There is one design idea, to design a delay pin for the ejector pin of runner, then the ejector pins push the part out of core firstly, part separated from the runner.
Some import tips might be ignored for slide gibs on mold design. But these tips are critical to ensure an injection mold with a long life.
1. Gib cavity depth “A” not less than 1/3H.
2. Gib height “B” not less than 2/3H, exceed the center of gravity because the slides usually lay horizontally when working.
3. Gib length “C” not less than 0.6H and 0.6L.
4. There are two rules related to Z:
-If Z wider than 6-1/2 inch, need to add one rail in the middle of the slide.
-If Z wider than 4-1/2 inch, need to design two cam pins.
All of these things we made just have one goal, to let the slide moves stably.
The mold below was injected PA66+30% GF, the warpage was huge could not be improved much even though we tried the different mold temperature on cavity and core side, or changed the injection speed, injection pressure, lengthened the packing time.
Until we changed the resin to PC approved by our client, the deformation issue was almost done.
Hope this case can be reference for you.
This white spots issue happened on a high gloss product in black color, which was not found on tryouts, but on mass production after injection molding about 50 shots.
The mold with banana gate inserts, so when the white spots appeared at the first time, we thought that there might be some oil inside the gate inserts cause the issue. So we disassembled the mold and clean the inserts and re-started the sampling, white spot did not show again until about 50 shots.
The issue happened after about 50 shots sampling, the mold was going to warm up, so temperature might be one root cause, but the white spots only showed up around the gate. And because the cosmetic surface is high gloss which need high mold temperature and high pressure to pack the part to have shining and without sink marks.
From the info above, we thought that the resin might have been degraded as the high shearing stress flowed through the gate when mold temperature went up, then white spot happened. So low down the injection pressure, melt temperature and mold temperature might be helpful.
We tried many different molding set up parameters to fix the issue, but it did not work. So enlarging gate size was the last option, and the issue was fixed.
Hope this case what we experienced can be a minnow to catch a whale. Please advise if you have any good idea.
Yes.
But please be aware of some points as below:
-Usually these resin can work with opened hot nozzle and valved gate, but not hot tip.
-These resins are very easily got degraded if the molding machine stops for tooling repair, and the power of heater of hot runner are not turned off, more than 5 minutes will cause issue. The degraded resin will stick at the corners inside the hot runner system could not be removed, this will cause black defect spots on samples, especially light color parts.
-If the production volume is high, it’s better to order two or more sets of hot runner as spare component to take place of the current hot runner when degraded defect spot issue happens.
When the production volume is low, consider cold runner for PEEK, PPS, PPSU, LCP will be better.
As for mold pre-shipment checking, except from the standard relates to details of molding machine, the most important thing is to check the fitting of movable components, such as the ejector pins, slides, angled lifters, floating core, etc.
Disassemble the mold, use hands to pull out and move back the slides, angled lifters, and ejection pins to feel the fitting, if they are moved smoothly.
There are some guidelines as below to place ejector pins on mold design.
1. Ejector pin location
1.1 The distance pin to the edge of the plastic part should be 0.04~0.10 inch.
1.2 To place the pin to bottom of part as A pin, and leave 0.01inch to the edge of core. Not good to place as B pin on top of part.
1.3 The locations as picture below, A better than B, B better than C.
If there is no choice, have to place pin at C location, then it’s better to add some small step on pin to increase the ejection force.
1.4 If must place pin on A location without better option.
1.4.1 Must make the pin lower the parting line 0.0005 inch, same as venting depth.
1.42 Add spring under the return pins to protect the ejector pin.
2. Pin fitting length and clearance.
3. Ejector pins should be locked if the pins placed on the non-flat surfaces of part.
On injected parts, the injected mark as picture below easily happened on the gate location with banana gate, especially on textured surfaces. due to resin flows through the gate with high pressure.
How to improve this kind of gate marks on injected parts by adjusting molding parameters?
The most important thing is: find out the switch point on molding machine of resin flows at gate point. Use low injection speed to fill the area of gate location, then can change to high speed after that point to inject other areas. It's vital to get the exact injection switch point.
The thickness of plastic product related to plastic material, part size, injection gate numbers and locations.
Same thickness may be fulfilled by PA resin, but it may not be workable for PC resin, due to different flowability of each resin.
There is a formula to calculate the plastic product thickness base on selected resin and the flow length = the distance from injection gate to end of the part. Please see image below:
Draft angle is import for plastic injected parts with texture. How to define it?
Refer to EDM texture VDI3400, there is a standard as picture below for reference. For chemical corroded textrue, can use Ra value to compare with EDM VDI3400.
It's better to add 1 more degree draft angle to standard for safety if possible.
An understanding of your Chinese mold supplier's capabilities and market is essential to getting the right tool for the job.
Purchasing injection tools in China to be run in the United States is a fact of life for U.S. molders. Many tens of thousands of injection tools are bought in China each year and sold in the United States. If you have not already bought a tool in China, you will. The cost difference is too great to ignore, and, unfortunately for North American toolmakers, the quality of the tools coming from China can reach North American workmanship and durability standards for the majority of applications.
However, the quality and capabilities of Chinese toolmakers run the gamut, from the great to the downright ugly. Having visited more than 60 toolrooms and purchased tools from a dozen of them in southern China and the Shanghai region, I can attest to the wide gulf that exists between the best and the worst. If you are buying tools for North American molding operations, how can you tell the difference? Well, the obvious solution is to visit. That, frankly, is a must.
There is a fundamental difference between two general groups of Chinese toolmakers, however, and being aware of this difference can save you a lot of time and trouble. They are the "domestic" toolmaker and the "export" toolmaker. Domestic toolmakers supply either themselves or molders within China. Export toolmakers send most of their tools overseas to be run by molders primarily in North America, Europe, and Japan. All toolmakers in China, naturally, are of one variety or the other or a combination.
We've all heard stories about the incredibly low-cost Chinese-made injection mold--perhaps a fairly complex, albeit low-cavitation, tool, say four cavities, but Class 101 (at least specified as such!), with lifters and cam actions--one that you might quote for about $50,000 in North America. The quote from China: $8000. We could barely buy the steel for that price! you may have exclaimed. This is an example of the domestic toolmaker delving into the export market. My advice: Run away as fast as you can. Take my word, and it is, unfortunately, the word of experience, you will get what you pay for: the world's heaviest paperweight.
The same tool from a Chinese shop that makes tools specifically for the export market will cost $20,000-$25,000. Add in the cost of duty and transportation (by air probably) and the price becomes $25,000-$30,000. Apples-to-apples, delivered, you will pay (on average) about 50-60% for a Chinese-made tool for the export market vs. a North American-made tool of like quality. That's reality. It's not as fantastic as the rumors, but still an impressive savings, and worth having.
Domestic moldmakers make tools for a market that pays $0.80/hr in molding floor direct labor, runs low-cost injection machines (generally smaller machines running lower-cavitation tools), and incurs low-cost tool repair and maintenance expenses ($5-$15/hr). Export toolmakers serve a world that pays $8-$15/hr in molding floor direct labor, runs higher-cost injection machines (generally larger injection machines running higher-cavitation tools), and faces high-cost tool repair and maintenance ($40-$60/hr).
Domestic vs. export tools
Following are some examples of domestic/export differences and their ramifications as they relate to a domestic Chinese moldmaker. (The following references to "they" refer to the domestic moldmaker.)
1 Characteristic: The domestic Chinese tool uses Chinese-made steels. They are softer and less durable than the Northern European, Japanese, and North American steels you favor.
Effect: Shorter tool life, loss of detail definition over time.
Why they don't care: Tools are so cheap that they just make another set once the current one wears out. One of my Chinese domestic tool suppliers provided me with a one-million-shot warranty on a tool that it was going to run itself. I knew it couldn't get 100,000 shots. When I inquired, the reply was that the moldmaker didn't care; it would just build a new tool when the old one wore out. I'm sure it would do just that, again and again, as long as the molding orders kept coming.
2 Characteristic: The domestic Chinese tool doesn't adhere to the same workmanship standards as an export tool. Components are made by "Zhou Blou," not Progressive, D-M-E, Precision Components, or another name. Attention to details that result in quicker setup times are not there.
Effect: Shorter tool life, slower setup.
Why they don't care: See the paragraph above regarding tool life (a recurring theme). Setup techs in China, as in the United States, are better paid but still $2-$3/hr on the high end vs. $15-$20/hr or more in the States.
3 Characteristic: The domestic Chinese toolmaker uses all metric dimensions no English units.
Effect: If this tool is exported, finding replacement components may be difficult and expensive; reworking the tool accurately may be difficult.
Why they don't care: The domestic toolmaker builds for a metric audience.
4 Characteristic: The domestic Chinese tool will have lower cavitation for the job vs. a tool designed to run overseas. In China, the moldmaker may choose to build four four-cavity tools instead of one 16-cavity tool. Several factors drive this decision. First, a lot of Chinese toolmakers have little confidence in their ability to achieve cavity-to-cavity consistency (and they are right to be concerned). Second, many Chinese molders are shy about running multiple-cavity tools. Third, larger-tonnage machines are scarcer in China than in North America.
Effect: Greater molding production cost in both labor and machine time.
Why they don't care: We already know that labor is cheap. However, smaller (30- to 150-ton) Chinese-made presses are dirt cheap 20-30% of the cost of a Japanese, North American, or European press. Even the latter frequently cost less in the Chinese market since machinery makers have to meet local market price level expectations or be totally shut out.
5 Characteristic: The domestic Chinese tool will have poorly designed, unbalanced, and inadequate cooling. When the tool is run, moreover, the molder will likely loop waterlines back and forth through the mold rather than use a manifold. This causes temperature differences from cavity to cavity and thus cooling rate variations from part to part.
Effect: Slower cycle times, possible
part quality inconsistency issues (perhaps warpage or splay).
Why they don't care: Getting the last tenth of a second out of the cycle time has not been a priority in most Chinese molding shops due to low labor and machine costs. Therefore, attention to waterline design and other cooling characteristics has been poor. The quality issues are real, however.
6 Characteristic: The domestic Chinese tool shop will run its EDM burns with no EDM tooling in place. When an electrode is replaced, the operator takes the time to attempt to manually reseat the electrode precisely where the old electrode left off.
Effect: Very slow electrode setups, definition of part details and consistency across cavities may suffer.
Why they don't care: They should care, for quality reasons, and because the person changing over that electrode is one of the more expensive people in the shop. However, EDM tooling is not commonly used. If you see it, it is a clear sign of a better export-oriented shop.
7 Characteristic: The domestic Chinese tool's A and B sides will have a poor fit.
Effect: Lots of flash and lots of flash trimmers with Exacto knives hunched under light bulbs next to molding machines trimming and trimming and trimming.
Why they don't care: Low labor cost, low labor cost, low labor cost.
Do yourself a favor and stay away from the domestic Chinese toolmaker. But wait: If you are just interested in getting a part, and that part isn't too tough to make, and that part is going to be made in China as a component of a larger assembly . . . then it might be fine, and certainly much lower-cost than an export-oriented shop attempting to make a tool for the local Chinese molder. But would you run this tool successfully in your shop here in the United States? Forget about it! Please be careful, and happy hunting.
Author: Carlton Harris
How Do I Narrow Down My Options?
You may have a long list of possible manufacturers at this point. To narrow it down, look for:
- Manufacturers that make products similar to yours. Ideally, you want a manufacturer that specializes in this type of product, as opposed to one that makes it as a sideline business. Some small Chinese manufacturers will offer to make just about anything—but that means quality may be poor.
- Ratings and reviews. Do Internet searches and look at online ratings and reviews to see what others are saying about the manufacturer.
- Manufacturers that do most of their exporting to the U.S. or other Western countries. These Chinese manufacturers will generally have higher quality standards, and have proven they are able to meet the expectations of Western importers in terms of compliance with product safety, labeling and packaging regulations. They're also more likely to have experience with the logistics of shipping products internationally and a greater ability to get your products through the accompanying red tape.
- Honesty. Reputable Chinese manufacturers should be willing to provide you with their business license, documentation of their quality control system and any related certifications.
Come up with a shortlist of three to five possible Chinese manufacturers that you're considering. Before proceeding any further, have them sign a nondisclosure agreement specifically for overseas manufacturers.
What Questions Should I Ask Potential Manufacturers?
Once the manufacturers have agreed to nondisclosure of your idea, your next step is getting a request for quotation (RFQ). Send them images of your product prototype with details such as what materials you want to use, the size of the product, and anything else they’ll need to know in order to make the item.
In your RFQ, find out:
- Minimum order quantity (MOQ). The more units of the product you’re ordering, the less each unit will cost. Every factory has a minimum order quantity. You need to strike a balance between not spending too much to buy way more than you need, but not seeking such a small amount that you have to use a second-rate factory.
- Prices for samples. Before you choose a Chinese manufacturer, you need to get a sample of your product made and inspect its quality. Prices for samples can vary widely, from free to a discount to the normal price of manufacturing the item.
- Prices for production. Find out how prices change depending on order volume. Ask for a breakdown of costs, such as the cost for the item, the cost of shipping, the cost of tariffs and anything else that the manufacturer includes in pricing.
- Time to manufacture. How long will it take to make your order? This can make or break your choice of supplier, since you don’t want to wait too long to get your products.
- Payment terms. How and when does the manufacturer expect to be paid? As a new customer, be aware that you might have to pay the entire amount of your first order upfront. Be sure to ask about future payment terms if you become a regular customer.
Be sure you get the same information from each Chinese manufacturer so you're making a straight comparison of what they offer.
How Do I Verify Product Quality?
Once you’ve gotten the RFQ from several manufacturers, choose the ones you like best and ask for a sample of your product. It’s rare that a manufacturer gets it right the first time, so don’t worry if there are slight disparities in the sample and your prototype. You may need to go back and forth a few times to fine-tune the sample until you're satisfied. This process also helps you and the manufacturer get comfortable with each other and feel that you can work as a team.
Do I Need to Visit the Factory in Person?
Unless you're placing a very large, complicated order, it shouldn’t be necessary. If you're at all concerned that the company is not legitimate, you can tell them that you will conduct a factory inspection before sealing the deal. Fraudulent companies will be scared off by this tactic, while legitimate ones will welcome it.
Written by Rieva Lesonsky