General Injection Molding Terms?

[Mech_E_Travis]

My company is new to injection molded components. Our first experience with a well known "rapid injection molding" company has not been very positive. The parts we received were not made to print, nor are they willing to take the parts back and work with our current mold. They insist on machining a whole new mold on each (slight) revision of our part (to be able to meet print specifications). Further, they insist that the molding process is simply trial and error at this point and they have no idea how many revisions it would take to make our part per the original print

Obviously, we are not happy with this. My question is, is this normal with injection molded parts? I would have thought that by paying for the mold and its associated costs, that we were guaranteeing that the parts would be made to print. I would like to quit working with this company, as I believe their business practices are less than proffessional. Are we going to encounter this with other molding companies? Any reccomendations on a good molder? The part we are doing is fairly simple, although the tolerances are fairly tight (+-.003 in places). Material is 30% carbon fiber composite.

Thanks For Your Feedback
Travis Sewell

[spider]

hmmm.

lot of times, bare minimum prototypes can be made (for a faction of the cost of a full mold) that can be used to work out the bugs out of the part. Plastic can sometimes behave really strange and there are a lot of things that can impact the final part (shrink, cooling, packing/cycle time, gating....) If we need to change the part for any reason, then we will eather weld, or insert the part.

The mold shop that i work at charges only for the engeneering changes to the part. If we can prove that we can get a part out of that mold, that is in tolarence, and was approved by molders project menagement....then it's not our problem anymore. It's the molders responability to replicate the condisions we had to get the same resoult.

[blowmebigtime]

I agree what spider says,, you can build a mold to very tight tolerances and then it's in the molders hands,, I have seen some crazy things happen during molding, even drying the material properly has to be considered. I can see some tolerance issues especially with 30% carbon or glass filled material, everytime the glass lays different in the finished part, you will get a different shrink. Most of the time we only charge for engineering changes like spider said, anything else we take care of as the mold builder. A automotive customer of ours even makes us responsibe for the shrink, even though we dont mold the parts for them.

[MnotLyon]

I will NOT be responsable for shrinkage rates. I don't run the molds, I only build them. There are too many things that can affect shrinkage that are simply out of my control as a mold builder. I meet with my customer (usually the molder), we discuss gate issues, and shrinkage. Then I build the mold to those specifications. They sign off on the prints before I start working. If I build to the prints, the only thing I will repair for free are craftsmanship issues, and vents.

[ceandro]

I agree with most of the above. The molder that I work with normally follows this general practice . Review of the job/part design ,and materials, he quotes the job as build and run, that is, he has the tool built and will run the parts for you to meet print dimensions and you maintain ownership of the mold . Any changes after the preliminary design is approved by you will be additional cost . Meeting the print dimensions is at his cost.He will provide the shrinkage number that will be used to build the tool. Typical practice in the industry is as Mnotlyon said , the toolmaker is not responsible to provide the shrinkage value to use in building the tool , realistically the data sheets from the material supplier are only a good starting point to know what shrinkage to use , only experience with the specific material can be relied upon , and even that can surprise you with abnormalities. An in house QC department provides a first article report on an initial sampling to see if dimensions need to be adjusted to unusual shrink or material conditions to meet print . Once the part meets print dimensions they prepare a first article report from the in house produced sample and the report is submitted with all dimensions listed to be approved by you,once it is approved then the mold is released for production. On domestically produced tooling he did guarantee that you will not see any maintenance costs for the life of the tool as long as he runs it. If you require lower cost tooling produced offshore it will not have this warranty. I believe he still offers this ( a good idea if the material is extremely aggresive or abrasive. )
This guy is a custom molder and does a lot of small volume and exotic material molding for a variety of industries and is well experienced , I have worked with them for about 10 years now so I have seen a lot of their tools come through my shop. Thats the way they do things , as you are unfortunately finding out ,practices vary widely.
As others stated , plastic is a very dynamic material , consitency from the compounder can vary greatly from batch to batch. Expereince is invaluable in specialized engineering grade materials .Hope this helps

[tooldzinr]

It all starts with part design.
~~Don't setup the toolmakers or molders to fail~~

Gate location, uniform wallstock, last places to fill, venting......

[ZipSnipe]

Travis the company I work for has done nothing but impress me from the get go. We have facilities in N. Carolina and Florida. I know for a fact that the guys in Florida that I work with are top notch. If those two locations work for ya let me know and I,ll hook you up with the owner.

[cpmfastools]

All our quotes are based on acceptance of 6 sample parts as molded from the tool. Not receipt of them, but acceptance. You are not only paying for the labor of building the tool but the experience that the tool maker brings to the table when building the tool. The downside to going with a rapid injection molding company is there lack of experience with production tooling and material characteristics. We use Direct to metal laser sintering machines to produce rapid production tooling, the emphasis is on production, not proto type tooling. You should not have to compromise in the design of your parts. If a company cannot meet a tolerance requirement they need to bring this up during the quote phase, not after the tool has been built. We find that between rapid proto type machines producing functional ABS parts, design/flow software and 20+ years of molding experience the ability to get a part that the customer expects is pretty easy. Shrinkage factors are only a start point, filled material, long fiber vs. short fiber. How your cooling passages are routed, gate location and how much deviation from a nominal wall thickness all effect how the end part will look, function and measure. In the end you cannot beat good old experience coupled with modern technology.

50% mineral filled PPS - 21days from PO to sample parts.

Steven

CPM Fastools, Inc

[MrMold]

My company is new to injection molded components. Our first experience with a well known "rapid injection molding" company has not been very positive. The parts we received were not made to print, nor are they willing to take the parts back and work with our current mold. They insist on machining a whole new mold on each (slight) revision of our part (to be able to meet print specifications). Further, they insist that the molding process is simply trial and error at this point and they have no idea how many revisions it would take to make our part per the original print

Obviously, we are not happy with this. My question is, is this normal with injection molded parts? I would have thought that by paying for the mold and its associated costs, that we were guaranteeing that the parts would be made to print. I would like to quit working with this company, as I believe their business practices are less than proffessional. Are we going to encounter this with other molding companies? Any reccomendations on a good molder? The part we are doing is fairly simple, although the tolerances are fairly tight (+-.003 in places). Material is 30% carbon fiber composite.

Thanks For Your Feedback
Travis Sewell

The company should make it right. That being said, it is also the responsibility of the company to tell you in advance of any problems they might see. If they do this in advance I believe they are covered. I still think they should make the customer happy. That's just good business practice. I'd go with a company (like Mine ) that can produce the mold and the part in house. Part shrinkage is not an exact science, it's getting closer. Alot of variables go into part shrink. Some materials have shrink rates you can expect all day long, and no matter what you do it's hard to change. Other materials have a shrink "range" and small variables in the process and material batches are very difficult to control consistently. The rule of thumb is the molder is allowed 90% of the tolerance. So the mold maker only gets 10% of the tolerance. +- .003 for that material is tight especially with that amount of filler, but they should have told you that up front. You also have a responsibility to be educated yourself. I don't neccesarily believe the cusatomer is always right, even when he's wrong. It used to be that vendors were looked upon as partners in a project and were called in early in a project for their advice and expertice. Now days it's lowest price is King and the value added stuff isn't taken into concideration. Try telling that to the bean counters though.