I have similar experience in my 1993 Suburban and of course my 1968 Pontiac (though the latter has very little plastic parts for operational items). I know plastic degrades over time. This is particularily true when exposed to UV. What gets me, is cars that are less than 10 years old and the plastic is breaking.
Back in the day (meaning when I was younger), I had a 1984 Oldsmobile with power seat. The motor for the seat was coupled to the track drive with a plastic coupler. The first time it broke, I thought maybe I was the fault as I am heavy and I probably was to much resistance for the coupler. $25 later and about 1 month it broke again! This time I asked the parts guy about it. He said they break all the time. This is a design feature! What? Yes, the plastic will break to prevent overloading the motor!
My point is, new cars are being built with more and more plastic to make them lighter for CAFE standards to be met. Service will evidently become part of the design feature. get out your wallet or plan on trading in the car every 5 to 10 years before the plastic gets brittle!
Wow, what an experience--but it's all too familiar now with the rampant use of plastic parts in automobiles. I am old enough to remember the days of chrome bumpers that would stay intact if you just nudged a wall or another car's bumper--now we have plastic ones that crumble or dent at the smallest impact. (Yes, I know I shouldn't be running into things, but it happens!) Plastic is on one hand one of the handiest inventions ever and also one of the most evil, in my opinion anyway. Yes it made things cheaper and lighter, but it's also taken its toll on quality and the environment.
All plastic is by no means created equal when it comes to strength and durability. The problem comes when lesser materials are spec'ed that will do the job, but won't do it long enough. But there are some places it should not be used at all. One of my favorite little desk clocks is now trash because it was made with, get this, plastic gears! And crummy cheapo plastic, at that. Of all the dumb things to use almost any plastic for, gears must be at the top of the list. Kind of like the brass gears in my old pretty but now useless hand coffee grinder: an equally dumb idea.
@Ann: Material selection is important, but part design is another big factor. Engineers who are designing plastic parts need to understand the properties of plastic materials. Don't assume that they deform linearly. Don't assume that they won't creep at room temperature. Don't assume that they will respond the same to a quickly-applied load as to a slowly-applied load. Don't assume that the properties are the same in every direction. Don't assume that the properties on the datasheet apply to anything other than a test bar.
I continue to refer people to an article that appeared in Design News nine years ago by Joseph Ogando titled The Misunderstood Material. It is a very good explanation of what plastic material properties actually mean.
Dave, good point about engineers having to understand the unique material properties of polymers.
Creep, stress relaxation, outgassing. What? You're using nylon in water?
I think I'm the only one of the 50-odd engineers at my company that has actually taken a course in design using polymers. Whenever there is an issue with a plastic design I always offer to help. Have they done a Time-Temperature transformation? Have you figured out the apparent modulus so you could design the part to the expected service life based on the stresses it will see?
Oh well, I'm just the old guy...what do I know? :D
Of course, Ann, you are right. It depends, as you said, what type of plastic is being used and what is being made of the material. Gears! Now that boggles the mind...even metal gears wear quite easily if they're not made quite durably! Yes, that was definitely a corner that could have been cut a different way. Still, I do miss chrome bumpers and other external car parts made of sturdier materials!
I agree with Elizabeth. Plastic isn't necessarily 'bad' but it needs to be done properly. My personal opinion is that steel would be a better choice for that application giving the cyclical and shock loading as well as the temp extremes (windows are more difficult to move when the temp is below freezing).
As I've written before I worked as an engineer in the auto industry. It's all about cost. I didn't engineer parts to do the job at the lowest cost. Instead purchasing gave me a low cost part that fit their material cost reduction target and we had to engineer to work (as best we could).
Since you had to buy the window part it's obvious that the OE part lasted longer than 3 years or 36,000 miles. That's all GM cares about. In fact they don't want your car to last too long - they want you to buy another one. It's all short term thinking. I think the desire for fuel economy today might make this more of an issue. The desire for EPA number could drive more compromises in duraibility for the sake of light weight. About 3 years ago we were told GM would pay $1 per pound for weight reduction. Since we sold them a couple hundred thousand units per year it definitely got the bean counters' attention.
That's a really interesting insider perspective and not surprising, nyeng. I am sure that is a story repeated across many industries. Engineers do their job by thinking about what would work best and design products (cars, devices etc.) according to what would be the best material for the application. Then the number crunchers give them a budget and instructions for what materials are cost effective for the job. I am sure they often don't match up and you have to make do with what you can get! It must be frustrating sometimes.
As someone who molds plastic gears, I should point out that plastic gears work very well in some applications! The main benefit is they run quiet and some plastics self lubricate. I believe they found their way into clocks and watches is the cost to mass produce gears in plastic is miniscule compared to a metal gear.
I also think that plastic gears found their way into other products, like cars and wash machines, is the cost to manufacture the plastic gear is low. Also, the plastic gear runs quieter in operation. However, they may not always last as long as the metal gears and are subject to enviromental degradation leading to premature failures.
Also Ann, glad to hear your husband is still kicking. I chuckled when I re-read your reference!
Thanks for weighing in on plastic gears, GTOlover. Tiny cheapo plastic gears in clocks mean that those clocks won't last long enough, at least for some of us. Way, way shorter of a lifetime than metal. It was evident to me that they were yet another mass-production lowering-prices strategy. And the quiet is a good thing. But as Elizabeth pointed out, it was a poor design decision to sue that particular material. Not only do they wear out much sooner, but clock repair guys tell me they can't repair them. So I'm left with a nice looking shell--which, of course, no one's making anymore--and gears that don't work but can't be replaced. All destined for the landfill.
The place I worked during the 80s & 90s bought a new lathe... It had plastic gearing in the headstock. The first time one of the gears failed every guy in the shop took his turn walking over to the opened machine and laughing or shaking their head... or both... mostly both.
It was a nice lathe for light work but we had to bar it from doing the bigger/tougher stuff. I'm sure the company thought the price was right and had never read about the plastic gears until they were buying repair parts.
I use plastic to make stuff all the time here. Right now I'm doing my first fixture made with PEEK. It's about 15 times as expensive as Delrin... which I normally use to make the same kind of fixtures. The main property that I need it to have is resistance to high temperatures.
It may see the plus side of 400F for a couple minutes at a time (I'm betting 480ish because the plastic will slow the normal radiant skin cooling that occurs). It will also see some nasty torques and G loads while at the minus side of zero or the plus side of 120F though not at max temp. Delrin is okay for the torques, G loads, and even the middling temperature stuff... But it will never survive the plus 400F. And since the PEEK is supposed to be 'a replacement for steel'... I think we're good. We'll find out by Friday.
Thanks Ralphy Boy. You should have seen the look on my face when my clock/watch repair guy told me a) the gears were plastic and b) he couldn't fix it. I think I'd be even madder about it if I was forced to deal with them in a machine I used every day at work. I know darn well how amazingly strong plastic can be. But the material has to be fitted correctly to the design and the usage model.
I read in another blog that the European car manufacturers (e.g. Mercedes) use biodegradable plastic to "save" the environment. After a few years, while the car is still in service, the parts start to degrade all on their own. So even if they survive the stress and strain of daily life, they will still fail early.
Leave it to the Europeans to come up with a planned obsolescence scheme that makes the old American GM/GE plans look amateurish.
While I have NO specific knowledge or experience w/ th plastic coupler of your seat, I would opine a bit about the retort that you received from the "parts guy". I suspect that he was quick-witted and sensed your frustration w/ this obviously ill-designed piece. In that vein, he quipped that they break all the time & that it was designed that way to protect the motor. In truth, this fellow was so far removed from the engineering dept. where that assembly was designed that he more than likely had NO specific knowledge of the company's thinking or their response. He probably was playing on your emotions.....
There is a similar problem with Buick Century vehicles of about 2004.
The drive mechanism is a cable with ball on each end that drives the window via a plastic slider that has two fingers that catch the balls on the end of the cable. The assembly is in tension.
There are three cars in my hot Arizona neighborhood that have had the plastic break and then the loose cable jams up in the drive pulley. In the three cases this happended on the side of the car that has the afternoon sun on it while parked in the driveway.
I fixed mine by carefully wrapping a steel wire in a sort of figure-8 that caught both ends of the cable and the wire now has the tension and not the plastic parts.
The author's experience reminds me of our driver door/window odyssey on my husband's (now departed) 1997 VW Jetta. We took it apart slowly over time--several weeks--to figure out what needed replacing where. It took so dang long because there was so much stuff on top of so much other stuff, and meanwhile, he had to drive it to work every day and secure the door somehow. That meant putting it back together every time after each disassembly.
I meant the Jetta was now departed, not my husband. He's still alive and kicking, and now fixing his latest used car, a Honda. Which, BTW, had a similar door/window problem on the driver's side, but didn't take nearly as long. Much saner design.
This story reminds me of a Subaru Justy i once owned. Normally Subarus are great cars, but this one was a very low end, tiny piece of junk. While still under warranty, the driver side seat back broke. You would think it would be covered, but the service manager told me it wasn't (I later came to believe he had lied to me to make more money, but that's another story). He said he could charge me $300 for the metal bracket inside the seat, plus labor to rebuild my seat. I knew it was a ripoff, and refused to pay it. Instead, I searched local junkyards, and managed to buy two front seats for a grand total of $70. They installed in less than 15 minutes, with four bolts each.
I had a similar problem with my 2006 Jeep Liberty. The plastic part that connects a cable to the window broke. I was told by the dealer that some of the Jeep Liberty window regulators were recalled and replaced for free. This was not the case for me. My plastic part was not sold separately. My new window regulator cost $30. I installed the new window regulator in one hour. The replacement part design was improved. There are some good youtube videos showing how to replace the Jeep Liberty window regulator. This seems to be a common problem.
I also have faced a same experience with my friends vehicle which is Jeep Liberty,
It's not only with the window regulator but with the door lock which is made out of plastic. The agent replaced the part without extra charging as yours. And they mention that it's a factory defect of the particular model of Jeep.
With the rapid improvements in 3D printing processes, equipment, and materials, perhaps we will see the day when a dealer (or even a handy product owner) could produce replacement parts inexpensively and on demand without keeping inventories of parts.
@Zippy: I could have used a 3D printer for the driver's side door handle on my 2005 Chevy Cobalt. I went through two of them in three years. The original broke when I accidentally closed the door on the seatbelt. I pulled too hard on the door trying to open it and the handle snapped. There was enough of it left, though, that I could still open the door (once I successfully extricated the seatbelt, that is). However, my wife thought it was a disgrace for an engineer to have a car without a drivers' side door handle. Later that year, we visited my wife's brother, who owns a car dealership. He asked me if there was anything I needed. I said, "Well, yes, actually, there is." He gave me a brand new chrome door handle as a Christmas present. Everything was great until the following winter, when on a particularly cold day, the chrome handle snapped. This time it didn't leave a stub to allow me to open the door. I decided to get used to the idea of not having a drivers' side door handle. This was no problem when taking my kids to school, since I would just let them in the car first, and have them open the door for me from the inside. Climbing in from the passenger side when driving by myself was a little inconvenient at first, but I got used to it - so much so that nw that I have a new car, I instinctively go to the passenger side.
Zippi--excellent point. I do work with "additative" manufacturing and the choices for materials and processes expands each year. This technology is truly moving and moving quickly. There are still limits relative to component size but those are beginning to fall by the wayside also. You thoughts about minimal inventory are quickly coming to pass, which will be a boon for the automotive parts industry.
Dave Palmer, THANK YOU for putting that link to Joseph Ogando's article on plastics. I read this years ago but couldn't remember the title or the author so was never able to find it again.
This article should be required reading for all plastics designers. And I will be keeping it in my back pocket as a reference when I have to explain what I call the "plastics uncertaintly principle" to non-plastics engineers or decision makers.
I had the same experience with my 1998 Saturn. First it was the window but after I purchased a new regulator assembly I decided to instead make a replacement part that would last. Shortly after the first window failed another failed. Then the sunroof failed. I found replacements for the plastic pieces made from machined aluminum online and installed a pair. They were over $100 but much less than replacing the entire sunroof and a replacement sunroof would have just failed agsain anyway.
Even when Saturn was separate from GM and made a relatively decent auto they apparently couldn't get away from using the same junk small parts. After GM became directly involved with Saturn they caused them to go bankrupt even before GM did.
It was an interesting comment about how strong plastics could be, but those strong ones are not the cheap ones, ever. Adding to the fun is the tendancy to use only enough material to just barely do the job under ideal conditions. That assures that the assembly will fail before the warranty runs out, unless the product has one of those 10-day warranties. The other thing that leads to failure is a lack of adequate understanding about stress levels in plastic parts that yield "just a bit." When the part deflects then the original analysis is no longer valid, and troubles begin. And the final source of failure is the purchasing mentality that always wants to buy cheaper plastic, not regarding the quality of the cheaper stuff.
I view this from two sides. Since I make my living producing things from metal, mostly steel, I am somewhat amused when plastic parts fail. My industry lost thousands of parts, dollars and jobs to molded plastic parts so when they fail I can be smug about it.
On the other hand, I am a fisherman and have many reels with plastic gears that have never given me a moments grief, so I know properly engineered and manufactured, plastic can be a great substitute for metal. Some of the most expensive tackle is made from composites rather than aluminum, but I do not know if that qualfies as plastic.
With 3D printers and scanners becoming common, a logical thing is to create the models for these parts, then print them on demand. Not sure what the softening point of PVC is (and another plastic is common, too), but better than losing an entire car. There are services that will print them in metal, too.
mr_bandit - That's a great idea. The local shops (or at least the local NAPA supplier that they get their stuff from) could invest in a small printer. No inventory required. In fact, the OEM could license the part libary and they would need to be in the manufacturing business for the small stuff - pure profit. This could also allow older cars to have the "right" components when the manufacturer no longer wants to see the actual hardware.
Thanks so much for finally getting to the applicability of this article. Future Designs.
We will see more and more abuse and misapplication of lightweight materials in air and surface vehicles as we strive to shed mass and the cost of accelerating it. I have a 1996 Yukon and a VW Touareg and one weighs 1.5 as much as the other and the mileage is 1.5 times better on one. The payload, size and comfort are similar. As well as the horsepower. Much of the difference in mass contributes to the improved fuel efficiency and the rest is from better application of the fuel-joules and combustion by the powerplant. My yukon is 17 years old, and the only thing inoperative is that the CD player skips alot. I'd be very surprised if VW really meant for my T'reg to last much beyond that age. Its a solid design but the materials are just not more GMC steel and less plastic. An interesting application of plastic gears is the sundancer in my kitchen window that is a low voltage solar panel driving high torque gear set to turn a crystal prism that throws light spots in different directions. The gears are in a clear plastic housing that clearly shows their condition and allows UV attack every day. They used to be vibrant colored. Now they're faded and probably distorted from the heat. They still work but they're purely decorative. They don't belong in cars where window cranks should last at least as long as the engine.
A few years ago a plastic part broke in the mechanical timer of our old dishwasher. Took it apart and with my Dremel reworked the broken area and made it work again.
In spite of my technical repair skills, the wife was not pleased - what she really wanted was a new da*n dishwasher. A year later, when the top rack started falling off its rails and no parts available, I gave in.
Now the "new" (2 yrs old) diswasher is already losing broken plastic rack clamps.
I had a similar issue issue with a 76 Datsun B210, the plastic had cracked vertically, fortunately the plastic piece was square so I removed the now two piece part rotated them 90 degress and reinstalled back in the sliding channel, as far as I know this lasted through my ownership and the two years my sister had it as well.
I owned a VW Passat. The plastic window clips (the ones that actually hold the window to the track) kept breaking. After the second time I got online and did some research. As it turns out, this is a very common problem with this vehicle; an Audi part (made by VW) was virtually identical except made from metal. I bought these and they fit perfectly. Never had the problem again. Being a design engineer myself, it hurt my brain a bit on this one; if both autos were using the same part, buying twice as many (simplifying the obvious here) should bring the part to a cost point where a plastic one wouldn't be needed. Never underestimate the bean counters...
What should be the perception of a productís real-world performance with regard to the published spec sheet? While it is easy to assume that the product will operate according to spec, what variables should be considered, and is that a designer obligation or a customer responsibility? Or both?
Biomimicry has already found its way into the development of robots and new materials, with researchers studying animals and nature to come up with new innovations. Now thanks to researchers in Boston, biomimicry could even inform the future of electrical networks for next-generation displays.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.