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.
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.
- Make sure the material has been dried properly to obtain the best adhesion possible (which may not be great).
- 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?
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.
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.
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.
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.
- 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.