Gear Haiku (Spring Fever in Wisconsin, Part II)

Design for function
Involute geometry
Mesh efficiency

Plastic injection
pressures, time, viscosity,
control the process.

Base arc inspection
roll test for consistency -
passes C of C.

Gear Design in Limerick Form (a.k.a. Spring Fever in Wisconsin)

(based on actual experience)

We once heard a gear box quite noisy.
So we flew engineers to Boise.
With prototyped gearing,
And straining of hearing,
There’s now no more sound from the toy’s knee.

Check out the tolerances on that…

Last week, I attended two back-to-back courses in geometric dimensioning and tolerancing, aka GD&T.   GD&T is a symbolic  language that connects engineers and inspectors the world over by creating a standard of communication on all blue prints.

I have had a special interest in GD&T for a while now and even requested a copy of Geo-metrics III by Lowell Foster for my birthday present last year.  That was not a typo – I actually requested a GD&T book for a present.  (This could be used as proof that engineers don’t have personality, but I would have run some numbers on that…)

The four days of training from the International Institute of Geometric Dimensioning & Tolerancing (IIGDT) covered many aspects of the ASME Y14.5 1994 standard including:

• Explanation of the 14 GD&T symbols with emphasis on the position and profile symbols
• Datums
• The feature modifiers for Maximum Material Condition (MMC), Least Material Condition (LMC) and Regardless of Feature Size (RFS)

I particularly enjoyed an in-depth discussion about the use of zero tolerance for holes at MMC to aid in the manufacturing of parts.

This course is not only applicable to the gears that we make, but the tools we use to mold them and the fixtures we use to test the conformance of our gears.  The education I received will be used to continually improve our blueprints, production techniques and inspection methods.

The Road to Micro-Molding

For a few years now, we have occasionally designed and molded very small gears, which have been a unique challenge to design and produce this type of gear.  It is quite a change from the larger gears with which we normally work.  By very small, I mean gears of 100 DP or greater, having 100 teeth per inch of pitch diameter or more.  The principle differences between micro-gears and their larger brothers are easy to catalog:

• The gears are very, very small, which means they have small intricate features that must be molded exquisitely.
• Micro-tooling is required for micro-gears.
• Very little material is required to mold these gears.

These differences create a challenge for the molder.  Most molding machines have large screws that are capable of injecting large volumes of plastic.  However, when molding very small gears with the very small quantities of plastic required, the process is like trying to extract a single drop from a gallon container – it can be done, but control is difficult.

One solution to this dilemma is to inject more plastic into the mold so that you create one little gear and one great big runner.  This can work quite well and we have molded gears in this fashion.  Unfortunately, this method wastes a lot of material and it causes a long molding cycle to assure that this large runner freezes enough to be ejected from the mold.  The gear itself may take only a few seconds to freeze into shape, while the  runner could easily take 10 times longer.

The next big challenge is simply handling the part after molding.  How do you grab a very small part, assure yourself that it has been molded correctly, and then put it in the right location?  Very small parts can’t be just dropped into a bin; they act more like dust than pieces of plastic.

The traditional approach to this problem is to use a traditional injection-molding machine which has been reduced to the smallest possible tonnage and injection capacity, make smaller tooling with smaller runners, and use robots to handle the parts being molded.  We’ve done this, too.  It can work, but the approach is similar to whittling down a baseball bat to swat a fly.  It creates problems – two of the biggest problems are timing and real estate.

Timing is an issue because a lot of things have to happen very quickly to make a cost-effective micro-gear.  The molding process will only require a few seconds.  All of the rest of the time will be used handling and inspecting the part.  Remember that we need inspection or verification because these parts are so small. It is quite possible to mold all day long with nothing being made because a passage was jammed or some such thing.  Since you can’t see the part, you can’t know if it’s being made without some independent verification, which video cameras can provide.

So we need to handle the part, inspect it, and place it in the proper container.  This takes time and requires real estate.  The robot has to remove the part, place it over a camera, and then move it to a selected storage container.  Usually there will be 3 container choices:

• The first container will store production parts.
• The second will store parts to be inspected more completely for statistical control.
• The third bin will store rejected parts.

Traditional robots and molding machines don’t have a lot of real estate for these actions and the molding stops during the majority of robot actuation.  There has to be a better way, and I think we found it.

Battenfeld has developed a new molding machine called the Microsystem 50. They have taken a fresh approach to the challenge of micro-molding and I think their work shows a lot of promise for precision micro-gears.  First of all, it’s a system – not just a molding machine.  Everything is enclosed in a single cabinet – molding, handling, inspection, material drying, and cooling are all enclosed in the workspace.

Secondly, Battenfeld chose to use a rotary shuttle with a mold at either end, therefore while one part or set of parts is being molded, the other frame is being relieved of its molded part.  This in itself nearly halves the required time for molding.  Rather than using one big mold and waiting for it to be unloaded, two smaller molds are used with one being unloaded while the other is making a part.  It is elegantly simple.

The Microsystem also opens up space.  The mold that is being unloaded is now entirely open to the robot handling system.  The robot has direct access to the face of the open mold – it can grab the part, present it to the camera and then bring it to containers or a belt or just about anything else the designer requires.

Battenfeld has also dealt with the auxiliaries.  The camera and robot are integrated into the basic machine controls, so you don’t need another keyboard to interface.  They have incorporated a small material drier into the Microsystem.  This is very important since most driers dry many pounds of material, while a complete day of molding with this machine might result in just few pounds of material usage.

Since the Microsystem is integrated in a single case, the molding environment is entirely controlled.  De-ionized air can be flooded into the space to control static. HEPA filters can eliminate dust.  Their method of injection is also unique.  They have a small screw that melts the pellets and feeds a plunger that prepares the next shot.  The shot is then charged into the final injection plunger and the entire melt is injected.  There is no possibility of material being left in the injection screw.

An even greater advantage is that the runner is simply there to feed the part. It becomes a nearly trivial attribute of the molding process. Did I mention that a sprue picker is also part of the system to ensure that the runner ejects as it is supposed to?

We think that this system will make it possible for us to produce the most accurate gears possible, and accuracy is the gold standard in this field. One does not have much tolerance to work with for micro-gears.  So, this is the logic behind what has brought us to this new molding solution.  We are building our first tools now and, in a few months, I’ll let you know how well we fared.

There are a lot of other challenges to making a successful micro-geared transmission.  The design of these little custom gears is critical. Just as there is no margin of error possible in molding, there can be nothing overlooked in the design.  We believe that micro-gears are an ideal application for our shape-form process of design.  Testing is also taken to a new level in micro-transmissions – the drive torques are so small that simply driving the gear train and trying to dynamically measure torque output, efficiency, and train accuracy is a daunting challenge.  I will further discuss our work in this area in future posts.

Real-World Math for High School Students

This week, we were happy to host geometry students from the local high school at our facility.  Grantsburg High School teacher Jay Gilhoi works every semester toward giving his geometry classes the privilege of some real-world math experience.  I think Jay has the right idea, and I’m happy he found Kleiss Gears to be a suitable partner.  Kleiss Gears’ employees enjoy taking the time to show students what we are all about.

One or two of our engineers go to Mr. Gilhoi’s classes for a day and explain to the students about the company and why gears are important to many industries.  The students also take a short field trip to our facility where they receive a plant tour that walks through the basic concepts behind Kleiss Gears’ philosophy about gear design, injection-molding, and gear inspection.  They get to learn first-hand how and why gears work, see the various instruments used in our inspection lab, and ask any questions they come up with.

Personally, I would find the whole experience quite fascinating if I were their age again.  I don’t remember if I saw anything about what people in the workforce did when I was in high school.  When I walk a group of kids through what we do here, my hope is that something sticks with the students that they can remember.

Maybe the experience piques interest in what a student wants to do after high school; maybe it does just the opposite and points a student in a different direction.  Either way, the students know more than they did before they visited us, and, in my eyes, when students are learning, the world is becoming a better place.  I’m glad we can help be a part of educational program like this one.

An Out-of-this-Country Experience a.k.a. Advanced Inspection Training from Werth

This past fall, I spent two weeks in Giessen, Germany, the home of Werth, Inc.  Werth makes precision inspection equipment, including the Coordinate Measuring Machine (CMM) we have here in our inspection lab.  When visiting Werth, I received a one-on-one advanced programming class which provided me with programming skills I can now use to better communicate with our CMM to tap its full potential for gear inspection.  We are inspecting features that are between 0.005 and 0.010 inches in size, and when we start making features smaller than that with our new micro-molding capabilities, we can measure those too!

Our Werth CMM has the capability of measuring precision parts either with video optics or with an inspection probe.  (Many CMMs are equipped with only one of these options.)  With this machine, we can scan a work piece with a probe which records data points on the surface of a part that we use to compare with the nominal shape of our part.  We can then scan the same part with the video optics, which is quicker to execute, but sometimes produces inconsistent results since the no-touch optics will sometimes interpret dust and small debris particles as part of the work piece – unlike a probe that can push these particles out of its way.  For this reason, we start our inspections of parts using a probe and we often use the video optics to verify the part-to-part consistency.

This was the first time I visited mainland Europe in my life.  I mainly stayed in the small town of Giessen, but it was beautiful in November.  The food sampling was a great experience and the folks I met appreciated me trying to speak their language (I took German class in high school but did not retain much of it) and helped me out when I had problems by speaking English to me.

It was a great experience for me to learn more about the world and my work and a needed experience for Kleiss Gears to have this programming knowledge to ensure we are inspecting pieces to the highest level of precision and accuracy possible.

Sounding off in Machine Design

Machine Design’s November 6th issue published my letter in response to their editorial piece on MPG figures.  Check it out here.

Welcome to the The Gear Ring!

At Kleiss Gears, our mission statement is “To make the best gears on the planet, and to have fun doing it”.   With this blog, I hope to share some of the behind the scenes stories of our process, our successes (and challenges), and to give you a look into the fascinating world of transferring power from point A to point B.

Kleiss Gears “The Gear Ring” blog opens

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  The engineering team at Kleiss Gears is serious about the science and methodology of polymer gearing - and not much else.
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  • Gear Haiku (Spring Fever in Wisconsin, Part II)
  • Gear Design in Limerick Form (a.k.a. Spring Fever in Wisconsin)
  • Check out the tolerances on that…
  • The Road to Micro-Molding
  • Real-World Math for High School Students
  • An Out-of-this-Country Experience a.k.a. Advanced Inspection Training from Werth
  • Sounding off in Machine Design
  • Welcome to the The Gear Ring!
  • Kleiss Gears “The Gear Ring” blog opens

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