Home » Mold Tips
We have received a lot of inquiries from start-up companies, some of them have a budget limit at the product development stage. Many of our existed customers started to cooperate with us when they were a startup company, ACO Mold is happy to be supportive to help customers develop new product. We can try to lower down the mold cost as much as possible via 4 ways.
Lower down the tolerance
There is a bit you can do to help improve adhesion between PC and TPE; two materials that don't typically love each other. I am working on a fix right now on one of our products having just this problem.
  1. Make sure the material has been dried properly to obtain the best adhesion possible (which may not be great).
  2. I believe you should expect better results in a two shot process as the initial shot is still warm when it receives the TPE attaining a better bond. In an insert mold operation, the part is rarely warm and sometimes has had the opportunity to take on moisture if it has been sitting around.
We had a clear nylon vessel that exhibited a "splay like" condition that emanated from the gate region. In our case, the mold had valve gates and what was happening is that some of the melt was being left on the face a sides of the valve pin. The next shot these now solidified pieces of nylon would break loose as the incoming melt stream re-melted the prior shot but because of the viscosity differences would result in a splay like appearance to the naked eye. Only under 30X microscopic exam could you actually see the residual debris and the flaring trails behind them like comets.
In general most feed throat temps are from 95 deg (f) to no more than 130 deg (f). There are some injection machines that have specific feed throat temperature specs. Husky PET machines are an example. However most injection machines do not. There are several things to avoid. Do not get any part of the feed throat cool enough to cause condensation. Do not let the feed throat get hot enough to let the material soften and clump. Outside these cautions you will usually find little effect of the process from FT temperature.
The fees for a set of plastic molds may cost thousands or even hundreds of thousands of dollars. What if the products have many styles but with a small quantity? Is it alright to go for 3D printing directly?

3D printing
Technically, there's no doubt that roof structures — large, small and modular (small units to cover larger areas — CAN benefit from a twin-wall construction afforded by rotational molding, as the hugely increased flexural and torsional stiffness is a very welcome property for this application. However, as with any application, the designers, developers and funders must satisfy themselves that the financial figures also stack up when considering process, material(s), numbers, operating environment, building regulations (not least fire performance), affordability by the purchaser, cost of ownership over its lifetime and design options.

Rotational molding process is unlimited in end product applications, whatever the roof size or shape make sure you study the environment in detail in which you plan to place it and design it accordingly based on all the controlling elements and the materials available to you in the rotational molding process, limited materials are available vs. the other plastic processes. Always know all of your options, cost, and market demands before choosing you end product process. Keep in mind if the rotational molding process does not fit for the long haul sometimes it will fit for the short run, i.e. (R/D phase, minimum capital on the front end, and allows for initial market studies).
The major culprit that I've found over the years, for electrostatic discharge during injection molding is caused by the friction of the plastic pellets through the delivery hoses for the hopper. The injection molding machines should definitely be grounded with copper rods in the floor and I believe they should reach nearly to the water table for optimum grounding. I have seen the "lightning bolt" jump about 6 inches between a hose and material handlers head when he was working near the hose while it was loading the hopper with PP. Obviously we weren't using the grounded hoses that have the internal grounding wire, which must be exposed to grounded metal at the connection to the hopper. Another source of shock for the operators is when molded parts (esp. PP and PE) are conveyed to a plastic tote or bin. You can see the small parts try to "climb" the wall of the container as the charge builds. I've attached bolts to a grounding wire to the conveyor and put them in the totes to help dissipate the charge so operators wouldn't get zapped when they reached into the tote.
It is no surprise to me that its uptake over the last three decades or so that it's been generically available has been limited compared to injection molding process simulation. The latter process involves very high-cost tooling, with (typically) many weeks of lead-time and is highly complex, impossible-to-see and susceptible to hugely expensive mistakes. In contrast, most thermoforming projects require low-cost, short lead-time, relatively simple tooling and you can see the forming process in real time. Mistakes of poor tooling and/or part design can be relatively quickly resolved. Ratios of cost of simulation studies to total capital expenditure are much more favorable for injection molding than thermoforming. Ditto for time of simulation studies to total lead-time before appearance of first-off samples.

This does not mean that I do not support the use of thermoforming process simulation: it can certainly allow more efficient use of material and energy. You can “tweak” your design to make it more process-friendly as well.
As for the quantities. 1000-10.000 units/ year might not be enough to justify investing in an injection molding tool. Depending on the complexity of the parts (e.g. undercuts with slides...) your mold can get rather expensive. While the finished products might not necessarily have better properties than your current one.

As a guideline I would not invest in hard injection molding tools if the part quantities are below 10,000 a year. Between 5,000 and 10,000 we sometimes stick with an aluminum mold that we design ourselves, and build ourselves. Where we just outsource the milling. If you study mold design a bit, this is doable + gives you a tremendous amount of knowledge for future injection molded parts that need to be designed.
In the commodity products area, there are lots of production buckets, pails and containers co-injected using the method described (Two shot), because it can be adapted to most any injection molding machine. Savings realized not only on the resin but color and additives like UV inhibitor. In many cases, the less expensive core constitutes over 60% of the total part volume.

More exotic (or lower volume) applications include soft over rigid, like a TPE over anything with some modulus. Also, structural foam parts with cosmetic skins; likewise, fiber or glass filled parts with cosmetic surfaces.

Co-injection or overmolding for a "soft-touch" or for a cosmetically clean surface over a fiber reinforced core is understandable. There is a value added feature there.
The process consists of the following steps, but the detail may vary depending on how formal you want to be about the project:
  • Establish the cost incentive using quotes or cost estimation tools.
  • Understand everything about the function of the "target" component to be replaced.
  • Develop thermoplastic concepts which reflect the required functions, including environmental considerations, temperature, structure, etc.
  • Validate the preliminary concept using simulation tools.
  • Validate the cost incentive - make sure the project is a net cost save given the geometry, material, and annual volume (i.e. tooling amortization).
  • Finalize design.
  • Prototype.
  • Validate with testing.
To increase the life expectancy of an injection mold, you need to do careful maintenance and avoid operation mistakes during molding plastic products. Water lines can be a major problem. Run treated water or build from stainless. Build the tool solid, large pins, support pins, locks etc. use the mold safety settings on the press. Chart the number of shots it takes for the mold to start to run less well, and set up a plan to pull, service and check it before it hits that number. Replace worn parts. Greasing the moving parts before they start to make noise. Blowing down the water lines when the plastic injection mold is pulled from the press, or using quick disconnects that seal the water lines when they are disconnected.
Spend the money on mold filling simulation analysis and allow the mold flow analyst to do the same things that create the variation, analyzing potential variables and review the results with your part designers, this will allow one the “wiggle” room needed for the best outcome. For example:

After running basic mold filling simulations - based on best practices or using molding parameters based on previous similar designs – start making simulation changes that allow one to understand the limits of the design tolerances based on varying the process – change materials, change the pressure, change the mold/process temperatures, change the filling parameters and gate freeze options to understand desired effects and those molding parameters that result in unwanted solutions. Each part geometry has its own optimized solution.
After we finish assembling a new mold, we need to launch it and do a mold tryout.

The mold designer and mold maker sometimes made mistakes, any small mistakes could lead to major damage of the injection mold, the purpose of mold tryout is to find out any potential defects and ensure the mold perform stable and efficiency during molding production. If the tryout process did not follow reasonable procedures and make the appropriate records, then we cannot guarantee smooth production, this could cause serious problem, it means much higher cost or even delay for mass production.
Just as well I would recommend you that any software you must verify first an structural analysis prior to validate your injection simulation to ensure you will not find bubbles, air trap and weld lines in areas of high or low strength. And also is very important to document the evidence you found, and take care later in a meeting with the tolling that will develop the tooling and take this into account in the development of possible new flow leaders, vents or put some specific flow to improve special parts of your model, don't forget to invite, or call to your resin representative, because they have some tunning recommendations regarding final gate designs as well processing guide lines.
As a injection mold manufacturer, we received a lot of inquiries from our website and B2B, an interesting phenomenon is the professional/ potential customers usually very clear about what they need, the information provided by them are very specific, we take serious for this kind of inquiries. On the other hand, inquiries with very little information could be a signal of no intention to purchase; we do not put it in priority. This explains why you get very few replies when you send inquiries to many injection mold manufacturers, you did not inquiry like a professional.

All the mold and injection molding project are custom manufacturing project, so it's not like other common product, the demands are always diverse, injection mold factories need to know the detailed demands of the customer before they can provide the most suitable solution, it's much more than pricing, it's a custom made solution.
Without doubt having own fully equipped tool room in plastic injection molding company has huge benefits over the years in terms of winning new customers and not just for injection mold tooling. We often describe the tool room as the "heart" of the business as although it's only a small part of our companies turnover it's what is produced in there that goes onto to contribute to that turnover. We need to make injection molds that run at a predicted cycle times and that don't cause a problem in the mold shop so we cannot compromise on the quality.

It is always best combination to have tool room and plastic part producing facility under one management. We are a company in China having only injection mold making facility at one location and component manufacturing facility at other location, though just five minutes away from each other. Here the advantage is that some customers come to us only to buy molds while some customers are interested in buying molds and plastic parts. Also tool room engineers have a different way of thinking while a production engineer thinks differently. So it is better that these two facilities are kept separate.
Mold design is the start of any successful mold-making project, so a careful evaluation and optimization process is very much necessary, review the design to verify the plastic parts requirements and mold manufacturability are all satisfied.
  1. Is there a "parts to customer" promised date?
  2. Has the mold completion date been established?
  3. Has the cavity level been established?
  4. Has the mold cost quote been completed?
  5. Has the cycle time been established?
  6. Has the material to be molded been determined?
  7. Is existing product available?
  8. If 7 is yes, should the existing gate location be used?
  9. If 7 is yes, is the product symmetrical in design?
  10. Are maintenance costs built into the price?
We are investigating an alternative method of making 200 small flat curved parts that are symmetrical relative to the midplane. Both sides are identical so the two mold cavities are identical. We are looking for an easy to cast material that has strength/toughness properties as HDPE or even as UHMW PE. The parts should never break but are allowed to bend (somewhat or even a lot) under exceptionally heavy loads. It can be a net casting or machined after casting but tolerances are not important as the parts are not attached to anything.

One of your choices can be Casting Polyurethane. Based on the situation, you must use Polyether - TDI base casting material if the environment is wet or these parts will work in water. This type of Polyurethane has moderate to high tensile properties and excellent resistant against water. But if you need a high property such as tensile strength or abrasion resistant, it's better to use Polyester- MDI or Polyester - TDI. You can use every colorant for this purpose.
China has a wide variety of skill sets available from high end to the lowest low. The culture is open to interpretation when the injection mold shop decides how to design the cavitation structures. I suggest having your own injection mold tooling expert and engineering determine the way the cavities function. I also suggest having certifications on hand for all the steel used in the plastic injection molds. This would include all receipts and traceability documentation. There are different levels of quality in China for steel and you made have a variety of heat transfer issues associated with it.

In short, the USA and others are leveraging the moment and getting some quality plastic injection molds out of China. Check the references and make sure you call non-competing companies to mitigate your risks. Also hire people that project managed these types of injection mold suppliers to deliver exactly what you ordered.
Multi-cavity molds produced parts in a much higher efficiency way, it's employed frequently on the occasion when the demands volume is high, the number of the cavities and mold construction depend on both economic and technical factors, quantity of parts to be molded at one cycle, required cycle time, and unit price are related with mold making cost. See below figure, mold cost and plastic parts cost need to be considered to achieved the best result of the project.
Mold cavity and costs

There are a few points need to be pay attention when we decide the numbers of cavity.
I work for a company that sells Moldflow and provides Moldflow services nationwide, but we have been seeing that Moldflow is making a move towards the front end of the design cycle and more design engineers are getting involved using simulation up front. It can help them in a number of ways, and it is much more cost effective to do your simulations early on. With tool makers doing less of it, and simply moving to creating molds per the specs of the designers, many make additional money off reworks - which everyone is looking to do in this economy. Thus, companies are taking back control of their designs...it is an interesting shift from the way Moldflow was used in the past vs. how its usage is evolving.
Some suggestions for effectively using in-house scrap, whether for injection molding, extrusion, vacuum forming (which generates a lot of offcuts).

1. For companies producing multiple products, a good strategy would be to use up in-house scrap in components/molding with lesser service severity requirements molded from the same polymer. e.g. scrap from moldings of high aesthetic requirements could be used up in molding where aesthetics are not so important/darker in color. Load bearing molding regrind could be used up in non-load bearing items.
Sometimes it is safer to use up all the regrind in a dark, non-critical item if such an item is in the manufacturing mix in sufficient numbers to be a scrap sink.
A typical injection mold RFQ that we see includes CAD files, quantities to quote, EAU quantities, on occasion program life expectancy and resin specifications. The RFQ information is quite limited considering the capital expenditure that will be based on the quotations received, not just the initial capital requirement, but production ramifications as well. The determinations as to press size, mold quality, sample size, length of sample size, run time, mold qualification requirements even basics such as tolerance requirements are left to the quoting facility to determine in the initial RFQ/quote package.
Many oversea buyers intend to send their inquiries to a bunch of Chinese plastic injection mold makers before they placed order to one of them, choices sometimes just simply made base on price. If you are lucky enough, you could probably get a qualified molded product at the cheapest price. But what about the next time?  Your business success should not be hanging on odds.

Whenever you get a quotation from a China mould supplier, you better have your own sense to estimate if it's competitive or reasonable or it's over-charged. It's very much necessary to understand the actual mold price in China.

Cost of a plastic molded part includes raw material, injection molding, labor cost, packing, transportation, management, and profit. Let ‘s get into each items one by one.
Plastic parts produced by the injection molding process are usually long lived consumer products. It's suitability depends on the properties of the finished part and surface quality, it required a lot of experiences of raw materials, processing condition, injection molding parameter to get optimum results. The reasons to cause problems could not be a certain answer as the processing condition is always different, on the basis of an individual case a decision has to be made as to whether simple and rapid fault correction is possible or whether intervention is the design of the parts or the layout of the mold and gating is necessary.
Slow cooling relieves internal stresses of metals. Plastics, especially ones with more crystaline (less amorphous) structure shrinks more as they cool slowly. Slower cooling promotes more internal crystaline structure, which is more brittle and shrinks more. If you want a more dimensional stable part, when the injection mold opens, drop the part into cold water (it will have less internal stress. Think of the melted plastic having no internal stresses. Then as it cools in the mold with varying rates, stresses are formed. Plastic parts shrink more when then they cool slowly.

Slower cooling does usually relieve some of the molded in stress. Many products are annealed after injection molding just for this purpose. The other factor that affects the linier stress is the velocity. At slower velocities a greater amount of stress in the direction of flow occurs. Of course faster velocities used to achieve a consistent viscosity will tend to entrap more air. Venting is very important. There must be vents along the entire flow path, not just at the end of fill. Weak weld lines may also become more evident after annealing, shrinkage will increase.
I've never relied on a mold company salesman or rep to try to explain what is the best choices for my company or my customer. I find that 95% of the time the mold salesman is just that, a salesman with little or no practical knowledge of the molding process or industry and certainly not the best source of information that works best for my plant or my customers' plant. There are a lot of companies that rely on the mold maker to decide what to quote and how to quote it. Including what materials, components to use and design criteria. If one goes this route and allows each supplier to quote the job as they see it, you'll end with a wide range of prices, and probably quire different molds from each. Now you need to compare apples and oranges and sense out of it.
Buyer and supplier always hunting each other, there is always a good mold supplier with reasonable price somewhere, that's why we need to do more sourcing and survey, nothing is VERY cheap and VERY good, only reasonable price, a number accepted by the mold buyer and supplier both party. Take it, leave it or go somewhere else.

You need to watch what you get and follow up with what you ask for. That is what we do at Aco Mold, we have such a large group of experienced staff here stateside to manage your tooling and molding projects so that you are getting what you expect. It can be difficult at times but we travel there and build relationships to better the outcome for your companies.
If the resin is in powder form then used high power magnets to remove them, and if it is in the form of granules then melt it in big volume in any bucket type (in this way metal parts will moved down in bottom) then in its molten state put it in extruder for re-granules or processing (molding).
Heat transfer from inside a thick molding will be far more limiting compared to heat removal from the tool. That is why conformal cooling or chilled air or more common systems that use nitrogen (very common in Germany) will not produce any substantial reduction in cycle time. Tool side cooling technologies work only when heat is delivered to tool fast enough and that is only in small thickness parts. Having rapid chilling can produce stress.

One thing that may really benefit with cooling time reduction will be to use as low as possible melt temperature. If melt is reduced by 20-30 deg. C you will get amazing cycle time reduction (combined with as high a practical ejection temperature). Look at frozen skin criterion for ejection, not text book % and adjust core cavity temperatures (differential) so that highest temperature is in geometric mid plane of part.
Gas Assisted Injection Molding chairs have been produced successfully for the last 20 years. My company (Aco Mold) has recently supplied gas assisted molding equipment for a customer in Brazil who is making Stadium Seating for the 2014 World Cup. We also supplied all of the gas assisted molding equipment for the London 2012 Olympic Stadium Seating and the Kiev Stadium seating for the last Euro championships. We have one customer in UK who is making all polymer (PP) chairs for schools and offices using our equipment. The MOST IMPORTANT thing is to get the chair properly designed for the gas assisted injection molding process.

However, it is very unlikely that it will be cost effective to modify an existing chair mold to a Gas Assist part. To get the best out of the process you would need to re-design the chair using a new mold tool. The use of "box beam sections" with gas assisted molding does enable you to reduce the General Wall Section of the part in many cases (stadium seating is a good example) which would offer a potential overall weight reduction.
Your Part size and Weight will also determine Press Size which will narrow the selection of manufactures, you will see that among your list of plastic injection molding machines, there are some that are very well suited for smaller parts whereas other excel in very large tonnage presses. The Resin used in your applications will also determine your choice of Barrel specified on your selection of the injection molding machines, this will relate to your part weight as it must be calculated to resident time in the barrel.
Because inserts are manually placed by an operator before the injection cycle you blow the tool surface with cold air, increase the residence time (furthermore not the same amount from one shot to another!) and bring potential pollution through the inserts and manual operation (even though operators usually wear gloves in this case). This makes a good number of possible root causes. I'd see the "over-shearing" as an interesting one to investigate (after moisture content of course) for 2 reasons: the PA12 you use has a high viscosity / low fluidity (it is hard to inject) + it first flows around an insert, that is made of metal. Trying to pre-heat these inserts (at least on 30 consecutive shots), this should ease the material flow near the sprue.
You are not alone with your difficulty finding talented injection molding technicians. With the industry down turn cycles and mass closing of many injection molding companies most of the junior technicians got laid off and found work in other industries. Now that our industry has taken a positive upturn there is no one in the talent pool to fill these roles. I blame the bean counters for this problem. They sacrificed the technical floor personal to secure their profit margin, knowing that at some time in the future the industry would pick up. Now they are scratching their heads wondering what they are going to do.
There's a big difference between making a good mold and saving money on manufacturing. You can make a good mold anywhere in the world. However having a good mold made is only a small part of the equation. It takes 6-12 weeks to make a tool. Material, product and production quality is a much bigger part and it can span years.

It's easy to save money on mold and lose tenfold on parts. What we do is make the mold in the most cost effective place worldwide but we always run production here in China. We tried to run production overseas only to come back with our tail between our legs after having to criss-cross the globe flying engineers to scratch their heads over supplier based failures spending weeks in hotels and eroding any potential savings.
That injection molding machines are not in the simulation is a problem we have to keep in mind. So there is the pressure loss in the nozzle. Some people create the nozzle in CAD to get this in the simulation. But what is with the quality of the injection molding machine. Old or new. Is the return valve working? Compression of the melt in the cylinder is not considered of simulation.
Any injection mold manufacturer can quote a low price mold, but it takes a committed partner who is familiar with your company and processes to engineer the lowest cost solution. That means an up-front investment in time and expertise which only comes out of strong working relationship.

The best practice is to avoid preparing the Excel sheet containing 3 to 4 different mold makers quote and make a rating based on the price. Visit the mold maker plant and check the facility available with him, his existing customers, past customers. Check the molds which are under manufacturing in the shop, see the procedures followed, look at the sample components made from the molds supplied by the mold maker. All this will give you an idea on the capability and the quality levels of the mold maker.
The two biggest determining factors of molding sink marks are product design and processing with the assumption that the tool is functioning correctly. With that being said there is a fine line between the two. You can over compensate for poor product design with molding parameters, and vise versa. If you over pack a part you can begin to effect it dimensionally or ride on the fringe of flashing your parting line. You can very easily make a part that is too big by trying to pack out molding sink marks that are caused by poor product design. The other down fall of over packing is a small processing window.
Contact Info
Copyright © 2023, ACO Mold. Terms of Service and Privacy Policy. All rights reserved.  Powered by ACO MOLD.
1 1.png

Join Our Network

Please email to sales@acomold.com
or fill out the contact form below: