrication gets to the bearings and the vibration subsides.
FORCED vibrations are those that are introduced to an object. Runout or unbalance in a tool assembly will create a once per revolution frequency. It is consistent, no matter what speed the tool assembly is rotating, it will always be once per revolution.
SELF-EXCITED vibration is the third and post challenging. It comes from an external force acting on an object. A tooth on a milling cutter strikes the workpiece and the force causes the tool to deflect. It rebounds back, but if the timing of the next tooth is off it either undercuts or overcuts changing the force and amplitude of each deflection. This modulation of the cutting depths of each tooth gets worse leading to chatter and tool failure.
A great example of self-excited vibration is the infamous Tacoma Narrows bridge, known as "Galloping Gerdie".
While it may be dubious that a human can accurately count the number of tooth impacts a milling cutter makes in one second, a computer can. Here is a demonstration of a version of Harmonizer software invented by our colleague Dr. Thomas Delio and the team at the Machine Tool Research Center at the University of Florida, patented way back in 1990. Harmonizer uses a microphone to record the sound of a milling cut, filters ambient noise, recognizes chatter frequencies and calculates a correcting stable speed. This is a "reactive" solution in that the process must be in chatter for it to work. We include this version with our "predictive" tap-testing software. A more advanced analytic version is available from Tom's company, Manufacturing Laboratories Inc. (MLI). Okuma's NAVI works in a similar manner using both audio and sensors.
You may have heard of a machinist who supposedly could optimize a cut by just listening to it.
Is this possible?
A stable milling cut has a pure sound. The tool point frequency (it’s back and forth vibration) matches the tooth impact frequency or one of its harmonics (more on that in another post) and therefore each tooth impact depth is equal. If there is a mismatch of these two frequencies, the tooth impact depths are unequal and this creates a feedback mechanism that, if large enough, will make the harsh sound we call chatter.
Here’s an example (from Dr. Scott Smith): a 2 flute endmill cutting at 15,000 RPM will have a tooth impact frequency of 30,000 per minute (2 teeth x 15,000) or 500 impacts per second (30,000/60 secs). That is expressed as 500 Hz. Now let’s say you hear chatter and then identified the frequency as 427 Hz. You would simply multiply 427 x 60 seconds and divided that by 2 teeth and you would come up with a stable new speed of 12,810 RPM. Problem solved.
But, can a human ear really hear and count an exact frequency that is in hundreds of cycles per second? There are people with “perfect pitch” but that requires them only to make a go/no go decision of a known frequency, such as a specific pitch for tuning a musical instrument.
With all due respect to additive, subtractive machining lives!
I need to put your big brains to work out there. I have a question to pose.
Ian Morton pointed out that there is now programming/design software that enables the inherent unbalance of spiral fluted endmills to be corrected in the grind by removing mass using the wheel washout. Haimer uses this.
Let's assume that the retention knob on steep taper tools could also be balanced with the right fixture, though I don't know if anyone does this (not an issue with HSK) and that the toolholder has been balanced by removing mass with drilled holes. Here's my question (maybe two):
If I have three (or two) balanced components is the final assembly then balanced?
Or, will the orientation of the components in relation to where each had mass removed to balance them make a difference?
I have been in many shops where it seems an extension of the tool crib is the back of the UPS truck. It would pull up and several machinists would be tearing into boxes looking for tools they needed that were shipped in.
You know what's crazy?
Amazon has an app called Package X-Ray where you scan the label and it tells you what's inside before you open the box. It was developed as a consumer service and only works with their shipments but a pretty darn good idea for business.
I am not one to quote ancient Greek philosophers and I have no idea what Euripides was going for here, But I am going to co-op it for my purposes anyway. I had an slightly odd experience at IMTS. We were demonstrating our new tap-testing software that instantly predicts the best speed for a milling tool. If I do say so myself, some pretty revolutionary stuff. Almost everyone we showed it to instantly replied with "What about the workholding?". Mind you none of these people made or sold workholding, they were in the tooling business. It was all very innocent, though sometimes we do run into people who are contrarian just for sake of being contrarian. Not on this trip, well maybe one :).
Years ago at a seminar, my friend and colleague, Dr. Tony Schmitz slightly exasperated from the fifth or so, "But, what about...?" question, replied: "How about let's fix what we can fix first?"
In other words, let's get the tooling right and if there are still workholding issues, you know its not you. It's not wrong to ask questions, but sometimes you have to go with an answer just to get something done.
Now, Euripides was to have also once said, "To a father growing old, nothing is dearer than a daughter." Amen, brother.
On the north east corner of the Penn State University campus is a remnant of the history of metalworking in America, the Centre Furnace. The Centre County region was rich with iron ore, limestone and lumber, thus became home for dozens of iron producing furnaces and forges in the 1700’s and 1800’s. Many are still in existence. These integrated ironworks produced tools, weapons, and cooking implements. The emergence of new steel making processes and shortages of natural resources led to the demise of these furnaces. The owners of Centre Furnace donated 250 acres of their property for the founding of the Farmer’s School in 1855, which later became Penn State University. Drive by it every day.
A typical car tire on the highway at 60 MPH is rotating at 700 RPM. If a wheel and tire assembly loses one of its balancing weights, you would immediately feel the forced vibration in the steering wheel and the ride of the car. If not fixed, over time the tire would wear unevenly and the bearings in the wheel hub (and other components impacted by the vibration) would likely fail sooner.
Knowing this, why do we put a minimum limit (e.g.>10,000 RPM) on balancing tool assemblies in CNC machines?
As we described in earlier posts, there what is called Process Damping (PD). The PD range starts at 0 RPM up to a speed where the geometry and edge prep of a tooth, "rubs-away" or dissipates vibration before the next tooth arrives. With some tools, this region has a very low max RPM, some are very high.
Here are two stability lobe diagrams of the same 1/2" 4 flute endmill in the same toolholder in the same machine. Figure 1 used the standard process damping wavelength for alloy steel. The PD region is the area from 0 to 6000 RPM. Figure 2, the PD wavelength was updated experimentally through guided cutting tests. That raised the PD almost two fold to 11,500 RPM.
The green area is the max SFM for this tool in this material (the pink area is the power curve of the spindle). In other words, this endmill could be run at the SFM limit (7500 RPM) at full depth and full width. It couldn't reach this speed in the figure 1 diagram. So if you make or use carbide endmills, the actual PD wavelength is good thing to know especially in low speed, tougher materials. Of course, it is not that easy. Even with an updated PD wavelength you still must tap-test the assembly in the machine to determine the PD range on the lobe diagram.
A Wikipedia article entitled “Speeds and Feeds” describes this:
“...the operator fine-tunes the (speed and feed) values while running the machine, based on sights, sounds, smells...".
At least for milling, there are technologies now available to quantifiably measure a tool in a machine and calculate its optimum speeds, feeds and depths of cut. As we face a skills gap in manufacturing, we need solutions that can succeed those "magical eyes, ears and noses".
That's it for now, off to Chicago!
I gave my highly qualified "depends on what your definition of is is" answer. Here's another response or a different reason.
An application engineer at Gosiger told me this: If you use dual contact holders, no debris or chips can get into the gap between the flange and the spindle face when it is in the spindle. If you use all dual contact holders this area stays clean. If you introduce just one or more gapped holders, chips and debris could accumulate when those tools are in the spindle and the when the next dual contact is indexed in you have mis-load. Conversely, if you used all gapped holders this debris will likely stay where it is and the subsequent tools would not mis-load.
The answer? Don't mix dual contact and conventional gapped holders in a dual contact spindle machine. If you have no choice, consider gluing in gasket material to close that gap. It won't improve anything stiffness-wise, but will keep the crap out.
I get this question a whole lot:
"Does Dual Contact (aka BIGPlus) make a difference?"
Before I answer, let me say that we are neutral. We are not endorsing any product or brand or system. We only have our experience of testing tens of thousands of tool assemblies.
So, the answer is: MAYBE...PROBABLY...MOST OF THE TIME
The reason for that non-answer is that if we are comparing a dual contact (where the taper and flange have simultaneous contact with the spindle) tool assembly and a conventional gapped one they are never the exact same dimensions of projection, wall thickness, taper, weight, etc. So it is not apples to apples and we don't know what really causes the differences in measurement results and performance. But, we have a good idea. So, in most cases the dual contact tool is stiffer and stiffer usually leads to higher speeds. Usually. Sometimes the added stiffness puts the most stable lobe beyond the speed capacity of the machine. Some longer, smaller diameter endmills or long projection holders are so flexible that they really don't benefit from the added stiffness of the dual contact.
I have learned of another non-scientific answer and I will post that next.
I recently watched someone tapping their endmill with a brass hammer to reduce its runout. I didn’t ask how long he expected that to last.
To paraphrase Mike Tyson:
"Zero runout won't survive the first impact of the first tooth"
Don't mis-understand what I am saying here. Runout is bad. Concentricity is good. But, all milling tools are flexible (after tap-testing tens of thousands of tools have yet to see one with zero deflection). If you have a concentric and balanced tool running at the right speed and depth of cut for its frequency, you are the champ.
If you attend IMTS, you will see a lot about Industry 4.0 and IIoT. Basically, it is using sensors to monitor a machine and collect data on its processes. There is some real value there, but what if you have a sub-optimal process?
You will be able to calculate OEECP (Overall Equipment Effectiveness of a Crappy Process).
Machine tools are not yet self-healing, although there are products like Caron's TMAC and Okuma's NAVI that will adjust feed rate or speeds and probes can update offsets. But, the distance between cruise control and fully autonomous cars is still quite large. Today, sensors cannot take a bad process and automatically make it a good one. Monitoring is reactive and there is still need to be predictive.
We cannot yet replace the skills needed to select the correct tool components, assemble and balance it correctly, find its optimum operating parameters and build the correct fixturing. We are using science (and yes, sensors) to help improve set-up and deliver optimized milling processes to be monitored. Gee, I guess we ARE Industry 4.0.
by Dr. Scott Smith, UNC Charlotte
June 19, 2014
1:39:12 Run Time
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Presented by Dr. Tony Schmitz and Dr. Scott Smith, University of North Carolina at Charlotte
Run Time: 11:32
Self-Grading Quiz Included
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Sharing information about high performance milling technologies, the result of 30 years of research.