Robots have come a long way…

I remember when I first started working with robotics on molding presses. Back then, they had to be adjusted by climbing all over the robot, and the programs were only capable of the basic “L” and “U” movements. In many cases the drop zone location on the up and down movement had to be set the same as the pick location on the up and down movement. The presses would have a mechanical stop to hold the mold in the open position and an alignment pin above the locating ring on the front half to verify that the mold was perfectly aligned each and every time it was set in the press. Even with this it was a challenge to keep everything aligned. It was also very important for the oil temp to be correct at startup. Old hydraulic presses would not open to the same distance or eject the parts correctly at the wrong oil temperature. You would need to re-adjust after running for a few hours or even days. It was an ongoing battle keeping everything lined up. The robots had pneumatic up and down movement with a servo drive existing only on the traversing and kick movements. For something designed to make a processor’s life easier they certainly brought their fair share of pain!

But like all newer technologies, issues were addressed one by one and improvements came out consistently. We now have servo movements on all three axises, with options for rotation and flip servos as well. We are able to tie the robotics directly into the process monitor on the press and automatically divert parts at startup and any time the process parameters move out of tolerance.

We continue to install alignment pins on the front half of the molds but the newer presses hold the open position / ejection forward position much better (especially newer electric presses). Now robots have evolved from the painful era of trial-and-error setup to a nearly scientific setup and operation.

I have worked with many different models and brands over the years and have been lucky to have worked with some of the best built and best supported robots on the market. Recently I attended a Flex Teach class for Yushin robots. The Flex Teach system allows the user to create motion programs for the robot using a personal computer. The same programs can also be modified using the touch panel controller. What I like best about the Flex system is that it utilizes the PC as a training tool for the robot when it is offline. This can save countless hours of down-time and allow operators that would not feel comfortable practicing on a live press to start learning the Flex Teach system. Just knowing that they won’t have to worry about damaging expensive molds or end of arm tools (or more importantly, themselves and others) opens the doors for every operator to catch up to speed.

Even robotic systems from just a few years ago were no comparison.They, too, were fully programmable and also had servos with CNC type controllers, but these models required hundreds of command lines and an extensive knowledge of the programming language to run. The program itself consisted of several parts:a run program, reference program, and home program for every job.Making adjustments to a program became a trial-and-error nightmare.More importantly, valuable press time was lost in the mix.Considering today’s shortened deliveries and 24/7 production jobs, fiddling with the programs is something most molders can live without.I wish I could have done some of the work offline with a program tool like the Flex Teach system.We now have the ability to take our time (with minimal pressure) and do most of the programming offline while the press is still running.

With the old system, programming mistakes would have to be caught during the standard process of verification referred to as “stepping through the program” and tweaked accordingly. The Flex system allows us to run the program or changes through a simulator and verify that it looks good on the computer screen before being transferred to the press via a SD memory card and loaded onto the robot.For good measure we continue to step through the program to verify a second time, but there is no doubt this saves time in the process.

All of these new features have made robots perform more consistently and adds to their versatility, performing tasks like sorting, de-gating, counting, boxing, and stacking.Robots can even place small inserts and verify their placement these days.

So molders, learn to love your robots. They work tirelessly, exactly, and without a complaint or absent day. They can be a molder’s best friend (though you can still keep the dog). Yes, robots surely have come a long way!

 

Written By:

Pat Collins
Molding Operations Mgr.

My favorite part about working on R&D projects is that they tend to challenge you to think outside the box, try new things, and learn about the latest technologies.  One of our recent development projects involved injection molding a long, thin-walled tube (picture a miniature drinking straw) with a wall thickness that shrinks down to .0035” over its nearly half-inch length.  By comparison, that’s roughly the same thickness as a human hair.  Even after running dozens of Moldflow® studies for gating locations and flow analysis, the only thing we were confident of was that it was going to be a challenge to fill the parts out completely.

After struggling on our first sampling, the instinct was to look for higher flowing materials to help make the distance more manageable.  We started with a PE material with a Melt Flow Rating (MFR) around 50 g/10min and then moved on to a similar material with a MFR of 110.  We were expecting to see a noticeable improvement in the 110, but what we found was no appreciable difference on the fill.  It was determined that this was primarily due to leakage at the check ring / non-return valve, common to all traditional, reciprocating screw injection machines.

This brought us to one of the more interesting suggestions on the project.  We decided to sample the tool in one of Sodick-Plustech’s (SPT) micro injection machines.  This machine piqued our interests initially because of its two-stage (plunger-style) injection approach, but as we found is well-suited for this type of application for several reasons.

Like a traditional, reciprocating screw machine, Sodick’s two-stage injection technology (shown here) utilizes a small screw to melt and convey material.  But unlike traditional machines the screw is not responsible for injecting plastic into the mold (or any high speed lateral movements).  It feeds a second chamber, which is metered precisely, and then injected into the mold via a high-speed piston.  The feed screw shuts off after material is loaded into the chamber, which eliminates back-flow without the use of a check ring / non-return valve.

Photo courtesy of SPT

On this particular machine, the piston is capable of reaching injection speeds of 450 mm/s, which isn’t particularly impressive by today’s standards.  Many other press manufacturers tout injection speeds well past 1,000 mm/s.  Sodick, too, offers a high-speed/high-pressure line that boasts an impressive 1,500 mm/s injection speed, but their selling point is based more on acceleration than on speed alone.  The Sodick machine utilizes an accumulator that works with the main piston to reach maximum speed almost immediately upon injection.

The next selling point is the consistent shot sizes due to the tightly metered second chamber.  For our application, this is critical because an inconsistent fill could cause a short shot, which would be nearly impossible to detect with the human eye or a vision system during production.  On a project that could expand to a 16 or 32 cavity tool, this becomes increasingly critical to maintain good production parts.

Another positive about the machine is a more consistent melt and material residence time.  Again, the lack of a check ring helps by allowing for a more reliable first-in/first-out material path.  And since the feed screw isn’t creating excess heat via shear, the material is subject to more uniform heat profiles as it moves through the processing stages.

One last positive about the machine is the capability to swap out injection units (smaller or larger) and match them with differently-sized platen and tie bar configurations.  Matrix is running quite a few bioresorbable/bioabsorbable polymers lately which require minimal shot sizes due to the extremely high material costs.  However the molds associated with these projects are often complicated and require multiple side actions, slides, and/or lifters, so running them in a traditional micro-molding machine with a 4-inch max opening and similar small distances between the tie bars doesn’t always lend itself to the mold design.

Written By:
Andy Ziegenhorn

Plastics have long been associated with environmental unfriendliness and wastefulness of crude oil and petroleum byproducts. The advent of bioplastics (biodegradable and biocompostable plastics) which are derived from renewable sources such as corn starch or vegetable oil is helping to improve the image of plastics among those concerned with the environment, carbon footprints, sustainability, and being “green.” Bioplastics are slowly but steadily being improved, and in some cases their abilities to process and end-use properties can mimic or even surpass those of traditional petroleum based materials.

Bioplastics, aside from being derived from renewable resources, have the advantage of not releasing harmful toxins during their production, processing or degradation. Many conventional plastics can release known or suspected carcinogens such as formaldehyde or benzene during production, processing or destruction.

Growing the sources for bioplastics also reduces carbon dioxide in our atmosphere. Since the production of conventional plastics produces so much CO2 the use of bioplastics in place of a conventional plastic has a cumulative effect, with the substitution of just one ton of bio for conventional plastic having the net effect of reducing multiple tons of CO2 in the atmosphere. This not only takes into account the production methods for each type of plastic, but also the photosynthesis process in growing biomass or raw material for bioplastics. Bioplastics show great promise in reducing both our industry’s carbon footprint and impact on rising global warming.

What can plastics processors do until bioplastics are perfected in properties and reduced enough in costs to truly compete on a large scale with conventional thermoplastics? This is where the 3 R’s apply in injection molding. The 3 R’s in molding don’t stand for “reading, riting and ‘rithmetic,” but rather: reduce, reuse, and recycle. At Matrix Tooling / Matrix Plastic Products, we have been molding with bioresins, including bioabsorbables for a number of years, but as responsible members of the environmental community, we also have been practicing the 3 R’s.

Reduce: Scrap (and resin usage) is reduced through cold runner and sprue size reduction where possible without affecting moldability. In many cases we have reduced sprues and runners to the prescribed percentage of regrind allowed in the product specification. Hot runners and hot sprue bushings also have been used wherever possible. We have also thinned out wall stocks on parts where the product integrity wouldn’t suffer.

Reuse: We reuse what regrind we can and have come up with applications to use up to 100% in-house regrind. We utilize returnable/reusable packaging where possible and where allowed by the customer. We also have a closed circuit water system to reduce consumption and also filter, monitor and analyze hydraulic oil to avoid indiscriminate unneeded oil changes.

Recycle: Where we can’t reuse in-house regrind, we try to find it a good home. We sell the regrind where possible or even give it away for free if it can be used but there isn’t a paying market. Packaging is recycled also. We even collect our soda pop cans!

Matrix is serious about being environmentally responsible, using bioresins, and abiding by the 3 R’s. It not only makes environmental sense, but favorably affects the bottom line.

Written By:

Brent Borgerson

Senior Process Engineer (Older Molder)