Launching Your Company into Over-Molding
by Joe Tito
The ability to over-mold cable assemblies is a capability many cable and harness manufacturers wish they had. It’s sort of a glass ceiling that more than a few companies find themselves under. Many have said they would like to grow and/or enter some other profitable markets within cable assembly, but just can’t without this crucial in-house offering.
Harald Giebel from ISC Engineering had a well-attended seminar at this past May’s Wire Processing Show in Milwaukee covering a myriad of encapsulation technologies for cables. He graciously accepted WHN’s request to provide a roadmap for bringing over-molding capabilities in-house.
First, a bit about ISC Engineering. WHN profiled the company back in the Jan-Feb 2018 issue. ISC Engineering specializes in custom molded cable assemblies and the technology that surrounds them. What is unusual about ISC is that they are also heavily involved in transferring over-molding technology to OEMs and other cable assembly suppliers. More on that later.
Harald began outlining some of the decisions that go into making the investment. “Look back at your quote history and see what RFQs you couldn’t quote,” he suggested, “then try to assess what other business you could get into should you have this technology.” He suggested taking a look at other industries that could be approached and highlighted high-reliability applications where assemblies must survive a harsh environment, and also the medical industry.
The conversation pivoted to gaining an understanding of the specific types of molding technologies by distinguishing between straight injection molding and insert molding; the latter being the type most commonly used for cable assemblies. “With straight injection molding, you are filling a cavity as fast as you can, with higher relative pressures, in order to get a good quality part,” he explained. “With insert molding, you have to inject slowly with lower relative pressures so as not to damage the connectors, or move the wires around.” He added you also have to be careful not to flow materials to areas of the connectors where they may inhibit mating or electrical contact.
Because of the propensity for damage of the wires and connectors that Harald described, molding of cable assemblies generally requires separate pre-mold and over-mold operations, as well as separate materials. “You generally use polypropylene for the pre-mold to keep the wires in place and not blowing everything apart, and then use PVC, TPE, TPU or similar softer materials for the cosmetics and strain relief on the final product.”
Next, he highlighted some of the capital equipment and costs. “First you need a molding machine and that can be anywhere between $60K and $120K depending on whether you buy new or used.” He warned the choice of used equipment adds risk and requires good mechanical support and more intricate knowledge of the equipment – an ability companies new to the process may not possess. “A new machine, in my experience, requires very little or no maintenance for the first five years of operation.”
Options for thermoplastic molding equipment would be stationary table, shuttle table, or rotary table machines (figure 1), and would depend on the volume of production (higher volumes would tend towards rotary equipment) the size and length of cables, and the ease of loading your particular molds. “The most common is the stationary table since cables are often attached to the over-mold, but even here we have options [for automation].”
Figure 1. From left to right, stationary table, shutter table, rotary table
The conversation moved to auxiliary equipment. “You will need a chiller to cool the machine, and that will run around $8K. Next you will need a thermolator to keep the mold at an even temperature (about $2K) and a material dryer that will run between $8K and $12K.” Herald also mentioned a workbench at around $2K and added that used options are more appropriate for the auxiliary equipment since it is simpler in design, and generally requires less maintenance.
From a facility standpoint, he advised you would need a minimum of an 8-ft. wide by 12-ft. space (includes space for operator) and some additional space for racks used to supply prepped cables for the operator, and the same for finished goods. “Electrical requirements are usually 360 V. It’s good to assure the chiller and secondary equipment are in line with 360 V, and they can usually be purchased accordingly.”
As one can imagine, the Human Resources aspect must also be taken into consideration, since insert over-molding (unlike the more common straight injection molding) requires specific technical knowledge for pre-molds. “It’s not easy these days to find people who know this technology. Since the early 2000’s, we have pushed much of the stamping and molding overseas, so we just don’t have a pool of trained people in this field,” he advised.
Personnel requirements would generally be a setup technician for the molding machine, as well as a machine operator. Generally, there needs to be adequate staff to run the machines non-stop through process runs. “Bathroom breaks and phone checks are not nice to molten plastic material as it degrades in the machine if it sits for a minute or longer.” He added that process times per process for pre-mold and over-mold are in the 30 second range.
Once the equipment and personnel are in place, Harald broke down some of the tooling costs to take into consideration. “For straight injection molding you are paying big time for molds, usually $20K on up to $50K.” Because volumes for this technology are generally in the tens of thousands or millions, hardened steel alloys are needed and are more expensive to machine. Insert molding is generally associated with lower pressures and volumes runs in the hundreds or thousands range; and aluminum is generally the more economical option. “So, the cost is generally around $6K, but it’s wise to have a spare set. Insert molding is more operator dependent, and lends itself to human error in loading. This will damage the softer aluminum tool and cause flash or extra rework on the final product,” he instructed.
So how can ISC help in a decision to bring over-molding in-house? Harald launched into a discussion of a current customer as a typical illustration. “It’s a sensor house and we have actually been running their product for two years. Six months ago, they came to us and said the volumes are enough to bring it in-house.” Harald and his team advised on the selection of molding equipment. “Right now, I’m working on a mold base for the machine as well as helping with the design of the mold,” he detailed. ISC will make the molds and test them at their facility. “When it comes time to run the product, we will train their people here, then transfer the mold base and mold into their facility.
ISC also acts a problem solver for companies looking to replace current suppliers. “We’ve got another company that does data collection on water, electrical, and gas meters. They were buying their existing molded connector from China and it wasn’t providing a watertight seal, so they asked us to improve it and we are now starting that production line. So, in this case, we didn’t just transfer or copy it, we actually improved it to meet IP 60-A (??) approval.”
ISC is definitely a problem solver when it comes to over-molding of cable assemblies, and Harald suggested WHN as a conduit for Q & A on the subject. As such, feel free to comment on the electronic version of this article, or email the author at [email protected]. We will forward to Harald and get back to you, then publish the questions and responses at a future date. Alternatively, if you would like to contact Harald directly, you can do so but emailing him at [email protected], or by phoning him at 909-342-7439.